## 3 Results  
### SEM and EDS Analysis  
SEM images of dentin-resin interface obtained after treatment of dentin with tested adhesives, according to the research model were presented in Figures 1-4.  
Figure 1: SEM micrographs of dentin specimens treated with Adper Easy One: (**a**) 1A20 (control); (**b**) 2A20; (**c**) 3A20; (**d**) 2A40; (**e**) 3A60; mag. 1000 x.  
Figure 3: SEM micrographs of dentin specimens treated with Single Bond Universal: (**a**) 1A20 (control); (**b**) 2A20; (**c**) 3A20; (**d**) 2A40; (**e**) 3A60; mag. 1000 x.  
Figure 2: SEM micrographs of dentin specimens treated with Xeno V: (**a**) 1A20 (control); (**b**) 2A20; (**c**) 3A20; (**d**) 2A40; (**e**) 3A60; mag. 1000 x.  
The mean values of ALT (\(\upmu\)m) obtained for the tested adhesives were presented in Table 3. For tested adhesives, except for Xeno V, double application in 20 s resulted in the thinnest adhesive layer among all study groups. The thinnest adhesive layer was obtained for Prime&Bond One Select (\(6.31\pm 0.91\)). Also, there was no statistically significant difference in adhesive layer thickness between groups within Prime & Bond One Select. Single Bond Universal, on the other hand, showed the thinnest adhesive layer in 2A20 group and it was significantly lower value than in the control group or in 3A20 group. Adper Easy One reached the lowest mean value in 2A20 group, which was significantly lower than in 3A60 group. The thickest adhesive layer presented Xeno V applied three times in 60 s (\(14.15\pm 0.67\)) and it was significantly higher, almost double, when compared to the control group.  
The results of EDS analyses of the resin-dentin interface (Figures 5-8) confirmed that the concentrations of different elements corresponded with specific layers of that interface. In dentin, mainly calcium and phosphorus were detected. The adhesive layer contained carbon, which is the main element present in resin polymer. Silicon was detected in adhesive layers of Adper Easy One and Single Bond Universal, which can be attributed to the presence of nanofiller in the composition of these adhesives. All tested specimens showed increased content of silicon and aluminum, derived from inorganic filler, in composite material.  
Figure 4: SEM micrographs of dentin specimens treated with Prime&Bond One Select: (**a**) 1A20 (control); (**b**) 2A20; (**c**) 3A20; (**d**) 2A40; (**e**) 3A60; mag. 1000 x.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Adhesive**} & \multicolumn{5}{c}{**Method of Application**} \\ \cline{2-6}  & **1A20 (Control Group)** & **2A20** & **3A20** & **2A40** & **3A60** \\ \hline Adper Easy One & 13.31 \(\pm\) 0.43 \({}^{\text{a}}\) & 9.85 \(\pm\) 0.62 \({}^{\text{a,b}}\) & 11.59 \(\pm\) 0.75 & 11.32 \(\pm\) 3.20 & 13.90 \(\pm\) 0.51 \({}^{\text{a}}\) \\ Xeno V & 7.40 \(\pm\) 0.82 \({}^{\text{a,b}}\) & 8.03 \(\pm\) 1.09 & 6.08 \(\pm\) 0.21 \({}^{\text{b}}\) & 13.13 \(\pm\) 0.08 \({}^{\text{b}}\) & 14.15 \(\pm\) 0.67 \({}^{\text{a,b}}\) \\ Single Bond Universal & 11.86 \(\pm\) 1.69 \({}^{\text{a}}\) & 6.43 \(\pm\) 0.88 \({}^{\text{a}}\) & 13.25 \(\pm\) 0.88 \({}^{\text{a,b}}\) & 12.48 \(\pm\) 12.80 & 9.32 \(\pm\) 0.36 \\ Prime \& Bond One Select & 7.89 \(\pm\) 1.09 & 6.31 \(\pm\) 0.91 \({}^{\text{b}}\) & 6.39 \(\pm\) 0.65 \({}^{\text{b}}\) & 6.86 \(\pm\) 0.76 & 6.38 \(\pm\) 0.91 \({}^{\text{a,b}}\) \\ \hline \end{tabular}  
* Within tested adhesives, means followed by the same lowercase letters in row and superscript letters in column indicate significant statistical differences.  
\end{table}
Table 3: Adhesive layer thickness (\(\upmu\)m) (mean values \(\pm\) standard deviation) of the tested adhesives.  
Figure 5: EDS line scan signals of individual elements present at dentin-resin interface obtained for Adper Easy One applied twice in 40 s (group 2A40).  
Figure 6: EDS line scan signals of individual elements present at dentin-resin interface obtained for Xeno V applied twice in 40 s (group 2A40).