الفهرس 
List of contentsOnly 14 pages are availabe for public view
 |  | from | 107 |  |  |
| | | from | 107 | | |
Abstract
Objectives : Despite innovations in resin composite (RC) restorative materials, some drawbacks still compromise their longevity. Attempts have been made to improve their physical and mechanical properties, including preheating technique. This study was undertaken to evaluate the effect of preheating on 3-year clinical performance of a nanofilled RC in Class I restorations. In addition, the effect of preheating on microhardness (HN), surface roughness and fracture toughness of a nanofilled RC was laboratory investigated. Materials and Methods: For clinical trial, 35 patients with a total of 70 posterior lesions were enrolled in the study. Every patient received one pair of Class I nanofilled RC (Filtek Z350 XT) posterior restorations in split-mouth design. One side of the mouth received preheated composite however in the other side the composite was placed in non-heated state following the manufacturer instructions. The restorations were evaluated using World Dental Federation (FDI) criteria to the periods of 1 week (baseline), 12-, 24- and 36-Month. The changes in the parameters during the evaluation period were statistically analyzed using Wilcoxon and Friedman test. The level of significance was set at p<0.05. Regarding laboratory investigations, a total of 28 disc-shaped specimens were fabricated from the tested nanofilled RC using a Teflon mold (10 mm diameter x 2 mm thickness) for HN and surface roughness tests. Half of the specimens (n=14) was fabricated from preheated composite however the remaining specimens were fabricated from non-heated one. Microhardness was measured by means of Vickers microhardness (VHN) tester. While surface roughness measurements (Ra) was obtained by atomic force microscope (AFM). For fracture toughness test, a total of 14 single-edge-notchedbeam specimens was fabricated from heated and non-heated nanofilled tested RC. The specimens were evaluated via three-point bending mode, using a universal testing machine at crosshead speed of 1.0 mm/min until failure occurred. The collected data were tabulated and subjected to statistical analysis. Results: Regarding clinical evaluation, all FDI parameters revealed insignificant differences between preheated and non-heated RC groups (p˃0.05) except a significant difference was detected for marginal staining criterion at 36- Month. In time, marginal staining of the nonheated restorations showed significant difference between evaluation periods (p<0.05). Postoperative sensitivity of either preheated or non-heated was prominent at baseline and disappeared gradually over the evaluation period. For laboratory investigations, independent sample t-tests revealed no significant difference between preheated and non-heated RC groups for all tests (p>0.05). However, for HN test, there were significant differences between top and bottom surfaces for preheated RC and non-heated RC groups (p<0.05). Moreover, surface roughness average Ra (nm) mean values of preheated RC group was higher than non-heated RC group but no significant difference between them was found (p>0.05). Conclusions: After 3-years, the preheated nanofilled resin composite showed acceptable clinical performance similar to that of the non-heated one in Class I restorations. Laboratory investigations revealed that preheating of nanofilled RC had no negative effect on microhardness, surface roughness and fracture toughness.