Intraoral Radiographic Techniques (Digital Radiology)-Chapter 6

Digital Radiology

Digital imaging was introduced into dentistry in 1987. Digital sensors are used instead of x-ray film. Sensors can be wired or wireless depending on the system used. (Figures 77 and 78) Sensors and tube head placement are the same for digital imaging as film and tube head placement is for traditional radiology. Most standard radiographic machines can be converted to acquire digital images. Digital imaging still uses ionizing radiation, and therefore, before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar. The apron must be properly placed to avoid interference with the radiographic exposure.

The sensors are slightly thicker than a regular film. Modified film holders must be utilized in the placement of the sensors. These modified holders can be purchased from any major dental supply company. The sensors can be reused several times. Proper use of intraoral barrier and OSHA techniques must be observed.

The advantages of digital radiology are decreased exposure time to the patient, elimination of darkroom processing time and exposure to processing chemicals, immediate viewing, and ability to easily and cost effectively transmit directly to third party facilities or affiliating dental offices. Additional computerized advantages include the ability to enhance the image for viewing. Once an image is in the computer, brightness and contrast and image reversal can be enhanced for optimal viewing of tissue and bone levels. The radiograph can be rotated and magnified to enhance details. An additional feature shows embossed images creating a stacked effect of the oral tissues.

The main disadvantages are substantial start up costs including machinery and operatory computer technology, and compatibility with other software program and RAM capacity. Considerations must also be noted that although your office may utilize digital radiography, other facilities may not and the transfer of images between them could be more difficult.

Figure 77

Figure 78

Summary

Proper film and tube head placement are a critical component of the total radiographic procedure.

Periapical, bitewing, and occlusal surveys are critical components of diagnosis and treatment of dental patients. Because of the exposure to ionizing radiation, proper techniques must be employed to reduce radiation exposure to the patient through the use of lead aprons, high speed film, and proper technique; thus decreasing additional film retakes. As technology advances in dental radiology operators must maintain current knowledge and adapt their abilities for the best treatment of the patient.

 

Intraoral Radiographic Techniques (Intraoral Occlusal Radiography)-Chapter 5

Intraoral Occlusal Radiography

Maxillary Topographical Occlusal
This projection (Figure 63) shows the palate (roof of the mouth), zygomatic process of the maxilla (a projection from the maxilla), antero-inferior aspects of each antrum (in this case, the maxillary sinuses), nasolacrimal canals (tear ducts), teeth from the left second molars to the central incisors, and the nasal septum (cartilage dividing the nose).

 

Figure 63

Uses:  To view the maxilla for anterior alveolar fractures, cysts, supernumerary teeth and impacted canines, and to view pathology at the apices of the incisors.  It is not used to diagnose peridontal conditions.

Patient positioning:  The patient is seated with the sagittal plane perpendicular to the floor and the occlusal plane parallel to the floor.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement:  With the tube side of the film (size #4) toward the maxilla, the film is placed crosswise in the mouth, like a sandwich.  It is gently pushed backwards until it contacts the anterior border of the mandibular ramus.  The patient bites down gently to maintain position.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer. 

Direction of the central ray:  The central ray is directed at the center of the film with a vertical angulation of +65 degrees and a horizontal angulation of 0 degrees.  In this case, the central ray will pass through the bridge of the nose, as in Figure 64.

 

Figure 64

Mandibular Topographical Occlusal
Uses:  To view the anterior portion of the mandible for fractures, cysts, root tip and periapical pathology.  It provides a very good view of the symphysis region of the mandible. (Figure 65)

 

Figure 65

Patient positioning:  The patient is seated with the head tilting slightly backward, so that the occlusal plane (ala-tragus line) is 45 degrees above the horizontal plane.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement:  With the tube side of the film (size #4) toward the mandible, the film is placed crosswise in the mouth, like a sandwich.  It is gently pushed backwards until it contacts the anterior border of the mandibular ramus.  The patient bites down gently to maintain position.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The central ray is directed between the apices of the mandibular central incisors and the tube is angled at -55 degrees relative to the film plane, as in Figure 66.

 

Figure 66

Maxillary Vertex Occlusal
 

Uses:  To view the buccopalatal relationships of unerupted teeth in the dental arch. (Figure 67)

 

Figure 67

Patient positioning:  The patient is seated with the sagittal plane perpendicular to the floor and the occlusal plane parallel to the floor.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement:  The film (size #4) is placed in the same manner as the Maxillary Topographical Occlusal.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The central ray is directed through the top of the skull (hence the name vertex occlusal). Since the beam must penetrate a considerable amount of bone and soft tissue, the exposure time must be increased.  The central ray is perpendicular to the film plane and is directed to the center of the film as in Figure 68.

 

Figure 68 

Mandibular Cross-Sectional Occlusal
 

Uses:  To view the entire mandible for fractures, foreign bodies, root tips, salivary calculi, tori, etc. (Figure 69)

 

Figure 69

Patient positioning:  The patient’s head may be in any comfortable position that allows the central ray to be directed perpendicular to the plane of the film packet.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement:  The film (size #4) is placed in the same manner as the Mandibular Topographical Occlusal.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The central ray is perpendicular to the film plane and is directed to the center of the film as in Figure 70.

 

Figure 70

Posterior Oblique Maxillary Occlusal
 

Uses:  To view the maxillary posterior region and provide a topographical view of the maxillary sinus.  The projection may be used in place of periapical films in patients who have a tendency to gag and for examining periapical pathology and root tips. (Figure 71)

 

Figure 71

Patient positioning:  The patient is seated with the occlusal plane parallel to the floor and the sagittal plane perpendicular to the floor.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure. 

Film placement:  The film (size #4) plane should be parallel to the floor, and the packet should be pushed posteriorly as far as possible.  The lateral border of the film should be positioned parallel to the buccal surfaces of the posterior teeth and extend laterally approximately one-half inch past the buccal cusps on the side of interest.  The patient should bite down gently to maintain film position.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The tube is directed at right angles to the curve of the arch, and strikes the center of the film packet as in Figure 72.

 

Figure 72

Posterior Oblique Mandibular Occlusal
Uses:  The projection is used to view the posterior teeth of the mandible to locate cysts, fractures, supernumerary teeth, and periapical pathology.  It can be used in place of posterior periapical films. (Figure 73)

 

Figure 73

Patient positioning: The patient is seated with the occlusal plane parallel to the floor and the sagittal plane perpendicular to the floor.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement: The film (size #4) plane should be parallel to the floor, and the packet should be pushed posteriorly as far as possible.  The lateral border of the film should be positioned parallel to the buccal surfaces of the posterior teeth and extend laterally approximately one-half inch past the buccal cusps on the side of interest.  The patient should bite down gently to maintain film position.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The tube is directed at the apex of the mandibular second premolar, and the central ray should strike the center of the film packet.  The vertical angulation is -50 degrees as in Figure 74.

 

Figure 74

Modified Oblique Posterior Mandibular Occlusal
Uses:  This projection is especially useful to detect calculi in the submandibular gland.  Calculi are often difficult to detect on conventional radiographs due to superimposition of the mandibular bone. (Figure 75)

 

Figure 75

Patient positioning and film placement:  With the tube side of the film (size #4) toward the mandible the film is placed in the patient’s mouth crosswise like a sandwich.  The film plane should be parallel to the floor, and the packet should be pushed posteriorly as far as possible.  The lateral border of the film should be positioned parallel to the buccal surfaces of the posterior teeth and extend laterally approximately one-half inch past the buccal cusps on the side of interest.  The patient’s head is then rotated to the side and lifted up.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The tube is positioned under and behind the mandible and the central ray is directed onto the center of the film so that it passes inside the ascending ramus so that the submandibular gland will be between the tube and the film as in Figure 76.

 

Figure 76

Intraoral Radiographic Techniques (Bitewing Radiography)-Chapter 4

Bitewing Radiography

Bitewing radiographs are of particular value in detecting interproximal caries in the early stages of development, before it is clinically apparent.  For this reason it is critical that horizontal angulation be accurately projected following the direction of the interproximal contacts and no overlapping contacts be present on the film.  Bitewing films are also useful in evaluation of the alveolar crests for detection of early periodontal disease.

Basic Principles
Bitewing radiographs are parallel films because the film is positioned parallel to the long axis of the teeth and the beam is perpendicular to the film as in Figure 59.  A bitewing tab is utilized to stabilize the film as the patient bites together (Figure 60).

Figure 59

Figure 60

Beam Angulation and Film Holding Devices

Bitewing radiographs are usually exposed with an indicated vertical angulation of +10 degrees (tube head points down for positive (+) angulation). This, angulation provides an acceptable compromise for the differences between the long axis inclinations of the maxillary and mandibular teeth.  Horizontal angulation is aligned with the direction of the contact, and the central ray is directed between the contact of the teeth to be radiographed.  Horizontal angulation is achieved when the central ray of the x-ray beam is directed specifically between the contacts of the teeth to be radiographed.

The interproximal examination may be done using special #3 bitewing film but is preferably achieved by using #2 films fitted with a tab.  There are also film holding devices available that support the film as well as provide an external reference for positioning the tube head.  The patient stabilizes the film by gently biting together on the manufactured tab or on the instrument.

Tube head position is illustrated in Figure 61, and a sample set of bitewing radiographs is illustrated in Figure 62.

Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar. The apron must be properly placed to avoid interference with the radiographic exposure.

Figure 61
 

 

Figure 62
 

 Quiz

1. What is the main purpose for taking bitewing radiographs?
2. Why are bitewings exposed with a vertical angulation of +10 degrees?

Answers

1. To detect interproximal caries.
2. To compromise for the differences in the long axis angulations of the maxillary and mandibular teeth.

Intraoral Radiographic Techniques (The Bisecting Angle Technique)-Chapter 3

Basic Principles
The bisecting-the-angle or bisecting angle technique is based on the principle of aiming the central ray of the x-ray beam at right angles to an imaginary line which bisects the angle formed by the longitudinal axis of the tooth and the plane of the film packet.  While it is not necessary to go into a long dissertation on plane geometry to understand this concept, a quick review will help make the technique more clear.  To bisect is to divide a line or angle into two equal portions.  A bisector is a plane or line that divides a line or angle into two equal portions.  Figure 37 shows an equilateral triangle, with legs AB=BC=CA, and the angles ABC=60 degrees, CAB=60 degrees and BCA=60 degrees.
 

Figure 37
 

We see in Figure 37 the following:

1. The dotted line BD bisects the triangle, dividing it exactly in half.  Thus, two equal triangles are formed from the original. Legs AB and BC were unchanged and thus are still equal.
2. The original line CA was divided in half by D, and thus the lines AD and CD are equal.
3. We know that the angle at point B was 60 degrees, and since it was bisected (divided equally), it now is 30 degrees at the intersections of AD and BD.
4. We also know that bisecting the angle did not affect the angle at the old point A which was 60 degrees, and still is.
5. The angle at the bisecting point DC must be 90 degrees because the sum of all the angles in any triangle is 180 degrees, and thus 180-(60+30)=90.
6. Cyzynski’s Rule of Isometry states that two triangles are equal when they share one complete side, and have two equal angles.  We can see that triangles ADB and BDC share the common side BD.
7. We know further that the angles ADB and BDC are equal because D was defined as a bisector of the old angle ABC.
8. Lastly, we know that the angles CAB and BCA were unchanged by bisecting and are still equal.  Therefore, under Cyzynski’s Theorem, we can prove the triangles ABD and CBD are equal.

In dental radiography, the theorem is applied in the following manner.  The film is positioned resting on the palate or on the floor of the mouth as close to the lingual tooth surfaces as possible.  The plane of the film and the long (vertical) axis of the teeth to be radiographed form an angle with the apex at the point where the film packet contacts the teeth.  The apex in Figure 38 is located at the point labeled B.
In Figure 38, the long axis through the tooth forms one leg of a triangle (AB), the plane of the film packet another leg, (BC), both of which intersect at the apex, point B.  A line representing the central x-ray beam will form the third leg of the triangle, AC.  If an imaginary line bisected this axis-packet-ray triangle, the bisector, DB, would form the common side of two equal triangles as defined by Cyzynski’s Theorem.
 

Figure 38
Since the sides formed by the tooth’s long axis and the film packet are equal, the image cast onto the radiographic film would be the same length as the tooth or teeth casting that image.  This linear equality is the basis for diagnostic quality bisecting angle radiographs.

The Bisecting Angle Technique

Anatomical Considerations
The bisecting angle technique is of value when the paralleling technique cannot be utilized.  This may include patients with small mouths and those with low palatal vaults.  Because of the increased exposure to radiation in this technique, it should only be employed as necessary.
Beam Angulation
The bisecting technique calls for varying beam angulations, depending on the region to be examined.
Horizontal angulation:  The horizontal angulation of the tube head should be adjusted for each projection to position the central ray through the contacts in the region to be examined.  This angulation will usually be at right angles to the buccal surfaces of the teeth to be radiographed.
Vertical angulation:  In practice, the operator should position the central ray of the x-ray beam so that it is perpendicular to the imaginary line bisecting the angle formed between the tooth long axis and the film.  This principle works well with flat, two-dimensional structures, but teeth that have depth or are multirooted will produce distorted images.  If the vertical angulation is excessive the image will appear foreshortened.  Insufficient vertical angulation produces an elongated image.
The optimum angle will vary from patient to patient, but the chart below serves as a general guideline for beam angulation.

Projection	Maxilla	Mandible
Incisors	+40 degrees	-15 degrees
Canine	+45 degrees	-20 degrees
Premolar	+30 degrees	-10 degrees
Molar	+20 degrees	2-5 degrees

Film Holding Devices
Supporting the film pack with the patient’s forefinger is not recommended.  This method has several drawbacks.  In addition to exposing the patient’s digit to additional radiation, the patient may exert excessive force, thus bending the film and distorting the radiograph.  The film may slip without the operator’s knowledge, and produce a radiograph outside the proper image field.  Therefore, intraoral support is best accomplished using instruments that restrain the film and help align the beam properly.


Quiz

1. On what principle is the bisecting angle technique based?
2. How did this principle originate?

Answers

1. The bisecting angle technique is based on the principle of aiming the central ray of the x-ray beam at right angles to an imaginary plane bisecting the angle formed by the longitudinal axis of the tooth and the plane of the film packet.
2. The principle originated from Cyzynski’s Rule of Isometry (Cyzynski’s Theorem) which states that two triangles are equal when they share one complete side and have two equal angles.

Bisecting Angle Methodology
 

Patient Positioning
Maxillary region:  For bisecting angle radiographs of the maxilla, the patient should be positioned so that the maxillary occlusal plane is parallel to the floor and the sagittal plane of the patient’s head is perpendicular to the floor.
Mandibular region:  For bisecting angle radiographs of the mandible, the patient should be positioned so that the mandibular occlusal plane is parallel to the floor and the sagittal plane of the patient’s head is perpendicular to the floor.
Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.
 

Full Mouth Exposure
Procedure for the Maxillary Central/Lateral Incisors

1. Assemble the anterior film holder and insert the film packet vertically on the biteblock.  Use a #1 film.
2. Center the film on the central/lateral incisors as close as possible to the lingual surfaces of the teeth with approximately a one-eighth inch border of the film extending below the incisal edge of the centrals (Figure 39).  Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 40).
3. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
4. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed.  Horizontally, the central ray should bisect the central/lateral (Figure 41).  For maxillary exposures the tube head will be pointed down for positive (+) angulation.
5. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.

Figure 39 

Figure 40 

Figure 41

Procedure for the Maxillary Canines

1. Assemble the anterior film holder and insert the film packet vertically on the biteblock.  Use a #1 film.
2. Center the film on the canine as close as possible to the lingual surfaces of the teeth with approximately a one-eighth inch border of the film extending below the incisal edge of the centrals (Figure 42).  Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 43).
3. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
4. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed.  Horizontally, the central ray should bisect the canine (Figure 44).  For maxillary exposures the tube head will be pointed down for positive (+) angulation.
5. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.

Figure 42

Figure 43

Figure 44

Procedure for the Maxillary Premolars

1. Assemble the posterior film holder and insert the film packet horizontally on the biteblock.  Use a #2 film.
2. Center the film on the premolars as close as possible to the lingual surfaces of the teeth (Figure 45).  Position the film in the palate so that the entire tooth length will appear on the film with approximately a one-eighth inch border below the cuspal ridge.  Align the anterior border of the film packet with the canine so that the image captured on the anterior edge of the film will be the distal third of the canine.  Position the biteblock on the occlusal surface of the teeth being radiographed (Figure 46).
3. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  (Watch the occlusal border of the film packet; it tends to slip down anteriorly.)
4. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed. Horizontally, the central ray should pass between the contact of the first and second premolar (Figure 47).  For maxillary exposures the tube head will be pointed down for positive (+) angulation.
5. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.

 

Figure 45

Figure 46

Figure 47

Procedure for the Maxillary Molars

1. Assemble the posterior film holder and insert the film packet horizontally on the biteblock.  Use a #2 film.
2. Center the film on the molars as close as possible to the lingual surfaces of the teeth (Figure 48).  Position the film in the palate so that the entire tooth length will appear on the film with approximately a one-eighth inch border below the cuspal ridge.  Align the anterior border of the film packet with the second premolar so that the image captured on the anterior edge of the film is the distal third of the second premolar.  Position the biteblock on the occlusal surface of the teeth being radiographed (Figure 49).
3. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
4. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed. Horizontally, the central ray should pass between the contact of the first and second molar (Figure 50).  For maxillary exposures the tube head will be pointed down for positive (+) angulation.
5. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.

 

Figure 48

Figure 49

Figure 50

Procedure for the Mandibular Central/Lateral Incisors

1. Assemble the anterior film holder and insert the film packet vertically on the biteblock.  Use a #1 film.
2. Center the film on the central/lateral incisors as close as possible to the lingual surfaces of the teeth with approximately a one-eighth inch border of the film extending above the incisal edge of the centrals.  Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 51).
3. A cotton roll may be inserted between the maxillary incisors and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  The film should be straightened as the patient closes and the floor of the mouth relaxes.
4. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed.  Horizontally, the central ray should pass between the central/lateral incisors (Figure 52).  For mandibular exposures the tube head will be pointed up for negative (-) angulation.
5. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.

 

Figure 51

 
Figure 52

Procedure for the Mandibular Canines

1. Assemble the anterior film holder and insert the film packet vertically on the biteblock. Use a #1 film.
2. Center the film on the canine as close as possible to the lingual surfaces of the teeth with approximately a one-eighth inch border of the film extending above the incisal edge of the canine. Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 53).
3. A cotton roll may be inserted between the maxillary teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position. The film should be straightened as the patient closes and the floor of the mouth relaxes.
4. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed. Horizontally, the central ray should bisect the canine (Figure 54). For mandibular exposures the tube head will be pointed up for negative (-) angulation.
5. Follow the film and equipment manufacturer’s recommendation concerning exposure factors. Make the exposure.

 

Figure 53

 
Figure 54

Procedure for the Mandibular Premolars

1. Assemble the posterior film holder and insert the film packet horizontally on the biteblock. Use a #2 film.
2. Center the film on the premolars as close as possible to the lingual surfaces of the teeth. Align the anterior border of the film packet with the canine so that the image captured on the anterior edge of the film will be the distal third of the canine. Position the biteblock on the occlusal surface of the teeth to be radiographed (Figure 55).
3. A cotton roll may be inserted between the maxillary premolars and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position. The film should be straightened as the patient closes and the floor of the mouth relaxes.
4. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed. Horizontally, the central ray should pass between the first and second premolars (Figure 56). For mandibular exposures the tube head will be pointed up for negative (-) angulation.
5. Follow the film and equipment manufacturer’s recommendation concerning exposure factors. Make the exposure.

 

Figure 55

Figure 56

Procedure for the Mandibular Molars

1. Assemble the posterior film holder and insert the film packet horizontally on the biteblock.  Use a #2 film.
2. Center the film on the molars as close as possible to the lingual surfaces of the teeth.  Align the anterior border of the film packet with the second premolar so that the image captured on the anterior edge of the film will be the distal third of the second premolar.  Position the biteblock on the occlusal surface of the teeth to be radiographed (Figure 57).
3. A cotton roll may be inserted between the maxillary molars and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  The film should be straightened as the patient closes and the floor of the mouth relaxes.
4. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed.  Horizontally, the central ray should pass between the contact of the first and second molar (Figure 58). For mandibular exposures the tube head will be pointed up for negative (-) angulation. 
5. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.

 

Figure 57   

Figure 58