[Spectroscopically controlled preparation of hard tooth structures using a UV laser]

During preparation of hard tooth structures with a 193nm-(ArF)*-excimer laser, the laser beam produces a specific fluorescent light whose spectrum is governed by the structure of the specimen. These fluorescence spectra allow an analysis of the removed tissues. The data thus obtained may be used to control the laser system so that only specific structures, such as carious tissue, are removed: reproducible fluorescence spectra were established by means of standardized samples (pure synthetic hydroxyl apatite ceramics, enamel, dentine and carious dentine) and the characteristic absorption bands (peaks) for the different substances were measured. With the aid of electronic data processing these reference spectra could be compared with the fluorescence spectra obtained during preparation. When a spectrum differed from the predefined limits of relative intensities, preparation was stopped. Since ablation per pulse is only to a small depth (0.04-4 microns) with the 193nm-(ArF)*-eximer laser, this feedback system of ablation and fluorescence spectroscopy allows decisions as to continuing or stopping the preparation process to be taken within the range of a few microns.