Effect of Preheating and Modelling Instrument Temperature on Composite Cooling

Objectives: To measure the kinetics of composite cooling, as a function of preheating and modelling instrument temperature.
Methods: A Class II cavity was prepared in a human third molar. The tooth was placed in the custom-made sample holder and kept in a water bath at 36°C. A K-type thermocouple was placed at the axial-gingival wall junction through a microperforation from the inside of the pulp chamber. Depending on the composite and modelling instrument temperature, four groups were defined:
Group 1: Composite and instrument at room temperature (23°C)
Group 2: Instrument preheated to 68°C, composite at 23°C
Group 3: Composite preheated to 68°C, instrument at 23°C
Group 4: Composite and instrument preheated to 68°C
Within 7±1s of compule removal from the heater, composite (Filtek Bulk Fill Posterior, 3M ESPE) was injected to fill the entire cavity and condensed with a stainless steel dental ball burnisher. Temperature was monitored at 1 scan/s rate using a PC and a data-logger (Measurement Computing). Data were statistically analyzed using one-way ANOVA with Tukey's post-test and t-test for independent samples at α=0.05.
Results: In groups 3 and 4 the highest temperatures were recorded 3-4s post-placement (mean± sd: 44.50±0.18°C; 43.19±0.11°C, respectively; p>0.05). At 15s and 30s post-placement, significantly higher temperature values were found in group 3 (40.25±0.44°C; 38.32±0.55°C, respectively) and group 4 (40.45±0.32°C; 38.76±0.97°C, respectively) than in group 1 (34.91±0.34°C; 35.44±0.31°C, respectively) and group 2 (36.35±0.83°C; 36.98±0.48°C, respectively) (p<0.05). No significant differences were found between groups 3 and 4 at all time intervals (p>0.05). Group 2 showed significantly higher temperatures than group 1 at 15s and 30s post-placement (p<0.05).
Conclusions: Composite preheated to 68°C increased temperature at the cavity bottom up to 7-8°C and cooled down to around 40°C within 15s post-placement. Instrument preheating had no additional effect on temperature increase or slower cooling of already preheated composite.