[A comparative study on the depth of cure, hardness and microleakage applied to primary teeth of different types of...

Objective: To compare the depth of cure, surface hardness and microleakage applied to primary teeth of three types of bulk-fill resins, so as to provide reference for clinical application. Methods: Composite resin Filtek^TM Z350 XT (group A) and giomer Beautifil Ⅱ (group B) were used as controls, high-viscosity bulk-fill resin Filtek^TM Bulk Fill (group C), sonic-activated bulk-fill resin SonicFill 2 (group D) and flowable bulk-fill resin SDR^® flow+(group E) were studied. The microstructure of each group was observed by scanning electron microscope (SEM). Specimens of each group were prepared (6 pieces per group), and the Vickers microhardness of the surface layer and different depths of each group were measured, and then the depths of cure were calculated. Twenty-five primary molars dentin were filled by resins of each group (5 teeth per group), sliced, then aged, slices of each group were developed by silver ion staining. SEM was used to observed the distribution of silver ions. Microleakage of each group were analyzed by Jonckheere-Terpstra rank sum test. Results: SEM showed that the filler particles in groups A and C were spherical and evenly distributed. The shape of the fillers in groups B, D and E were polygonal and unevenly distributed. The surface hardness of groups A, B, C, D and E were (84.97±6.30), (65.04±5.95), (57.80±1.18), (60.77±2.34), (33.32±1.83) MPa respectively. Group A had the highest hardness, while group E was the lowest, and the differences between the two groups and other groups was statistically significant (P<0.05). There were no statistically significant differences among groups B, C, and D (P>0.05). The curing depths of groups A, B, C, D and E were 2.6, 3.4, 5.8, 3.8 and 7.8 mm respectively. The largest microleakage was found in group E [2% (1/50) for grade 0, 22% (11/50) for grade 1, 30% (15/50) for grade 2, 24% (12/50) for grade 3, and 22% (11/50) for grade 4], which was statistically different from other groups (P<0.05). No statistically significant differences were found among other 3 groups (P>0.05). Conclusions: Both high-viscosity and sonic-activated bulk-fill resins have the greater depth of cure, the same hardness and microleakage as giomer, which might be an option for restoration in primary teeth.