Preprosthetics










Preprosthetics
1
Functional Disorders After Tooth Loss
The masticatory system is a unit made up of functio nally oriented tissue parts, and it
only functions properly if all parts of the system are present and working smoothly. If
normal functioning of the masticatory system no longer exists—whether because of
loss or because disease has changed one part of the system—this is referred to as a
functional disorder, malfunction, or dysfunction. In relation to the position and size of an
edentulous space between teeth or a shortened dental arch, changes in facial expression
and articulation may be observed as well as effects on masticatory function, the muscles
of mastication, and the temporomandibular joints (TMJs). Above all, however, there is
an adverse effect on the remaining dentition.
If there is an edentulous space, the supporting function of the closed dental arch af-
forded by the approximal contact points is lost and the teeth migrate into the space (Fig
1-1). Under the pressure of tooth migration, the bony alveolar wall opposing the eden-
tulous space is broken down. At the same time, the alveolar bone beneath the space is
resorbed. The consequence is the formation of a periodontal pocket in the area bordering
the edentulous space. In addition, the approximal contacts with adjacent teeth become
loose. As a result, the interdental areas open up and are no longer protected against food
particles, which can become trapped there. This is followed by the formation of approxi-
mal caries and in ammation, which will damage the marginal periodontium.
As a result of the tipping of teeth, the normal occlusal contacts with the opposing teeth
are lost. The occlusal surface inclines toward the normal occlusal level, so that some
occlusal points migrate beyond the normal level and others fall below what is normal.
The antagonists then overerupt until they regain occlusal contact, giving rise to severe
malocclusions.

2
Preprosthetics
The elongation (lengthening) of teeth may be
due to the reactive behavior of the periodontal
tissues (Fig 1-2): If the tooth is not pressed into
the socket by masticatory force, the pressure in
the blood vessels lifts the tooth out of the socket.
The gentle but continuous pull on the ligamen-
tous apparatus acts as a stimulus on the alveolar
bone, which grows in the direction of the pull un-
til the tooth is held by antagonist contact or the
opposing jaw.
The overeruption of an antagonist has two re-
percussions. First, in the dental arch from which
the tooth is overerupting, all of the teeth become
more mobile, bringing consequences such as
loss of sagittal support, opening of the interden-
tal spaces, approximal caries, and damage to the
marginal periodontium. Second, the elongation
gives rise to an occlusal disorder as the over-
erupting tooth interferes with gliding movements
(Fig 1-3). Smooth occlusal gliding out of centric
occlusion is no longer possible.
Enlargement of edentulous spaces means that
the stresses on the residual teeth become greater
and the periodontal damage more pronounced.
Deterioration of the dentition progresses rapidly
(Fig 1-4).
Malocclusions in a partially edentulous denti-
tion arise because the continuous masticatory
eld is interrupted and sagittal or occlusal sup-
port contacts are lost. As a result, centric stops
no longer meet simultaneously in their contact
areas: some have premature contact and others
no contact at all. This brings about uneven dis-
tribution of forces in the masticatory eld: some
teeth are overloaded and others underloaded. Be-
cause the sagittal support is missing, tipping and
migration of teeth will occur whereby the tipped
and migrated teeth are loaded eccentrically and
hence nonphysiologically.
In all lateral or protrusive movements, all the
mandibular teeth glide downward and forward
on the posterior sloping surfaces of their maxil-
Fig 1-1 If a tooth is missing within an arch, the remaining
teeth migrate into the edentulous space. As a result, the sup-
porting function is lost, the interdental papillae are no longer
protected, and caries develops in the approximal areas. In ar-
eas bordering the space, pocketing occurs at the marginal peri-
odontium. In addition, the opposing tooth overerupts into the
space, potentially causing tooth mobility, loss of support, and
approximal caries in that arch as well.
Fig 1-2 If the antagonists are missing, the teeth overerupt
until they are stopped by the opposing jaw. This overeruption
looks like lengthening of the tooth and is referred to as elon-
gation. This exposes the cervical areas of the teeth so that
cervical caries may develop. Prosthetic restoration becomes
difcult under these conditions.

3
Functional Disorders After Tooth Loss
lary antagonists because of condylar, neuromus-
cular, and tooth guidance. If the cuspal paths are
no longer arranged in the right spatial inclination
because of tipping of teeth, the centric stops lose
their antagonist contact.
Condylar and neuromuscular guidance are
therefore abnormally stressed, which may result
in TMJ and muscle diseases (Fig 1-5). Joint dam-
age is often evident as disc dislocation with acute
joint clicking when the disc pops out of its nor-
mal position beyond the edge of the mandibular
fossa. This will result in pain of varying severity
on loading.
Myopathies are diseases of the neuromuscular
system that are evident initially as muscle tension
and induration and later as disorders of metabol-
ic breakdown and associated muscle pains.
Fig 1-3 As a result of tipping, the distal occlusal points migrate
beyond the occlusal line and the mesial points migrate below
it. Consequently, the stress relationships for the affected teeth
are also altered. Interference with gliding movements within
the dental arch occurs during mandibular movements.
Fig 1-4 Early signs of destruction of a partially edentulous
dentition can be seen from the migration of posterior teeth,
which results in loss of interdental support. Tipping of teeth
and hence a change in occlusal relationships are always associ-
ated with tooth migration.
Fig 1-5 In the fully dentate dentition, the condyle is in a
neutral position in the fossa when in centric occlusion. If the
supporting function of the teeth is lost because of shorten-
ing of the dental arch, there is inevitably abnormal loading of
the TMJs. The condyle is pressed into the mandibular fossa by
the activity of the masticatory muscles. This leads to traumatic
changes to the TMJs.

4
Preprosthetics
Functional Disorders and
Loading of Residual
Dentition
Abnormal loading of the TMJs and the mastica-
tory muscles appears when the supporting func-
tion of the posterior teeth is lost and the muscles
of mastication press the condyle into the man-
dibular fossa. The abnormal loading of the masti-
catory muscles leads to displacement of the bite
position; the mandible is shifted forward, which
accelerates deleterious changes in the TMJ.
Displacement of the bite position inuences the
residual dentition. Either the remaining anterior
teeth are moved labially by occlusal pressure, or
an edge-to-edge bite arises with severe abrasion
of the incisal edges. This results in severe mobil-
ity of teeth and even complete deterioration of
the dentition.
The progressive destruction of a partially eden-
tulous dentition may be delayed over prolonged
periods. For instance, given normal loading and
a resistant periodontium, a dentition may even
make up for the loss of several molars itself. In
most cases, however, the described symptoms
occur within a few years and quickly lead to loss
of all the teeth if the deterioration is not halted by
prosthetic treatment.
The changes are most striking in complete
edentulism. As a result of complete tooth loss,
the mandible or maxilla collapses, lip support is
lost, and the vertical dimension of occlusion is
reduced, which inevitably pushes the mandible
forward. All of these changes cause the lips to
cave in; in addition, the vermilion of the lips dis-
appears, the mouth becomes thin, and the lower
part of the face is shortened. This results in an
aged facial appearance with pronounced wrin-
kles around the mouth area caused by general
slackness of the muscles of mastication and the
perioral musculature, because normal mastica-
tory function no longer places any load on these
tissue parts (Figs 1-6 and 1-7). The bony areas to
which the masticatory muscles attach are also re-
sorbed.
Fig 1-6 In the face of an aged edentulous patient, the extreme
wrinkling around the sunken mouth becomes pronounced, the
nose appears to lengthen, the cranial fossae at the sides are
also sunken, and the slack buccal muscles cause the cheeks to
sag. The facial proportions are therefore shifted.
Fig 1-7 Changes to the masticatory system and face are most
striking in complete edentulism: The alveolar ridges and bony
tissue for the muscle attachments are resorbed, the mandible
moves closer to the maxilla, lip support is lost, the vermilion of
the lips disappears, and the face looks more aged.

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Preprosthetics1Functional Disorders After Tooth LossThe masticatory system is a unit made up of functio nally oriented tissue parts, and it only functions properly if all parts of the system are present and working smoothly. If normal functioning of the masticatory system no longer exists—whether because of loss or because disease has changed one part of the system—this is referred to as a functional disorder, malfunction, or dysfunction. In relation to the position and size of an edentulous space between teeth or a shortened dental arch, changes in facial expression and articulation may be observed as well as effects on masticatory function, the muscles of mastication, and the temporomandibular joints (TMJs). Above all, however, there is an adverse effect on the remaining dentition.If there is an edentulous space, the supporting function of the closed dental arch af-forded by the approximal contact points is lost and the teeth migrate into the space (Fig 1-1). Under the pressure of tooth migration, the bony alveolar wall opposing the eden-tulous space is broken down. At the same time, the alveolar bone beneath the space is resorbed. The consequence is the formation of a periodontal pocket in the area bordering the edentulous space. In addition, the approximal contacts with adjacent teeth become loose. As a result, the interdental areas open up and are no longer protected against food particles, which can become trapped there. This is followed by the formation of approxi-mal caries and in ammation, which will damage the marginal periodontium. As a result of the tipping of teeth, the normal occlusal contacts with the opposing teeth are lost. The occlusal surface inclines toward the normal occlusal level, so that some occlusal points migrate beyond the normal level and others fall below what is normal. The antagonists then overerupt until they regain occlusal contact, giving rise to severe malocclusions. 2PreprostheticsThe elongation (lengthening) of teeth may be due to the reactive behavior of the periodontal tissues (Fig 1-2): If the tooth is not pressed into the socket by masticatory force, the pressure in the blood vessels lifts the tooth out of the socket. The gentle but continuous pull on the ligamen-tous apparatus acts as a stimulus on the alveolar bone, which grows in the direction of the pull un-til the tooth is held by antagonist contact or the opposing jaw.The overeruption of an antagonist has two re-percussions. First, in the dental arch from which the tooth is overerupting, all of the teeth become more mobile, bringing consequences such as loss of sagittal support, opening of the interden-tal spaces, approximal caries, and damage to the marginal periodontium. Second, the elongation gives rise to an occlusal disorder as the over-erupting tooth interferes with gliding movements (Fig 1-3). Smooth occlusal gliding out of centric occlusion is no longer possible.Enlargement of edentulous spaces means that the stresses on the residual teeth become greater and the periodontal damage more pronounced. Deterioration of the dentition progresses rapidly (Fig 1-4).Malocclusions in a partially edentulous denti-tion arise because the continuous masticatory eld is interrupted and sagittal or occlusal sup-port contacts are lost. As a result, centric stops no longer meet simultaneously in their contact areas: some have premature contact and others no contact at all. This brings about uneven dis-tribution of forces in the masticatory eld: some teeth are overloaded and others underloaded. Be-cause the sagittal support is missing, tipping and migration of teeth will occur whereby the tipped and migrated teeth are loaded eccentrically and hence nonphysiologically.In all lateral or protrusive movements, all the mandibular teeth glide downward and forward on the posterior sloping surfaces of their maxil-Fig 1-1 If a tooth is missing within an arch, the remaining teeth migrate into the edentulous space. As a result, the sup-porting function is lost, the interdental papillae are no longer protected, and caries develops in the approximal areas. In ar-eas bordering the space, pocketing occurs at the marginal peri-odontium. In addition, the opposing tooth overerupts into the space, potentially causing tooth mobility, loss of support, and approximal caries in that arch as well.Fig 1-2 If the antagonists are missing, the teeth overerupt until they are stopped by the opposing jaw. This overeruption looks like lengthening of the tooth and is referred to as elon-gation. This exposes the cervical areas of the teeth so that cervical caries may develop. Prosthetic restoration becomes difcult under these conditions. 3Functional Disorders After Tooth Losslary antagonists because of condylar, neuromus-cular, and tooth guidance. If the cuspal paths are no longer arranged in the right spatial inclination because of tipping of teeth, the centric stops lose their antagonist contact.Condylar and neuromuscular guidance are therefore abnormally stressed, which may result in TMJ and muscle diseases (Fig 1-5). Joint dam-age is often evident as disc dislocation with acute joint clicking when the disc pops out of its nor-mal position beyond the edge of the mandibular fossa. This will result in pain of varying severity on loading.Myopathies are diseases of the neuromuscular system that are evident initially as muscle tension and induration and later as disorders of metabol-ic breakdown and associated muscle pains.Fig 1-3 As a result of tipping, the distal occlusal points migrate beyond the occlusal line and the mesial points migrate below it. Consequently, the stress relationships for the affected teeth are also altered. Interference with gliding movements within the dental arch occurs during mandibular movements.Fig 1-4 Early signs of destruction of a partially edentulous dentition can be seen from the migration of posterior teeth, which results in loss of interdental support. Tipping of teeth and hence a change in occlusal relationships are always associ-ated with tooth migration.Fig 1-5 In the fully dentate dentition, the condyle is in a neutral position in the fossa when in centric occlusion. If the supporting function of the teeth is lost because of shorten-ing of the dental arch, there is inevitably abnormal loading of the TMJs. The condyle is pressed into the mandibular fossa by the activity of the masticatory muscles. This leads to traumatic changes to the TMJs. 4PreprostheticsFunctional Disorders and Loading of Residual DentitionAbnormal loading of the TMJs and the mastica-tory muscles appears when the supporting func-tion of the posterior teeth is lost and the muscles of mastication press the condyle into the man-dibular fossa. The abnormal loading of the masti-catory muscles leads to displacement of the bite position; the mandible is shifted forward, which accelerates deleterious changes in the TMJ.Displacement of the bite position inuences the residual dentition. Either the remaining anterior teeth are moved labially by occlusal pressure, or an edge-to-edge bite arises with severe abrasion of the incisal edges. This results in severe mobil-ity of teeth and even complete deterioration of the dentition.The progressive destruction of a partially eden-tulous dentition may be delayed over prolonged periods. For instance, given normal loading and a resistant periodontium, a dentition may even make up for the loss of several molars itself. In most cases, however, the described symptoms occur within a few years and quickly lead to loss of all the teeth if the deterioration is not halted by prosthetic treatment.The changes are most striking in complete edentulism. As a result of complete tooth loss, the mandible or maxilla collapses, lip support is lost, and the vertical dimension of occlusion is reduced, which inevitably pushes the mandible forward. All of these changes cause the lips to cave in; in addition, the vermilion of the lips dis-appears, the mouth becomes thin, and the lower part of the face is shortened. This results in an aged facial appearance with pronounced wrin-kles around the mouth area caused by general slackness of the muscles of mastication and the perioral musculature, because normal mastica-tory function no longer places any load on these tissue parts (Figs 1-6 and 1-7). The bony areas to which the masticatory muscles attach are also re-sorbed.Fig 1-6 In the face of an aged edentulous patient, the extreme wrinkling around the sunken mouth becomes pronounced, the nose appears to lengthen, the cranial fossae at the sides are also sunken, and the slack buccal muscles cause the cheeks to sag. The facial proportions are therefore shifted.Fig 1-7 Changes to the masticatory system and face are most striking in complete edentulism: The alveolar ridges and bony tissue for the muscle attachments are resorbed, the mandible moves closer to the maxilla, lip support is lost, the vermilion of the lips disappears, and the face looks more aged. 5Functional Disorders and Loading of Residual DentitionImpaired masticatory function affects the en-tire digestive process. The inability to crush food properly, together with insufcient insalivation and predigestion, will initially lengthen the time food stays in the stomach; the stomach muscles slacken, and diseases of the intestinal tract devel-op because of the abnormal decay and fermenta-tion processes.The consequences of tooth loss that impairs function suggest that prosthetic replacement of missing teeth is indispensable. The prosthetic replacement has to be anchored to the residual teeth that are still present or supported on the mucosa, which is unsuitable for absorbing mas-ticatory forces.Periodontal tissues are far better suited to ab-sorbing masticatory forces than the mucosal and bony foundation for a denture base (Fig 1-8). The cells of the periodontal tissue have differentiated to absorb forces: Sharpey bers convert pres-sure into tension, stabilizing the alveolar cortical bone, which can dissipate force effectively. Bone is known to grow in the direction of pull and is broken down under pressure—a functional rela-tionship that is exploited to achieve orthodontic tooth movements.The mucosal and bony base can absorb moder-ate masticatory force because of shifts of uid in the soft tissue. The mucosa transfers masticatory force to the bone, for which a moderate masti-catory force is favorable because the periosteum here is stimulated by brous anchorage of the at-tached mucosa. The bone will atrophy if there is complete inactivity. However, even at masticatory forces that are normal for the periodontium, the bone is subject to compressive loading to such an extent that it is resorbed; this has to be corrected by constant rebasing.If the loading of the residual dentition is greater than normal because of the prosthetic replace-ment, there is a pronounced increase in the Sharpey ber bundles, and hence periodontal loading capacity is higher. It is important that the higher load contacts the periodontium centrally and does not tip the tooth, causing nonphysiolog-ic loading of the brous tissue.In a fully dentate dentition, tipping of the teeth is compensated for by the sagittal support from approximal contacts, tissue interlinking, double interlocking with antagonists, and the neuromus-cular reex arc. In a partially edentulous dentition, sagittal support, tissue interlinking, and antago-nist contacts are largely lost; only the reex arc remains. However, the arc only works when there is overloading and not with below-threshold con-tinuous loads. This can give rise to and explain specic denture requirements.Fig 1-8 If a force hits the tooth centrally, the whole periodon-tium is physiologically under tension. On transverse loading and tooth tipping, only a third of the periodontal brous surface is physiologically under tensile stress (green bracket), a third remains neutral and unloaded, and a third is nonphysiologically compressed. 6PreprostheticsFunction of Dental ProsthesesThe term prostheses refers to all mechanical de-vices that serve as a functional or cosmetic re-placement for lost anatomical tissue. Hence every tooth replacement—whether a crown or a partial denture—is a prosthesis. The term partial prosthe-sis is actually a tautology because any prosthesis is essentially a partial replacement. The following grouping of teeth replacements is useful in dis-tinguishing the different types of prostheses, and their names emphasize the design features of the specic replacements (Fig 1-9):• A crown replaces hard dental tissue in a wide variety of xed designs; in the broadest sense, this also includes restorative treatment.• A xed partial denture replaces teeth, dental hard substance, and alveolar bone; this xed prosthet-ic replacement is rmly spanned between abut-ments, which is why they are also called bridges.• A removable partial denture is a removable tooth replacement that replaces single teeth and alveolar bone in a partially edentulous dentition.• A complete denture is a removable full denture that replaces all the teeth and missing alveolar bone.Depending on the amount of time a prosthesis is used, a distinction is made between interim/provisional or immediate prostheses and deni-tive prostheses. The terms immediate prosthesis and interim prosthesis denote the instant pros-theses used for a specic indication.An immediate prosthesis is fabricated accord-ing to a model prepared before extraction of the teeth that are going to be replaced. The teeth are ground on the model and replaced by a prosthe-sis construction. An immediate denture is insert-ed directly after extraction of the teeth.An interim prosthesis is a provisional removable tooth replacement that is fabricated and inserted immediately after tooth extraction as a form of wound closure and is used until the denitive re-placement is inserted. After tooth extraction, an impression is taken, models are made, and the prosthesis is fabricated with the same design fea-tures and functions as an immediate prosthesis.Interim prostheses offer good wound closure and better adaptation of the alveolar ridge tissue to loading. Researchers have observed that pa-tients who are tted with interim prostheses ex-perience less shrinkage of the alveolar ridge than those who are not. Interim prostheses offer an es-thetic replacement until the denitive restoration is inserted; they maintain the vertical dimension of occlusion, allow natural chewing movements, and as spacers prevent any displacement of teeth bordering edentulous spaces. Another advantage of these interim prostheses lies in the recording of the maxillomandibular relationship for the denitive prosthesis, especially in the case of complete dentures. Furthermore, speech function is preserved for the patient. Denitive prostheses are the form of tooth replacement that is intended to be in place in the long term.The aim of prosthetic treatment is to replace lost tissue and avoid, or at least reduce, all the functional disorders that occur because of tooth loss. The specic functions of a tooth replacement can thus be identied as follows (Fig 1-10):• Biomechanical function involves restoring the closed dental arch by replacing the missing tis-sue parts. The aim is to secure the supporting function within the dental arch, create a normal occlusal situation, and enable physiologic load-ing of the available tissue.• Therapeutic function involves halting any dete-rioration of the dentition that has already start-ed. This also relates to delaying or preventing changes to other tissue parts of the masticatory system by means of correct prosthetic design.• Prophylactic function means stopping secondary damage resulting from the prosthetic replace-ment and preventing future pathologic changes.• Regulating function concerns prosthetic mea-sures intended to improve or establish the func-tioning of a masticatory system. This includes esthetic aspects and unimpaired phonetics.Design principles and the criteria of functional testing can be deduced from this general descrip-tion of functions. Descriptions of specic prosthe-ses in the following sections not only explain the constructional measures but also cover the func-tional references of the tooth replacement. Possi-ble errors that may result are examined in detail. 7Function of Dental ProsthesesCrownResidual dentitionReplacementFunctional valueFixed partial denture Removable partial denture Complete denture 0% 50% 100% 0% 50% 100% 0% 50% 100% 0% 50% 100%Fig 1-9 The possible functional value that can be achieved by a dental replacement in the ideal situation can be cor-related with the different prosthesis and tooth replacement groups. A functional value of 100% in single-tooth reha-bilitation can be achieved by dentistry and dental technology methods, whereas severe loss of masticatory function can be expected in the case of complete prostheses. Functions of prosthetic treatmentBiomechanical function: Restoration of masticatory functionTherapeutic function: Stopping deterioration of the dentitionProphylactic function: Preventing secondary damageRegulating function: Improving esthetics and phoneticsFig 1-10 The functions of prosthetic treatment can be broken down into four functional areas for teaching purposes. No area has particular prior-ity, and all functions need to be accomplished equally. 8PreprostheticsRestorative TreatmentRestorative treatment refers to a single-tooth restoration in which the diseased dental hard substance is replaced by tissue-compatible ma-terial. Restorative treatment becomes necessary for dental defects resulting from chipping of the teeth during trauma, caries lesions, or abrasive wear.Restorations are intended to restore the origi-nal morphology of the tooth and to be resistant to conditions in the oral cavity, dimensionally stable, and tissue compatible. Their color should not differ from that of the natural tooth, and res-torations should be cost-effective to produce. The margins of the restoration are placed in areas that are accessible to mechanical oral hygiene mea-sures or subject to self-cleaning. The restoration must withstand masticatory loads and must not fall out. Restorations can be classied according to the following:• The extent of dental destruction or the dimen-sions of the tooth surfaces to be replaced• The nature of the restorative material (ie, plastic or metal)• The nature of the fabrication process (ie, direct or indirect fabrication)Cavity or tooth preparation refers to preparing the tooth to receive a restoration. The process in-volves removing the caries or preparing the de-fect in the dental tissue and treating the wound in the dentin. To remove the soft carious tissue with a low-speed drill, the hard enamel layer is rst removed at high speed under water cooling. Tooth preparation is intended to spare hard dental tis-sue, provide permanent retention for the restora-tion, and prevent new caries from developing. It is done with rotary instruments at low or normal speed (4,500 rpm and above) and under water cooling and is not extended to the gingival margin.The cavity to receive a restoration has the fol-lowing basic features (Fig 1-11):• The cavity oor is the interface directed toward the pulp, which must be a minimum of 1.5 mm from the tooth surface in order to create high enough walls for the restoration.• The cavity walls are the lateral borders to the enamel and dentin. The transitions between the oor and wall are rounded. For plastic restor-ative materials, the cavity walls are slightly un-dercut. For metal restorative materials, the oor and wall form a nearly 90-degree angle.• The cavity margin, or the border between the cavity wall and the tooth surface, forms the sub-sequent restorative margin. For cast restorations and adhesive restorations made of composite, the cavity margin is beveled in the enamel.• Extension surfaces are the cavity walls that bor-der the vertical pulpoaxial cavity oor on the ap-proximal surfaces.Caries lesions are subdivided into ve classes according to Black’s classication (Fig 1-12):• Class I caries refers to occlusal lesions in the area of the pits and ssures in molars and pre-molars. The term is used for ssure caries that starts in spots in the ssures and runs along the dentinoenamel junction. Any overhanging enamel areas that arise will break off under masticatory pressure.• Class II caries describes approximal lesions in premolars and molars. An approximal defect in posterior teeth in a closed dental arch can only be prepared occlusally so that a multisurface cavity is formed. A box-shaped preparation with rounded transitions is required to restore an ap-proximal caries lesion. The approximal-cervical shoulder lies perpendicular to the crown axis or slopes slightly from the outside inward.• Class III caries refers to approximal cavities in anterior teeth without involvement of the inci-sal edge. The small, round cavity opening in the area of the anterior teeth is prepared from the lingual, and the cavity margins are extensively beveled to achieve a wide retentive surface on the dental enamel.• Class IV caries relates to approximal defects in anterior teeth involving damage to the incisal edge. Loss of the incisal edge necessitates ex-tensive beveling of the enamel (1 to 2 mm), which is mainly restored with a tooth-colored restora-tion retentively xed to the dental enamel by the enamel etching technique.• Class V caries denotes defects close to the gin-giva on the labial and buccal tooth surfaces. Cervical cavities are surrounded by enamel on all sides. 9Restorative TreatmentFig 1-11 Tooth preparation removes carious dental hard substance and shapes a cavity to receive a restoration. Cavity oorBuccal cavity wallBuccal cavity marginLingual cavity wallApproximal-cervical shoulderBuccal extension surfaceTooth surfaceDistal cavity wallPulpal cavity wallFig 1-12 Caries classes I through V can be distinguished based on Black’s systematic classication. Class IV: Approximal-incisal cavities in anterior teethClass V: Cervical cavities on smooth surfacesClass I: Occlusal cavities in posterior teethClass II: Approximal cavities in posterior teethClass III: Approximal cavities in anterior teeth 10PreprostheticsRestorative MaterialsRestorations made from plastic restorative mate-rial are fabricated by the dentist in the patient’s mouth using the direct method. A distinction is made between a provisional restoration as a tem-porary seal and the denitive restoration for the long-term restoration. Hardening substances in the form of ready-to-use mixtures of zinc and cal-cium sulfate from tubes, zinc oxide–clove oil with additives, and heat-deformable gutta-percha are used as temporary restorative materials.Amalgam, composites, glass-ionomer cements, and gold leaf or crystalline gold (sponge gold) are used for denitive restorations. Tooth preparation is performed as described, depending on the re-storative material used.Amalgam restorations for caries treatment in conservative dentistry are made of a heteroge-neous alloy of mercury with other metals. They are used in the occlusion-bearing posterior re-gion and to build up cusps (Figs 1-13 and 1-14); amalgam restorations are not used for anterior restorations for esthetic reasons. The liquid mix-ture of mercury and other metals can be readily packed into the cavity before it hardens into its solid form. The ready-to-use amalgam alloy is mechanically blended from two components at a 1:1 ratio of liquid mercury and powdered amal-gam particles. Correctly prepared amalgam resto-rations are extremely durable and leak only small amounts of mercury. However, because of this leakage, amalgams are suspected of being dele-terious to health. Measurements of mercury in sa-liva, blood, and urine show a correlation between the concentration of inorganic mercury com-pounds and the number of teeth lled with amal-gam. Therefore, amalgam restorations are unsuit-able for children younger than 6 years, pregnant women, and patients with kidney disease. Owing to the hazard posed by mercury vapors and their chemical afnity for precious metals, amalgams are rarely used. Similarly, amalgam in direct con-tact with metallic crowns will release mercury be-cause of electrogalvanic corrosion.Composite restorations are made of tooth-colored acrylic resin reinforced with inorganic llers. The composite is packed into the cavity in its liquid state and sets chemically or under ul-traviolet light. Composite is not as mechanically durable as amalgam because it shrinks during curing and has high thermal expansion. Compos-ites are not as suitable for posterior restorations as they are for the anterior region. They can be 2 mmFig 1-13 The buccal and lingual cavity walls for an amalgam restoration are prepared slightly undercut. The minimum cavity depth is 2 mm. The transitions are rounded at the cavity oor to prevent a notching effect with the dental tissue.Fig 1-14 The approximal cavity walls for an amalgam restoration are pre-pared slightly divergent, in an occlusal direction, so that the marginal ridge ar-eas cannot break. The buccal and lingual walls are slightly undercut to give the restoration material sufcient retention. 11Restorative Materialsused for small occlusal cavities if the antagonist contacts lie on the natural dental hard substance. Composite restorations are adhesively and reten-tively bonded to the dental enamel by the enamel etching technique, for which an absolutely dry cavity must be maintained (rubber dam).The marginal integrity of composite restora-tions is ensured by the preparation of mechanical retentions (grooves, adhesive points) and with dentin bonding agents. In addition, a tight, acid-resistant cavity lining is placed to protect the pulp against the acrylic resin monomer or phosphoric acid (etching gel). The composite material is ap-plied layer by layer, nished, and polished and thus provides esthetically superior restorations with a tight marginal seal (Fig 1-15).Glass-ionomer cement restorations may be used for small caries lesions. Glass-ionomer cements bond well to dentin and enamel so that a restora-tion with marginal integrity is produced. Cements cannot be polished, are light impermeable, and are not abrasion resistant. Their use is conned to cervical caries lesions bordered by enamel as well as caries lesions in the cementum. Glass-ionomer cement is mainly used as a tooth prepa-ration lining material and for buildups on crown stumps.Gold compaction restorations are very rarely fabricated for small occlusal and approximal car-ies lesions. Tooth preparation must be box shaped with sharp edges. The cavity walls are parallel or undercut to provide sufcient retention (Fig 1-16). The restorative material consists of a special gold foil (gold leaf) or crystalline gold. The core of the restoration is built up with the crystalline gold, which is coated on the outside with gold leaf. The gold is packed in portions into the cavity and cold-welded with hammer blows so that it wedg-es into the cavity with a tight marginal seal. Fab-rication is time-consuming and costly but does produce long-lasting, dimensionally stable inlay restorations that are appropriate when a patient is allergic to other restorative materials and their ingredients.Fig 1-16 For a multisurface cavity, a gold inlay restoration is generally made; the same design is chosen as in Fig 1-15, with a depth of 2 mm, the extension surfaces, and the enamel bevel. The occlusal antagonist contacts must always lie outside the cavity margin. Cavity oorEnamel bevelExtension surfaceEnamel bevelExtension surfacesFig 1-15 In a multisurface cavity for a composite restoration, the cavity oor is at least 2 mm deep. The approximal exten-sion surfaces are clearly directed in a lingual and buccal direc-tion. The cavity margin is encircled by an enamel bevel. Condi-tioning with an etchant gel is performed in this enamel area. 12PreprostheticsInlay RestorationsInlay restorations made from metal, ceramic, or composite can be used to restore occlusal, ap-proximal, or approximal-incisal cavities caused by carious defects, fracture, or other damage af-ter they have been prepared. Inlay restorations are only indicated for patients who have good oral hygiene, minimal susceptibility to caries, and healthy periodontal conditions. Inlay restorations can be placed over several surfaces and may be retained by shoulders and pins (Fig 1-17). They differ depending on the amount of tooth structure to be replaced (Fig 1-18). The term inlay restora-tions encompasses inlays, onlays, overlays, and onlay partial crowns.While an inlay is xed entirely intracoronally without covering the occlusal surface of a tooth, an onlay covers the entire occlusal surface, and an overlay encompasses the occlusion-bearing cusps and includes both approximal surfaces. There is a smooth transition from overlay to par-tial crown when the cervical area of the tooth and the occlusal and approximal defects need to be restored.The design for inlay restorations is extended and demands plenty of dental hard tissue, espe-cially if a metal and porcelain restoration cover-ing the occlusal surface is to be placed. The cavity walls are not undercut occlusally, in contrast to the preparation for plastic restorative materials (Fig 1-19). Cavity walls close to the pulp are coat-ed with a lining so that even undercut areas are blocked out. The cavity walls and the liner should be smoothed, and then an impression is taken. The prepared teeth are tted with a temporary acrylic resin restoration until an inlay restoration has been made in the dental laboratory. Inlay restorations are fabricated using dental technology measures. First an impression is tak-en of the cavity, and the restoration is made indi-rectly on a model by the following methods:• Cast in metal using the lost wax technique• Milled out of a ceramic block using computer numeric controlled (CNC) technology• Compressed in ceramic by the extrusion tech-nique• Ceramic red onto galvanic carrier layers• Cured in composite using the layering techniqueAfter fabrication, inlay restorations are inserted with cement or special bonding agents. They ad-here to the cavity walls by a gripping effect and static friction.Metal inlay restorations are made from gold al-loys; other metal alloys (non–precious metal and palladium alloys) are rarely used. A working mod-el and opposing jaw model are rst fabricated from articial stone and placed in the articulator. By the traditional method, the inlay restoration is carved in wax, sprued, invested, and cast. Metal inlay restorations can also be milled out of a full metal block using CNC technology.Composite and ceramic inlay restorations can be fabricated by the indirect technique using an impression and plaster cast and adhesively xed in the cavity by the acid-etching technique.Various methods are used for fabricating ce-ramic inlay restorations. In the sintering method, a split model made of plaster and a duplicate model made of castable material are prepared, onto which the restoration is sintered. If the ce-ramic inlay restoration is made of castable ce-ramic (eg, glass-ceramic) or pressed ceramic, the restoration must be carved out of wax on the working model and invested. For fabrication by computer-controlled techniques, an optical im-pression of the prepared cavity must be made us-ing special imaging methods. On the basis of this impression, the inlay restoration is ground out of a compact ceramic block using CNC techniques. In the copy-grinding method, a restorative block made of acrylic resin is mechanically scanned, and a ceramic duplicate is milled out of a ceramic block.Composite inlay restorations are made of com-posite with a high proportion of inorganic llers. They can be fabricated directly in the mouth or by indirect fabrication on a working model in the dental laboratory.In the case of electroformed inlays, tooth-colored ceramic is red onto a thin carrier layer of electro-formed gold. A thin gold layer is electrogalvani-cally deposited on the model die in order to re on a ceramic layer. These inlay restorations have very good accuracy of t and are inserted using phosphate cement. A thin gold margin remains visible, which is esthetically unsightly. 13Inlay RestorationsOcclusal inlaysFor occlusal inlays, the width of the cavity is half the intercuspal distance in order to maintain the stability of the dental substance and leave the occlusal contacts on the natural dental tissue. An occlusal cavity is 1.5 mm wide and deep and includes the main ssures. The cavity walls have a common path of insertion without undercuts. The inner edges of the cavity are rounded, and Inlay OnlayOverlayOnlay partial crownFig 1-17 An extensive cavity restoration can be created with additional retentions in the form of pinholes. Short pins engage in these holes to secure the restoration. The term pinlays is used for restorations that mainly gain their retention in the den-tal tissue by means of pinholes or pins.Fig 1-19 The bevel of the cavity margins for metal inlay restorations is designed differently, depending on the cavity volume: A at cavity is given 45-degree bevels; a very deep cavity is given steeper bevels; and very deep and wide cavities are prepared with round bevels.Fig 1-18 The term inlay restoration encompasses restorations made of metal in differing dimensions; they are classied ac-cording to the amount of dental substance to be replaced— inlays: intracoronal cavities; onlays: cavities on occlusal surfaces; overlays: cavities on occlusal surfaces and the occlusion-bearing cusps; onlay partial crowns: cavities involving the vertical smooth surfaces outside the portion visible from the vestibular view. 14Preprostheticsthe occlusal margin is beveled so that the margin of the metal restoration can be rened by rework-ing (Fig 1-20). Antagonist contacts lie either com-pletely on the natural dental substance or on the surface of the restoration.Inlay splints refer to cast restorations that are soldered together; they are used to x mobile teeth to adjacent teeth and stabilize them. Inlays can be used to anchor partial dentures, but they offer less retention to abutment teeth than the use of crowns.Onlays and overlaysOnlays or overlays are prepared when the dental hard tissue is weakened by large caries lesions and occlusal corrections are also necessary. For an onlay, preparation involves the occlusal sur-face, including the cusp tips, and usually extends into both approximal surfaces (Fig 1-21). Overlay preparation incorporates the bearing cusps and ends in a shoulder preparation with bevel. The preparation margin runs level with the height of the contour and extends into both approximal surfaces. There is a smooth crossover between overlays and partial crowns (Fig 1-22).A core buildup made of plastic restorative ma-terials (glass-ionomer cement or composite) be-comes necessary for badly damaged teeth before the onlay or overlay preparation can be started. All restorative margins must lie within healthy dental hard substance and not in the buildup material. Such core buildups are anchored with parapulpal pins in the form of root canal screws unless a cast post and core is being fabricated.Fig 1-20 The cavity for a single-surface metal inlay has a mini-mum depth of 1.5 mm; preparation is slightly divergent, and there are no undercuts. The cavity margin does not lie in the area of occlusal contacts and is prepared with an enamel bevel.Fig 1-21 An onlay incorporates the whole occlusal surface and extends into the approximal surfaces. The approximal exten-sions run lingually or vestibularly; an approximal-cervical shoul-der is usually prepared. An enamel bevel is prepared around the cavity margin.Fig 1-22 The overlay replaces the occlusal surface and fully encompasses the occlusion-bearing cusps. A shoulder is usu-ally prepared around these cusps, while the nonsupporting cusp is surrounded by a simple enamel bevel. 15Inlay RestorationsVeneersVeneers, also known as laminates or facings, are fabricated when circular preparation of den-tal crowns is to be avoided in order to preserve ample natural dental tissue as well as esthetics. Veneers can be made individually out of acrylic resin, composite, and ceramic directly in the mouth or in the dental laboratory, or they can be milled out of prefabricated ceramic blocks using CNC machining. Veneers are indicated for discol-ored facets or large anterior restorations, enamel cracks or chips, and morphologic or positional corrections.To prepare a veneer stump, the labial enamel and the incisal edge into the approximal surfaces are removed to a thickness of about 0.5 mm with-out exposing the dentin. The preparation surface is slightly curved in the horizontal and vertical di-rection and should be smooth without undercuts. The approximal surfaces can be incorporated as far as halfway; if the approximal areas are intact and not discolored, the approximal contact made of natural dental tissue can remain unchanged.The veneers are retained on the dental enam-el by micromechanical adhesive means. For the purposes of micromechanical retention, the enamel is conditioned at the cavity margin using the acid-etching technique, which enlarges the surface of this enamel area and renders it wet-table (Fig 1-23). The inside of the veneer is also conditioned (porcelain veneers are etched with hydrouoric acid) and prepared with adhesive silane as a bonding agent to the composite. Ad-hesive cementation can be done with self-curing dual cement or light-curing composite cement.The acid-etching technique is used to condition the surface of the enamel for adhesive cementa-tion of ceramic or composite inlay restorations. The enamel surfaces intended for adhesive bond-ing are cleaned and treated with orthophospho-ric acid (H3PO4) or phosphoric acid gel so that the apatites of the enamel prism cores partially dissolve. After 30 to 60 seconds, the etchant and dissolved enamel constituents are rinsed off. This leaves surface roughness between 5 and 8 µm deep, creating an enlarged surface with pores for micromechanical retention of the cementing acrylic resin. The roughened cavity margins and the restoration etched on the underside are si-lanized and cemented in place with a composite bonding agent. During acid etching and insertion with the composite bonding agent, irritation of the pulp and prolonged hypersensitivity of the re-stored tooth can arise if dentin areas are touched. Therefore, the cavity margins for adhesively ce-mented inlay restorations must lie within the area of etchable enamel.Fig 1-23 Veneers replace the labial facet of an anterior tooth. For this purpose, a consistent layer approximately 0.8 mm thick is ground out of the enamel into the approximal areas; the incisal edge is prepared into the lingual area. The approximal crown width is retained, and undercuts are avoided. The prepared surface is conditioned by acid etching to receive the ceramic veneer and there-fore must lie solely within the enamel area. A composite bonding agent is used to achieve the adhesive bond.

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