Comparison of the bond strength to titanium of resin-based materials fabricated by additive and subtractive manufacturing methods following surface treatments

Objective: The aim of this thesis was to compare the shear bond strength (SBS) of resin-based CAD/CAM materials, fabricated using different manufacturing techniques, to titanium following various surface treatments. Materials and Methods: In this study, a total of four resin-based CAD/CAM materials were used: two additively manufactured materials—Crowntec (Saremco Dental AG; Rebstein, Switzerland) and VarseoSmile Crown Plus (BEGO, Bremen, Germany)—and two subtractively manufactured materials—Tetric CAD (Ivoclar Vivadent AG, Schaan, Liechtenstein) and Cerasmart (GC Corporation, Tokyo, Japan). A total of 120 cylindrical specimens (Ø3 × 3 mm) were prepared. Three different surface treatment protocols were applied to each material: (1) primer only, (2) sandblasting with 50 μm Al₂O₃ followed by primer application, and (3) phosphoric acid etching followed by primer application, resulting in 12 experimental groups. Surface morphology analysis was conducted using scanning electron microscopy (SEM) on two specimens per group. All specimens were then cemented onto Grade V titanium abutments (Dentium Superline Pre-Milled Abutment) using a dual-cure resin cement (GCem LinkForce). After being stored in distilled water at 37 °C for 24 hours, shear bond strength tests were conducted using a universal testing machine at a crosshead speed of 1 mm/min. Failure modes were evaluated by examining the titanium surfaces under a stereomicroscope. The data were statistically analyzed using one-way analysis of variance (ANOVA) and post hoc Duncan tests at a significance level of 5%. Results: Additively manufactured resin-based materials exhibited higher bond strength values across all surface treatment protocols compared to their subtractively manufactured counterparts. Among all tested groups, the sandblasting + primer group of the Crowntec material showed the highest mean SBS value (18.4804 MPa), while Tetric CAD, a subtractively manufactured material, presented the lowest bond strength (8.0714 MPa). Groups subjected to Al₂O₃ sandblasting + primer demonstrated significantly higher SBS values than those treated with other protocols. Overall, micromechanical surface treatments were found to be more effective than chemical treatments in enhancing bond strength, and the combination of aluminum oxide sandblasting with universal adhesive was identified as the most effective surface preparation method. Fracture analysis revealed a higher incidence of adhesive failures in subtractive manufacturing groups, while cohesive and mixed failure modes were more frequently observed in additive groups, supporting the notion of superior bonding performance in the latter.