10 Accessory Radiographic Techniques










107
10
Accessory Radiographic
Techniques: Bisecting Technique
and Occlusal Projections
EDUCATIONAL OBJECTIVES
Upon completing this chapter, the student will be able to:
1. Dene the key terms listed at the beginning of the chapter.
2. Discuss the following related to the bisecting technique:
• Knowthebasicprinciplesofthebisectingtechnique.
• Statetheindicationforuseofthebisectingtechniqueas
an accessory intraoral radiographic technique.
• Listandexplaintheadvantagesanddisadvantagesof
the bisecting technique.
• Describethethreemethodsofutilizingthebisecting
technique.
3. Listanddescribethetwomostcommonerrorsproduced
withtheuseofincorrectverticalangulationinthebisecting
technique, as well as the remedies for each.
4. Discuss the following related to occlusal lm projections:
• Statethepurposeandtheindicationsforuseof
theocclusalexposuretechniqueindentalintraoral
radiography.
• Statethetwotypesofocclusalprojectionsandwhat
each is generally used for in dental radiography.
• Listthestepsinvolvedinpreparationandexposureof
occlusal projections on the dental patient.
• Statetherecommendedverticalangulationforthe
maxillaryandmandibularright-angleandtopographic
occlusal projections.
possible. Because of the anatomy of the mouth, the long
axis of the tooth is not parallel in most areas to the plane
of the receptor with this placement. e vertical angula-
tion of the tube head is directed so that the central ray is
perpendicular to an imaginary line that bisects the angle
formed by the long axis of the tooth and the plane of the
receptor (see Fig. 3.14). With this receptor placement, the
object-receptor distance is minimal. No compensation for
image enlargement is necessary; therefore, the technique
usually calls for an 8-inch target-receptor distance (or focal-
lm distance [FFD]). Although a “short cone” is used, this
is not the determining factor in the technique. Bite pieces
without localizing rings and aiming arms should be used
in this method.
Before listing the (supposed) advantages of the bisecting
technique, we must note again that the consensus of opinion
among dental professionals and the American Academy of
Introduction
An accessory technique in dental radiography is employed
when there is a specic indication for its utilization.
is indication for use is usually based on the patient’s
individual dental health needs, anatomic constraints, the
need for further radiographic evaluation, or a deviation
from the usual course of radiographic examination. is
chapter discusses the use of, principles of, and information
gathered from the bisecting-angle and occlusal radiographic
techniques in dental radiography.
Bisecting Technique
Another method for taking intraoral periapical radiographs
is the bisecting-angle technique (BAT). In the bisecting
technique, the receptor is placed as close to the tooth as
KEY TERMS
bisecting-angle technique (BAT)
dimensional distortion
imaginary bisecting line
occlusal receptor
occlusal projection
receptor plane
right-angle occlusal projection
topographic occlusal projection

108 CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal Projections
are unacceptably exposed to primary radiation. A bite piece
should always be used instead of the patient’s nger.
Method
In this technique, the receptor is held as close to the tooth
as possible without bending the receptor. e long axis of
the receptor therefore is not parallel to the long axis of the
tooth. An imaginary bisecting line is drawn to bisect the
angle formed by the long axis of the tooth and the plane of
the receptor. e central ray of the x-ray beam is directed
perpendicular to this bisecting line; this determines the
vertical angulation of the x-ray beam (see Fig. 3.14). For
the maxillary teeth, positive angulation (position-indicating
device [PID] pointing down) is used; for mandibular teeth,
negative angulation (PID pointing up) is used. At zero-
degree angulations, the PID is parallel to the oor; this
becomes the reference point from which vertical angulations
are measured. erefore, it is crucial to have the occlusal
plane of the jaw being radiographed positioned parallel to
the oor for predetermined angulations to be valid.
Oral and Maxillofacial Radiology (AAOMR) regarding the
standard of care for intraoral periapical radiography is the
paralleling technique. e bisecting technique should be
considered an ancillary or accessory method that can be used
in special circumstances when it is not possible to use the
paralleling technique. Basically, if the dental radiographer
cannot position the receptor parallel to the teeth because
of anatomic constraints or any other feasible reason, the
bisecting technique is recommended as a substitute method
for exposing the desired intraoral images. It is in this context
that the bisecting technique is presented in this textbook.
Advantages of the Bisecting-Angle Technique
e bisecting technique is said to be easier to perform than
the paralleling technique. For patients with small mouths,
children, and patients with low palatal vaults, paralleling
devices may be extremely dicult to use. e BAT is cur-
rently used with simple receptor-holding devices and, in
the past, with the patient’s nger as a holding device for the
receptor. It is no longer acceptable for the patient to hold
the receptor with the nger, because this practice unneces-
sarily exposes the patient’s nger to radiation.
Because the receptor is held close to the tooth, it is
acceptable to use an 8-inch target-receptor distance (or
FFD) with the bisecting technique as opposed to the 12- to
16-inch target-receptor distance used with the paralleling
technique. Shorter exposure times can be used in the bisect-
ing technique because of the shorter target-receptor distance
(or FFD) and the use of faster-speed lm and digital sensors;
hence, there is less of a chance for patient movement.
Disadvantages of the
Bisecting-Angle Technique
e major disadvantage of the bisecting technique is that
the image projected is dimensionally distorted. Dimen-
sional distortion is a variation in the true size and shape
of the structure being radiographed and is inherent in the
use of the bisecting technique, as discussed in Chapter 9.
e bisecting technique is dicult to perform with the
patient in a contour chair or in the supine or semi-supine
position. With the newer dental chairs, it is very hard
to place the patient in the correct position so that the
occlusal plane of the jaw being radiographed is parallel to
the oor and all vertical angulations used in the bisecting
technique are measured from this line. Other disadvan-
tages of the bisecting technique are related to the use of
an 8-inch target-receptor distance (or FFD). e 8-inch
target-receptor distance (or FFD), when compared with
the extended 16-inch target-receptor distance (or FFD),
causes greater image enlargement and distortion (see Fig.
3.8). ere is also more tissue volume exposed with an
8-inch target-receptor distance (or FFD) than with a
16-inch target-receptor distance (or FFD; see Chapter 6).
If the patients nger is used to support the receptor, as is
common in this method, then the patient’s nger and hand
Occlusal Projections
Occlusal projections are used to localize objects and
pathologic conditions in the buccolingual dimension and
Text continued on p. 115
NOTE
There are basically three bisecting methods that can be used,
two of which are outlined in Procedure 10.1. These two
methods for vertical angulation involve using predetermined
vertical angles or using the operator’s subjective placement of
the central ray perpendicular to the imaginary bisector. Both
of these methods are dependent on the patient’s occlusal
plane being positioned properly (parallel to the oor). The third
method is more simplied, not dependent on the occlusal
plane orientation of the patient, and can leave less room for
human error if utilized properly. The procedural steps for this
method are:
1. Place the receptor in a simple receptor-holding device,
such as an XCP bite piece (without the aiming bar or
localizing ring) or a Stabe.
2. Place the receptor as close to the teeth being
radiographed as possible.
3. Set the central ray (PID) so that it is perpendicular to the
receptor.
4. Check the vertical angle setting on the yolk of the x-ray
unit.
5. Divide that noted vertical angle in half.
6. Reset the vertical angulation at that half-way setting.
7. Expose the projection.
For example, the operator is exposing a mandibular
central/lateral incisor radiograph and sets the central ray
(PID) so that it is perpendicular to the receptor (Step 3). The
operator notes that it is at a 20-degree angle (Step 4) and
then divides that noted vertical angle in half (Step 5). Finally,
the operator resets the adjusted angulation to 10 degrees
(Step 6). Using this principle of the bisecting technique, which
involves aiming the central ray at the imaginary bisector in a
more concrete, objective way, makes it easier to standardize
from one operator to the next.

109CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal Projections
PROCEDURE 10.1 THE FULL-MOUTH BISECTING SERIES
Note: This procedure can be applied to conventional or digital
radiography.
Maxillary Central and Lateral Incisors (Left or
Right or Midline; Figs. 10.1 and 10.2)
Chair Position. The maxillary occlusal plane is positioned
parallel to the oor, and the sagittal plane of the patient’s face
is perpendicular to the oor.
Point of Entry. For the maxillary central/lateral projection,
the central ray is directed just below the midpoint of the nares
(the nostrils) and aimed at the center of the receptor (see Fig.
10.1). For the maxillary right and maxillary left central and
lateral incisors projection, the center of the receptor is placed
between the central incisors, and the central ray is directed
just below the tip of the nose (see Fig. 10.2).
Vertical Angulation. Can be preset at +50 degrees or
aimed perpendicular to the imaginary bisector in the vertical
plane.
Horizontal Angulation. The central ray is aimed
perpendicular to the receptor in the horizontal plane. To avoid
horizontal overlap, the dental professional should be sure to
place the receptor parallel to the teeth in the horizontal plane.
Maxillary Canines (Fig. 10.3)
Chair Position. The maxillary occlusal plane is positioned
parallel to the oor, and the sagittal plane of the patient’s face
is perpendicular to the oor.
Receptor Position. The receptor is held vertically and
extends
1
8
inch below the tip of the canine. The canine is
in the center of the receptor, which is held rmly against the
lingual surface of the canine.
Point of Entry. The central ray is directed at the base of
the lateral nasal groove, aimed at the center of the receptor.
Vertical Angulation. Can be preset at +50 degrees or
aimed perpendicular to the imaginary bisector in the vertical
plane.
Horizontal Angulation. The central ray is perpendicular
to the receptor in the horizontal plane. To avoid horizontal
&
A
Figure 10.1 Maxillary central and lateral incisors. A, Receptor and position-indicating device (PID).
B, Radiograph. C, Diagram.
HELPFUL HINT
Make sure that the occlusal plane is kept parallel to the oor
in the event that the patient changes position in the chair.
A
Figure 10.2 Right and left central and lateral incisors. A, Receptor packet and position-indicating
device (PID). B, Radiograph.
Continued

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10710 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsEDUCATIONAL OBJECTIVESUpon completing this chapter, the student will be able to:1. Dene the key terms listed at the beginning of the chapter.2. Discuss the following related to the bisecting technique:• Knowthebasicprinciplesofthebisectingtechnique.• Statetheindicationforuseofthebisectingtechniqueasan accessory intraoral radiographic technique.• Listandexplaintheadvantagesanddisadvantagesofthe bisecting technique.• Describethethreemethodsofutilizingthebisectingtechnique.3. Listanddescribethetwomostcommonerrorsproducedwiththeuseofincorrectverticalangulationinthebisectingtechnique, as well as the remedies for each.4. Discuss the following related to occlusal lm projections:• Statethepurposeandtheindicationsforuseoftheocclusalexposuretechniqueindentalintraoralradiography.• Statethetwotypesofocclusalprojectionsandwhateach is generally used for in dental radiography.• Listthestepsinvolvedinpreparationandexposureofocclusal projections on the dental patient.• Statetherecommendedverticalangulationforthemaxillaryandmandibularright-angleandtopographicocclusal projections.possible. Because of the anatomy of the mouth, the long axis of the tooth is not parallel in most areas to the plane of the receptor with this placement. e vertical angula-tion of the tube head is directed so that the central ray is perpendicular to an imaginary line that bisects the angle formed by the long axis of the tooth and the plane of the receptor (see Fig. 3.14). With this receptor placement, the object-receptor distance is minimal. No compensation for image enlargement is necessary; therefore, the technique usually calls for an 8-inch target-receptor distance (or focal-lm distance [FFD]). Although a “short cone” is used, this is not the determining factor in the technique. Bite pieces without localizing rings and aiming arms should be used in this method.Before listing the (supposed) advantages of the bisecting technique, we must note again that the consensus of opinion among dental professionals and the American Academy of IntroductionAn accessory technique in dental radiography is employed when there is a specic indication for its utilization. is indication for use is usually based on the patient’s individual dental health needs, anatomic constraints, the need for further radiographic evaluation, or a deviation from the usual course of radiographic examination. is chapter discusses the use of, principles of, and information gathered from the bisecting-angle and occlusal radiographic techniques in dental radiography.Bisecting TechniqueAnother method for taking intraoral periapical radiographs is the bisecting-angle technique (BAT). In the bisecting technique, the receptor is placed as close to the tooth as KEY TERMSbisecting-angle technique (BAT)dimensional distortionimaginary bisecting lineocclusal receptorocclusal projectionreceptor planeright-angle occlusal projectiontopographic occlusal projection 108 CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal Projectionsare unacceptably exposed to primary radiation. A bite piece should always be used instead of the patient’s nger.MethodIn this technique, the receptor is held as close to the tooth as possible without bending the receptor. e long axis of the receptor therefore is not parallel to the long axis of the tooth. An imaginary bisecting line is drawn to bisect the angle formed by the long axis of the tooth and the plane of the receptor. e central ray of the x-ray beam is directed perpendicular to this bisecting line; this determines the vertical angulation of the x-ray beam (see Fig. 3.14). For the maxillary teeth, positive angulation (position-indicating device [PID] pointing down) is used; for mandibular teeth, negative angulation (PID pointing up) is used. At zero-degree angulations, the PID is parallel to the oor; this becomes the reference point from which vertical angulations are measured. erefore, it is crucial to have the occlusal plane of the jaw being radiographed positioned parallel to the oor for predetermined angulations to be valid.Oral and Maxillofacial Radiology (AAOMR) regarding the standard of care for intraoral periapical radiography is the paralleling technique. e bisecting technique should be considered an ancillary or accessory method that can be used in special circumstances when it is not possible to use the paralleling technique. Basically, if the dental radiographer cannot position the receptor parallel to the teeth because of anatomic constraints or any other feasible reason, the bisecting technique is recommended as a substitute method for exposing the desired intraoral images. It is in this context that the bisecting technique is presented in this textbook.Advantages of the Bisecting-Angle Techniquee bisecting technique is said to be easier to perform than the paralleling technique. For patients with small mouths, children, and patients with low palatal vaults, paralleling devices may be extremely dicult to use. e BAT is cur-rently used with simple receptor-holding devices and, in the past, with the patient’s nger as a holding device for the receptor. It is no longer acceptable for the patient to hold the receptor with the nger, because this practice unneces-sarily exposes the patient’s nger to radiation.Because the receptor is held close to the tooth, it is acceptable to use an 8-inch target-receptor distance (or FFD) with the bisecting technique as opposed to the 12- to 16-inch target-receptor distance used with the paralleling technique. Shorter exposure times can be used in the bisect-ing technique because of the shorter target-receptor distance (or FFD) and the use of faster-speed lm and digital sensors; hence, there is less of a chance for patient movement.Disadvantages of the Bisecting-Angle Techniquee major disadvantage of the bisecting technique is that the image projected is dimensionally distorted. Dimen-sional distortion is a variation in the true size and shape of the structure being radiographed and is inherent in the use of the bisecting technique, as discussed in Chapter 9.e bisecting technique is dicult to perform with the patient in a contour chair or in the supine or semi-supine position. With the newer dental chairs, it is very hard to place the patient in the correct position so that the occlusal plane of the jaw being radiographed is parallel to the oor and all vertical angulations used in the bisecting technique are measured from this line. Other disadvan-tages of the bisecting technique are related to the use of an 8-inch target-receptor distance (or FFD). e 8-inch target-receptor distance (or FFD), when compared with the extended 16-inch target-receptor distance (or FFD), causes greater image enlargement and distortion (see Fig. 3.8). ere is also more tissue volume exposed with an 8-inch target-receptor distance (or FFD) than with a 16-inch target-receptor distance (or FFD; see Chapter 6). If the patient’s nger is used to support the receptor, as is common in this method, then the patient’s nger and hand Occlusal ProjectionsOcclusal projections are used to localize objects and pathologic conditions in the buccolingual dimension and Text continued on p. 115NOTEThere are basically three bisecting methods that can be used, two of which are outlined in Procedure 10.1. These two methods for vertical angulation involve using predetermined vertical angles or using the operator’s subjective placement of the central ray perpendicular to the imaginary bisector. Both of these methods are dependent on the patient’s occlusal plane being positioned properly (parallel to the oor). The third method is more simplied, not dependent on the occlusal plane orientation of the patient, and can leave less room for human error if utilized properly. The procedural steps for this method are:1. Place the receptor in a simple receptor-holding device, such as an XCP bite piece (without the aiming bar or localizing ring) or a Stabe.2. Place the receptor as close to the teeth being radiographed as possible.3. Set the central ray (PID) so that it is perpendicular to the receptor.4. Check the vertical angle setting on the yolk of the x-ray unit.5. Divide that noted vertical angle in half.6. Reset the vertical angulation at that half-way setting.7. Expose the projection.For example, the operator is exposing a mandibular central/lateral incisor radiograph and sets the central ray (PID) so that it is perpendicular to the receptor (Step 3). The operator notes that it is at a −20-degree angle (Step 4) and then divides that noted vertical angle in half (Step 5). Finally, the operator resets the adjusted angulation to −10 degrees (Step 6). Using this principle of the bisecting technique, which involves aiming the central ray at the imaginary bisector in a more concrete, objective way, makes it easier to standardize from one operator to the next. 109CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsPROCEDURE 10.1 THE FULL-MOUTH BISECTING SERIESNote: This procedure can be applied to conventional or digital radiography.Maxillary Central and Lateral Incisors (Left or Right or Midline; Figs. 10.1 and 10.2)Chair Position. The maxillary occlusal plane is positioned parallel to the oor, and the sagittal plane of the patient’s face is perpendicular to the oor.Point of Entry. For the maxillary central/lateral projection, the central ray is directed just below the midpoint of the nares (the nostrils) and aimed at the center of the receptor (see Fig. 10.1). For the maxillary right and maxillary left central and lateral incisors projection, the center of the receptor is placed between the central incisors, and the central ray is directed just below the tip of the nose (see Fig. 10.2).Vertical Angulation. Can be preset at +50 degrees or aimed perpendicular to the imaginary bisector in the vertical plane.Horizontal Angulation. The central ray is aimed perpendicular to the receptor in the horizontal plane. To avoid horizontal overlap, the dental professional should be sure to place the receptor parallel to the teeth in the horizontal plane.Maxillary Canines (Fig. 10.3)Chair Position. The maxillary occlusal plane is positioned parallel to the oor, and the sagittal plane of the patient’s face is perpendicular to the oor.Receptor Position. The receptor is held vertically and extends 18 inch below the tip of the canine. The canine is in the center of the receptor, which is held rmly against the lingual surface of the canine.Point of Entry. The central ray is directed at the base of the lateral nasal groove, aimed at the center of the receptor.Vertical Angulation. Can be preset at +50 degrees or aimed perpendicular to the imaginary bisector in the vertical plane.Horizontal Angulation. The central ray is perpendicular to the receptor in the horizontal plane. To avoid horizontal &A• Figure 10.1 Maxillary central and lateral incisors. A, Receptor and position-indicating device (PID). B, Radiograph. C, Diagram. HELPFUL HINTMake sure that the occlusal plane is kept parallel to the oor in the event that the patient changes position in the chair.A• Figure 10.2 Right and left central and lateral incisors. A, Receptor packet and position-indicating device (PID). B, Radiograph. Continued 110 CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsPROCEDURE 10.1 THE FULL-MOUTH BISECTING SERIES—cont’doverlap, the dental professional should be sure to place the receptor parallel to the teeth in the horizontal plane.Maxillary Premolars (Fig. 10.4)Chair Position. The maxillary occlusal plane is positioned parallel to the oor, and the sagittal plane of the patient’s face is perpendicular to the oor.Receptor Position. The receptor is held horizontally and extends 18 inch below the occlusal surfaces of the teeth. The second premolar is in the center of the receptor. The receptor is held in position against the lingual surfaces. If a lm packet is being used, the operator should avoid shaping the packet to the arch to the point of bending the lm enough to actually crack the emulsion.Point of Entry. The central ray is directed at the most anterior part of the cheekbone, aimed at the center of the receptor.CA• Figure 10.3 Maxillary canines. A, Receptor and position-indicating device (PID). B, Radiograph. C, Diagram. NOTEWhen a lm packet is used for this projection, try to avoid bending the lm packet in a small mouth to prevent overbending (crescent-shaped marks). It is important to remember that fast-speed lms (i.e., F-speed lm) are more sensitive to the consequences of excessive manipulation.CA• Figure 10.4 Maxillary premolars. A, Receptor and position-indicating device (PID). B, Radiograph. C, Diagram. 111CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsPROCEDURE 10.1 THE FULL-MOUTH BISECTING SERIES—cont’dVertical Angulation. Can be preset at +40 degrees or aimed perpendicular to the imaginary bisector in the vertical plane.Horizontal Angulation. The central ray is perpendicular to the receptor in the horizontal plane and is directed through the interproximal spaces. To avoid horizontal overlap, the dental professional should be sure to place the receptor parallel to the teeth in the horizontal plane.Maxillary Molars (Fig. 10.5)Chair Position. The maxillary occlusal plane is positioned parallel to the oor, and the sagittal plane of the patient’s face is perpendicular to the oor.Receptor Position. The receptor is held horizontally and extends 18 inch evenly below the occlusal surfaces of the teeth. The second molar is in the center of the receptor. The receptor is held against the lingual surfaces of the teeth.Point of Entry. The central ray is directed through the zygomatic arch at the center of the receptor. The distal curvature of the open-ended collimator should not be distal to the outer canthus (corner) of the eye.Vertical Angulation. Can be preset at +30 degrees or aimed perpendicular to the imaginary bisector in the vertical plane.Horizontal Angulation. The central ray is perpendicular to the receptor in the horizontal plane and is directed through the interproximal spaces. To avoid horizontal overlap, the dental professional should place the receptor parallel to the teeth in the horizontal plane.Mandibular Incisors (Fig. 10.6)Chair Position. The patient is positioned so that when the mouth is open, the mandibular occlusal plane is parallel to the oor, and the sagittal plane of the patient’s face is perpendicular to the oor.Receptor Position. The receptor is held vertically so that it extends 18 inch above the incisal edges of the incisors. The midpoint of this 18-inch border should be between the central incisors. All four lower incisors are shown on one image. The receptor is held against the lingual surfaces of the incisors.Point of Entry. The central ray is directed at the depression in the face just above the chin (mental groove), aimed at the center of the receptor.Vertical Angulation. Can be preset at –20 degrees or aimed perpendicular to the imaginary bisector in the vertical plane.Horizontal Angulation. The central ray is perpendicular to the receptor in the horizontal plane. To avoid horizontal overlap, the dental professional should place the receptor parallel to the teeth in the horizontal plane.Mandibular Canines (Fig. 10.7)Chair Position. The patient is positioned so that when the mouth is open, the mandibular occlusal plane is parallel to the oor, and the sagittal plane of the patient’s face is perpendicular to the oor.Receptor Position. The receptor is held vertically and extends 18 inch above the tip of the canine, which is at the center of the receptor. The receptor is held against the lingual surface of the canine.HELPFUL HINTMake sure that the middle of the receptor in the horizontal position is at the center of the second molar.CA• Figure 10.5 Maxillary molars. A, Receptor and position-indicating device (PID). B, Radiograph. C, Diagram. HELPFUL HINTMake sure that the anterior part of the receptor is positioned behind the center of the canine to include the distal part of the canine in the premolar projection.HELPFUL HINTIn some small and crowded arch shapes, it may be necessary to use a smaller-sized receptor (#1 receptor) for a lower anterior projection.Continued 112 CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsPROCEDURE 10.1 THE FULL-MOUTH BISECTING SERIES—cont’dPoint of Entry. The central ray is directed at the root of the canine, aimed at the middle of the receptor.Vertical Angulation. Can be preset at –20 degrees or aimed perpendicular to the imaginary bisector in the vertical plane.Horizontal Angulation. The central ray is perpendicular to the receptor in the horizontal plane. To avoid horizontal overlap, the dental professional should place the receptor parallel to the teeth in the horizontal plane.Mandibular Premolars (Fig. 10.8)Chair Position. The patient is positioned so that when the mouth is open, the mandibular occlusal plane is parallel to the oor, and the sagittal plane of the patient’s face is perpendicular to the oor.CA• Figure 10.6 Mandibular incisors. A, Receptor and position-indicating device (PID). B, Radiograph. C, Diagram. NOTEIn the canine area, it may be necessary to use one or two extra size #1 receptors to cover the canine area completely.CA• Figure 10.7 Mandibular canines. A, Receptor and position-indicating device (PID). B, Radiograph. C, Diagram. 113CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsReceptor Position. The receptor is held horizontally and extends 18 inch above the occlusal surfaces of the teeth. The second premolar is in the center of the receptor. The receptor is held against the lingual surfaces of the teeth.Point of Entry. The central ray is directed at the mental foramen, aimed at the center of the receptor.Vertical Angulation. Can be preset at –15 degrees or aimed perpendicular to the imaginary bisector in the vertical plane.Horizontal Angulation. The central ray is perpendicular to the receptor in the horizontal plane. To avoid horizontal overlap, the dental professional should place the receptor parallel to the teeth in the horizontal plane.Mandibular Molars (Fig. 10.9)Chair Position. The patient is positioned so that when the mouth is open, the mandibular occlusal plane is parallel to the oor, and the sagittal plane of the patient’s face is perpendicular to the oor.Receptor Position. The receptor is held horizontally and extends 18 inch above the occlusal surfaces of the molars. The second molar is in the middle of the receptor. The receptor is held against the lingual surface of the molars. Because of the anatomy of the area, the receptor is almost parallel to the long axis of the tooth; consequently, most molar periapical projections exposed with the bisecting technique are really paralleled projections.Point of Entry. The central ray is directed at the roots of the molars, aimed at the center of the receptor.Vertical Angulation. Can be preset at –5 degrees or aimed perpendicular to the imaginary bisector in the vertical plane.NOTEIt may be necessary to bend the inferior anterior corner of the receptor (if a lm packet is being used) to follow the curve of the arch.PROCEDURE 10.1 THE FULL-MOUTH BISECTING SERIES—cont’dCA• Figure 10.8 Mandibular premolars. A, Receptor and position-indicating device (PID). B, Radiograph. C, Diagram. CA• Figure 10.9 Mandibular molars. A, Receptor and position-indicating device (PID). B, Radiograph. C, Diagram. Continued 114 CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsPROCEDURE 10.1 THE FULL-MOUTH BISECTING SERIES—cont’dHorizontal Angulation. The central ray is perpendicular to the receptor in the horizontal plane. To avoid horizontal overlap, the dental professional should place the receptor parallel to the teeth in the horizontal plane.BitewingsThe technique for the bitewing projection is the same as in the paralleling method, because both call for the receptor and the teeth to be parallel and the x-ray beam to be perpendicular (at right angles) to both.HELPFUL HINTWhen inserting the receptor in the patient’s mouth, it is advised to use a nger from your other hand to depress the oor of the mouth if needed.HELPFUL HINTMake sure that the patient closes in centric and not protrusive relation when biting on the bitewing receptor-holding device or bitewing tab. COMMON ERRORS 10.1 Bisecting TechniqueNote: Refer to the Appendix for a detailed description of each of the following exposure errors.The following text presents the most common errors seen in the bisecting technique. Recognition and correction of occasional errors in technique are important. Not all patients are cooperative or have mouths that are anatomically easy to radiograph. Remember that images retaken because of poor technique add unnecessarily to the patient’s radiation burden. See Chapter 9 for a discussion of other chairside errors. The following errors, elongation and foreshortening, can occur with both conventional (lm-based) and digital radiography.Elongation (Fig. 10.10). Elongation, or lengthening of the image, can be caused by inadequate vertical angulation, improper occlusal plane orientation because of patient positioning, or poor receptor placement.Remedy. The receptor and the central ray must be in the correct relationship. In the bisecting-angle technique (BAT), the vertical angulation should be increased to correct elongation. The occlusal plane of the jaw being radiographed should be parallel to the oor. Patients may tend to move after a few exposures or lift their heads to watch the operator or observe their surroundings. Their movements disorient the occlusal plane. Check the patient’s head position before taking each exposure.Foreshortening (Fig. 10.11). Foreshortening (the shortening of the image) is not as common an error as elongation. It can be caused by excessive vertical angulation or poor occlusal plane orientation.Remedy. In the BAT, the vertical angulation should be decreased to overcome errors of foreshortening.Sagittal plane orientation (Fig. 10.12). When the periapical radiographs show the occlusal surfaces of the teeth, the patient’s head has tipped away from the proper sagittal plane. This is accompanied by elongation of the image.Remedy. The operator should make sure that the patient does not tip their head away from the tube head as it is brought into approximation with the facial skin.• Figure 10.10 Elongated image. • Figure 10.11 Foreshortened image. 115CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsCOMMON ERRORS 10.1—cont’dB• Figure 10.12 A, Elongated and distorted radiograph caused by poor sagittal plane orientation of the patient’s head. B, Poor sagittal plane orientation. to visualize areas that would not be seen on periapical and bitewing projections because of insucient eld size. e right-angle occlusal technique is used for localizing struc-tures and lesions in the (extreme) buccolingual dimension; the topographic occlusal technique is used to view larger structures and pathologic areas. Occlusal receptors can also be used when proper placement of periapical receptors is not possible in children or handicapped patients (Box 10.1; see Chapter 18).Right-Angle ProjectionWith right-angle occlusal projections (also known as the 90-degree or cross-sectional projection) the central ray is directed at an angle of 90 degrees to the receptor. is technique would be used, for example, to locate an object such as an impacted tooth in the third dimension. It has been mentioned that dental radiographs picture a three-dimensional subject in a two-dimensional plane, usually vertical and horizontal. e radiographs do not indicate depth. In the example of the impacted tooth, one might know from a conventional radiograph the impaction’s mesiodistal location and its vertical height from the crest of the alveolar ridge, but we would not know its depth in the bone in a buccolingual dimension. One way to deter-mine whether an impacted mandibular molar lies buccal or lingual to the alveolar ridge is to take a radiograph from another direction. In this example, it would be an occlusal radiograph, with the central ray coming from underneath the mandible, directed at a right angle to a receptor placed on the occlusal surface of the mandibular teeth.Topographic Projectionse angulation of the topographic occlusal projection may vary from 35 to 75 degrees, depending on the anatomic area and arch being radiographed. Because the occlusal receptor is larger than the size of the intraoral receptor, it can record areas that would not be seen on the smaller receptor. e extreme vertical angulations are necessary to compensate for the lack of parallelism between the object and the receptor. is is a modication of the BAT.Occlusal Receptore occlusal receptor (size #4) is 212 × 3 inches. When it is a lm packet, it can be supplied with either single- or double-packet lms (Fig. 10.13) and is available in various • BOX 10.1 Use of Occlusal ProjectionsClinical examples of the use of occlusal projections include the following:• Tolocateretainedrootsofextractedteeth• Tolocatesupernumerary(extra),unerupted,orimpactedteeth• Tolocateforeignbodiesinthemaxillaorthemandible• Tolocatesalivarystonesintheoorofthemouthandinthe submandibular duct and gland (mandibular right-angle projection)• Tolocateandevaluatetheextent(i.e.,buccalboneexpansion) of intraosseous lesions (e.g., cysts, tumors, malignancies) in the maxilla or mandible• Toevaluatetheboundariesofthemaxillarysinus(maxillaryocclusal projection)• Toevaluatefracturesofthemaxillaormandible• Toaidintheexaminationofpatientswhocannotopentheirmouths more than a few millimeters• Toexaminetheareaofacleftpalate(maxillaryocclusalprojection)• Toevaluatechangesinthesizeandshapeofthemaxillaormandible• Toevaluateteethforverticalfracturesthatcannotbeseenon periapical radiographs due to superimposition of normal tooth structure• Toexaminethedepth(buccolingualperspective)ofperiapicallesions 116 CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal Projections• Figure 10.13 Front and back of moisture-proof dental lm packet. (Courtesy Carestream Health, Inc., Rochester, NY.)lm speeds, including F speed. Phosphor plates for indirect digital radiography systems are also available in the #4 size for occlusal radiography. ese #4 size receptors are some-times called sandwich receptors, because they are positioned in the patient’s mouth with the teeth closed on the receptor, resembling the position for biting on a sandwich. e #2 size receptor can be used for pediatric occlusal projections if the #4 size cannot be accommodated. When lm packets are used, the occlusal lm is processed in the same way as other intraoral lms. e exposure time setting used for occlusal projections is equivalent to that which is used for the maxillary molar intraoral periapical projection.Mandibular Occlusal TechniqueIn the mandibular occlusal technique, the receptor is placed in the patient’s mouth on the occlusal surfaces of the lower teeth. If a #4 size lm packet is being used, the front (white side) of the packet should be facing the mandible on the occlusal surfaces of the lower teeth. e lm is placed horizontally (with the longer side extending from right to left) as long as it can be accommodated in that direction and as far posterior on the mandible as possible. e patient is directed to bite gently on the receptor. For the right-angle projection, the central ray of the x-ray beam is directed from under the mandible so that it is perpendicular to the center of the lm packet at a 90-degree angle to the receptor (Figs. 10.14 and 10.15). e back of the chair is lowered and the patient’s chin is tilted up so that the PID can be positioned below the mandible. For the topographic view of the mandible, the central ray is directed at a point just above the mental eminence at a vertical angulation of 35 to 45 degrees (Figs. 10.16 and 10.17).Maxillary Occlusal TechniqueIn an anterior topographic occlusal view of the maxilla, the receptor is placed in the patient’s mouth on the occlusal surfaces of the maxillary teeth. When the patient is ready, the patient is instructed to close lightly (gently) on the receptor. If a lm packet is being used, the packet is placed with the front of the lm packet facing the palate and the B90A• Figure 10.14 A, Receptor placement and position-indicating device (PID) position for mandibular right-angle occlusal projection. Note that the central ray is directed at 90 degrees to center of lm packet. B, Diagram. • Figure 10.15 Right-angle occlusal radiograph of patient’s man-dibular posterior area. Note buccal and lingual cortex of bone and central position of the impaction. long dimension of the packet running across the mouth (unless the patient cannot accommodate it in that position, in which case it should be placed with the long end running from anterior to posterior). e receptor is positioned as far posterior as possible so that the posterior edge of the lm packet touches the ascending ramus of the mandible. With the patient’s head positioned so that the receptor plane is parallel to the oor, the central ray is directed at a 65 to 75 degree vertical angulation aimed at the bridge of the nose (point of entry; Figs. 10.18 and 10.19). In the right-angle occlusal view of the maxilla, the receptor is placed in the same position as the maxillary topographic projection, but the central ray is directed perpendicular to the center of the lm packet. To do this, the PID must be positioned above the patient’s head at about the hairline. e vertical angulation is 90 degrees (Figs. 10.20 and 10.21). When using rectangular collimation with any of these occlusal 117CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsBA35• Figure 10.16 A, Topographic mandibular occlusal projection. B, Diagram. • Figure 10.17 Topographic occlusal projection of mandible. B65A• Figure 10.18 A, Receptor placement and position-indicating device (PID) position for topographic occlusal view of maxilla. Note that the central ray is directed at 65 to 75 degrees to the bridge of the nose. B, Diagram. • Figure 10.19 Occlusal radiograph of the maxilla, topographic view. projections, make sure that there is at least a 5-inch distance from the end of the rectangular column to the point of entry. is ensures a larger beam diameter, which is needed to expose a larger area and receptor size.e posterior occlusal topographic view can be considered a topographic view of the maxillary sinus and surrounding structures. e receptor is positioned on either the left or the right side of the patient’s mouth, from the midline, laterally with the long side running anteroposteriorly. e central ray is directed to a point just above the apices of the premolars at a vertical angulation of approximately 65 degrees (Figs. 10.22 and 10.23). 118 CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal ProjectionsB90A• Figure 10.20 A, Receptor placement and position-indicating device (PID) position for a right-angle occlusal view of the maxilla. Note that the central ray is directed at 90 degrees to the receptor. B, Diagram. • Figure 10.21 Right-angle occlusal projection of the maxilla showing the palatal relationship of the impacted canine. %A• Figure 10.22 A, Posterior topographic occlusal projection. B, Dia-gram. The point of entry corresponds to the apices of the premolars; vertical angulation is approximately 65 degrees. 119CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal Projections• Figure 10.23 Topographic occlusal radiograph of the maxillary sinus. Chapter Summary• Anaccessorydentalradiographictechniqueisemployedwhen there is a specic indication for its use. is indica-tion for use is usually based on the patient’s anatomic constraints, dental health needs, need for further radio-graphic evaluation, or a cause for a deviation from the usual course of radiographic examination.• ebisectingtechniqueisconsideredanaccessorytech-nique, because it is employed only when the paralleling technique cannot be used to expose periapical radio-graphs. is usually occurs when it is not possible to place the receptor parallel to the teeth due to a patient’s anatomic constraints or for another valid reason.• etwo basicprinciplesofthebisectingtechniquearethat the receptor is placed as close to the tooth as pos-sible and the central ray is aimed perpendicular to the imaginary bisector that divides the angle formed by the tooth and the receptor in half.• emostimportantadvantageofthebisectingtechniqueis that the receptor placement is easy to achieve and is also more comfortable for the patient once it is in place. e greatest disadvantage of the bisecting technique is that the resultant images are dimensionally distorted.• erearebasicallythreemethodsforexposingbisectingperiapical radiographs. e rst method consists of using predetermined vertical angles, the second uses the basic principles of the bisecting technique, and the third is a more standardized way of using the basic concepts of the technique.• Occlusal projections are used to localize structures inthe buccolingual dimension and to visualize areas that would not be seen on periapical and bitewing projec-tions because of insucient eld size. ey are used to visualize salivary stones in the submandibular gland, cleft palate, buccal bone expansion, impacted teeth, and other conditions of the teeth and bones in the buccolingual dimension.• eocclusalreceptoristhe#4sizereceptor.Itisplacedon the occlusal surfaces of either the maxillary or man-dibular teeth. e lm is usually held with the longer side positioned from the right to the left unless the posterior teeth are being exposed or the patient cannot accommodate the receptor in the horizontal position. In this case, the receptor is positioned with the longer side in the anteroposterior position.• ere are two types of occlusal projections: (1) thetopographic projection and (2) the right-angle projection (also known as the 90-degree or cross-sectional projection) used to view dierent perspectives of the buccolingual dimension.Chapter Review QuestionsMultiple Choice1. In the bisecting angle technique, the central ray is positioned: a. Perpendicular to the receptor b. Perpendicular to the tooth c. Perpendicular to the bisector between the tooth and the receptor d. Parallel to the bisector between the tooth and the receptor e. Parallel to the receptor2. ebisectingtechniqueisutilizedwhen: a. e insurance company requests that the images be taken with that technique b. When the patient cannot open the mouth at all c. When the receptor cannot be held parallel to the tooth because of anatomic constraints d. When it is required to see dimensional accuracy on the dental image e. When paralleling receptor-holding devices are used 120 CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal Projections a. e mandibular right-angle projection b. e mandibular topographic projection c. e mandibular 90-degree projection d. e maxillary topographic projection e. e maxillary right-angle projection5. Occlusallmpacketsare: a. A #4 size lm packet b. Held at on the biting surfaces of the teeth c. Nicknamed “the sandwich receptor” d. Used to project the buccolingual dimension e. All are correct3. e two errors that are caused by incorrect vertical angu-lation and are very common with the bisecting technique areknownas: a. Overlapping and reversed image b. Collimator cuto and overlapping c. Collimator cuto and elongation d. Foreshortening and elongation e. Foreshortening and overlapping4. e occlusal radiograph utilized for viewing a salivary stone in the submandibular gland is (indicate all that apply):Case-Based Critical Thinking ExerciseA patient presents with redness and swelling in the oor of the mouth. e area is sensitive upon palpation, and the patient reports decreased salivary ow, especially after eating. A panoramic radiograph shows a superimposed radiopacity in the mandibular region.1. What should the next step be in identifying this radiopacity? a. Expose a periapical projection in the area of the lesion. b. Expose an anterior vertical bitewing in the area of interest. c. Expose another panoramic radiograph to make sure that the radiopacity seen was not an artifact on the previous projection taken. d. Expose a mandibular topographic occlusal projection. e. Expose a mandibular right-angle occlusal projection.2. What dimension of the oral cavity should be projected in order to show this radiopacity without superimposition? a. e mesial-distal dimension b. e buccolingual dimension c. e incisal-apical dimension d. e occlusal-apical dimension e. e vertical dimension3. Considering the signs, symptoms, and radiographic nding, what could this nding potentially be identied as? a. A calculus deposit b. An extra tooth (supernumerary tooth) c. An amalgam restoration d. a salivary stone in the submandibular gland e. a salivary stone in the parotid glandRadiographic Interpretation1. isimage: a. Was produced by too much vertical angulation b. Was produced by too little vertical angulation c. Is known as foreshortening d. Both a and c are correct. e. Both b and c are correct.2. e following diagram shows the relationship of the tooth,receptor,andcentralrayforthe: a. Maxillary right-angle occlusal technique b. Mandibular topographic occlusal technique c. Paralleling technique d. Bisecting technique e. Maxillary topographic occlusal technique 121CHAPTER 10 Accessory Radiographic Techniques: Bisecting Technique and Occlusal Projectionsompson EM, Johnson ON: Essentials of dental radiography for dental assistants and hygienists, ed 9, Upper Saddle River, NJ, 2012, Pearson Education, Inc.WhiteSC,PharoahMJ:Oral radiology: Principles and interpretation, ed 7, St Louis, MO, 2013, Mosby.BibliographyIannucciJM,HowertonLJ:Dental radiography: Principles and tech-niques, ed 5, St Louis, MO, 2016, Elsevier Saunders.Langland OE,Langlais RP: Principles of dental imaging, Baltimore, MD, 1997, Williams & Wilkins.3. e following diagram shows the relationship of the centralrayandthereceptorforthe:90 a. Maxillary right-angle occlusal technique b. Mandibular topographic occlusal technique c. Paralleling technique d. Bisecting technique e. Mandibular right-angle occlusal technique

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