Abstract
Objective: To evaluate the effect of a new application method of bulk-fill flowable composite resin material on bond-strength, nanoleakage, and mechanical properties of dentine bonding agents. Materials and methods: Sound extracted human molars were randomly divided into: manufacturer’s instructions (MI), manual blend 2 mm (MB2), and manual blend 4 mm (MB4). Occlusal enamel was removed and flattened, dentin surfaces were bonded by Prime & Bond universal (Dentsply and Optibond FL, Kerr). For the MI group, adhesives were applied following the manufacturer’s instructions then light-cured. For MB groups, SDR flow+ bulk-fill flowable composite resin was applied in 2- or 4-mm increment then manually rubbed by a micro brush for 15 s with uncured dentine bonding agents and the mixture was light-cured. Composite buildup was fabricated incrementally using Ceram.X One, Dentsply nanohybrid composite resin restorative material. After 24-h water storage, the teeth were sectioned to obtain beams of about 0.8 mm2 for 24-h and thermocycled micro-tensile bond strength at 0.5 mm/min crosshead speed. Degree of conversion was evaluated with micro-Raman spectroscopy. Contraction gaps at 24 h after polymerization were evaluated and atomic force microscopy (AFM) nano-indentation processes were undertaken for measuring the hardness across the interface. Depth of resin penetration was studied using a scanning electron microscope (SEM). Bond strength data was expressed using two-way ANOVA followed by Tukey’s test. 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 between baseline and aged specimens; significant difference in nanoleakage score was observed in MB2 groups. Confocal microscopy analysis showed MB2 Optibond FL and Prime & Bond universal specimens diffusing within the dentine. Contraction gap was significantly reduced in MB2 specimens in both adhesive systems. Degree of conversion (DC) of the MB2 specimens were numerically more compared to MS1 in both adhesive systems. Conclusion: Present study suggests that the new co-blend technique might have a positive effect on bond strengths of etch-and-rinse adhesives to dentine.
Highlights
Resin-based composite restorative materials are a cornerstone in modern-day dental practice because of their excellent esthetics and chemo-mechanical properties [1,2,3]
Acid-etching (35–37% phosphoric acid) procedure improves the performance of composite resin restorations when placed on enamel, but [9] this does not work as well with dentine [10] because of its heterogeneity in structure and composition representing a complex biological substrate [11,12]
The use of hydrophilic resin monomers to penetrate acid-etched demineralized dentine have improved the immediate performance of resin–dentine bonding systems [4]; but is not the same in terms of performance for long-term periods
Summary
Resin-based composite restorative materials are a cornerstone in modern-day dental practice because of their excellent esthetics and chemo-mechanical properties [1,2,3]. Almost all of the products currently in the market can achieve acceptable immediate bond strength, adhesive bonds degrade over a period of time [6]. Solutions to this have always remained elusive, as contributing mechanisms and the degree of degradation analyzed has never been consistent for all adhesive systems [7,8]. The use of hydrophilic resin monomers to penetrate acid-etched demineralized dentine have improved the immediate performance of resin–dentine bonding systems [4]; but is not the same in terms of performance for long-term periods
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