Effect of C-Factors on the Marginal Gap around two types of Composite

Method: 128 extracted human sound molars were used. The occlusal surface was wet-ground to obtain flat dentin.. Teeth were divided into four main groups (thirty two each) in which cylindrical cavities were prepared representing different C-factors: 2.6 , 3, 4.2 and 5.  each group was subdivided into 2 subgroups (sixteen each) according to the type of composite. The cavities in subgroup A were restored with  Futurabond DC and Grandio SO  while those in subgroup B were  restored with Clearfil SE bond and Clearfil Majesty Esthetic.  Eight samples in each subgroup were thermo-cycled at 5ºc & 55ºc for 600 cycles. 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

Result: The median values (IQR) of the marginal gap were 0 (0) in all the samples restored with Grandio SO (subgroup A) either subjected or not subjected to thermo-cycling. The same was found in subgroup B restored with Clearfil Majesty Esthetic 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. Thermo-cycling had a significant effect on marginal gap formation particularly in samples restored with Clearfil Majesty Esthetic composite (subgroup B) with high C-factor preparations (group III & IV).

Conclusion:

The C-factor could predict the performance of the composite resin restorations,