Optical technology for early caries detection and laser-induced hard dental tissue ablation have broad applications in dentistry. The basic research and development of new medical technologies related are the hot topics in the field of laser dentistry. Based on the development status of domestic laser dentistry and clinical needs, systematic studies on the composition changes induced by laser irradiation, water-mediated ablation, caries process accessment and evaluation of bonding ability between human dental tissue and restored materials were presentd in the dissertation.

The effect of Er:YAG (2.94 (am) and Er,Cr:YSGG (2.78 jam) laser irradiation under water spray on dentin component and surface morphology were examined. The microstructural changes induced by Erbium lasers with various laser parameters were observed by scanning electronic microscope (SEM),and compositional changes of human dentin were evaluated by Raman spectroscopy, respectively.

The exploratory experiments of water-mediated hard dental tissue ablation with pulsed CO2 (10.6 jam) and Ho:YAG (2.08 jam) laser were carried out. The dynamic interaction process between water and pulsed lasers were recorded by high speed camera.The pulsation period, the maximum length and width of vapor channel/cavitation bubble as a function of laser power were attained. On this basis, the dynamic process of hard dental tissue ablation induced by pulsed lasers under water environment was monitored to explore the ablation mechanism of water augmentation.

The caries processes of human molars from Chinese subjects were mornitored with spectral methods. The whole process of demineralization and remineralization in human dentin was evaluated using Raman spectroscopy and fluorescence spectrometer. The peak intensity changes of inorganic and organic constituents were compared and analysed.
The bonding ability between adhesives (self-etch and total-etch adhesives) and dentin (normal and caries-affected dentin) after Er:YAG laser preparation were systematicly studied. The micro morphology of the resin-dentin interface and shear bond strength were evaluated by confocal laser scanning microscope (CLSM) and material testing machine, respectively. The effect of various preparation methods on the bonding ability of different adhesives to the prepared dentin were compared and analysed.

Keywords: Pulse laser, caries, Dental tissue ablation, Raman spectra, High speed photography, Confocal laser scanning microscopy, Bond strength.dental laser tips,