## 4 Discussion  
The results obtained in the present study lead to the acceptation of the null hypothesis (H0), which states that the restoring materials tested has no statistically significant effect on the fracture resistance of endodontically treated teeth, however there was statistically significant differences between elastic FRC post restored with CR (3510 N) and FRC post with CR (2420 N) and only CR (2560 N). Besides, if we compare the FRC post/CR (2420 N) and FRC post/FRC resin core (3620 N) pairs, we also find statistically significant differences. In endodontically treated teeth with substantial loss of structure, intraradicular posts are recommended to provide sufficient retention of restorative materials [23]. [PERSON] et al. [15] evidenced that elastic fiber reinforced posts offered a better behavior to physiological occlusal forces. Likewise, we reported that posts, especially elastic FRC post, showed greater fracture resistance to compression forces and this may be due to a modulus of elasticity more similar to dentin. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **m = Weibull Shape (\(\beta\))** & \multicolumn{6}{c}{**\(\sigma\)0 = Weibull Scale (n)**} \\ \hline  & **Estimate** & **St Error** & **Lower** & **Upper** & **Estimate** & **St Error** & **Lower** & **Upper** \\ \hline Conventional FRC & 27.410 & 0.6686 & 16.992 & 44.213 & 27.270 & 0.3333 & 21.461 & 34.651 \\ Post-CR Core & 70.055 & 19.508 & 40.589 & 120.914 & 37.789 & 0.1774 & 34.468 & 41.431 \\ Conventional FRC & 106.744 & 29.247 & 62.390 & 182.628 & 38.129 & 0.1184 & 35.878 & 40.521 \\ Post-FRC CR & 72.262 & 20.690 & 41.228 & 126.655 & 37.814 & 0.1718 & 34.592 & 41.336 \\ CR Core (Gardia Core) & 56.240 & 14.407 & 34.040 & 92.917 & 27.773 & 0.1645 & 24.729 & 31.191 \\ FRC CR (Ever-X) & 35.211 & 0.9514 & 20.735 & 59.795 & 33.993 & 0.3202 & 28.263 & 40.884 \\ Control & 44.830 & 10.508 & 28.317 & 70.974 & 35.997 & 0.2687 & 31.099 & 41.667 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Weibull statistics of the fracture resistance of the study groups after bending test. Figure 7: Weibull probability plot of the fracture resistance values (N) of the study groups after bending test. [PERSON] et al. [24] stated that elastic fiber reinforced posts have a better resistance to physiological occlusal forces. In our study, fiber post, especially elastic ones, showed greater resistance to compression forces and this may be because these posts have an elastic module which is more similar to dentin. [PERSON] et al. [21] concluded that teeth restored with an elastic fiber posts showed a significantly greater fracture resistance than those restored with conventional fiber posts. In our study, the elastic posts showed better results in terms of fracture resistance; although, in some tests the conventional posts achieved some positive results, this could be due to the fact that they were used with a reinforced fiberglass composite. The elastic FRC posts significantly increased the mean fracture resistance values (3510 N) with respect to non-elastic FRC posts (2420 N) when they were directly restored with CR. Nevertheless, non-elastic FRC posts slightly increased the mean fracture resistance values (3620 N) with respect to elastic FRC posts (3520 N) when they were restored with FRC resin core. The mechanical properties of elastic FRC posts should influence over the fracture resistance of the endodontically treated premolar teeth but it seems that FRC resin core influences to a greater extent. [PERSON] et al. [25] highlighted that the presence and orientation of the glass fibers inside the FRC resin core might influence over the fracture resistance of the restoration of the endodontically treated teeth. Upper premolars have been shown to be more prone to root fractures, what justifies the selection of these teeth for this study [26; 27; 5; 28]. [PERSON] et al. [28] stated that maxillary bicuspids with MOD restorations showed the lowest overall survival rate. [PERSON] et al.