In 1993 laser dentistry will be 30 years old. Stem, one of the pioneers of dental laser research, dedicated his activity to the investigation of how a very powerful light interacts with the tooth structure. As we know, laser radiation, or light energy has to be converted into some other form of energy in order to produce a therapeutic tissue effect. The atoms and molecules that comprise biological tissue are ultimately responsible for absorbing laser radiation and converting it into other energy forms. Laser-tissue interactions are often categorized according to whether laser energy is converted into heat, chemical energy or acoustic (mechanical) energy. Today in dentistry, C02 and Nd:Yag lasers are available for clinical applications. Both of them emit an infrared type of radiation which interacts with the tissue through a thermal effect. This type of interaction with the tissue has to be carefully controlled. This thermal effect, however, can cause complications by damaging the pulp or the surrounding tissues of the tooth. In 1972 a report by R. Stern showed that over an applied density Of energy of 25 joules/cm2 from a CO2 laser, enamel shows cracks, microfractures and a crumbly mineralized structure. The water content of tissue usually plays a dominant or important role in the absorption of laser energy, specifically for the C02 laser beam. In vivo studies have shown that because enamel contains only 2.3% water the transfer of heat through the dentinal layer to the pulp chamber occurs very fast and pulpal tissue can be damaged when enamel is irradiated.2 When enamel is exposed to a CO2 laser beam with a density of energy of 20 to 200 joules/cm2 the intrapulpal temperature increased from 5.5°C to 32°C above body temperature.3 The conclusion was that, for cavity preparation, the use of a C02 laser would be limited for sterilization of dentinal surfaces. The Nd:Yag lasers appear to cause less damage to the pulp. Even when the energy was more than twice the maximum energy delivered by a C02 laser, no coagulation or necrosis occurred. This wavelength has also been tested successfully on pits and fissures of monkeys with an energy density of 20 to 120 joules/cm2. Minimal changes on histological examination of the pulp have been found.4'5 In 1987 a remark was made by Launay and Mordon, ",,.medical lasers have been tried on dental tissues, but the effects of the lasers on the pulp have not been studiedt'. Immediately after that, the conclusions were that more research and quantitative analysis of laser thermal effects on the dental tissues was needed6 Since that time, different authors have reported quantitative results of the thermal effects analysis. Our intention was to explore new methods to facilitate dissipation of surface heat generated by laser exposure of enamel to a pulsed Nd:Yag laser beam. The pupose of the study was to compare the elevation of temperature inside the )ulp chamber at different levels of energy, for different methods of cooling and without cooling during the exposure of enamel to a pulsed Nd:YAG laser beam.