The purpose of this study was to evaluate the temperature rise during polymerization of three different provisional materials by direct method on two different dentin disc thicknesses. Two autopolymerizing; bis-acrylic composite (Fill-in; Kerr), polymethyl methacrylate (Temdent; Weil Dental), and one light polymerizing composite (Revotek LC; GC) provisional restoration materials were used in this study. Sixty dentin discs were prepared from extracted molars (diameter, 5 mm; height, 1 or 2 mm). These dentin discs (1 or 2 mm) were placed on apparatus developed to measure temperature rise. The temperature rise during polymerization was measured under the dentin disc with a J-type thermocouple wire that was connected to a data logger. Statistical analysis was performed with two-way analysis of variance followed by Tukey HSD test (alpha=0.05). Temperature rise values statistically varied according to the provisional restoration material used (light polymerized, auto polymerized; P < 0.001) and the dentin thickness (1 and 2 mm; P < 0.001). The polymethyl methacrylate based provisional material induced significantly higher temperature rise than other provisional restoration materials at 2-mm dentin thickness (P < 0.01). At 1-mm dentin thickness, polymethyl methacrylate and composite induced significantly higher temperature increase than bis-acrylic composite provisional material (P < 0.05). The risk for heat-induced pulpal damage should be taken into consideration during polymerization of provisional materials in deep cavities in which dentin thickness is less than 1 mm.