In vitro evaluation of alternative dentin conditioning agents based on ferric chloride and citric acid or nitric acid

Abstract

This study will evaluate the effects of dentin conditioning with 37% phosphoric acid, 10-3 solution (10% citric acid and 3% ferric chloride) or 1.4% nitric acid and post-etching dentin moisture on dentin bond strength, failure mode, ultramorphology, nanoleakage, mechanical properties and enzymatic activity of the dentin-adhesive interface, on the morphology of etched dentin, and on the transdentinal cytotoxicity caused by the conditioners. Two "universal" adhesive systems with different solvents (alcohol or acetone) will be tested on wet (positive controls) or dry (negative controls) demineralized dentin of human third molars. Adhesives will be applied to phosphoric acid-etched dentin (wet or dry), dry dentin previously treated with 10-3 solution or nitric acid (15 s), or in the self-etching mode. The bond strength test (n=8) and failure mode analysis will be performed at 24 hours and 18 months. Adhesive interface ultramorphology and nanoleakage will be analyzed by transmission electron microscopy (n=6). Bonding interface mechanical properties will be analyzed by nanoindentation (n=5), performing five equally spaced nanoindentations along the adhesive interface (load: 1000 µN). Enzymatic activity at the bonding interface will be determined by multifoton confocal microscopy (n=5), using fluorescein-conjugated gelatin. The morphology of etched dentin will be observed by scanning electron microscopy (n=5) using critical-point drying. Conditioners will by evaluated regarding cytotoxicity on odontoblast-like cells (MDPC-23) through dentin discs. Bond strength, nanoindentation, and cytotoxicity data will be analyzed by ANOVA and Tukey's test, while the remaining data will be analyzed descriptively. (AU)