EFFECTS OF PULSED ND-YAG LASER-RADIATION ON ACTION-POTENTIAL CONDUCTION IN NERVE-FIBERS INSIDE TEETH IN-VITRO

Objective: This study aimed to simulate the effects of lasing dentine on pulpal nerve function. Methods: Rat spinal nerve roots were threade d through the prepared pulp canal of a 10 mm long tooth root Segment w hich was mounted in a perspex bath. The protruding ends of the nerve w ere placed on platinum wire electrodes used to elicit and to record co mpound nerve action potentials (CAPs). Laser energy (average power = 0 .3-3.0 W) was applied to the surface of the root segment using a pulse d Nd:YAG dental laser (dLase 300). Results: With the laser probe tip p laced in static contact with the tooth surface, the nerve CAP was irre versibly abolished within 60 s of lasing at 1.0-3.0 W power. When the laser tip was moved to and fro over the root surface in a scanning mod e, similar levels of radiation produced less marked effects. In the la tter mode, CAP attenuation increased with increasing power and duratio n of lasing. After 60 s lasing at 0.3 W, the CAP size was 95% (+/- 5, S.D.) of the prelasing controls value; with 2.0 W the CAP was reduced to 54% (+/- 33). The CAP recovered to 90% of control levels after lasi ng at powers up to 1.5 W, but reached only 72% of control values after lasing at 2.0 W power. Conclusions: Laser radiation applied to dentin e caused a dose-dependent block of action potential conduction in nerv e fibres in the underlying pulp chamber. (C) 1998 Elsevier Science Ltd . All rights reserved.