Effect of Intermediate Layer Thickness of Stress-decreasing Resin Composite on the Fracture Resistance of teeth restored with Resin Composite Restorations: An In-Vitro Study

Background: Conventional composite resins can develop stress during the hardening process, which can lead to problems in restoring maxillary premolars with MOD cavities. These problems include reduced durability and compromise mechanical performance. Aim of the study: This study aimed to compare the effects of 1-mm and 3-mm SDR thicknesses as an intermediate layer on the fracture resistance of MOD cavities in maxillary premolars. Materials and Method: A total of 20 sound maxillary premolars were selected and MOD cavities were prepared with specific dimensions. The teeth were divided into 2 groups, Group I (GI) is restored with 1 mm SDR (SDR Plus, Dentsply Sirona) as an elastic flowable liner while Group II (GII) is restored with 3mm SDR base, followed by using universal composite (Essentia Universal, GC, Japan) to fill the cavity. The restored teeth were then subjected to axial loading in the universal testing machine. The quantitative data was checked for normality using Shapiro-wilk test, and a parametric statistical test; Student’s t-test was used to compare between both groups. Results: GII using SDR flowable bulk-fill base, demonstrated significantly higher fracture resistance (539.34 ± 108.09 N) than Group I (539.34 ± 108.09 N), which used SDR flowable cavity liner. Conclusion: SDR as an intermediate layer improved fracture resistance in MOD restorations, with a 3-mm thickness being more effective than a 1-mm thickness.