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Simplified and standarized bisecting-angle technic for dental radiography
ORIGINAL ARTICLES
Simplified and standarized bisecting-angle technic for däntal radiography
W. J. Updegrave, DDS, Philadelphia Film holders have been devised to standardize the bisecting-angle technic, thus eliminating the ne cessity for specific head position and predeter mined tube angulation. This simplified technic produces accurate duplication of radiographs and reduces technical errors.
In the March, 1904, issue of Dental Items of In terest, Dr. Weston A. Price presented a technic for radiography of the teeth which produced images of correct longitudinal dimension. He ap plied the rule of isometry formulated several years later by Cieszynski, the principle being to direct the central ray through the apex of the tooth perpendicular to a plane bisecting the angle formed by the mean plane of the tooth and the mean plane of the film. The theoretical principle of this technic for pro ducing a tooth image of correct longitudinal di mension was universally accepted, but the prac tical application was not readily accomplished. Considerable responsibility for its success de pended on the judgment of the operator. To solve this problem, average vertical angles of inclination of the central ray for the various regions of the oral cavity were established by Harold Raper, Clarence Simpson, and Joseph
Pollia. They made studies of cross sections of the teeth and jaws and determined the optimal angle for each area of the mouth which would fulfill the bisecting-angle principle. Calibrated angle scales then became standard equipment on the dental radiographic: units which enabled the operator to readily set the tube at the selected angle for the area examined. However, a range rather than a specific angle was usually recommended for each area. This range, along with the differences in recommended angles which appeared in texts and manuals (a difference of 25 degrees for the same area was noted between two authors), made the selection of the correct angula tion a matter of judgment based on the experience of the operator. Efforts to reduce these variables resulted in the development of film holders and beam-directing instruments, some of which are as follows: 1920—dental film holder, W. O. Houser, Lin coln, 111. 1921— dental film holder, H. G. Ralph, Edenton, N.C. 1922—combination film holder and gravity angle indicator, Harris and Leach, Emporia, Kan. 1927—X-ray apparatus, R. J. Levy, New York 1932—dental X-ray focusing instrument, Hen ry Harrison, New York 1933— device for positioning X-ray film, S. G. Bolin, Chicago 1936—ortholator, film holder, and pointer, New York Institute of Clinical and Oral Pathology 1361
1940—X-ray angulator instrument, J. M. Gold berg, New York 1952—dental X-ray film holder, J. M. Gold berg, New York 1959— instruments for right-angle radiography, W. J. Updegrave, Philadelphia 1962— instruments for film positioning, limit ing, and directing the X-ray beam, F. Medwedeff, W. Knox, and P. Latimer, Nashville, Tenn. Some of the instruments in the previous list are used for directing the beam perpendicularly to the film, and others are used for directing the beam perpendicularly to the bisecting plane. Various types of bite blocks were also developed concur rently with these. A well-organized dental practice demands that as many duties as possible be delegated to auxiliary personnel. Instruments are available to simplify and standardize intraoral ‘technics and to enable the dental auxiliary to produce high-quality and anatomically accurate radiographs. The practicality and value of any radiographic technic is based on its simplicity of accomplish ment and standardization of results. The bisectingangle (short cone) technic for dental radiography generally fails to meet these criteria because of application variables. Film placement and reten tion, vertical and horizontal angulating of the Xray beam, and aligning of the beam with the film are the major variables that control the geometric projection of the image. These must be reduced to a minimum to simplify and standardize the tech nic. Milliampere seconds, kilovoltage, and the processing procedure are also variables, but these are readily controllable and will not be considered in this paper. (
Film placement and retention (standard procedure)
coronally. Furthermore, the digital method of re tention may result in a curved film plane that will produce a characteristically distorted image. Film impingement on the tissues or unstable retention may result in gagging or movement during the ex posure. Any of these variables will influence the interpretive value of the radiograph.
Vertical angulation of X-ray beam (standard procedure)
Correct vertical angulation requires that the Xray beam be directed perpendicular to an imag inary plane that bisects the angle formed by the long axes of the teeth and the plane of the film. Accurately determining this imaginary plane and directing the beam perpendicularly to it require precision and judgment gained from experience. To help achieve this relationship, numerical angulations of the X-ray tube for the different areas of the mouth have been suggested in various texts and manuals.1-5 However, even these dis close variable ranges as can be seen when the sug gested angulations are reviewed (Table 1): One author6 gives no specific angulations, saying that, “Since the shape of the dental arches and position ing of the teeth in these arches vary greatly, the use of predetermined angles is contraindicated if superior results are to be obtained.” Furthermore, these angulations depend on specific positioning of the patient’s head. The sagittal plane must be perpendicular to the floor, and the tragus-ala line (for maxillary teeth) and tragus-commissure line (for mandibular teeth) must be parallel to the floor. Careless positioning of the head, an unnoticed change of the head po sition, and incorrect vertical angulation of the Xray beam are variables that can produce elongated or foreshortened images on the radiograph.
Incorrect film placement may result in incomplete coverage of the area mesially, distally, apically, or Table 1 ■ Recommended angulations of the X-ray tube for different areas of the mouth. Recommended a n g u la tio n s ’ (degrees)
Teeth M a x illa ry M a x illa ry M a x illa ry M a x illa ry
m olars prem olars canines incisors
M a n d ib u la r M a n d ib u la r M a n d ib u la r M a n d ib u la r
m olars prem olars canines incisors
+ 20 + 30 +40 + 40
to to to to
+ 35 + 40 + 50 +^5
0 -1 0 -1 5 -1 5
ta to to to
-2 -2 -3 -3
0 0 0 0
-
f,; tv i '
------------------------------- :-------------------------------‘----------------------------------------« i f
1362 ■ JADA, Vol. 75, Dec. 1967
,
IV />
Range (degrees) 15 10 10 25 20 10 15 15
Horizontal angulation of X-ray beam (standard procedure)
For correct horizontal angulation, the beam should be directed perpendicular to the mean tangent of the teeth being radiographed.1 One procedure recommends that the sagittal plane of the head be the base line toward which the beam is angulated at varying degrees on the horizontal plane. An other procedure recommends that the beam be directed parallel to the proximal surfaces of the
teeth (assuming that the film has been positioned perpendicular to these interproximal spaces).2 Variations of angles in the horizontal plane can produce an overlapping of the contact areas, a closing of the embrasure spaces, and a distortion of the anatomic structures on the radiograph.
Tube-film alignment (standard procedure)
To direct the X-ray beam through the apexes of the teeth being examined, the tip of the cone of the X-ray unit should be directed along the traguaala line for maxillary teeth and 0.25 inch above the lower border of the jaw for mandibular teeth.1-6 The points of entry of the beam for the various teeth are located where lines dropped from the external canthus of the eye, the pupil, the ala of the nose, and the tip of the nose inter sect the horizontal lines. Since the diameter of the X-ray beam is regulated to 2.75 inches at the cone tip, the variables in tube alignment can re sult in incomplete coverage of the film by the Xray beam (cone cutting). Considering the aforementioned facts, it must be concluded that the bisecting-angle technic re quires good judgment and much effort and expe rience for successful accomplishment. Because of the many variables, teaching the technic to auxil iary personnel is also difficult, and standardiza tion of the procedure is impossible. Thus, com parison of radiographs taken to check the progress of a condition or results of therapy are of ques tionable validity.
Fig. 1 ■ Instrument for determining relationship of long axes of teeth to fixed angulation of film .
To reduce these variables to a minimum and thereby simplify and standardize the bisectingangle technic, film-positioning and beam-directing instruments have been devised to indicate auto matically the correct horizontal and vertical angu lation in reference to the teeth and film, thus eliminating the necessity for numerically setting the angulation and for placing the patient’s head in a predetermined position. Accurate duplication of radiographs is then possible. The instruments also eliminate the curved film plane and conecutting and simplify the technic.
Rationale for standardization of bisecting-angle technic
To ascertain the average mean angular relation ship between a fixed film plane and the long axis
B IS E C T O R
RED B LU E GREEN
Updegrave: BISECTING-ANGLE TECHNIC FOR RADIOGRAPHY ■ 1363
[Parallel in g I
■ B isec ting I An g le
B Al -5 0
I
B A +
5°
1L i
i I I k à à H
U
Fig. 3 ■ Paralleling (right-angle) radiographs compared with bisecting-angle radiographs. Third and fourth rows are images of teeth taken at 5 degrees plus and minus, respec tively, of perfect bisecting-angle relationship. Note dimen sional distortion of maxillary molars that is unavoidable in bisecting-angle radiography.
of the teeth when the bisecting-angle principle is used, an instrument was devised (Fig. 1) which consisted of the following parts: a clear plastic protractor that slides on the rod and that has in scribed lines to indicate the plane of the film, the plane of the teeth, and the bisecting plane. Ad ditional lines were inscribed 5 degrees to the right and left, respectively, of the line representing the ideal bisecting-angle position (Fig. 2); a rightangle metal rod for insertion into receptacles of the block, and a plastic bite block with the backing plate angulated at 105 degrees to the occluding surface. Tests showed this angulation to be opti1364 ■ JADA, Vol. 75, Dec. 1967
mal for production of images of accurate linear dimension (Fig. 3).
Procedure
With the testing instrument assembled, the film was then positioned in the mouth adjacent to the lingual surface of the teeth being examined, and the patient was directed to close the teeth on the block to retain the instrument in place. The pro tractor was then moved on the rod until the long axis of the tooth to be radiographed was aligned with one of the three lines on the right or left side of the bisector line, and its position was recorded (Fig. 4). The middle line, blue in color, is angulated 15 degrees to the vertical bisector line in the center of the protractor, which is perpendicular to the occluding surface of the block. If the long axis of the tooth being examined aligned with the blue line, a perfect bisecting-angle relationship was indicated since the film on the opposite side of the center line was at a fixed 15-degree relation ship to the vertical center line that is the bisector (Fig. 2). If the long axis aligned within the area between the red and green lines on each side of the blue line, the range was ideal, as seen when radiographs of the teeth taken at all three posi tions are compared (Fig. 3). One hundred patients were examined by four investigators with the previously described pro cedure. Eight representative areas (maxillary and mandibular incisor, canine, premolar, and molar) of each patient were selected, making a total of 800 areas examined of which 90 percent were within a perfect or ideal tolerance range of angu lation (Table 2). The remaining 10 percent not within the tolerance area were usually only slight-
Table 2 ■ Results of survey of angular relationships be tween fixed film position and long axes of teeth. No. o f areas No. o f areas w ith p e rfe c t w ith in 5 b ise ctin g -an g le degrees o f re la tio n ship tolerance range
Teeth M a x illa ry M a x illa ry M a x illa ry M a x illa ry
m olars prem olars canines incisors
M a n d ib u la r M a n d ib u la r M a n d ib u la r M a n d ib u la r To ta l
m olars prem olars canines incisors
No. o f areas beyond range
16 22 14 23
76 72 57 66
8 6 29 10
32 47 18 34
68 52 65 58
0 1 17 9
206
514
*80
Fig. 4 ■ Recording relationship of mandibular incisors, left, and maxillary premolars, right, to fixed plane of film . Both areas record on outside green line.
ly beyond it, and the balance represented abnor mally positioned teeth. Based on this investigation, a set of instruments for periapical radiography was designed which uses the bisecting-angle principle but eliminates most of the variables that control the geometry of the radiographic image. These bisecting-angle instruments consist of anterior and posterior plastic bite blocks, anterior and posterior stainless steel indicator rods that are inserted into the bite blocks, and anterior and posterior plastic localizing rings that slide on the indicator rods (Fig. 5).
Hold the offset portion of indicator rod away from the biting surface of the block, and insert the pins into the receptacles of the block. Slide the plastic localizing ring onto the rod and insert the film in the mouth, approximating it to the teeth being examined and as close to the lingual surface as anatomy permits (Fig. 6, 7). Instruct the patient to close his mouth on the block to retain the film and instrument in posi tion. Then slide the localizing ring on the rod to approximate the skin surface and to align the tube with the rod and ring on the vertical and horizon tal planes and make the exposure. A short (8-inch focal-film distance) open-end tube is recommended for this technic.
Anterior technic
Open the slot of the anterior (narrow) block by exerting pressure on backing support, insert the film vertically with the shielded (printed) side against backing support, then release. A narrow anterior film is recommended.
Posterior technic
Insert the film horizontally in the posterior block, then hold the right-angle portion of posterior indi cator rod anterior to the block and away from the
/ I V
Fig. 5 ■ Instruments to simplify and standardize bisecting-angle technic. Anterior instrument, left, and posterior instrument, right.
Updegrave: BISECTING-ANGLE TECHNIC FOR RADIOGRAPHY ■ 1365
Fig. 6 ■ Maxillary anterior technic. Film-tooth-beam align ment, left, and short open-end"tube aligned with instrument on vertical and horizontal planes, right. Small cotton roll can be placed between undersurface of block and opposing teeth to ensure stability.
rationship, left, and short open-end tube aligned with in strument on vertical and horizontal planes, right. Small cotton roll can be placed between upper surface of block and opposing teeth to ensure stability.
Fig. 8 ■ Maxillary posterior technic. Film-tooth-beam align ment, left, and short open-end tube aligned with instrument on vertical and horizontal planes, right. Small cotton roll can be placed between undersurface of block and opposing teeth to ensure stability.
1366 ■ JADA, Vol. 75, Dec. 1967
lationship, left, and short open-end tube aligned with in strument on vertical and horizontal planes, right. Small cotton roll can be placed between undersurface of block and opposing teeth to ensure stability.
film, and insert the pins into the receptacles of the block. Slide the plastic localizing ring onto the rod, and then locate the film behind the teeth being ex amined and position it against the lingual surface (Fig. 8, 9). Instruct the patient to close his mouth on the block to retain the film and instrument in position. Slide the localizing ring on the rod to approxi mate the skin surface and to align the tube with rod and ring on vertical and horizontal planes, and make the exposure. Sample radiographs are shown in Figure 10.
Summary
Because of the variables in the bisecting-angle technic as it is generally practiced, standardization of procedure and uniformity of results are seldom accomplished. To minimize these variables, film holders have been devised to indicate the correct beam-object-film alignment, thus eliminating the necessity for specific head position and prede termined tube angulation. The rationale establishing the validity of these instruments is given and basic technics for anterior and posterior regions are described.
Conclusion Fig. 10 ■ Anterior, top, and posterior, bottom, radiographs produced with this technic.
The bisecting-angle technic for periapical radiog raphy has been standardized and simplified and
Updegrave: BISECTING-ANGLE TECHNIC FOR RADIOGRAPHY ■ 1367
can be easily taught and readily mastered. It pro duces anatomically correct images, makes possible the accurate duplication of radiographs, and re duces technical errors to a minimum. Presented at th e Th o m a s P. H in m an M idw inter Clinic, Atlanta, Ga., M arch, 1967. D o ctor Updegrave is professor of dental radiology, Te m p le U n ive rsity School of Dentistry, Philadelphia 19140. 1. Ennis, L. R., and Berry, H. M. Dental roentgenology, ed. 5. Philadelphia, Lea & Febiger, 1959.
2. W ald, S. S., and M cCall, J. 0 . Clinical dental roent genology: te chn ic and interpretation, ed. 4. Philadelphia, W. B. Saunders Co., 1957. 3. W ainw right, W. W. Dental radiology. New York, M cG raw H ill Book Co., 1965. 4. Blackm an, Sydney, and Poyton, H . G. A m anual of dental and oral radiography. Bristol, England, Jo h n W righ t & Sons, Ltd., 1963. 5. O 'B rie n , R. C . Dental radiography: an introduction for dental hygienists and assistants. Philadelphia, W. B. S aunders Co., 1966. 6. W uehrm ann, A. H., and M anson-H ing, L. R. Dental radiology. St. Louis, C. V. M osby Co., 1965.
Canine Rhyme T h e beagle is a canine pet, beloved o f y o u n g a n d old W ith lo w -s lu n g chassis, m ou rn fu l eyes a n d ta il held h ig h a n d bold. A nursem aid for the little ones, for w ho m he greatly cares H is sole a n tip a th y reserved, for leverets a n d hares. A n d now, dear god, it looks as if A function less congenial for this T h e y 'v e discovered th a t he suffers W h ic h laym en still call pyorrhoea,
the backroom boys h ave found versatile hound-— from the sam e disease as us i.e. a flow of pus.
A t the dental schools in U tah a n d C h ica g o , Illinois, T h e y 'v e set up beagle colonies a n d started to em ploy Devoted team s of w orkers to exam ine all the issues W h ic h affect the h ealth y function of th e ir paradontal tissues. For diet th ey served th em pellets of a form ula ted feed A n d frequent drinks of w ater to suffice th eir d a ily need— N o fibrous ch unks of uncooked m eat to exercise th eir jaws O r ju ic y bones to g n a w a t, held between th e ir gen tle paws. A n d so, surprise? the w retched beasts form ed m ounds of calculus T h a t led to pyorrhoea, or as we said a flow of pus. But do we really need to sacrifice our doggy chum s, W h e n all th ey do is tell us w h a t we k n o w ab o u t o u r gum s?
H. Colin Davis 43 Portman Square London, W. 1, England.
1368 ■ JADA, Vol. 75, Dec. 1967
Simplified and standarized bisecting-angle technic for däntal radiography
W. J. Updegrave, DDS, Philadelphia Film holders have been devised to standardize the bisecting-angle technic, thus eliminating the ne cessity for specific head position and predeter mined tube angulation. This simplified technic produces accurate duplication of radiographs and reduces technical errors.
In the March, 1904, issue of Dental Items of In terest, Dr. Weston A. Price presented a technic for radiography of the teeth which produced images of correct longitudinal dimension. He ap plied the rule of isometry formulated several years later by Cieszynski, the principle being to direct the central ray through the apex of the tooth perpendicular to a plane bisecting the angle formed by the mean plane of the tooth and the mean plane of the film. The theoretical principle of this technic for pro ducing a tooth image of correct longitudinal di mension was universally accepted, but the prac tical application was not readily accomplished. Considerable responsibility for its success de pended on the judgment of the operator. To solve this problem, average vertical angles of inclination of the central ray for the various regions of the oral cavity were established by Harold Raper, Clarence Simpson, and Joseph
Pollia. They made studies of cross sections of the teeth and jaws and determined the optimal angle for each area of the mouth which would fulfill the bisecting-angle principle. Calibrated angle scales then became standard equipment on the dental radiographic: units which enabled the operator to readily set the tube at the selected angle for the area examined. However, a range rather than a specific angle was usually recommended for each area. This range, along with the differences in recommended angles which appeared in texts and manuals (a difference of 25 degrees for the same area was noted between two authors), made the selection of the correct angula tion a matter of judgment based on the experience of the operator. Efforts to reduce these variables resulted in the development of film holders and beam-directing instruments, some of which are as follows: 1920—dental film holder, W. O. Houser, Lin coln, 111. 1921— dental film holder, H. G. Ralph, Edenton, N.C. 1922—combination film holder and gravity angle indicator, Harris and Leach, Emporia, Kan. 1927—X-ray apparatus, R. J. Levy, New York 1932—dental X-ray focusing instrument, Hen ry Harrison, New York 1933— device for positioning X-ray film, S. G. Bolin, Chicago 1936—ortholator, film holder, and pointer, New York Institute of Clinical and Oral Pathology 1361
1940—X-ray angulator instrument, J. M. Gold berg, New York 1952—dental X-ray film holder, J. M. Gold berg, New York 1959— instruments for right-angle radiography, W. J. Updegrave, Philadelphia 1962— instruments for film positioning, limit ing, and directing the X-ray beam, F. Medwedeff, W. Knox, and P. Latimer, Nashville, Tenn. Some of the instruments in the previous list are used for directing the beam perpendicularly to the film, and others are used for directing the beam perpendicularly to the bisecting plane. Various types of bite blocks were also developed concur rently with these. A well-organized dental practice demands that as many duties as possible be delegated to auxiliary personnel. Instruments are available to simplify and standardize intraoral ‘technics and to enable the dental auxiliary to produce high-quality and anatomically accurate radiographs. The practicality and value of any radiographic technic is based on its simplicity of accomplish ment and standardization of results. The bisectingangle (short cone) technic for dental radiography generally fails to meet these criteria because of application variables. Film placement and reten tion, vertical and horizontal angulating of the Xray beam, and aligning of the beam with the film are the major variables that control the geometric projection of the image. These must be reduced to a minimum to simplify and standardize the tech nic. Milliampere seconds, kilovoltage, and the processing procedure are also variables, but these are readily controllable and will not be considered in this paper. (
Film placement and retention (standard procedure)
coronally. Furthermore, the digital method of re tention may result in a curved film plane that will produce a characteristically distorted image. Film impingement on the tissues or unstable retention may result in gagging or movement during the ex posure. Any of these variables will influence the interpretive value of the radiograph.
Vertical angulation of X-ray beam (standard procedure)
Correct vertical angulation requires that the Xray beam be directed perpendicular to an imag inary plane that bisects the angle formed by the long axes of the teeth and the plane of the film. Accurately determining this imaginary plane and directing the beam perpendicularly to it require precision and judgment gained from experience. To help achieve this relationship, numerical angulations of the X-ray tube for the different areas of the mouth have been suggested in various texts and manuals.1-5 However, even these dis close variable ranges as can be seen when the sug gested angulations are reviewed (Table 1): One author6 gives no specific angulations, saying that, “Since the shape of the dental arches and position ing of the teeth in these arches vary greatly, the use of predetermined angles is contraindicated if superior results are to be obtained.” Furthermore, these angulations depend on specific positioning of the patient’s head. The sagittal plane must be perpendicular to the floor, and the tragus-ala line (for maxillary teeth) and tragus-commissure line (for mandibular teeth) must be parallel to the floor. Careless positioning of the head, an unnoticed change of the head po sition, and incorrect vertical angulation of the Xray beam are variables that can produce elongated or foreshortened images on the radiograph.
Incorrect film placement may result in incomplete coverage of the area mesially, distally, apically, or Table 1 ■ Recommended angulations of the X-ray tube for different areas of the mouth. Recommended a n g u la tio n s ’ (degrees)
Teeth M a x illa ry M a x illa ry M a x illa ry M a x illa ry
m olars prem olars canines incisors
M a n d ib u la r M a n d ib u la r M a n d ib u la r M a n d ib u la r
m olars prem olars canines incisors
+ 20 + 30 +40 + 40
to to to to
+ 35 + 40 + 50 +^5
0 -1 0 -1 5 -1 5
ta to to to
-2 -2 -3 -3
0 0 0 0
-
f,; tv i '
------------------------------- :-------------------------------‘----------------------------------------« i f
1362 ■ JADA, Vol. 75, Dec. 1967
,
IV />
Range (degrees) 15 10 10 25 20 10 15 15
Horizontal angulation of X-ray beam (standard procedure)
For correct horizontal angulation, the beam should be directed perpendicular to the mean tangent of the teeth being radiographed.1 One procedure recommends that the sagittal plane of the head be the base line toward which the beam is angulated at varying degrees on the horizontal plane. An other procedure recommends that the beam be directed parallel to the proximal surfaces of the
teeth (assuming that the film has been positioned perpendicular to these interproximal spaces).2 Variations of angles in the horizontal plane can produce an overlapping of the contact areas, a closing of the embrasure spaces, and a distortion of the anatomic structures on the radiograph.
Tube-film alignment (standard procedure)
To direct the X-ray beam through the apexes of the teeth being examined, the tip of the cone of the X-ray unit should be directed along the traguaala line for maxillary teeth and 0.25 inch above the lower border of the jaw for mandibular teeth.1-6 The points of entry of the beam for the various teeth are located where lines dropped from the external canthus of the eye, the pupil, the ala of the nose, and the tip of the nose inter sect the horizontal lines. Since the diameter of the X-ray beam is regulated to 2.75 inches at the cone tip, the variables in tube alignment can re sult in incomplete coverage of the film by the Xray beam (cone cutting). Considering the aforementioned facts, it must be concluded that the bisecting-angle technic re quires good judgment and much effort and expe rience for successful accomplishment. Because of the many variables, teaching the technic to auxil iary personnel is also difficult, and standardiza tion of the procedure is impossible. Thus, com parison of radiographs taken to check the progress of a condition or results of therapy are of ques tionable validity.
Fig. 1 ■ Instrument for determining relationship of long axes of teeth to fixed angulation of film .
To reduce these variables to a minimum and thereby simplify and standardize the bisectingangle technic, film-positioning and beam-directing instruments have been devised to indicate auto matically the correct horizontal and vertical angu lation in reference to the teeth and film, thus eliminating the necessity for numerically setting the angulation and for placing the patient’s head in a predetermined position. Accurate duplication of radiographs is then possible. The instruments also eliminate the curved film plane and conecutting and simplify the technic.
Rationale for standardization of bisecting-angle technic
To ascertain the average mean angular relation ship between a fixed film plane and the long axis
B IS E C T O R
RED B LU E GREEN
Updegrave: BISECTING-ANGLE TECHNIC FOR RADIOGRAPHY ■ 1363
[Parallel in g I
■ B isec ting I An g le
B Al -5 0
I
B A +
5°
1L i
i I I k à à H
U
Fig. 3 ■ Paralleling (right-angle) radiographs compared with bisecting-angle radiographs. Third and fourth rows are images of teeth taken at 5 degrees plus and minus, respec tively, of perfect bisecting-angle relationship. Note dimen sional distortion of maxillary molars that is unavoidable in bisecting-angle radiography.
of the teeth when the bisecting-angle principle is used, an instrument was devised (Fig. 1) which consisted of the following parts: a clear plastic protractor that slides on the rod and that has in scribed lines to indicate the plane of the film, the plane of the teeth, and the bisecting plane. Ad ditional lines were inscribed 5 degrees to the right and left, respectively, of the line representing the ideal bisecting-angle position (Fig. 2); a rightangle metal rod for insertion into receptacles of the block, and a plastic bite block with the backing plate angulated at 105 degrees to the occluding surface. Tests showed this angulation to be opti1364 ■ JADA, Vol. 75, Dec. 1967
mal for production of images of accurate linear dimension (Fig. 3).
Procedure
With the testing instrument assembled, the film was then positioned in the mouth adjacent to the lingual surface of the teeth being examined, and the patient was directed to close the teeth on the block to retain the instrument in place. The pro tractor was then moved on the rod until the long axis of the tooth to be radiographed was aligned with one of the three lines on the right or left side of the bisector line, and its position was recorded (Fig. 4). The middle line, blue in color, is angulated 15 degrees to the vertical bisector line in the center of the protractor, which is perpendicular to the occluding surface of the block. If the long axis of the tooth being examined aligned with the blue line, a perfect bisecting-angle relationship was indicated since the film on the opposite side of the center line was at a fixed 15-degree relation ship to the vertical center line that is the bisector (Fig. 2). If the long axis aligned within the area between the red and green lines on each side of the blue line, the range was ideal, as seen when radiographs of the teeth taken at all three posi tions are compared (Fig. 3). One hundred patients were examined by four investigators with the previously described pro cedure. Eight representative areas (maxillary and mandibular incisor, canine, premolar, and molar) of each patient were selected, making a total of 800 areas examined of which 90 percent were within a perfect or ideal tolerance range of angu lation (Table 2). The remaining 10 percent not within the tolerance area were usually only slight-
Table 2 ■ Results of survey of angular relationships be tween fixed film position and long axes of teeth. No. o f areas No. o f areas w ith p e rfe c t w ith in 5 b ise ctin g -an g le degrees o f re la tio n ship tolerance range
Teeth M a x illa ry M a x illa ry M a x illa ry M a x illa ry
m olars prem olars canines incisors
M a n d ib u la r M a n d ib u la r M a n d ib u la r M a n d ib u la r To ta l
m olars prem olars canines incisors
No. o f areas beyond range
16 22 14 23
76 72 57 66
8 6 29 10
32 47 18 34
68 52 65 58
0 1 17 9
206
514
*80
Fig. 4 ■ Recording relationship of mandibular incisors, left, and maxillary premolars, right, to fixed plane of film . Both areas record on outside green line.
ly beyond it, and the balance represented abnor mally positioned teeth. Based on this investigation, a set of instruments for periapical radiography was designed which uses the bisecting-angle principle but eliminates most of the variables that control the geometry of the radiographic image. These bisecting-angle instruments consist of anterior and posterior plastic bite blocks, anterior and posterior stainless steel indicator rods that are inserted into the bite blocks, and anterior and posterior plastic localizing rings that slide on the indicator rods (Fig. 5).
Hold the offset portion of indicator rod away from the biting surface of the block, and insert the pins into the receptacles of the block. Slide the plastic localizing ring onto the rod and insert the film in the mouth, approximating it to the teeth being examined and as close to the lingual surface as anatomy permits (Fig. 6, 7). Instruct the patient to close his mouth on the block to retain the film and instrument in posi tion. Then slide the localizing ring on the rod to approximate the skin surface and to align the tube with the rod and ring on the vertical and horizon tal planes and make the exposure. A short (8-inch focal-film distance) open-end tube is recommended for this technic.
Anterior technic
Open the slot of the anterior (narrow) block by exerting pressure on backing support, insert the film vertically with the shielded (printed) side against backing support, then release. A narrow anterior film is recommended.
Posterior technic
Insert the film horizontally in the posterior block, then hold the right-angle portion of posterior indi cator rod anterior to the block and away from the
/ I V
Fig. 5 ■ Instruments to simplify and standardize bisecting-angle technic. Anterior instrument, left, and posterior instrument, right.
Updegrave: BISECTING-ANGLE TECHNIC FOR RADIOGRAPHY ■ 1365
Fig. 6 ■ Maxillary anterior technic. Film-tooth-beam align ment, left, and short open-end"tube aligned with instrument on vertical and horizontal planes, right. Small cotton roll can be placed between undersurface of block and opposing teeth to ensure stability.
rationship, left, and short open-end tube aligned with in strument on vertical and horizontal planes, right. Small cotton roll can be placed between upper surface of block and opposing teeth to ensure stability.
Fig. 8 ■ Maxillary posterior technic. Film-tooth-beam align ment, left, and short open-end tube aligned with instrument on vertical and horizontal planes, right. Small cotton roll can be placed between undersurface of block and opposing teeth to ensure stability.
1366 ■ JADA, Vol. 75, Dec. 1967
lationship, left, and short open-end tube aligned with in strument on vertical and horizontal planes, right. Small cotton roll can be placed between undersurface of block and opposing teeth to ensure stability.
film, and insert the pins into the receptacles of the block. Slide the plastic localizing ring onto the rod, and then locate the film behind the teeth being ex amined and position it against the lingual surface (Fig. 8, 9). Instruct the patient to close his mouth on the block to retain the film and instrument in position. Slide the localizing ring on the rod to approxi mate the skin surface and to align the tube with rod and ring on vertical and horizontal planes, and make the exposure. Sample radiographs are shown in Figure 10.
Summary
Because of the variables in the bisecting-angle technic as it is generally practiced, standardization of procedure and uniformity of results are seldom accomplished. To minimize these variables, film holders have been devised to indicate the correct beam-object-film alignment, thus eliminating the necessity for specific head position and prede termined tube angulation. The rationale establishing the validity of these instruments is given and basic technics for anterior and posterior regions are described.
Conclusion Fig. 10 ■ Anterior, top, and posterior, bottom, radiographs produced with this technic.
The bisecting-angle technic for periapical radiog raphy has been standardized and simplified and
Updegrave: BISECTING-ANGLE TECHNIC FOR RADIOGRAPHY ■ 1367
can be easily taught and readily mastered. It pro duces anatomically correct images, makes possible the accurate duplication of radiographs, and re duces technical errors to a minimum. Presented at th e Th o m a s P. H in m an M idw inter Clinic, Atlanta, Ga., M arch, 1967. D o ctor Updegrave is professor of dental radiology, Te m p le U n ive rsity School of Dentistry, Philadelphia 19140. 1. Ennis, L. R., and Berry, H. M. Dental roentgenology, ed. 5. Philadelphia, Lea & Febiger, 1959.
2. W ald, S. S., and M cCall, J. 0 . Clinical dental roent genology: te chn ic and interpretation, ed. 4. Philadelphia, W. B. Saunders Co., 1957. 3. W ainw right, W. W. Dental radiology. New York, M cG raw H ill Book Co., 1965. 4. Blackm an, Sydney, and Poyton, H . G. A m anual of dental and oral radiography. Bristol, England, Jo h n W righ t & Sons, Ltd., 1963. 5. O 'B rie n , R. C . Dental radiography: an introduction for dental hygienists and assistants. Philadelphia, W. B. S aunders Co., 1966. 6. W uehrm ann, A. H., and M anson-H ing, L. R. Dental radiology. St. Louis, C. V. M osby Co., 1965.
Canine Rhyme T h e beagle is a canine pet, beloved o f y o u n g a n d old W ith lo w -s lu n g chassis, m ou rn fu l eyes a n d ta il held h ig h a n d bold. A nursem aid for the little ones, for w ho m he greatly cares H is sole a n tip a th y reserved, for leverets a n d hares. A n d now, dear god, it looks as if A function less congenial for this T h e y 'v e discovered th a t he suffers W h ic h laym en still call pyorrhoea,
the backroom boys h ave found versatile hound-— from the sam e disease as us i.e. a flow of pus.
A t the dental schools in U tah a n d C h ica g o , Illinois, T h e y 'v e set up beagle colonies a n d started to em ploy Devoted team s of w orkers to exam ine all the issues W h ic h affect the h ealth y function of th e ir paradontal tissues. For diet th ey served th em pellets of a form ula ted feed A n d frequent drinks of w ater to suffice th eir d a ily need— N o fibrous ch unks of uncooked m eat to exercise th eir jaws O r ju ic y bones to g n a w a t, held between th e ir gen tle paws. A n d so, surprise? the w retched beasts form ed m ounds of calculus T h a t led to pyorrhoea, or as we said a flow of pus. But do we really need to sacrifice our doggy chum s, W h e n all th ey do is tell us w h a t we k n o w ab o u t o u r gum s?
H. Colin Davis 43 Portman Square London, W. 1, England.
1368 ■ JADA, Vol. 75, Dec. 1967