Changes in compressive strength of composite resin in different prepolymerization temperatures

In modern dentistry, resin composite is one of most usually used materials for restoration of hard tissues of teeth. At room temperature it is viscous; therefore border adaptation is more difficult. It was observed in clinical practices that when viscous composite is preheated before polymerization it becomes more plastic and after heating some more it gains fluidity. Therefore, aim of this study is to determine if different temperatures of prepolymerization heating affects the compressive strength of resin composites. Material and methods: 4 groups of resin composites were chosen: Micerium HRi Enamel Function, Micerium Enamel HRi Universal, Itena Reflectys, Syntheos. Preheating temperatures used with each composite group: control – room temperature (20 ± 2) (KT), 39o C ± 2 (T1), 55o C ± 2 (T2), 68° C ± 2 (T3), repeated heating was also used (raising of temperature to 55° C ± 2, cooling down to room temperature; three cycles were repeated) (T4). Samples (ø 5 x 6mm) were made according to manufacturer‘s instructions, 10 samples in each group. Compressive strength (MPa) of samples was examined using special testing machine till complete decay. Statistical data analysis was carried out using data storage and analysis application pack SPSS 22. Results: after heating of resin composite, higher level of fluidity of material was observed. Higher compressive strength of samples was found when preheating temperature was T2, T3, T4 (p < 0,05) when compared to control group. Statistically significant reduction of compressive strength was not observed in any of the groups when compared to control group (p < 0.05). Conclusions: Raising of prepolymerization temperature of examined resin composites results in higher compressive strength of restoration (p < 0,05). Also it was found that three repeated thermal cycles does not lower the compressive strength (p < 0,05)