An In Vitro Evaluation of the Effect of Saliva and Thermal Aging on Micro Shear Bond Strength of surface treated Zirconia to Resin Cement

INTRODUCTION: Zirconia materials are being extensively used in dentistry in recent years because of their strong mechanical properties, biocompatibility, and esthetic benefits. Apart from these advantages zirconia restorations have some disadvantages, one of the disadvantages include improper bonding with the resin based cements, as proper micro mechanical interlocking and chemical adhesion on to ceramic surfaces are important for creating a strong bond between zirconia and resin cements. The silica free and glass free structure of zirconia makes it a special material where excessive mechanical or abrasion methods are required to increase the surface roughness. AIM OF THE STUDY: The aim of this in vitro study is to evaluate the effect of saliva and thermal aging on the micro shear bond strength of surface treated zirconia to resin cement. MATERIALS AND METHODS: Thirty zirconia specimens with final dimensions of (12 mm ± 0.4 mm × 10 mm ± 0.4 mm × 3 mm ± 0.3 mm ) are prepared and subjected to hot chemical etching for 30 minutes. MDP containing resin cement is cemented to the hot chemical etched zirconia surfaces and divided into following groups;(Group I )Specimens subjected to immediate micro shear bond strength(after 24 hours);(Group II) Specimens subjected to salivary storage for 30 days without thermocycling and tested for micro shear bond strength; (Group III) Specimens subjected to artificial salivary storage for 30 days followed by thermocycling and tested for micro shear bond strength. Specimens in Group I are subjected to immediate micro shear bond strength- after 24 hours, specimens in Group II and Group III are subjected to micro shear bond strength followed by salivary storage without thermocycling and salivary storage with thermocycling using universal testing machine at a crosshead speed of 0.5 mm/min .The statistical analyses are performed using ANOVA test for overall Intragroup Comparison, Post-hoc analysis for Individual Intra-group Pair-wise Comparison and Paired-t-Test for Surface roughness analysis. RESULTS AND STATISTICAL ANALYSIS : Statistical significant difference is found between all the three groups (p < 0.05). Group 1 showed higher micro shear bond strength values than group II and group III . Group II showed higher micro shear bond strength values than group III .Least micro shear bond strength values are noted for group III specimens. Surface roughness values are greater for the specimens after hot chemical etching. CONCLUSION: Hot chemical etching method increased the surface roughness and immediate micro shear bond strength. The MDP containing resin cement showed improved initial bond strength. Hot chemical etching for 30 minutes followed by artificial salivary storage both with and without thermocycling had effect on the micro shear bond strength as it reduced the bond strength values