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Purpose: To three-dimensionally evaluate the interfacial gap of bulk-fill resin composites applied in deep Class-I restorations with different layering techniques and curing modes. Materials and Methods: Ninety-six (n = 96) samples were prepared with standardized deep Class-I cavities and adhesive procedures. Four materials were tested: SDR (SDR), SonicFill2 (SF), Admira Fusion X-Tra (AFXT), Filtek Supreme XTE (FS). Four subgroups (n = 6) were created according to layering and curing techniques: 2+2mm increments with soft start curing (SG1), 2+2 mm with conventional curing (SG2), a 4-mm increment with soft start curing (SG3), a 4-mm increment with conventional curing (SG4). All samples underwent micro-CT scans; afterwards, voids surrounding the restorations automatically underwent a thresholding procedure (Mimics, Materialise; Geomagic Studio 12, 3D Systems) to analyze the 3D interfacial gap. Statistical analysis was performed using three-way ANOVA with Tukey’s test (significance p < 0.05). Results: Statistically significant differences were reported between materials, layering techniques and their interaction. No statistically significant differences were reported for polymerisation mode. Bulk-fill materials showed average interfacial gap volumes ranging from 0.031 mm³ to 0.200 mm³, while FS showed volumes ranging from 0.416 mm³ to 1200 mm³. Conclusions: All bulk-fill materials performed statistically significantly better than did FS (p < 0.05), with no statistically significant differences between them. Curing mode did not influence interfacial gap volume in any group (p > 0.05), while bulk-filling vs layering influenced the volume of interfacial gaps only in the FS group, which performied better when incrementally applied. Regarding gap localisation, the floor of the cavity was the area with the highest likelihood of gaps in all samples. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this in vitro study was to evaluate the effect of three different CAD/CAM processed materials on the interfacial gap, wear, and fracture resistance of endodontically treated molars. Materials and Methods: 48 maxillary molars were selected and endodontically treated. On each specimen a standardized MOD cavity was prepared. Specimens were then divided in two groups (n = 24 each) according to the build-up technique employed: G1) build-up with a bulk fill composite material (Admira Fusion X-Tra, Voco); G2: fiber post-supported buildup. Then, a 2-mm-thick standardized overlay preparation exposing enamel margins was performed. Specimens were scanned with Cerec Omnicam (Denstply Sirona) and the indirect restoration was milled with Cerec MXCL. Each group was divided into 3 subgroups (n = 8 each) according to the CAD/CAM material employed: SG1) Grandio-Bloks (Voco); SG2) Cerasmart (GC); SG3) Celtra Duo (Dentsply). Each overlay, once completed, was luted following a standardized procedure. All specimens were scanned with micro-CT at high-resolution scans (voltage 100kV, current 80A, source-to-object distance 80 mm, source-to-detector distance 220 mm, pixel binning 292, exposure time/projection 3 s). Then, specimens of each group were subjected to mechanical fatigue testing in a dual-axis chewing device (CS-4.4, SD Mechatronik). A force of 5 kg was applied using a ceramic steatite ball for 500,000 cycles. After fatigue, micro-CT scanning was performed to evaluate the interfacial gap. Replicas were obtained for external gap evaluation with SEM. Micro-CT images, before and after cycling load, were analyzed with Geomagic Software and Mimics to evaluate interfaces gap progression before and after mechanical load. Statistical analysis was performed with two-way ANOVA. Results: The interfacial gap was not significantly influenced by the build-up technique (p = 0.061). SG2 and SG3 showed a smaller gap (p = 0.001) and a higher fracture resistance rate (p = 0.0001). No differences were found between SEM and 3D gap evaluation. Conclusion: Interfacial gap and fracture resistance could be influenced by the CAD/CAM material employed to restore endodontically treated molars. [ABSTRACT FROM AUTHOR]