Three-dimensionally printed and milled composite materials for definitive restorations. Part 2: Effect of surface treatment on the bond strength of light-polymerized resin cement and surface morphology

ABSTRACTStatement of problemEvidence regarding the effect of surface treatment on the bond strength and surface morphology of 3-dimensionally (3D) printed and computer-aided design and computer-aided manufacturing (CAD-CAM) composite materials is sparse. Enhancing the bond strength to these materials and their surface modifications is essential for ensuring clinical success.PurposeThe purpose of this in vitro study was to evaluate the microshear bond strength (µSBS) of light-polymerized resin cement and the surface morphology of composite materials for definitive indirect restorations after different pretreatments.Material and methodsSpecimens (6×7×9 mm) from composite CAD-CAM materials were fabricated: 5 by 3D printing (Varseosmile Crown Plus - BEGO (VSC), Crowntec - Saremco Print (CWT), Biocrown - Prizma (BCN), Ceramic Crown - SprintRay (CCN), and Voxel Print – FGM (VXP) and 3 by milling: Cerasmart - GC (CSM), Brilliant Crios - Coltène (BCR), and Enamic - Vita (ENA). Thirteen specimens of each material were selected: 10 for μSBS and 3 for scanning electron microscopy (SEM). Two surface pretreatment protocols were applied: Airborne-particle abrasion with aluminum oxide followed by silane (AL+S), and 5% hydrofluoric acid followed by silane (HF+S). For µSBS testing, transparent cylindrical matrices were filled with light-polymerized resin cement. After 24-hour storage, the specimens were subjected to shear testing (crosshead speed of 1.0 mm/minute). The data were analyzed by 2-way variance analysis and the Bonferroni post hoc test (α=.05).ResultsWithin the HF+S groups, ENA exhibited the highest µSBS values (18.47 ±1.0 MPa), although no significant differences were found with VXP (16.12 ±1.4 MPa). The highest µSBS mean value was observed on the CCN surface after AL+S (19.49 ±2.8 MPa), followed by VSC (18.74 ±2.2 MPa) and CSM (18.45 ±1.1 MPa). The surface pattern with AL+S presented more evident irregularities on both printable and machinable materials.ConclusionsAirborne-particle abrasion with aluminum oxide was found to be appropriate for both milled and printed materials. Hydrofluoric acid etching was not recommended for all types of CAD-CAM resin ceramics, even when followed by silane application.