## 3 Results
### Shear Bond Strength  
Among all tested adhesives, the highest SBS results were obtained for Single Bond Universal, a universal adhesive (Table 4). The increase in number of applications up to three along with 60 s application time resulted in higher SBS for Single Bond Universal adhesive than the control group (from \(16.34\pm 4.62\) up to \(31.40\pm 2.83\) MPa).  
Figure 8: EDS line scan signals of individual elements present at dentin-resin interface obtained for Prime&Bond One Select applied twice in 40 s (group 2A40).  
Figure 7: EDS line scan signals of individual elements present at dentin-resin interface obtained for Single Bond Universal applied twice in 40 s (group 2A40).  
When multi-mode adhesives were considered, Prime & Bond One Select presented lower bond strength values in all study groups compared with Single Bond Universal (Figure 9). None of the modifications of application procedures contributed to a significant increase of SBS of Prime&Bond One Select. In case of Single Bond Universal doubling or tripling the number of applications along with prolonged application time in groups 2A40 and 3A60 resulted in a statistically significant increase in SBS.  
The lowest values of SBS were observed for SE adhesive, Xeno V applied once (\(2.24\pm 1.0\) MPa), however the bond strength significantly increased when application methods were modified. The highest mean SBS was observed in group 3A60 (\(7.68\pm 4.04\) MPa) (Table 4, Figure 9(b)).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Adhesive**} & \multicolumn{5}{c}{**Method of Application**} \\ \cline{2-6}  & **1A20 (Control Group)** & **2A20** & **3A20** & **2A40** & **3A60** \\ \hline Adper Easy One & 6.10 \(\pm\) 2.39 ab \({}^{\text{a}}\) & 9.27 \(\pm\) 2.50 cd \({}^{\text{a}}\) & 9.14 \(\pm\) 2.95 \({}^{\text{a}}\) & 15.19 \(\pm\) 2.15 ac \({}^{\text{a}}\) & 16.86 \(\pm\) 2.29 bd \({}^{\text{a}}\) \\ Xeno V & 2.24 \(\pm\) 1.02 ab \({}^{\text{a}}\) & 3.91 \(\pm\) 2.48 ab \({}^{\text{a}}\) & 7.00 \(\pm\) 2.11 b \({}^{\text{a}}\) & 7.67 \(\pm\) 2.15 a \({}^{\text{a}}\) & 7.68 \(\pm\) 4.04 b \({}^{\text{b}}\) \\ Single Bond Universal & 16.34 \(\pm\) 4.62 ab \({}^{\text{c}}\) & 19.40 \(\pm\) 4.45 c b \({}^{\text{c}}\) & 20.7 \(\pm\) 4.17 b \({}^{\text{c}}\) & 30.40 \(\pm\) 6.69 ab \({}^{\text{c}}\) & 31.40 \(\pm\) 2.83 bc \({}^{\text{c}}\) \\ Prime&Bond One Select & 4.04 \(\pm\) 1.40 b \({}^{\text{c}}\) & 4.88 \(\pm\) 2.36 c \({}^{\text{c}}\) & 2.42 \(\pm\) 1.06 c \({}^{\text{c}}\) & 4.65 \(\pm\) 3.25 ac \({}^{\text{c}}\) & 3.83 \(\pm\) 2.08 ac \({}^{\text{c}}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Shear bond strength (MPa) (mean values \(\pm\) standard deviation) of the tested adhesives.  
Figure 10: SBS results of self-etch adhesives: (**a**) Adper Easy One; (**b**) Xeno V.  
Figure 9: SBS results for multi-mode adhesives: (**a**) Single Bond Universal; (**b**) Prime & Bond One Select.  
With regard to self-etch adhesives, SBS of Adper Easy One was higher than of Xeno V adhesive in all respective study groups. Bond strength values of both Adper Easy One and Xeno V increased in groups, which involved doubling or tripling application time: 2A40, 3A60 (Figure 10).  
A significant interaction between factors (type of adhesive, modification of application procedure) was revealed using Kruskal-Wallis ANOVA. For most adhesives, except Prime & Bond One Select, each modification contributed to an increase in SBS. However, [PERSON]'s post hoc test showed that the difference in bond strength was statistically significantly higher than the control only in 2A40 and 3A60 groups for Adper Easy One, Single Bond Universal and Xeno V (Figures 9 and 10).  
For tested adhesives, there was no statically significant correlation between adhesive layer thickness and SBS: Adper Easy One (\(p\) = 0.909), Prime One Select (\(p\) = 0.568), Single Bond Universal (\(p\) = 0.698), and Xeno V (\(p\) = 0.841).