الفهرس 
Resin based compositesOnly 14 pages are availabe for public view
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Abstract
Keywords:C-factor, Marginal gap formation,Self-etch adhesives,Composite resin,Thermo-cycling.Aim: To evaluate the effect of different factors on the marginal gap formation of two types of contemporary composite resin systems.Materials and methods:One hundred and twenty eight freshly extracted human sound molars were used.The occlusal surface of each tooth was wetground until flat dentin surfaces were obtained. Teeth were divided into four main groups(thirty two each)in which cylindrical cavities were prepared representing different C-factors: 2.6 in group I,3 in group II,4.2 in group III and 5 in group IV. Samples in each group were subdivided into 2 subgroups sixteen each) according to the type of composite resin system to be used for restoration. The cavities in subgroup A were restored with two-step self-etch adhesive (Clearfil SE bond) and nanohybrid composite (Clearfil Majesty Esthetic) while those in subgroup B were restored with one-step self-etch I adhesive (Futurabond DC) and nanohybtjid composite (Grandio SO).Eight samples in each subgroup were thermo-cycled at 5°c & 55°c for 600 cycles(30 second dwell time, 20 second transfer time). Samples of both subgroup were processed for SEM evaluation to examine the restoration margins at(25x and 500x) magnification. The marginal gap was measured for all the samples using AutoCAD software.Results: The median values (IQR) of the marginal gap were 0 (0) in all the samples restored with Clearfil Majesty Esthetic(subgroup A)either subjected or not subjected to thermo-cycling. The same was found in subgroup B restored with Grandio SO in the samples not subjected to thermo-cycling, while those subjected to thermo-cycling,a direct relation was.found between C-factor and gap length recording values of 6(7.3),12.27(14.33), 23.71(26.10) and 32.57(13.10) for groups I, II,III and IV respectively.Thermocycling had a significant effect on marginal gap formation particularly in samples restored with Grandio SO composite (subgroup B) with high Cfa, ptorpreparations (group III & IV). The two tested composite resin systems had a significant effect on the marginal gap particularly in high factor preparations (group III and IV). The C-factor had no significant effect on the marginal gap except in samples restored with Grandio SO composite(subgroup B)Clinical significance: The C-factor could predict the performance of the composite resin restorations, as it is related to the restoration’s capacity for relieving stress by flow.