A New Method for Caries Diagnosis by Characteristic Spectrum

Abstract

A new and non-invasive method adapted for optical diagnosis of early caries is proposed by researching on the interaction mechanism of laser with dental tissue and relations of remitted light with optical properties of the tissue. This method without light filter, differed from the DIAGNodent ® and PNC method in its ability for registering fluorescence spectrum. The characteristic spectrum of dental tissue contains rich information about caries components, structure, spatial conformation, and so on. The research was conducted in vitro, and three components of characteristic spectrum are analyzed: backscattering, reflection and auto-fluorescence. It enables not only to evaluate chemical changes in tooth by analyzing characteristic frequencies of auto-fluorescence spectrum, but also to estimate structure and morphological changes in tissue by means of anti-stokes fluorescence spectrum. Preliminary results show that this method has a potential application in the quantitive diagnosis of various stages of dental caries and high sensitivity for detecting early caries and the surface damage of health enamel. Dental caries is oral disease with high incidence caused by bacterial infection, which seriously endangers human health. Conventional procedures for caries detection are unable to detect the lesions until they are well advanced and involve about one-third of the thickness of enamel. The problem of early caries lesions formation and development is still present for scientific debates. The first sign of the caries demineralization is concerned with the increase of microporosity of enamel. Additionally it is known that caries process is periodic and with the increased penetration of acids. It is possible to eliminate micro-lesions of crystalline structure of enamel by controlling environmental factors of oral cavity. Total reconstruction of tooth tissue is possible only in very early stage. A caries diagnosis method by detecting fluorescence spectrum including backscattering, back-reflected and auto- fluorescence is proposed, which is more sensitive to detect early caries, surface damage of health enamel. II. CARIES PROCESS It is generally recognized that that the caries process results from a shift in the oral equilibrium favoring demineralization over re-mineralization for a prolonged period of time. Thus, the body's natural defense mechanisms are simply unable to repair the damage at the same rate that demineralization continues to occur. Eventually, an "incipient" caries lesion is detected as a so-called "white spot". An examination of this stage of the lesion reveals a thin layer of partially-dematerialized enamel covering a large de-mineralized area. Caries occurs regardless of the type of tooth surface, the age of the host or whether the tooth is deciduous or permanent. It is also known that re- mineralization of these lesions at this stage can only occur as long as the thin layer of enamel remains intact over the lesion; if the surface layer is broken, the lesion may become arrested but total re-mineralization to restore the original tooth structure will not occur (1). Acidification process can be expressed by chemical formula: