## 3 Results
### Results of Failure Mode  
The results of the failure modes of SBS measurements are presented in Figure 8 in the aspect of section ingredients (epoxy, bone, titanium) with different adhesives.  
Figure 7: Mean shear bond strengths (SBS) value with standard error mean (SEM) at epoxy, bone, and titanium samples in the aspects of thermoplastic adhesive (Group 1), MDP containing bond material + resin matrix (Group 2), protonated glass surface, MDP containing bond material + resin matrix (Group 3) (n = 15). * \(p<0.05\).  
The failure mode was adhesive in 92%, 75%, and 83% for epoxy, in 81%, 60%, and 54% for bone and in 83%, 55%, 61% for titanium at Groups 1, 2, and 3, respectively. The epoxy, bone, and titanium substrates broke in two ways with thermoplastic adhesive (Group 1). In most cases the failure was adhesive-interface 1 (Figure 2) i.e., the thermoplastic adhesive separated from the smooth glass surface; and in a smaller part, fracture was inside the thermoplastic adhesive layer (Figure 2, cohesive failure 1).  
Epoxy sample of Group 2 and Group 3 showed an increased number of failure modes at the adhesive-interface 1 because of the nonreactive molecular motif of epoxy. The number of cohesive 1 failures were raised in Group 2 compared to Group 1 that indicates the higher binding affinity of MDP containing bond to substratum and adherents than thermoplastic adhesive. Besides, the adhesive-interface 2 failure mode appeared in 11% at epoxy of Group 3 compared to Group 2 where this failure mode was not detected. Regarding the epoxy sample, it was showed that the MDP containing bond material provide stronger adhesion than thermoplastic adhesive. Moreover, this adhesion can be further improved by protonation of the glass slide.  
Adhesive-interface 1 failures of the bone in Group 2 were around 55% that showed a decreased tendency compared to Group 1 (81%). The numbers of cohesive failure 1 elevated from 19% (at Group 1) to 27% (at Group 2) and additionally cohesive failure 2 appeared in 13% at Group 2 that increased to 30 % at Group 3 i.e., the fracture appeared in glass substratum. Overall, the adhesive and cohesive failure modes ratio was around 50-50% at the bone substrate of Group 3. It was showed that the MDP molecule helps to prevent the separation of bone sample from glass compared to TPA, that positive effect is reflected in numbers of cohesive fractures. With the application of MDP containing bond material, the numbers of cohesive fractures increased that were raised by the protonation of glass.  
Adhesive failures at interface 1 of titanium samples decreased from 83% (Group 1) to 50% (Group 2) that did not change at Group 3. The numbers of cohesive failure mode elevated from 17% (Group 1) to 33% (Group 2). The numbers of adhesive-interface 2 elevated from 5% to 12% at Group 2 vs. Group 3. Overall it was found that the titanium has a stronger affinity to glass through MDP containing bond material than TPA similar to epoxy and bone sample. The fracture between the adherent and adhesive  
Figure 8: Failure mode (%) of the tested specimens after shear bond strength measurements.  
appeared in larger numbers at glass surface protonation but the adhesive- interface 1 fracture numbers are not changed considerably. Cohesive 1 failure numbers decreased by glass protonation that can indicate the stronger bonds between the sample and glass.