## 4 Discussion  
[PERSON] et al. [22] found that the fracture resistance of zirconia specimens have positive correlation with prosthesis thickness, and the mean cyclic number of broken specimens on 0.5 mm thickness was 8480 \(\pm\) 2009. This study demonstrated breakage in 11 of 15 specimens (73%) and a similar cyclic number of broken specimens for 0.5 mm (SA100) zirconia specimens (Table 1). In addition, the breakage percentage of SA75 specimens (6/15) showed no statistical significance (P \(>\) 0.05) compared to SA50 specimens (5/15). On the other hand, only one SA25 zirconia specimen (1/15) broke during 300 N vertical loading. The results supported the speculation that the implant abutment occlusal surface area affects the fracture resistance of the zirconia crown, although only a moderately strong correlation was found (\(r\) = 0.475). The FEM showed the lowest peak stress value for SA25 specimen in all loading types, hence, we speculated that the implant abutment occlusal area has an inverse proportion to fracture resistance of the zirconia specimens (Figures 1 and 2). Under oblique loading, the peak value of the crown from the lingual side was lower than that from the buccal and distal side. This difference was attributed to the contact area of the prosthesis because the radius of the contact area from the lingual side was greater than other surfaces (Figure 5 bottom row). Moreover, the radius of the contact area negatively affecting the stress under constant loading is clarified by the Hertzian theory [28; 29]. On the other hand, the oblique buccal loading and oblique distal loading showed similar peak stress, which may be attributed to the same contact area between the indenter and zirconia crown (Figure 6 top and bottom row). Cyclic loadings could cause an accumulation of deformation and decrease the load resistance of the tested materials. Static loadings were loads with a very low rate of change to maximum stresses on specimens. [PERSON] et al. [32] showed the cyclic fatigue behavior of zirconia at loads between 50 and 200 N and indicated that zirconia can tolerate the severe cyclic loading in the molar area. On the other hand, static FEM analysis was shown the maximum stress value and stress distribution from an applied load 250 N on the specimens. For brittle materials, [PERSON] and [PERSON] [33] mentioned the prediction of cyclic fatigue lifetime from static lifetime by using the ratio of static to cyclic fatigue life. These results demonstrated the similar failure trend between static and cyclic fatigue for brittle materials, and the fracture of brittle materials would be induced immediately when the maximum stress was higher than the flexural strength. In addition, in this present study, the cyclic experimental tests showed the positive correlation between the percentage of broken specimens over total specimens with the peak stress value of FEA corresponding to four types of abutment designs (\(r\) = 0.391). Moreover, both cyclic experimental tests and static FEM analysis were shown the same results that the SA25 specimens had the lowest stress values and higher fracture resistance under 300 N loading. The results hence rejected the hypothesis described in the introduction. [PERSON] et al. [34] reported that an increase of TOC (from 12 to 20 degree) did not affect marginal and internal fit but resulted in higher load to fracture values of ceramic crowns. A similar finding was reported by [PERSON] et al. [35], who compared the influence of 6\({}^{\circ}\), 12\({}^{\circ}\), and 20\({}^{\circ}\) TOC on the fracture load of yttria partially stabilized zirconia veneered with feldspathic porcelain. The 20\({}^{\circ}\) TOC had the best outcome. On the other hand, it could be reasonably speculated that the SA25 specimen allowed for greater implant body tilting.