Effect of surface conditioning on the adhesive bond strength of 3D-printed resins used in permanent fixed dental prostheses

Although pre-treatment parameters for subtractive computer-aided design/computer-aided manufacturing (CAD/CAM) materials have been thoroughly investigated, data regarding additive restorative materials designed for permanent use in the oral cavity are scarce. This study investigated the effects of abrasive materials and blasting pressure on the bond strength of 3D-printed resins used in permanent restorations. A total of n = 44 test specimens additively manufactured from Formlabs' 'Permanent Crown Resin' were prepared. Three groups with n = 11 specimens were airborne-particle abraded with 50 µm aluminium oxide at 1 bar, 2 bar or 3 bar. The control group did not receive any further airborne-particle abrasion after post-processing with 50 µm glass beads. Cylindrical superstructures were bonded to the prepared surfaces using RelyX Unicem 2. The bonded specimens were then subjected to artificial ageing via thermocycling. Subsequently, shear bond strength (sbs) tests were conducted. Data were analysed with the Kruskal-Wallis test (α = 0.05). After post-processing with glass beads, average shear bond strength values of 10.13 ± 7.62 MPa were achieved. When using aluminium oxide and 1 bar blasting pressure, significantly higher average sbs values of 25.57 ± 7.04 MPa were revealed (p = 0.009). The bond strength increased with higher blasting pressures (28.14 ± 6.35 MPa at 2 bar (p = 0.005); 30.15 ± 6.46 MPa at 3 bar (p < 0.001)). However, the shear tests revealed increased failure within the specimen base at higher blasting pressures. Bond strength significantly improved when airborne-particle abrasion with aluminium oxide was applied. However, increased airborne-particle abrasion pressure led to more failures at the base plate level of the specimens. Aluminium oxide increases the adhesive strength of 3D-printed dental restorative materials. Although the adhesive bond increased slightly with increasing airborne-particle abrasion pressure, the 3D restorative materials also exhibited an increased failure rate within the restorative material in the shear bond strength test with increasing blasting pressure.