In vitro study of marginal gap and microleakage of three type of cements in zirconia crowns Download PDF

Background and Aim: One of the concerns of dentists in full coverage restorations, is microleakage and marginal gap of crowns. Due to the high prevalence of decay in society and inefficiency of common treatments in some dental restorations, demand for ceramic restorations with convenient features is increasing day by day. Information about these kinds of restorations particularly those that are made of zirconia is limited. Studies showed certain inconsistencies, such as some studies suggested that most microleakage and marginal gap ocuurs in glass ionomer cements whereas some others showed more microleakage and marginal gap in self adhesive resin cements. Due to the lack of information about the physical characteristics of majority of luting cements, this in vitro study designed to investigate the influence of RelyX Unicem, RelyX ARCand RMGI cements on microleakage and marginal gap in zirconia fullcoverage crowns. Methods and Materials: According to similar articles and considering of Kruskal-Wallis One-way ANOVA test which is used for comparison between the three groups; 10 samples for each group and a total of 30 samples were collected for this study. 30 intact human premolar teeth which have been recently extracted for orthodontic purposes, were selected. After extraction, teeth being drawn in distilled water at room temperature. For storing samples 0/1% thymol solution were used. Then samples were mounted by Speedex putty and teeth preparation was done by high speed bur. By 3shape device samples were scaned at 3 angles and die spacer thickness selected as 30 micrometers on device computer. Then chosen zirconia blocks choice inserted in imes-icore CAD/CAM system and milling stage was done. Sintering processe was done by putting samples in MIHM-VOGT and and after seven hours this step completed. The samples were tested on teeth with fit checker and after the correction porcelain applied by layering technique and vacuum infusion process. After final preparations, crowns margins were checked. To evaluate the marginal gap of samples before cementation, crowns filled with light body impression and then put on teeth. After setting time excess material protruding from the edge of crowns margins was cut and the samples were analyzed by a stereo microscope eqquipped with a digital micro meter. Results: The results showed that after the cementation the marginal gap was significantly increased in all 3 groups of cements. The marginal gap of RelyX ARC cement was significantly higher than two other cements, while the microleakage of RelyX Unicem cement and RMGI showed no significant difference. There was no significant difference in the evaluation of microleakage between 3 groups of cements. In the context of evaluating the relationship between the marginalgap and microleakage no significant relationship was found (P> 0.001). Conclusion: Based on resuts of our study and due to other researches, we could conclude that self-adhesive luting cements have better physical and clinical characteristics than dual-cure or glass-ionomer cements. In current study the amount of marginal gap of RelyX Unicem cements was significantly less than RelyX ARC, and due to the more convenient clinical application and lower level of technique sensitivity, and also taking into account the better physical properties of resin cements than glass ionomer cements, we can recommend to use RelyX Unicem self-adhesive cement instead of older RelyX ARC and RMGI cement.