Objective: The aim of this in vitro study to compare µTBS of two low shrink, TCD- based and dimer acid-based and one flowable SDR-based bulk-fill, resin composites; on the bottom of high C-factor cavities.
Materials & methods: Thirty extracted noncarious human mandibular molars were used in the study. The occlusal enamel, in each tooth, was cut parallel to the occlusal surface, to expose a flat dentin surface. The cut teeth were randomly divided into two main groups (n=15), depending on the preparation of dentin i.e., group I: high C-factor occlusal class I cavity, and group II: flat dentin surface at the same depth of the cavity floor. Single Bond Universal adhesive was used to bond the resin composites to dentin in the two groups. Teeth in each group were further subdivided into three subgroups (n=5) according to the restorative materials used. In subgroup a: Surfil SDR flow, bulk-fill flowable resin composite. In subgroup b, TCD-DI-HEA based, Charisma Topaz, nano-hybrid resin composite. In subgroup c, DDCDMA based, N'Durance, nano-hybrid resin composite. All the samples were subjected to 5000 cycle, thermocycling. Each specimen was sectioned longitudinally in both mesio-distal and bucco-lingual directions to obtain four beams per each sample. A total of 20 sticks were collected from each subgroup and subjected to µTBS evaluation using universal testing machine and the results were then subjected to statistical analysis. The fractured surfaces were inspected under a stereomicroscope to determine the failure modes.
Results: The collected data were subjected to two way AOVA, followed by Tuky's post hoc test. Dentin preparation factor afforded insignificant higher µTBS values with samples prepared in flat dentin surface compared to Samples with high C-factor class I cavities, when TCD- based, restorative material was used. DDCDMA based, ND, nanohybrid and SDR-based restorative material resulted in significant increase in the µTBS when applied to the flat dentin surfaces in comparison with the high C-factor class I cavities. The three restorative materials were arranged in a descending order from TCD- based, DDCDMA based, followed by SDR resin, with no significant difference, when applied to the flat dentin surfaces. Yet, with high C-factor class I cavity restorations, µTBS in SDR-based resin revealed the lowest significant values. Most of the failure modes are adhesive in nature.
Conclusions: Under the conditions of the present study, it might be concluded that TCD-based low-shrink resin composite investigated in this study perform well, in terms of compensation of polymerization shrinkage at the restoration/dentin interface and µTBS in high C-factor cavities. Conversely, the investigated Dimer acid-based and low-viscosity bulk-fill material based on SDR technology demonstrated unfavorable performance in high C-factor cavities.