Shrinkage stress of high and low viscosity bulk-fill composites with incremental and bulk fill techniques

Abstract

Purpose Evaluate shrinkage stress of incremental and bulk filling techniques of high and low viscosity bulk fill nanohybrid resin-based composites (RBCs) by assessing cuspal deflection, microleakage, and gap formation. Flexural modulus of different RBCs was also studied. Patients and methods Eighty molars were divided into four groups according to the type of RBCs. Each group subdivided into two subgroups (n = 10) depending on application techniques; A: bulk fill and B: incremental filling. Buccal and palatal cuspal deflection was measured by strain gauge. All teeth were subjected to several steps to evaluate cervical microleakage% by Stereomicroscope. Scanning electron microscope was used to estimate gap formation%. Flexural modulus was measured by three-point bending test. Kruskal–Wallis's test was used for comparison of quantitative variables and post hoc test was used for multiple comparisons. χ2 test was used to test the qualitative data. P value less than or equal to 0.05 was considered statistically significant. Results Cuspal deflection: bulk filled teeth of low viscosity SDR flow (group III) and incremental filled teeth of the four groups were not significantly different from each other and were significantly lower than bulk filled teeth of high viscosity materials. Cervical microleakage%: the lowest scores were recorded in group II and group III which were not significantly different between both application techniques. Gap formation%: the two lowest means % were recorded for bulk filled teeth of group III and incremental filled teeth of group IV. There was a positive correlation between cuspal deflection, cervical microleakage% and gap formation%. Flexural modulus of group III was significantly lower than other groups which were not significantly different from each other. Conclusion Incremental filling technique was the best technique to decrease contraction stress and its complications. Bulk filling technique of low viscosity SDR achieved comparable results to incremental filling technique.