Influence of Bonding Strategies on the Fracture Resistance and Failure Mode of CAD/CAM Resin Composite Overlays Following Simulated Aging: An In Vitro Comparison.

OBJECTIVE

To assess the influence of various bonding protocols on the fracture resistance and failure mode of CAD/CAM-milled hybrid resin composite occlusal overlays.

MATERIALS AND

METHODS

Fifty sound human premolars (n = 50) were sectioned to expose superficial dentin surrounded by enamel. Each specimen was digitally scanned and restored with a CAD/CAM-milled hybrid resin composite overlay designed in Exocad DentalCAD. The restorations were assigned to five groups (n = 10) based on the luting protocol: Group I, Calibra Ceram; Group II, SDR Flow; Group III, heated Grandio; Group IV, Panavia F2 (self-etch), and Group V, Calibra Universal (self-adhesive). All specimens underwent thermomechanical aging simulating 1 year of clinical service, followed by compressive load testing at 1 mm/min until fracture. Failure modes were examined under magnification. Statistical significance was set at p < 0.05.

RESULTS

Group III (heated Grandio) exhibited the highest mean fracture load (1728.28 ± 156.64 N), whereas Group II (SDR Flow) showed the lowest (835.49 ± 151.69 N). Groups I, IV, and V demonstrated intermediate, statistically comparable values (p > 0.05). Tukey's HSD confirmed significant differences between Groups II and all others (p < 0.001) and between Group III and Groups IV-V (p < 0.001).

CONCLUSIONS

Bonding strategy significantly affects the mechanical performance of hybrid resin composite overlays. All tested protocols achieved clinically acceptable strength based on ISO DIS 6872, confirming milled hybrid resin overlays as a conservative and durable restorative option.

CLINICAL SIGNIFICANCE: Selecting an optimal bonding strategy, particularly using heated resin composites, can enhance the durability and fracture resistance of conservative CAD/CAM hybrid resin overlays, offering a viable minimally invasive alternative to full-coverage crowns.