Shear bond strength of laser-sintered orthodontic appliances bonded to enamel using various bonding protocols: an in vitro study

This in vitro study compared the shear bond strength (SBS) and failure mode of laser-sintered orthodontic metal specimens bonded to enamel using different bonding protocols (with or without enamel sandblasting and four adhesive systems). Two hundred and forty bovine teeth were randomly allocated to no sandblasting (control) or sandblasting (50 µm, 1 bar) and bonded with 3D-printed Co-Cr discs using either light-curing orthodontic adhesives (Transbond XT, Transbond LR) or dual-curing resin cements (RelyX Unicem 2 Automix, Panavia SA Cement Universal Automix) (2 × 4 design; n = 30/group). After SBS testing, the failure mode was documented. Welch's ANOVA was used to compare SBS across groups (S, C, and subgroups); p < 0.05 was considered significant. Dual-curing adhesives (RX, PA) showed higher SBS than light-curing adhesives (XT, LR) ( p = 0.001). The highest SBS was observed in RX (33 MPa), and the lowest in XT (18 MPa). A surface treatment × adhesive effect was found, although not statistically significant ( p = 0.21). Failures occurred mainly on the metal side (> 50%; 140/240). Dual-curing adhesives showed higher SBS when bonding laser-sintered Co-Cr appliances to bovine enamel, with failures predominantly occurring on the metal side. Sandblasting of enamel did not increase SBS under the conditions tested. As SBS values exceeded the clinically acceptable range, additional enamel sandblasting may not be clinically necessary. For bonding laser-sintered Co–Cr appliances, dual-curing adhesives may provide clinically acceptable SBS, but higher values could increase enamel damage risk during debonding. Enamel sandblasting showed no SBS benefit in this protocol.