Effect of Disposable Sheaths on the Vickers Microhardness of Resin Composites

Abstract

Objective:The aim of this study was to evaluate the effect of disposable sheaths on microhardness of resin composites.Methods: A total of 40 resin composite specimens were fabricated with disc-shaped perspex molds (5x2 mm). Specimens were divided into 4 groups: Irradiated by 1-Elipar LCU (EL), 2-Elipar LCU with sheath (ELS), 3-Valo LCU (VL), 4-Valo LCU with sheath (VLS), (n=10). The specimens were subjected to surface microhardness (SMH) test (Tronic, Digital Microhardness Tester DHV-1000) on the top and bottom surfaces under 200 g load applied for 10 s with a Vickers indenter. The specimens were stored in the distilled water at 37 °C for 24 hours and the same measurements were repeated. One-way ANOVA test, Tukey and Tamhane post-hoc tests were used for intergroup comparisons. Also paired sample t-test was used for comparisons of the different time results. Results:According to the 1st-hour data from the top and bottom SMH measurements, EL and VL groups have significantly higher microhardness values than VLS and ELS groups (p<0.05). There was a dependent change in the top surface measurements with the time (p=0.000), but also interaction with the LCU (p=0.000). All groups showed significant microhardness decrease from 1st to 24th-hour for both top and bottom values (p<0.05) except for top SMH of VLS group (p=0.151). Conclusion:Disposable sheaths decreased the light output of the LCU's and caused reduction in the SMH. Although they are effective in preventing cross-infection, they significantly reduced the polymerization efficiency, thereby mechanical properties of resin composites.