## 4 Discussion  
Tooth preparations and removal of sound tooth structure generate varying results and no single mechanical test can give statistical results that can be relative to tooth loading  
Figure 4: Peak von Mises stress values in MPa of Vita Enamic® crown, dentin, and cement in conventional preparation design. Figure 5: Stress generation on the crown (**A**), stress generation in cement layer of conventional preparation design (**B**), and stress generation in the dentin of conventional preparation design (**C**). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Vita Enamic Crown layer** & **Dentine Layer** & **Cement Layer** \\
**Von Mises Stress (MPa)** & **Von Mises Stress (MPa)** & **Von Mises Stress (MPa)** \\ \hline \hline
9.43 & 7.80 & 3.34 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The von Mises stress values (MPa) in the crown–tooth complex for Vita Enamic® (VITA, Zahnnfabrik, Germany) crown. encountered in the mouth. A particular system evolves a particular tooth preparation with manufacturer guidelines. Metal ceramics, all ceramics, and a more recent innovation are of polymer-based ceramic crowns. These crowns have preparation guidelines that require a hefty amount of tooth preparation. Thus, we rendered an overall weak tooth structure under a biological cost that is unmatched by the natural tooth. Therefore, we need to address the survivability of the crown-tooth complex rather than an individual entity. In this study, to evaluate the stress pattern generated in a tooth restored with a machined polymer-based hybrid ceramic crown, a 3D model was created. A conventional preparation design model was chosen according to the manufacturer's guidelines. The tooth and Vita(r)Enamic (VITA Zahnfabrik, Bad Sackingen, Germany) manufacturer's guidelines crown complex underwent loading conditions of 150 N at a buccal incline of the palatal cusp and palatal incline of the buccal cusp (total 300 N). The stress patterns were simulated using 3D finite element study [34]. In the FE analysis, some assumptions were made, which are relayed as follows: (i) there was a perfect bond between the machined hybrid dental ceramic crown, the dentine, and the cement layer; (ii) all layers of the structures were assumed to be linear, elastic, and isotropic; and (iii) enamel was considered as homogenous and isotropic [31]. For load distribution, it has been reported that oblique loads are of much more clinical relevance and generate more stress than vertical loads [35]. In this study, to compare the stresses generated within a crown-tooth complex, axial loading was opted for, as it is more effective and the point of application of load can be promptly reproduced [36; 37; 38]. FE analysis can be only done with the establishment of boundary conditions and, in this study, we created it on the outer 2/3 surface of the tooth root which is where most of the movement occurs during loading conditions or occlusal forces in the mouth [31]. According to the data obtained for von Mises stress, the manufacturer's preparation design showed the variation of stress pattern amongst all three layers of crown, dentine, and cement. There were high stresses in the crown, dentine, and less in cement, which is in agreement with [PERSON] et al. (2013), as they compared different lute parameters, which we did in this study. [PERSON] et al. [39] investigated different occlusal designs and documented more stress in the anatomical design than in the flat. Moreover, they reported less stress in the dentine layer for the anatomic design. This stress they reported may be due to the amount of reduction at 2 mm. In this study, we had an occlusal preparation of 1.5 mm, and results for this design were in accordance with the [PERSON] et al. study results for von Mises stress [39]. It is of importance to note that [PERSON] et al. [30] demonstrated similar results for their anatomical design for cement and dentine von Mises analysis when a cement of elastic modulus of 8 GPa was used. In this study, the cement used had an elastic modulus of 7.7 GPa.