CAD/CAM Hybrid Resin Ceramic Crown Retention Following Various Surface Treatments

Objectives: To measure crown retention of a CAD/CAM-based resin ceramic crown following various surface treatments.
Methods: 48 human molars were prepared with diamond bur to produce 30-degree total occlusal convergence, 1.5mm height, and axial walls in dentin. Surface area was measured by digital microscope. Prepared teeth were scanned with an intraoral scanner. Crowns were milled from a novel experimental hybrid resin ceramic with 4mm occlusal height and occlusal wings to debond the crowns. Teeth were randomly allocated to 6 groups (n= 8); G1: Control; G2: Sandblast; G3: Hydrofluoric acid (HF) etch; G4: HF etch + silane; G5: HF etch + silane (without adhesive). Sandblasting was performed (G2) with 50 micron Al₂O₃ for 10s at 40psi. HF etching was performed (G3, G4, G5) with 5% HF for 20s. Teeth were coated with Optibond XTR primer and adhesive (Kerr) and light cured (10s). Optibond XTR adhesive was applied to intaglio of crowns (excluding group 5) and light cured (10s). Crowns were bonded with Maxcem Elite cement (Kerr) with 40s light cure at margins on all sides. Fatigue was performed with 100N for 100,000 cycles in water. Crown retention force was measured by fastening a metal wire loop from the wings of the crowns to a universal testing machine and testing with a crosshead speed of 1mm/min. Crown retention stress (maximum load/area of preparation) was analyzed using one-way ANOVA and Tukey post-hoc analysis (α=0.05).
Results: Stress values were (mean±SD): 2.78±0.60 (G1), 3.11±0.41 (G2), 2.53±0.65 (G3), 3.19±0.45 (G4), and 1.76±0.34 (G5). Groups were significantly different (p<0.01). G5 was significantly lower than G2 and G4; and there was no difference between other groups.

Conclusions: Sandblasting or HF etching followed by application of silane on the intaglio of the hybrid resin ceramic crowns produce favorable bonds strength when paired with the use of the recommended adhesive and cement.