Influence of collagen cross-linkers addition in phosphoric acid on dentin biomodification and bonding of an etch-and-rinse adhesive

Objective. To investigate the effects of natural collagen cross-linkers incorporation in phosphoric acid etchant on dentin biomodification, microtensile bond strength (mu TBS) and nanoleakage (NL) of a two-step etch-and-rinse adhesive. Methods. Experimental aqueous solution of 37% ortho-phosphoric acid were prepared with the addition of 2% biomodification agents: Lignin (LIG) from industrial paper production residue, Cardanol (CARD) from cashew-nut shell liquid, and Proanthocyanidin (PAC) from grape-seed extract. Negative control (NC) was acid solution without cross-linker whilst commercial control (CC) was Condac 37 gel (FGM). Dentin specimens were assayed by FTIR after 15 s etching to detect collagen cross-linking. Extracted third molars were used for mu TBS (n = 7) and fracture mode analysis of Optibond S (Kerr), tested after 24 h or 1000 thermal cycles. NL was surveyed by SEM. Statistical analysis was performed with two-way ANOVA and Tukey's test (p <0.05). Results. FTIR confirmed cross-linking for all agents. mu TBS of CC was the highest (46.6 +/- 6.2 MPa), but reduced significantly after aging (35.7 +/- 5.2 MPa) (p < 0.001). LIG (30.6 +/- 3.7 MPa) and CARD (28.3 +/- 1.8 MPa) attained similar ii,TBS which were stable after aging (p > 0.05). Fracture mode was predominantly adhesive. At 24h, all groups showed presence of silver uptake in hybrid layer, except CARD. After aging, CARD- and LIG-treated specimens exhibited little amount of silver penetration. CC, PAC and NC showed gaps, great nanoleakage at hybrid layer and presence of water channels in adhesive layer. Significance. Altogether, ortho-phosphoric acid incorporated with LIG and CARD promotes stable resin-dentin bond strength with minor nanoleakage after aging, thereby achieving therapeutic impact without additional clinical steps. (C) 2019 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.