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Dental radiographic techniques and normal roentgen anatomy
Dental Radiographic Techniques Normal Roentgen Anatomy By
JOHN
W.
FFCEECE,
and
D.D.S.
INCE THE DISCOVERY OF THE X RAY, the dentist has been involved in the development of intraoral and extraoral film placement techniques. The compelling necessity to record the teeth and their contiguous structures on film has culminated in the refinement of two fundamental intraoral techniques known as bisecting-the-angle and paralleling, or long cone. Supplemental techniques in dental radiology are generally limited to occlusal, lateral jaw, and panoramic surveys.
S
BISECTING TECHNIQUE
Historically, initial dental radiographic techniques consisted, at best, of individual, haphazard trial and error experimentation. Then in 1907, Cieszynski presented the radiologic world with the first standardized theory for achieving periapical radiographic success.Although not of immediate impact, this formulation was based upon the geometric theorem of isometry which, when applied to dental radiology, states: when the angle formed by the plane of the tooth and the plane of the film is bisected, with the central ray directed perpendicular to the bisector through the apex of the tooth, the length of the image on the film equals the length of the root1 (Fig. 1). The radiographic procedure utilizing Cieszynski’s rule of isometry is called bisecting-the-angle or bisecting technique. It requires a standardized head position in which the occlusal plane is parallel to the floor and the sagittal plane perpendicular to the floor .2 Specific vertical angles for each area of the arch are utilized and any deviation from the rules of isometry results in marked elongation or foreshortening of the radiographic image. PARALLEL
TECHNIQUE
McCormack, in 1920, originated the use of the long cone and paralleling techniques for intraoral radiography. lo The plane of the film is placed parallel to the long axis of the teeth with the beam of radiation directed perpendicular to the object and film (Fig. 2). Variations in size, shape, and curvature of the palate necessitate film placement relatively far fro19 the crowns of the teeth. A longer target-to-object distance is essential to compensate for the magnification of the radiographic image resulting from the increased objectto-film distance. McCormack recommended a 36- to do-inch target-to-object distance which was subsequently modified to 20 inches by Fitzgerald.374 Recently, van Aken recommended a minimum of 12- to 16-inch target-to-object distance using the paralleling technique. The reduction in cone length may be
JOHN W.
PREECB,
D.D.S.: University
of North
Carolina School
of
Den&try,
Chapel
Hill,
N. C. 27514.
SEMINARS
IN ROENTGENOLOGY.
VOL. 6.
No. 4 ( OCTOBER j. 1971
359
360
JOHNW.
PREECE
BISECTING
Fig. L-Bisecting-the-angle
Fig. 2.-Paralleling
principle. CR: central ray.
principle.
Lo
attributed in part to the use of smaller focal spot size in modern radiographic equipment (0.8 mm compared with 1.4 to 2.8 mm used by Fitzgerald). SHADOW
CASTING
Whether the clinician chooses the bisecting or parallel technique, certain principles of shadow casting must be followed to insure as accurate a roentgen image as possible. The extent to which a particular technique follows these principles is frequently used as a criterion for determining the superiority of one technique over another. A brief review of the principles of shadow casting is useful and will aid in evaluating the two intraoral procedures. The five principles of shadow casting are: la,23 ( 1) the source of radiation should be as small as possible; (2) the object-to-film distance should be as small as possible; (3) the target-to-object distance should be as great as possible; (4) the film and object should be parallel to each other; and (5) the beam of
RADIOGRAPHIC
TECHNIQUES
AND
ROENTGEN
ANATOMY
361
Fig. 3.-Commercially available paralleling devices: (1) precision X-ray
instrument (Precision Xray Co., Nashville, Tenn.); (2) Rinn XCP instrument (Rinn Corp., Elgin, Ill.); (3) Hemostat and rubber block; (4) STABE disposable dental X-ray holder (Greene Dental Products, Inc., San Fernando, Calif.).
radiation should be perpendicular to the object and film or directed perpendicular to a plane bisecting the angle between the tooth and film.19 The bisecting technique routinely satisfies rule 2; rule 3 and 5 may be fulfilled, provided an extended target-to-object distance is used and the central ray is directed through the apex of the tooth perpendicular to the bisector. A recommended beam diameter of 2%inches does not permit directing the beam through the apex of the tooth without cone cutting the film; however, van Aken has demonstrated that when a beam other than the central ray is directed perpendicular to the bisecting plane through the apex of the tooth, conditions of the bisecting technique are satisfied.19 The parallel technique satisfies shadow casting rules 3, 4, and 5. Rule 4 may be compromised due to variations in anatomic structure which limit the operator’s ability to place the film perpendicular to the long axis of the teeth. Rule 1 is determined by the manufacturer of the particular X-ray equipment. In a recent comparison of the bisecting and parallel techniques, both produced radiographs of comparable quality (no distortion or enlargement), providing a long target-to-object distance was used;rQ the bisecting technique, however, demonstrated inferior roentgen reproduction of the cervical line area despite the absence of distortion and magnification. When fixed target-to-object distances were used ( asnecessary in dentistry), the parallel technique produced superior quality radiographs with less distortion of the image. Anatomic structures preventing placement of the film parallel to the long axis of the teeth had little effect on the radiographic image if three conditions were observed: (1) the film was placed within 20” of parallel to the long axis of the teeth, (2) the beam of radiation was directed perpendicular to the film, and (3) a target-to-object distance of 12 inches (30 cm) or greater was used. The parallel technique necessitates the use of a film holding device to stabilize the film in the mouth away from the teeth (Fig. 3). Each film holding device has particular advantages and disadvantages which the operator should evaluate and select to meet his own radiographic purposes,
362
JOHN
W.
PREECE
Fig. 4.-Cross-section occlusal technique. A. Film placement and beam angu-
lation. B. Periapical film showsa foreign body (piece of rubber). C. Occlusal view demonstratesits facial-lingual location.
The increased interest and emphasis on patient protection from unnecessary and excessive exposure necessitate the use of “D speed” film, lead apron, timetemperature development, increased source-object distances, and the use of as small a beam as possible. Weissman and Sobkowski, compared exposures to various areas of the head and neck using a variety of techniques and cones (short pointed cone with bisecting technique; unshielded open cone, shielded open cone, and shielded cone with rectangular collimating device using parallel technique). s2 The authors concluded that shielded cones and devices for rectangularly collimating the beam significantly reduced exposure to the patient’s head and reproductive organs. Lap doses were reported to be 1.0 mr for the pointed plastic and unshielded open cones and 0.2 mr for the rectangularly collimated beam. When a lead apron was used, exposures were 0.3 mr for the short pointed cone and 0.03 mr for the shielded cone and rectangular collimator, They concluded: “Metal rectangular collimators when used with a 16 inch shielded open-end cone provide the most acceptable intraoral periapical
RADIOGRAPHIC TECHNIQUES AND ROENTGEN ANATOMY
363
survey technique.” Their conclusions were based on the utilization of the parallel technique and the reduction in exposure at anatomic sites not involved with the radiographic image. SUPPLEMENTARY
RADIOGRAPHIC TECHNIQUES
Occlusal Techniques When intraoral periapical surveys employing the preceding methods prove inadequate for demonstrating the full extent of pathologic conditions, it becomes necessary to supplement the intraoral study with larger films to show broader anatomic areas and relationships. Occlusal radiographic techniques are a useful adjunct in the clinician’s roentgen armamentarium and may be divided into cross section and topographic occlusal methods. Both techniques utilize large “D speed” film 2.25 x 3.0 inches inserted into the oral cavity (emulsion side toward the area of interest) and retained in position by light occlusal or finger pressure. In the cross-section occlusal method, the X-ray beam is directed perpendicular to the film (Fig. 4A). The resultant radiograph shows the maxilla or mandible in cross section and is useful for demonstrating the facial-lingual location of an impacted tooth or foreign body (Figs. 4B and C), expansion or thinning of the cortex, fracture, sialolith within the submandibular duct, and for rapid survey of an edentulous patient. The procedure is extremely useful for demonstrating the mandible in cross section. However, when used for filming the maxilla, a special intraoral cassette with intensifying screens (and light sensitive film) is necessary to prevent inordinately long exposure. Modification of the occlusal technique by utilizing a small intraoral periapical film placed on the occlusal surface is useful to show a small area to localize a fractured root tip or broken instrument. Topographic accusal technique may be considered an extreme example of the bisecting angle technique (Fig. 5A). The film is placed as in the cross section technique and the beam of radiation is directed perpendicular to an imaginary plane bisecting the planes of the film and of the teeth. A vertical angle of 65-70” (occlusal plane parallel to the floor) is generally used to record the anterior teeth (Figs. 5B and C). Smaller film may be used conveniently for small children or for adults when circumstances prevent placement of the film adequateiy for other techniques (Fig. 5D). Lateral Jaw Projection Oblique or lateral jaw projections permit visualization of the entire mandible or maxilla. The film is placed externally, the beam of radiation is directed obliquely toward the area of interest, perpendicular to the film. Wuehrmann and Manson-Hing suggest the central ray be directed through a point just medial to the ramus and one-half inch above the angle of the mandible (on the side of the face closest to the X-ray machine) toward a point above the occlusal plane just anterior to the area of interests3 (Fig. 6A). Placement of the film against the patient’s face depends upon the curvature of the mandibular arch and the area to be radiographed.
JOHN
W.
PREECE
Fig, 5.-Topographic occlusal technique. A. Film placement and beam angulation. Cl: Long axis of central incisor. B. Mandibular radiograph. Dentigerous cyst. C. Maxillary radiograph. Incisive canal cyst. D. Maxillary topographic occlusal radiograph of a small child using a 1.2 size periapical film.
The lateral jaw view provides a means of obtaining information on patients unable to cooperate or tolerate intraoral placement of films (Fig. 6B). Several lateral oblique films may serve as an alternate method when panoramic radiographic methods are unavailable or for special procedures such as sialography. Panoramic Radiography The application of laminagraphic principles to curved surfaces of the head and neck by Paatero has been fundamental in the development of the panoramic X-ray machine .r1-r3 Panoramic radiography is an extraoral procedure utilizing the simultaneous rotation of the X-ray tube and film about the patient’s head. This synchronous movement of the tube and film causesa specific layer within the head to be projected sharply onto the film, while structures external or internal to this layer (lamina) are blurred and distorted. Panoramic X-ray machines commonly used in the United States are the
RADIOGRAPHIC
A
TECHNIQUES
AND
ROENTGEN
ANATOMY
365
FILM FOSlTlOh
CENTRA
Fig. 6.-Lateral oblique technique. A. Beam angubtion and film placement. (Redrawn from Wuehrmann and Manson-Hing; reproduced with permission of C. V. Mosby Co .ss) B. Lateral oblique radiograph. Fibrosarcoma.
Panorex (S.S. White Co.), Orthopantomograph (Siemens Co.), and most recently the G.E.-3000 (General Electric Co.). All of the presently available panoramic machines are designed for use on the average patient, and there are relatively few alterations that can be made to compensate for individuals who deviate significantly from the norm. The Panorex has a separate adjustment for young children while the G.E.-3000 is adjustable for a wide variety of arch sizes making it most versatile.9 Panoramic radiography is a useful screening device, permitting rapid evalu-
Fig. S.-Maxillary periapical radiographs illustrating common anatomic landmarks. A. Central incisor region: (1) incisive foramen; (2) median palatal suture; (3) anterior wall of nasal fossa; (4) nasal septum; (5) nasal fossa; (6) shadow of nose. Small black arrows outline a periapical radiolucency. B. Canine-lateral incisor region: (1) nasal fossa; (2) junction of the lateral wall of the nose with the maxillary sinus; (3) maxillary sinus. White arrows point to the lip line. C. Premolar region: (1) septum in the maxillary sinus; (3) lamina dura. D. Molar region: (1) maxillary sinus; (2) coronoid process of the mandible; (3) lateral pterygoid plate; (4) hamular process. Small black arrows indicate zygomatic arch.
ation of the teeth, alveolar processes, and large sections of the mandible and maxilla (Fig. 7). Radiographic image quality, however, varies from patient
to patient because of the inability of the laminagraphic characteristics of the machines to adapt to individual arch forms. The need for long object-to-film distance and intensifying screens, and the frequency of vertical and horizontal distortion somewhat diminish the quality of the radiographic image.s,sgr4,15,17, ls panoramic radiography has not replaced As a result of these shortcomings, intraoral periapical surveys for the diagnosis of caries and periodontal disease. It serves mainly to supplerlent intraoral radiography and provide the clinician
RADIOGRAPHIC
TECHNIQUES
AND
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367
ANATOMY
Fig. 9.-Mandibular periapical radiographs illustrating commonanatomiclandmarks. A. Central incisor region: (1) lingual forarnen; (2) mental ridge; (3) lower border of mandible. White arrows outline the genial tubercles. B. Canine-lateral region: (1) mental ridge. C. Premolar region: (1) mental foramen; (2) mandibular canal. D. Molar region:
(1) external
oblique
line; (2) mylohyoid
line; (3) mandibular
canal.
with a diagnostic overview of the mandible and maxilla beyond the capabilities of periapical films. Radiation exposure to patients from panoramic equipment is controversial and varies from author to author depending on the method of measurement. Exposure to the reproductive organs was reported to vary with the Panorex between 0.4 and 0.1 mr;s,a with the Orthopantomograph it measured 0.1 mr.6 Exposure of 0.01 mr was reported when the lead apron was used for either machine. Comparison of the total integral absorbed dose from a 16 film (Ultraspeed) intraoral survey with that of an Orthopantomographic survey indicated that total dosage to the patient is relatively small from the panoramic procedure.2a Radiation measurements for the G.E.-3000 have not yet been reported.
368
JOHN
W. PREECE
No matter how precise the radiographic techniques, if the clinician does not have the training to interpret the films properly in terms of abnormal conditions, the patient will have received unnecessary exposure without benefit. A thorough knowledge of the normal anatomic structures observed in each periapical film and variations in their appearance with film packet placement and tube angulation is also necessary for correct interpretation of the abnormal radiograph, Anatomic structures frequently encountered in periapical radio/graphs are presented in Figs. 8 and 9. Dental radiography is still striving for its impossible dream, a radiographic technique that will consistently produce radiographic images which are accurate jn every anatomic detail for every patient regardless of anatomic variations. The use of the least amount of radiation to accomplish this result and the availability of someone trained to accurately interpret the radiographs are additional parts of this dream. Seventy five years of evolution in intraoral radiographic procedures have not yet brought about the fulfillment of this dream, but perhaps we are just a bit closer.
REFERENCES i. Cieszynski, M. A.: The position of the dental axis in the jaws and the exact adjustment of the chief ray in the intraoral method Int. J. Ortho. 4:742, 1925. 2. Ennis, L. M., Berry, H. M., Phillips, J. E.: Dental Roentgenology ( ed. 6). Philadelphia, Lea & Febiger, 1967. 3. Fitzgerald, G. M.: Dental roentgenology. I: An investigation in adumbration, or the factors that control geometric unsharpness. J. Amer. Dent. Ass. 34:1, 1947. 4. -: Dental roentgenography. II: Vertical angulation, film placement and increased object-film distance. J, Amer. Dent. Ass. 34: 160, 1947. 5. Hudson, D. C., Kumpula, J. W., and Dickson, G.: A panoramic x-ray dental machine. U.S. Armed Forces Med. J. 8:46, 1957. 6. Jung, T.: Gonadal doses resulting from panoramic x-ray examinations of the teeth. Oral Surg. 19:745, 1965. 7. Kite, 0. W., Swanson, L. T., Levin, S., and Bradbury, E.: Radiation and image distortion in the Panorex x-ray unit. Oral Surg. 15: 1201, 1962.
8. Kuba, R. K., and Beck, J. O., Jr.: Radiation dosimetry in Panorex roentgenography: parts I, II, III. Oral Surg. 25:380, 1968. 9. Manson-Hing, L. R.: Advances in dental pantomography: the G.E.-3000. Orai Sing. 31:430, 1971. 10. McCormack, F. W.: A plea for a standardized technique for oral radiography, with an illustrated classification of findings and their verified interpretations. J. Dent. Res. 2:467, 1920. 11. Paatero, Y. V.: The use of a mobile source of light in radiography. Acta Radiol. 29:221, 1924. 12. -: A new tomographical method for radiographing curved outer surfaces. Acta Radio]. 32: 177, 1949. 13. -: Geometrical study on possibilities of making double-eccentric pantomograms with a single exposure. Strom. Hammaslaak Toim. 50:36, 1954. 14. -: Pantomography and orthopantomography. Oral Surg. 14:947, 1961. 15. Phillips, J. E.: Principles and function of the Orthopantomograph. Oral Surg. 24:41, 1967.
RADIOGRAPHIC
TECHNIQUES
AND
ROENTGEN
16. Silha, R. E.: Maxillary occlusal radioginfluences of vertical angulations. raphy, Dent. Radiog. Photog. 37:38, 1964. 17. Turner, K. 0.: Limitations of panoramic radiography. Oral Surg. 26:312, 1968. 18. Updegrave, W. J.: The role of panoramic radiography in diagnosis. Oral Surg. 22:49, 1966. 19. van Aken, J.: Optimum conditions for intraoral roentgenograms, Oral Surg. 27: 475, 1969. 20. -, and van der Linden, L. W. J.: The integral absorbed dose in conventional
ANATOMY
369
and panoramic-complete mouth examinations. Oral Surg. 22:603, 1966. 21. Weissman, D. D., and Feinstein, R. B.: X-ray beam profiles and oral radiography. Oral Surg. 31:546, 1971. 22. -, and Sobkowski, F. J.: Comparative thermoluminescent dosimetry in intraoral periapical radiography. Oral Surg. 29:376, 1970. and Manson23. Wuehrmann, A. H., Hing, L. R.: Dental Radiology (ed. 2). St. Louis, Mosby, 1969.
JOHN
W.
FFCEECE,
and
D.D.S.
INCE THE DISCOVERY OF THE X RAY, the dentist has been involved in the development of intraoral and extraoral film placement techniques. The compelling necessity to record the teeth and their contiguous structures on film has culminated in the refinement of two fundamental intraoral techniques known as bisecting-the-angle and paralleling, or long cone. Supplemental techniques in dental radiology are generally limited to occlusal, lateral jaw, and panoramic surveys.
S
BISECTING TECHNIQUE
Historically, initial dental radiographic techniques consisted, at best, of individual, haphazard trial and error experimentation. Then in 1907, Cieszynski presented the radiologic world with the first standardized theory for achieving periapical radiographic success.Although not of immediate impact, this formulation was based upon the geometric theorem of isometry which, when applied to dental radiology, states: when the angle formed by the plane of the tooth and the plane of the film is bisected, with the central ray directed perpendicular to the bisector through the apex of the tooth, the length of the image on the film equals the length of the root1 (Fig. 1). The radiographic procedure utilizing Cieszynski’s rule of isometry is called bisecting-the-angle or bisecting technique. It requires a standardized head position in which the occlusal plane is parallel to the floor and the sagittal plane perpendicular to the floor .2 Specific vertical angles for each area of the arch are utilized and any deviation from the rules of isometry results in marked elongation or foreshortening of the radiographic image. PARALLEL
TECHNIQUE
McCormack, in 1920, originated the use of the long cone and paralleling techniques for intraoral radiography. lo The plane of the film is placed parallel to the long axis of the teeth with the beam of radiation directed perpendicular to the object and film (Fig. 2). Variations in size, shape, and curvature of the palate necessitate film placement relatively far fro19 the crowns of the teeth. A longer target-to-object distance is essential to compensate for the magnification of the radiographic image resulting from the increased objectto-film distance. McCormack recommended a 36- to do-inch target-to-object distance which was subsequently modified to 20 inches by Fitzgerald.374 Recently, van Aken recommended a minimum of 12- to 16-inch target-to-object distance using the paralleling technique. The reduction in cone length may be
JOHN W.
PREECB,
D.D.S.: University
of North
Carolina School
of
Den&try,
Chapel
Hill,
N. C. 27514.
SEMINARS
IN ROENTGENOLOGY.
VOL. 6.
No. 4 ( OCTOBER j. 1971
359
360
JOHNW.
PREECE
BISECTING
Fig. L-Bisecting-the-angle
Fig. 2.-Paralleling
principle. CR: central ray.
principle.
Lo
attributed in part to the use of smaller focal spot size in modern radiographic equipment (0.8 mm compared with 1.4 to 2.8 mm used by Fitzgerald). SHADOW
CASTING
Whether the clinician chooses the bisecting or parallel technique, certain principles of shadow casting must be followed to insure as accurate a roentgen image as possible. The extent to which a particular technique follows these principles is frequently used as a criterion for determining the superiority of one technique over another. A brief review of the principles of shadow casting is useful and will aid in evaluating the two intraoral procedures. The five principles of shadow casting are: la,23 ( 1) the source of radiation should be as small as possible; (2) the object-to-film distance should be as small as possible; (3) the target-to-object distance should be as great as possible; (4) the film and object should be parallel to each other; and (5) the beam of
RADIOGRAPHIC
TECHNIQUES
AND
ROENTGEN
ANATOMY
361
Fig. 3.-Commercially available paralleling devices: (1) precision X-ray
instrument (Precision Xray Co., Nashville, Tenn.); (2) Rinn XCP instrument (Rinn Corp., Elgin, Ill.); (3) Hemostat and rubber block; (4) STABE disposable dental X-ray holder (Greene Dental Products, Inc., San Fernando, Calif.).
radiation should be perpendicular to the object and film or directed perpendicular to a plane bisecting the angle between the tooth and film.19 The bisecting technique routinely satisfies rule 2; rule 3 and 5 may be fulfilled, provided an extended target-to-object distance is used and the central ray is directed through the apex of the tooth perpendicular to the bisector. A recommended beam diameter of 2%inches does not permit directing the beam through the apex of the tooth without cone cutting the film; however, van Aken has demonstrated that when a beam other than the central ray is directed perpendicular to the bisecting plane through the apex of the tooth, conditions of the bisecting technique are satisfied.19 The parallel technique satisfies shadow casting rules 3, 4, and 5. Rule 4 may be compromised due to variations in anatomic structure which limit the operator’s ability to place the film perpendicular to the long axis of the teeth. Rule 1 is determined by the manufacturer of the particular X-ray equipment. In a recent comparison of the bisecting and parallel techniques, both produced radiographs of comparable quality (no distortion or enlargement), providing a long target-to-object distance was used;rQ the bisecting technique, however, demonstrated inferior roentgen reproduction of the cervical line area despite the absence of distortion and magnification. When fixed target-to-object distances were used ( asnecessary in dentistry), the parallel technique produced superior quality radiographs with less distortion of the image. Anatomic structures preventing placement of the film parallel to the long axis of the teeth had little effect on the radiographic image if three conditions were observed: (1) the film was placed within 20” of parallel to the long axis of the teeth, (2) the beam of radiation was directed perpendicular to the film, and (3) a target-to-object distance of 12 inches (30 cm) or greater was used. The parallel technique necessitates the use of a film holding device to stabilize the film in the mouth away from the teeth (Fig. 3). Each film holding device has particular advantages and disadvantages which the operator should evaluate and select to meet his own radiographic purposes,
362
JOHN
W.
PREECE
Fig. 4.-Cross-section occlusal technique. A. Film placement and beam angu-
lation. B. Periapical film showsa foreign body (piece of rubber). C. Occlusal view demonstratesits facial-lingual location.
The increased interest and emphasis on patient protection from unnecessary and excessive exposure necessitate the use of “D speed” film, lead apron, timetemperature development, increased source-object distances, and the use of as small a beam as possible. Weissman and Sobkowski, compared exposures to various areas of the head and neck using a variety of techniques and cones (short pointed cone with bisecting technique; unshielded open cone, shielded open cone, and shielded cone with rectangular collimating device using parallel technique). s2 The authors concluded that shielded cones and devices for rectangularly collimating the beam significantly reduced exposure to the patient’s head and reproductive organs. Lap doses were reported to be 1.0 mr for the pointed plastic and unshielded open cones and 0.2 mr for the rectangularly collimated beam. When a lead apron was used, exposures were 0.3 mr for the short pointed cone and 0.03 mr for the shielded cone and rectangular collimator, They concluded: “Metal rectangular collimators when used with a 16 inch shielded open-end cone provide the most acceptable intraoral periapical
RADIOGRAPHIC TECHNIQUES AND ROENTGEN ANATOMY
363
survey technique.” Their conclusions were based on the utilization of the parallel technique and the reduction in exposure at anatomic sites not involved with the radiographic image. SUPPLEMENTARY
RADIOGRAPHIC TECHNIQUES
Occlusal Techniques When intraoral periapical surveys employing the preceding methods prove inadequate for demonstrating the full extent of pathologic conditions, it becomes necessary to supplement the intraoral study with larger films to show broader anatomic areas and relationships. Occlusal radiographic techniques are a useful adjunct in the clinician’s roentgen armamentarium and may be divided into cross section and topographic occlusal methods. Both techniques utilize large “D speed” film 2.25 x 3.0 inches inserted into the oral cavity (emulsion side toward the area of interest) and retained in position by light occlusal or finger pressure. In the cross-section occlusal method, the X-ray beam is directed perpendicular to the film (Fig. 4A). The resultant radiograph shows the maxilla or mandible in cross section and is useful for demonstrating the facial-lingual location of an impacted tooth or foreign body (Figs. 4B and C), expansion or thinning of the cortex, fracture, sialolith within the submandibular duct, and for rapid survey of an edentulous patient. The procedure is extremely useful for demonstrating the mandible in cross section. However, when used for filming the maxilla, a special intraoral cassette with intensifying screens (and light sensitive film) is necessary to prevent inordinately long exposure. Modification of the occlusal technique by utilizing a small intraoral periapical film placed on the occlusal surface is useful to show a small area to localize a fractured root tip or broken instrument. Topographic accusal technique may be considered an extreme example of the bisecting angle technique (Fig. 5A). The film is placed as in the cross section technique and the beam of radiation is directed perpendicular to an imaginary plane bisecting the planes of the film and of the teeth. A vertical angle of 65-70” (occlusal plane parallel to the floor) is generally used to record the anterior teeth (Figs. 5B and C). Smaller film may be used conveniently for small children or for adults when circumstances prevent placement of the film adequateiy for other techniques (Fig. 5D). Lateral Jaw Projection Oblique or lateral jaw projections permit visualization of the entire mandible or maxilla. The film is placed externally, the beam of radiation is directed obliquely toward the area of interest, perpendicular to the film. Wuehrmann and Manson-Hing suggest the central ray be directed through a point just medial to the ramus and one-half inch above the angle of the mandible (on the side of the face closest to the X-ray machine) toward a point above the occlusal plane just anterior to the area of interests3 (Fig. 6A). Placement of the film against the patient’s face depends upon the curvature of the mandibular arch and the area to be radiographed.
JOHN
W.
PREECE
Fig, 5.-Topographic occlusal technique. A. Film placement and beam angulation. Cl: Long axis of central incisor. B. Mandibular radiograph. Dentigerous cyst. C. Maxillary radiograph. Incisive canal cyst. D. Maxillary topographic occlusal radiograph of a small child using a 1.2 size periapical film.
The lateral jaw view provides a means of obtaining information on patients unable to cooperate or tolerate intraoral placement of films (Fig. 6B). Several lateral oblique films may serve as an alternate method when panoramic radiographic methods are unavailable or for special procedures such as sialography. Panoramic Radiography The application of laminagraphic principles to curved surfaces of the head and neck by Paatero has been fundamental in the development of the panoramic X-ray machine .r1-r3 Panoramic radiography is an extraoral procedure utilizing the simultaneous rotation of the X-ray tube and film about the patient’s head. This synchronous movement of the tube and film causesa specific layer within the head to be projected sharply onto the film, while structures external or internal to this layer (lamina) are blurred and distorted. Panoramic X-ray machines commonly used in the United States are the
RADIOGRAPHIC
A
TECHNIQUES
AND
ROENTGEN
ANATOMY
365
FILM FOSlTlOh
CENTRA
Fig. 6.-Lateral oblique technique. A. Beam angubtion and film placement. (Redrawn from Wuehrmann and Manson-Hing; reproduced with permission of C. V. Mosby Co .ss) B. Lateral oblique radiograph. Fibrosarcoma.
Panorex (S.S. White Co.), Orthopantomograph (Siemens Co.), and most recently the G.E.-3000 (General Electric Co.). All of the presently available panoramic machines are designed for use on the average patient, and there are relatively few alterations that can be made to compensate for individuals who deviate significantly from the norm. The Panorex has a separate adjustment for young children while the G.E.-3000 is adjustable for a wide variety of arch sizes making it most versatile.9 Panoramic radiography is a useful screening device, permitting rapid evalu-
Fig. S.-Maxillary periapical radiographs illustrating common anatomic landmarks. A. Central incisor region: (1) incisive foramen; (2) median palatal suture; (3) anterior wall of nasal fossa; (4) nasal septum; (5) nasal fossa; (6) shadow of nose. Small black arrows outline a periapical radiolucency. B. Canine-lateral incisor region: (1) nasal fossa; (2) junction of the lateral wall of the nose with the maxillary sinus; (3) maxillary sinus. White arrows point to the lip line. C. Premolar region: (1) septum in the maxillary sinus; (3) lamina dura. D. Molar region: (1) maxillary sinus; (2) coronoid process of the mandible; (3) lateral pterygoid plate; (4) hamular process. Small black arrows indicate zygomatic arch.
ation of the teeth, alveolar processes, and large sections of the mandible and maxilla (Fig. 7). Radiographic image quality, however, varies from patient
to patient because of the inability of the laminagraphic characteristics of the machines to adapt to individual arch forms. The need for long object-to-film distance and intensifying screens, and the frequency of vertical and horizontal distortion somewhat diminish the quality of the radiographic image.s,sgr4,15,17, ls panoramic radiography has not replaced As a result of these shortcomings, intraoral periapical surveys for the diagnosis of caries and periodontal disease. It serves mainly to supplerlent intraoral radiography and provide the clinician
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Fig. 9.-Mandibular periapical radiographs illustrating commonanatomiclandmarks. A. Central incisor region: (1) lingual forarnen; (2) mental ridge; (3) lower border of mandible. White arrows outline the genial tubercles. B. Canine-lateral region: (1) mental ridge. C. Premolar region: (1) mental foramen; (2) mandibular canal. D. Molar region:
(1) external
oblique
line; (2) mylohyoid
line; (3) mandibular
canal.
with a diagnostic overview of the mandible and maxilla beyond the capabilities of periapical films. Radiation exposure to patients from panoramic equipment is controversial and varies from author to author depending on the method of measurement. Exposure to the reproductive organs was reported to vary with the Panorex between 0.4 and 0.1 mr;s,a with the Orthopantomograph it measured 0.1 mr.6 Exposure of 0.01 mr was reported when the lead apron was used for either machine. Comparison of the total integral absorbed dose from a 16 film (Ultraspeed) intraoral survey with that of an Orthopantomographic survey indicated that total dosage to the patient is relatively small from the panoramic procedure.2a Radiation measurements for the G.E.-3000 have not yet been reported.
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No matter how precise the radiographic techniques, if the clinician does not have the training to interpret the films properly in terms of abnormal conditions, the patient will have received unnecessary exposure without benefit. A thorough knowledge of the normal anatomic structures observed in each periapical film and variations in their appearance with film packet placement and tube angulation is also necessary for correct interpretation of the abnormal radiograph, Anatomic structures frequently encountered in periapical radio/graphs are presented in Figs. 8 and 9. Dental radiography is still striving for its impossible dream, a radiographic technique that will consistently produce radiographic images which are accurate jn every anatomic detail for every patient regardless of anatomic variations. The use of the least amount of radiation to accomplish this result and the availability of someone trained to accurately interpret the radiographs are additional parts of this dream. Seventy five years of evolution in intraoral radiographic procedures have not yet brought about the fulfillment of this dream, but perhaps we are just a bit closer.
REFERENCES i. Cieszynski, M. A.: The position of the dental axis in the jaws and the exact adjustment of the chief ray in the intraoral method Int. J. Ortho. 4:742, 1925. 2. Ennis, L. M., Berry, H. M., Phillips, J. E.: Dental Roentgenology ( ed. 6). Philadelphia, Lea & Febiger, 1967. 3. Fitzgerald, G. M.: Dental roentgenology. I: An investigation in adumbration, or the factors that control geometric unsharpness. J. Amer. Dent. Ass. 34:1, 1947. 4. -: Dental roentgenography. II: Vertical angulation, film placement and increased object-film distance. J, Amer. Dent. Ass. 34: 160, 1947. 5. Hudson, D. C., Kumpula, J. W., and Dickson, G.: A panoramic x-ray dental machine. U.S. Armed Forces Med. J. 8:46, 1957. 6. Jung, T.: Gonadal doses resulting from panoramic x-ray examinations of the teeth. Oral Surg. 19:745, 1965. 7. Kite, 0. W., Swanson, L. T., Levin, S., and Bradbury, E.: Radiation and image distortion in the Panorex x-ray unit. Oral Surg. 15: 1201, 1962.
8. Kuba, R. K., and Beck, J. O., Jr.: Radiation dosimetry in Panorex roentgenography: parts I, II, III. Oral Surg. 25:380, 1968. 9. Manson-Hing, L. R.: Advances in dental pantomography: the G.E.-3000. Orai Sing. 31:430, 1971. 10. McCormack, F. W.: A plea for a standardized technique for oral radiography, with an illustrated classification of findings and their verified interpretations. J. Dent. Res. 2:467, 1920. 11. Paatero, Y. V.: The use of a mobile source of light in radiography. Acta Radiol. 29:221, 1924. 12. -: A new tomographical method for radiographing curved outer surfaces. Acta Radio]. 32: 177, 1949. 13. -: Geometrical study on possibilities of making double-eccentric pantomograms with a single exposure. Strom. Hammaslaak Toim. 50:36, 1954. 14. -: Pantomography and orthopantomography. Oral Surg. 14:947, 1961. 15. Phillips, J. E.: Principles and function of the Orthopantomograph. Oral Surg. 24:41, 1967.
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16. Silha, R. E.: Maxillary occlusal radioginfluences of vertical angulations. raphy, Dent. Radiog. Photog. 37:38, 1964. 17. Turner, K. 0.: Limitations of panoramic radiography. Oral Surg. 26:312, 1968. 18. Updegrave, W. J.: The role of panoramic radiography in diagnosis. Oral Surg. 22:49, 1966. 19. van Aken, J.: Optimum conditions for intraoral roentgenograms, Oral Surg. 27: 475, 1969. 20. -, and van der Linden, L. W. J.: The integral absorbed dose in conventional
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and panoramic-complete mouth examinations. Oral Surg. 22:603, 1966. 21. Weissman, D. D., and Feinstein, R. B.: X-ray beam profiles and oral radiography. Oral Surg. 31:546, 1971. 22. -, and Sobkowski, F. J.: Comparative thermoluminescent dosimetry in intraoral periapical radiography. Oral Surg. 29:376, 1970. and Manson23. Wuehrmann, A. H., Hing, L. R.: Dental Radiology (ed. 2). St. Louis, Mosby, 1969.