## 4 Discussion
Mechanical properties, [PERSON]'s modulus of elasticity, and Poisson's ratios, entered in the FEA model for analysis, are different between the PEEK and high noble alloy posts. We found no differences in the stress distribution pattern or strength of the crown or roots. Usually stress distribution patterns are related to structural and shape differences in the models. This is true for our model and can be explained by the fact that the only difference is in the material properties rather than in the shapes of the model. If both models are similar in shape but different in properties, strengths, and stress values, the FOS would be different in our comparison. We are concerned with four components: bone, root, crown, and the post itself. Therefore, we found slight differences in only the von Mises stresses, and principal stresses of roots and bones are usually higher in PEEK than in high noble alloys. This means that the values of stresses are not affected so much in those two components by the differences in the mechanical properties of those two posts. This indicates that bones and roots are not affected by those differences. Therefore, roots will not fracture differently by changing the materials of the posts from alloys to PEEK. Also, bones might not be stressed differently, which might not cause problems in the surrounding bones. Meanwhile, the strengths are different within the two compared posts, which are higher for the alloys than for the PEEK. It is also noticed that the safety factor is higher for the high noble alloys than for the PEEK in the post and within the covering crown due to the alloy's high strength. This might indicate that the PEEK posts might withstand less stresses than the alloy, and their strength is much less than that of the alloy. And the safety factor is less for the PEEK than for the alloy, making it more prone to failure than the alloy. Given that information, the PEEK posts may break more easily than in the alloy's case. Regarding the retrievability of post, given that the PEEK hardness is less than the alloy's, it can be drilled easier than the hard alloy, making reposting much easier clinically. The shift between the PEEK and alloy affects the covering crown von Mises and principal stresses. They are higher in the PEEK than in the alloy. This may indicate that having PEEK in the background base or under the crown can dampen the forces subjected onto the crown, making it more resistive to failure in PEEK than in alloy posts. This is an essential protective mechanism for the crown. We did not vary the force values; therefore, we cannot show the effects on these components with varying force values by simulating the varying force values within the oral cavities at different locations. Therefore, having PEEK posts under zirconia crowns may offer a protective mechanism to the overlying crown. If failure occurs in the system, it may happen in the PEEK post in an easily retrievable way, with not much stress on the root and surrounding bone. The current study's limitations were that we used only one ferrule design on a central incisor tooth. The only material used was PEEK compared to a high noble alloy. We implemented only one post design: the custom post and core. Prefabricated post and core materials were not modeled in the current study. Only static loads, not dynamic loads, were applied to the tested model. Future studies will include dynamic stresses, various ferrule designs, different materials, and other tooth types.