Dental caries is a multifactorial disease that localized the dissolved inorganic structure of dental hard tissue [1]. Effectively delaying and preventing tooth decay is crucial in maintaining healthy teeth, clinicians and researchers are increasingly using technologies and medications to accomplish the concept of minimally invasive restorative. One notable innovation is silver diamine fluoride (SDF), which was first introduced in the 1970 s based on its arrest of dental caries [2], [3]. SDF or Ag(NH3)2F consists of approximately 253,870 ppm silver, 44,880 ppm fluoride, and amine as a solvent. SDF showed superior performance over fluoride vanish alone in terms of effectiveness on caries arrest and safety [4], [5]. Unlike other fluoride products, SDF contains both fluoride and silver. The interaction of fluoride ions with calcium and phosphate produces fluorohydroxyapatite, which reduces the solubility of the mineral [6]. Furthermore, silver was proven to have an antimicrobial effect [7], [8], [9]. Subsequently, in 2014, the Food and Drug Administration (FDA) approved SDF to be used as a tooth desensitizer [10]. All of the above, SDF has been continuously used for arresting caries [4], [11], [12], [13], caries prevention [5], [14], [15], cavity cleanser [16], tooth desensitizer [17], [18], [19], [20], root canal irrigant [21], and newly introduced to use as caries detector due to the darkening effect on caries-affected dentin [22].

During application for caries arrest, SDF could inevitably contaminate sound dentin surfaces. Previous studies have shown that there was no adverse effect of SDF contamination on adhesive-dentin bond performance in self-etch mode (SE) and etch-and-rinse mode (ER) to sound dentin of permanent [23], [24] and primary teeth [25]. However, the bond strength of SDF on sound dentin is affected by various factors such as SDF application technique [26], concentration and duration of SDF application [24], [27], the type of application modes of adhesive [28], and the type of adhesives and restorations [16], [29], [30], [31].

The newest type of adhesive called universal adhesive has been developed, which can be used in a variety of cases in clinical settings and it is simple to use. This adhesive has improved the bond durability of bonding [32], [33] and can be applied with SE, ER, and selective enamel etching mode which exhibited a different bonding mechanism to the substrates [32]. However, it is still unclear whether the application of SDF affects the dentin bonding performance of universal adhesives and no study has been conducted on the ultra-morphological characteristic changes in sound dentin after bonding with them. Therefore, this study aimed to evaluate the microtensile bond strength (μTBS) of SDF-contaminated sound dentin to different universal adhesives, and ultra-morphological characteristic changes induced by SDF. The null hypotheses were; (1) there were no effects of SDF on the bond strength of adhesives to sound dentin, (2) there were no effects of the application modes of adhesive on the bond strength of SDF-contaminated dentin, and (3) there were no difference in the bond strengths among adhesives.