Laser Induced Fluorescence Of Dental Caries

Abstract

ABSTRACT Significant differences between the optical spectra taken from sound regions of teeth and carious regions have been observed. These differences appear both in absorption and in laser induced fluorescence spectra. Excitation by the 488 nm line of an argon ion laser beam showed a peak in the emission intensity around 553 nm for the sound dental material while the emission peak from the carious region was red-shifted by approximately 40 nm. The relative absorption of carious region was significantly higher at 488 nm/ however its fluorescence intensity peak was lower by an order of magnitude compared to the sound tooth. Implications of these results for a safe, reliable and early detection of dental caries are discussed.IntroductionThe early detection of dental caries allows preventive measures to be taken before physical and chemical changes in tooth enamel and dentin cause irreversible damage to teeth. Clinical examination and microradiographic techniques are currently used to identify dental caries. Clinical examination is effective only for well developed cases of caries and hence is not suitable for early detection. Radiography is not suitable for caries in pits or fissures, but it is the only effective method for early identification of caries on the proximal surfaces of premolars and molars. Unfortunately radiography involves repeated exposures to X-radiation and the risks attendent to this exposure.Since dental material is transluscent, illumination may reveal areas where the refractive index has changed. This technique called trans-illumination using white light has been used to locate areas of tooth decay 1. A coherent monochromatic source is better than broadband radiation for trans- illumination ^ m Spectroscopic techniques capable of identifying tooth decay have also been demonstrated 3 m A schematic diagram of a longitudinal section of a tooth is shown in Figure 1.REFLECTEDINCIDENT TRANSMITTEDFLUORESCENFigure 1. Longitudinal section of a tooth showing carious regions. The incident radiation can induce fluorescence, be reflected, absorbed or transmitted.The sound areas of enamel and dentin are marked 'S1 and the carious regions are marked 'C1 . The sound regions have the structure and chemical composition of hydroxyapatite. Dental caries is accompanied by the decalcification of mineral components and dissolution of organic matrix of hydroxyapatite, hence carious regions are expected to have different physical structure and chemical composition. Therefore, we expect differences in the absorption and fluorescence spectra from these two regions. These spectroscopic differences may be used to develop a means to identify dental caries. Since optical