Up to now lasers have not achieved any practical importance in dentistry for drilling teeth because of considerable damage to the surrounding tissue. We studied the application of pulsed 2.94 microns Er:YAG laser radiation in vitro on extracted teeth to remove enamel, dentin, and carious lesions. The depth and diameter of laser-drilled holes were measured as a function of pulse number and radiant exposure. The tissue removal is very effective both for dentin and enamel.

The absorption and transport scattering coefficients of biological tissues determine the radial dependence of the diffuse reflectance that is due to a point source. A system is described for making remote measurements of spatially resolved absolute diffuse reflectance and hence noninvasive, noncontact estimates of the tissue optical properties. The system incorporated a laser source and a CCD camera. Deflection of the incident beam into the camera allowed characterization of the source for absolute reflectance measurements. It is shown that an often used solution of the diffusion equation cannot be applied for these measurements. Instead, a neural network, trained on the results of Monte Carlo simulations, was used to estimate the absorption and scattering coefficients from the reflectance data. Tests on tissue-simulating phantoms with transport scattering coefficients between 0.5 and 2.0 mm(-1) and absorption coefficients between 0.002 and 0.1 mm(-1) showed the rms errors of this technique to be 2.6% for the transport scattering coefficient and 14% for the absorption coefficients. The optical properties of bovine muscle, adipose, and liver tissue, as well as chicken muscle (breast), were also measured ex vivo at 633 and 751 nm. For muscle tissue it was found that the Monte Carlo simulation did not agree with experimental measurements of reflectance at distances less than 2 mm from the incident beam.

Many studies have been undertaken trying to use various laser systems as optical drills on dental enamel and dentin, but the high radiant exposure needed and subsequent high temperature rises lead to fractures of the hard substances and possible damages to the pulp. Compared to the other laser systems, the use of the Er:Yag laser has given encouraging results. Optical and scanning electron microscopy showed only minimal if any damage of the surrounding tissue.

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The onset of caries is characterized by demineralization of dental hard tissues. Optimal fluoridation with respective oral hygiene habits and diet may stop the progression of a lesion and even allow for its remineralization. The aim of modern dentistry must be a preventive approach rather than invasive repair of the disease. This is possible only with early detection and respective preventive measures. Some of today's diagnostic tools are not sensitive enough to detect this early onset of destruction. Tools based on fluorescence could have the possibility to overcome this problem. This overview will focus on today's knowledge of one possible tool, the DIAGNOdent.