The Nd:YAG laser has been marketed as an instrument for use on both hard and 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 procedures. The aim of this study was to examine the effects of the Nd:YAG laser on amalgam restorations which frequently occur on tooth surfaces adjacent 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 constant repetition rate of 40 Hz was used. Energy per pulse was altered as follows, 30 mJ, 40 mJ. 60 mJ, 80 mJ. 120 mJ and 140 mJ. Exposure times of 0.05 sec (2 pulses). 0. 125 sec (5 pulses), 0.25 sec (10 pulses). 0.5 sec (20 pulses). 1 sec (40 pulses). 2 sec (80 pulses). 3 sec (120 pulses). 4 sec (160 pulses), and 5 sec (200 pulses) were used. The width of defect was measured using a Nikon measurescope with lOx magnification and it was established that the damage threshold lies between 0. 125 sec (5 pulses) and 0.25 sec (10 pulses) for 30 mJ per pulse. The data was analyzed using a one way ANOVA statistical test. There was a significant (p

The Nd:YAG laser has been marketed as an instrument for use on both hard and 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 procedures. 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 adjacent 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 constant repetition rate of 40 Hz was used. Energy per pulse was altered as follows: 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 microscope with 10ϫ magnification and it was established that the damage threshold 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 observed 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 defect and exposure time up to an exposure time of 4 s and the width of d e f e c t and the energy per pulse setting. The findings indicate that amalgam restorations are damaged by inadvertent laser exposure and clinicians must take measures to protect such restorations during lasing of soft tissues.