A Novel Primer Increases Dentin Bond Strengths Of Self-Etch And Universal Adhesives

Objectives:The present study investigated the effects of dentin surface pretreatment with a novel primer containing MDP(methacryloyloxydecyl dihydrogen phosphate)and MMPs inhibitors(Benzalkonium chloride,BAC)on the short-and long-term dentin bond strength of self-etch and universal adhesives.Materials and Methods:The mid-coronal dentin of 126 human third molars was exposed using a slow-speed saw and polished with 360-grit and 600-grit SiC paper under running water.They were randomly divided into 3 groups according to the different dentin surface treatments(N=42):1)Control(one-step self-etch approach):The polished dentin surface was not further treated before the application of dentin adhesive;2)Prime-and-rinse approach:The polished dentin surface was treated with a novel primer containing 15wt%of MDP and lwt%of Benzalkonium chloride(BAC)for 15 s and water-sprayed for 30 s before the application of dentin adhesive;3)Prime-and-nonrinse approach(reverse two-step self-etch approach):The dentin surface was treated with a novel primer containing MDP and Benzalkonium chloride for 15 s and dried with strong air flow for 5 s.Subsequently,the adhesives were applied to the polished and pretreated dentin surfaces following the manufacturers' instructions.They included a one-bottle self-etch adhesive Clearfil S3 Bond(S3),composite resin Clearfil Majesty(Kuraray-Noritake,Tokyo,Japan);two one-bottle universal adhesives in self-etch mode Scotchbond Universal(SU)(3M ESPE,St.Paul,MN,USA)and All-bond Universal(AU)(Bisco,Schaumburg,USA)as well as the respective composite resin Filtek Z250 and Light-Core.The respective composite resin from the same manufacturer was placed over the adhesive-treated dentin surface in four 1-mm thick increments,and each increment was light-cured for 20 s.The all light-curing was performed using a light-curing unit with an output intensity of 800mW/cm2(Elipar S10,3M ESPE,USA).After storage in distilled water for 24 h at 37?,all the dentin-bonded specimens were sectioned to 0.8 mm*0.8 mm*8 mm long sticks.The sticks of 5 teeth each subgroup were immediately subjected to tensile loading with a micro-tensile tester(Bisco,Inc.,Schaumburg,IL,USA)until failure and those of another 5 teeth each subgroup were test after storage in distilled water at 37 C for 6 month-water storage.The fracture modes of all specimens were observed by stereomicroscope at 50-fold magnification after failure.The morphology of resin-dentin interface(each subgroup)was investigated by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Data were analyzed by two-way ANOVA and Tukey's test(IBM SPSS Statistics ver.22.0,IBM Corp.New York,USA).The statistic significance was set at ?=0.05.Results:The pre-treatment with the novel primer containing MDP and BAC could result in significant increase of dentin MTBS for all the three adhesive systems regardless of water storage time,prime-and-rinse approach and prime-and-nonrinse approach(p<0.05).The prime-and-rinse approach could could significantly increase the dentin MTBS than the prime-and-nonrinse approach(p<0.05)after 24 hours of water storage,but not after 6 months of water storage.The frequency of mixed failure either in the prime-and-rinse approach or in prime-and-nonrinse approach were significantly higher than that of the control groups(P<0.05).The predominant failure modes in all groups were adhesive failure after 6 months of water storage.The SEM findings showed that the resin-dentin interfaces were tight contact after 24 hours of water storage,but,some micro-gaps were detectable after 6 months of water storage.The TEM micro-photographs reveal that hydroxyapatite crystallites remained abundantly within the hybrid layers in all groups.Conclusions:The pre-treatment with the novel primer containing MDP and BAC could increase the short-and long-term dentin MTBS of the one-bottle self-etch adhesive and universal adhesives in self-etch mode,regardless of storage time,prime-and-rinse approach or prime-and-nonrinse approach.The prime-&-rinse approach could significantly increase the short-term dentin MTBS than prime-&-nonrinse approach,but not the long-term dentin MTBS.