Abstract
This study evaluated the effect of matrix metalloproteinase (MMP) inhibitors - 2% (CHX) and sodium fluoride (NaF) (5000 ppm) - on microtensile bond strength (μTBS) of composite resin to Er:YAG laser-irradiated dentin after chemical degradation of the bond interface. The occlusal surface of forty sound human molars was removed exposing the dentin surface (n=10), which was polished, irradiated with Er:YAG laser, acid etched and dried. Twenty specimens were rewetted with 2% CHX (control group) and 20 were rewetted with NaF (5000 ppm). The adhesive system was applied and a 4-mm-high plateau of light-cured composite resin was built up. Resin-dentin sticks were obtained with a rectangular cross-sectional area (0.8-1 mm2) and were either stored in water at 37 ?#61616;C for 24 h or submitted to chemical degradation. For chemical degradation, they were immersed in 10% NaOCl aqueous solution for 5 h and rinsed in water for 1 h. The sticks were submitted to microtensile test in a mechanical testing machine at 0.5 mm/min until failure. Fracture pattern was analyzed using SEM. μTBS values were calculated in MPa and submitted to analysis of variance ANOVA (α=0.05). The variance analysis showed that the 'MMP inhibitor' and 'degradation' factors (p=0.214 and p=0.093, respectively) and interaction between the factors were not statistically significant (p=0.143). Mixed failure predominated in all groups. In conclusion, the 2% CHX and NaF 5000 ppm presented similar μTBS of composite resin to laser-irradiated dentin before and after chemical degradation.
Highlights
Preparation with Er:YAG laser has been proposed as an alternative technique for removing carious tissue and preparation of micro-cavities [1]
Many studies have demonstrated that CHX may improve the structural stability of collagen matrix in the hybrid layer and decrease time-dependent reduction in resin-dentin bond strength [14,17,19,20]
CHX was used as control group due to a large number of studies demonstrating its efficacy to decrease the degradation of the resin-dentin bonding interface
Summary
Preparation with Er:YAG laser has been proposed as an alternative technique for removing carious tissue and preparation of micro-cavities [1]. The bonding mechanism for irradiated dentin and the impact of the Er:YAG lasers on the collagen fibers have not been completely clarified. Previous studies showed microstructural changes, microruptures and denaturation of collagen fibers [6,7], which may affect the bonding mechanism between the resin materials and dentin, due the bond direct dependence on the interaction of resin monomers with the exposed collagen fibers [8]. Studies have shown that matrix metalloproteinase (MMP) inhibitors, such as chlorhexidine (CHX) and more recently sodium fluoride (NaF), are able to preserve the structural integrity of the hybrid layer and improve the longevity of restorations [11,12,13,14]
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