## 3 Results
### Extrusion (Figure 3, Table 2)  
Quantitatively, in intact periodontitis, 0.6 N produced the highest amount of stress (i.e., 299.4 KPa, Figure 3A and Table 2) at bracket level, with a visible decreasing pattern in the other components. Qualitatively, the highest stress concentrated on and around the bracket (Figure 3B,C). However, when individually assessing each component, the most heavily stressed were dentin (Figure 3D), NVB (Figure 3E), and PDL (Figure 3F). In the  
\begin{table}
\begin{tabular}{c c c c} \hline
**Material** & **Young’s Modulus, E (GPa)** & **Poisson Ratio, v** & **Refs.** \\ \hline Eamel & 80 & 0.33 & [2,3,5,6,9,10,16,48] \\ Dentin/Cementum & 18.6 & 0.31 & [2,3,5,6,9,10,16,48] \\ Pulp & 0.0021 & 0.45 & [2,3,5,6,9,10,16,48] \\ PDL & 0.0667 & 0.49 & [2,3,5,6,9,10,16,48] \\ Cortical bone & 14.5 & 0.323 & [2,3,5,6,9,10,16,48] \\ Trackular bone & 1.37 & 0.3 & [2,3,5,6,9,10,16,48] \\ Bracket (Stainless Steel) & 190 & 0.265 & [2,3,5,6,9,10,16,48] \\ \hline \end{tabular}
\end{table}
Table 1: Elastic properties of materials.  
dentine-cementum component, the vestibular cervical third displayed orange-yellow high stress areas, which are prone to external root resorption risks (i.e., 107.5 KPa, 6.7 times higher than the physiological MHP of 16 KPa). Qualitatively, despite the fact that PDL, pulp, and NVB displayed red-orange high stress areas, they did not quantitatively exceed MHP; thus, they can be safely applied in intact periodontitis (Table 2). Moreover, despite the fact that bone and dentine-cementum (due to lesser vascularization) components exceeded MHP, they are not as sensitive to high pressures; thus, the resorptive and ischemic risks are smaller. The absorption-dissipation ability pattern of the above structures was clearly visible (Table 2): a progressive decrease in stress in radicular dentine (14.76-35.9%), alveolar bone socket (12.51-50.04%), PDL (1-2.24%), pulp (0.05%), and NVB (0.57%) when compared with the initial stress applied on the bracket (299.4 KPa).  
In reduced periodontitis (1-8 mm), the quantitative amount increases in correlation with bone loss. Nevertheless, the decreasing stress pattern (i.e., absorption-dissipation ability) in the model's components, which is visible in intact periodontitis, was maintained. Qualitatively and quantitatively, coronal stress around and on the bracket increases (red-orange visible in Figure 3B,C), while radicular stress (Figure 3D) extends in the entire root (i.e., visible external resorptive risk areas are in the middle third). The progression of bone loss increases stresses in the entire alveolar socket (Figure 3G) and PDL (Figure 3F). Quantitatively, 0.6 N induces stresses in PDL cervical third exceeding MHP after 6 mm of loss, with higher ischemic and resorptive risks. From stresses manifested on the bracket level (305.5-392.5 KPa), only 1.24-5.75% was displayed in PDL, 0.05-0.09% in dental pulp, 0.63-1.11% in NVB, 14-50% in alveolar socket bone, and 24.51-63.47% in radicular dentine (Table 2). There was a visible increasing stress pattern in radicular dentine component from 24.51-42.77% in 1 mm loss to 63.47% in 8 mm loss, which is strictly correlated with periodontal breakdown.  
The bracket absorption-dissipation ability (difference between tooth with bracket and without bracket coronal stress) was 15.48% in 0 mm, 16.43% in 1 mm, and 4.02% in 8 mm loss.  
The enamel absorption-dissipation ability (difference between coronal tooth without bracket and coronal dentine stress) was 62.26% in 0 mm, 62.26% in 1 mm, and 65.44% in 8 mm loss.  
Figure 3: Extrusion—Tresca stress display in dental tissues subjected to 0.6 N for 0, 4, and 8 mm bone loss: (**A**)—dental tissues’ structure, (**B**)—tooth with bracket, (**C**)—tooth without bracket, (**D**)—dentine component, (**E**)—dental pulp and NVB, (**F**)—PDL, (**G**)—bone with alveolar socket.