[Effects of soft laser irradiation on dentinal pain]

The use of soft lasers in dental therapy has increased dramatically in recent years. However, there is a dearth of reports in the literature of controlled in vivo and in vitro studies of soft laser effectiveness with respect to dentinal pain. The purpose of this study was to assess the analgesic effects of soft laser treatment by the following five studies: (1) Clinical evaluation of soft laser irradiation of hypersensitive dentin. (2) Morphological study of dentinal surfaces following soft laser irradiation. (3) Study of the effect of soft laser irradiation on dentinal fluid movement. (4) Study of the effect of soft laser irradiation on the jaw opening reflex (JOR) in rats. (5) Study of thermal changes on the internal wall of pulp chamber with soft laser irradiation. After soft laser treatment of 3 min to hypersensitive dentin, patients experiences diminished sensitivity in 46 of 55 teeth (83.6%). In model experiment with extracted human teeth, the energy levels of this laser were too low to produce any morphological changes on the surface of exposed dentin, and dentinal fluid movements induced by air blasts for 15 sec to exposed dentin were not affected by laser irradiation to the dentin for 3 min. Moreover, there was an immediate 0.7 degree C increase in the temperature of the internal wall of the pulp chamber by laser irradiation to the tooth surface. In experimental rats, the digastric EMG induced by 1.3 x T (T: threshold value producing the JOR) was reduced by 3 min soft laser irradiation to teeth or Ho-ku points, but not at 2.0 x T. These results suggest that soft lasers have an analgesic effect, but the latter is affected by the degree of stimuli-elicited pain, and may be due in addition to descending inhibition in the central nervous system.