Microtensile Bond Strength and Microhardness of Resin–dentin Bonds using Different Resin-based Composite Systems

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Abstract
Introduction: Dental caries remain a major global health concern, emphasizing the need for durable restorative materials with reliable mechanical properties. This study aimed to compare the μTBS and Vickers hardness number (VHN) of three composite materials (3M Filtek Z250, Kerr OptiShade, and SHOFU Beautifil II LS) on sound coronal dentin using a corresponding bonding system (3M Universal Bond, Kerr OptiBond, and SHOFU BeautiBond Universal Adhesive, respectively). Methods: Dentin surfaces were exposed from twelve extracted molars. Each composite and its respective adhesive were applied and cured. The teeth were cut into 1 × 1 × 8 mm beams. Twenty beams per group were tested for μTBS. Additionally, 20 composite discs (2 x 10 mm) were prepared for each material. VHN was measured at three sites per disc, and mean values were calculated. Results: Filtek Z250 showed the highest VHN, followed by OptiShade and Beautifil II LS, with significant differences among all groups. OptiShade demonstrated the highest μTBS, followed by Filtek Z250 and Beautifil II LS. μTBS differed significantly between Beautifil II LS and both Filtek Z250 and OptiShade but not between Filtek Z250 and OptiShade. Discussion: Differences in filler composition, resin matrix characteristics, and adhesive protocols likely contributed to the variations observed in microhardness, bonding performance, and restoration longevity. Conclusions: Filtek Z250 exhibited superior microhardness, while OptiShade demonstrated superior bond strength. Beautifil II LS performed the worst in both tests. These findings support evidence-based material selection to enhance restoration longevity.

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