- Email: [email protected]
A clinical comparison of xeroradiography and conventional film for the interpretation of periapical structures
0099-2399/86/1208-0346/$02.00/0 JOURNALOF ENDODONTICS Copyright 9 1986 by The American Associationof Endodontists
Printed in U.S.A. MOL. 12, NO. 8, AUGUST 1986
A Clinical Comparison of Xeroradiography and Conventional Film for the Interpretation of Periapical Structures Barton M. Gratt, DDS, Stuart C. White, DDS, PhO, Frank M. Lucatorto, DDS, J. Philip Sapp, DDS, MS, and Israel Kaffe, DMD
diseases. The dental literature indicates that the ability of dentists to interpret periapical changes on conventional dental radiographs could be improved (1-6). The availability of new dental imaging modalities may help to improve this situation. Currently in the United States, Japan, and selected areas of Europe there are three alternative methods for conducting intraoral radiography, conventional film technique (using either D-speed or E-speed film) and dental xeroradiography. Xeroradiography uses a conventional dental X-ray generating unit and an X-raysensitive photoreceptor selenium plate. The plate is electrically charged just prior to use and placed within a lightproof cassette covered by a disposable plastic bag. After intraoral placement and exposure, the cassette is reinserted into the xeroradiography unit and a dry permanent image is produced in 25 s. The dental xeroradiography process has been described in detail by Jeromin et al. (7). A preliminary clinical study reported the use of xeroradiography in endodontics and found encouraging results with improvement in imaging of root morphology, periodontal ligament space, and bone details (8). The major imaging advantage reported with xeroradiography is termed "edge enhancement" (9). This effect makes areas of subtle tissue density difference more visible and is especially useful when interpreting fine bony details (10). In 1984 Peterson et al. (11) examined the use of xeroradiography and conventional film radiography for the overall interpretation of the periapical regions of treated, diseased, and normal teeth. They reported a large observer variation in radiographic interpretation with the use of either conventional film radiography or xeroradiography. They found no differences in interobserver variations or intraobserver reproducibility using either radiographic technique. Interpretative differences, however, were found within the results scored by six dentists. They used the "normal" category more often than the "probably normal" category when viewing xeroradiographs as compared with conventional film
Xeroradiography and D-speed and E-speed film radiography were evaluated for the radiographic interpretation of periapical disease. Fifty-six consenting dental patients, either with or without periapical disease, were studied. Each patient received two radiographic examinations, one using xeroradiography and the other using either D-speed or E-speed film. Each tooth in the study population was evaluated independently relative to its history, clinical appearance, and clinical test results. Diseased teeth were endodontically treated. Teeth judged to be normal were followed for 1.5 yr to verify a clinically asymptomatic state. In both cases clinical assessments determined the true presence or absence of disease. Ten dentists scored the radiographic images for the presence of periapical disease and changes of various anatomical structures. Receiveroperating-characteristic (ROC) analysis of the three imaging techniques demonstrated no statistical difference in the diagnostic utility of xeroradiography (0.842 receiver-operating characteristic value) versus conventional radiography (0.843 receiver-operating characteristic value). In terms of radiation dose, xeroradiographic and E-speed film images required about one half the patient radiation exposure of D-speed film radiography. Therefore, xeroradiography or E-speed film techniques are preferred over conventional D-speed film radiography for the interpretation of periapical structures.
Radiographic evaluation of the periapical area has been reported to be unpredictable because of large variations between observers (1-5). Goldman et al. (1) found the agreement between observers viewing the same radiograph to be less than 50% when determining the presence of an area of bone rarefaction. Consistency of the same observer at repeated examinations was found by Brynolf (6) to be only 70% in agreement when a single film was used for the interpretation of periapical 346
Vol. 12, No. 8, August 1986
radiographs. This would suggest that the six observers were more confident in determining a normal periapical image with xeroradiography than with the use of conventional film radiography (11). However, White et al. (12), in a study using cadaver material, reported no diagnostic advantage of xeroradiography over film radiography for detection of periapical disease. Recently there have been several reports in the dental literature on the use of the new lower dose E-speed dental X-ray film (Kodak Ektaspeed) (13-16). E-speed film is reported to require approximately one half the radiation exposure of D-speed film and to produce an image of equal quality if processed in a carefully controlled environment (14, 15, 17). Most studies report that it is diagnostically equivalent to D-speed film (12, 18, 19). However, objective clinical trials need to be completed for a thorough assessment of this alternative to conventional D-speed film imaging. This study utilized receiver-operating characteristic analysis (ROC), a reliable measure of the diagnostic value of competing imaging systems. With this method one measures the performance of dental observers in solving specific diagnostic problems (20). This method of analysis is used in clinical decision making as a measure of diagnostic accuracy that is free of judgmental bias. Accordingly, the purpose of this study was to determine the diagnostic utility of xeroradiography compared with D-speed, or E-speed film radiography when a detailed radiographic interpretation of periapical dental structures was performed. The study was conducted in a clinical setting using ROC analysis. MATERIALS AND METHODS Population Studied
Fifty-six patients came to the UCLA School of Dentistry presenting with (a) "toothache" or (b) normal teeth. The patients gave their informed consent to be included in this study. In the toothache group of patients a history was obtained as to: elicited transient pain, constant pain, dull ache, throbbing or, sharp pain; spontaneous pain when lying down, pain due to occlusion, pain upon air breathing, localization of pain to tooth, history of similar pain, recent maxillary sinus infection, presence of referred pain, and duration of pain (recorded in hours). Each patient's mouth was charted as to observed biological changes, including tooth mobility, heavy occlusal tooth contacts (observe wear facets), crown discoloration, deep restorations (or bases), caries, recurrent caries, crown fracture, root fracture, craze lines, overlying tissue changes of erythema, swelling, cellulitis, draining sinus tract, or discharge from periodontal ligament space. The patients' temperatures were also determined. Finally, the suspected tooth was clinically tested for sensitivity by means of an air blast, cold (ice), heat (hot gutta-percha), electric
Xeroradiography and Conventional Film
347
pulp testing, percussion, and apical compression. Teeth with necrotic pulps or irreversible pulpitis were then treated with endodontic therapy (opening of pulp chamber, enlargement, cleaning and filling). The following information was obtained for all opened pulp chambers: bleeding, dry, purulent exudate, clear fluid, odor, and possibility of fracture through pulp chamber. These detailed clinical assessments were used to determine the classification of "true pulpal disease present" for 28 patients. The second group, consisting of 28 patients, was followed for a period of 1.5 to 2.0 yr. The teeth were determined to be normal by lack of any pain history, sensitivity to clinical tests, or observed biological changes. The pulp chambers of these teeth were not opened nor were any of these teeth extracted. Only teeth without caries and with shallow or no existing restorations were considered within this group. This clinical evaluation with its follow-up examinations was used to establish a group of normal teeth. RADIOGRAPHIC TECHNIQUES
A conventional dental X-ray unit was used to produce the clinical radiographs (GE-1000 dental x-ray system; General Electric Co., Milwaukee, Wl). The unit was operated at 70 kVp, 15 ma, and 2.5 mm of aluminum filtration. Intraoral radiographs were produced using a paralleling technique employing Precision film holders (Masel, Philadelphia, PA) and a 16-inch (40.5 cm) focal spot-to-image detector distance. In order to obtain similarly projected periapical radiographs, film holders were positioned in a standardized way. Film holders were modified to fit the xeroradiographic cassette, which is approximately two and one-half times as thick as a D- or E-speed film packet. Intraoral film examinations were conducted using Kodak UItraspeed D-film and Ektaspeed E-film (Eastman Kodak Co., Rochester, NY). Exposure times for D-speed film ranged from 0.50 to 1.0 s (30 to 60 impulses) and for E-speed film ranged from 0.25 to 0.40 s (15 to 24 impulses) (Table 1). Automatic processing was conducted using an All Pro Model AT film processor (Air Techniques Inc., Hicksville, NY) at a 5min cycle. It employed an automatic replenisher and Xonics Redichemistry (Xonics Inc., Los Angeles, CA) with developing chemistry at 80~ ___1 ~ Daily sensitometric and densitometric tests of film processing was conducted in order to obtain consistent processing conditions (_+15% optical density using a speed index). Xeroradiography was conducted using the Xerox 110 dental system (Xerox Medical Systems, Pasadena, CA). The maximum contrast setting of image processing was used. Exposure times for dental xeroradiography ranged from 0.20 to 0.35 s (12 to 21 impulses, Table 1). The microprocessor within the Xerox 110 unit maintained processing density. Quality control testing indi-
348
Journal of Endodontics
Gratt et al.
TABLE 1. Intraoral radiation exposures (mR)* comparing xeroradiography with E-speed film and D-speed film for endodontic
radiography Xeroradiography Site
Maxillary region Midline (centrals) Lateral incisors Canine Premolar Molar Mandibular region Midline (centrals) Canine Premolar Molar Bite-wing projections Premolar Molar
E-Speed Film
D-Speed Film
TimeX (Impulses)
Skin Surface
Cassette Surface
Time? (Impulses)
Skin Surface
Film Surface
Time? (Impulses)
Skin Surface
Film Surface
18 18 21 21 24
120 120 145 145 180
30 30 35 35 40
18 18 21 21 24
120 125 150 145 180
30 30 35 35 40
36 36 48 48 60
270 270 340 330 420
60 60 75 90 70
18 21 21 24
120 145 140 170
30 35 40 35
18 21 21 24
120 145 140 170
30 40 40 35
36 48 48 60
250 320 310 420
60 80 80 80
21 24
160 180
40 40
21 24
160 180
45 40
48 60
380 460
80 70
9Measurementsare baseduponthe averageof threetrialsand are accurateto +10 mR below 100 mR and _+10%above100 mR. Thermoluminescentdosimeterswereplacedon the skin and imagereceptor.Standarddeviationsand standarderrorshavebeencalculated. i" Timein impulsed(60 = 1 s) is for examinationof an averagesizemaleadultpatientand is basedupon machinesettingsof 70 kVp, 15 mA, at a 17-inchtarget-to-detectordistancewith 2.5 mm Eq of AI filtration.All readingsare _+1impulse.
cated no significant changes (+15% in optical density) in image processing over a 6-month period.
VIEWING CONDITIONS, EXAMINERS, AND DIAGNOSTIC CRITERIA The images of the crowns of all teeth were covered with black tape on all radiographs and xeroradiographs and the films were mounted in opaque film mounts (Figs. 1 and 2). All images were evaluated using a conventional viewbox; however, the xeroradiographs could be viewed in reflected light if the observer desired. A magnifying viewer (X-produkter, Maim6, Sweden) and a magnifying glass were made available to all examiners. The images were randomly ordered and were viewed separately by 10 dentists on different occasions to avoid rememberance biases. Eighteen detailed anatomical structures were evaluated by each of the 10 observers as was an overall radiographic interpretation of the periapical condition present (Table 2). The following scale was used in the assessment of normal: 5 = Definitely not normal; 4 = Probably not normal; 3 = I cannot tell; 2 = Probably normal; and 1 = Definitely normal.
DATA ANALYSIS AND STATISTICAL METHOD On the basis of the judgments made by the observing dentists and knowledge by the investigators of the true condition of the tooth, the true-positive (TP) and falsepositive (FP) values at each level of confidence were calculated for each dentist. The TP value is the fraction of diseased apices that was correctly recognized, while the FP value is the fraction of normal root ends that was judged to be diseased. A ROC curve was con-
FIG 1. A, Xeroradiographic image demonstrating a normal root end with the masking of the crown region of the tooth. B, The same root end as in A imaged with D-speed film as used in study 1.
structed. The first plot point of the ROC curve was determined by calculating the TP and FP values using only the judgments where periapical disease was assessed to be definitely present. The second pair of TP and FP values were determined by also including those judgments of periapical disease as probably present. Successive data points resulted from the successive addition of judgments at each lower level on the confidence scale. ROC curves were computed for each imaging system for each category and for all observers combined. The area under each computed ROC curve, reported here in Tables 2 and 3, were used as they are the best of the single-parameter indices for diagnostic
Vol. 12, No. 8, August 1986
Xeroradiography and Conventional Film
accuracy (20). Student's t test for paired samples was used to distinguish between groups. RESULTS The results of 10 observers' interpretations of periapical structures comparing D-speed film and xeroradiography (study 1) are presented in Table 2. The overall radiographic interpretation for xeroradiography compared with D-speed film was 0.799 versus 0.768 ROC value (not statistically significant, p < 0.05 level). However, statistical significance was found in the evaluation of the "imaging of the periodontal ligament space" and in the evaluation of the "imaging of the lamina dura." For the interpretation of these anatomical regions, xeroradiography appeared to be superior to Dspeed film at the p < 0.05 level. Whereas for the evaluation of "imaging of trabecular bone in apical region," D-speed film was found to be statistically superior to xeroradiography for the interpretation of disease. The results of the same 10 observers comparing E-speed film with xeroradiography (study 2) are presented in Table 2 also. The overall radiographic inter-
pretation of ROC values (Table 2, E) showed no statistical significance (p < 0.05). In fact, for the 18 anatomical structures evaluated no statistical significance was found between the two image detectors. We also found that the mean of all E-speed film and xeroradiography ROC area values for study 2 (0.905) was significantly greater than the mean ROC area
FIG 2. A, Xeroradiographic image demonstrating a "pathological" root end with the masking of the crown region of the tooth. B, The same pathological root end as in A imaged with E-speed film as used in study 2.
TABLE 2. Scoring of detailed root end structures by 10 dentists comparing xeroradiography with D-speed film and E-speed film Area under the ROC Curve Study 1 D-Speed Film A. Imaging of root end (hard tissue) 1. Is there resorption within the root canal? 2. Is there deposition within the root canal? 3. Can the apical foramen at the root end be seen? 4. Is there resorption on apical root surface? 5. Is there hypercementosis on apical root surface? 6. Is the overall imaging of the root end normal? B. Imaging of periodontal ligament (PDL) space 1. Is the shape of PDL space normal at the apex? 2. Is the width of PDL space normal near the apex? 3. Is the radiodensity of PDL space normal near the apex? 4. Is the overall imaging of the periodontal ligament space normal? C. Imaging of lamina dura 1. Is the lamina dura continuous? 2. Is the shape of lamina dura normal? 3. Is the radiopacity of lamina dura normal? 4. Is the overall imaging of lamina dura normal? D. Imaging of trabecular bone in apical region 1. Are there a normal number of trabeculae present? 2. Are the sizes of trabeculae present normal for this region? 3. Is the radiopacity of trabeculation normal for this region? 4. Is the overall imaging of trabecular bone in region normal? E. Overall radiographic interpretation (diagnosis) 1. Normal periapical condition present? * Xeroradiography significantly better than D-speed film, p < 0.05. 1 D-speed film significantly better than xeroradiography, p < 0.05.
349
Study 2
Xeroradiography
E-Speed Film
Xeroradiography
0.361 0.490 0.427 0.2811 0,382 0.667
0.358 0.506 0.437 0.360 0.422 0.678
0.322 0.533 0.453 0.297 0.467 0.782
0.305 0.444 0.426 0.296 0.459 0.731
0.741 0.732
0.804* 0.808*
0.902 0.910
0.901 0.902
0,742
0.785
0.901
0.892
0.733
0.790*
0.901
0.903
0.798 0,775 0,765 0.797
0.821 0.835* 0.801" 0.809
0.918 0.905 0.890 0.891
0.932 0.908 0.913 0.926
0,847t
0.737
0.822
0.839
0.787t
0.722
0.830
0.833
0,7951"
0.744
0.849
0.850
0,8091"
0.743
0.847
0.841
0,768
0.799
0.906
0.897
350
Gratt et al.
Journal of Endodontics
TABLE 3. Area under the ROC curve by technique for each of 10 dental observers Study 1" Dentist
Study 21
D-Speed versus Xeroradi- E-Speed versus XeroradiFilm ography Film ography
1 0.814 0.832 0.957 2 0.908 0.901 0.931 3 0.714 0.768 1.000 4 0.793 0.959 0.926 5 0.689 0.622 0.857 6 0.753 0.755 0.883 7 0.656 0.768 0.811 8 0.819 0.755 0.890 9 0.821 0.875 0.946 10 0.737 0.768 0.857 Mean 0.767 0.796 0.917 Overall film (mean values of studies 1 + 2) = 0.842$ Overall xeroradiography (mean values of studies 1 + 2) = 0.843:1:
0,959 0,962 0.969 0,957 0.806 0,913 0,821 0,878 0,921 0,786 0.893
9 No significant difference between means at p > 0.05 level comparing D-speed with xeroradiography. 1 No significant difference between means at p > 0.05 level comparing E-speed film with xeroradiography. :1:No significant difference at p > 0.05 level comparing all films with xeroradiography from studies 1 and 2.
values obtained in study 1 (0.784). This difference was found to be statistically different at p < 0.001 level. The ROC values of each observer for study 1 and study 2 are presented in Table 3. It should be noted that a large variation was found among observers. In study 1 the range was 0.622 to 0.959. In study 2, the range was 0.786 to 1.000. Figure 3 demonstrates the distribution between observers and the distribution between film and xeroradiography. DISCUSSION
The results of this clinical study indicated that for the overall radiographic interpretation of periapical structures, there was no demonstrated diagnostic difference between xeroradiography and D-speed or E-speed film. The majority of observers, however, when queried in this study subjectively preferred xeroradiographic images over film images and preferred D-speed over Espeed film. However, no differences were found in the accomplishment of the overall diagnostic task of assessing normal periapical structures. This finding is consistent with the results of White et al. using cadaver material (12) and suggests that even lower dose and faster imaging systems may be possible for future use in endodontics in particular and for dental radiography in general. The results of the 10 dentists' assessment of detailed root end structures comparing xeroradiography and Dspeed film (Table 2, study 1) indicated differences in the interpretation of root resorption; shape, width, and overall imaging of the periodontal ligament space; shape and radiopacity of the lamina dura; and number, size, radiopacity, and overall imaging of trabecular bone. Of the 18 detailed structures interpreted by the
m (~
1.00
> o 0.900
98 ~
or-
J "9
"4
E 0.80~
LL
10
UJ
-o 0.70 E
=
a 9"o 0 . 6 0
bserver
number
f r o m T a b l e II
03
0.50 0.50
I
I
l
i
0.60
0.70
0.80
0.90
Averaged Xeroradiography
1.00
ROC Values
FIG 3. Graph demonstrating observer differences (distribution along 45-degree line) comparing D- and E-speed film and xeroradiography. Note that the distance between observers is greater than the distance between each of the imaging techniques from the center line.
10 dentists, xeroradiography was more useful than Dspeed film on 5 of the 18 areas assessed; likewise Dspeed film was more useful on 5 of the 18. General trends suggest that D-speed film is more useful for the interpretation of area densities (such as the overall density of trabecular bone in the periapical region) while xeroradiography is more useful for the interpretation of lines (such as the periodontal ligament space and the lamina dura). This is probably due to the fact that Dspeed film has greater broad area contrast than xeroradiography, which is advantageous for imaging general areas of bone, especially differences in bone density. Although xeroradiography with its edge enhancement properties is best at depicting discontinuities or lines whether radiopaque like lamina dura or radiolucent like periodontal ligament spaces. These findings would suggest that an optimum system of diagnosis might include two images, one film radiograph and one xeroradiograph. The use of multiple images was proposed by Brynolf (21) to aid interpretation (1970) prior to the technological advances of xeroradiography or digital subtraction radiography (22). More research is needed in the area of interpretation of periapical radiographs to enable dentists to be more consistent in this common diagnostic task. We noted that the ROC values for study 2 were significantly higher than those values in study 1. We believe this to be due to differences in the population of teeth studied. The teeth imaged and evaluated in study 1 were much more difficult to interpret than those of study 2. When ROC values approach 1.00, difficulties arise in analysis as the diagnostic task being performed is so easy that potential differences in imaging systems
Vol. 12, No. 8, August 1986
may disappear. As the diagnostic task becomes more difficult the ROC area values decrease. However, as the task becomes very very difficult random guessing takes over and ROC area values of 0.500 or lower may be expected. Generally a ROC value of 0.75 is ideal for differentiating between competing diagnostic systems. Therefore, we believe the difference in ROC values between study 1 and study 2 is due to differences in the interpretative difficulty of the individual cases. A graph of the 10 dentists' ROC scores for film and xeroradiography is shown in Fig. 3. The graph indicates (by the 45-degree line separating film systems from xeroradiography) that there is a greater range between the 10 dentists than between either film system (D- or E-speed) and xeroradiography. It appears that an excellent observer (high ROC score) would perform better with his individual weakest (of the three) imaging systems as compared with the less-best observer (low ROC score) using the best of his individual imaging systems. The knowledge, training, motivation, skill, and experience of the individual dentist appears to be the major variable in these two studies. We believe this to be another important area for future research. CONCLUSIONS In summary, this clinical trial indicated that there is no significant diagnostic difference between xeroradiography and D- or E-speed film for the radiographic interpretation of periapical structures. Radiation exposures used in this clinical study demonstrated that either xeroradiography or E-speed film are low-dose alternatives to conventional D-speed film for intraoral periapical radiography. Wide variations were found among observers of periapical structures but little variation was found among imaging systems. This study was funded in part by Grant DE 06379 from the National Institutes of Dental Research, United States Public Health Service, Bethesda, MD. Dr. Gratt is associate professor, Section of Oral Radiology, UCLA School of Dentistry, Center for the Health Sciences, Los Angeles, CA. Dr. White is professor and chairman, Section of Oral Radiology, UCLA School of Dentistry,
Xeroradiography and Conventional Film
351
Center for the Health Sciences. Dr. Lucatorto is clinical professor, Section of Oral Diagnosis/Oral Medicine/Oral Pathology, UCLA School of Dentistry, Center for the Health Sciences. Dr. Sapp is professor and chairman, Section of Oral Diagnosis/Oral Medicine/Oral Pathology, UCLA School of Dentistry, Center for the Health Sciences. Dr. Kaffe is senior lecturer, Section of Oral Pathology/ Oral Medicine, School of Dental Medicine, TeI-Aviv University, TeI-Aviv, Israel, and is visiting professor, Section of Oral Radiology, UCLA School of Dentistry, Center for the Health Sciences, Los Angeles, CA.
References 1. Goldman M, Pearson AH, Darzenta N. Endodontic success--Who's reading the radiograph? Oral Surg 1972;33:432-7. 2. Goldman M, Pearson AH, Darzenta N. Reliability of radiographic interpretations. Oral Surg 1974;38:287-93. 3. Duinkerke ASH, Van de Poel ACM, DeBoo Th, Doesburg WH. Variations in the interpretation of periapical radiolucencies. Oral Surg 1975;40:414-22. 4. Nielsen J. Reliability in reading endodontic radiographs [Abstract 27]. J Dent Res 1979;58:2296. 5. Gelfand M, Sunderman EJ, Goldman M. Reliability of radiographical interpretations. J Endedon 1983;9:71-5. 6. Brynolf I. A histological and roentgenological study of the periapical region of human upper incisors. Odont Revy 1967;18:1-176. 7. Jeromin LS, Geddes GF, White SC, Gratt BM. Xeroradiography for intraoral dental radiology. A process description. Oral Surg 1980;49:178-83. 8. Gratt BM, Sickles EA, Nguyen NT. Dental xeroradiography for endodontics: a rapid x-ray system that produces high-quality images. J Endodon 1979;5:266-70. 9. Gratt BM, Sickles EA, Gould RG, Jeromin LS, White SC. Xeroradiography of dental structures. IV. Image properties of a dedicated intraoral system. Oral Surg 1980;50:572-9. 10. Kashima I, Gratt BM, White SC. Power spectrum method used for comparing film and xeroradiography. Dentomaxillofacial Redio11985;14:25-30, 11. Petersson AR, Petersson K, Krasny R, Gratt BM. Observer variations in the interpretation of periapical osseous structures. J Endedon 1984;10:2059. 12. White SC, Hollender L, Gratt BM. Comparison of xeroradiographs and film for detection of periapical lesions. J Dent Res 1984;63:910-3. 13. Frykhoim A. Kodak Ektaspeed--A new dental x-ray film. DentomaxilIofac Radio11983;12:47-9. 14. Thunthy K, Weinberg R. Sensitometric comparison of dental films of groups D and E. Oral Surg 1983;54:250-2. 15. Kaffe I, Littner MM, Kuspet ME. Densitometric evaluation of intraoral x-ray films: Ektaspeed versus Ultraspeed. Oral Surg 1984;57:338-42. 16. Horton PS, Sipps FH, Kohout FJ, Nelson JF, Kienzle GC. A comparison of speed group D and E dental x-ray films. Oral Sug 1984;58:104-8. 17. Diehl R, Gratt BM. An assessment of radiographic quality control measurements comparing D-speed film, E-speed film and xeroradiography, Oral Surg (in press). 18. Grondahl H-G. The influence of observer performance in radiographic caries diagnosis. Swed Dent J 1979; 3:101-7. 19. Left GS, Schwartz SF, del Rio CE. Xeroradiographic interpretation of experimentally induced jaw lesions J Endodont 1984;10:188-98. 20. Swets JA. ROC analysis applied to the evaluation of medical imaging techniques. Invest Redio11979;14:109-21. 21. Brynolf I. Roentgenologic periapical diagnosis. I. Reproducibility of interpretation. Swed Dent J 1970;63:339-44. 22. Grondahl H-G, Grondahl K, Webber RL. A digital subtraction technique for dental radiography. Oral Surg 1983;55:96-102.
Printed in U.S.A. MOL. 12, NO. 8, AUGUST 1986
A Clinical Comparison of Xeroradiography and Conventional Film for the Interpretation of Periapical Structures Barton M. Gratt, DDS, Stuart C. White, DDS, PhO, Frank M. Lucatorto, DDS, J. Philip Sapp, DDS, MS, and Israel Kaffe, DMD
diseases. The dental literature indicates that the ability of dentists to interpret periapical changes on conventional dental radiographs could be improved (1-6). The availability of new dental imaging modalities may help to improve this situation. Currently in the United States, Japan, and selected areas of Europe there are three alternative methods for conducting intraoral radiography, conventional film technique (using either D-speed or E-speed film) and dental xeroradiography. Xeroradiography uses a conventional dental X-ray generating unit and an X-raysensitive photoreceptor selenium plate. The plate is electrically charged just prior to use and placed within a lightproof cassette covered by a disposable plastic bag. After intraoral placement and exposure, the cassette is reinserted into the xeroradiography unit and a dry permanent image is produced in 25 s. The dental xeroradiography process has been described in detail by Jeromin et al. (7). A preliminary clinical study reported the use of xeroradiography in endodontics and found encouraging results with improvement in imaging of root morphology, periodontal ligament space, and bone details (8). The major imaging advantage reported with xeroradiography is termed "edge enhancement" (9). This effect makes areas of subtle tissue density difference more visible and is especially useful when interpreting fine bony details (10). In 1984 Peterson et al. (11) examined the use of xeroradiography and conventional film radiography for the overall interpretation of the periapical regions of treated, diseased, and normal teeth. They reported a large observer variation in radiographic interpretation with the use of either conventional film radiography or xeroradiography. They found no differences in interobserver variations or intraobserver reproducibility using either radiographic technique. Interpretative differences, however, were found within the results scored by six dentists. They used the "normal" category more often than the "probably normal" category when viewing xeroradiographs as compared with conventional film
Xeroradiography and D-speed and E-speed film radiography were evaluated for the radiographic interpretation of periapical disease. Fifty-six consenting dental patients, either with or without periapical disease, were studied. Each patient received two radiographic examinations, one using xeroradiography and the other using either D-speed or E-speed film. Each tooth in the study population was evaluated independently relative to its history, clinical appearance, and clinical test results. Diseased teeth were endodontically treated. Teeth judged to be normal were followed for 1.5 yr to verify a clinically asymptomatic state. In both cases clinical assessments determined the true presence or absence of disease. Ten dentists scored the radiographic images for the presence of periapical disease and changes of various anatomical structures. Receiveroperating-characteristic (ROC) analysis of the three imaging techniques demonstrated no statistical difference in the diagnostic utility of xeroradiography (0.842 receiver-operating characteristic value) versus conventional radiography (0.843 receiver-operating characteristic value). In terms of radiation dose, xeroradiographic and E-speed film images required about one half the patient radiation exposure of D-speed film radiography. Therefore, xeroradiography or E-speed film techniques are preferred over conventional D-speed film radiography for the interpretation of periapical structures.
Radiographic evaluation of the periapical area has been reported to be unpredictable because of large variations between observers (1-5). Goldman et al. (1) found the agreement between observers viewing the same radiograph to be less than 50% when determining the presence of an area of bone rarefaction. Consistency of the same observer at repeated examinations was found by Brynolf (6) to be only 70% in agreement when a single film was used for the interpretation of periapical 346
Vol. 12, No. 8, August 1986
radiographs. This would suggest that the six observers were more confident in determining a normal periapical image with xeroradiography than with the use of conventional film radiography (11). However, White et al. (12), in a study using cadaver material, reported no diagnostic advantage of xeroradiography over film radiography for detection of periapical disease. Recently there have been several reports in the dental literature on the use of the new lower dose E-speed dental X-ray film (Kodak Ektaspeed) (13-16). E-speed film is reported to require approximately one half the radiation exposure of D-speed film and to produce an image of equal quality if processed in a carefully controlled environment (14, 15, 17). Most studies report that it is diagnostically equivalent to D-speed film (12, 18, 19). However, objective clinical trials need to be completed for a thorough assessment of this alternative to conventional D-speed film imaging. This study utilized receiver-operating characteristic analysis (ROC), a reliable measure of the diagnostic value of competing imaging systems. With this method one measures the performance of dental observers in solving specific diagnostic problems (20). This method of analysis is used in clinical decision making as a measure of diagnostic accuracy that is free of judgmental bias. Accordingly, the purpose of this study was to determine the diagnostic utility of xeroradiography compared with D-speed, or E-speed film radiography when a detailed radiographic interpretation of periapical dental structures was performed. The study was conducted in a clinical setting using ROC analysis. MATERIALS AND METHODS Population Studied
Fifty-six patients came to the UCLA School of Dentistry presenting with (a) "toothache" or (b) normal teeth. The patients gave their informed consent to be included in this study. In the toothache group of patients a history was obtained as to: elicited transient pain, constant pain, dull ache, throbbing or, sharp pain; spontaneous pain when lying down, pain due to occlusion, pain upon air breathing, localization of pain to tooth, history of similar pain, recent maxillary sinus infection, presence of referred pain, and duration of pain (recorded in hours). Each patient's mouth was charted as to observed biological changes, including tooth mobility, heavy occlusal tooth contacts (observe wear facets), crown discoloration, deep restorations (or bases), caries, recurrent caries, crown fracture, root fracture, craze lines, overlying tissue changes of erythema, swelling, cellulitis, draining sinus tract, or discharge from periodontal ligament space. The patients' temperatures were also determined. Finally, the suspected tooth was clinically tested for sensitivity by means of an air blast, cold (ice), heat (hot gutta-percha), electric
Xeroradiography and Conventional Film
347
pulp testing, percussion, and apical compression. Teeth with necrotic pulps or irreversible pulpitis were then treated with endodontic therapy (opening of pulp chamber, enlargement, cleaning and filling). The following information was obtained for all opened pulp chambers: bleeding, dry, purulent exudate, clear fluid, odor, and possibility of fracture through pulp chamber. These detailed clinical assessments were used to determine the classification of "true pulpal disease present" for 28 patients. The second group, consisting of 28 patients, was followed for a period of 1.5 to 2.0 yr. The teeth were determined to be normal by lack of any pain history, sensitivity to clinical tests, or observed biological changes. The pulp chambers of these teeth were not opened nor were any of these teeth extracted. Only teeth without caries and with shallow or no existing restorations were considered within this group. This clinical evaluation with its follow-up examinations was used to establish a group of normal teeth. RADIOGRAPHIC TECHNIQUES
A conventional dental X-ray unit was used to produce the clinical radiographs (GE-1000 dental x-ray system; General Electric Co., Milwaukee, Wl). The unit was operated at 70 kVp, 15 ma, and 2.5 mm of aluminum filtration. Intraoral radiographs were produced using a paralleling technique employing Precision film holders (Masel, Philadelphia, PA) and a 16-inch (40.5 cm) focal spot-to-image detector distance. In order to obtain similarly projected periapical radiographs, film holders were positioned in a standardized way. Film holders were modified to fit the xeroradiographic cassette, which is approximately two and one-half times as thick as a D- or E-speed film packet. Intraoral film examinations were conducted using Kodak UItraspeed D-film and Ektaspeed E-film (Eastman Kodak Co., Rochester, NY). Exposure times for D-speed film ranged from 0.50 to 1.0 s (30 to 60 impulses) and for E-speed film ranged from 0.25 to 0.40 s (15 to 24 impulses) (Table 1). Automatic processing was conducted using an All Pro Model AT film processor (Air Techniques Inc., Hicksville, NY) at a 5min cycle. It employed an automatic replenisher and Xonics Redichemistry (Xonics Inc., Los Angeles, CA) with developing chemistry at 80~ ___1 ~ Daily sensitometric and densitometric tests of film processing was conducted in order to obtain consistent processing conditions (_+15% optical density using a speed index). Xeroradiography was conducted using the Xerox 110 dental system (Xerox Medical Systems, Pasadena, CA). The maximum contrast setting of image processing was used. Exposure times for dental xeroradiography ranged from 0.20 to 0.35 s (12 to 21 impulses, Table 1). The microprocessor within the Xerox 110 unit maintained processing density. Quality control testing indi-
348
Journal of Endodontics
Gratt et al.
TABLE 1. Intraoral radiation exposures (mR)* comparing xeroradiography with E-speed film and D-speed film for endodontic
radiography Xeroradiography Site
Maxillary region Midline (centrals) Lateral incisors Canine Premolar Molar Mandibular region Midline (centrals) Canine Premolar Molar Bite-wing projections Premolar Molar
E-Speed Film
D-Speed Film
TimeX (Impulses)
Skin Surface
Cassette Surface
Time? (Impulses)
Skin Surface
Film Surface
Time? (Impulses)
Skin Surface
Film Surface
18 18 21 21 24
120 120 145 145 180
30 30 35 35 40
18 18 21 21 24
120 125 150 145 180
30 30 35 35 40
36 36 48 48 60
270 270 340 330 420
60 60 75 90 70
18 21 21 24
120 145 140 170
30 35 40 35
18 21 21 24
120 145 140 170
30 40 40 35
36 48 48 60
250 320 310 420
60 80 80 80
21 24
160 180
40 40
21 24
160 180
45 40
48 60
380 460
80 70
9Measurementsare baseduponthe averageof threetrialsand are accurateto +10 mR below 100 mR and _+10%above100 mR. Thermoluminescentdosimeterswereplacedon the skin and imagereceptor.Standarddeviationsand standarderrorshavebeencalculated. i" Timein impulsed(60 = 1 s) is for examinationof an averagesizemaleadultpatientand is basedupon machinesettingsof 70 kVp, 15 mA, at a 17-inchtarget-to-detectordistancewith 2.5 mm Eq of AI filtration.All readingsare _+1impulse.
cated no significant changes (+15% in optical density) in image processing over a 6-month period.
VIEWING CONDITIONS, EXAMINERS, AND DIAGNOSTIC CRITERIA The images of the crowns of all teeth were covered with black tape on all radiographs and xeroradiographs and the films were mounted in opaque film mounts (Figs. 1 and 2). All images were evaluated using a conventional viewbox; however, the xeroradiographs could be viewed in reflected light if the observer desired. A magnifying viewer (X-produkter, Maim6, Sweden) and a magnifying glass were made available to all examiners. The images were randomly ordered and were viewed separately by 10 dentists on different occasions to avoid rememberance biases. Eighteen detailed anatomical structures were evaluated by each of the 10 observers as was an overall radiographic interpretation of the periapical condition present (Table 2). The following scale was used in the assessment of normal: 5 = Definitely not normal; 4 = Probably not normal; 3 = I cannot tell; 2 = Probably normal; and 1 = Definitely normal.
DATA ANALYSIS AND STATISTICAL METHOD On the basis of the judgments made by the observing dentists and knowledge by the investigators of the true condition of the tooth, the true-positive (TP) and falsepositive (FP) values at each level of confidence were calculated for each dentist. The TP value is the fraction of diseased apices that was correctly recognized, while the FP value is the fraction of normal root ends that was judged to be diseased. A ROC curve was con-
FIG 1. A, Xeroradiographic image demonstrating a normal root end with the masking of the crown region of the tooth. B, The same root end as in A imaged with D-speed film as used in study 1.
structed. The first plot point of the ROC curve was determined by calculating the TP and FP values using only the judgments where periapical disease was assessed to be definitely present. The second pair of TP and FP values were determined by also including those judgments of periapical disease as probably present. Successive data points resulted from the successive addition of judgments at each lower level on the confidence scale. ROC curves were computed for each imaging system for each category and for all observers combined. The area under each computed ROC curve, reported here in Tables 2 and 3, were used as they are the best of the single-parameter indices for diagnostic
Vol. 12, No. 8, August 1986
Xeroradiography and Conventional Film
accuracy (20). Student's t test for paired samples was used to distinguish between groups. RESULTS The results of 10 observers' interpretations of periapical structures comparing D-speed film and xeroradiography (study 1) are presented in Table 2. The overall radiographic interpretation for xeroradiography compared with D-speed film was 0.799 versus 0.768 ROC value (not statistically significant, p < 0.05 level). However, statistical significance was found in the evaluation of the "imaging of the periodontal ligament space" and in the evaluation of the "imaging of the lamina dura." For the interpretation of these anatomical regions, xeroradiography appeared to be superior to Dspeed film at the p < 0.05 level. Whereas for the evaluation of "imaging of trabecular bone in apical region," D-speed film was found to be statistically superior to xeroradiography for the interpretation of disease. The results of the same 10 observers comparing E-speed film with xeroradiography (study 2) are presented in Table 2 also. The overall radiographic inter-
pretation of ROC values (Table 2, E) showed no statistical significance (p < 0.05). In fact, for the 18 anatomical structures evaluated no statistical significance was found between the two image detectors. We also found that the mean of all E-speed film and xeroradiography ROC area values for study 2 (0.905) was significantly greater than the mean ROC area
FIG 2. A, Xeroradiographic image demonstrating a "pathological" root end with the masking of the crown region of the tooth. B, The same pathological root end as in A imaged with E-speed film as used in study 2.
TABLE 2. Scoring of detailed root end structures by 10 dentists comparing xeroradiography with D-speed film and E-speed film Area under the ROC Curve Study 1 D-Speed Film A. Imaging of root end (hard tissue) 1. Is there resorption within the root canal? 2. Is there deposition within the root canal? 3. Can the apical foramen at the root end be seen? 4. Is there resorption on apical root surface? 5. Is there hypercementosis on apical root surface? 6. Is the overall imaging of the root end normal? B. Imaging of periodontal ligament (PDL) space 1. Is the shape of PDL space normal at the apex? 2. Is the width of PDL space normal near the apex? 3. Is the radiodensity of PDL space normal near the apex? 4. Is the overall imaging of the periodontal ligament space normal? C. Imaging of lamina dura 1. Is the lamina dura continuous? 2. Is the shape of lamina dura normal? 3. Is the radiopacity of lamina dura normal? 4. Is the overall imaging of lamina dura normal? D. Imaging of trabecular bone in apical region 1. Are there a normal number of trabeculae present? 2. Are the sizes of trabeculae present normal for this region? 3. Is the radiopacity of trabeculation normal for this region? 4. Is the overall imaging of trabecular bone in region normal? E. Overall radiographic interpretation (diagnosis) 1. Normal periapical condition present? * Xeroradiography significantly better than D-speed film, p < 0.05. 1 D-speed film significantly better than xeroradiography, p < 0.05.
349
Study 2
Xeroradiography
E-Speed Film
Xeroradiography
0.361 0.490 0.427 0.2811 0,382 0.667
0.358 0.506 0.437 0.360 0.422 0.678
0.322 0.533 0.453 0.297 0.467 0.782
0.305 0.444 0.426 0.296 0.459 0.731
0.741 0.732
0.804* 0.808*
0.902 0.910
0.901 0.902
0,742
0.785
0.901
0.892
0.733
0.790*
0.901
0.903
0.798 0,775 0,765 0.797
0.821 0.835* 0.801" 0.809
0.918 0.905 0.890 0.891
0.932 0.908 0.913 0.926
0,847t
0.737
0.822
0.839
0.787t
0.722
0.830
0.833
0,7951"
0.744
0.849
0.850
0,8091"
0.743
0.847
0.841
0,768
0.799
0.906
0.897
350
Gratt et al.
Journal of Endodontics
TABLE 3. Area under the ROC curve by technique for each of 10 dental observers Study 1" Dentist
Study 21
D-Speed versus Xeroradi- E-Speed versus XeroradiFilm ography Film ography
1 0.814 0.832 0.957 2 0.908 0.901 0.931 3 0.714 0.768 1.000 4 0.793 0.959 0.926 5 0.689 0.622 0.857 6 0.753 0.755 0.883 7 0.656 0.768 0.811 8 0.819 0.755 0.890 9 0.821 0.875 0.946 10 0.737 0.768 0.857 Mean 0.767 0.796 0.917 Overall film (mean values of studies 1 + 2) = 0.842$ Overall xeroradiography (mean values of studies 1 + 2) = 0.843:1:
0,959 0,962 0.969 0,957 0.806 0,913 0,821 0,878 0,921 0,786 0.893
9 No significant difference between means at p > 0.05 level comparing D-speed with xeroradiography. 1 No significant difference between means at p > 0.05 level comparing E-speed film with xeroradiography. :1:No significant difference at p > 0.05 level comparing all films with xeroradiography from studies 1 and 2.
values obtained in study 1 (0.784). This difference was found to be statistically different at p < 0.001 level. The ROC values of each observer for study 1 and study 2 are presented in Table 3. It should be noted that a large variation was found among observers. In study 1 the range was 0.622 to 0.959. In study 2, the range was 0.786 to 1.000. Figure 3 demonstrates the distribution between observers and the distribution between film and xeroradiography. DISCUSSION
The results of this clinical study indicated that for the overall radiographic interpretation of periapical structures, there was no demonstrated diagnostic difference between xeroradiography and D-speed or E-speed film. The majority of observers, however, when queried in this study subjectively preferred xeroradiographic images over film images and preferred D-speed over Espeed film. However, no differences were found in the accomplishment of the overall diagnostic task of assessing normal periapical structures. This finding is consistent with the results of White et al. using cadaver material (12) and suggests that even lower dose and faster imaging systems may be possible for future use in endodontics in particular and for dental radiography in general. The results of the 10 dentists' assessment of detailed root end structures comparing xeroradiography and Dspeed film (Table 2, study 1) indicated differences in the interpretation of root resorption; shape, width, and overall imaging of the periodontal ligament space; shape and radiopacity of the lamina dura; and number, size, radiopacity, and overall imaging of trabecular bone. Of the 18 detailed structures interpreted by the
m (~
1.00
> o 0.900
98 ~
or-
J "9
"4
E 0.80~
LL
10
UJ
-o 0.70 E
=
a 9"o 0 . 6 0
bserver
number
f r o m T a b l e II
03
0.50 0.50
I
I
l
i
0.60
0.70
0.80
0.90
Averaged Xeroradiography
1.00
ROC Values
FIG 3. Graph demonstrating observer differences (distribution along 45-degree line) comparing D- and E-speed film and xeroradiography. Note that the distance between observers is greater than the distance between each of the imaging techniques from the center line.
10 dentists, xeroradiography was more useful than Dspeed film on 5 of the 18 areas assessed; likewise Dspeed film was more useful on 5 of the 18. General trends suggest that D-speed film is more useful for the interpretation of area densities (such as the overall density of trabecular bone in the periapical region) while xeroradiography is more useful for the interpretation of lines (such as the periodontal ligament space and the lamina dura). This is probably due to the fact that Dspeed film has greater broad area contrast than xeroradiography, which is advantageous for imaging general areas of bone, especially differences in bone density. Although xeroradiography with its edge enhancement properties is best at depicting discontinuities or lines whether radiopaque like lamina dura or radiolucent like periodontal ligament spaces. These findings would suggest that an optimum system of diagnosis might include two images, one film radiograph and one xeroradiograph. The use of multiple images was proposed by Brynolf (21) to aid interpretation (1970) prior to the technological advances of xeroradiography or digital subtraction radiography (22). More research is needed in the area of interpretation of periapical radiographs to enable dentists to be more consistent in this common diagnostic task. We noted that the ROC values for study 2 were significantly higher than those values in study 1. We believe this to be due to differences in the population of teeth studied. The teeth imaged and evaluated in study 1 were much more difficult to interpret than those of study 2. When ROC values approach 1.00, difficulties arise in analysis as the diagnostic task being performed is so easy that potential differences in imaging systems
Vol. 12, No. 8, August 1986
may disappear. As the diagnostic task becomes more difficult the ROC area values decrease. However, as the task becomes very very difficult random guessing takes over and ROC area values of 0.500 or lower may be expected. Generally a ROC value of 0.75 is ideal for differentiating between competing diagnostic systems. Therefore, we believe the difference in ROC values between study 1 and study 2 is due to differences in the interpretative difficulty of the individual cases. A graph of the 10 dentists' ROC scores for film and xeroradiography is shown in Fig. 3. The graph indicates (by the 45-degree line separating film systems from xeroradiography) that there is a greater range between the 10 dentists than between either film system (D- or E-speed) and xeroradiography. It appears that an excellent observer (high ROC score) would perform better with his individual weakest (of the three) imaging systems as compared with the less-best observer (low ROC score) using the best of his individual imaging systems. The knowledge, training, motivation, skill, and experience of the individual dentist appears to be the major variable in these two studies. We believe this to be another important area for future research. CONCLUSIONS In summary, this clinical trial indicated that there is no significant diagnostic difference between xeroradiography and D- or E-speed film for the radiographic interpretation of periapical structures. Radiation exposures used in this clinical study demonstrated that either xeroradiography or E-speed film are low-dose alternatives to conventional D-speed film for intraoral periapical radiography. Wide variations were found among observers of periapical structures but little variation was found among imaging systems. This study was funded in part by Grant DE 06379 from the National Institutes of Dental Research, United States Public Health Service, Bethesda, MD. Dr. Gratt is associate professor, Section of Oral Radiology, UCLA School of Dentistry, Center for the Health Sciences, Los Angeles, CA. Dr. White is professor and chairman, Section of Oral Radiology, UCLA School of Dentistry,
Xeroradiography and Conventional Film
351
Center for the Health Sciences. Dr. Lucatorto is clinical professor, Section of Oral Diagnosis/Oral Medicine/Oral Pathology, UCLA School of Dentistry, Center for the Health Sciences. Dr. Sapp is professor and chairman, Section of Oral Diagnosis/Oral Medicine/Oral Pathology, UCLA School of Dentistry, Center for the Health Sciences. Dr. Kaffe is senior lecturer, Section of Oral Pathology/ Oral Medicine, School of Dental Medicine, TeI-Aviv University, TeI-Aviv, Israel, and is visiting professor, Section of Oral Radiology, UCLA School of Dentistry, Center for the Health Sciences, Los Angeles, CA.
References 1. Goldman M, Pearson AH, Darzenta N. Endodontic success--Who's reading the radiograph? Oral Surg 1972;33:432-7. 2. Goldman M, Pearson AH, Darzenta N. Reliability of radiographic interpretations. Oral Surg 1974;38:287-93. 3. Duinkerke ASH, Van de Poel ACM, DeBoo Th, Doesburg WH. Variations in the interpretation of periapical radiolucencies. Oral Surg 1975;40:414-22. 4. Nielsen J. Reliability in reading endodontic radiographs [Abstract 27]. J Dent Res 1979;58:2296. 5. Gelfand M, Sunderman EJ, Goldman M. Reliability of radiographical interpretations. J Endedon 1983;9:71-5. 6. Brynolf I. A histological and roentgenological study of the periapical region of human upper incisors. Odont Revy 1967;18:1-176. 7. Jeromin LS, Geddes GF, White SC, Gratt BM. Xeroradiography for intraoral dental radiology. A process description. Oral Surg 1980;49:178-83. 8. Gratt BM, Sickles EA, Nguyen NT. Dental xeroradiography for endodontics: a rapid x-ray system that produces high-quality images. J Endodon 1979;5:266-70. 9. Gratt BM, Sickles EA, Gould RG, Jeromin LS, White SC. Xeroradiography of dental structures. IV. Image properties of a dedicated intraoral system. Oral Surg 1980;50:572-9. 10. Kashima I, Gratt BM, White SC. Power spectrum method used for comparing film and xeroradiography. Dentomaxillofacial Redio11985;14:25-30, 11. Petersson AR, Petersson K, Krasny R, Gratt BM. Observer variations in the interpretation of periapical osseous structures. J Endedon 1984;10:2059. 12. White SC, Hollender L, Gratt BM. Comparison of xeroradiographs and film for detection of periapical lesions. J Dent Res 1984;63:910-3. 13. Frykhoim A. Kodak Ektaspeed--A new dental x-ray film. DentomaxilIofac Radio11983;12:47-9. 14. Thunthy K, Weinberg R. Sensitometric comparison of dental films of groups D and E. Oral Surg 1983;54:250-2. 15. Kaffe I, Littner MM, Kuspet ME. Densitometric evaluation of intraoral x-ray films: Ektaspeed versus Ultraspeed. Oral Surg 1984;57:338-42. 16. Horton PS, Sipps FH, Kohout FJ, Nelson JF, Kienzle GC. A comparison of speed group D and E dental x-ray films. Oral Sug 1984;58:104-8. 17. Diehl R, Gratt BM. An assessment of radiographic quality control measurements comparing D-speed film, E-speed film and xeroradiography, Oral Surg (in press). 18. Grondahl H-G. The influence of observer performance in radiographic caries diagnosis. Swed Dent J 1979; 3:101-7. 19. Left GS, Schwartz SF, del Rio CE. Xeroradiographic interpretation of experimentally induced jaw lesions J Endodont 1984;10:188-98. 20. Swets JA. ROC analysis applied to the evaluation of medical imaging techniques. Invest Redio11979;14:109-21. 21. Brynolf I. Roentgenologic periapical diagnosis. I. Reproducibility of interpretation. Swed Dent J 1970;63:339-44. 22. Grondahl H-G, Grondahl K, Webber RL. A digital subtraction technique for dental radiography. Oral Surg 1983;55:96-102.