Laser hard tissue interactions: energy transmission through human dental tissue using a holmium:YAG laser

摘要

Abstract: Laser energy transmission through hard tissue was investigated using a pulsed Holmium:YAG laser (2.12 $mu@m wavelength). The surface of extracted human dental tissue, 200 $mu@m to 700 $mu@m in thickness, was irradiated by a laser beam of various fluences between 3 J/cm$+2$/ to 28 J/cm$+2$/. The transmitted energy through different dentinal components of the tooth was measured. For the mature teeth, the region of the dentinoenamel junction showed the least transmission and the coronal the most; the difference between the two regions could be as large as 20%. The unerupted or young teeth revealed the opposite transmission characteristics. Repeated laser treatment revealed an enhanced transmissibility and the transmitted energy reached a plateau after certain irradiation exposure. Also studied were the effects of various media on the dental transmissibility. For example, surface application of a smear layer of unfilled resin did not change the transmissibility but appeared to slow down the temperature build-up. Visible surface damage - a yellow or a white spot on the treatment site - appeared when the fluence reached beyond 20 J/cm$+2$/. SEM samples revealed three different surface structural changes: melting with tubule closures, surface removal with tubule exposures, and surface cracking with crater formation, depending on the level of irradiation. !30