الفهرس 
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Abstract
This in vitro study was performed to evaluate the effect of preheating the composite and flowable composite on the marginal integrity of class II composite resin restorations Forty extracted human sound molars were used in this study. These teeth were collected from Oral Surgery Department at Tanta University. The teeth were extracted due to periodontal diseases form diabetic patients aged (25-40) years old. Class II cavities with parallel walls were prepared. The cavities were prepared using carbide bur with water spray and finished with fine- grained stone. The cervical margin was established 1.5 mm above the cement - enamel junction. The overall dimensions and depth of the cavities were standardized as follow: 4 mm length occlusocervically and 4 mm width buccolingually and 2 mm depth axially. The cavity depth and length were judged with a permanent mark on the diamond stone and then verified using a periodontal probe. Each bur was replaced after 5 preparations. The teeth were randomly divided into four groups (n=10 each). The prepared cavities were restored with adhesive and composites according to manufacturer’s instructions .The cavites of group 1were restored bycomposite (Grandio) ,those of group 2 were restored by preheated composite, (Grandio), those of group 3 were restored by Flowable composite followed by composite, (Grandio Flow and Grandio) and those of group 4 were restored by Flowable composite followed by preheated composite, (Grandio Flow and Grandio) n 71 In all groups ( Futurabond DC) Universal adhesive (one-step self-etch adhesive) was applied by disposable micro-brush, rubbed for 20s, dried with gentle steam of air for 5s and light cured for 10s according to manufacturer’s instructions.In group2&4 Grandio composite was pre-heated to 60℃ in the C-Warmer device. The samples in each group were thermocycled in a thermo-cycling apparatus (by alternating immersion in water bath at 50c and 500c with a dwell time of 2min) for 600 thermal cycles. Impressions of the teeth were made and then poured with epoxy resin. These replicas were left 24 h for complete setting. Then were examined under SEM with different magnifications (50x, 500x) to study restoration-tooth interface. The result of current study revealed that, the highest mean value of gap length and width proximally and cervically was recorded for group1followed by group 3, while the lowest mean marginal gap length was found at group 4 There were no significant difference between using the composite alone and using flowable composite under it. The lowest mean marginal gap length and width was found at group 4(restored with preheated Grandio &Grandio Flow).There were no significant difference between group2 (preheated Grandio) and group 4 (Grandio Flow& preheated Grandio).