## 3 Results  
The mean shear bond strengths and differences among groups are illustrated in Figure 3 and shown in Table 3.  
The highest bond strengths were recorded in specimens repaired with Single Bond Universal Adhesive (21.54). These data were comparable to the data regarding specimens repaired with Clearfil Universal Bond GC (21.17), silane/PQ1 (20.43), and composite primer (17.15) (\(p>0.05\)). The lowest repair strengths were obtained from specimens in the control group, in which the resin composite was repaired without any adhesive layer (8.86 MPa). Specimens repaired with PQ1 had a mean value of 12.90, which is significantly different than all the other groups (\(p<0.05\)). All-Bond Universal (15.92) presented significantly similar strength values to those of the composite primer and silane/PQ1 (\(p>0.05\)).  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Surface Treatments**}} & \multicolumn{1}{c}{**Mean Bond**} & \multicolumn{1}{c}{**von Mises Stress**} & \multicolumn{1}{c}{**Displacement (mm)**} & \multicolumn{1}{c}{\(r\)} \\  & **Strength (MPa)** & **Value (MPa)** & **Value (MPa)** & **Value (MPa)** & **Value (mm)** & **\(r\)** \\ \hline Control & 8.86 & 9.91 & 1.044 & 0.276 \\ \hline PQ1 & 12.90 & 14.075 \({}^{\text{a}}\) & 1.521 & 0.152 \\ \hline All-Bond Universal & 15.92 \({}^{\text{a}}\) & 17.671 \({}^{\text{b}}\) & 0.071 \({}^{\text{a}}\) & 0.835 \\ \hline GC Composite Primer & 17.15 \({}^{\text{ab}}\) & 14.991 \({}^{\text{a}}\) & 0.691 & \(-\)0.694 \\ \hline Silane + PQ1 & 20.43 \({}^{\text{ab}}\) & 18.312 \({}^{\text{b}}\) & 0.055 \({}^{\text{a}}\) & \(-\)0.461 \\ \hline Clearfil Universal Bond & 21.17 \({}^{\text{b}}\) & 22.455 & 0.093 \({}^{\text{b}}\) & 0.066 \\ \hline
3M Single Bond Universal & 21.54 \({}^{\text{b}}\) & 26.963 & 0.097 \({}^{\text{b}}\) & 0.724 \\ \hline \(p\) & 0.001 & 0.001 & 0.001 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The bond strength, von Mises stress, and significance among the test groups.  
Figure 3: Bar graph showing the mean shear bond strength values (MPa) of composite specimens repaired with different adhesive protocols.  
Fracture analysis revealed that all test groups presented cohesive failures in the aged composite, except for one specimen in PQ1 and one specimen in the All-Bond Universal adhesive groups. These two specimens and all the specimens in the control group presented adhesive failures (Figure 4).  
The finite element analysis (FEA) results indicate variations in von Mises stress values across different surface treatments. The control group exhibited the lowest von Mises stress (9.91 MPa) and, correspondingly, had the lowest mean bond strength (8.86 MPa). In contrast, the highest von Mises stress was observed for Single Bond Universal (26.963 MPa), which also demonstrated one of the highest bond strengths (21.54 MPa). These findings indicate a positive correlation between shear bond strength values and von Mises stress values (\(r\) = 0.825). In contrast, this correlation was not found to be statistically significant for the GC Composite Primer and PQ1 + silane groups (\(p\) > 0.05).  
The displacement findings reveal notable differences among the treatments. The All-Bond Universal and Silane + PQ1 groups showed minimal displacement (0.071 mm and 0.055 mm, respectively), suggesting a more stable bond. Conversely, PQ1 exhibited the highest displacement (1.521 mm), indicating a less stable interface despite its moderate bond strength (12.90 MPa). Overall, treatments with higher bond strength, such as Clearfil Universal Bond and Single Bond Universal, also demonstrated relatively low displacement values (0.093 mm and 0.097 mm, respectively) (\(p\) < 0.05).