The influence of acid etching time on the bonding performance of universal resin adhesives to dentin

Objective: To study the impact of different phosphoric acid etching time on the bonding strength and durability betweentwo universal resin adhesives.Method: The study was conducted at the Oral and Maxillofacial Surgery Department of the Affiliated StomatologicalHospital of Nanjing University Medical College, China, from August to October 2020, and comprised fresh human molarswithout caries that were exposed to the dentin surface. They were randomly divided into 4 groups based on differentphosphoric acid etching time; 0s, 5s, 10s and 15s. Each group was bonded by composite resin columns with general resinadhesives Clearfil Universal Bond and All-bond Universal to form micro-tensile bonding specimens. After 24h of storage indistilled water, micro-tensile bond strength tests were carried out directly or after thermocycled for 10,000 cycles. Afterfracture, the bonding interface was observed by stereomicroscope and the fracture mode was recorded. Data was analysedusing SPSS 22.Results: Of the 72 tooth specimens 18(25%) were in each of the 4 groups. Micro-tensile bond strength of Clearfil UniversalBond groups of 10s and 15s and All-bond Universal groups of 0s, 5s and 10s was higher than that of the other groups beforeand after thermocycling (p<0.05). The thermocycling treatment significantly reduced the micro-tensile bond strength of0s, 10s and 15s groups of All-bond Universal (p<0.01), but had no significant effect on Clearfil Universal Bond groups (p>0.05).The micro-tensile bond strength of 10s and 15s group of Clearfil Universal Bond was higher than that of correspondinggroups of All-bond Universal groups before and after thermocycling (p<0.05).Conclusion: Etching time of dentin surface could affect the micro-tensile bond strength and durability of universal resinadhesives.Keywords: Universal resin adhesive, Dentin, Bond strength, Etching time, Durability.