EFFECT OF TIME ELAPSED BETWEEN MIXING AND PHOTOACTIVATION ON DEGREE OF CONVERSION, WATER SORPTION AND WATER SOLUBILITY OF SELF-ADHESIVE RESIN CEMENTS

Abstract

INTRODUCTION: Self-adhesive resin cements are designed to adhere to tooth structures without separate adhesive or etchant. The major benefit of these materials would appear to be simplicity of applications with the goal of optimizing adhesive cementation procedures, selfadhesive resin cements were developed to simplify the technique and reduce the possibility of failure on the part of the operator. Low degree of conversion (DC), water sorption and solubility can compromise the mechanical properties and longevity of restorations (1-6). OBJECTIVES: Is to determine the influence of the photoactivation protocol on the degree of conversion, sorption and solubility in water of two different types of self-adhesive resin cements. MATERIALS AND METHODS: Two different types of self-adhesive, dual cure resin cements were tested: TEGDMA (Tri-ethylene glycol di-methacrylate) based resin cement [RelyXU200 (RU), 3M ESPE] and UDMA (Urethane di- methacrylate) based resin cement [SmartCem™2 (SC2), Dentsply Caulk]. A total of one hundred and twenty cured disc shaped resin cement specimens were prepared for this study using a split teflon mold to be tested for degree of conversion, water sorption and solubility. The specimens were divided into two groups (n=60) according to the type of the cement used, group A was prepared from RU and group B was prepared from SC2. Each group was divided according to the time elapsed between handling of the resin cement and photo-activation into three subgroups (1, 2 and 3) where n=20. Half of each subgroup specimens (n=10) were used for degree of conversion test while the other half was used for water sorption and solubility test [subgroups A1 & B1 were immediately photo-activated, subgroups A2 & B2 were photo-activated 1 minute after handling the cement and subgroups A3 & B3 were photo-activated 2 minutes after handling the cement]. Ceramic disc (1.5 mm thickness and 10 mm diameter) was fabricated using copper split mold to simulate clinical condition. The specimens were irradiated for 40 seconds using LED light applied perpendicular to the specimens at zero distance between the tip of the light cure unit and the ceramic disc. Fourier transformer infrared spectroscopy (FTIR) was used to determine the degree of conversion. For the water sorption and solubility tests specimens were stored in water bath containing distilled water at 37◦C for 90 days. Data were analyzed using IBM SPSS software package version 20.0 RESULTS: UDMA based cements showed statistically lower degree of conversion for all subgroups compared to TEGDMA based cements which showed significantly higher water sorption than the UDMA based that photo activated after 2 minutes. CONCLUSIONS: The time interval between mixing and photo activation can significantly influence the properties of the cements and modify their behavior