Laser-induced breakdown spectroscopy: a tool for real-time, in vitro and in vivo identification of carious teeth

A one-fibre light delivery / collection assembly for LIBS analysis was used, which in principle lends itself for routine in vitro / in vivo applications in a dental practice. A number of evaluation algorithms for LIBS data can be used to assess the similarity of a spectrum, measured at specific sample locations, with a training set of reference spectra. Here, the description has been restricted to one pattern recognition algorithm, namely the so-called Mahalanobis Distance method.The plasma created when the laser pulse ablates the sample (in vitro / in vivo), was spectrally analysed. We demonstrated that, using the Mahalanobis Distance pattern recognition algorithm, we could unambiguously determine the identity of an "unknown" tooth sample in real time. Based on single spectra obtained from the sample, the transition from caries-affected to healthy tooth material could be distinguished, with high spatial resolution.The combination of LIBS and pattern recognition algorithms provides a potentially useful tool for dentists for fast material identification problems, such as for example the precise control of the laser drilling / cleaning process.Numerous techniques have been devised to examine dental caries; many of these have been reviewed e.g. by Murray [1] and Niemz [2]. However, most promising some newly emerging technological realisations in analytical spectroscopy, including laser fluorescence (already a commercial diagnostic system KaVo DIAGNOdent is available) [3,4], digital imaging fibre optics transillumination [4,5], tuned-aperture computer tomography [6,7], and digital radiography [6,8]. The great sensitivity of some of these methods allows the detection of caries at earlier stage than conventional methods [1,2,9]. Unfortunately, none of these techniques can normally be used for real-time detection of demineralized enamel / dentin (accompanied with loss of calcium Ca and phosphorus P[10]), associated with caries, directly during the application of laser dril