Microtensile dentin bond strength evaluation of different adhesive systems: in vitro study

Abstract

Introduction: Modern restorative dentistry has been extensively influenced by the fast progress in dental adhesive technology. To assess the effectiveness of adhesive systems and to predict their clinical performance the resin-dentin bond strength tests has been widely used. Purpose: The goal of this study was to compare the microtensile bond strength of five different adhesives systems at the dentin-composite interface and evaluate failure modes. Materials and methods: Flat dentin surfaces were prepared in 25 non-carious human molars. Exposed dentin surfaces were wet-grounded with 240-, 400- and 600-grit silicon-carbide sandpaper to create bonding surfaces with a standardized smear layer. The teeth were randomly divided into 5 distinct groups according to the adhesive system tested: three self-etching adhesive systems, Xeno® V+ (Dentsply DeTrey, Konstanz, Germany); Xeno® III (Dentsply DeTrey, Konstanz, Germany) and ClearfilTM SE Bond (Kuraray Medical Inc., Okayama, Japan), and two etch-and-rinse adhesive systems, OptiBondTM FL (Kerr, Orange, CA, USA) and Prime&Bond® NT (Dentsply DeTrey, Konstanz, Germany) applied with respect to manufacturer’s instructions. After adhesive procedures a 4-mm thick composite crown was built over the bonded surface. Following the storage in distilled water at 37 ºC, the samples were vertically cross-sectioned until obtaining sticks with 1.37mm2 of cross-sectional area which were tested in tension in a universal testing machine at 0.5 mm/min. Data were analyzed by one-away ANOVA and a Tukey HSD post-hoc test (p<0.05). The mode of failure was also analysed with optical microscopy. Additionally, dentin disks were obtained, treated with the different conditioners and primers and observed by scanning electron microscopy (SEM). Results: The following microtensile bond strengths were registered (mean in MPa±SD): Group I – Xeno® V+ 3.70±5.01; Group II - Xeno® III 18.94±13.87; Group III – OptiBondTM FL 43.29±12.74; Group IV- Prime&Bond® NT 39.64±15.06 and Group V – ClearfilTM SE Bond 42.80±10.65. Etch-and-rinse (OptiBondTM FL; Prime & Bond® NT) and two-step self-etching (ClearfilTM SE Bond) adhesive systems attained significant higher microtensile bond strength, without statistically significant differences between them. Significant lower values were obtained for Xeno® V+ comparing to Xeno® III. Cohesive composite failures were related with the higher bond strength values, whereas the adhesive failures were associated with the lowest bond strength values. Conclusion: Among the materials evaluated, etch-and-rinse and two-step self-etching adhesive systems presented higher dentin bond strength than the one-step self-etching adhesive systems.