Role of adjunctive methacryloyloxydecyl dihydrogen phosphate primers on dentin bond strength of universal adhesives under saliva and artificial aging

Abstract

This study evaluated whether adjunctive 10-methacryloyloxydecyl dihydrogen phosphate (MDP) primers enhance the microtensile bond strength (µTBS) of two universal adhesives (UAs) to dentin under artificial aging and repeated salivary contamination applied at each bonding step. One hundred fifty-two human molars were assigned to 24 groups based on UA type, MDP primer application, contamination, and aging period (1, 30, and 180 d). Resin–dentin beams were sectioned and loaded to failure to determine µTBS. Failure modes were analyzed, and scanning electron microscopy (SEM) was used to assess hybrid layer quality and interfacial morphology. FTIR–ATR evaluated the effect of MDP primers on the degree of conversion (DC). Data were analyzed using one and three-way anova, Scheffé’s test, and Weibull statistics. Under uncontaminated conditions, MDP primers significantly increased µTBS for both UAs after 180 d. Repeated contamination significantly reduced µTBS; however, adjunctive MDP priming restored bond strength to levels comparable to uncontaminated controls. FTIR–ATR demonstrated higher DC in MDP primer groups, suggesting enhanced interfacial polymerization. Weibull analysis confirmed improved bonding reliability with primer use. SEM revealed continuous hybrid layers in MDP groups regardless of contamination, whereas failure modes shifted toward more cohesive patterns. Adjunctive MDP priming mitigates the adverse effects of salivary contamination and aging on UA-dentin bonding.