Effect of Dimethyl Sulfoxide Primer on Microtensile Bond Strength and Micromorphological Pattern of HEMA-free Universal Adhesive to Dry/Wet Dentin After Thermomechanical Aging.

Background: To evaluate the effect of dimethyl sulfoxide (DMSO) primer on microtensile bond strength (µTBS) and the micromorphological pattern of a hydroxyethyl methacrylate (HEMA)-free universal adhesive (UA) applied on wet/dry dentin in etch and rinse (E&R) mode before/after thermomechanical aging. Material and Methods: For the µTBS test, the mid-coronal dentin of 80 human mandibular first molars was exposed and etched with 35% phosphoric acid. Teeth were randomly divided into two equal groups: dry and wet dentin (n = 40). Then, each group was subdivided according to dentin pretreatment by DMSO before UA (Gluma Bond Universal, Heraeus Kulzer, Hanau, Germany) application into unpretreated and 10% DMSO/water (OT Primer S100, OT Oy Dent, Turku, Finland) pretreated (n = 20). Resin composite blocks were built up using a specially designed Teflon mold. In every subgroup, both the µTBS test and failure analysis by stereomicroscope were evaluated immediately after 24 h and after thermomechanical aging (n = 10). The data were statistically analyzed using a three-way analysis of variance (ANOVA) (p = 0.05). For the micromorphological pattern, 16 maxillary first premolars were distributed as mentioned in the µTBS test, prepared, and buccolingually sectioned. The dentin-resin interface was examined using an environmental scanning electron microscope (ESEM) (n = 2). Results: Three-way ANOVA revealed that the main effects and interactions between dentin wetness, dentin pretreatment, and evaluation time (thermomechanical aging) were not significant for µTBS (p> 0.05). Adhesive failure was the predominant type in all immediate and delayed specimens. Longer and more prominent resin tags were observed at dentin-resin interfaces after DMSO application. Conclusions: Neither the initial dentin wetness condition, dentin pretreatment, nor thermomechanical aging could affect the dentin bond strength. No correlation was found between the bond strength and the micromorphology findings. Key words:Wet/dry dentin bonding, Microtensile bond strength, Micromorphology, Universal adhesive, Dimethyl sulfoxide, Thermomechanical aging.

Depth of cure of dual- and light-cure bulk-fill resin composites.

PURPOSE: To evaluate the degree of conversion (DC), Vickers microhardness (VMH), and depth of cure of dual-cure and light-cure bulk-fill resin composites (BFRCs). METHODS: One dual-cure (Fill-Up) and two light-cure (QuiXfil and Tetric N-Ceram Bulk Fill) BFRCs were investigated. For each tested BFRC, 11 cylindrical specimens (5 mm diameter, 4 mm height) were prepared, and light cured for 10 seconds (n= 11). DC was obtained by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and VMH was obtained using a VMH tester. The specimens were measured for DC and VMH at top and bottom surfaces. Statistical analysis was performed using two-way ANOVA, Tukey's post-hoc, and Pearson correlation tests (P< 0.05). RESULTS: Fill-Up and Tetric N-Ceram Bulk Fill revealed significantly higher DC and VMH values on the top surfaces than that on the bottom surfaces, whereas QuiXfil revealed no significant difference between top and bottom surfaces for DC and VMH. All tested BFRCs showed bottom/top ratios >80% for both DC and VMH. Each tested BFRC showed a significant positive correlation between DC and VMH. All tested BFRCs had adequate depth of cure, but only QuiXfil had a uniform depth of cure. Both DC and VMH bottom/top ratios were effective for depth of cure evaluation. CLINICAL SIGNIFICANCE: QuiXfil, Tetric N-Ceram Bulk Fill, and Fill-Up BFRCs were well cured up to a 4 mm depth. Although Fill-Up (dual-cure) can be used with its chemical-curing mode, light curing improved DC and VMH values of the top layer. Distinct variance in DC and VMH among the three tested BFRCs may affect their clinical performance.

Bonding of single-component adhesives to dentin following chemomechanical caries removal.

PURPOSE: To determine the effect of chemomechanical caries removal on the bonding quality of contemporary single-component adhesives to dentin. MATERIALS AND METHODS: N-monochloro-DL-2-aminobutyrate solution (NMAB) and Carisolv gel were used to chemomechanically remove dentin caries in 60 extracted human molars. Caries removal with rotating instruments served as the control. Two single-component adhesive systems, Syntac Single Component and Excite, were applied to bond the hybrid composite Tetric Ceram to the treated dentin surfaces. The prepared samples were sectioned for microtensile bond strength testing and SEM examination of the bonding interfaces. The debonding patterns of the fractured samples were also assessed. RESULTS: No statistically significant differences were found between the bond strengths of either adhesive to the conventionally and the NMAB-treated dentin (p > 0.05). However, the Carisolv-treated dentin yielded significantly higher (p > 0.05) bond strength values with both adhesives compared to those on dentin prepared with rotating instruments. No statistical difference could be discerned between the 2 adhesive systems (p > 0.05), nor was the interaction between the 2 variables under investigation (method of caries removal and the type of adhesive) statistically significant (p = 0.7712). SEM images indicated unspecific effects of the tested variables on both the thickness of the hybrid layer and the length of the resin tags. CONCLUSION: Under the conditions of this study, using the Carisolv chemomechanical caries removal system to prepare dentin surfaces enhanced the dentin/adhesive bond strength. In addition, the chemical nature of the adhesive systems seems to have no effect on the values of bond strength.