الفهرس 
REVIEW OF LITERATURE16Only 14 pages are availabe for public view
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Abstract
Many efforts have been made to improve the clinical behavior and mechanical properties of dental composite resin restorations, one of these efforts was introducing flowable bulk-fill composites, which are low viscosity materials with reduced percentage of inorganic filler particles and can be placed in a 4 mm bulk increment, with significant flow and low polymerization shrinkage. Secondly, searching for new modes of LED light for curing of composite resin restorations. Consequently, the present in-vitro study was done to evaluate the effect of three curing modes of LED light (high, low, soft-start) on polymerization shrinkage and marginal integrity of Tetric EvoFlow and CLEARFIL AP-X Flow flowable bulk-fill composites at two curing distances of 0 mm and 3 mm..
For polymerization shrinkage test, composite specimens with dimensions of 2 mm thickness and 5 mm diameter were fabricated. After curing, strain gauge was centralized on top of each specimen and was connected to a strain monitoring device, connected to the computer software program which recorded the shrinkage values. Strain measurements were recorded immediately after application of the light source up to 3 minutes following light irradiation in 10 seconds interval. For marginal integrity evaluation, class II OM cavities (3 mm width x 2.5 mm depth at the occlusal box and 3 mm width x 1.5 mm depth x 1 mm occluso-cervical height of the proximal box) were done and restored with the two composite resins, where the molars were immersed in 0.5% basic fuchsin dye at 37°C for 24 hours then washed by water to remove excess dye, then the teeth were sectioned longitudinally in a mesio-distal direction through the center of the restoration. Microleakage was evaluated with a stereomicroscope at 20X magnification at the occlusal and proximal margins. Then scanning electron microscope was used to measure the marginal gap, where samples were mounted to a cupper stub using a
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carbon double face, then coated with gold and photographs of the tested samples were taken at 1000 X magnification for the gap evaluation. The gap width was measured using Orion 6 camera connected to the scanning electron microscope device in micrometers.
The data obtained from polymerization shrinkage, microleakage and marginal gap tests were recorded and statistically analyzed.
There was no difference in shrinkage between both materials, between the three curing modes and between both curing distances except when soft-start mode was used to cure Tetric EvoFlow at 0 mm curing distance, where it showed less shrinkage than the 3 mm curing distance.
There was no difference in microleakage between both materials, between the three curing modes except proximally in Tetric EvoFlow, where soft-start mode showed the least microleakage followed by high mode then low mode, between both distances except when high mode was used to cure CLEARFIL AP-X Flow proximally, where 0 mm distance resulted in less microleakage than 3 mm distance.
The results of marginal gap showed that Tetric EvoFlow resulted in less marginal gap formation than CLEARFIL AP-X Flow. No difference was found between all curing modes except occlusally in CLEARFIL AP-X Flow and occlusally in Tetric EvoFlow, where high mode resulted in the smallest marginal gap followed by soft-start mode then low mode and proximally in Tetric EvoFlow, where soft-start mode showed the smallest marginal gap followed by high mode then low mode. No difference was found between both curing distances, except when low mode was used to cure CLEARFIL AP-X Flow occlusally and when soft-start mode was used to cure Tetric EvoFlow proximally, where 3 mm distance showed less gap than 0 mm distance and when low mode was used to cure Tetric EvoFlow proximally , where 0 mm distance showed less marginal gap than 3 mm distance.