Effect of Stress Generated by Occlusal Cyclic Force on Class I Bulk-Fill Composite Restoration Microleakage

Objective This study aimed to evaluate the effects of different types and restorative techniques of Class I composite restorations with a single loading force on stress distribution and cyclic loading force on microleakage formation. Materials and Methods Class I cavities were prepared in premolars with 4 mm depth and divided into six groups of different restorations with: (1) Filtek Z250; (2) a 3-mm-thick layer of Filtek Bulk Fill Flowable Restoration and covered with Z250; (3) a 1.5-mm-thick layer of flowable composite and covered with Z250; (4) lining all cavity with flowable composite and restored with Z250; (5) Filtek Bulk Fill Posterior Restoration; and (6) lining all cavity with flowable composite and restored with bulk-fill composite. The specimens with and without cyclic occlusal loading were subjected to microleakage observation. In addition, six different models of Class I restorations corresponding to the microleakage study were generated. Finite element analysis (FEA) was used to identify the stress distribution under a single loading force. Statistical Analysis Data were statistically analyzed by two-way analysis of variance and multiple comparison. The significance level set at 0.05. Results Cavity lining or restoration with flowable composite underneath conventional composite reduced stress on composite resin based on FEA (groups 2 and 3). The cyclic stress on composite increased microleakage. Restoration with flowable composite underneath conventional composite reduced the microleakage in Class I restoration (groups 2, 3, and 4). Conclusion The most effective cavity lining with a flowable composite underneath conventional composite restoration was stress reduction under loading force resulting in microleakage reduction.