dental radiology Editor: LINCOLN American
R. MANSON-HING, Academy of Dental
School of Dentistry, University 1919 Seventh Avenue South Birmingham, Alabama 35233
D.M.D., Radiology
M.S.
of Alabama
A quantitative comparison of paralleling long-cone and bisection-of -angle periapical radiography Robert H. Biggerstaf, M.X., Lexington, Ky. COLLEGE
OF DENTISTRY,
D.D.S., Ph.D.,* and John R. Phillips, D.M.D., UNIVERSITY
OF KENTUCKY
Quantitative data permit the variability comparison of crown-root ratios computed from periapieal fdms of a single central incisor taken by five technicians using the bisection-of-angle and the paralleling long-cone techniques. The paralleling long-cone technique produces significantly less distortion and is less variable. It is the method of choice for assessing natural root resorption and resorption due to orthodontic therapy.
D
istortion is an inherent and undesirable component of bisection-of-angle periapical radiography.’ It is a product of differences in target-film distance, variability in film position, and position of the radiation source (Fig. 1). Foreshortened and elongated images are typical byproducts of this technique. Distortion occurs along the entire length of the produced image, even if a 13 object-image ratio is produced. Distortion does not permit the accurate computation of compensating crown-root ratios. By contrast, the long-cone paralleling technique is more readily standardized.” Theoretically, the film is positioned parallel to the tooth at, a consistent target-film distance. Any distortion, therefore, should be equally distributed along the entire tooth image (Fig. 2). The probability of perfect application is improved with this technique, and the accuracy of crown-root ratio computations is enhanced. The purpose of this article is to compare, quantitatively, the degree of distor*Chairman,
Department
of Orthodontics.
673
674
Biggerstat
and Phillips
Oral Surg. May, 1976
Fig. 1. The distortion produced by bisection-of-angle periapical radiography. The x-ray source positioned at S, produces distortion along the entire image in spite of an accurate (A’,B’) over-all image-object dimension. The x-ray source positioned at S, produces an elongated (A’,E’) image; at S, foreshortening (A’J) is produced.
tion produced by the two periapical radiographic techniques. This study is requisite for validating or invalidating retrospective research designs using periapical films (for example, the study of root length changes) as the primary data base. MATERIALS AND METHODS Five different radiographic technicians exposed, with standardized timing, two radiographic film packets of the samecentral incisor. One film packet was exposed by the B-inch focal-film-distance bisection-of-angle technique, the other by the 16-inch focal-film-distance (Rinns XCP) paralleling cone technique. A total of ten film packets were exposed, half the number routinely taken for a fullmouth series. Ultra-high-speed film, a lead apron, and a lead-lined collimated tube were used to minimize radiation levels. The exposed film packets were developed in an automatic film processor. To determine the error of locating measurement end points, one radiograph obtained by the long-cone paralleling technique was rigidly positioned in a cardboard mounting. Three arbitrarily positioned orientation points were placed on the mounting. Matte acetate tracing paper was then placed over the film and cardboard to permit the transfer of the orientation points and points locating the mesial point angle on the incisal edge, the mesial cementoenamel junction, and the most apical point on the mesial root apex. Ten repetitions of the above
Volume Number
Fig. Distortion distance
Two periapical
41 5
8. Minimal distortion produced is consistent produces nearly parallel
M
radiographic
techniques
675
is produced by long-cone paralleling periapical radiography. because object-film distance is constant and the target-object x-rays.
P
D
7
Fig. 9. Seven variations in apical root morphology. root apex is the defined measurement end point in this
The study.
most apical M, Mesial;
point on the distal.
mesial
D,
procedure, 8 hours apart, produced no measurable differences when the ten tracing paper sheets were superposed. The radiographs were measured at random by one person using needle-pointed Helios dial calipers reading to the nearest 0.05 mm. Measurements were made along the mesial tooth surfaces. (It is interesting to note that root apices exhibit a wide range of variation. Fig. 3 shows seven categories.) Crown length (mesioincisal point angle to mesial cementoenamel junction) and root length (mesial cementoenamel junction to mesial root apex) were recorded and root ratios were
676
Biggerstaff
Oral Surg.
aand Phillips
May,
1976
Table I. The computed crown-root ratios for the central incisor x-rayed by five technicians using the bisection-of-angle and paralleling long-cone techniques Technicians I
2
3
4
5
0.720 0.765
0.713 0.687
0.708 0.714
0.711 0.735
0.713 0.745
Technique
Long-cone Bisection-of-angle
Table II. Mean crown-root ratios, variances, and F ratio comparing the paralleling long-cone and bisection-of-angle techniques Technique
1 Mean
crown-root
ratio
(
Variances
(Sj
Bisection-of-angle
0.729
0.000894
St,
Paralleling long-cone
0.713
0.000019
s:,,
F ratio
47.052*
*P > 0.0005. computed. Descriptive statistics were computed, as were appropriate correlation coefficients and F ratios. RESULTS The root-ratio data are presented in Table I, representing both radiographic techniques. As expected, there is a greater range of variability associated with the bisection-of-angle method. This is even more apparent when the variances of the two techniques are compared (Table II). The F ratio, 47.05, suggeststhat the variances are significantly different at the 0.0005 level of probability. The longcone paralleling technique is, therefore, the method of choice, particularly if periapical radiographs are to be used in studies involving crown-root ratios. DISCUSSION Past studies evaluating the degree of root resorption during orthodontic treatment3-5have not adequately considered the methodologic problems of radiograph acquisition and measurement. Specifically, the use of a scoring system0 with 76 to 79.5 per cent interobserver agreement leaves much to be desired. The methods presented in this article are simple and readily quantifiable, so that measurement correlations of 0.99 are readily achieved. Moreover, the superiority of the longcone paralleling technique (that is, over 16 inches) should be apparent. The variation of the periapical radiographs taken by the five technicians using the long-cone paralleling technique was low, with a standard deviation of 0.0044. This suggests that periapical radiographs taken in this manner may be utilized for research purposes becausethe results are consistent. Variations in root apex morphology6 cause problems when attempts are made to locate measurement end points. These can be overcome by careful definition. The methodologic assessmentsand comparisons presented may permit an accurate assessmentof natural root resorption and that associated with orthodontic therapy.
Volume Number
41 5
Two periapical
radiographic
techniques
677
REFERENCES 1. O’Brien, R. C.: Dental Radiology, Philadelphia, 1972, W. B. Saunders Company, pp. 88-93. 2. Beane, L. R.: Personal Communication, Aug. 22, 1975. 3. De Shields, R. W.: A Study of Root Resorption in Treated Class II, Division 1 Malocclusions, Angle Orthod. 39: 619-633, 1954. 4. Phillips, J. R.: Apical Root Resorption Under Orthodontic Therapy, Angle Orthod. 25: l-22, 1955. 5. Pelts, 5. H., Issacson, R. J., Speidel, T. M., and Worms, F. W.: Maxillary Central Incisor Root Length in Orthodontically Treated and Untreated Patients, Angle Orthod. 65: 43-47, 1974. 6. Goldson, L., and Henrickson, C. 0.: Root Resorption During Begg Treatment, Am. J. Orthod. 68: 55-66, 1975. Reprint requests to : Dr. Robert H. Biggerstaff Department of Orthodontics College of Dentistry University of Kentucky Lexington, Ky. 40502
R. MANSON-HING, Academy of Dental
School of Dentistry, University 1919 Seventh Avenue South Birmingham, Alabama 35233
D.M.D., Radiology
M.S.
of Alabama
A quantitative comparison of paralleling long-cone and bisection-of -angle periapical radiography Robert H. Biggerstaf, M.X., Lexington, Ky. COLLEGE
OF DENTISTRY,
D.D.S., Ph.D.,* and John R. Phillips, D.M.D., UNIVERSITY
OF KENTUCKY
Quantitative data permit the variability comparison of crown-root ratios computed from periapieal fdms of a single central incisor taken by five technicians using the bisection-of-angle and the paralleling long-cone techniques. The paralleling long-cone technique produces significantly less distortion and is less variable. It is the method of choice for assessing natural root resorption and resorption due to orthodontic therapy.
D
istortion is an inherent and undesirable component of bisection-of-angle periapical radiography.’ It is a product of differences in target-film distance, variability in film position, and position of the radiation source (Fig. 1). Foreshortened and elongated images are typical byproducts of this technique. Distortion occurs along the entire length of the produced image, even if a 13 object-image ratio is produced. Distortion does not permit the accurate computation of compensating crown-root ratios. By contrast, the long-cone paralleling technique is more readily standardized.” Theoretically, the film is positioned parallel to the tooth at, a consistent target-film distance. Any distortion, therefore, should be equally distributed along the entire tooth image (Fig. 2). The probability of perfect application is improved with this technique, and the accuracy of crown-root ratio computations is enhanced. The purpose of this article is to compare, quantitatively, the degree of distor*Chairman,
Department
of Orthodontics.
673
674
Biggerstat
and Phillips
Oral Surg. May, 1976
Fig. 1. The distortion produced by bisection-of-angle periapical radiography. The x-ray source positioned at S, produces distortion along the entire image in spite of an accurate (A’,B’) over-all image-object dimension. The x-ray source positioned at S, produces an elongated (A’,E’) image; at S, foreshortening (A’J) is produced.
tion produced by the two periapical radiographic techniques. This study is requisite for validating or invalidating retrospective research designs using periapical films (for example, the study of root length changes) as the primary data base. MATERIALS AND METHODS Five different radiographic technicians exposed, with standardized timing, two radiographic film packets of the samecentral incisor. One film packet was exposed by the B-inch focal-film-distance bisection-of-angle technique, the other by the 16-inch focal-film-distance (Rinns XCP) paralleling cone technique. A total of ten film packets were exposed, half the number routinely taken for a fullmouth series. Ultra-high-speed film, a lead apron, and a lead-lined collimated tube were used to minimize radiation levels. The exposed film packets were developed in an automatic film processor. To determine the error of locating measurement end points, one radiograph obtained by the long-cone paralleling technique was rigidly positioned in a cardboard mounting. Three arbitrarily positioned orientation points were placed on the mounting. Matte acetate tracing paper was then placed over the film and cardboard to permit the transfer of the orientation points and points locating the mesial point angle on the incisal edge, the mesial cementoenamel junction, and the most apical point on the mesial root apex. Ten repetitions of the above
Volume Number
Fig. Distortion distance
Two periapical
41 5
8. Minimal distortion produced is consistent produces nearly parallel
M
radiographic
techniques
675
is produced by long-cone paralleling periapical radiography. because object-film distance is constant and the target-object x-rays.
P
D
7
Fig. 9. Seven variations in apical root morphology. root apex is the defined measurement end point in this
The study.
most apical M, Mesial;
point on the distal.
mesial
D,
procedure, 8 hours apart, produced no measurable differences when the ten tracing paper sheets were superposed. The radiographs were measured at random by one person using needle-pointed Helios dial calipers reading to the nearest 0.05 mm. Measurements were made along the mesial tooth surfaces. (It is interesting to note that root apices exhibit a wide range of variation. Fig. 3 shows seven categories.) Crown length (mesioincisal point angle to mesial cementoenamel junction) and root length (mesial cementoenamel junction to mesial root apex) were recorded and root ratios were
676
Biggerstaff
Oral Surg.
aand Phillips
May,
1976
Table I. The computed crown-root ratios for the central incisor x-rayed by five technicians using the bisection-of-angle and paralleling long-cone techniques Technicians I
2
3
4
5
0.720 0.765
0.713 0.687
0.708 0.714
0.711 0.735
0.713 0.745
Technique
Long-cone Bisection-of-angle
Table II. Mean crown-root ratios, variances, and F ratio comparing the paralleling long-cone and bisection-of-angle techniques Technique
1 Mean
crown-root
ratio
(
Variances
(Sj
Bisection-of-angle
0.729
0.000894
St,
Paralleling long-cone
0.713
0.000019
s:,,
F ratio
47.052*
*P > 0.0005. computed. Descriptive statistics were computed, as were appropriate correlation coefficients and F ratios. RESULTS The root-ratio data are presented in Table I, representing both radiographic techniques. As expected, there is a greater range of variability associated with the bisection-of-angle method. This is even more apparent when the variances of the two techniques are compared (Table II). The F ratio, 47.05, suggeststhat the variances are significantly different at the 0.0005 level of probability. The longcone paralleling technique is, therefore, the method of choice, particularly if periapical radiographs are to be used in studies involving crown-root ratios. DISCUSSION Past studies evaluating the degree of root resorption during orthodontic treatment3-5have not adequately considered the methodologic problems of radiograph acquisition and measurement. Specifically, the use of a scoring system0 with 76 to 79.5 per cent interobserver agreement leaves much to be desired. The methods presented in this article are simple and readily quantifiable, so that measurement correlations of 0.99 are readily achieved. Moreover, the superiority of the longcone paralleling technique (that is, over 16 inches) should be apparent. The variation of the periapical radiographs taken by the five technicians using the long-cone paralleling technique was low, with a standard deviation of 0.0044. This suggests that periapical radiographs taken in this manner may be utilized for research purposes becausethe results are consistent. Variations in root apex morphology6 cause problems when attempts are made to locate measurement end points. These can be overcome by careful definition. The methodologic assessmentsand comparisons presented may permit an accurate assessmentof natural root resorption and that associated with orthodontic therapy.
Volume Number
41 5
Two periapical
radiographic
techniques
677
REFERENCES 1. O’Brien, R. C.: Dental Radiology, Philadelphia, 1972, W. B. Saunders Company, pp. 88-93. 2. Beane, L. R.: Personal Communication, Aug. 22, 1975. 3. De Shields, R. W.: A Study of Root Resorption in Treated Class II, Division 1 Malocclusions, Angle Orthod. 39: 619-633, 1954. 4. Phillips, J. R.: Apical Root Resorption Under Orthodontic Therapy, Angle Orthod. 25: l-22, 1955. 5. Pelts, 5. H., Issacson, R. J., Speidel, T. M., and Worms, F. W.: Maxillary Central Incisor Root Length in Orthodontically Treated and Untreated Patients, Angle Orthod. 65: 43-47, 1974. 6. Goldson, L., and Henrickson, C. 0.: Root Resorption During Begg Treatment, Am. J. Orthod. 68: 55-66, 1975. Reprint requests to : Dr. Robert H. Biggerstaff Department of Orthodontics College of Dentistry University of Kentucky Lexington, Ky. 40502
