Gallic acid as a biointeractive dentin conditioning agent for universal adhesives: bond strength, iron retention, and surface characterization following ferric sulfate hemostatic contamination

Objectives This study evaluated the effects of two universal adhesives, applied under three protocols, self-etch (SE), conventional total-etch (CTE), and modified total-etch (MTE) with 1% (w/v) gallic acid, on shear bond strength (SBS), iron retention, and surface characteristics of noncontaminated and ferric sulfate-contaminated dentin. Materials and methods One hundred eighty dentin specimens prepared from ninety extracted human molars were allocated to 12 groups ( n = 15) by adhesive type (All Bond Universal [ABU] or Tokuyama Universal Bond [TUB]), application protocol (SE, CTE, or MTE), and contamination condition (noncontaminated or 20% ferric sulfate-contaminated [ViscoStat]. After composite build-up and 5,000x thermocycling, SBS was measured. Surface morphology ( n = 3, 6 groups) and elemental composition ( n = 5, 5 groups) were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). SBS data were analyzed by three-way ANOVA (α = 0.05). Results All three variables significantly affected SBS ( p < 0.001). SE yielded the lowest SBS values (17.46 ± 3.19 MPa) among all protocols ( p < 0.001). CTE and MTE protocols showed comparable SBS values (20.30 ± 3.20 vs. 20.80 ± 3.05 MPa; p = 0.591). After ferric sulfate contamination, CTE produced no detectable iron residue, whereas MTE retained iron-associated surface deposits. EDS revealed descriptively higher mineral content in gallic acid-conditioned dentin, and SEM showed protocol-dependent surface patterns. Conclusions Gallic acid yielded short-term bond strength comparable to phosphoric acid, while inducing a more conservative surface modification. However, gallic acid conditioning following ferric sulfate contamination should be regarded cautiously, as iron-associated deposits are preserved. Clinical relevance Gallic acid may be considered a conservative preconditioning option for noncontaminated dentin. After ferric sulfate contamination, phosphoric acid remains the more predictable choice given its iron-removal capacity.