Transillumination of interproximal caries lesions with 830-nm light

Abstract

New imaging technology is needed for the early detection of dental caries (decay) in the interproximal contact sites between teeth. Previous measurements have demonstrated that dental enamel is highly transparent in the near-IR near 1310-nm making that wavelength range ideal for the transillumination of interproximal lesions. However, imaging at 1310-nm involves the use of expensive InGaAs technology. The purpose of this study was to compare the performance of a low cost near-IR sensitive imaging system employing a CCD camera with enhanced near-IR sensitivity operating at 830-nm with the 1310-nm InGaAs system. Images of simulated caries lesions were acquired through tooth sections of varying thickness and whole teeth in order to demonstrate the utility of a near-IR dental transillumination system for the imaging of early dental caries (decay). Simulated lesions, representing the optical scattering of natural dental caries, were placed in plano-parallel dental enamel sections and whole anterior teeth. The contrast ratio between the simulated lesions and surrounding sound enamel was calculated from analysis of the respective spatial intensity profiles in the acquired projection images. This study shows that near-IR transillumination at 830-nm offers significantly improved image contrast over the visible range, but less image contrast than at 1310-nm.

Diagnostic Imaging and Spectroscopy

“…Interproximal lesions can be viewed using transillumination with the light source and detector placed on opposite sides of the tooth or NIR light can be delivered near or below the gum-line and both interproximal and occlusal lesions can be imaged from directly above the occlusal surface, as demonstrated in Figure 68.5 for a natural interproximal lesion. Shorter NIR wavelengths have also been investigated in the region that is accessible to conventional silicon-based charge-coupled device (CCD) cameras with the NIR filter removed, namely at 830 nm [68]. Figure 68.6 compares the image contrast of tooth sections of increasing thickness with simulated lesions in the visible region at 830 and 1310 nm [68].…”

“…Shorter NIR wavelengths have also been investigated in the region that is accessible to conventional silicon-based charge-coupled device (CCD) cameras with the NIR filter removed, namely at 830 nm [68]. Figure 68.6 compares the image contrast of tooth sections of increasing thickness with simulated lesions in the visible region at 830 and 1310 nm [68]. Simulated lesions were produced by drilling small 1 mm diameter cavities on the mesial or distal aspect of tooth sections of varying thickness or whole teeth.…”

“…Simulated lesions were produced by drilling small 1 mm diameter cavities on the mesial or distal aspect of tooth sections of varying thickness or whole teeth. The imaging system operating near 830 nm, utilizing a low-cost silicon CCD optimized for the NIR region, is capable of significantly higher performance than a visible system, but the contrast is significantly lower then that attainable at 1310 nm [68]. Owing to the high transparency of the enamel in the NIR region, NIR imaging also has great potential to examine defects in tooth structure and cracks in enamel can be clearly resolved with this method.…”

“…PS-OCT is advantageous for providing a quantitative measure of the lesion severity for monitoring lesion progression and for assessing the success of chemical intervention on arresting and remineralizing lesions. 68.6 Fluorescence Imaging…”

Use of an optical clearing agent to enhance the visibility of subsurface structures and lesions from tooth occlusal surfaces

“…19,20 Optical clearing agents have routinely been used in biological microscopy and have found recent application in clinical imaging, including OCT. 21,22 We postulate that OCT is ideally suited for monitoring and improving the diagnosis of QOCs, and methods can be developed to enhance the visibility of hidden subsurface lesions. Even though the optical penetration of near-IR light can easily exceed 7 mm through sound enamel to image lesions on proximal surfaces with high contrast, 23 the large increase in light scattering due to demineralization 24 typically limits optical penetration in highly scattering lesions (also dentin and bone) to 1 to 2 mm, thus cutting off the OCT signal before it reaches the dentinal-enamel junction (DEJ). However, most occlusal lesions rapidly spread laterally under the enamel upon contacting the more soluble softer dentin.…”