## 4 Discussion  
The null hypothesis was that PEKK primary crown could present a similar mechanical response when supported by different primary crown materials during chewing load incidence. The results showed that the primary crown material influenced the biomechanical response of the telescopic attachment system. Thus, the hypothesis of the present study was rejected. It was observed that the restorative material with high elastic modulus allowed less stress to reach the cement layer; however, it increased the stress magnitude in the primary crown as well as in the secondary crown's intaglio surface. In addition, a previous study affirmed that a more flexible dental material was a promising alternative for telescopic crowns systems [20]. This study complements this finding, showing that the PC material stiffness can modify the stress concentration in the set during compressive loading. The use of a milled telescopic crown is indicated to improve the long-term longevity; therefore, the proper digital workflow must be considered to ensure clinical success with predictable retentive force and abutment maintenance [2, 3, 20]. Therefore, reports suggest high risk for debonding when considering the stress magnitude at the cement layer [25, 26, 27, 28, 35, 36, 37]. In the present simulation, the models with zirconia in the PC showed the highest stress at the cement layer in comparison with PEKK. Previous studies reported that stress during secondary crown removal could be affected by the shape of the preparation model and the shear force between primary and secondary crowns [4]. In relation to this, the findings of the present study suggest that primary crowns should be selected to avoid higher stress concentration in the presence of compressive occlusal forces. Considering the retention, path of insertion, and ease of insertion of over-dentures, the recommended angle of convergence for the telescopic system is between 0\({}^{\circ}\) and 6\({}^{\circ}\)[4]. The present study used 6\({}^{\circ}\), as the maximum angle possible to represent the conical system. According to a review evaluating the clinical behavior of telescopic crowns, the success rate for conventional telescopic crown retained removable partial dentures was approximately 95.1%. In addition, the three most common complications for overdentures were the need for relining (34.8%), facing repair (26.95%), or re-cementation of primary crowns  
Figure 8: Strain energy (mJ) in the set according to the PC material: (a) PEKK; (b) Titanium; (c) CoCr; and (d) Zirconia. (20.6%) [38]. Based on that, the present results suggest that PEKK material can offer a more reliable treatment option in terms of stress reduction on the cement layer and, therefore, potentially minimizing the incidence of primary crown re-cementation. The stress level in the cement layer is usually proportional to the debonding failure risk [25; 39], and thicker cement layers will promote higher stress magnitude due to the higher polymerization shrinkage [38; 40]. However, in the present study, all models were simulated with a uniform cement layer thickness [25] to allow standardized comparison between groups; however, clinically, cement layer thickness differs. In addition to the evaluated materials, the masteratory load can also affect the mechanical response to the removable denture treatment [26; 39]. In the present study, axial loads were applied in order to simulate the most common load (axial) in the posterior region of the mouth [25]. However, as the dentures have free end saddles, the load on the cantilever arm should also be considered [26; 27; 35; 36; 37]. Therefore, it is possible to suggest that the non-axial chewing loads can negatively influence the telescopic crown system mechanical response in comparison with the axial loading. However, the effect of different load orientations can be evaluated in further studies.