Degradation of resin-cements in intraradicular environment: a micro-hardeness study

Objectives: Analyze the micro-hardness of four dual-cured resin-cements used for cementing glass fiber posts, in the following periods: initial, after 24 hours of immersion in 75% ethanol and after 3 months of storage in water, in the cervical, middle and apical root thirds. Methods: Forty bovine incisors were prepared for cementing Fibrekor® glass fiber pins (Jeneric/Pentron) with 1mm in diameter, using resin-cements PanaviaF 2.0 (Kuraray), VariolinkII (Ivoclar-Vivadent), RelyX Unicem (3M ESPE) and Duolink (Bisco). Half of the roots were longitudinally sectioned after 7 days to analyze the initial micro-hardness along the cement line, immersed in 75% ethanol for 24 hours and reassessed; and half were kept in deionized water for 3 months, for later sectioning and micro-hardness assessment. Results: Data were analyzed by ANOVA and Tukey test (p<0.05). Statistically significant differences were identified among cements, thirds and storage periods, as well as between cements/thirds and cements/assessment periods. PanaviaF exhibited significantly higher hardness values to other cements in the initial period, which showed no statistical difference among them. VariolinkII and Duolink showed significantly higher micro-hardness values in the cervical third, without significant difference among the thirds for other cements. Immersion in ethanol significantly reduced hardness values for all cements. Storage in water for 3 months had no influence on hardness of most of the cements, with the exception of RelyX Unicem, which showed significant increase in hardness values after this period. Conclusion: Panavia F showed highest values in initial micro-hardness results; Variolink and Duolink showed significantly higher micro-hardness values in cervical third, without significant difference among thirds for others cements; Immersion in ethanol significantly reduced micro-hardness values for all cements and the behavior by thirds was material dependant; Storage in water had influence only for Unicem cement, which showed significant increase in micro-hardness values after this period.