Co-blend application mode of bulk fill composite resin

Abstract

Objective:To evaluate the effect of a new application method of bulk-fill flowable compositeresin material on bond-strength, nanoleakage, and mechanical properties of dentine bonding agents.Materials and methods: Sound extracted human molars were randomly divided into: manufacturer ’sinstructions (MI), manual blend 2 mm (MB2), and manual blend 4 mm (MB4). Occlusal enamelwas removed and flattened, dentin surfaces were bonded by Prime & Bond universal (Dentsplyand Optibond FL, Kerr). For the MI group, adhesives were applied following the manufacturer’sinstructions then light-cured. For MB groups, SDR flow+bulk-fill flowable composite resin wasapplied in 2- or 4-mm increment then manually rubbed by a micro brush for 15 s with uncured dentinebonding agents and the mixture was light-cured. Composite buildup was fabricated incrementallyusing Ceram.X One, Dentsply nanohybrid composite resin restorative material. After 24-h waterstorage, the teeth were sectioned to obtain beams of about 0.8 mm2for 24-h and thermocycledmicro-tensile bond strength at 0.5 mm/min crosshead speed. Degree of conversion was evaluatedwith micro-Raman spectroscopy. Contraction gaps at 24 h after polymerization were evaluated andatomic force microscopy (AFM) nano-indentation processes were undertaken for measuring thehardness across the interface. Depth of resin penetration was studied using a scanning electronmicroscope (SEM). Bond strength data was expressed using two-way ANOVA followed by Tukey’stest. Nanoindentation hardness was separately analyzed using one-way ANOVA. Results: Factors“storage F=6.3” and “application F=30.11” significantly affected the bond strength to dentine.For Optibond FL, no significant difference in nanoleakage was found in MI/MB4 groups betweenbaseline and aged specimens; significant difference in nanoleakage score was observed in MB2 groups.Confocal microscopy analysis showed MB2 Optibond FL and Prime & Bond universal specimensdiffusing within the dentine. Contraction gap was significantly reduced in MB2 specimens in bothadhesive systems. Degree of conversion (DC) of the MB2 specimens were numerically more comparedto MS1 in both adhesive systems. Conclusion: Present study suggests that the new co-blend techniquemight have a positive effect on bond strengths of etch-and-rinse adhesives to dentine.