Purpose:This study measured the temperature increase induced by various types of curing units during resin cement polymerization under ceramic restorations. Materials and Methods:The resin cement was polymerized between a ceramic specimen (diameter 5 mm, height 2 mm) and a dentin disk (diameter 5 mm, height 1 mm) with a conventional halogen light, a high-intensity halogen light, a plasma-arc light, and a light-emitting diode unit. The temperature increase was measured under the dentin disk with a J-type thermocouple wire connected to a data logger. Ten measurements were carried out for each curing unit. Difference between starting and highest temperature readings was measured, and the 10 calculated temperature changes were averaged. Results:Temperature increase varied significantly depending on curing unit used. The plasma-arc light induced significantly higher temperature increases than any other curing unit. The light-emitting diode unit produced the lowest temperature changes. There were no statistically significant differences between the conventional and highintensity halogen curing units. Conclusion:Polymerization with curing units characterized by high energy output (plasma-arc light) caused higher temperature changes compared to other curing units, but the temperature increase detected was not viewed as critical for pulpal health. Int J Prosthodont 2004;17:200–204.