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Influence of Bonding Strategies on the Fracture Resistance and Failure Mode of CAD/CAM Resin Composite Overlays
Ali A Elkaffas1,2, Abdullah Alshehri1, Ali R Alqahtani1
1Department of Conservative Dental Sciences, College of Dentistry, Prince Sattam Bin Abdulaziz University, Alkharj, Saudi Arabia.
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.
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