الفهرس 
Factors affect the color stability of dental ceramicOnly 14 pages are availabe for public view
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Abstract
Tooth bleaching has become popular in dentistry since it has been shown to be an effective and noninvasive treatment. Despite the fact that microscopic alterations could themselves cause undesirable effects. so Restorations (especially polymer-containing restorative materials) should be protected before any bleaching procedure due to the high risk of color change. Purpose: To evaluate in- office light activated bleaching on translucency of hybrid ceramic by measuring transmittance and absorption of light by Spectrophotometer. A. ENAMIC The specimens were rectangular in shape and their dimensions will be 20mm of length,10 mm of width and 0.8mm of thickness. and these specimens will be randomly divided into 2 groups .Translucency of the samples of group I act as controlled group which were not received32% hydrogen peroxide bleaching agent was measured by measuring transmittance and absorption of light by Spectrophotometer. Samples of group II received 3 times applications of the bleaching agent. Each cycle ranges 15-20 minutes .Then exposed to a LED power bleach system for three cycles – 15 min each with 10 min resting time. new translucency evaluation by the spectrophotomer in the same way as samples of group I. Differences in the translucency between group I & II were statistically analyzed using Independent-samples T test. Results: In this study, comparison of the groups using Independent t-test revealed statistically significant differences in translucency values before and after bleaching (P<0.001) .After bleaching we can observe decrease in absorption of light. Also there was increase in transmittance of light in group II samples when compared with samples of group I. This is proved that bleaching caused highly significant change in translucency values of hybrid ceramic. Materials and Methods: Twenty specimens were prepared in(3M2-T) shade and were cut from CAD/CAM blocks of hybrid ceramic. The study will consist of twenty specimens of hybrid ceramic (VITA Conclusion: In conclusion, statistically significant differences among the translucency changes of all tested samples of groupII were found after exposing them to bleaching agent. Therefore, restorations (especially those with polymer content) should be protected before any bleaching, for fear of color change.