Hard Biotissue Ablation With Pulse Lasers And Its Novel Medical Technology

Laser-induced hard biotissue ablation has broad applications in dentistry and bone surgery, the related basic research and development of new medical technologies are the hot topics in the field of laser surgery and medicine. Systematic studies on hard biotissue ablation charactcristics, dynamic light dosimetry, and water-mediated ablation with typical wavelength of lasers were presented in the dissertation by combining theoretical analysis and experimental means. The exploratory experiments of novel v medical technologies based on laser-induced hard tissue ablation were also provided.At first, the fundamental interactions of hard biotissue with lasers were reviewed, and the knowledge for understanding laser-induced hard biotissue ablation was provided. The quantities to describe laser-tissue ablation were presented, the optical, thermal and mechanical properties of hard biotissue were summarized, and tissue model and mechanism of laser-induced hard biotissue ablation, as well as light dosimetry were discussed.The ablation characteristics and dose-effect relationship of dental hard tissue (enamel and dentin) and middle ear mastoid bone in vitro irradiated with Er: YAG (2.94μm), Er,Cr:YSGG (2.78μm) and CO2 (10.6μm) lasers were reported. The related ablation threshold and the dependents of ablation crater geometry, thermal injury, ablation rate and efficiency, as well as the morphological and micro-structural changes, on incident radiant exposure were evaluated.A novel concept, dynamic light dosimetry, was first presented. The definition and formula expression of related quantities, such as pulse overlap factor, the equivalent number of pulses, ablation rate and efficiency, were deduced. Then, experimental study of one-dimensional dynamic ablation of hard biotissue with pulse CO2 laser (10.6μm) was carried out to evaluate the influence pf scanning velocity and defocus conditions on ablation effects.Water-mediated hard bone tissue ablation with pulse CO2 laser (10.6μm) was systematic studied firstly. The influence of water flow rate and the thickness of water film attached on target tissue surface on ablation effects, such as the appearance of ablation incision, ablation rate and efficiency, thermal injury and morphological and micro-structural changes, were evaluated with stereomicroscope, OCT, histopathology, and scanning electron microscopy.The exploratory experiments of novel medical technologies based on laser ablation were carried out. Laser ablation technology was firstly introduced to perform fenestration surgery with a big size on middle ear mastoid bone of rabbit in vivo, and the feasibility, validity, and safety of pulse CO2 (10.6μm) and Er:YAG (2.94μm) lasers to perform this kind of surgery were evaluated. In addition, the feasibility of above two laser systems to perform skull surgery on rabbit in vivo was also assessed.