Actual Bonding State of Class-1-restoration Using Flowable-resin-composites Compared to Universal-resin-composite

Objectives: The purpose of this study was to examine the actual bonding state of class-1-restoration using flowable-resin-composites compared to universal-resin-composite.
Methods: Standardized class-1-occlusal-cavity was prepared in 15 extracted human upper molars with a cavity duplicator. The cavities were pretreated by an all-in-one adhesive system, Scotchbond Universal Adhesive(3M ESPE), according to the manufacturer’s instructions. Two flowable-resin-composites, Clearfil Majesty ES Flow(Low-flow)(EF, Kuraray Noritake Dental) and MI Low Flow(MF, GC), and a universal-resin-composite as control, Filtek Supreme Ultra(SU, 3M ESPE), were filled into the cavities using two-layered incremental technique and then were cured. After 24h in water at 37°C, those specimens were trimmed to Three standardized beam specimens(1x1mm) were obtained from each restored cavity, and micro-tensile bond strengths(μ-TBS) to pulpal dentin floor were measured. The data of μ-TBS(n=15) were examined using t-test and Weibull analysis.
Results: Mean μ-TBS in MPa/Weibull modulus(Wm) of three class-1-composite-restorations were EF;24.0/8.1, MF;26.2/4.8, SU;24.4/6.6. There were no significant differences in the mean μ-TBS among three composites. Wm of EF was statistically greater than the value of SU and MF. Wm of MF was significantly smaller than the value of SU at p<0.01. There was no significant difference in the stress to give 10% failure among EF(19.3MPa), MF(17.9MPa) and SU(18.6MPa). In addition, the stress of MF(34.2MPa) to give 90% failure was statistically greater than the values of SU(29.6MPa) and EF(28.25MPa) at p<0.05, and no significant difference in the stress to give 90% failure was recognized between EF(28.25MPa) and SU(29.6MPa).
Conclusions: The intra-cavity dentin bond strengths of two flowable-resin-composites examined in this study were statistically similar to the value of universal-resin-composite. In the bonding reliability based on Weibull modulus, EF was statistically greater than both SU and MF, but MF was significantly smaller than SU. There was no significant difference in the stress to give 10% failure among three composites.