## 2 Materials and Methods
### Finite Element Model Preparation  
To generate a 3D model, micro-CT scans of the restored specimens were made. Scanning was performed using a high-resolution micro-CT scanner SkyScan 1172 (SkyScan, Aartselaar, Belgium). After scans, micro-CT reconstruction was conducted to shrink the number of output data. This volumetric reconstruction was carried out using Skyscan's NRecon(r) software. A cross-section of slices was generated through the scanned sample. NRecon(r) software was used to reduce errors by optimizing alignment. All unwanted data was removed, and beam hardening was done along with image sharpening, wherein any ring artifacts were corrected. This data was cropped using the cropping tool CTAn(r) analyzer (SkyScan, Aartselaar, Belgium). The only region of interest was included using the ROI tool. All images were reduced to a file size of fewer than 1 GB and reconstructed and converted to bitmap (.bmp) files.  
To obtain a 3D model from 2D images via a micro-CT scan, a medical imaging software Mimics(r) 13.1 (Materialise NY, Leuven, Belgium) was used (Figure 2A). The object was seen in 3 views on the screen sagittal, coronal, and axial. Default x and y line axis represented the horizontal and vertical 2D of the body, respectively, and was adjusted within the frames by slight adjustments (Figure 2B). To create a mask of the object the first step was \"thresholding\". Thresholding visualizes the tooth in separate components; for example, a crown, cement, enamel, dentine, and pulp could be separately seen as masks. Segmentation was used to separate any component from each other. It allows for the creation of an accurate individual mask. The boolean operation was used to add or remove masks from each other; for example, crown and enamel masks were removed for a dentine mask. A boundary condition (zero displacements) was defined at all nodes of the teeth that were constrained in all directions (X, Y, and Z). Then, the coordinate axes were directed, as shown in Figure 2. In the end, the calculated mask option was used to generate a 3D model after the final optimization of each layer (Figure 2C).  
\begin{table}
\begin{tabular}{c c} \hline
**Tooth Reduction** & **Vita Enamic® (VITA, Zahnfabrik, Germany) Manufacturer’s Protocol** \\ \hline Occlusal reduction & Should be at least 1.5 mm \\ Bucco-labial or linguo-palatal reduction & At the bottom of the fissure: at least 1 mm, In the area of the cusps at least 1.5 mm \\ Margin all around & 0.8 to 1.5 mm \\ \hline \end{tabular}
\end{table}
Table 1: Tooth reduction parameters for Vita®Enamic (VITA, Zahnfabrik, Germany) manufacturer’s guidelines [24; 25].  
The final 3D models for each component were exported in a standard triangle language (STL) format which consists of a mesh of small objects in a shell format (Figure 3). This high-quality mesh was created using models Hypermesh(r) (HyperWorks software, Version 11.0, Altair Engineering, Inc., Troy, MI, USA).  
Figure 3: Model mesh. (**A**), the 2D model mesh. (**B**), the 3D mesh generation of conventional crown–tooth complex from Hypermesh® (HyperWorks software, Version 11.0, Altair Engineering, Inc., Troy, MI, USA). (**C**), the 3D model showing the crown and root, as well as the load application.  
Figure 2: The 3D model generation. (**A**) Micro-Computed Topography images of the restored specimen. Scanning was performed using a high-resolution micro-CT scanner SkyScan 1172 (SkyScan, Aartselaar, Belgium). (**B**) The 2D model of the tooth with crown. (**C**) The 3D model generated from 2D images secured from micro-CT scan from Mimics® 13.1 (Materialise NY, Leuven, Belgium).