Influence Of Chlorhexidine Pretreatment On Durability Of Resin-dentin Bonds

Background:The longevity of resin restorations is currently an hotspot in adhesive dentistry. Microleakage and the dentine collagen fibrils breakdown has been referred as factors determining the long-term success of composite resin restoration. Ideal marginal seal of resin restorations can be obtained if the margin is on sound enamel. Chlorhexidine (CHX) has an inhibitory effect of the endogenous collagenolytic activity in dentine. It is reported that applying CHX to acid-etched dentin prior to the etch-and-rinse adhesives may prevent the degradation of collagen fibrils and preserve the integrity of hybrid layer.Objectives:To evaluate the influence of enamel border and chlorhexidine pretreatment on resin-dentin microtensile bond strength (μTBS) over time. Methods:Fifty-six extracted non-carious human third molars had a flat dentine surface exposed. Two adhesive systems (Panavia F 2.0, PF; RelyX Unicem Aplicap, UR) were applied and composite resin crowns (Filtek Z250) were constructed. Teeth were divided into 7 groups. Group A, specimens were stored for 3 days. Group B1, specimens were stored for 6 month. Group B2, specimens were stored for 6 month without outer enamel. Group C1, specimens were pre-treated by 2% chlorhexidine then stored for 6 month. Group C2, specimens were pre-treated by 2% chlorhexidine then stored for 6 month without outer enamel. Group D1, specimens were pre-treated by 0.2% chlorhexidine then stored for 6 month. Group D2, specimens were pre-treated by 0.2% chlorhexidine then stored for 6 month without outer enamel. The bonded teeth were sectioned into beams with a cross-sectional area of 0.9mmx0.9mm and further stressed to failure in tension (1mm/min). The data for each adhesive were subjected to a Explore and Univariate Analysis of Variance. The fractured surfaces were examined by scanning electron microscopy (SEM).Results:1,Tensile strength test:the resin cements and margin and chlorhexidine pretreatment had significant effects onμTBS (p<0.05). For PF, lower concentration of CHX digluconate (0.2%) was not able to diminish the loss of bond strength. For UR, lower concentration of CHX digluconate (0.2%) was not able to diminish the loss of bond strength.2,SEM observation:2.1,Panavia FGroup A(3 days):Total cohesive in resin cement and/or in low-viscosity composite layer. Most of the resin tags remained firmly embedded in the tubules. Group B1(6 month&with enamel&no CHX pretreatment):cohesive failure in resin cement.Group B2(6 month&without enamel&no CHX pretreatment):Showing complete removal of the smear plugs, exposed outer peritubular collagen fibers and small traces of the smear layer.Group C1(6 month&with enamel&2% CHX pretreatment):failure at hybrid layer, no dentin surface can be seen.Group C2(6 month&without enamel&2% CHX pretreatment):showing residual smear layer and smear plug partially obliterating the dentinal tubules orifices. The dentine surface with collagen fibrils partially covered by the adhesive resin.Group D1(6 month&with enamel&0.2% CHX pretreatment):failure at hybrid layer, no dentin surface can been seen.Group D2(6 month&without enamel&0.2% CHX pretreatment):Adhesive resin plugs are less than the group C2.2.2,Relyx Unicem:Group A(3 days):A debonded deep dentin specimen that cohesively failed, and luting resin remaining on the dentin surface.Group B1(6 month&with enamel&no CHX pretreatment):Showing failure along the dentin interface.Group B2(6 month&without enamel&no CHX pretreatment):Showing complete removal of the smear plugs.Group C1(6 month&with enamel&2% CHX pretreatment):Demonstrating cohesive failure at the cement-adhesive interface.no dentin surface can been seen.Group C2(6 month&without enamel&2% CHX pretreatment):Failure can be observed to be partially adhesive, where remnants of the resin cement remained on the tooth surface.Group D1(6 month&with enamel&0.2% CHX pretreatment):cohesive failure at the cement-adhesive interface, no dentin surface can been seen.Group D2(6 month&without enamel&0.2% CHX pretreatment):failure along the dentin surface, partial removal of the smear plugs in dentinal tubules.Conclusions:enamel border and chlorhexidine pretreatment are capable of preventing the loss ofμTBS in both PF and UR. Lower concentration of CHX is effective for UR while not useful for PF.