الفهرس 
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Abstract
To assess the effect of storage temperature on marginal adaptation of class II cavities restored with an ormocer, a nanoceramic and, a nanohybrid composite. In time, the effect of storage temperature on microhardness and degree of conversion of these restorative materials was assessed.Materials and methods:Three commercially-available composite restorative systems were enrolled in this study; an ormocer based composite (Admira Fusion/Futurabond M+, Voco GmbH), a nanoceramic composite, (Ceram.X SphereTEC One/Prime&Bond Universal, Dentsply Sirona GmbH), and a nanohybrid composite (Tetric N-Ceram/Tetric N-Bond Universal, Ivoclar Vivadent AG). For marginal adaptation test, 42 sound human extracted molars were assigned into three main groups (n=14) according to composite restorative system used. Each molar received two proximal Class II cavities, one with the gingival margin placed above cementoenamel junction (C.E.J), while the other placed below. Half of the specimens of each group were restored with one of the restorative composite materials stored at room temperature while the other half was restored after storage of the composite material in the refrigerator at 4°C-5°C. All the restorations were finished and polished with a multistep finishing system (Sof-Lex XT Pop On, 3M ESPE). A replica was performed for each specimen and assessed under a scanning electron microscope (SEM) at 200x and 1000x magnifications. For microhardness and degree of conversion tests, 60 disc-shaped composite specimens were randomly divided into 3 groups (n=20) according to the restorative material used. Half of the specimens of each group was prepared from one of the restorative composite materials stored at room temperature while the other half was prepared after storage of the composite material in the refrigerator at 4°C-5°C. Microhardness was evaluated using micro-Vickers hardness tester. Degree of conversion (DC) was evaluated using a Fourier-transform infrared spectrometer coupled to an attenuated total reflectance accessory. The results were analyzed by Chi square test for marginal adaptation test in addition to ANOVA, post-hoc LSD, and Independent t tests for the other two tests at a significance level p≤0.05.Results: None of the tested restorative systems could exhibit 100% gap-free margins irrespective of the margin location or the storage temperature. Marginal adaptation was insignificantly affected by the restorative system and the margin location. Regarding the effect of storage temperature, a statistically significant difference was only observed between the supragingivally-restored room-stored groups and their corresponding groups stored at refrigerator (p≤0.005). While, there was no statistically significant difference between the subgingivally-restored room-stored groups and their corresponding groups stored at refrigerator (p>0.005). For microhardness and DC tests, all groups showed statistically significant differences at both storage temperatures with the ormocer based composite having the highest mean values. There was a statistically significant difference between all room-stored groups and their corresponding groups stored at refrigerator (p≤0.005). Conclusions: Although all the tested composite systems failed to achieve gap-free margins with Class II cavities, the refrigeration of the materials revealed the worst results especially for restorations with supragingival margins. Irrespective of the type of composite material, the refrigeration had a deleterious effect on degree of conversion and microhardness.