Ideal Implant Positioning










670
28
Ideal Implant Positioning
RANDOLPH R. RESNIK AND CARL E. MISCH
T
o obtain ideal esthetics and function of an implant-supported
prosthesis, the three-dimensional positioning of the den-
tal implant within the bone is critical. e malposition of
the dental implant can lead to signicant implant complications
and increased morbidity. Nonideal implant positioning may result
in undesirable outcomes that may ultimately aect the success and
longevity of prosthetic rehabilitation.
1
To achieve an ideal result for
the patient, a clinician must be conscious of the implant placement
with respect to the ideal and correct orientation of the nal prosthesis
design. Optimal dental implant positioning is dictated by the three-
dimensional placement of implants with respect to the biomechanical
and prosthetic principles related to the nal implant prosthesis.
Recently advances in implant dentistry technology have created
a greater appreciation for the esthetic results of the implant restora-
tion. Implant dentistry has experienced a profound shift from a func-
tional thought process with a surgical approach to esthetics, to a more
prosthetically and biologically driven protocol.
2
e dental implant
should be positioned in ideal relationship to the position of the exist-
ing teeth, vital structures, and other implants, as well as the buccolin-
gual, mesiodistal, and apicocoronal dimensions. When implants are
positioned with no emphasis to the three-dimensional location, any
of the following detrimental eects may occur (Fig. 28.1) Box 28.1:
e ideal three-dimensional positioning of a dental implant
needs to be addressed before the surgical procedure. Lack of proper
planning may lead to malpositioning which may be evaluated in
the three spatial planes. e placement of a dental implant in
available bone is comparable to an object in space that is dened
by “x,” “y,” and “z” coordinates. In implant dentistry, the x-axis
is dened by the mesiodistal plane, the y-axis is the buccolingual
dimension, and the z-axis is known as the apicocoronal (length
of implant body in relation to the osseous crest).
3
Unfortunately,
many dental implants are placed within the existing available
bone without respect to the three dimensions. In this chapter, the
proper positioning of implants will be discussed according to the
nal prosthetic needs and demands of the patient and the treat-
ment protocols for implants that are placed in nonideal positions.
“X”-Axis (Mesial-Distal) Positioning
Insufficient Implant–Tooth Distance (Apical)
Ideal Positioning
Ideally, it is best to allow at least a minimum of 1.5 mm from the
adjacent tooth root or tooth structure.
4
Maintaining this amount
of space from a tooth root decreases the possibility of causing
damage to the tooth and postoperative complications (Fig. 28.2).
Pretreatment Evaluation
Preoperatively, the most accurate technique to determine available
space for an implant adjacent to a tooth is with a cone beam comput-
erized tomography (CBCT) axial image. e ideal x-axis angulation
and position needs to be determined via interactive CBCT treatment
planning and transferred to the surgical procedure. is is most eas-
ily accomplished with a CBCT-generated surgical template. If the
implant placement is being completed freehand, then an intraoral
radiograph (e.g., periapical) should be used after the rst pilot drill
to determine ideal positioning with respect to the adjacent teeth.
After initial evaluation, the osteotomy positioning may be changed
or modied via a Lindemann drill (i.e., side-cutting bur) (Fig. 28.3).
Implants that are positioned too close to an adjacent tooth root are
usually the result of poor treatment planning (inadequate space), poor
surgical technique (improper angulation), or placement of an implant
body that is too wide. is may also occur when root dilacerations of
an adjacent tooth exist or if a tooth has been orthodontically reposi-
tioned to where the tooth root has encroached on the intraroot space.
e maxillary lateral incisor position may pose a signicant chal-
lenge in some cases, especially if the area is replacing a congenitally
missing lateral incisor. Often, after orthodontic treatment, there
exists an ideal mesiodistal distance of the clinical crowns; however,
compromised intraroot distance may result because of tilting the
teeth orthodontically into position (i.e., clinical crown of the cen-
tral incisor moves mesially and apical root moving distally). Lack
of space may contraindicate implant placement or require orth-
odontic treatment for repositioning of the roots (Fig. 28.4).
Another common area for root approximation complications is
the maxillary rst premolar edentulous site. Careful consideration for
the angulation of a natural canine must be evaluated. e 11-degree
• Increasedimplantmorbidity
• Increasedprostheticcomplications(e.g.,esthetics,prosthesis)
• Increasedprostheticcosts(e.g.,implantparts,laboratorycosts)
• Increasedperi-implantcomplications
• Decreasedlongevityofprosthesis
• Lesspatientacceptance
BOX
28.1
Non-Ideal Implant Positioning
Complications
Deceased

671
CHAPTER 28 Ideal Implant Positioning
average distal inclination and distal curvature of the canine root fre-
quently place the apex of the root into the rst premolar implant area.
e implant should be angled to follow the root of the canine and
prevent contact or perforation of the natural root. A shorter implant
often is indicated, especially when a second premolar is also present.
In some cases, an implant may be contraindicated (Fig. 28.5).
Complications
Implants positioned too close to a tooth risk damage to the peri-
odontal ligament (PDL) and surrounding structures. is may
cause displacement of bone into the PDL space and result in altered
blood supply to the adjacent tooth, loss of tooth vitality, apical peri-
odontitis, and internal or external resorption (Fig. 28.6).
5
A
CD
B
Fig. 28.1 Malpositioned implants. (A) Mandibular posterior implants placed too close together, too much
distance from anterior adjacent tooth, and poor angulation. (B) Maxillary left implant with poor positioning
and angulation. (C and D) Maxillary implant placement with no regards to positioning and final prosthesis.
1.5mm
1.5mm
Fig. 28.2 Ideal implant placement with regards to the apical area of the adjacent teeth (>1.5 mm). If the
implant encroaches upon the root, complications may result.

672
PART VI Implant Surgery
AB
Fig. 28.3 Cone beam computerized tomography (CBCT) evaluation. (A) Axial three-dimensional CBCT
view measuring midroot distance. (B) Axial view measuring at the most apical extent of the tooth roots.
AB
Fig. 28.4 (A) Postorthodontic treatment exhibiting tilting of the maxillary central crown mesially, which results in
the root apex tilting distally, resulting in less available space for a lateral incisor implant. (B) Poor treatment plan of
two congenitally missing lateral incisors with insufficient space resulting in impingement on the adjacent tooth roots.
AB
Fig. 28.5 Maxillary first bicuspid area. (A) Often the maxillary first bicuspid is placed and may encroach
on the natural curvature of the maxillary cuspid. (B) Ideally the implant should be placed parallel to the
cuspid root or a shorter implant to minimize the possibility of root encroachment.

673
CHAPTER 28 Ideal Implant Positioning
Because of the close proximity of implants to an adjacent
tooth, the implant may fail because of infection or bone resorp-
tion. If less than 1.5 mm of space exists between the implant
and the root apex, then the PDL may be damaged, which can
result in irreversible trauma and internal or external resorption
of the natural tooth. erefore placing an implant too close to
the root surface may ultimately lead to implant or tooth loss,
which can occur in the short term or the long term.
In the eld of orthodontics today, temporary anchorage devices
(TADs) have become popular for cases requiring anchorage.
TAD implants are smaller diameter implants (<1.8 mm) that are
inserted perpendicular to the long axis of the tooth in the inter-
radicular spaces of the maxilla and mandible. TADs are used
for tooth movement (e.g., labial segment retraction or mesial
movement of teeth) or for intraoral anchorage, in which tooth
movement in all three planes may be accomplished. Interradicu-
lar orthodontic implant complications may include loss of tooth
vitality, tooth loss, osteosclerosis, and dentoalveolar ankylosis.
6,7
ese implants should be cautiously placed because they often
are positioned in areas of minimal intraroot distance and above
the mucogingival line in attached tissue, which often leads to
detrimental eects on adjacent tooth structure
8
(Fig. 28.7).
Treatment
Initial placement. If there is insucient space between an implant
and the root apex after initial placement, then the implant
should be removed and repositioned, especially if the adjacent
tooth becomes symptomatic. If available space is compro-
mised, then the roots should be repositioned via orthodontics
or the treatment plan changed to a dierent type of prosthesis.
Past placement. If an implant has been restored and root approxima-
tion (<1.5 mm) exists, then the tooth/implant should be moni-
tored on a more stringent clinical and radiographic recall basis
along with informing the patient of possible morbidity. e pa-
tient should be made aware of the proximity and possible compli-
cations that may result. If symptomatic or radiographic pathology
is present, then the implant should be removed and repositioned
along with vitality testing of the tooth (Fig. 28.8; Box 28.2).
Insufficient Implant–Tooth Distance (Coronal)
Ideal Positioning
For tissue health and ideal emergence prole, a minimum of 2.0
mm should be present from the implant neck to the adjacent
tooth
9
(Fig. 28.9). When the implant is closer than mm to the
adjacent tooth, any bone loss related to the microgap, the biologic
width, or stress concentration may cause the implant and adjacent
tooth to lose bone. More space is required at the coronal area (1.5
mm vs. 2.0 mm) to accommodate a papilla.
Within an edentulous space, the implant should be placed in
the middle of the space, with an equal amount of interproximal
bone toward each adjacent tooth. Ideally, there should exist 2.0 mm
or more from the adjacent cement-enamel junction (CEJ) of each
tooth. When evaluating defect width around an implant with bone
loss, it is usually less than 1.5 mm wide. Hence, if bone loss around
the implant occurs, then the bone loss will remain a vertical defect
and is less likely to cause bone loss on the adjacent natural tooth.
If bone is maintained and no bone loss occurs around the adjacent
tooth, then the interdental papilla height will be maintained.
Pretreatment Evaluation
e coronal implant–tooth distance may be determined by evaluat-
ing CBCT images (i.e., axial images) or the use of study casts in
conjunction with diagnostic wax-ups. On preoperative evaluation,
if inadequate space exists for implant placement, then the following
treatment may be completed to increase mesiodistal distance:
1. Enameloplasty (modication of the interproximal contact
areas) may be completed on the proximal contours of the
Fig. 28.6 Nonideal positioning with respect to the root apex. Implant
has an ideal crestal positioning; however, apical positioning results in the
implant being too close to the root apex.
AB
Fig. 28.7 Orthodontic implants (temporary anchorage devise [TADs]) that are used for anchorage usually will
be very close to adjacent roots. (A) Clinical image depicting a TAD that is placed in between two tooth roots
and perpendicular to the bone. (B) Intraoral radiograph showing minimal space for implant placement between
tooth roots.

674
PART VI Implant Surgery
adjacent teeth to increase mesiodistal dimensions. However,
care should be exercised in the amount of enamel removed
because aggressive modication may lead to hypersensitivity
and possible endodontic intervention (Fig. 28.10A, 28.10D).
2. Orthodontic intervention may be used to upright a tilted adja-
cent tooth to increase the intratooth space. For larger spaces
(multiple spaces), one implant may be placed, and an orth-
odontic spring incorporated in the transitional crown. e
spring pushes the distal tooth more distal and, after orthodon-
tic movement, the second implant may be inserted with less
risk and improved hygiene between each implant. Another
option is to reduce the space orthodontically and place only
one implant and crown (see Fig. 28.10B).
3. For larger spaces (multiple implants) the implants may be o-
set, with one implant placed buccal and the other implant on a
diagonal toward the lingual.
9
e diagonal dimension increases
the mesiodistal space by 0.5 to 1 mm. In the mandible, the most
anterior implant is placed to the lingual aspect of the midcrest and
the more distal implant is placed to the facial aspect to facilitate
access of a oss threader from the vestibule into the intraimplant
space. e occlusal contacts also are slightly modied on the buc-
cal aspect of the mesial implant to occlude over the central fossa.
In the maxilla, the anterior implant is placed facially and the distal
implant palatally to improve esthetics. e distal occlusal contact
is placed over the lingual cusp, and the mesial occlusal contact is
located in the central fossa position. e cervical esthetics of the
maxillary molar are compromised on the distal half of the tooth
to achieve greater intratooth distance and easier access for home
care. is maxillary implant placement requires the intraimplant
furcation to be approached from the palate, rather than the buccal
approach, as for the mandible Fig. 28.10D.
Prevention
A common technique to avoid placing implants too close to a tooth is
the use of a surgical template. A pilot, universal or fully guided surgical
template may be used that will prevent the implant from being placed
too close to the tooth. In addition, if a template is not used, there exist
multiple positioning devices that allow for ideal osteotomy position-
ing (i.e., 1.5–2.0 mm from the adjacent tooth). A surgical spacer may
be used, which enables the initial osteotomy site to be placed at the
correct position, allowing for adequate space between the tooth and
nal implant position (Fig. 28.11A–B). Surgical guidance systems
(Salvin, Charlotte, North Carolina) also may be used to ensure ideal
implant placement (buccolingual and mesiodistal spacing) and may
be used with any surgical drill system (see Fig. 28.11C–D). However,
the most accurate positioning adjunct is the use of CBCT-generated
surgical templates (tooth supported) (see Fig. 28.11E).
Complications
Lack of space between the implant platform and the coronal
aspect of the adjacent tooth occurs most likely from poor initial
osteotomy positioning, poor treatment planning, or the use of
Fig. 28.8 Tooth root proximity existing on a final prosthesis. Patients
should be informed and a more frequent evaluation should be completed
along with regular pulp vitality testing.
Complication:
• Toothhypersensitivity
• Lossoftoothvitality
• Periapicalpathology
• Toothloss
• Implantloss
Prevention:
• Idealpositioning(>1.5mm)
• Accurateradiographicevaluation(conebeamcomputerizedtomography)
• Diagnosticwax-up/interactivetreatmentplanning
Treatment:
• Preprosthetic
• Removeimplant
• Checktoothvitality
• Postprosthetic
• Strictrecallevaluation
• Monitortoothvitality
BOX
28.2
Lack of Space Between Tooth/Implant
(Apical)
Fig. 28.9 In some cases, insufficient mesial-distal space will be present
which decreases clinical crown space. Ideally, 2.0 mm should be present
between implant and adjacent tooth (crestally).

675
CHAPTER 28 Ideal Implant Positioning
an implant body that is too large. is will lead to a situation in
which the implant encroaches on the adjacent tooth. Implant
clinicians must be aware that most implant crestal platforms
are larger than the implant body, which will result in decreased
space between the adjacent tooth (e.g., a 3.8-mm implant may
have a 4.1-mm platform) (Fig. 28.12; Table 28.1).
Prosthetically, when there exists a lack of space between the
adjacent clinical crown and implant, it may be dicult, if not
impossible, to form an ideal emergence prole in the new nal
prosthesis. Lack of proper emergence prole leads to esthetic,
hygienic, and soft tissue complications, which increases implant
morbidity (Fig. 28.13A–C). Hygiene diculties will become
more frequent because of the unnatural contours of the prosthesis
and the lack of space for cleansability. is usually will result in
plaque buildup and related peri-implant complications. Normal
hygiene techniques will be modied to access the areas for proper
cleansability.
Also, because of the lack of space between the implant and
coronal portion of the tooth, bone loss will likely occur. Inter-
proximal bone loss may result from lack of sucient blood sup-
ply. Esposito and colleagues have shown a correlation between
increased bone loss and decreased distance of the implant from the
adjacent tooth.
10
ey reported bone loss increased with decreas-
ing distance, especially in the maxillary incisor region. Because of
interproximal bone loss caused by the proximity of the implant to
the coronal portion of the tooth, a lack of or reduction in the size
of papilla will be present. is will result in peri-implant condi-
tions and resultant esthetic issues (see Fig. 28.13D).
A
B
C
L
B
D
Fig. 28.10 Possible treatment options for inadequate spacing. (A) Determine the exact measurement of available space for an edentulous space via
cone beam computerized tomographic images. (B) Orthodontic repositioning allowing additional spacing. (C) Enameloplasty of adjacent tooth allows for
additional space for prosthesis emergence. (D) In some cases two smaller diameter implants may be placed to replace one molar, however care should
be exercised not to position implants too close to each other or too close to adjacent tooth.

676
PART VI Implant Surgery
Treatment
Initial placement. On surgical implant placement, if the position of
the implant is less than 2.0 mm from the adjacent clinical crown,
removal and reposition of the implant should be completed. If
the implant is positioned 1.5–2.0 mm from the adjacent tooth,
a possible option would include modifying (enameloplasty) the
adjacent tooth, as long as irreversible damage to the tooth is not
done and an ideal emergence prole can be established.
Past placement. If the implant has been restored and approxima-
tion (<1.5 mm) exists, then the tooth/implant should be strict-
ly monitored. If the natural tooth becomes symptomatic, then
the implant should be removed and repositioned, along with
long-term vitality testing of the tooth (Box 28.3).
A
B
C
D
Fig. 28.11 Ideal implant placement. (A) Positioning device placed on the distal contact of the adjacent
tooth allows for the ideal osteotomy site in the edentulous space. (B and C) Surgical guidance systems
may be used for various situations and spacing between teeth. (Courtesy Salvin Dental Specialties, Inc.,
Charlotte, NC.) (D) Tooth-supported surgical template allowing for accurate implant positioning.)
Fig. 28.12 Implant placement too close to the clinical crown of the adja-
cent tooth (<2.0 mm).
Average Mesiodistal Width of Permanent Teeth
Tooth Mandibular (mm) Maxilla (mm)
Centralincisor 5.3 8.6
Lateralincisor 5.7 6.6
Cuspid 6.8 7.6
Firstbicuspid 7.0 7.1
Secondbicuspid 7.1 6.6
Firstmolar 11.4 10.4
Secondmolar 10.8 9.8
From Hebel MKS, Gajjar R. Anatomic basis for implant selection and positioning. In: Babbush
C, ed. Dental implants: The art and science. 2nd ed. Philadelphia, PA: Saunders; 2001.
TABLE
28.1

677
CHAPTER 28 Ideal Implant Positioning
Excessive Implant–Tooth Distance (Coronal)
Ideal Positioning
If excessive space (>4.0 mm) exists between the implant body
and adjacent tooth, a biomechanical disadvantage will result
because of the cantilever eect (i.e., contact area of the adja-
cent tooth). Ideally, the implant should be loaded along the
long axis of the implant body. Because of the excessive space
between the implant and tooth, overcontouring of the nal
prosthesis is required to achieve a contact area with the adja-
cent tooth (Fig. 28.14).
Pretreatment Evaluation
To prevent the placement of an implant too far from an adjacent
tooth, a CBCT-generated template may be used to accurately
place the implant. Because teeth are present, a tooth-supported
guide would be the most accurate template compared with bone-
borne or tissue-borne guides. In addition, special positioning
devices allow for ideal osteotomy placement and adherence to the
ideal placement of 1.5 to 2.0 mm from the adjacent tooth. ese
predetermined distance spacers will minimize the possibility of
placing the implant too close or too far from the adjacent tooth
(Fig. 28.15).
Complications
e excessive space present between the implant and adjacent
tooth will result in biomechanical issues and possible esthetic com-
plications. Loading of the cantilever area will produce - a resultant
shear force. Because bone is weakest with shear forces, bone loss
will most likely occur around the crestal area of the implant. Can-
tilevers present on implant prostheses are more problematic than
on natural teeth for several reasons. Forces are magnied to the
A
B
C
Fig. 28.13 Complications resulting from impingement on adjacent teeth. (A and B) Poor implant position-
ing resulting in inability to create an emergence profile for crowns. (C) Implant body that is too wide results
in bone loss followed by tissue loss.
Complication:
• Interproximalboneloss
• Compromisedemergenceprole
• Complicatesprostheticprocedures
• Reducedpapillaheight
• Hygienedifculties
Prevention:
• Idealpositioning(~2.0mm)
• Accurateradiographicevaluation(conebeamcomputerizedtomography)
• Diagnosticwax-up/interactivetreatmentplanning
• Useofasurgicaltemplate
Treatment:
• Preprosthetic
• Enameloplasty,crownnaturaltooth
• Possibleremovalofimplantandreposition
BOX
28.3
Lack of Space Between Tooth/Implant
(Coronal)

678
PART VI Implant Surgery
entire implant system, which may result in implant screw loosen-
ing, cement retention failure, or even possibly the mobility and
failure of the implant itself. Second, because the implant is void
of a PDL, there is no stress release system in place to protect the
implant. Studies have shown a 1-mm increase in the horizontal
oset of an implant restoration may produce a 15% increase in
torque during function, and a 1-mm increase in the vertical o-
set introduces a 5% increase.
11
e overcontoured crown leads to
resultant shear forces, which may lead to component failure (i.e.,
screw loosening, screw fracture, implant fracture).
Because of the need to obtain interproximal contact, the nal
prosthesis will be atypical, which may lead to increased diculty
in prosthetic impression, laboratory, and insertion procedures
(Figs. 28.16 and 28.17). Food impaction is a common complaint
from patients with an increased implant–tooth distance because
periodontal maintenance is dicult as a result of related soft tis-
sue complications. e chronic soft tissue problems may lead to
peri-implant disease (i.e., peri-mucositis, peri-implantitis) which
results in an increased implant morbidity.
Treatment
Initial placement. If nonideal placement is determined during sur-
gery, the implant should be repositioned in the ideal position
(i.e., 1.5–2.0 mm from the adjacent tooth). To prevent malposi-
tion the following osteotomy formula may be used: ½ diameter
of the implant + 2.0 mm from tooth = osteotomy site initiation.
In other words, a 4.0-mm implant pilot osteotomy would be
2.0 mm + 2.0 mm = 4.0 mm from the adjacent tooth. If the
initial osteotomy is not ideal, then a Lindemann drill (side
cutting) is used to reposition the osteotomy into the correct
position.
A
B
Fig. 28.14 Implant placed too far from the adjacent tooth. (A) The implant
should be placed at the midpoint of the mesiodistal distance. (B) Nonideal
placement may result in cantilever effect biomechanical disadvantages.
Fig. 28.15 Implant should be placed in the midpoint of the mesiodis-
tal distance via three-dimensional cone beam computerized tomographic
interactive treatment planning.
Fig. 28.16 Clinical image depicting poor implant positioning leading to
a significant cantilever effect. Forces placed on the mesial cantilever will
result in shear forces to the implant crestal area.

679
CHAPTER 28 Ideal Implant Positioning
Past placement. If the implant has already been placed and is ready
to be restored, then the amount of occlusal force should be as-
sessed to determine the ideal treatment:
Minimal occlusal forces: If favorable force factors exist (e.g.,
opposing removable prosthesis, lack of parafunction) then
a cantilever (overcontoured crown) may be fabricated with
(Fig. 28.18A) the following:
• Narrowocclusaltable
Minimalcuspheight:Ithasbeenreportedthatevery10-de-
gree increase in cusp inclination leads to a 30% increase in
the torque applied to the restoration during function
10
• Nolateralcontacts
• Strong,longcontactarea
High occlusal forces: If unfavorable forces (e.g., opposing
xed or implant prosthesis, parafunction) are present, then
a cantilever is contraindicated and the mesiodistal distance
is reduced by either:
• Overcontouringadjacent crown(e.g., crown,compos-
ite) (see Fig. 28.18B)
• Removeimplantandreposition(Box 28.4).
Lack of Implant–Implant Distance
Ideal Positioning
e distance between two implants has been determined to be a
signicant factor with respect to crestal bone loss, the presence
of interimplant papilla, and generalized tissue health. Ideally,
there should exist 3 mm or more space between any two adjacent
implants. is will allow adequate room for interdental papilla
and tissue health, cleansability, transfer copings during prosthetic
impressions, and minimizing horizontal bone loss. When implants
are placed too close together, it is usually the result of poor treat-
ment planning or surgical technique (Fig. 28.19).
A
D
C
B
Fig. 28.17 Implant positioning too far from tooth. (A) Implant placement too far posterior leading to the
implant being non-restorable, (B) Poor implant positioning resulting in prosthesis that has resultant anterior
and posterior cantilevers. (C and D) Atypical prosthesis because of nonideal implant placement and need
to obtain contact area, which results in biomechanical complications and food impaction.

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67028Ideal Implant PositioningRANDOLPH R. RESNIK AND CARL E. MISCH†To obtain ideal esthetics and function of an implant-supported prosthesis, the three-dimensional positioning of the den-tal implant within the bone is critical. e malposition of the dental implant can lead to signicant implant complications and increased morbidity. Nonideal implant positioning may result in undesirable outcomes that may ultimately aect the success and longevity of prosthetic rehabilitation.1 To achieve an ideal result for the patient, a clinician must be conscious of the implant placement with respect to the ideal and correct orientation of the nal prosthesis design. Optimal dental implant positioning is dictated by the three-dimensional placement of implants with respect to the biomechanical and prosthetic principles related to the nal implant prosthesis.Recently advances in implant dentistry technology have created a greater appreciation for the esthetic results of the implant restora-tion. Implant dentistry has experienced a profound shift from a func-tional thought process with a surgical approach to esthetics, to a more prosthetically and biologically driven protocol.2 e dental implant should be positioned in ideal relationship to the position of the exist-ing teeth, vital structures, and other implants, as well as the buccolin-gual, mesiodistal, and apicocoronal dimensions. When implants are positioned with no emphasis to the three-dimensional location, any of the following detrimental eects may occur (Fig. 28.1) Box 28.1:e ideal three-dimensional positioning of a dental implant needs to be addressed before the surgical procedure. Lack of proper planning may lead to malpositioning which may be evaluated in the three spatial planes. e placement of a dental implant in available bone is comparable to an object in space that is dened by “x,” “y,” and “z” coordinates. In implant dentistry, the x-axis is dened by the mesiodistal plane, the y-axis is the buccolingual dimension, and the z-axis is known as the apicocoronal (length of implant body in relation to the osseous crest).3 Unfortunately, many dental implants are placed within the existing available bone without respect to the three dimensions. In this chapter, the proper positioning of implants will be discussed according to the nal prosthetic needs and demands of the patient and the treat-ment protocols for implants that are placed in nonideal positions.“X”-Axis (Mesial-Distal) PositioningInsufficient Implant–Tooth Distance (Apical)Ideal PositioningIdeally, it is best to allow at least a minimum of 1.5 mm from the adjacent tooth root or tooth structure.4 Maintaining this amount of space from a tooth root decreases the possibility of causing damage to the tooth and postoperative complications (Fig. 28.2). Pretreatment EvaluationPreoperatively, the most accurate technique to determine available space for an implant adjacent to a tooth is with a cone beam comput-erized tomography (CBCT) axial image. e ideal x-axis angulation and position needs to be determined via interactive CBCT treatment planning and transferred to the surgical procedure. is is most eas-ily accomplished with a CBCT-generated surgical template. If the implant placement is being completed freehand, then an intraoral radiograph (e.g., periapical) should be used after the rst pilot drill to determine ideal positioning with respect to the adjacent teeth. After initial evaluation, the osteotomy positioning may be changed or modied via a Lindemann drill (i.e., side-cutting bur) (Fig. 28.3).Implants that are positioned too close to an adjacent tooth root are usually the result of poor treatment planning (inadequate space), poor surgical technique (improper angulation), or placement of an implant body that is too wide. is may also occur when root dilacerations of an adjacent tooth exist or if a tooth has been orthodontically reposi-tioned to where the tooth root has encroached on the intraroot space.e maxillary lateral incisor position may pose a signicant chal-lenge in some cases, especially if the area is replacing a congenitally missing lateral incisor. Often, after orthodontic treatment, there exists an ideal mesiodistal distance of the clinical crowns; however, compromised intraroot distance may result because of tilting the teeth orthodontically into position (i.e., clinical crown of the cen-tral incisor moves mesially and apical root moving distally). Lack of space may contraindicate implant placement or require orth-odontic treatment for repositioning of the roots (Fig. 28.4).Another common area for root approximation complications is the maxillary rst premolar edentulous site. Careful consideration for the angulation of a natural canine must be evaluated. e 11-degree • Increasedimplantmorbidity• Increasedprostheticcomplications(e.g.,esthetics,prosthesis)• Increasedprostheticcosts(e.g.,implantparts,laboratorycosts)• Increasedperi-implantcomplications• Decreasedlongevityofprosthesis• Lesspatientacceptance • BOX 28.1 Non-Ideal Implant Positioning Complications†Deceased 671CHAPTER 28 Ideal Implant Positioningaverage distal inclination and distal curvature of the canine root fre-quently place the apex of the root into the rst premolar implant area. e implant should be angled to follow the root of the canine and prevent contact or perforation of the natural root. A shorter implant often is indicated, especially when a second premolar is also present. In some cases, an implant may be contraindicated (Fig. 28.5). ComplicationsImplants positioned too close to a tooth risk damage to the peri-odontal ligament (PDL) and surrounding structures. is may cause displacement of bone into the PDL space and result in altered blood supply to the adjacent tooth, loss of tooth vitality, apical peri-odontitis, and internal or external resorption (Fig. 28.6).5ACDB• Fig. 28.1 Malpositioned implants. (A) Mandibular posterior implants placed too close together, too much distance from anterior adjacent tooth, and poor angulation. (B) Maxillary left implant with poor positioning and angulation. (C and D) Maxillary implant placement with no regards to positioning and final prosthesis.1.5mm1.5mm• Fig. 28.2 Ideal implant placement with regards to the apical area of the adjacent teeth (>1.5 mm). If the implant encroaches upon the root, complications may result. 672PART VI Implant SurgeryAB• Fig. 28.3 Cone beam computerized tomography (CBCT) evaluation. (A) Axial three-dimensional CBCT view measuring midroot distance. (B) Axial view measuring at the most apical extent of the tooth roots.AB• Fig. 28.4 (A) Postorthodontic treatment exhibiting tilting of the maxillary central crown mesially, which results in the root apex tilting distally, resulting in less available space for a lateral incisor implant. (B) Poor treatment plan of two congenitally missing lateral incisors with insufficient space resulting in impingement on the adjacent tooth roots.AB• Fig. 28.5 Maxillary first bicuspid area. (A) Often the maxillary first bicuspid is placed and may encroach on the natural curvature of the maxillary cuspid. (B) Ideally the implant should be placed parallel to the cuspid root or a shorter implant to minimize the possibility of root encroachment. 673CHAPTER 28 Ideal Implant PositioningBecause of the close proximity of implants to an adjacent tooth, the implant may fail because of infection or bone resorp-tion. If less than 1.5 mm of space exists between the implant and the root apex, then the PDL may be damaged, which can result in irreversible trauma and internal or external resorption of the natural tooth. erefore placing an implant too close to the root surface may ultimately lead to implant or tooth loss, which can occur in the short term or the long term. In the eld of orthodontics today, temporary anchorage devices (TADs) have become popular for cases requiring anchorage. TAD implants are smaller diameter implants (<1.8 mm) that are inserted perpendicular to the long axis of the tooth in the inter-radicular spaces of the maxilla and mandible. TADs are used for tooth movement (e.g., labial segment retraction or mesial movement of teeth) or for intraoral anchorage, in which tooth movement in all three planes may be accomplished. Interradicu-lar orthodontic implant complications may include loss of tooth vitality, tooth loss, osteosclerosis, and dentoalveolar ankylosis.6,7 ese implants should be cautiously placed because they often are positioned in areas of minimal intraroot distance and above the mucogingival line in attached tissue, which often leads to detrimental eects on adjacent tooth structure8 (Fig. 28.7). TreatmentInitial placement. If there is insucient space between an implant and the root apex after initial placement, then the implant should be removed and repositioned, especially if the adjacent tooth becomes symptomatic. If available space is compro-mised, then the roots should be repositioned via orthodontics or the treatment plan changed to a dierent type of prosthesis.Past placement. If an implant has been restored and root approxima-tion (<1.5 mm) exists, then the tooth/implant should be moni-tored on a more stringent clinical and radiographic recall basis along with informing the patient of possible morbidity. e pa-tient should be made aware of the proximity and possible compli-cations that may result. If symptomatic or radiographic pathology is present, then the implant should be removed and repositioned along with vitality testing of the tooth (Fig. 28.8; Box 28.2). Insufficient Implant–Tooth Distance (Coronal)Ideal PositioningFor tissue health and ideal emergence prole, a minimum of 2.0 mm should be present from the implant neck to the adjacent tooth9 (Fig. 28.9). When the implant is closer than mm to the adjacent tooth, any bone loss related to the microgap, the biologic width, or stress concentration may cause the implant and adjacent tooth to lose bone. More space is required at the coronal area (1.5 mm vs. 2.0 mm) to accommodate a papilla.Within an edentulous space, the implant should be placed in the middle of the space, with an equal amount of interproximal bone toward each adjacent tooth. Ideally, there should exist 2.0 mm or more from the adjacent cement-enamel junction (CEJ) of each tooth. When evaluating defect width around an implant with bone loss, it is usually less than 1.5 mm wide. Hence, if bone loss around the implant occurs, then the bone loss will remain a vertical defect and is less likely to cause bone loss on the adjacent natural tooth. If bone is maintained and no bone loss occurs around the adjacent tooth, then the interdental papilla height will be maintained. Pretreatment Evaluatione coronal implant–tooth distance may be determined by evaluat-ing CBCT images (i.e., axial images) or the use of study casts in conjunction with diagnostic wax-ups. On preoperative evaluation, if inadequate space exists for implant placement, then the following treatment may be completed to increase mesiodistal distance: 1. Enameloplasty (modication of the interproximal contact areas) may be completed on the proximal contours of the • Fig. 28.6 Nonideal positioning with respect to the root apex. Implant has an ideal crestal positioning; however, apical positioning results in the implant being too close to the root apex.AB• Fig. 28.7 Orthodontic implants (temporary anchorage devise [TADs]) that are used for anchorage usually will be very close to adjacent roots. (A) Clinical image depicting a TAD that is placed in between two tooth roots and perpendicular to the bone. (B) Intraoral radiograph showing minimal space for implant placement between tooth roots. 674PART VI Implant Surgeryadjacent teeth to increase mesiodistal dimensions. However, care should be exercised in the amount of enamel removed because aggressive modication may lead to hypersensitivity and possible endodontic intervention (Fig. 28.10A, 28.10D). 2. Orthodontic intervention may be used to upright a tilted adja-cent tooth to increase the intratooth space. For larger spaces (multiple spaces), one implant may be placed, and an orth-odontic spring incorporated in the transitional crown. e spring pushes the distal tooth more distal and, after orthodon-tic movement, the second implant may be inserted with less risk and improved hygiene between each implant. Another option is to reduce the space orthodontically and place only one implant and crown (see Fig. 28.10B). 3. For larger spaces (multiple implants) the implants may be o-set, with one implant placed buccal and the other implant on a diagonal toward the lingual.9 e diagonal dimension increases the mesiodistal space by 0.5 to 1 mm. In the mandible, the most anterior implant is placed to the lingual aspect of the midcrest and the more distal implant is placed to the facial aspect to facilitate access of a oss threader from the vestibule into the intraimplant space. e occlusal contacts also are slightly modied on the buc-cal aspect of the mesial implant to occlude over the central fossa. In the maxilla, the anterior implant is placed facially and the distal implant palatally to improve esthetics. e distal occlusal contact is placed over the lingual cusp, and the mesial occlusal contact is located in the central fossa position. e cervical esthetics of the maxillary molar are compromised on the distal half of the tooth to achieve greater intratooth distance and easier access for home care. is maxillary implant placement requires the intraimplant furcation to be approached from the palate, rather than the buccal approach, as for the mandible Fig. 28.10D. PreventionA common technique to avoid placing implants too close to a tooth is the use of a surgical template. A pilot, universal or fully guided surgical template may be used that will prevent the implant from being placed too close to the tooth. In addition, if a template is not used, there exist multiple positioning devices that allow for ideal osteotomy position-ing (i.e., 1.5–2.0 mm from the adjacent tooth). A surgical spacer may be used, which enables the initial osteotomy site to be placed at the correct position, allowing for adequate space between the tooth and nal implant position (Fig. 28.11A–B). Surgical guidance systems (Salvin, Charlotte, North Carolina) also may be used to ensure ideal implant placement (buccolingual and mesiodistal spacing) and may be used with any surgical drill system (see Fig. 28.11C–D). However, the most accurate positioning adjunct is the use of CBCT-generated surgical templates (tooth supported) (see Fig. 28.11E). ComplicationsLack of space between the implant platform and the coronal aspect of the adjacent tooth occurs most likely from poor initial osteotomy positioning, poor treatment planning, or the use of • Fig. 28.8 Tooth root proximity existing on a final prosthesis. Patients should be informed and a more frequent evaluation should be completed along with regular pulp vitality testing.Complication:• Toothhypersensitivity• Lossoftoothvitality• Periapicalpathology• Toothloss• ImplantlossPrevention:• Idealpositioning(>1.5mm)• Accurateradiographicevaluation(conebeamcomputerizedtomography)• Diagnosticwax-up/interactivetreatmentplanningTreatment:• Preprosthetic • Removeimplant • Checktoothvitality• Postprosthetic • Strictrecallevaluation • Monitortoothvitality • BOX 28.2 Lack of Space Between Tooth/Implant (Apical)• Fig. 28.9 In some cases, insufficient mesial-distal space will be present which decreases clinical crown space. Ideally, 2.0 mm should be present between implant and adjacent tooth (crestally). 675CHAPTER 28 Ideal Implant Positioningan implant body that is too large. is will lead to a situation in which the implant encroaches on the adjacent tooth. Implant clinicians must be aware that most implant crestal platforms are larger than the implant body, which will result in decreased space between the adjacent tooth (e.g., a 3.8-mm implant may have a 4.1-mm platform) (Fig. 28.12; Table 28.1).Prosthetically, when there exists a lack of space between the adjacent clinical crown and implant, it may be dicult, if not impossible, to form an ideal emergence prole in the new nal prosthesis. Lack of proper emergence prole leads to esthetic, hygienic, and soft tissue complications, which increases implant morbidity (Fig. 28.13A–C). Hygiene diculties will become more frequent because of the unnatural contours of the prosthesis and the lack of space for cleansability. is usually will result in plaque buildup and related peri-implant complications. Normal hygiene techniques will be modied to access the areas for proper cleansability.Also, because of the lack of space between the implant and coronal portion of the tooth, bone loss will likely occur. Inter-proximal bone loss may result from lack of sucient blood sup-ply. Esposito and colleagues have shown a correlation between increased bone loss and decreased distance of the implant from the adjacent tooth.10 ey reported bone loss increased with decreas-ing distance, especially in the maxillary incisor region. Because of interproximal bone loss caused by the proximity of the implant to the coronal portion of the tooth, a lack of or reduction in the size of papilla will be present. is will result in peri-implant condi-tions and resultant esthetic issues (see Fig. 28.13D). ABCLBD• Fig. 28.10 Possible treatment options for inadequate spacing. (A) Determine the exact measurement of available space for an edentulous space via cone beam computerized tomographic images. (B) Orthodontic repositioning allowing additional spacing. (C) Enameloplasty of adjacent tooth allows for additional space for prosthesis emergence. (D) In some cases two smaller diameter implants may be placed to replace one molar, however care should be exercised not to position implants too close to each other or too close to adjacent tooth. 676PART VI Implant SurgeryTreatmentInitial placement. On surgical implant placement, if the position of the implant is less than 2.0 mm from the adjacent clinical crown, removal and reposition of the implant should be completed. If the implant is positioned 1.5–2.0 mm from the adjacent tooth, a possible option would include modifying (enameloplasty) the adjacent tooth, as long as irreversible damage to the tooth is not done and an ideal emergence prole can be established.Past placement. If the implant has been restored and approxima-tion (<1.5 mm) exists, then the tooth/implant should be strict-ly monitored. If the natural tooth becomes symptomatic, then the implant should be removed and repositioned, along with long-term vitality testing of the tooth (Box 28.3). ABCD• Fig. 28.11 Ideal implant placement. (A) Positioning device placed on the distal contact of the adjacent tooth allows for the ideal osteotomy site in the edentulous space. (B and C) Surgical guidance systems may be used for various situations and spacing between teeth. (Courtesy Salvin Dental Specialties, Inc., Charlotte, NC.) (D) Tooth-supported surgical template allowing for accurate implant positioning.)• Fig. 28.12 Implant placement too close to the clinical crown of the adja-cent tooth (<2.0 mm). Average Mesiodistal Width of Permanent TeethTooth Mandibular (mm) Maxilla (mm)Centralincisor 5.3 8.6Lateralincisor 5.7 6.6Cuspid 6.8 7.6Firstbicuspid 7.0 7.1Secondbicuspid 7.1 6.6Firstmolar 11.4 10.4Secondmolar 10.8 9.8From Hebel MKS, Gajjar R. Anatomic basis for implant selection and positioning. In: Babbush C, ed. Dental implants: The art and science. 2nd ed. Philadelphia, PA: Saunders; 2001. TABLE 28.1 677CHAPTER 28 Ideal Implant PositioningExcessive Implant–Tooth Distance (Coronal)Ideal PositioningIf excessive space (>4.0 mm) exists between the implant body and adjacent tooth, a biomechanical disadvantage will result because of the cantilever eect (i.e., contact area of the adja-cent tooth). Ideally, the implant should be loaded along the long axis of the implant body. Because of the excessive space between the implant and tooth, overcontouring of the nal prosthesis is required to achieve a contact area with the adja-cent tooth (Fig. 28.14). Pretreatment EvaluationTo prevent the placement of an implant too far from an adjacent tooth, a CBCT-generated template may be used to accurately place the implant. Because teeth are present, a tooth-supported guide would be the most accurate template compared with bone-borne or tissue-borne guides. In addition, special positioning devices allow for ideal osteotomy placement and adherence to the ideal placement of 1.5 to 2.0 mm from the adjacent tooth. ese predetermined distance spacers will minimize the possibility of placing the implant too close or too far from the adjacent tooth (Fig. 28.15). Complicationse excessive space present between the implant and adjacent tooth will result in biomechanical issues and possible esthetic com-plications. Loading of the cantilever area will produce - a resultant shear force. Because bone is weakest with shear forces, bone loss will most likely occur around the crestal area of the implant. Can-tilevers present on implant prostheses are more problematic than on natural teeth for several reasons. Forces are magnied to the ABC• Fig. 28.13 Complications resulting from impingement on adjacent teeth. (A and B) Poor implant position-ing resulting in inability to create an emergence profile for crowns. (C) Implant body that is too wide results in bone loss followed by tissue loss.Complication:• Interproximalboneloss• Compromisedemergenceprole• Complicatesprostheticprocedures• Reducedpapillaheight• HygienedifcultiesPrevention:• Idealpositioning(~2.0mm)• Accurateradiographicevaluation(conebeamcomputerizedtomography)• Diagnosticwax-up/interactivetreatmentplanning• UseofasurgicaltemplateTreatment:• Preprosthetic • Enameloplasty,crownnaturaltooth • Possibleremovalofimplantandreposition • BOX 28.3 Lack of Space Between Tooth/Implant (Coronal) 678PART VI Implant Surgeryentire implant system, which may result in implant screw loosen-ing, cement retention failure, or even possibly the mobility and failure of the implant itself. Second, because the implant is void of a PDL, there is no stress release system in place to protect the implant. Studies have shown a 1-mm increase in the horizontal oset of an implant restoration may produce a 15% increase in torque during function, and a 1-mm increase in the vertical o-set introduces a 5% increase.11 e overcontoured crown leads to resultant shear forces, which may lead to component failure (i.e., screw loosening, screw fracture, implant fracture).Because of the need to obtain interproximal contact, the nal prosthesis will be atypical, which may lead to increased diculty in prosthetic impression, laboratory, and insertion procedures (Figs. 28.16 and 28.17). Food impaction is a common complaint from patients with an increased implant–tooth distance because periodontal maintenance is dicult as a result of related soft tis-sue complications. e chronic soft tissue problems may lead to peri-implant disease (i.e., peri-mucositis, peri-implantitis) which results in an increased implant morbidity. TreatmentInitial placement. If nonideal placement is determined during sur-gery, the implant should be repositioned in the ideal position (i.e., 1.5–2.0 mm from the adjacent tooth). To prevent malposi-tion the following osteotomy formula may be used: ½ diameter of the implant + 2.0 mm from tooth = osteotomy site initiation.In other words, a 4.0-mm implant pilot osteotomy would be 2.0 mm + 2.0 mm = 4.0 mm from the adjacent tooth. If the initial osteotomy is not ideal, then a Lindemann drill (side cutting) is used to reposition the osteotomy into the correct position.AB• Fig. 28.14 Implant placed too far from the adjacent tooth. (A) The implant should be placed at the midpoint of the mesiodistal distance. (B) Nonideal placement may result in cantilever effect biomechanical disadvantages.• Fig. 28.15 Implant should be placed in the midpoint of the mesiodis-tal distance via three-dimensional cone beam computerized tomographic interactive treatment planning.• Fig. 28.16 Clinical image depicting poor implant positioning leading to a significant cantilever effect. Forces placed on the mesial cantilever will result in shear forces to the implant crestal area. 679CHAPTER 28 Ideal Implant PositioningPast placement. If the implant has already been placed and is ready to be restored, then the amount of occlusal force should be as-sessed to determine the ideal treatment:Minimal occlusal forces: If favorable force factors exist (e.g., opposing removable prosthesis, lack of parafunction) then a cantilever (overcontoured crown) may be fabricated with (Fig. 28.18A) the following: • Narrowocclusaltable • Minimalcuspheight:Ithasbeenreportedthatevery10-de-gree increase in cusp inclination leads to a 30% increase in the torque applied to the restoration during function10 • Nolateralcontacts • Strong,longcontactareaHigh occlusal forces: If unfavorable forces (e.g., opposing xed or implant prosthesis, parafunction) are present, then a cantilever is contraindicated and the mesiodistal distance is reduced by either: • Overcontouringadjacent crown(e.g., crown,compos-ite) (see Fig. 28.18B) • Removeimplantandreposition(Box 28.4). Lack of Implant–Implant DistanceIdeal Positioninge distance between two implants has been determined to be a signicant factor with respect to crestal bone loss, the presence of interimplant papilla, and generalized tissue health. Ideally, there should exist 3 mm or more space between any two adjacent implants. is will allow adequate room for interdental papilla and tissue health, cleansability, transfer copings during prosthetic impressions, and minimizing horizontal bone loss. When implants are placed too close together, it is usually the result of poor treat-ment planning or surgical technique (Fig. 28.19). ADCB• Fig. 28.17 Implant positioning too far from tooth. (A) Implant placement too far posterior leading to the implant being non-restorable, (B) Poor implant positioning resulting in prosthesis that has resultant anterior and posterior cantilevers. (C and D) Atypical prosthesis because of nonideal implant placement and need to obtain contact area, which results in biomechanical complications and food impaction. 680PART VI Implant SurgeryABC• Fig. 28.18 Treatment of excessive distance. (A) Prosthesis with narrow occlusal table, minimal cusp height, and no lateral contacts maintains implant-protected occlusion. (B and C) To decrease implant–tooth distance, the natural tooth may be elongated or overcontoured by the use of a crown or bonding.14 mm3 mm1.5 mm1.5 mm44• Fig. 28.19 Ideal interimplant distance: 3.0 mm between implants and 1.5 mm 1.0-2.0 mm from adjacent teeth.Complication• Overcontouredcrowns• Atypicalprosthetics• Cantilevereffect(biomechanics)• Foodimpaction• Periodontalcomplications Prevention• Idealpositioning(1.5–2.0mmfromtooth)• Accurateradiographicevaluation(conebeamcomputerizedtomography)• Diagnosticwax-up/interactivetreatmentplanning• Parallellongaxisofadjacenttooth• Useofasurgicaltemplate TreatmentMinimal occlusal forces:1. Narrowocclusaltable2. Minimalcuspheight3. Nolateralcontacts • Cantilever(overcontouredcrown)High occlusal forces:1. Overcontouradjacenttooth • Reducemesiodistaldistance2. Removeimplantandreposition • BOX 28.4 Excessive Space Between Tooth/ImplantPretreatment Evaluatione preliminary evaluation to determine distance for multiple implants is the evaluation and measurement of space in the axial dimension. is may be accomplished by use of a CBCT image (axial) depicting the adjacent tooth roots for measurement (Fig. 28.20).Osteotomy Measurement. A formula exists for ideal place-ment of initial osteotomies in anticipation of the nal implants. For example, when placing 5.0- and 4.0-mm implants, add ½ diameter of implant + 3.0 mm between implants and 2.5 mm + 2.0 mm + 3.0 mm = 7.5 mm between osteotomy sites. In this example, the initial osteotomy sites may be placed at approxi-mately 7.5 mm between the two pilot holes. In addition, spe-cial spacing guides may be used for ideal positioning. Ideally, the implant diameter width should correspond to the width of the natural tooth at the level 2 mm below the CEJ.  681CHAPTER 28 Ideal Implant PositioningComplicationsWhen lack of interproximal bone (i.e., <3.0 mm) is present, a decreased blood supply will result, eventually leading to bone loss. Tarnow and colleagues have shown that implants placed less than 3.0 mm apart may have adequate stability and function; however, this placement will likely result in crestal bone loss. In this study, implants with a greater than 3-mm distance between implants resulted in a 0.45-mm bone loss, whereas implants positioned less than 3 mm had over twice the amount of bone loss, or approximately 1.04 mm12 (Fig. 28.21).In addition, when lack of space exists between the implants, the resultant bone loss will be responsible for the loss of the papilla. As the bone resorbs, the distance between the contact point of the crowns and the bone level increases. As this distance increases (i.e., >5 mm), the papilla will become smaller in size and contour.Lack of space may also lead to diculty in hygiene access, which will result in poor tissue health. e resultant tissue condition will most likely lead to peri-mucositis or peri-implantitis. Prosthetically, lack of space may result in diculty in obtaining a nal impression (i.e., placement of impression transfer copings) and seating the nal prosthesis. With some implant systems, the transfer copings may be adjusted to allow for impression of the implant bodies. Additionally, an unconventional implant prosthesis (irregularly contoured) will most likely need to be fabricated (Fig. 28.22). TreatmentInitial placement. If implants are not ideally positioned, then the osteotomy should be repositioned to ideal positions (3 mm be-tween implants). e implant positions may be altered with the side-cutting Lindemann drill (Fig. 28.23).ABCD• Fig. 28.20 Evaluation of intertooth distance. (A) Clinical crown measurement. (B) Cement-enamel junc-tion measurement. (C) Midroot distance. (D) Apical distance.3.0mmA B• Fig. 28.21 (A) Implants placed too close together. (B) Ideally, the space should be 3.0 mm. 682PART VI Implant SurgeryPast placement. If implants have been restored, then removal of implants and repositioning should be completed if the patient cannot adequately clean the prosthesis. In some situations, the abutment/implant body may be minimally modied to gain extra space, usually with a ame-shaped diamond bur. is is best completed with external hex im-plants because modication of internal hex implants may alter structural integrity of the implant, leading to possible fracture (Box 28.5). Buccolingual Positioning(“Y-Axis”)e faciopalatal (buccolingual) positioning of the dental implant is crucial to the esthetic and biomechanical eectiveness of the nal prosthesis. Frequently, implant positioning is dictated by the resulting available bone, leading to angulation complica-tions. Bone remodeling after tooth extractions is common, with resorption occurring from the buccal plate initially, decreasing the width of bone and shifting the ridge position more lingual. When evaluating the faciopalatal positioning, two dimensions need to be investigated: 1. Faciopalatal ridge position 2. Faciopalatal angulation positionIdeal Positioning (Faciopalatal Ridge Dimensions)e faciopalatal position of the implant with adequate bone width is mid to slightly palatal of the edentulous ridge. is approach permits the use of the largest diameter implant to be placed in the space with respect to the natural tooth dimensions. Ideally, after implant placement, the crestal bone should be at least 2.0 mm wide on the facial aspect of the implant and 1.0 mm or more on the palatal aspect (Fig. 28.24).13 Pretreatment EvaluationWith this positioning protocol, if implant bone loss occurs, then the facial plate will remain intact and not cause recession on the facial aspect of the implant crown. erefore for a 4-mm-diam-eter implant, a minimum of 7-mm faciopalatal width of bone is required (i.e., 4.0-mm-diameter implant + 2.0 mm buccal bone + 1.0 mm lingual bone). Bone spreading in conjunction with implant placement or bone grafting on the facial aspect of the edentulous site may be indicated when the ridge is compromised in width.When evaluating the CBCT images, the available bone width may be determined via the cross-sectional images. With the use of interactive treatment planning, implant positions can be evalu-ated to ensure a minimum of 2.0 mm present on the buccal and 1.0 mm on the lingual aspects of the ridges (Fig. 28.25). e faciopalatal width is not as critical on the palatal aspect (i.e., with respect to the buccal bone) of the implant because it usually con-tains dense cortical bone, which is more resistant to bone loss and is usually not in the esthetic zone.When present, the buccal cortical bone minimizes future hard and soft tissue recession. In this scenario, if bone loss occurs on the implant, the facial plate will remain intact, and minimal reces-sion on the facial aspect of the implant will result. Spray and col-leagues have shown that if the facial bone is more than 1.8 mm in ABCD• Fig. 28.22 Complications. (A) Close proximity of posterior implants resulting in bone loss. (B and C) When implants are too close together, the prosthetic procedures may be difficult or impossible to com-plete. (D) Implant proximity resulting in hygiene difficulty and resultant peri-implant disease. 683CHAPTER 28 Ideal Implant Positioningthickness (after implant placement), recession infrequently results. However, if the facial plate is less than 1.8 mm, vertical resorp-tion occurs quickly, mainly because of the lack of blood supply.14 erefore improper buccolingual positioning has a direct eect on the long-term health of the implant and prosthesis.A common mistake, especially with clinicians early on their learning curve, is to use solely two-dimensional radiographs or clinical evaluation of the soft tissue thickness. Often this is mislead-ing and may pose a signicant change to the implant placement or nal prosthesis. us viewing the third dimension of bone (i.e., CBCT survey) will allow for the accurate assessment of available bone width and ideal position of the implant (Fig. 28.26). Ideal Positioning (Faciopalatal Angulation)e faciopalatal angulation is a crucial factor in the long-term success of the dental implant and prosthesis. One area that facio-palatal positioning is most critical is the maxillary anterior region. Because of the inherent angulation issues (i.e., trajectory of the natural teeth with respect to the available bone), coupled with being in the esthetic zone, there is very little room for error when placing implants in this area. In the literature, three dierent protocols for the buccolingual (faciopalatal) angulations of the implant body have been discussed: (1) similar to the facial posi-tion of the adjacent natural teeth, (2) under the incisal edge of the nal restoration, and (3) within the cingulum position of the implant crown (Fig. 28.27).Facial Implant Body Angulation (Anterior). In theory, a max-illary anterior implant body angulation should be positioned at the facial emergence of the nal crown, and this position should be in the same position as a natural tooth.However, the facial crown contour of a natural tooth has two planes, and its incisal edge is palatal to the facial emergence of the natural tooth by 12 to15 degrees (Fig. 28.28). is is why maxillary anterior crown preparations are in two or three planes (Fig. 28.29). In addition, because the implant is narrower in diameter than the faciopalatal root dimension, when the implant body is oriented as a natural tooth and has a facial emergence, a straight abutment is not wide enough to permit the two-plane or three-plane reduction to bring the incisal edge of the preparation more palatal. As a result, the incisal edge of the preparation remains too facial and will require signicant modication or an angled abutment.erefore the implant body should be more palatal than a natural root, so 2.0 mm of bone exists on the facial aspect. Many ABCD• Fig. 28.23 Inadequate space between implants. (A) The prevention of multiple implants being placed too close together includes the use of interactive treatment planning (multiple cone beam computerized tomography views) to ensure ideal spacing. (B) Inadequate space between implants; ideally one of the implants should be removed and replaced in a more ideal position. (C) When implants are already restored, a strict recall should be followed to monitor bone loss and related periodontal complications. (D) Two implants placed in anterior mandible with insufficient space between implants (> 3.0mm) and lack of space between adjacent teeth (1.5–2.0 mm). 684PART VI Implant Surgeryimplant clinicians, especially early on their learning curve, will attempt to align the implant body with the facial aspect of adjacent teeth and the implant may inadvertently be inserted too facial. When this occurs, no predictable method exists to restore proper esthetics. At best, the nal crown will appear too long. is problem is compounded when the implant is also inserted too shallow and insucient room is present to obtain a proper emergence prole. To correct a maligned implant with soft tissue grafts or bone augmentation is rarely successful after the implant is already inserted in a nal position (Fig. 28.30).In the maxillary anterior area, natural teeth are loaded at an angle because of their natural angulation compared with the mandibular anterior teeth. is is one reason why maxillary anterior teeth are wider in diameter than mandibular anterior teeth (i.e., which are loaded in their long axis). e facial angulation position of the implant body often corresponds to an implant body angulation, often with up to 15 degrees o-axial loads. is angled load increases the force to the abutment screw–implant–bone complex by 25.9% compared with a long-axis load.15 ese oset loads increase the risks of abutment screw loosening, crestal bone loss, and cervical soft tissue marginal Complication:• Increasedboneloss• Lossofinterdentalpapilla• Hygieneissues• Prosthesiscomplications (Pooremergenceprole/impression) Prevention:• Idealpositioning(3.0mmbetweenimplants)• Accurateradiographicevaluation(conebeamcomputerizedtomography)• Diagnosticwax-up/interactivetreatmentplanning• UseofasurgicaltemplateTreatment:• Customabutments• Strictrecall• Removeimplantsandreposition• Minimalocclusalforces • BOX 28.5 Lack of Space Between Implants (Implant:Implant)ABC D• Fig. 28.24 Buccal-Lingual Positioning: (A) Non-ideal maxillary positioning, (B) Ideal maxillary positioning, (C) Non-ideal positioning in mandible too facial, (D) Ideal positioning in central fossa of restoration. 685CHAPTER 28 Ideal Implant PositioningA B• Fig. 28.25 Implant placement too deep. (A) Implant placed greater than 4.0 mm from free gingival mar-gin, which increases potential complications. (B) The crown height is not a multiplier of force when the load is in the long axis of the implant. However, any angled force or cantilever increases the force and the crown height magnifies the effect.AB• Fig. 28.26 (A) Two-dimensional radiograph not depicting the true bone dimensions because of inherent inaccuracies. (B) Cone beam computerized tomography cross-sectional image allowing for the accurate representation of bony dimensions.ABC• Fig. 28.27 Three implant angulation positions are suggested in the literature for a maxillary anterior single-tooth implant. (A) Under the incisal edge. (B) Similar to the facial position of the adjacent teeth (B). (C) Under the cingulum position of the implant crown. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.) 686PART VI Implant Surgeryshrinkage.16 As a result, implants angled facially may compromise the esthetics and increase the risk of complications (Fig. 28.31). Cingulum Implant Body Angulation. A second angulation sug-gested in the literature is more palatal, with an emergence under the cingulum of the crown. is may also be the result of an implant insertion in a width-decient ridge (division B) because the bone is lost primarily from the facial aspect and the ridge shifts toward the lin-gual. is position is also often the goal when a screw-retained crown is used in the nal restoration. e prosthesis xation screw (i.e., to retain a maxillary anterior crown) cannot be located in the incisal or facial region of the crown because this will compromise the esthetics.is position also is suggested to increase the bone thickness on the facial aspect of the implant body. However, the cingu-lum implant position may cause a considerable hygiene compro-mise.17 e implant body in the anterior maxilla is round and usually 3.5 to 5.5 mm in diameter. e labial cervical contour of the implant crown must be similar to the adjacent teeth for the ultimate esthetic eect. Because the long axis of the implant for a screw-retained crown must emerge from the cingulum posi-tion, this requires a facial projection of the crown or “buccal correction” facing away from the implant body. e facial ridge lap must extend 2 to 4 mm and is often similar in contour to the modied ridge lap pontic of a three-unit xed prosthesis.e modied ridge lap crown has become a common solution to correct the esthetics of the restoration when the implant is placed in narrow bone or follows a palatal angulation position.18,19 However, plaque control on the facial aspect of the implant is almost impos-sible. Unlike a pontic for a xed partial denture (FPD), the ridge lap crown has a gingival sulcus that requires sulcular hygiene. Even if the toothbrush (or probe) could reach under the facial ridge lap to the gingival sulcus, no hygiene or measuring device could be manip-ulated to a right angle to proceed into the facial gingival sulcus. As a result, although an acceptable esthetic restoration may be devel-oped, especially with the additional cervical porcelain, the hygiene requirements render this approach less acceptable (Fig. 28.32).Some authors argue that an improved contour may be devel-oped subgingivally rather than supragingivally with a palatal implant position. To create this contour, the implant body must be positioned more apical than desired. is position may pre-vent food from accumulating on the cervical “table” of the crown. However, the “subgingival ridge lap” does not permit access to the facial sulcus of the implant body for the elimination of plaque and to evaluate the bleeding index or facial bone loss (Fig. 28.33). erefore the maintenance requirement for the implant facial sul-cular region suggests this modality is not a primary option.Greater interarch clearance is often needed with an implant palatal position because the permucosal post exits the tissue in a more palatal position. Inadequate interarch space may especially • Fig. 28.28 Maxillary anterior teeth have an incisal edge 12 to 15 degrees more palatal than the facial emergence position of the crown. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.)ABC• Fig. 28.29 (A) Maxillary anterior crown preparations are made in two or more planes. (B, C) When the plane of the emergence profile is only used, the incisal edge of the preparation is too facial. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.)• Fig. 28.30 Implant positioned too facial and too shallow. The angled abutment must be prepared to make room for restorative materials and to allow a more apical position of the crown margin. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.)• Fig. 28.31 Implant placed too facial and the thin tissue receded after crestal bone loss. (From Misch CE. Single-tooth implant restoration: maxil-lary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.) 687CHAPTER 28 Ideal Implant Positioninghinder the restoration of Angle’s class II, division 2 patients with the implant in this position. Ideal Implant Angulation. e third implant angulation in the literature describes the most desirable implant angulation. e clinician determines the line for the best angulation by the point of the incisal edge position of the implant crown and the midfaciopalatal (i.e., or slightly palatal) position on the crest of the bone. e center of the implant is located directly under the incisal edge of the crown so that a straight abutment for cement can be used. Because the crown prole is in two planes, with the incisal edge more palatal than the cervical portion, the incisal edge position is ideal for implant placement and accommodates some of the facial bone loss that often occurs before implant placement.e facial emergence of the crown mimics the adjacent teeth, proceeding from the implant body under the tissue (Fig. 28.34). e angle of force to the implant is less from the long axis, which decreases the crestal stresses to the bone and abutment screws. When in doubt, the implant surgeon should err toward the pala-tal aspect of the incisal edge position, not to the facial aspect, because it is easier to correct a slight palatal position in the nal crown contour, compared with the implant body angled too facial.e implant body angulation slightly lingual to the incisal edge may also be used for cement or screw-retained restorations. In screw-retained restorations, an angled abutment for screw retention is inserted, and the coping screw for the crown may be located within the cingulum. is method does not require a facial ridge lap of the nal crown, which decreases the risk of compromised hygiene. However, it should be noted that pros-thetic screw loosening is one of the more common complications of maxillary anterior screw-retained crowns.20 When this occurs, there is an increased risk of marginal bone loss as a result of the crown movement and microgap created by the loose screw. When ideal bone volume is present, a surgical template that indicates the incisal edge and facial contour of the nal prosthesis may be used. Faciopalatal PositioningA. Angulation with Respect to Prosthesis Type1. FP-1 & FP-2 ProsthesisCement-retained (anterior). e ideal angulation for an FP-1 or FP-2 in the anterior is slightly lingual to the incisal edge. is is advantageous for two reasons. First, a straight abut-ment may be used, which is esthetically more pleasing and prosthetically less complex. When an FP-1/FP-2 prosthesis is indicated, precise buccolingual angulation implant place-ment is necessary to obtain an ideal esthetic result. In the anterior region, the ideal implant position allows the place-ment of a straight abutment slightly lingual to the incisal edge of the nal crown for a cemented prosthesis. e re-sulting forces are concentrated along the long axis of the implant, minimizing damaging shear forces. In addition, if access is ever required to treat screw loosening, the existing crown may be retained, preventing a new crown from hav-ing to be fabricated.• Fig. 28.32 Implant crown with a “modified ridge lap.” The tissue periodi-cally becomes inflamed because hygiene aids (or a dental probe) cannot enter the sulcus of the implant; instead, it can only slide along the facial ridge lap to the free gingival margin. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Pros-thetics. St Louis, MO: Elsevier Mosby; 2015.)• Fig. 28.33 Implant with a “subgingival ridge lap crown” and an inflamed gingival sulcus. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.)• Fig. 28.34 Left: Implant crown is positioned under the incisal edge and has a facial emergence profile similar to the adjacent teeth. Right: The implant was positioned under the cingulum and requires a screw-retained crown with a facial ridge lap to have a similar facial crown emergence as the adjacent teeth. (From Misch CE. Single-tooth implant restoration: max-illary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.) 688PART VI Implant SurgeryScrew-retained (anterior). For screw-retained prostheses in the ante-rior, the implant should emerge within the cingulum area of the anterior tooth so the access hole does not aect the esthetics of the restoration. If the implant is placed too facially, then the access hole will impinge on the esthetics of the restoration (i.e., screw hole through the facial of the restoration). If the implant is placed too far lingually, overcontouring of the nal crown may result in biomechanical issues and possible occlusal interferences (Fig. 28.35A–C).Posterior region (cement retained or screw retained). In the posterior region, the long axis of the implant should emerge within the approximate center (central fossa) of the prosthesis for a screw-retained or cement-retained FP-1 or FP-2. is allows occlusal forces to be directed ideally along the long axis of the implant (see Fig. 28.35D–E).ComplicationsFacial. If the implant is placed too facial for an FP-1 or FP-2 pros-thesis, then esthetic issues will result from overcontouring of the prosthesis. Bone dehiscence usually will be accompanied by tissue recession, and this complication is more pronounced in thin biotype patients. Facial positioning is often a complica-tion when implants are placed in immediate extraction sites. To correct the facial position of the implant, an angled abutment must be used. However, because of the access hole, the facial of the abutment is more bulky. is results in overcontouring of the facial aspect of the prosthesis, which will lead to tissue recession and bone loss (Fig. 28.36).Lingual. Implants placed too far to the lingual can result in facial overcontouring of the nal prosthesis (ridge lap) for esthetic rea-sons. e prosthetic impression and placement of the prosthesis is also complicated, which results in diculty with the seating of the abutments. Because of the overcontouring of the lingual contours, patients often complain of lack of space for the tongue, which may impede speech. In the anterior region, a lingual-placed implant may make the implant nonrestorable if the patient has a deep bite occlusion and insucient interocclusal space (Fig. 28.37). FP-3 ProsthesisScrew retained. After evaluation of the articulated setup, arch form, available bone, and force factors, the FP-3 prostheses should be determined to be either screw retained or cement retained. For screw-retained prostheses, ideal positioning should be slightly lingual to the denture/porcelain/zirconia teeth to minimize tooth fractures and delamination in the anterior. In the poste-rior, the implant positioning should be within the central fossa of the Prostheses teeth.Cement retained. For cement-retained restorations, implant posi-tioning should be located slightly lingual to the incisal edge in the anterior region and in the central fossa area in the posterior. If force factors are a concern, then ideal implant placement is crucial to minimize biomechanical overload. However, if force factors are low, then nonideal placement is less of a problem with cement-retained prostheses because abutment angulation may be modied (Fig. 28.38). ComplicationsFacial. Implants positioned too facially will impinge on the esthet-ics, complicate screw insertion, and result in increased prosthe-sis component fractures. Because the access holes will extrude through the facial contours of the teeth, the access will need to be covered with composite. is predisposes the prosthesis to loss or discoloring of the composite plugs. Also, facially in-clined implants may lead to soft tissue irritation because of lack of attached tissue.Lingual. Implants placed too far lingually will result in an overcon-toured prosthesis, resulting in possible speech problems in the maxilla and crowding of the tongue in the mandible. Because the bulk of the material is needed for strength of the prosthesis, often this overcontouring results in an atypical prosthesis. In addition, lingually placed implants usually will result in lack of attached tissue, which may lead to chronic soft tissue problems (Figs. 28.39 and 28.40).CDScrew retainedCementedAB• Fig. 28.35 (A, B) Ideal implant placement for a cement and screw-retained prosthesis in the anterior, (C, D) Ideal posterior implant placement in line with the adjacent teeth central fossa’s. 689CHAPTER 28 Ideal Implant PositioningRP-4 and RP-5. e faciopalatal angulation for implants placed for removable overdentures should be positioned to emerge within the body of the denture base. is is crucial so the components (e.g., attachments, bar) that are attached to the implant do not impinge on the ideal setting of the den-ture teeth. Denture acrylic requires a minimum of 2.0 mm of bulk for strength and resistance form to prevent fractures and delamination.  MalpositioningLingual. Implants that are positioned too far lingually for an over-denture will result in overcontouring the lingual surface of the denture. is may interfere with phonetics, and often patients will complain of lack of space for the tongue. If the lingual aspect of the denture is thinned too much during adjustment, this will result in an area of possible fracture or loss of attach-ment.Facial. Implants placed too far facially will interfere with ideal denture tooth placement, leading to possible denture tooth “pop os.” Often the esthetics are compromised because of the required malpositioning of the denture teeth. In addition, facially positioned implants often result in lack of adequate at-tached tissue and potential periodontal concerns because gin-gival irritation and recession are more likely to result. is may lead to chronic pain, and remediation is usually unsuccessful (Fig. 28.41; Boxes 28.6 and 28.7). Apicocoronal (Z-Axis)e depth of implant placement in the bone is a signicant factor in relation to the longevity of the implants. Whether the implant is placed too deep or not apical enough, prosthetic and periodon-tal complications may increase implant morbidity.Ideal PositioningIn most regions of the mouth, it has been suggested that the implant platform be placed approximately 2 to 4 mm apical to the adjacent cemento-enamal junction (CEJ) or free gingival margin (FGM). Most recently, the free gingival margin is used as the anatomic landmark as this will allow for more accurate representation when soft and hard tissue recession is present.21 (Fig. 28.42).e best platform level for a two-stage implant is similar to the most desirable bone level before the loss of a natural tooth, which is 2 mm below the adjacent tooth CEJ.22 is positions the plat-form of the implant approximately 3 mm below the facial FGM ABCDE• Fig. 28.36 Facially positioned implant complications. (A) Clinical image showing the facial positioning which results in peri-mucositis, (B) Pre-treatment evaluation should be completed to avoid malposition. (C) Facially positioned anterior implant often will require an angled or custom abutment. (D) Facially inclined implants resulting in esthetic and bone loss issues. (E) Facial positioning leading to the implant being non-restorable. 690PART VI Implant SurgeryA BCD• Fig. 28.37 Lingual positioned implant complications. (A) Lingually placed abutment requiring overcon-touring and possible tongue impingement complications. (B) Usually lingually placed implants can be restored with a screw-retained prosthesis. (C) Posterior implant placed too far to the lingual requiring angled abutment. (D) Lingually placed posterior implant perforating the lingual plate.AB• Fig. 28.38 FP-3 Ideal Implant Positioning (A) Immediate placement/load positioning, (B) Final mono-lithic zirconia prosthesis. 691CHAPTER 28 Ideal Implant Positioningof the implant crown. is position will allow for 3 mm of soft tissue for the emergence of the implant crown on the midfacial region and more as the soft tissue measurements proceed toward the interproximal regions. is depth also increases the thickness of the soft tissues over the facial aspect of the titanium implant body, which masks the darker color. It is easier to use the FGMs of the adjacent teeth to help determine the depth than it is to attempt to use the CEJ as a landmark (Fig. 28.43).In conclusion, the ideal anterior and posterior implant body position is 2 to 4 mm below the facial FGM of the adjacent teeth. e depth of an implant platform greater than 4 mm below the adjacent CEJ is too deep. An implant platform position less than 2 mm below the FGM of the crown is too shallow. erefore the ideal depth position of the implant platform is more than 2 mm and less than 4 mm below the FGM. Excessive DepthSome authors have suggested that the implant be deepened (coun-tersunk) below the crestal bone more than 4 mm below the facial CEJ of the adjacent teeth to develop a crown emergence prole sim-ilar to a natural tooth (Fig. 28.44).22,23 is provides a subgingival emergence transition of about 5 mm on the facial aspect to achieve the width of the natural tooth (4 mm below the CEJ, and the ideal FGM on the facial is 1 mm above the CEJ). is concept was origi-nally developed for a 4-mm-diameter implant, and the diameter of a central incisor root is 4 mm at a position 4 mm below the CEJ24 (Fig. 28.45). Very esthetic restorations may be fabricated with this implant depth position because the bulk of subgingival porcelain provides good color and contour for the crown. However, several concerns arise regarding the long-term sulcular health around the implant when it is seated greater than 4 mm below the CEJ.Various studies have shown during the rst year of function, a mean bone loss range of 0.5 to 3.0 mm, depending partly on implant design. e bone maybe lost at least 0.5 mm below the connection of the abutment to the implant body and extends to any smooth or machined surface beyond the crest module.25 For example, Malevez and colleagues noted more pronounced bone loss for conical implants that had long, smooth, tapered crest modules.26 is may lead to facial sulcular probing depths of 7 to 8 mm or greater. Grunder evaluated single-tooth A BC• Fig. 28.39 (A and B) Facially positioned implants. (C) 3D CBCT image showing lack of bone from facially inclined implant.A B C• Fig. 28.40 (A) Lingually placed implant impinging on the tongue space. Note the overcontoured buccal cantilever for occlusal purposes, (B) Lingual placed implant requiring large ridge lap pontic and fractured screw. (C) Maxillary lingually angled implant. 692PART VI Implant Surgeryimplants in function for 1 year and noted the bone levels were 2 mm apical to the implant–abutment connection, and sulcu-lar probing depths were 9.0 to 10.5 mm, using a Brånemark implant design.27 As a result, daily care devices cannot main-tain the sulcus health, and anaerobic bacteria are more likely to develop. e interproximal regions of the implant crown, which correspond to the incidence or absence of interdental papillae, usually exhibit even greater probing depths. As a result, gingival shrinkage of the tissue is more likely to occur when the implant is placed more than 4 mm below the facial position of the adjacent CEJ.ABC• Fig. 28.41 (A) Pretreatment planning for ideal implant placement. (B) Facially angled implant impinging on the esthetics and prosthesis. (C) Ideal implant placement.Complication:• Boneloss(dehiscence)• Esthetics(overcontour)• Thintissue(recession)• Prostheticcomplications• ImplantfailurePrevention:• Understandidealangulationwithrespecttonalprosthesistype• Accurateradiographicevaluation(conebeamcomputerizedtomography)• Diagnosticwax-up/interactivetreatmentplanning• UseofasurgicaltemplateTreatment:• Customabutments• Possibleremovalofimplant • BOX 28.6 Excessive Angulation (Facially)Complication:Maxilla: • Ridge-lap • CrownbulkyMandible: • Lackoftonguespace • Speechissue • OvercontourPrevention:• Understandidealangulationwithrespecttonalprosthesistype• Accurateradiographicevaluation(conebeamcomputerizedtomography)• Diagnosticwax-up/interactivetreatmentplanning• UseofasurgicaltemplateTreatment:• Modiedridgelapscrewretained• Decreaseocclusalforcefactors• Remove/repositionimplant • BOX 28.7 Excessive Angulation (Lingual)1.5 mm 1.5 mm3 mm• Fig. 28.42 Image depicting ideal implant positioning (1.5 mm from adja-cent teeth and 3 mm below the free gingival margin). 693CHAPTER 28 Ideal Implant Positioninge attachment mechanism of the soft tissue above the bone is less tenacious compared with a tooth, and the defense mechanism of the peri-implant tissues may be weaker than that of teeth.28 To err on the side of safety for the best sulcular health conditions, it is recommended that the clinician should limit sulcular depths adjacent to implants to less than 5 mm.29 is may be even more relevant for single-tooth implants because of the devastating consequences of gingival shrinkage for long-term esthetics. In addition, the inter-proximal regions of the single-tooth implant crown is shared with the adjacent teeth, and anaerobic bacteria that form in the region next to the implant may aect the adjacent natural tooth as a result of a horizontal defect (especially when the implant is closer than 1.5 mm to the tooth).When the implant is countersunk below the crestal cortical bone (as with this depth technique), the trabecular bone around the crest module is weaker against occlusal loads. In addition, when the implant is placed below the crestal bone, the resultant initial crown height is increased, as are moment forces. An increased risk of addi-tional bone loss also is present from the increased moment loads applied to weaker trabecular bone, which may also result in soft tissue shrinkage over the long term. e end result is longer clinical crowns, which also decrease gradually in width (as the narrowing dimensions approach the implant body). e interproximal region may result in black triangular spacings in lieu of interdental papillae.e increased crown height also increases forces to the abut-ment screw and increases the risk of screw loosening.FP-1, FP-2, and FP-3Placement Too Deep. When implant placement results in positioning deeper than 4 mm below CEJ or FGM, many com-plications may result: 1. Unfavorable crown height space (CHS; crown-implant ratio). 2. Periodontal complications because of the inability to perform proper hygiene and associated bone loss on adjacent teeth. 3. Higher moment forces, which cause biomechanical overload with resultant crestal bone loss. 4. Prosthetics are more complicated, with diculty in impression taking, placing abutments, and seating the prosthesis. 5. With deeply placed implants, often the facial plate will resorb, especially if facial inclination is present. 6. Long-term sulcular health is decreased because there is mini-mal to no cortical bone present. e trabecular bone around the crest module is weaker against occlusal loads. 7. Resultant initial crown height and moment forces are increased. A further increased risk of soft tissue shrinkage occurs long term, with additional bone loss at the crest module. e result is longer clinical crowns, which also decrease gradually in width (as the narrowing dimensions approach the implant body), with resultant black triangular spacings in lieu of interdental papillae and compromised long-term esthetics (Figs. 28.46 and 28.47). TreatmentTreatment planning phase. During the treatment planning phase, if it is determined there exist no alternatives to placing the implants at a compromised depth (i.e., bone grafting contraindicated), the fol-lowing can be completed to decrease the possible of complications: 1. Increase the number of implants. 2. Increase the diameters of implants.• Fig. 28.43 Ideal implant depth is 3 mm below the free gingival margin of the future implant crown. This implant is too shallow for an ideal place-ment. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.)• Fig. 28.44 Implant position too deep in apicocoronal position.CEJ—4 mmCEJ—2 mmCEJ• Fig. 28.45 Central incisor root is 4 mm in diameter when it is measured 4 mm below the cement-enamel junction. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.) 694PART VI Implant Surgery 3. Design implants to maximize the surface area. 4. Fabricate removable restorations (less retentive) and incorpo-rate soft tissue support. 5. Remove the removable restoration during sleeping hours to reduce the noxious eects of nocturnal parafunction. 6. Splint implants together, regardless of whether they support a xed or removable prosthesis (Fig. 28.48).At the time of surgery. If an implant is inserted and the position is known to be excessively deep, ideally the implant should be removed, site bone grafted, and then the implant replaced at an ideal position after sucient healing. If rigid xation cannot be accomplished, then the implant should be removed and graft-ing allowed to heal, with future implant placement.Integrated implant. If it is determined after integration that the im-plant position is compromised, then the risk versus benet of removing the implant needs to be determined. If the morbidity of removing the implant is too signicant, then the implant may be restored with the following guidelines: 1. Shorten cantilever length. 2. Minimize buccal and lingual oset loads.AB C• Fig. 28.46 (A) Apically positioned implant resulting in atypical prosthesis and predisposing the implant to bone loss and peri-implant disease. (B) Resultant prosthesis from apically positioned implant. (C) Mandibu-lar implant apically positioned too close to mandibular canal.AB• Fig. 28.47 (A) Black triangle formation as a result of apical positioned implant. (B) Implant placement too deep resulting in significantly larger clinical crown.• Fig. 28.48 The greater the crown-implant ratio, the greater is the need for more implants and splinting the implants. 695CHAPTER 28 Ideal Implant Positioning 3. Ideal emergence prole. 4. Occlusal contact load should be reduced on any oset load from the implant support system. 5. Occlusal contact load should be reduced on any oset load from the implant support system.Occlusal contacts in centric relation (CR) occlusion may be eliminated on the oset load area. A parafunction load may be reduced because the most cantilevered portion of the prosthesis is loaded only during functional activity while eating food.30N: Questionable treatments, including segmental osteoto-mies, are not recommended because of the invasiveness, length of treatment time, and questionable prognosis (Box 28.8). Inadequate DepthWhen the implant body is positioned less than 2 mm below the facial FGM of the crown, the cervical esthetics of the restoration are at an increased risk because limited space is present subgingivally to develop the facial emergence prole of the crown. e porcelain or zirconia of the crown may not be subgingival enough to mask the titanium color of the abutment or implant below the crown margin (Fig. 28.49A). If bone loss occurs, then the titanium implant abutment or body may Complication:• Unfavorablecrownheightspace• (Crown:implantratio)• Highermomentforces:boneloss• Periodontalcomplications• ProstheticsmoredifcultPrevention:• Ideal: • 3mmbelowfreegingivalmargin(2–4mm)• Options: • Graft • ChangetoxedpartialdentureTreatment:1. Removeimplant2. Idealemergenceprole3. Monitor4. ?Treatment • BOX 28.8 Implant Placement Too Deep (Apicocoronally)A BC D• Fig. 28.49 (A) An implant replacing a maxillary lateral incisor that is inserted too shallow. The implant crown is not placed subgingival enough to develop an emergence profile or to mask the color of the abut-ment. (B) The implant is positioned too shallow. (C) An abutment is inserted, and a subgingival margin is created on the implant body. (D) The final implant crown is inserted below the tissue 1.5 mm and on the implant body. (From Misch CE. Single-tooth implant restoration: maxillary anterior and posterior regions. Dental Implant Prosthetics. St Louis, MO: Elsevier Mosby; 2015.) 696PART VI Implant Surgeryalso cast a dark shadow on the gingival tissues. If apical shrinkage of tissue occurs, then the dark titanium abutment and implant body may become directly visible. Periodontal surgical procedures to posi-tion soft tissue over the exposed titanium are unpredictable.On occasion, the crestal bone height is coronal to the ideal bone height (3 mm below the facial FGM). e two most common con-ditions that result in this nding are (1) when the adjacent teeth are closer than 6 mm (in agenesis of a lateral incisor) and (2) when a block bone graft regenerated excess width and height of bone. Ideally, the midcrestal bone is 3 mm below the interproximal bone and fol-lows the interproximal scallop of the CEJ of the missing tooth. When the teeth are closer than 6 mm (i.e., a lateral incisor in the maxilla), the interproximal bone height of each adjacent tooth to the miss-ing space is able to stimulate and maintain bone at the interproximal bone level. e same conditions may occur when bone augmentation gains height to the interproximal height of bone.When a single-tooth implant replaces a missing tooth with these conditions, an osteoplasty should be performed so that the midcrestal region is 3 mm apical to the FGM of the adjacent tooth; otherwise, the implant position will be too shallow and result in a short crown height at the gingival margins.To solve the problem of an implant body placed too shallow, the restoring dentist may need to prepare the implant crest module and place the margin of the crown directly on the implant body (even if esthetic crown lengthening of the surrounding bone and soft tissue is necessary) (see Fig. 28.49B–D). Also feather edge margin should be used to minimizes this weakening of the abutment or implant body.e following may occur when implant positioning is not deep enough (<3 mm from CEJ, <2 mm from FGM): 1. Inadequate emergence prole (transition from the narrower diam-eter of the implant compared with the wider dimension of the crown). 2. Decreased retention of the implant, which may lead to unce-mentable restorations or component fracture. 3. Poor resultant esthetics because implant abutment or implant body will show through, resulting in cervical darkness, and if this occurs in the anterior region, it may be unpleasant for the patient. Normally, the facial margin of the crown will not be able to be placed subgingival enough to mask the titanium color of the abutment below the margin. 4. Inadequate running room because the location of the crest module will leave inadequate room for adequate hygiene. An abrupt change from the prosthetic platform to the diameter of the restoration will result. Normally, this will most likely result in hygiene diculty (Fig. 28.50). TreatmentTreatment planning phase. If it is determined during the treat-ment planning phase that implant positioning would result in an implant being in a nonideal location with respect to the FGM, modications to the treatment plan or nal prosthesis may be indicated. Skeletal discrepancies (deep bite), reduced occlusal vertical dimension (OVD) from attrition or abrasion, minimal bone atrophy after tooth loss, and supraeruption of unopposed teeth may all result in less than ideal space for pros-thetic replacement of the dentition. Traditional prosthetic and restorative procedures are indicated to restore the proper OVD and plane of occlusion and increase the CHS: 1. Modication or adjustment of opposing occlusion should always be explained to the patient at the initiation of treatment to prevent miscommunication issues. is is extremely important, especially if alteration of the opposing tooth would result in the need for endodontic therapy. 2. Ideally, 8.0 mm of space is required for a cementable pros-thesis. e 8-mm requirement for CHS consists of 2 mm of occlusal material space, 4 mm minimum abutment height for retention, and 2 mm above the bone for the biologic width dimension (which does not include the sulcus because a crown margin may be 1 mm subgingival for retention or esthetics). If this cannot be accomplished, a screw-retained prosthesis or change to an FPD treatment plan is indicated.At time of surgery. If the implant is inserted and the position is known to be excessively shallow, removal of the implant is indicated, the osteotomy should be deepened if available bone is present, and the implant is reinserted at a more favorable depth. e location of vital structures should always be deter-mined before deepening of the osteotomy.Integrated implant. After implant integration, if the implant is determined to be of inadequate depth, the implant should be ideally removed. However, if the morbidity of removing the implant is too signicant, then the following may be evaluated as possible treatment options: • Ascrew-retainedprosthesis • Shortencantileverlength/Narrowocclusaltable • Minimizebuccalandlingualosetloads • Idealemergenceprole(Fig. 28.51) • Increasemechanicalandchemicalretentionoftheabutmentby roughening the abutment surface or retentive grooves. RP-4 and RP-5When evaluating a treatment plan for a removable implant pros-thesis, numerous factors need to be addressed. First, it must be determined that adequate interocclusal space is present, especially is a connecting bar is to be utilized. For a bar and overdenture with attachments, 15 mm of space is required from the crest of the ridge to the incisal edge is suggested. If interocclusal space is insucient, then an osteoplasty at the time of surgery should be completed to increase space for the nal prosthesis. Interactive • Fig. 28.50 Poor emergence profile as a result of inadequate implant depth. 697CHAPTER 28 Ideal Implant Positioningtreatment planning may be used to fabricate a reduction guide, which will allow the implant clinician to remove the ideal amount of bone. A minimum of 2.0 mm of acrylic is required to ade-quately retain denture teeth and maintain structural integrity of the prosthesis.Complications: More than 15 mmFor an RP-5 prosthesis, greater interocclusal space is usually not problematic because of the soft tissue support. However, with an RP-4 (implant-supported) prosthesis, greater interocclusal space may pose a problem, with increased “rocking” of the prosthesis because of the lack of soft tissue support (i.e., RP-4 is completely implant supported). With removable prostheses, two prosthetic levels of height should be taken into consideration. e rst is the height of the attachment system to the crest of the bone. e greater the height distance, the greater the forces applied to the bar, screws, and implant structures. e second CHS to consider is the distance from the attachment to the occlusal plane. is distance represents the increase in prosthetic forces applied to the attachment. For example, in a CHS of 15 mm, a locator attach-ment may be 7 mm from the crest of bone, resulting in a lever action of 7 mm applied to the implants. e distance from the rotation point of the locator attachment to the occlusal plane may be an additional 8 mm. Under these conditions, a greater lever action is applied to the prosthesis than to the implant interface. is results in increased instability of the restoration under lateral forces (Fig. 28.52).30 TreatmentIf more than 15 mm of space is present, an RP-5 prosthesis should have ideal interocclusal space for the nal prosthesis. Peripheral extension and the primary stress-bearing area sup-port (maxilla–horizontal palate, residual ridge; mandible–buc-cal shelf) should be used to decrease excessive loading force. e occlusion should include bilateral balanced contacts with no occlusal prematurities. If excessive force exists (i.e., exces-sive CHS and/or parafunction), then an RP-4 (totally implant supported) may be changed to an RP-5 (soft tissue supported) to decrease the force.Complications: Less than 15 mmWhen sucient CHS is lacking and the prosthesis is more prone to component fatigue and fracture, an overdenture is more dicult to fabricate than a porcelain-to-metal xed prosthesis or zirconia mono-lithic prosthesis. e 15-mm minimum CHS provides an adequate bulk of acrylic to resist fracture; space to set denture teeth with-out modication; and room for attachments, bars, soft tissue, and ABC• Fig. 28.51 Implant positioning that is too shallow. (A) Cone beam computerized tomography image depicting an implant placement that is too shallow. (B) Periapical radiograph showing insufficient depth (red) and ideal placement (yellow). (C) Inadequate depth, which led to fracture of implant abutment screw.• Fig. 28.52 Interocclusal space (Crown-Height Space) evaluated via CBCT 3D imaging. 698PART VI Implant Surgeryhygiene. In the mandible (Fig. 28.53) the soft tissue is often 1 to 3 mm in thickness above the bone, so the occlusal plane to soft tissue should be at least 9 to 11 mm in height. An osteoplasty to increase CHS before implant placement or a xed restoration is often indi-cated when abundant bone height and width are present (Fig. 28.54). TreatmentIf less than 15 mm of CHS is present, then an RP-4 and RP-5 may present issues. Without sucient space for tissue health, attachment space, bulk of acrylic, and nonmodied denture teeth, the overdenture may undergo fatigue and possible fractures. An RP-4 may be changed to an RP-5 to obtain soft tissue support to minimize forces to the attachments. Additionally, the overdenture prosthesis should be changed to a metal base, metal reinforced, or ber mesh to increase the strength of the prosthesis, to prevent prosthesis fracture (Box 28.9). Implant Position with Respect to Vital StructuresInferior Alveolar Nerve Canal or Mental ForamenAccurate positioning of implants in approximation to the infe-rior alveolar canal and mental foramen is crucial in preventing neurosensory impairment. e correct location of the nerve and canal should be ascertained via three- dimensional imaging, especially when the implant may be within 2 mm of the nerve. After identication of the vital structures, the implant should be placed greater than 2 mm from the inferior alveolar canal or mental foramen. Implant placement less than 2 mm increases the risk of compression or traumatic injuries to the nerve trunk, which may result in neurosensory decits (Fig. 28.55) Inferior Border of MandiblePlacement of dental implants in the anterior mandible can lead to signicant and even life-threatening complications. Care should be noted to evaluate the angulation and trajectory of the anterior man-dible with three-dimensional imaging to minimize the possibility of perforating the lingual cortex. Two-dimensional radiographs (i.e., panoramic) may lead to false representation of the amount of bone available. If the inferior border of the mandible is perforated, then bleeding may become evident from the sublingual and submental blood vessels. Because this area is dicult to access, dangerous sub-lingual bleeding complications may arise (Fig. 28.56). Nasal Cavitye anterior maxilla is often a very challenging area to place implants. Because of the compromised bone in width and height, along with angulation issues, implants are often malpositioned. Placement of implants in the anterior maxilla may be very challenging, especially when a minimal height of bone is present. Ideally, implants should be positioned just short of the nasal oor, without engaging the thin inferior oor of the nasal cavity. ere do exist more advanced surgical techniques in which the implants may extend into the nasal cavity 1 to 2 mm via a subnasal graft; however, these procedures should be completed with caution (Fig. 28.57).31 Distance from the Maxillary Sinus (Inferior Border)One of the more challenging areas for implant placement involves the posterior maxilla. e implant dentist often encounters compromised bone height and poor bone quality in this area because of bone loss and pneumatization of the maxillary sinus. ere are four treatment options (Misch clas-sication) for implants placed in this area, with respect to the quantity of bone from the crest of the ridge to the inferior border of the sinus (Fig. 28.58):32 1. SA-1: Implant placement that does not penetrate the maxillary sinus proper 2. SA-2: Implant placement with penetration into the sinus approximately 1 to 2 mm without bone grafting. 3. SA-3: Implant placement along with bone grafting, either with the crestal or lateral approach 4. SA-4: Sinus augmentation from a lateral approach with delayed implant placement Prevention of Implant MalpositionIdeal Treatment Planninge surest way to minimize errors in positioning during implant surgery is to develop a comprehensive strategy during the preop-erative assessment phase of treatment. CBCT analysis oers the clinician an excellent evaluation of the patient’s anatomy to prop-erly plan implant position, diameter, and length, which helps to prevent positional, spacing, and depth issues. Ideal Available Bonee amount of available bone width (faciopalatal) should be at least 3.0 mm greater than the implant diameter at implant insertion (i.e. 2.0 mm of buccal bone and 1.0 mm of lingual bone). For example, a 4.0-mm implant requires at least 7.0 mm of bone width (minimum). Augmentation has become very pre-dictable and accepted in the profession, therefore the clinician should never compromise when adequate bone is not available. Various bone grafting techniques and materials are available that the clinician should implement in treating these compro-mised cases. Understanding the Prosthesis Type and Associated Ideal PositioningWhen treatment planning, the nal prosthesis should always be evaluated rst, before implant placement. e implant clini-cian must have a strong understanding of the various prosthesis types (e.g., FP-1, FP-2, FP-3, RP-4, RP-5) along with the posi-tional and prosthesis demands and needs. e prosthesis type • Fig. 28.53 Minimum interocclusal space for an FP-3 prosthesis. 699CHAPTER 28 Ideal Implant Positioning(xed [FP-1, FP-2, FP-3] or removable [RP-4, RP-5]) dictates the ideal placement of implants. It is imperative the patient be fully informed of the various prosthesis types along with the advantages and disadvantages. Soft Tissue Evaluatione biotype (thin versus thick) tissue should always be evalu-ated before implant placement. in biotypes are at higher risk of gingival recession and esthetic issues, especially in the anterior part of the mouth. in biotype patients are more susceptible to malpositioning issues, and greater emphasis should be noted on ideal conditions. If needed, soft tissue augmentation should be completed before implant placement. Condition of the Adjacent TeethBefore implant placement in edentulous sites, the adjacent natural teeth should be evaluated for restorability and existing pathology that may be present. A 5- to 10-year prognostic window should be established for each natural tooth before the completion of an implant treatment plan. If a tooth does not possess a favorable 5- to 10-year prognosis, extraction should be discussed or alternative treatment options. < 2.0 mmABCD• Fig. 28.54 Lack of interocclusal space for removable prosthesis. (A) Evaluation in the treatment planning phase with patient occluding in centric occlusion. (B) The amount of osteoplasty should be determined preoperatively (red line). (C) Osteoplasty via course acrylic bur. (D) Lack of acrylic bulk leads to poor reten-tion of denture teeth and possible fracture of denture base (<2 mm); at least 2 mm of acrylic is required for adequate strength. 700PART VI Implant SurgeryPresence of Pathologye intended implant site should be carefully evaluated for the presence of pathology at the site or latent adjacent pathology asso-ciated with natural teeth, which may lead to increased implant morbidity. It is common to have residual bacteria present, espe-cially if a recently infected natural tooth extraction was performed. Additionally, the adjacent teeth should be evaluated for periapical pathology, because this may lead to a retrograde peri-implantitis. Good Surgical TechniqueTo minimize the possibility of improper positioning, the implant clinician should evaluate the osteotomy location after the use of the rst pilot drill. Usually, the pilot drill is used to a depth of 6 to 8 mm. A direction indicator is placed and should be evaluated both radiographically and with a surgical template for proper posi-tioning. e position can also be evaluated by having the patient close lightly to determine the interocclusal positioning with the direction indicator. Any modications of the angulation should be completed with a Lindemann drill. Poorly Dense BoneIn poorly dense bone (~D4), overpreparation of the osteotomy site may lead to redirection of the implant on placement. Addi-tionally, implants should be inserted with a handpiece rather than a hand ratchet. When implants are placed in poorly dense bone with a ratchet, the implant may be easily redirectioned by placing it in a more elliptical direction.Understand the True Location of Vital StructuresKnowing the exact location of the vital structures is paramount in avoiding complications. Impinging on vital structures such as the mandibular canal, maxillary sinus, or nasal cavity may Complication:• Decreaseretention• Pooremergenceprole• ComponentfracturePrevention:• Ideal: • 3mmbelowfreegingivalmargin(2–4mm)• Options: • ChangetoxedpartialdentureTreatment:• Screwretained• Removeimplant,replacewithdeeperimplant • BOX 28.9 Implant Placement Insucient Depth (Apicocoronally)• Fig. 28.55 Poor positioning leading to inferior alveolar canal impingement.• Fig. 28.56 Poor positioning leading to perforation of the inferior border of mandible.• Fig. 28.57 Poor positioning leading to perforation of the nasal cavity. 701CHAPTER 28 Ideal Implant Positioningincrease morbidity and place the patient at risk for irreversible complications. Use of Surgical TemplatesA surgical template is dened by the prosthodontics glossary as a guide used to assist in ideal surgical placement and angulation of dental implants.21 e objective of using a surgical template is to provide accurate placement of the implant according to a surgical treatment. ere are many dierent types of surgical templates used today. Stumpel classied surgical templates according to the amount of surgical restriction that is used in the template. e design categories are (1) nonlimiting, (2) partial limiting, and (3) complete limiting.33Non-Limiting Designe nonlimiting template allows the implant surgeon dimensional variability in the implant location because the template indicates the ideal space (location) for the nal restoration, not the actual mesiodistal angulation. e nonlimiting template is advantageous because of the ease in fabrication and the low cost involved. ese templates allow the implant surgeon only an initial loca-tion of the proposed prosthesis, not the exact angulation (buc-colingual) and position (mesiodistal). A great deal of exibility and latitude regarding the nal position of the implant is inherent with this type of template (Fig. 28.59). Partial Limiting Designe partial limiting design incorporates a guided sleeve or a slot that allows for angulation of one drill size (usually the pilot drill). After the rst drill is used, the rest of the osteotomy sites are completed freehand. Various techniques can be used in fabricating a partial limiting template, including manual laboratory-fabricated templates or templates fabricated from a radiographic template, which is then converted to a surgical guide template.Complication. Although the partial limiting design is more accurate than the nonlimiting design, these templates still do not allow for nal, positioning of the implant. Clinical studies have shown these types of templates to have a high degree of error in the buccolingual orientation (Fig. 28.60).34 ABCD• Fig. 28.58 Implant placement in posterior maxilla without bone grafting. (A and B) Implant penetration into the sinus cavity. (C) Implant placed into the sinus depicting no bone in the sinus, leading to inadequate support for the prosthesis. (D) Implant placed into sinus causing rhinosinusitis. Complete Limiting DesignWith the complete limiting template design, the position, angula-tion, and depth of the osteotomy are dictated by the guided tubes or sleeves, restricting any variation by the implant surgeon. is type of guide prevents any osteotomy error in the buccolingual and mesiodistal planes. Additionally, drill stops can be incorpo-rated to prevent overpreparation in depth of the site. Basically, with the complete limiting design, the nal position of the implant is known before the actual surgery. is technique is extremely popular because the prosthetic nal abutment or provisional res-toration can be prefabricated for immediate provisionalization after implant placement.Complication. e use of complete limiting surgical templates that are fabricated from interactive treatment planning with cone beam technology has been shown to be highly accurate. However, caution must be used when employing surgical templates that are fabricated conventionally (not from CBCT) on dental study casts, which are rigid, nonfunctional surfaces without information of the soft tissue thickness and bone morphology. ese types of surgical templates, usually made from study casts, allow for place-ment of implants according to an estimate of location of teeth, soft and hard tissue, and vital structures without three-dimensional guidance (Figs. 28.61, 28.62, and 28.63).35 Use of CBCT Surgical GuidesTo overcome the limitations and complications inherent with conventional surgical templates, the use of CBCT-generated tem-plates has evolved in implant dentistry today. A computer-gener-ated surgical guide (partial limiting or complete limiting) provides a link between the CBCT treatment plan and the actual surgery by transferring the interactive plan accurately to the surgical site. With the use of CBCT-generated software programs, this anatomic relationship can be predictably determined before sur-gery. After the scan is completed the data must be converted into a format that can be used by the scanning software. Every treatment-planning software program has its own specic pro-tocol, but all software is compatible with Digital Imaging and Communication in Medicine (DICOM) les that are generated and downloaded from the scanner. Although many third party companies complete the interactive treatment planning process, it is highly recommended the implant dentist be involved in the process. After the les have been converted into the software program, evaluation of potential implant sites in the desired prosthetic locations can be completed. Virtual implants may be placed via comprehensive implant libraries, which include the implant brand, type, diameter, and length. e available bone BA• Fig. 28.59 Nonlimiting surgical templates: (A) Mandibular prosthesis with lingual contour removed. (B) Maxillary prosthesis with lingual contour removed and retention of the palate for support.AB• Fig. 28.60 Complete limiting surgical templates. (A and B) Complete fabricated limiting templates, which allows for accurate placement in the mesiodistal and buccolingual dimensions.702PART VI Implant Surgery AB• Fig. 28.61 Bone-supported surgical template. (A and B) Template requires the exposure of the bone and the complete seating of the surgical template.A B• Fig. 28.62 Tooth-supported surgical template. (A and B) Template requires adequate remaining teeth for complete seating and stabilization over the teeth.A B• Fig. 28.63 Soft tissue–supported surgical template. (A and B) Template requires adequate soft tissue to allow for complete seating and stabilization. 704PART VI Implant Surgerydimensions may be ascertained, along with the density and angu-lation with respect to the planned prosthesis. After completion of the nal implant positions, the treatment plan is saved, and the surgical template is designed.29 it is well documented in the literature that surgical templates are signicantly more accurate than freehand insertion.36 With all types of guides the implant clinician must show good judgment regarding the accuracy of the template and must be able to determine any discrepancies (especially in bone volume) between the intended osteotomy site and the actual current bony architecture of the patient. SummaryOne of the most critical skills in the practice of implant den-tistry is the ability to place an implant in the ideal and cor-rect position. e complexity of this skill set is underrated; the clinician needs to understand the three planes of placement, along with maintaining a safe distance from vital structures. Malpositioning may result in a successful integration of the implant, but it may place the intended restoration at signicant risk for complication and/or failure. Technological advances such as guided surgery and surgical templates have proven to be helpful to implant clinicians, especially those early on their surgical learning curve or in cases in which space tolerances are low. However, even these techniques have margins of error and tolerances that need to be fully understood. With a combina-tion of proper treatment planning and ideal positioning guide-lines, the implant clinician can ensure a predictable surgical and prosthetic outcome (Box 28.10).References 1. Katona TR, Goodacre CJ, Brown DT, etal. Force-moment systems on single maxillary anterior implants: eects of incisal guidance, xture orientation, and loss of bone support. Int J Oral Maxillofac Implants. 1993;8:512–522. 2. Priest GF. e esthetic challenge of adjacent implants. J Oral Maxil-lofac Surg. 2007;65(suppl 1):2–12. 3. Stumpel L. Model-based guided implant placement; planned preci-sion. Inside Dent. 2008;4(9):72–77. 4. Buser D, Martin W, Belser UC. Optimizing esthetics for implant restorations in the anterior maxilla: anatomic and surgical consider-ations. Int J Oral Maxillofac Implants. 2004;19(suppl):43–61. 5. Margelos JT, Verdelis KG. Irreversible pulpal damage of teeth adjacent to recently placed osseointegrated implants. J Endod. 1995;21:479–482. 6. Asscherickx K, Vannet BV, Wehrbein H, et al. Root repair after injury from miniscrew. Clin Oral Implants Res. 2005;16:575–578. 7. Kravitz ND, Kusnoto B. Risks and complications of orthodontic miniscrews. Am J Orthod Dentofacial Orthop. 2007;131:S43–S51. 8. Brisceno CE, Rossouw PE, Carrillo R. Healing of the roots and surrounding structures after intentional damage with miniscrew implants. Am J Orthod Dentofacial Orthop. 2009;135:292–301. 9. Buser D, Martin W, Belser UC. Optimizing esthetics for implant restorations in the anterior maxilla: anatomic and surgical consider-ations. Int J Oral Maxillofac Implants. 2004;19(suppl):43–61. 10. Esposito M, Ekestubbe A, Grondahl K. Radiologic evaluation of marginal bone loss at tooth surfaces facing single Branemark implants. Clin Oral Implants Res. 1993;4:151–157. 11. Rieger MR, Mayberry M, Brose MO. Finite element analysis of six endosseous implants. J Prosthet Dent. 1990;63:671–676. 12. Tarnow DP, Cho SC, Wallace SS. e eect of inter-implant distance on the height of inter-implant bone. J Periodontol. 2000;71:546–549. 13. Su CY, Fu JH, Wang HL. e role of implant position on long‐term success. Clin Adv Periodontics. 2014;4(3):187–193. 14. Spray JR, Black CG, Morris HF. e inuence of bone thickness on facial marginal bone response: stage 1 placement through stage 2 uncovering. Ann Periodontol. 2000;5:119–128. 15. Misch CE, Bidez MW. Occlusion and crestal bone resorption:etiology and treatment planning strategies for implants. In: McNeil C, ed. Science and Practice of Occlusion. Chicago: Quintessence; 1997. 16. Ha CY, Lim YJ, Kim MJ, etal. e inuence of abutment angula-tion on screw loosening of implants in anterior maxilla. J Oral Max-illofac Implants. 2011;26:45–55. 17. Misch CE. e maxillary anterior single tooth implant aesthetic–health compromise. Int J Dent Symp. 1995;3:4–9. 18. Perel S, Sullivan Y, eds. Esthetics and Osseointegration. Chicago: Quintessence; 1994. 19. Saadouin AP, Sullivan DY, Korrschek M, etal. Single tooth implant management for success. Pract Periodontics Aesthet Dent. 1994;6:73–82. 20. Goodacre CJ, Kan JK, Rungcharassaeng K. Clinical complications of osseointegrated implants. J Prosthet Dent. 1999;81:537–552. 21. Nisapakultorn K, Suphanantachat S, Silkosessak O, Rattanamong-kolgul S. Factors aecting soft tissue level around anterior maxillary single-tooth implants: soft tissue level at single-tooth implants. Clin Oral Implants Res. 2010;21(6):662–670. https://doi.org/10.1111/j.1600-0501.2009.01887.x. 22. Misch CE. e maxillary anterior single tooth implant aesthetic–health compromise. Int J Dent Symp. 1995;3:4–9. 23. Saadouin AP, Sullivan DY, Korrschek M, et al. Single tooth implant management for success. Pract Periodontics Aesthet Dent. 1994;6:73–82.Implant Distances:• Implant-Tooth:1.5mm(apical),2.0mm(coronal)• Implant–implant:3.0mm Bone Thickness: (after implant placement)• Buccal=2.0mm• Lingual=1.0mmIdeal Positioning:• Apicocoronal:2.0–3.0mmapicaltofreegingivalmarginProsthesis Type: (Cement vs. Screw Retained)• Anterior • Cement:Slightlylingualtoincisaledge • Screw:CingulumArea• Posterior • Cement/Screw:CentralFossaInterocclusal Space: (minimum)• Cement-RetainedProsthesis • 7–8.0mm(Zirconia),8–10.0mm(PorcelainFusedMetal)• Screw-RetainedProsthesis • 5.0–6.0mm(Zirconia/PFM)• Overdenture • Bar-Retained:14–16mm(dependingonattachment) • IndependentAttachment:9mm(e.g.Locator)Vital Structure Distance:• NasalCavity:mayengagecorticalbonewithoutperforation• MaxillarySinus:(intosinusproper) • SA-1:Implantplacementbelowsinusoor • SA-2:1.0–2.0mmmembraneelevation • SA-3:Transcrestal(3.0-4.0mm),LateralWall(>4.0mm) • SA-4:LateralWall:minimumof5mmhostbone• MandibularAnterior:Nocorticalboneperforation• MandibularPosterior:2.0mmfrommandibularcanal/mentalforamen • BOX 28.10 Ideal Implant Positioning Summary 705CHAPTER 28 Ideal Implant Positioning 24. Perel S, Sullivan Y, eds. Esthetics and Osseointegration. Chicago: Quintessence; 1994. 25. Hansson S. e implant neck smooth or provided with retention elements. Clin Oral Implants Res. 1999;10:394–405. 26. Malevez C, Hermans M, Daelemans P. Marginal bone levels at Brånemark system implants used for single tooth restoration: the inuence of implant design and anatomical region. Clin Oral Implants Res. 1996;7:162–169. 27. Grunder U. Stability of the mucosal topography around single tooth implants and adjacent teeth: 1 year results. Int J Periodontics Restor-ative Dent. 2000;20:11–17. 28. Berglundh T, Lindhe J, Ericsson I, et al. e soft tissue barrier at implants and teeth. Clin Oral Implants Res. 1991;2 :81–90. 29. Yukna RA. Periodontal considerations for dental implants. In: Block MS, Kent JN, eds. Endosseous Implants for Maxillofacial Reconstruc-tion. Philadelphia: WB Saunders; 1995. 30. Misch CE, Goodacre CJ, Finley JM, etal. Consensus conference panel report: crown-height space guidelines for implant dentistry—part 2. Implant Dent. 2006;15:113–121. 31. Naitoh M, Ariji E, Okumura S, etal. Can implants be correctly angulated based on surgical templates used for osseointegrated den-tal implants? Clin Oral Implants Res. 2000;11:409–414. 32. Ha CY, Lim YJ, Kim MJ, etal. e inuence of abutment angula-tion on screw loosening of implants in anterior maxilla. Int J Oral Maxillofac Implants. 2011;26:45–55. 33. Stumpel 3rd LJ. Cast-based guided implant placement: a novel tech-nique. J Prosthet Dent. 2008;100:61–69. 34. Almog DM, Torrado E, Meitner SW. Fabrication of imaging and sur-gical guides for dental implants. J Prosthet Dent. 2001;85:504–508. 35. Ramasamy M, Giri RR, etal. Implant surgical guides: from the past to the present. J Pharm BioAllied Sci. 2013;5(suppl 1):S98–S102. 36. Nickenig HJ, Wichmann M, Hamel J, etal. Evaluation of the dif-ference in accuracy between implant placement by virtual planning data and surgical guide templates versus the conventional free-hand method—a combined invivo—invitro technique using cone-beam CT (Part II). J Cranio-Maxillo-Fac Surg. 2010;38(7):488–493.

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