Surface Treatment and Pre-Repair Thermal Aging Effects on Repair Bond Strength of Resin-Matrix CAD/CAM Ceramics

Conservative repair motivates investigation of bonding to heterogeneous restorative substrates. This in vitro study evaluated initial composite repair shear bond strength (SBS) following surface conditioning of aged and non-aged resin-matrix CAD/CAM materials. VITA Enamic, GC Cerasmart, and Shofu Block HC received either 25,000 pre-repair thermal cycles or no thermocycling, followed by ground control, hydrofluoric acid (HF), Al2O3 abrasion, CoJet, or diamond bur treatment (n = 7/cell; 210 specimens). Following silane, universal adhesive, and composite application, SBS was tested at 1 mm/min. Three-way ANOVA identified surface treatment as the largest main effect (partial η2 = 0.694), with significant material × surface treatment (p < 0.001) and three-way (p = 0.016) interactions. The post-hoc pattern was particularly associated with Al2O3-treated GC Cerasmart: SBS decreased from 15.55 to 7.54 MPa after pre-repair aging (Bonferroni-adjusted p < 0.001); no statistically significant aging difference was detected in the other material–treatment combinations. No statistically significant HF–CoJet difference was detected within VITA Enamic or Shofu Block HC. Material-dependent pairwise patterns did not identify a single universally optimal surface-conditioning protocol across the tested materials. These findings concern initial repair bonding to previously aged substrates; post-repair durability and biomimetic tissue preservation were not evaluated.