Abstract
Introduction: The durability of marginal ridges has a significant effect on maintaining the structural integrity and functional performance of primary molar teeth. This study evaluates and compares marginal ridge fracture resistance of restored primary molars using two innovative restorative materials: flowable bulk-fill composite and smart monochromatic composite. Materials and Methods: In this experimental study, 38 primary molar teeth were randomly divided into two binary groups. After removal of caries and undermined enamel, conventional amalgam class II preparation (≈ 3mm × 3mm × 4mm) were prepared in one proximal surface. In one group, flowable bulk fill universal composite (Palfique® Bulk Flow, Tokuyama, Japan) was applied and in another group, smart monochromatic universal composite (Omnichroma, Tokuyama, Japan) was placed and cured. All samples subjected to 5000 thermal cycles ranging from 5 to 55 °C. Next, the teeth were mounted with self-curing acrylic resin 1 mm above the CEJ. The fracture resistance of the teeth was measured using a universal testing machine with a maximum force of 1000 N. The intact marginal ridges of the opposite sides were also tested for resistance to failure as control groups. The force at which the marginal ridge is broken indicated the resistance to failure in Newton units. Data were analyzed using the Kolmogorov-Smirnov test. Results: The Kolmogorov-Smirnov test showed that the fracture resistance measurements in both groups have a normal distribution (p>0.05). Also, the comparison of the average resistance in the two composite groups showed that the resistance in the Omnichroma group is significantly higher than the flowable bulk-fill group (p<0.001). Conclusion: Smart monochromatic (Omnichroma) composites have higher marginal fracture resistance than flowable bulk-fill (Bulk-Flow U) composites in the restoration of posterior primary teeth.