"Influence of macroretention in polymer-infiltrated ceramic network- and zirconia crowns and different roughness values of titanium bases on adhesive bond strength of hybrid abutment crowns: an in vitro study".

BACKGROUND: Two-piece hybrid abutment crowns (HACs) are CAD/CAM-fabricated implant restorations adhesively bonded to prefabricated titanium bases (Ti-bases). Since adhesive bond represents a potential weakness, methods to enhance long-term durability are being investigated. The aim of this in vitro study was to evaluate the influence of additional macroretention, specifically a circumferential groove, incorporated into polymer-infiltrated ceramic network (PICN) and zirconia crowns, and two Ti-base sandblasting protocols on adhesive bond strength of HACs. METHODS: Ninety Ti-bases, 45 zirconia and 45 PICN crowns were divided into six groups (N = 15). Prior to conventional cementation (Panavia V5, Kuraray) of zirconia control group (Z1), Ti-bases and internal crown surfaces were sandblasted (Al₂O₃; 50 μm; 1.0 bar) and treated with MDP primer. In PICN control group (H1), Ti-bases were sandblasted identically and pretreated with Adiva M-Prime. Internal surfaces of PICN crowns were etched (5% hydrofluoric acid) and primed with Adiva C-Prime. In Z2 and H2, a circular groove in the internal crown surface was prepared as a macroretention in addition to conventional pretreatment as performed in Z1 and H1. Z3 and H3 were also conditioned conventionally, as in Z1 and H1, but Ti-bases were sandblasted with 250 μm at 2.0 bar. After sandblasting, surface roughness values (RV) of Ti-bases were measured. Following thermocycling, tensile shear test was performed, and failure mode was analysed. Mean values were compared using t-test. RESULTS: RV differed significantly between differently blasted Ti-bases (p < 0.001). Both crown materials achieved significantly higher mean pull-off forces (Z1: 1085 N ± 79; H1 = 664 N ± 68) in control groups than in groups with macroretention (Z2: 1017 N ± 65; H2 = 438 N ± 48) (Z: p = 0.024, H: p < 0.001), and significantly lower pull-off forces than in groups with rougher Ti-bases (Z3: 1298 N ± 98, H3: 744 N ± 64) (Z: p < 0.001, H: p = 0.0023). CONCLUSIONS: Increasing pressure and grit size during corundum blasting of Ti-bases can achieve higher pull-off force for zirconia and PICN crowns. Additional macroretention, at least in the form used here, offers no advantage regarding bond strength.