2020 Volume 63 Issue 1 Pages 44-51
Purpose: One of the key factors of root fracture, which has increased as a cause of tooth extraction, has been found to depend on the difference in elastic modulus between post metals and root dentin. To address this issue, attempts have been made to approximate the elastic modulus of the abutment construction to that of dentin by using a fiber post with composite resin. Recently, with the aim of increasing the bond strength between root dentin and resin abutment construction, the method of using resin cement for the post part with flowable resin for the core part has been used. However, there have been no reports on the assessment of bond strength between resin cement and flowable resin. In this study, we used two types of resin cement, methyl methacrylate (MMA) resin and composite resin, and 1) analyzed the difference in bond strength between each resin cement and composite resin, and 2) assessed the bond strength by observing the morphology of the fractured surface of the samples.
Methods: Two resin cements, MMA resin (Super-Bond; SB) and composite resin (ChemiaceⅡ; CAⅡ), and a flowable resin, Bulk Base Hard (BBH), were used. Each resin cement was attached to BBH at 10, 60 or 600 s after filling into the mold, and was stored for 15min at 37℃ after hardening BBH by light irradiation. Furthermore, shear strength was analyzed after warm bathing for 24 h at 37℃ and the morphology of the fractured surface was observed by optical microscope.
Results: In SB, the group of 10 s after beginning of polymerization exhibited significantly higher shear strength than the group of 600 s. However, CAⅡ showed no significant difference between any groups. Furthermore, the SB group of 10 s showed higher shear strength than the 10 s group of CAⅡ whereas there was no significant difference between the SB and CAⅡ groups of 60 and 600 s. Regarding the morphology of the fractured surface, SB indicated 90% mixed destruction of SB and BBH at 600 s whereas 90% BBH destruction was observed in the other conditions. CAⅡ showed BBH destruction of 100%, 90% or 70% at 10, 60 or 600 s, respectively. There was no destruction in SB and CAⅡ.
Conclusion: Unpolymerized SB demonstrated the highest bond strength by attaching to BBH in 10 s after filling into the mold. Furthermore, the bond strength of SB was almost equivalent to that of composite resin when BBH was attached to SB in 60 s. The bond strengths of SB and CAⅡ were stable because there was no destruction in both cements.
