Bonding of Composite Resin Pre- or Post-cured to Primary Dentine

Conventionally, adhesive (Adh) is pre-cured before resin composite (RC) placement. Saving time by post-curing Adh with RC is valuable in restorative treatment in children. Unlike permanent teeth, effects of pre-curing Adh before RC placement vs post-curing in primary teeth appear unknown. Objective: To compare in vitro microshear bond strength (MSBS) and failure modes of two systems: RC (TPH®3 Micro Matrix Restorative, Dentsply) + Adh (Prime&BondNT™, Dentsply) termed TPH/P&B, with RC (Clearfil™ Majesty Esthetic, Kuraray-Dental) + Adh (Clearfil™SE Bond, Kuraray-Dental), termed CME/SEB. Methods: Extracted primary molars provided 20 dentine substrates for MSBS testing (UTM, crosshead speed: 1 mm/min) with a ligature wire loop. Paired samples of RC (20 TPH/P&B; 20 CME/SEB) were pre- or post-cured with Adh on substrates using a self-aligning rig, tested to failure, and de-bonded surfaces (tubes, dentine) examined microscopically. Results: Mean MSBS (MPa) of TPH/P&B and CME/SEB differed significantly (11.83, 15.44; 20.16, 10.97; ANOVA: F ratio: 10.481; df = 3; p= 0.0001). Mean (±SD) MSBS values for pre-and post-cured TPH/P&B samples did not differ (11.83 ± 5.35 vs 15.44 ±3.39; paired data t test: p = 0.106). The mean MSBS value for pre-cured CME/SEB samples significantly exceeded that for post-cured (20.16 ±2.70 vs 10.97 ±4.39; p = 0.0001). Overall, mean MSBS values for TPH/P&B vs CME/SEB did not differ (13.64 ± 4.74 vs 15.57 ± 5.90; p = 0.144). Failures in TPH/P&B samples were: pre-cured: adhesive-dentine: 9; mixed (cohesive-RC+adhesive-dentine):1; post-cured: adhesive-dentine: 9; mixed (cohesive-dentine+adhesive-dentine):1. Failures in CME/SEB samples were: pre-cured: adhesive-dentine: 3; mixed: 7 (cohesive-dentine+adhesive-dentine: 6, cohesive-RC+adhesive-dentine: 1); post-cured: adhesive-dentine: 10. Conclusion: While overall microshear bond strengths of both systems to primary dentine were similar, pre-curing CME/SEB resulted in significantly higher strength than post-curing and less likelihood of adhesive failure to dentine. Combined with no etchant rinsing, pre-curing provided increased strength which is valuable in treating children.