Effect of degree of conversion on the surface properties of polymerized resin cements used for luting glass fiber posts
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Statement of problem: Lack of conversion of resin cements for luting glass fiber posts in deeper levels of the root canal may compromise clinical performance. Purpose: The purpose of this in vitro study was to evaluate the effect of the degree of conversion on the surface properties of dual-polymerized resin cements used for cemented glass fiber posts according to the root level. Material and methods: Fifty maxillary central incisor teeth were endodontically treated, and glass fiber posts were cemented using the following systems: self-adhesive dual-polymerized resin luting cement (RelyX U200) and dual-polymerizing flowable core and a post luting system (Rebilda DC) with a self-etching adhesive (Futurabond DC). The degree of conversion was determined via attenuated total reflectance and Fourier transform infrared spectroscopy, and surface microhardness and cement film thickness were measured. The intraradicular fit was evaluated with microscopy. All tests were performed in the coronal, middle, and apical third of the root canal. Statistical analysis was done with ANOVA and the multiple comparison Tukey test (α=.05). Results: The degree of conversion was higher in the coronal third using Rebilda DC (65.3 ±4.8%25) than RelyX U200 (38.7 ±5.3%25) (P<.05); on both resin cements, these values decreased from the coronal to the apical third (30.9 ±3.7%25, 61.9 ±8.7%25, respectively). The cement film thickness was higher for RelyX U200 in the 3 thirds than for Rebilda DC; significant differences (P[removed].05). The mean surface microhardness values increased in the coronal thirds and decreased with increasing root canal depth. The marginal seal in the coronal thirds and the intraradicular fit in the middle thirds showed closer adaptation; however, some tags were observed in the interface resin cement and radicular dentin. Gap and tag formations were observed in the apical third. Conclusions: Depending on the root canal third, the surface properties of dual-polymerized resin cements are influenced by the degree of conversion.
