Influence of filling technique on fracture resistance of giomer-restored MOD-cavities

Abstract 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. Clinical significance Clinicians frequently opt for bulk-fill restorative materials due to their efficiency and user-friendliness compared to traditional incremental layering techniques. However, evidence regarding the fracture resistance of giomers placed via different techniques remains limited. Injectable giomers represent a viable alternative, offering superior handling and precise adaptation while maintaining favorable mechanical properties. This study provides critical insights into optimizing placement strategies to balance clinical efficiency and biomechanical performance.