In vitro comparison of enamel shear bond strength to four restorative substrates used in resin-bonded prostheses

The success of resin-bonded restorations relies on durable adhesion to enamel; however, the choice of restorative substrate may affect initial bonding behavior. This in vitro investigation evaluated and compared the micro-shear bond strength (SBS) to human enamel of 4 materials commonly used as substrates for resin-bonded prostheses: polyetherketoneketone (PEKK), cobalt-chromium (CoCr) alloy, zirconia ceramic, and a fiber-reinforced resin composite. Twenty-four extracted third molars with intact enamel surfaces were assigned to 4 groups (n = 6 per material). Standardized specimens measuring 5 × 5 × 3 mm were subjected to mechanical surface treatment by airborne-particle abrasion using 90-μm aluminum oxide at 0.30 MPa for 20 seconds, followed by ultrasonic cleaning. The specimens were then bonded to flattened enamel surfaces with an adhesive resin cement using a template that standardized the bonding area to a diameter of 1.5 mm. Following 24 hours of storage at 37°C, without thermocycling or fatigue loading, SBS was determined under monotonic loading at a crosshead speed of 0.5 mm/minute. Statistically significant differences in SBS were observed among the tested materials (P < .05). CoCr demonstrated the highest mean SBS (0.61 ± 0.20 MPa), followed by zirconia (0.36 ± 0.08 MPa), fiber-reinforced resin (0.29 ± 0.20 MPa), and PEKK (0.19 ± 0.08 MPa). CoCr showed significantly greater bond strength than all other groups, while zirconia also outperformed PEKK; no other pairwise comparisons reached statistical significance. Scanning electron microscopy revealed that failure patterns were predominantly mixed. Under these short-term, nonaged laboratory conditions, initial enamel bond strength differed by substrate type; these findings are limited to comparative laboratory adhesion behavior and should not be interpreted as evidence of long-term clinical performance or as a ranking of clinically optimized bonding protocols.