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.
Institute of Biomedical and Life Sciences, University of Glasgow, UK. R.Orchardson@bio.gla.ac.uk
R
R
Orchardson
J M
JM
Peacock
C J
CJ
Whitters
D000200:Action Potentials / Q000502:physiology / Q000528:radiation effects*; D000538:Aluminum Silicates; D000818:Animals; D003782:Dental Pulp / Q000294:innervation*; D003786:Dental Pulp Cavity / Q000294:innervation; D003804:Dentin / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007834:Lasers; D008963:Molar; D009354:Neodymium; D009412:Nerve Fibers / Q000502:physiology / Q000528:radiation effects*; D009431:Neural Conduction / Q000502:physiology / Q000528:radiation effects*; D051381:Rats; D011930:Reaction Time / Q000502:physiology / Q000528:radiation effects; D013126:Spinal Nerve Roots / Q000502:physiology / Q000528:radiation effects; D013997:Time Factors; D015019:Yttrium
D000538:Aluminum Silicates; D009354:Neodymium; D015019:Yttrium