New diagnostic tools are needed for the characterization of dental caries in the early stages of development. If carious lesions are detected early enough, they can be arrested without the need for surgical intervention. The objective of this study was to demonstrate that polarization sensitive optical coherence tomography (PS-OCT) can be used for the imaging of early caries lesions and for the monitoring of lesion progression over time. High-resolution polarization resolved images were acquired of natural caries lesions and simulated caries lesions of varying severity created over time periods of 1 to 14 days. Linearly polarized light was incident on the tooth samples and the reflected intensity in both orthogonal polarizations was measured. PS-OCT was invaluable for removing the confounding influence of surface reflections and native birefringence necessary for the enhanced resolution of the surface structure of caries lesions. This study demonstrated that PS-OCT is well suited for the imaging of interproximal and occlusal caries, early root caries, and for imaging decay under composite fillings. Longitudinal measurements of the reflected light intensity in the orthogonal polarization state from the area of simulated caries lesions linearly correlated with the square root of time of demineralization indicating that PS-OCT is well suited for monitoring changes in enamel mineralization over time.

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Background and Objectives: The mechanism of water augmentation during IR laser ablation of dental hard tissues is controversial and poorly understood. The influence of an optically thick applied water layer on the laser ablation of enamel was investigated at wavelengths in which water is a primary absorber and the magnitude of absorption varies markedly. Study Design/Materials and Methods: Q-switched and free running Er: YSGG (2.79 mm) and Er:YAG (2.94 mm), free running Ho:YAG and 9.6 mm TEA CO 2 laser systems were used to produce linear incisions in dental enamel with and without water. Synchrotron-radiation IR spectromicroscopy with the Advanced Light Source at Lawrence Berkeley National Laboratory was used to determine the chemical changes across the laser ablation profiles with a spatial resolution of 10-mm. Results: The addition of water increased the rate of ablation and produced a more desirable surface morphology during enamel ablation with all the erbium systems. Moreover, ablation was markedly more efficient for Q-switched (0.15 microsecond) versus free-running (150 microsecond) erbium laser pulses with the added water layer. Although the addition of a thick water layer reduced the rate of ablation during CO 2 laser ablation, the addition of the water removed undesirable deposits of non-apatite mineral phases from the crater surface. IR spectromicroscopy indicates that the chemical composition of the crater walls deviates markedly from that of hydroxyapatite after Er:YAG and CO 2 laser irradiation without added water. New mineral phases were resolved that have not been previously observed using conventional IR spectroscopy. There was extensive peripheral damage after irradiation with the Ho:YAG laser with and without added water without effective ablation of enamel. Conclusions: We postulate that condensed mineral phases from the plume are deposited along the crater walls after repetitive laser pulses and such non-apatitic phases interfere with subsequent laser pulses during IR laser irradiation reducing the rate and efficiency of ablation. The ablative recoil associated with the displacement and vaporization of the applied water layer removes such loosely adherent phases maintaining efficient ablation during multiple pulse irradiation.

New diagnostic tools are needed for the characterization of dental caries in the early stages of development. If carious lesions are detected early enough, they can be arrested without the need for surgical intervention. The objective of this study was to demonstrate that polarization sensitive optical coherence tomography (PS-OCT) can be used for the imaging of early caries lesions and for the monitoring of lesion progression over time. High-resolution polarization resolved images were acquired of natural caries lesions and simulated caries lesions of varying severity created over time periods of 1 to 14 days. Linearly polarized light was incident on the tooth samples and the reflected intensity in both orthogonal polarizations was measured. PS-OCT was invaluable for removing the confounding influence of surface reflections and native birefringence and for resolving the surface structure of caries lesions. This study demonstrated that PS-OCT is well suited for the resolution of interproximal and occlusal caries, early root caries, and secondary caries around composite fillings. Longitudinal measurements of lesion progression established a strong correlation (p<0.001) between the reflected light from the lesion area and the square root of time indicating that PS-OCT is well suited for monitoring changes in enamel mineralization over time.

No abstract