Effects of Self-etching Primers on the Conversion of Adhesive Resin Components

Objective: Two-step products incorporating a primer and adhesive resin are the most common delivery modes of self-etching adhesives. Upon primer application, dentin demineralization and partial neutralization of the acidic primer takes place. Following adhesive resin application, intermixing of the primer and adhesive resin occurs to a depth up to the demineralization front. Since the primer and adhesive components differ in composition, questions have been raised as to the whether the partially neutralized primer components affect the conversion of adhesive resins. Methods: Three self-etching adjhesives were selected (Optibond Solo Plus Self-Etching/OS, SE Bond/SE, and UniFil Bond/UF). Coronal dentin disks were prepared by horizontally sectioning the crowns of extracted third molars. Ten ìl of each self-etching primer were brushed on dentin as instructed, the liquid film was then recovered and mixed with 10 ìl of adhesive resin. Micro-MIR FTIR spectra of the mixtures (group A) and of original adhesive resins (group B) were taken before and after 20s irradiation, and the degree of cure was calculated in a relative % basis using the two frequency technique. Three measurements were performed per product. Results: The result of % DC were: [Group A] OS: 38.3(3.4), SE: 70.2(4.8), UF: 40.2(2.6); [Group B] OS:58.3(4.4), SE:56.84(2.2) and UF:52.9(3.2). T-test demonstrated statistically significant differences in %DC between the two conditions tested. SE showed enhanced conversion after mixing with the primer, whereas OS and UF reduced. Conclusion: The results of the present study show that copolymerization of the primer with the adhesive resin components modify the curing efficiency of the latter.