Effect of Hydrochloric Acid on Resin Cement Microleakage in Zirconia-Reinforced Lithium Silicate Crowns

Purpose: To evaluate the microleakage of different resin cements after immersion of zirconia-reinforced lithium silicate crowns (ZLS) in hydrochloric acid (HCl) solution. Materials and Methods: Forty-five extracted non-carious human molars were prepared for porcelain crowns. The teeth were randomized into three different groups according to the resin cements tested: RelyX™ UniCem (3M, ESPE), Variolink® Esthetic Dual-cure (Ivoclar Vivadent) and Panavia™ 21 (Kuraray America Inc.). Five replicates were used as a control for each of the resin cements. ZLS crowns were designed and milled from Celtra® Duo blocks using CEREC computer–aided design, computer assisted manufacturing (CAD/CAM) system and then cemented to the prepared teeth using the assigned cement according to the manufacturers' guidelines. The samples were thermal cycled between water temperatures of 5℃ and 55℃ for 5,000 cycles with a 15 second dwell-time after each temperature. In order to mimic one year of clinical time in a patient's mouth, the samples of the experiment group were subjected to 91 one-hour cycles in HCl (pH 2) followed by one hour in artificial saliva; samples were submersed in artificial saliva for 91 hours. The specimens then were submerged in 50% silver nitrate solution for 24 hours followed by a developer solution for eight hours. All samples were embedded in clear epoxy resin and sectioned in a buccolingual direction at 0.5 mm. Sections were analyzed by a stereomicroscope at a magnification of 10X. Proportion of microleakage was calculated by dividing the total length of the dye penetration by the total length of the restoration. Data were analyzed with the Kruskal-Wallis test and Mann-Whitney U test with the Bonferroni correction. Results: All experimental groups demonstrated higher microleakage scores than the control groups for all types of cement. There was no statistically significant difference in median microleakage among the three cements tested (p>.05). Panavia 21 group showed the highest median microleakage score (59.24%) followed by Rely-X UniCem (54.95%) and Variolink Esthetic (45.83%). Conclusion: Within the limitations of this in-vitro study, all the resin cements tested exhibited microleakage to some degree, especially when they were exposed to the hydrochloric acid solution.