Effect of surface conditioning and adhesive strategies on the repair bond strength of resin matrix ceramics.

OBJECTIVES: To evaluate the effect of different surface pretreatment protocols on the repair bond strength and integrity of resin composite to three different resin matrix ceramics (RMCs). MATERIAL AND METHODS: Three RMCs - Cerasmart (CS), Grandio blocs (GB) and Katana Avencia (KA) - were subjected to one of three mechanical surface treatments: polishing, diamond bur roughening, or sandblasting. These were randomly assigned to four conditioning groups: 10-MDP and silane-containing adhesive (Clearfil Universal Bond Quick), 10-MDP-based adhesive (G-Premio Bond), 9% buffered hydrofluoric acid (HF) plus silane, and a 10-MDP and silane-free adhesive (Heliobond). A nanohybrid composite (Reflectys) was applied as the repair material. Specimens were sectioned into sticks and subjected to micro-tensile bond strength (µTBS) testing using a universal testing machine. The surface treatments were compared by one-way ANOVA and post-hoc tests for different cases of the variables µTBS and surface roughness. RESULTS: For CS, the combination of sandblasting and 10-MDP plus silane-containing adhesive yielded the highest µTBS (46.42 ± 3.12 MPa), with no significant difference observed between polishing and bur roughening. Similarly, GB showed significantly higher µTBS when sandblasted and treated with 10-MDP plus silane adhesive (42.01 ± 5.06 MPa). However, for KA, the most effective protocol was the combination of sandblasting and 9% buffered HF with silane (48.31 ± 8.46 MPa). CONCLUSIONS: Repair bond strength is highly dependent on the specific RMC used. No single universal mechanical surface treatment or conditioning protocol was found to be optimal across all materials. Clinicians should utilise individualised repair protocols - specifically 10-MDP and silane-containing adhesives for CS and GB, and HF and silane for KA - to achieve maximum repair bond strength. CLINICAL SIGNIFICANCE: When repairing RMC restorations chairside, clinicians should identify the specific material brand, whenever possible, as the chemical composition of the RMC dictates whether a universal adhesive or a traditional HF and silane protocol will provide the most durable immediate repair.