الفهرس 
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Abstract
Wear of restorative materials is a very complex phenomenon that is affected by several extrinsic and intrinsic factors. Wear of restorative materials in the oral environment results from direct contact between tooth and the restoration during mastication, oral parafunctions, as well as toothbrushing .
The purpose of this study was to evaluate and compare the wear resistance of two resin composite restoratives under simulated tooth brushing machine.
A total of 90 specimens of two different types of light curing resin composite restoratives; (Methacrylate composite,ALPHA-DENT® and Silorane based composite Filtek P90 ) were made for this study. The specimens were made in the form of cylindrical disks, a major group of 45 specimens of each material were randomly divided into three minor groups (15 specimens) in each group according to the brushing load used in the study: ( 250gm, 500gm, 750gm).
Every specimen was measured for the detection of the average pre-brushing weight (W1).Then two random specimens represent each major group were observed in scanning electron microscope at magnification (1000x).the specimens then brushed for 10 min. with a medium brush bristle, under a specific load. Then all the specimens were re-measured after brushing for the detection of the average of the post-brushing weight, and then the weight loss has been calculated (W1-W2) , and the results are represented percentage in table (3) . Two random specimens represent each group were observed in scanning electron microscope at magnification (1000x)
Data analysis was performed in several steps. Initially, descriptive statistics for each group results. One way ANOVA followed by pair-wise Tukey’s post-hoc tests was performed to detect significance between brushing load. Then separate student t-test to detect significance between type of composite at different brushing load. Two factors analysis of variance ANOVA test of significance comparing variables affecting wear; composite and brushing load. Statistical analysis was performed using Graphpad Prism-4 statistics software for Windows. P values ≤ 0.05 are considered to be statistically significant in all tests.
The results revealed a significant (ً p< 0.05) influence of the composite tested (Methacrylate > silorane) on wear mean values.A significant (ًp < 0.05) influence of the brushing load tested (750mg>500mg>250mg) on wear mean values.The interaction of these two factors was statistically significant (p < 0.05),table(3),figure(10,16).
Under the conditions of this study, the following conclusions can be drawn:
1. Toothbrushing simulation procedure has an influence on the abrasion resistance of resin composite restoratives, and should be considered when in vitro studies are conducted.
2. Loads of brushing used had a direct effect on the increase of the abrasion and weight loss of the resin- based restorative materials.
3. Chemistry of organic matrix plays a role in abrasion resistance of resin composite.
4. Percentage of weight loss of the resin composite as a function of toothbrushing, is directly proportional to the load; specifically for methacrylate based composite.
5. Toothbrushing loads dramatically affect surface topography of resin composite.
Recommendations:
1) The wear and weight loss of different resin based restorative materials tested were variable and material dependent. Further research regarding the brushing force directions should be conducted to better understand their effect on the wear and weight loss of resin based restorative materials.
2) The main problem encountered in this analysis was the underestimated variability among the processes in the same experiment, which led to a lot of significant results and significant interactions. It would be interesting to repeat such an analysis using measurements from a simulation process which uses specimens of different materials in the same experiment to get a better estimate of the true variability.