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Aim of the study: This study aimed at evaluating the internal adaptation in terms of percentage of contact using micro-CT (μCT) for three resin-based composite restorations placed with different filling techniques. Materials and methods: Three resin-based composites were investigated in this study: Low shrinkage resin-based composite applied incrementally Filtek TM P90, Bulk-fill resin-based composite Tetric EvoCeram® Bulk Fill and Sonic Fill composite (Kerr corp. USA) packed using Sonic Fill handpiece. Fifteen maxillary 1 st premolars were collected. A Class II mesio-occlusodistal cavity was prepared on each tooth. After a matrix was applied, all resin composites were used according to their manufacturers' instructions then light cured. Scanning of the specimens was performed using a μCT machine. The percentage of contact (%) for each sample was done by measuring the length of restoration margin and dividing it by the entire length cavity walls in gingival, middle and occlusal μCT sections and calculating their average in percentage. Data was collected and statistically analyzed. Results: Percentage of contact of P90 to their cavities' walls was significantly higher than that of TEC BE which was in turn significantly higher than that of SF. There was no significant difference in percentage of contact of P90 and TEC BF to different parts of their cavities. Percentage of contact of SF was significantly higher in occlusal and middle thirds of their cavities than to the gingival third. Adaptation of P90 to different parts of their cavities was significantly higher than adaptation of SF to the corresponding parts. Conclusions: Bulk fill TEC BF and SF composites did not improve percentage of contact compared to low shrinkage silorane based incrementally placed P90 composite. Furthermore, no difference in adaptation of P90 and TEC BF composites to different parts of cavities, however, adaptation of the SF to the occlusal parts of cavities was much better than to gingival parts.

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