In-vitro Pulp Temperature During Setting of Temporary Restorations

Objective: To assess the influence of material and type of restoration on pulp temperature during setting of temporary crowns or bridges. Method: One extracted canine, premolar and molar each was prepared for receiving a crown or bridge, equipped with a thermocouple probe in its pulp chamber and embedded in a gypsum model of an alveolar ridge at position 3, 5 and 7, respectively. Model and surrounding experimental chamber were kept at 36°C. Nine materials for temporary restorations were selected for the study: seven chemically curing resins (six dimethacrylate composites, one PEMA) and two light curing resins (one dimethacrylate composite, one PMMA). With all materials being at 23°C initially, the following types of temporary restorations were fabricated sevenfold each, using silicone impressions as a mould in direct technique: bridge 3-7, bridge 5-7 and crown 7. Additionally, bridges 3-5, crowns 3 and crowns 5 were each made exemplarily with two materials. During setting of the resins, pulp temperatures were recorded by means of a digital multimeter and a PC. Maximum differences to initial temperatures (dTmax) were determined for each sensor location and subjected to univariate analyses of variance and Tamhane tests in order to detect significant influences of material or type of restoration. Results: All temperature curves showed an initial drop due to cooling by the relatively cold resin. With increasing generation of reaction heat, temperatures rose, but seldom exceeded 36°C again during experiments. Highest temperatures were observed for bridge 3-7 in the central abutment’s pulp chamber, the highest single value for dTmax being only +1,7 K. Both material and type of restoration had a statistically significant effect on dTmax. Conclusions: With all materials tested, critical pulp temperatures of 41°C and higher are unlikely to occur during fabrication of temporary restorations, even under more unfavourable conditions than those prevailing in this study.