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The determination of the thermal effects of Nd:YAG laser energy on enamel and dentin is critical in understanding the clinical applications of caries removal and surface modification. Recently extracted non-carious third molars were sterilized with gamma irradiation. Calculus and cementum were removed using scaling instruments and 600 grit sand paper. The smear layer produced by sanding was removed with a solution of 0.5 M EDTA (pH 7.4) for two minutes. Enamel and dentin surfaces were exposed to a pulsed Nd:YAG laser with 150 microsecond(s) pulse duration. Laser energy was delivered to the teeth with a 320 micrometers diameter fiberoptic delivery system, for exposure times of 1, 10 and 30 seconds. Laser parameters varied from 0.3 to 3.0 W, 10 to 30 Hz and 30 to 150 mJ/pulse. Other conditions included applications of hot coffee, carbide bur in a dental air-cooled turbine drill and soldering iron. Infrared thermography was used to measure the maximum surface temperature on, and thermal penetration distance into enamel and dentin. Thermographic data were analyzed with a video image processor to determine the diameter of maximum surface temperature and thermal penetration distance of each treatment. Between/within statistical analysis of variance (p <EQ 0.05) determined a difference existed between enamel and dentin in thermal effects from the Nd:YAG laser. Enamel had lower maximum surface temperatures than dentin for all laser powers and times. The surface temperature ranged from 34 +/- 1 degree(s)C to 110 +/- 4 degree(s)C on enamel and 62 +/- 5 degree(s)C to 392 +/- 82 degree(s)C on dentin. As power and time of exposure increased, both the maximum surface temperature and thermal penetration distance increased. The greatest length of thermal effect on the surface (11.0 +/- 0.9 mm) and thermal penetration distance (4.7 +/- 0.4 mm) recorded were caused by the air-cooled turbine drill on dentin. Surface temperatures were much higher for the Nd:YAG laser applied to enamel and dentin than those of the air-cooled turbine drill with carbine bur. Although temperatures created with the laser were higher, the diameter of the hot spot on the surface and the thermal penetration distance in the pulpal direction were significantly less than those of the dental drill. Therefore, the pulsed infrared Nd:YAG laser, with 320 micrometers fiber optic delivery, can be applied to enamel and dentin without detrimental thermal pulpal effects.
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