Shear bond strength of sandblasted base metal alloys to self-adhesive resin cement: effects of delay time and storage

This study evaluated the effect of delay time and storage conditions after sandblasting on the shear bond strength between base metal alloys (BMA) and selfadhesive resin cement. It also assessed whether vacuum sealing or re-sandblasting could counteract time-related degradation of bond strength. Sixty BMA specimens were sandblasted and divided into six groups (n = 10): immediate bonding, 1-day, 7-day, and 14-day delays; 14-day vacuum-sealed; and 14-day delay with re-sandblasting. Resin cement was applied to standardized bond areas, and composite rods were bonded. All specimens were stored in water at 37°C for 24 hours before shear bond strength testing. Failure modes were examined under a stereomicroscope. One-way ANOVA revealed significant differences among groups (p < 0.05). Immediate bonding yielded the highest strength (26.50±2.74 MPa). Bond strength declined with delay: 1-day (21.19±4.94 MPa), 7-day (15.20±4.52 MPa), and 14-day (16.01±4.69 MPa), with no significant difference between the 7- and 14-day groups. Vacuum sealing for 14 days preserved bond strength (25.92±3.94 MPa), comparable to immediate bonding. Resandblasting restored bond strength (20.66±3.70 MPa). Prolonged delays resulted in 100% adhesive failures, whereas immediate bonding and intervention groups showed 80% adhesive and 20% mixed failures. Delayed bonding after sandblasting significantly reduces bond strength due to oxide layer formation on the BMA surface. However, surface sealing might prevent surface oxidation and maintain bonding potential, while re-sandblasting can restore bond strength when delays are unavoidable. Clinically, bonding should be performed immediately after sandblasting, or appropriate surface management protocols should be implemented to maintain optimal adhesion.