## 2 Materials and Methods
### SEM and EDS Analysis  
In order to evaluate the interfacial morphology, for each tested adhesive, 3 dentin samples with adhesives applied according to the research model (Table 2) were prepared as described in 2.1. Using 180, 600 and 1000-grit silicon carbide paper under running water, the resin-dentin interface was exposed and polished. The dental etchant, 37% orthophosphoric acid solution, was applied for 1 min on the samples in order to demineralize dentin, which was later rinsed with distilled water for 1 min. Next, to remove the organic debris, the specimens were treated by soaking in 5% NaOCl for 5 min. The solution was replaced after each minute to prevent it from deactivation. After another distilled water-wash and air-drying, the specimens were dehydrated in ascending ethanol concentration (50%, 70%, 90% and 95% for 20 min each and 100% for 1 h), and then transferred to a critical point dryer for 30 min. All specimens were mounted on aluminium stubs, so that the specimens' surface was parallel to the stubs' surface, and sputter-coated with gold layer. The adhesive/dentin interfaces were then examined using a scanning electron microscope (SEM, FEI Nova NanoSEM 450, FEI, Hillsboro, OR, USA) under 1000\(\times\) and 2000\(\times\) magnification, at 90\({}^{\circ}\) tilt angle. In order to measure adhesive layer thickness (ALT), three different points of adhesive interface: the middle part and both extremities of the interface were evaluated [30]. At each point, four measurements were taken using software that enabled vertical positioning of the adhesive layer and marking parallel measuring lines (perpendicular to the adhesive interface). In total, 12 measurements were taken along the interface of each sample based on SEM images at 2000 x magnification. Further, the dentin-resin interface was analyzed from a chemical aspect, using energy dispersive spectrometry (EDS, EDAX/AMETEK, Materials Analysis Division, Model Octane Super, Mahwah, NJ, USA).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Adhesive** & **Manufacturer** & **Composition** & **pH** & **Mode of Etching** \\ \hline \multirow{4}{*}{Prime \& Bond One} & \multicolumn{2}{c}{Bifunctional acryl resin with amide} & \\  & & functions, Acryloylamino alkylsulfonic & \\  & & acid, “inverse” functionalized phosphoric & \\  & & GmbH, Germany & acid ester, Camphorquinone, Coinitiator & \\  & & Butylated benzenediol, Water, & \\  & & tert-Butanol & \\ \hline \hline \end{tabular}  
* MM = ER \& SE \& SEE (MM-multimode, ER-etch \& r\), SE-self-etch, SEE-selective enamel etch).
* Information obtained from the manufacturer (safety data sheet).  
\end{table}
Table 1: _Cont._  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Group** & **Application Mode** \\ \hline
1A20 (control) & Adhesive was applied according to the manufacturers’ instructions: Apply adhesive and rub into the entire dentin surface with disposable microbrush for 20 s. Gently air-dry the surface for 5 s at a distance of 10 cm to form a slightly shiny adhesive film. Light-cure for 20 s. \\ \hline
2A20 & Adhesive was applied two times in the abovementioned manner during 20 s and light-cured for 20 s afterwards. \\ \hline
3A20 & Adhesive was applied three times in the abovementioned manner during 20 s and light-cured for 20 s afterwards. \\ \hline
2A40 & Each of the 2 applications of adhesive lasted 20 s, which made 40 s in total. The adhesive was light-cured for 20 s. \\ \hline
3A60 & Each of the 3 applications of adhesive lasted 20 s, which made 60 s in total. The adhesive was light-cured for 20 s. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Research model.