RÉSUMÉ
Statement of problem: New dental materials and techniques have been introduced in the past few years of fabricate all ceramic crowns with improved strength, biocompatibility and better fit. However poor marginal fit still considered a common disadvantage of these esthetic crowns
Purpose: This study investigated the influence of different luting agents and thermalcycling on the microleakage of recently developed all-ceramic crowns
Materials and Methods: A hundred twenty human maxillary premolars were prepared for all-ceramic crowns with the following preparation criteria: 6-degree axial taper, 1.5 mm shoulder finish line placed 0.5 mm occlusal to the CEJ, 2 mm occlusal reduction and occluso-gingival height of 5 mm. prepared teeth were restored with Empress 2 all-ceramic crowns. Six luting agents [Superbond C and B; [SB], Rely X ARC; [RX], Mirage FLC; [MF], GC Fuji CEM; [FC], ProTec CEM; [PT] and Zinc phosphate cement; [ZP]] were used for cementation [n=20]. After 1-week storage in water, half of the specimens of each group [n=10] were thermal cycles for 70000 cycles. Specimens were then immersed in 50 wt% aqueous solution of silver nitrate for 2 hours. Each specimen was embedded in clear acrylic resin and aqueous solution of silver nitrate for 2 hours. Each specimen was embedded in clear acrylic resin and sectioned mid mesiodistally and buccolingually using Isomet 1000 Precision Saw. For each section the degree of microleakage was graded 0, 1, 2, 3 or 4 starting from the cervical margin using a stereomicroscope at 150 X original magnification. The Kruskal-Wallis test was used first to detect overall significance, followed by Mann-Whitney U tests to identify which pairs of groups had significant differences [alpha = 0.5]
Results: Thermalcycling significantly increased the degree of microleakage for all test groups at tooth/cement [T/C] and ceramic/cement [C/C] interfaces as follow, ZP [T/C, P = 0.0002], [C/C, P=0.0001]; PT [T/C, P = 0.0003], [C/C, P= 0.004]; FC, [T/C, P = 0.001], [C/C, P= 0.003]; SB, [T/C, P=0.002], [C/C, P=0.001]; RX, [T/C, P = 0.004], [C/C, P=0.011] and MF, [T/C, P = 0.008], [C/C, P = 0.009]. However adhesive resin cements and the paste form of hybrid glass ionomer cement significantly decreased the degree of microleakage compared to zinc phosphate cement [P<.05]Conclusion: There was a significant increase in the degree of microleakage after thermal cycling for all test groups at both tooth/cement and ceramic/cement interfaces. Adhesive resin cements and the past form of hybrid glass ionomer cement decreased the degree of microleakage
Clinical implications: Within the limitations of this in vitro study, the use of adhesive resin cements with a compatible dentin bonding agent and the paste form of hybrid glass ionomer cement are preferred for cementation of Empress 2 all ceramic crowns. These luting agents could improve the longevity of Empress 2 all-ceramic crowns