Effects of pulsed Nd:YAG laser radiation on action potential conduction in nerve fibres 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 threaded through the prepared pulp canal of a 10 mm long tooth root segment which was mounted in a perspex bath. The protruding ends of the nerve were placed on platinum wire electrodes used to elicit and to record compound nerve action potentials (CAPs). Laser energy (average POWER = 0.3–3.0 W) was applied to the surface of the root segment using a pulsed Nd:YAG dental laser (dLase 300). Results: With the laser probe tip placed in static contact with the tooth surface, the nerve CAP was irreversibly 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 mode, similar levels of radiation produced less marked effects. In the latter mode, CAP attenuation increased with increasing power and duration 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 lasing 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 dentine caused a dose-dependent block of action potential conduction in nerve fibres in the underlying pulp chamber.