The Effect of Surface Pretreatments on the Bond Strength of Hybrid CAD/CAM with Composite Elevation

In computer-aided design/computer-aided manufacturing (CAD/CAM) restorations for severely damaged teeth, the cavity floor or proximal margins may be elevated with composite resin to improve adhesion. This in vitro study investigated how different surface pretreatment methods affect the shear bond strength (SBS) of hybrid CAD/CAM materials to dentin or composite surfaces, simulating clinical situations of composite elevation. Hybrid CAD/CAM samples were bonded to dentin or composite substrates following different surface pretreatment protocols and cemented using a dual-cure adhesive resin cement. The samples were thermocycled and subjected to shear bond strength testing, and failure modes were analyzed. The SBS in the sandblasting (SB)+Dentin group and hydrofluoric acid (HF)+Dentin was significantly higher than that in the SB+Composite and HF+Composite groups (p < 0.05). Untreated+composite and untreated+dentin groups showed significantly lower SBS (p < 0.05). Failure mode analysis revealed a predominance of cohesive failures in the SB+Dentin group, while adhesive failures were more frequently observed in most of the other groups. SB-treated and HF-etched hybrid CAD/CAM materials showed more favorable bonding behavior to dentin than to composite, highlighting that bonding to the elevated composite layer may be less effective than bonding directly to prepared dentin.