Method: Specimens were divided into four groups (n=20) according to treatment as follows: Group 1-control, Group 2-pre-heated, Group 3-thermocycled and Group 4-heated plus thermocycled. Specimens were fabricated (2x2x25mm) and cured (700mW/cm2 , Optilux 501) in overlapping segments for 60 seconds. Groups 2 and 4 composite shades were heated to 55°C in a composite heater (T2, ENA Heat/Micerium) prior to curing. Specimens in Groups 3 and 4 were cycled from 5°C to 55°C for 1000 cycles, 10 second dwell time. Specimens were finished to 400 grit and stored in water at 37 °C for at least 24 hours before testing. The flexural strength test was conducted using the Instron machine at a crosshead speed of 0.5 mm/min. Data was analyzed using ANOVA and Tukey post hoc test at the 0.05 level of significance.
Result:
Mean (SD) flexural strengths, MPa, for various conditions are reported below:
Composite Shade |
Group1-Control |
Group2- Pre-Heated |
Group-3 Thermocycled |
Group-4 Pre-Heated Thermocycled |
Enamel |
130.1(31.3) |
122.5(23.3) |
95.0(12.9) |
94.6(16.1) |
Dentin |
152.4(33.8) |
141.9(19.6) |
114.2(23.5) |
120.9(30.9) |
The results of ANOVA showed significant main effects for composite shade (p<0.01) and temperature conditions (p<0.01). There was no significant interactions between shade and temperature conditions (p=0.92). Tukey post hoc test showed no difference between control and heated group (p=0.12), while the addition of thermocycling significantly reduced flexural strengths (p<0.01).
Conclusion: Heated microhybrid composite showed similar flexural strengths to the non-heated control (p=0.01). Thermocycling resulted in a significant reduction in flexural strength (p<0.01). The mean flexural strength between shades was highest among dentin shade (p<0.01) compared to enamel shade.
Acknowledgements: Thank you to SYNCA/Micerium for supplying materials.