## 4 Discussion
This study revealed that there is an optimum at 3 h for acid soaking of pathological grade borosilicate surface regarding shear bond strengths measurement (Figure 3). In aqueous suspension, the hydroxylation of the glass surface can result in the formation of silanol groups (Si-OH). The surface silanol (Si-OH) groups can pick up a proton from the nitric acid solution through the following reaction ([PERSON] et al., 2016):  
\[\text{Si-OH}+\text{H}^{+}\leftrightarrows\text{SiOH}^{+}{}_{2}+\text{H}_{2}\text {O}\]  
That is why the glass particles are positively charged under acidic pH after nitric acid etching (Table 3). Based on the contact angle measurements, it was revealed that the adhesive has a better wetting ability on the acid-etched, positively charged surface than unprotonated glass which can contribute to the higher bond strength as a part of chemical adhesion (Table 4). The zeta potential measurements, which were calculated by Smoluchowski coagulation equation, revealed that the glass surface becomes positively charged after nitric acid etching (Table 2). [PERSON] et al. described that insoluble silica salts formed on the surface after acid exposure of glass. These precipitates are not removable not even in an ultrasonic bath ([PERSON] et al., 2016). Based on our XPS measurements, it was revealed that nitric acid treatment causes the dealkalization process in that alkaline ions are leached out from the glass surface (Figure 4, Table 3) and may form insoluble salts. These salts have a positive effect on the chemical bonding of PO\({}_{4}\) groups of 10-MDP to precipitated salts of the glass surface. [PERSON] at al. reported mismatched interaction between zirconia primer (MDP) and the glazed surface ([PERSON] et al., 2016). Therefore, it was assumed that insoluble salts on the glass surface by [PERSON] may have a determining factor in the chemical affinity of MDP containing bond to the etched glass surface. At bone and titanium, the MDP containing bond material on the protonated glass surface resulted in a higher bond strength value compared to the unprotonated version (Figure 7). Based on the research studies it can be concluded that positively charged surface--in the case of apatite is Ca\({}^{2+}\)--favorably influences the connection of phosphate group of 10-MDP. By glass protonation SiOH\({}^{+}{}_{2}\) positively charged ions are formed on the surface that can explain the larger number of cohesive fractures in interface 2 (from 13% to 30%) at bone substratum (Figure 8). In the case of titanium, the 10-MDP adhesive has better adhesive strength than thermoplastic adhesive. By glass protonation, the SBS value increased significantly and the frequency of cohesive failure 2 was the highest at titanium. The explanation is a strong ionic bond between the titanium and 10-MDP that was justified by research studies. In that case, the SBS data are only analyzed from the side of the protonated glass slide and there would not be a difference in bond strengths measurements because the bond strength of 10-MDP and glass is measured at every measurement but there was a difference in SBS data at bone and titanium on protonated and unprotonated glass. Therefore, it can be concluded that the other side--adherents, 10-MDP--connection parallelly has an important role in the formation of failure modes and SBS values. Figure 10 shows two sections with the thick thickness (A part) and optimum thickness (B part) after hematoxylin-eosin (H&E) staining. The procedure step by step for section preparation from sintered titanium implant in the animal bone sample is shown in Figure 11.  
Our findings suggest that the components of titanium implant containing undecalcified bone section showed higher SBS data with 10-MDP containing adhesive than in metallography routinely used thermoplastic adhesive. The MDP containing bond material provided chemical-micromechanical retention that resulted in higher cohesive failure mode frequencies and SBS values.