The effects of the Nd : YAG laser on amalgam dental restorative material.

The Nd:YAG laser has been marketed as an instrument for use on both hard an d soft dental tissues. Its potential for use on hard tissues is limited but it may be the instrument of choice for use in certain soft tissue procedur es. The aim of this study was to examine the effects of the Nd:YAG laser on amalgam restorations which are frequently placed on tooth surfaces adjacen t to areas of soft tissue which may be subjected to the laser. The amalgam used was Tytin. The laser firing was controlled by a computer and a constan t repetition rate of 40 Hz was used. Energy per pulse was altered as follow s: 30 mJ, 40 mJ, 60 mJ, 80 mJ, 120 mJ and 140 mJ. Exposure times of 0.05 s (2 pulses), 0.125 s (5 pulses), 0.25 s (10 pulses), 0.5 s (20 pulses), 1 s (40 pulses), 2 s (80 pulses), 3 s (120 pulses), 4 s (160 pulses), and 5 s ( 200 pulses) were used. The width of defect was measured using a measuring m icroscope with 10X magnification and it was established that the damage thr eshold lies between 0.125 s (5 pulses) and 0.25 s (10 pulses) for 30 mJ per pulse. Scanning electron microscope observations revealed that the melting of amalgam at exposure times of 5 s actually decreased the size of the obs erved defect, The data were analysed using a two-way ANOVA statistical test . There was a significant (p<0.001) correlation between the width of the de fect and exposure time up to an exposure time of 4 s and the width of defec t and the energy per pulse setting. The findings indicate that amalgam rest orations are damaged by inadvertent laser exposure and clinicians must take measures to protect such restorations during lasing of soft tissues.