Influence of Filling Technique on Fracture Resistance of Giomer-Restored Mod-Cavities

Aim: This study assessed the fracture resistance of upper premolars based on the placement technique of giomer restoration in MOD cavities. Materials and Methods: Seventy sound maxillary premolars were divided into five groups (n=14). A standardized MOD cavity was prepared in each tooth (2 mm buccolingual width, 2±0.2 mm central floor depth, and 4±0.2 mm proximal depth). Teeth were assigned to four experimental groups: Group I received Packable material (Beautifil II LS, Shofu Inc, Japan) applied in 2mm increments; Group II received Injectable material (Beautifil Flow Plus X, Shofu); Group III received a packable bulk-fill variant (Beautifil-Bulk Restorative Packable); and Group IV received flowable bulk-fill material (Beautifil-Bulk Flowable, Shofu), each followed by a 2mm occlusal capping layer. A fifth group of intact premolars served as the control. All specimens were embedded in self-cure acrylic resin blocks with simulated periodontal ligaments at temperatures ranging from 5 to 55°C, utilizing a thermocycling machine (SD Mechatronic Thermocycler, Germany). Fracture resistance was assessed using a universal testing machine (Instron 3345 Series, UK) at 1 mm/min crosshead speed. Data were analyzed using One-way ANOVA, followed by Tukey’s post hoc test. The level of statistical significance was set at p<0.05. Results: The results indicated a significant difference in fracture resistance across groups (p<0.001). The control group exhibited the highest strength (935.12±114.52 N), followed by the Packable (926.79±229.36 N) and Injectable groups (923.29±110.28 N), with no significant differences. In contrast, the Bulk-Restorative and Bulk-Flowable groups had the lowest strengths (684.20±163.60 N and 616.08±132.54 N, respectively). Post hoc comparison showed significantly lower fracture resistance values in the bulk-restorative and bulk-flowable groups (p<0.001). Conclusion: Incremental placement of packable or injectable giomers restored fracture resistance to levels comparable to sound teeth, while bulk-fill techniques yielded inferior outcomes.