The effect of contamination stage and adhesive strategy on the durability of repair bond strength of blood-saliva contaminated aged composite resin.

This study evaluated whether the stage of contamination (before vs. after adhesive polymerization) and the application strategy of a universal adhesive (GLUMA Bond Universal, Kulzer, Hanau, Germany) used in total-etch (TE) or self-etch (SE) mode affect the durability of repair shear bond strength (RSBS) in aged composite after immediate storage (24 h) and artificial aging (10.000 thermocycles). One hundred twenty composite specimens were thermocycled (5.000 cycles) and assigned to 12 groups based on contamination stage (control, pre-adhesive, post-adhesive), adhesive strategy (TE or SE), and aging period (24 h or 10.000 cycles). A fresh blood/saliva mixture was applied for 1 min and rinsed. In post-adhesive groups, re-bonding was performed, with additional re-etching in the TE subgroup. RSBS was measured at a crosshead speed of 1 mm/min. Data were analyzed by three-way robust ANOVA based on 20% trimmed means (α = 0.05). Effect sizes were estimated using bootstrap partial eta squared (η²p) with 95% confidence intervals. Failure modes were analyzed using Fisher's Exact Test. All main effects were significant: contamination stage (η²p = 0.191, 95% CI: 0.093-0.309), adhesive strategy (η²p = 0.360, 95% CI: 0.263-0.478), and aging period (η²p = 0.805, 95% CI: 0.799-0.838) (all p ≤ 0.001). Significant interactions emerged between contamination stage and aging (p = 0.020, η²p = 0.070, 95% CI: 0.012-0.161) and between adhesive strategy and aging (p = 0.001, η²p = 0.133, 95% CI: 0.047-0.254). The three-way interaction was not significant (p = 0.078). Pre-adhesive contamination significantly reduced bond strength compared to the control and post-adhesive conditions (p < 0.001). TE showed higher RSBS than SE (p < 0.001), whereas aging reduced RSBS (p = 0.001). The highest RSBS was observed in the control + TE + 24 h group (31.11 ± 1.32 MPa), and the lowest in the pre-adhesive + SE + 10.000 TC group (5.33 ± 0.56 MPa). Failure mode distribution shifted from cohesive to adhesive after aging. Re-bonding after post-adhesive contamination restored bond strength to control levels. In conclusion, pre-adhesive blood/saliva contamination is most detrimental to repair durability; the total-etch protocol produced higher RSBS values than the self-etch protocol, although both strategies demonstrated significant degradation after thermal aging.