OBJECTIVE: To assess the fracture resistance of maxillary premolars with mesio-occluso-distal (MOD) Class II cavities restored with lab composite and microhybrid resin composite, with or without a short fiber-reinforced composite (SFRC) base. METHODS: Fifty sound maxillary premolars were divided randomly into 5 groups (n = 10)
G1: Intact teeth (negative control), G2: Unrestored MOD cavities (positive control), G3: MOD inlay cavities restored with indirect lab composite, G4: MOD cavities restored with an SFRC base and microhybrid composite, and G5: MOD cavities restored with microhybrid composite. All specimens were thermocycled for 5000 cycles, then subjected to an axial static compressive load until fracture occurred. Failure modes were inspected. RESULTS: Negative control group exhibited maximum fracture resistance, whereas positive control revealed the lowest (p <
0.05). Microhybrid composite restorations with an SFRC base demonstrated fracture thresholds not significantly different from indirect lab composite (p = 0.22)
however, those without an SFRC base presented the least resistance to fracture among restored groups (p <
0.05). Cohesive failure of restorative material was mainly noted in the microhybrid composite group without an SFRC base, whereas adhesive failures were observed in all groups. CONCLUSIONS: The resistance of teeth to fracture is significantly influenced by the restorative material. Under compressive loads, the teeth restored with microhybrid composite restorations incorporating a short fiber-reinforced composite base exhibited comparable fracture resistance to laboratory composite restorations. CLINICAL SIGNIFICANCE: Considering that short fiber-reinforced composites revealed experimental outcomes comparable to those of indirect lab composites, along with the added benefits of shorter treatment time and cost-effectiveness, the direct approach becomes an ideal option for restoring teeth with Class II MOD cavities.