Influence of dimethyl sulfoxide used as a solvent on the physical properties and long-term dentin bonding of hydrophilic resins

Objective: To examine the feasibility of dimethyl sulfoxide (DMSO) incorporation into relatively hydrophilic resins as a new potential method to improve the durability of resin dentin bonds. Methods: Six experimental light-curing BisGMA/HEMA resins solvated in ethanol and DMSO with increasing concentrations of DMSO (0, 0.5, 1, 2, 4 and 10 wt%) were prepared. The degree of conversion (DC) was evaluated by Fourier Transform Infrared Spectroscopy (n=8); water sorption (Wsp) and water solubility (Wso) were gravimetrically assessed (n=10); and flexural strength (FS) and elastic modulus (E) were determined by a three-point bending flexural test (n=10). Flat dentin surfaces on sound third molars (n=10/group) were bonded with resins containing 0, 2, 4 and 10 wt% DMSO used as a two-step etch-and-rinse system. Dentin microtensile bond strength was determined at 24 h and after two-year aging in artificial saliva at 37 degrees C. Results: DMSO significantly affected Wsp (p=0.0006), DC, Wso, FS, and E (p <0.0001). In general, the resins' mechanical/physical properties were not affected by 2% or lower DMSO incorporation. Incorporation of 4% or higher DMSO content significantly increased DC, Wsp and Wso, but 2% or higher DMSO concentrations significantly reduced FS and E. No influence on immediate dentin bond strength occurred up to 4% DMSO incorporation. While 4% or higher DMSO concentrations impaired bond strength over time, the resin containing 2% DMSO presented significant higher dentin bond strength compared to the control resin after two year-aging. Significance: The use of DMSO as a new solvent in adhesive dentistry improves dentin bonding of relatively hydrophilic resins over time. 2% DMSO incorporation in BisGMA/HEMA resins should be sufficient to reduce bond strength loss without compromising polymer mechanical strength and physical properties. (C) 2016 Elsevier Ltd. All rights reserved.