Effects of dimethyl sulfoxide pretreatment on the bonding properties of fluorotic dentin of different severity: An in vitro study

Statement of problem: Bonding to fluorotic dentin is weaker than to sound dentin, but methods to improve bonding have not been well addressed. Purpose: The purpose of this in vitro study was to investigate the effects of dimethyl sulfoxide (DMSO) pretreatment on the bond strength and resin-dentin surface of fluorotic dentin of different severity. Material and methods: Phosphoric acid-etched dentin specimens exhibiting mild fluorosis (ML-F), moderate fluorosis (MD-F), and severe fluorosis (SE-F) were randomly bonded with Single Bond 2 (SB2) pretreated with 50% DMSO (experimental groups) or deionized water (control groups). The bonded teeth were sectioned for microshear bond strength (mu SBS) testing immediately or after aging, for micromorphology observation of the bonding interface under a scanning electron microscope, and for resin tags and microleakage evaluation under a confocal laser scanning microscope. The degree of conversion of the adhesive resin was calculated by Fourier transform infrared spectroscopy. According to varying bonding steps, the mineralized dentin powders of ML-F, MD-F, and SE-F were randomly divided into 4 subgroups (blank, PA, PA+SB2, and PA+DMSO+SB2) and incubated in artificial saliva to examine the level of enzymatic degradation product of type I collagen. Data were analyzed by using ANOVA and the Tukey test (alpha=.05). Results: Dental fluorosis and thermocycling had negative effects on mu SBS (P<.001), while DMSO pretreatment preserved or even improved mu SBS (P<.001). DMSO had no influence on the degree of conversion (P=.618). Significant effects were found for bonding steps (P<.001), but not that of dental fluorosis (P=.131) on the enzymatic degradation product of type I collagen. Images showed sparser and more expanded collagen fibril meshwork, deeper resin penetration, and less microleakage in the experimental groups. Conclusions: DMSO pretreatment provided increased and durable dentin bonding to fluorotic dentin probably by dispersing collagen fibrils into a sparser network and inhibiting the degradation of type I collagen.