Abstract
The aim of this study was to characterize the degree of conversion and the bond strength of experimental adhesive systems formulated with elastomeric monomers (Exothanes). Two-step self-etch adhesive systems were formulated, where the primer was constituted by HEMA, HEMA-P, water and ethanol, and the resin bonds were prepared mixing one type of Exothane (8, 9, 10, 24, or 32) (75 wt%) with TEGDMA (25 wt%). CQ, EDAB, and DPI were added as photo-initiation system. UDMA was used as control, so six different resin bonds were formulated at all. The adhesive system Clearfil SE Bond (CLSE) was used as a commercial control. The degree of conversion (DC) of each resin bond was evaluated in infrared spectroscopy (RT-FTIR, Shimadzu Prestige-21) using a diamond crystal (n = 3). The microshear bond strength (μSBS) test was performed using a universal testing machine (EMIC DL-500). While the DC data was analyzed by one-way ANOVA and Tukey (p < 0.05), the μSBS data was analyzed by Kruskal-Wallis test and Student-Newman-Keuls (p < 0.05). The resin bonds containing the Exothanes 8, 9, and 32 demonstrated DC values higher than 80%, differently to the other Exothane-based adhesives, which showed DC values close to 50%. UDMA and CLSE demonstrated lower DC than E8, E9, and E32 (p < 0.001). The Exothane 24 resulted in the lowest DC value of the study (p < 0.001), although it was similar to the E10 and UDMA adhesives (p > 0.05). Low μSBS results were seen for the Exothane-based materials. CLSE demonstrated significantly higher bond strength than the other materials (p < 0.001). UDMA has also presented low μSBS to the dentin substrate. It can be concluded that the Exothanes evaluated demonstrated satisfactory degree of conversion, with some of them reaching almost full conversion of monomers in polymer. However, considering the formulations investigated, they were not good bonding agents. So, they were not reliable options for composing the polymeric matrix of dental adhesive materials.
Highlights
Dental adhesive systems are commonly used for bonding the restorative material to the tooth structure
There are several in vitro studies which evaluated the bond strength stability between tooth substrates and restorative materials and most of them have concluded that the adhesive interface degrades over time [2,3,4,5], mainly because of the monomers used in their composition
The resin bonds containing the Exothanes 10 and 24 presented degree of conversion (DC) values near to 50%, which were similar to the experimental control group (59%) (p = 0.769 and p = 0.257, respectively)
Summary
Dental adhesive systems are commonly used for bonding the restorative material to the tooth structure. The monomeric nature plays important roles for each bonding step, where the primer should be a polar substance (hydrophilic) as the tooth is a humid substrate, and the resin bond should be a more non-polar substance (hydrophobic) than the former as this characteristic increases its mechanical strength and reduces the polymer network degradation (hydrolysis) This dual characteristic (polarity and nonpolarity) are very important for acquiring high adhesion between the tooth and the restorative material. There are several in vitro studies which evaluated the bond strength stability between tooth substrates (enamel or dentin) and restorative materials and most of them have concluded that the adhesive interface degrades over time [2,3,4,5], mainly because of the monomers used in their composition. Materials showing higher strength and stability to wet environment are still needed in dentistry
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