Effect of dynamic loading and different adhesive systems on microleakage

Microleakage is an important factor, because it influences the initiation of secondary caries, as well as the survival rate of posts and restorations, ultimately, the failure of endodontic treatment. Microleakage is related to the rigidity of the post, the solubility of the cement, and the strength of the adhesive bond between posts and tooth structure. Clinically, microleakage is caused by fatigue, a form of failure that occurs in structures subjected to dynamic stress. Fatigue is influenced by stress levels, design geometry, the condition and configuration of component surfaces, and the environment. Fatigue occurring as a result of repeated loading can induce microcracks and adhesive failure along the interface between the core and tooth structure.The purpose of the recent in vitro study is to evaluate of influence of dynamic loading and different adhesive systems on the microleakage. SEM microphotographs were used to evaluate the interfacial regions around the posts. 80 premolars periodontically and orthodontically-extracted used for thisvstudy. The crown of the teeth was sectioned at the cementoenamel junction using a low speed diamond saw. A working lenght for each root was then establised at 1 mm short of the apical foramen using digital radiography and a #10 file. After post preperation, the roots randomly were assigned 4 groups and restored with different adhesive systems. Group 1; Rely X ARC (RA) + Single Bond (SA), Group 2; Clearfil SA Cement (CL) , Group 3; Panavia F 2.0 (PAN), Group 4; Rely X Unicem (RU). All the groups restored one type of glass fiber post. All the samples restored with hybrid composite resin and Ni-Cr metal alloys. Half of specimes of each subgroup (n=10) were dynamically loaded in a universal testing machine, (50.000 cycles, 1.7 Hz, 98 N). For leakage study apical part of the roots were attached computerized fluid filtration device. Leakage quantity was determine of %Lp .Following the leakage test the roots were sectioned transversally in three slices (apical, middle, coronal) and processed for scanning electron microscopic analysis to observe bonding interface formation, quality of the hybrid layer and density of resin tags using a four-step scale method. The Two Way ANOVA test was used first to detect overall significance, followed by Two Sample T Test to identify which pairs of groups had significant differences (P ?.05). According to result of this study dynamic loading significantly increased the microleakage values Rely X ARC (p=0.005), Clearfil SA Cement (p=0.002) and Rely X Unicem (p=0.001). But Panavia F 2.0 was not effected by the cyclic loading (p=0.111). Formation of a hybrid layer and resin tags were evident in all groups. There was statistically (p=0.039) significant difference between the regions analysed in each group (Friedman test) and between groups (p=0.048) in each section depth (Kruskal?Wallis test). More resin tag formation in the group of RA created the significant difference (D12, D13, D14 ? Dmax = 14.67). Dynamic loading significantly increased microleakage values of the groups RA, RU, CL (p ? 0.05). But the group PAN was not effected by the dynamic loading (p ? 0.05). Using different adhesive systems effected the formation of hybrid layer and quantitiy of the resin tags.Key words: Dynamic loading, adhesive systems, computerize fluid filtration, hybrid layer, SEM investigation