Ann Wenzel, DDS, PhD, Dr Odont,” and Agnar Halse, DDS, Dr Odont,” Aarhms, Denmark, and Bergen, Norway ROYAL

DENTAL

COLLEGE,

AARHUS,

AND

SCHOOL

OF DENTISTRY,

BERGEN

The material in this study consisted of 38 fully erupted, extracted third molars without clinical cavitation in the occlusal surface. A radiograph was made of each tooth before and after 5, IQ, and 20 minutes of stannous fluoride treatment. The radiographs were digitized and subtraction performed between the images obtained after stannous fluoride treatment and the pretreatment image. Two observers assessed the stannous fluoride treated radiographic and the subtraction images on a monitor: 0 = no change, 1 = intensity increase (white area interpreted as a carious lesion) in dentinoenamel area. Caries was assessed on conventional film radiographs made before treatment: 0 = no caries in dentin, 1 = caries in dentin. The presence of caries in dentin was validated histologically. Sensitivity for intensity increase as a sign of caries was overall higher for the subtraction images based on 20-minute treatment than for the radiographic images (0.025 > p > 0.01) but not significantly higher than for the conventional radiographs. However, neither observer gave false-positive scorings in the subtraction images, whereas observer 1 had five false-positive scorings on the conventional films. Observer 2 had none. The subtraction method did not provide a higher sensitivity for dentinal occlusal caries than conventional film radiography, but the intensity increase could be trusted more than the traditional radiolucency as a sign of a dentinal lesion. (ORALSURGORALMEDORALPATHOL~~~~;~~:S~~-8)

n the examination for occlusal caries, visual inspection has been claimed unsatisfactory for detection of even deep dentinal lesions, as such lesions may progress under an apparently intact outer enamel surface.lm4 Recent studies agree that radiography is a significant adjunct to clinical examination for the diagnosis of occlusal caries, 1, 5 though it is still not possible by this method to detect more than half of the histologically validated dentinal lesions.2, 4 Newly developed digital radiographic methods possesspossibilities for enhancing image contrast and preserving edges of the imaged structures. Accuracy of occlusal caries detection has been shown to increase aAssociate Professor and Head, Department of Oral Radiology, Royal Dental College Aarhus, Faculty of Health Sciences, University of Aarhus. bProfessor and Head, Department of Oral Radiology, School of Dentistry, Bergen.

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with the use of such methods compared with conventional film radiography. 2, 3 Another digital imaging method, subtraction radiography, has been established as a sensitive technique for the detection of small changes in hard tissues.6 It has recently been documented to be useful for the visualization of remineralization and demineralization in an in vitro study of dentinal caries progression.9 Subtraction images based on radiographs made before and after treatment with a stannous fluoride (SnF2) solution have been demonstrated to reveal an intensity increase in regions with approximal caries.8 The uptake of the stannous ion thus leads to increased radiopacity in areas of demineralization as interpreted on conventional film radiographs. Whether an uptake of stannous ions will occur in occlusal carious lesions in clinically noncavitated teeth has not been investigated. Halse et al.* suggested that treatment with a SnFz solution in combination with digital subtraction radi-

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Fig. 1. Two third molars. A and B Dentinal occlusalcarious lesion detected on the conventional radiograph (radiolucency) before SnF2 treatment (A) and on the subtraction image (intensity increase) made between the pretreatment and a 20-minute posttreatment radiograph (B). C and D Dentinal occlusal lesion not detected on the conventional radiograph before SnFs treatment(C) but detected on the subtraction image made between the pretreatment and 20-minute posttreatment radiograph (D).

ography might facilitate detection of caries lesions not perceptible by direct inspection of conventional radiographs. However, subtraction radiography as a diagnostic aid for caries detection had not been investigated. The aims of this study were therefore twofold: (1) to evaluate the uptake of stannous ions in carious lesions in occlusal surfaces that result in an increase in radiopacity in digitized radiogra.phic images as well

as an intensity increase in subtraction images; and (2) to evaluate the diagnostic validity of the intensity increase as a sign of caries in subtraction radiographic

images compared with the conventional radiolucency in film radiographs for the detection of dentinal carious lesions in noncavitated occlusal surfaces. MATERIAL AND METHODS Teeth Thirty-eight fully erupted third molars without clinical cavitation in the occlusal surface extracted from 18 to 20-year-old Danish males were used. Varying degrees of fissure discoloration were present.

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After extraction, the teeth were stored wet on cotton saturated with 1% thymolized water. adiographic

examination

A radiograph of each tooth was obtained with Kodak Ultraspeed film (Eastman Kodak Co., Rochester, N.Y.) with the use of a paralleling technique and a source-to-film distance of 30 cm. Without removing the tooth under examination or the x-ray tube, a 10% SnF2 solution was appiied to the occlusal surface with a cotton swab. New radiographs were taken after 5, 10: and 20 minutes. Exposure parameters (65 kV, lo-mA) were identical for all radiographs. Exposure time was individually adjusted but kept for the series of radiographs of the same tooth. Processing was automatic. The radiographs were recorded as square images (3 x 3 cm) by a video camera and sampled in a spatial resolution of 512 X 512 pixels and 256 shades of gray. The frame grabber was a PC Vision+ card (Imaging Technology Inc., Woburn, Mass.) mounted in a personal computer (Olivetti M240, Olivetti USA, Somerville, N.J.). The digitized radiographic images, Ru-, Rs-, Rio-, and Rzo-images, were displayed on a quality video monitor for assessment (Fig. 1). The hardware was controlled by a subtraction program specifically developed for dental radiography93 to and described in detail elsewhere.‘“> t2 With the initial pretreatment image as reference, subtractions were performed of the images of the SnFz-treated teeth taken after 5, 10, and 20 minutes. Three subtraction images were thus acquired for each tooth, Ss-, Sto-, and Szo-images (Fig. 1). These images were likewise assessed on the monitor. The data comprised seven digital radiographic images of each tooth: four radiographs, one without and three with various SnFz application times, and three subtraction images. In total, 266 digital images and 37 conventional film radiographs made before SnF2 treatment were viewed (one film had disappeared at the time for assessment of the conventional films). To evaluate intraobserver reproducibility, 34 replicate digital images were generated at random by the computer from the 266 digital images. The 300 digital images were displayed to the observers at random. Accordingly, scorings were blind among the R- and the S-images with regard to SnFz treatment times. Assessments were performed by two oral radiologists, observer 1 and observer 2. Tine images displayed on the monitor were recorded by the observers independently (Ro-, Rs-, RIO-, RIO- and Ss-, Sta-, Sze-images) as follows: 0 = no change, 1 = increased intensity in dentinoenamel area. In the subtraction images, intensity increase (white area) was interpreted as an indicator of the presence of a carious lesion. On the

1992

conventional film radiograph before SnFz treatment, the observers recorded caries in the occlusal surface in the traditional way as follows: 0 = no caries in dentin, 1 = caries (radiolucency) in dentin. The ratio between diseased and healthy teeth in the sample was not known to the observers. Histologic validation

The teeth were serially sectioned through the occlusal fissure system in the buccolingual direction. Each section was 500 to 600 pm thick resulting in 9 to 15 sections from each tooth. The sections were dried in air and examined with the use of a stereomicroscope (X 10 magnification). The histologic sections were scored 0 = no caries or caries confined to enamel, 1 = caries in dentin. If a lesion could be demonstrated in one of the sections, the tooth was deemed carious. Data treatment

The histologic assessment was the validation for the true state of decay in the occlusal surface. Diagnostic accuracy was evaluated by the parameters of sensitivity, specificity, and predictive values of the positive and negative test outcome. The diagnostic threshold was the presence of caries in dentin. For the evaluation of differences between the methods, these parameters were tested by McNemar’s chi-squared test as previously described by Berkey et all3 The first of the duplicate registrations were used in the evaluation of diagnostic accuracy. The tooth was the statistical unit. ESULTS

According to the histologic examination, 24 of 38 teeth had dentinal caries. Evaluation of intraobserver agreement demonstrated that both observers disagreed on two (6%) of the replicate images on their second examination. Both observers falsely reported one tooth with an intensity increase in the Ro-images. In Table I, sensitivity rates are given for scorings by the two observers of intensity increase on the radiographic images (Rs, RIO, and Rza) exposed to various minutes of SnF2 treatment. No significant differences were observed among the sensitivity rates obtained from assessment of the R-images after application of SnF2 for various time intervals (p > 0.05) or between the observers. Sensitivity rates obtained from assessment of the subtraction images (Ss, Sto, and S& increased under increasing SnF2 influence. Observer 1 obtained higher sensitivity rates than observer 2 when assessing the subtraction images, irrespective of SnF2 treatment times (Table I). The differences between scorings by the two methods (R and S) for observer

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Table I. Sensitivity rates for intensity increase as a

Table II. Sensitivity, specificity, positive and

sign of dentinal caries in radiographic images after minutes of SnF2 treatment (Rs, RIO, and R2o) and in subtraction images (Ss, Sto, and $0) obtained by two observers (n = 38; 24 of which had caries)

negative predictive values for detection of dentinal caries on film radiographs made before SnF2 treatment by two observers (n = 37; 23 of which had caries)

Observer Observer Observer Observer

1 2

0.21 0.33

0.42 0.21

0.33 0.29

0.54 0.13

0.29 0.25

1 2

0.78 0.48

0.64 1 .oo

0.78 1 .oo

0.64 0.58

0.58 0.42

1 clearly favored the S-method (0.1 > p > 0.05 for images after 5 and :lOminutes of SnF2 treatment) and were statistically significant for the 20-minute treatment images (0.025 >p > 0.01). In addition, a statistically significant difference was found between observer 1 and oblserver 2 when scoring the Rioimages (0.01 > p >. 0.001) but not when scoring the other groups of R- nor S-images. Specificity for scorings by both methods was 1.O for all SnF2 times, except for observer 2 who in one instance (Rio-imag,es) falsely deemed one tooth as having an intensity increase which in fact was caries free according to the histologic test. Therefore the positive prediction rate was also 1.0 in all instances but one. In accordance with the differences in sensitivity rates obtained by the two observers with the two methods, the negat.ive prediction rate also differed between the methods (range 0.44 to 0.46 for R-images and 0.40 to 0.74 for S-images). Detection of dentinal caries on the conventional film radiographs resulted in a high detection rate for observer 1 (sensitivity 0.78) but with five false-positive scorings (positive predictive value 0.78). Observer 2, on the other hand, maintained the sensitivity (0.48) obtained bly scoring intensity increase in the Szo-images, still without any false positive scorings (Table II). DISCUSSION

The present study demonstrated that application of an SnFz solution resulted in an increase in radiopacity, obviously caused by penetration of stannous ions into the occlusal caries lesion. In relation to the appearance on the monitor, this resulted in an intensity increase (a white area) in both the R- and the S-images. The intensity increase could be perceived significantly more clearly in subtraction images after elimination of structured noise than in the original radiographic images. This was true particularly for the subtraction images performed after 20 minutes of

SnF2 treatment. Similar results have been demonstrated in a previous study of SnF2 treatment of interproximal carious lesions.* In this previous study, an increase in radiopacity could be observed in half of the film radiographs where caries had been noted before SnF2 treatment, whereas subtraction radiography revealed all the known lesions as an intensity increase seen on monitor. It was therefore concluded that stannous ions probably penetrated into the demineralized approximal enamel. In the study, however, no parameter existed for the true state of decay in the surface, and teeth without radiographically detectable caries were not included. It was therefore not possible to evaluate subtraction radiography as a diagnostic method for the detection of caries compared with conventional radiography. In the current study, the presence of a carious lesion was validated histologically. Lesion detection was performed on the conventional film radiographs to compare the traditional diagnostic method for caries detection to subtraction radiography. In the original radiographic images that were made after various SnF2 times, the presence of stannous ions may have obscured the conspicuousness of the carious lesion, which resulted in the tooth being recorded as sound. Thus it follows that an increase in radiopacity as a sign of dentinal caries is not useful in conventional films. However, in the subtraction images, the intensity increase may be recognized as a sign of caries on a par with the traditional radiolucency in a conventional radiograph. Observer 2 achieved a sensitivity rate (approximately 0.5) on the conventional film radiographs comparable to that on the 20-minute subtraction images. Observer 2 showed a strict diagnostic behavior, deeming a tooth carious only when he was absolutely positive. This attitude resulted in no false-positive scorings by this observer on the conventional films or (except in one case) on the digitized radiographs or subtraction images when scoring intensity increase. Observer 1 obtained a high sensitivity rate (78%) on the conventional films, but with five false-positive

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scorings. This is a large percentage of false-positive scores if we take into account the distribution (not known beforehand) of diseased and healthy teeth in the study, which was almost 2: I ” Observer 1 has previously assessed occlusal caries on conventional and digitized radiographs,2T 3 and obtained sensitivities of 60% to 70% but always with 10% to 15% false-positive scorings. The subtraction method, however, provided a sensitivity of almost 60% for observer 1 without any false-positive scorings. On this basis (though in this study only two observers scored the images), it is interesting and remarkable for a diagnostic tool to be reliable to an extent that no false positives are scored at the same time that it maintains a high sensitivity rate. Whenever a positive test result is obtained, it may thus be highly trusted. That the signs of stannous ion uptake are quite unequivocal in the subtraction images is also reflected by the fact that the observers, when they assessed the replicate images, disagreed with themselves in only two of the R-images and in none of the S-images. Still, more than 40% of teeth with dentinal caries were not detected (false negatives) by any of the diagnostic methods in this study. For the conventional film radiographs, this is in accordance with previous findings on occlusal caries diagnosis in a comparable tooth sample.4 These findings are indicative of the difficulties that exist in present day populations in detecting occlusal carious lesions that may progress into dentin without a macroscopically visible enamel surface breakdown. In a former study in which the teeth were assessed visually, it appeared that “microcavities” existed in the occlusal enamel in about half of the lesions when in fact histologically they were found to penetrate deep into the dentin4 In the other half, no breakdown could be demonstrated in the outer surface of teeth that still had dentinal caries. As in the present study, conventional film radiography improved diagnostic accuracy only to some extent. It may be speculated that the stannous ion is able to penetrate only into surfaces with microcavities. Further studies should correlate the clinical appearance of the teeth and the ability of the stannous ions to penetrate into the dentin. The subtraction radiographic technique has been previously demonstrated to be a refined instrument for revealing small tissue density changes.14 The present results indicate that subtraction radiography after SnFz treatment may be well trusted (high positive prediction) as a tool in caries diagnosis when it reveals dentinal occlusal caries as an intensity increase in the subtraction image. The subtraction method did not, however, provide a higher detection rate (sensitivity) for dentinal occlusal caries than

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conventional film radiography. Results from this in vitro study cannot be directly transferred to clinical trials where standardization of the radiographic recordings is facing more difficulties, but clinical studies are needed to achieve more knowledge of the performance of subtraction radiography in caries diagnosis. The help of S$ren Koch in sectioning the teeth for histologic analysis is gratefully acknowledged. REFERENCES 1. Creanor SL, Russell

JI, &rang DM, Stephen XW, Burchell CK. The prevalence of clinically undetected occlusal dentine caries in Scottish adolescents. Br Dent J 1990,169:126-9. A, Larsen MJ, Fejerskov 0. Detection of occlusal 2. Wenzel caries without cavitation by visual inspection, film radiographs, xeroradiographs, and digitized radiographs. Caries Res 1991;25:365-71. 3. Wenzel A, Hintze H, Mikkelsen L, Mouyen F. Radiographic detection of occlusal caries in noncavitated teeth: a comparison of conventional film radiographs, digitized film radiographs, and Radio VisioGraphy. ORAL SURG ORAL MED ORAL PATHOL

1991;72:621-6.

4. Wenzel A, Fejerskov 0. Validity of diagnosis of questionable caries lesions in occlusal surfaces of extracted third molars. Caries Res 1992;26:188-94. 5. Weerheijm KL, van Amerongen WE, Eggink CO. The clinical diagnosis of occlusal caries: a problem. J Dent Child 1989;56:196-200. H-G, Grondahl K. Subtraction radiography for the 6. Grondahl diagnosis of periodontal bone lesions. ORAL SURG ORAL MED ORAL

PATHOL

1983;55:208-13.

I. Maggio JJ, Hausmann EM, Allen K, Potts TV. A modei for dentinal caries progression by digital subtraction radiography. J Prosthet Dent 1990;64:727-32. 8. Halse A, White SC, Espelid I, Tveit AB. Visualization of stannous fluoride treatment of carious lesions by subtraction radiography. ORAL SURC ORAL MED ORAL PATHOL 1990; 69:378-81.

9. Depenau J, Hansen A, Kirkegaard BB, et al. Subtraktion af intraorale rylntgenbilleder. Aalborg: Aalborg Universitetscenter, 1987 (in Danish). 10. Andersen H, Gunnarsson A, J#rgensen T, Nielsen LH. Detektion af paradentose. Aalborg: Aalborg Universitetscenter, 1988 (in Danish). 11. Wenzel A. Effect of manual compared with reference point superimposition on image quality in digital subtraction radiography. Dentomaxillofac Radio1 1989;18: 145-50. 12. Wenzel A, Sewerin I. Sources of noise in digital subtraction radiography. ORAL SURC ORAL MED ORAL PATHOL 1991; 71:503-g.

13. Berkey CS, Douglass CW, Valachovic RW, Chauncey HH, McNeil BJ. Statistical methods for comparing dental diagnostic procedures. Community Dent Oral Epidemiol 1990; 18169-76. 14. Wenzel A. Influence of computerized information technologies on image quality in dental radiographs. Danish Dent 1991;95:527-59. Reprint requests: Ann Wenzel, DDS, PhD, Dr Odont Department of Oral Radiology Royal Dental College Faculty of Health Sciences University of Aarhus Vennelyst Boulevard DK-8000 Aarhus C, Denmark