Effect of Dynamic Load on Microleakage of MODB Hybrid Ceramic Onlay Restoration

 Purpose: Every patient would like minimally invasive and aesthetic dental treatment; hybrid ceramic restoration is one treatment that can satisfy such desires. This study examined the effect of dynamic load simulating mastication on the microleakage of MODB hybrid ceramic onlay restorations.<br> Methods: The standardized MODB onlay cavity was prepared in 32 extracted human lower molars using a cavity duplicator with a master cavity. The dentin surfaces of duplicated cavities were pretreated with an all-in-one adhesive system (Crearfil Tri-S Bond, Kuraray Noritake Dental) and were sealed with a low-viscosity resin composite (Clearfil Protect Liner, Kuraray Noritake Dental). Impressions of immediate sealed cavities were taken and were poured with a high-strength dental stone. MODB onlays were fabricated on the stone dies with a hybrid ceramic material (Estenia C & B, Kuraray Noritake Dental). The onlays were bonded with a dual-cure resin luting cement (Clearfil Esthethic Cement, Kuraray Noritake Dental). Restored specimens were divided into two groups (n=16) : a group with dynamic load stress (S+) simulating mastication, and a group without stress (S−, control). For the S+ group, dynamic load stress (16.0 kgf×3×10⁵ times) was applied to the restored specimens in circulated water at 37°C. For the S− group, no stress was applied. The restored specimens with and without dynamic load stress were immersed in 1% methylene blue solution at 37°C for 60 min. Each specimen was sectioned mesiodistal-vertically to obtain two slabs of 1.0-mm thickness. The slabs were polished with a series of SiC papers up to 2,000 grid. Microleakage in the lingual (L) and gingival (G) walls of each slab was evaluated by a graded criterion. The data of microleakage were examined using the Kruskal-Wallis test.<br> Results: Microleakage of L (S+) was significantly greater than that of L (S−) at p<0.01, although no difference was found between the microleakage of G (S+) and G (S−). The leakage of L (S+) was significantly greater than that of G (S+) at p<0.05, but the leakage of L (S−) was statistically similar to that of G (S−).<br> Conclusion: The dynamic load significantly increased the microleakage in the lingual wall of the MODB hybrid ceramic onlay restoration. However, the leakage in the gingival wall did not vary with the stress. The difference in the microleakage between lingual and gingival walls was recognized only under the dynamic load condition.