Techniques based on transillumination of teeth with visible light will be a valuable aid in caries diagnosis, if a higher sensitivity than that of the present Foti method is achieved. Therefore, a better understanding of light propagation through teeth is required, and hence it is useful to investigate the propagation of light through sound dental material. In this study the intensities emanating from the surfaces of enamel and dentine bars were measured when these bars were illuminated using a fibre rod transporting the light from a HeNe laser (λ = 633 nm) as a light source. From the measured intensities, the radiant fluxes emanating from the surfaces were calculated. To account for a directional dependence of these fluxes, optical anisotropy in dental material was investigated by comparing the transmitted light intensity in a direction perpendicular and parallel to the approximal surface of the tooth from which the sample was cut. The mean ratio of the transmitted intensities in perpendicular and parallel direction was 0.86 ± 0.06 for enamel and 2.88 ± 0.43 for dentine. In addition, for enamel the asymmetry parameter, g, was estimated. The averaged value was g= 0.68 ± 0.09. It was concluded that for dentine the optical anisotropy as measured supports the idea that tubules are the predominant cause of scattering in dentine. For enamel the results indicate that the hydroxyapatite crystals contribute significantly to scattering and that the influence of the prism structure on the light propagation is small.

For both general practitioners and researchers in caries diagnostics, the true validity of available diagnostic techniques is of considerable interest. Yet, for both bitewing radiography and fiber-optic transillumination, this is still not accurately known, nor is it clear which of the two techniques performs best clinically. This study's purpose was to estimate the clinical performance of the two techniques in diagnosing approximal caries lesions in low-caries-prevalence populations. Clinical studies that compare the two techniques were selected from literature. We determined 2 x 2 contingency tables from these studies and calculated one overall contingency table. The cut-off for decay was at dentinal caries. Assuming that erroneous outcomes from both techniques are mutually independent, we expressed diagnostic sensitivity and specificity of the two techniques as functions of the contingency table cell contents, with caries prevalence as the parameter. Because the caries prevalence was unknown, every sensitivity and specificity value was possible. From the conditions that sensitivity, specificity, and caries prevalence are always between one and zero, a limited range of sensitivity and specificity values was obtained. Three situations were examined: Bitewing radiography specificity is 1, fiber-optic transillumination specificity is 1, and both specificities are equal. Under these conditions, the bitewing radiography sensitivity was between 1.00 and 0.71 +/- 0.01, and the fiber-optic transillumination sensitivity was between 0.70 +/- 0.01 and 0.50 +/- 0.02. Both specificities were between 1.00 and 0.99. We concluded that the two techniques have comparable specificities. but that the fiber-optic transillumination sensitivity is significantly lower than that for bitewing radiography.

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Abstract. The methods currently utilized in dentistry to detect caries lesions have their limitations and alternatives are being investigated* A promising option is tooth transillumination which is based on an increase of light scattering or light absorption in the affected tissue region. In this study transillumination applied to detect approximal caries lesions was investigated using premolar teeth containing simulated caries lesions. Cavities were drilled at the approximal surtnce ami filled with light absorbing and light scattering fluids in different dye and particle concentrations to model successive stages of lesion progress. For light absorbing cavities the extinction as function of the deeadic absorption coefficient measured at the occlusal surface could be approximated by the Lambert-Beer law (/* = 0,98 ±0.01). For light scattering cavities the extinction as a function of the decadic reduced scatter coefficient wad fitted to a straight line (r *= 0.98 ± 0.03) for /t'(X -633 nm) < 1.25 m m "1. For higher reduced decadic scatter coefficients the curves levelled off due to multiple scattering. In addition, the contribution of the dentinal cavity part to the radiance change induced by the total cavity was estimated. For light absorbing cavities illuminated with red light the average contribution was 10.5 (SD 4.2)% and for those illuminated with green light it was 1.4 (SD 0.9)%, indicating that the radiance change caused by a caries lesion is mainly determined by the enamel lesion part. L IntroductionHuman teeth consist of the turbid materials enamel and dentine, and soft tissue, the pulp. Hnamel is the very hard outer tooth crown layer exposed to the oral environment and dentine is the softer, bone-like material covered by the enamel. Enamel and dentine can be subject to dental decay, a process which ultimately can lead to the total destruction of the tooth. One of the predilection places for dental caries is at the contacting, approximal, surface of the tooth (ligure 1 ). These approximal surfaces are for the greater part inaccessible for direct visual inspection, which seriously hampers an early detection of caries lesions.'The methods currently in use to detect approximal caries lesions at molar and premolar teeth are visual inspection and bitewing radiography. Yet, it is known that during clinical examination a large number of incipient caries lesions are being missed, whereas a great number ot* sound surfaces are wrongly being diagnosed as carious (Wenzel 1993

A b stra c t. The in s tru m e n ts clin ically a v ailab le fo r the diagnosis of approxim al caries lesions are in ad eq u ate to detect lesions early and quantitatively. The aim of this study w as to investigate w h eth er w av elen g th -d ep en d en t light scattering and absorption of carious tissues m ay be utilized for the quantitative diagnosis of these sm all approxim al caries lesions. Seventeen extracted p rem o lar teeth w ere transilluminated at an approximal surface w ith a glass fiber, which transported the light from a halogen light bulb. Seven approximal surfaces contained a naturally developed small white-spot lesion, and 5 surfaces a small discolored lesion. Five teeth were sound. The occlusal surface w as im aged w ith a CCD camera. Light in the blue and red portions of the electrom agnetic spectrum w as selected b y m eans of Schott glass filters. From the o btained im ages, average effectiv e d e c a d ic o p tic a l th ic k n e ss d iffe re n c e s w e re determ ined. These w ere plotted as a function of average mineral loss assessed by means of w avelength-independent m icroradiography. The correlation coefficient betw een the average effective decadic optical thickness difference and average m in e ra l loss w as f -0.79 (95% Cl: 0.47,..0.93). Different sources of variation that influence the observed c o rre la tio n w e re d e fin e d a n d q u a n tifie d . F rom these measurem ents, the correlation coefficient between average effective decadic optical thickness difference and 'tru e ' average mineral loss was estim ated to be £ = 0.92 (95% Cl: 0.77...0.97). The results indicate that early and, in principle, also quantitative diagnosis of approxim al caries lesions is feasible w h en w a v elen g th -d ep en d en t light p ro p ag ation through carious tissues is utilized.