Evaluation of thermocycling and cyclic loads on the amount of microleakage of resin bonded restorations Dr. H. Siadat* - Dr. A. Mirfazaelian* - Dr. S. Mirmohammadrezaee* *- Assistant Professor of Removable Prosthodontics Dept. - Faculty of Dentistry – Tehran University of Medical Sciences. Background and Aim: Resin bonded restorations are preferred to the conventional ones due to their potential prevention of the unwanted tooth structure destruction, however the rate of success depends on different factors such as: resin cements and metal surface treatment. The aim of this study was to compare the amount of microleakage between two methods of metal surface treatments and three kinds of resin cements. Materials and Methods: In this experimental study, 96 disks were cast with Cr-Co alloy and machined to 15 mm diameter and 2 mm thickness with a handle in the center by an engineering lathe. Half of the samples were sandblasted with 50 µm Aluminium oxide at 7 bars of air pressure. The other half were firstly sandblasted and degazed. Then one layer of slurry opaque (1 gr of opaque porcelain powder plus 0.5 ml of distilled water) was applied on their surfaces. Disks in opaque and sandblast groups were divided randomly into two equal groups of case and control. Each group was divided into 3 groups of 8 each. In each group, the disks were mounted on a surveyor two by two against each other and cemented by a load of 20 N using one of these 3 resin cements: Panavia 21, All - bond 2 and Enforce. All samples of case group were thermocycled 2000 times (temperature between 5° C - 55° C) and then cyclic loading was applied with a force of 100 N for 112000 times at 1.5 Hz frequency. All samples were then immersed in a 0.5% basic fushin solution for 24 hours. Then were separated and scanned. Colored surface of each image of disks surfaces was calculated by Auto-CAD. Data were subjected to one - way ANOVA and Post Hoc test of Scheffe type. Results: All samples of Panavia 21 + opaque (case) were failed during cyclic loading. The group of Panavia 21 + opaque (control) showed the highest microleakage (10.27±11.25) and the difference between this group and the other ones was highly significant (P<0.001). Enforce + opaque (case) group showed microleakage (4.39±6.91) and the difference between this group and other groups was significant was found between other groups. Conclusion: The application of Panavia 21 and Enforce with slurry opaque porcelain as a metal surface treatment is not recommended. Key words: Thermocycling – Cyclic loading – Microleakage – Resin bonded restorations – Dentin bonding - Opaque | 
