## 3 Results  
The present FEA totaled 486 simulations, displaying qualitative and quantitative results for PDL for both criteria. The qualitative results displayed similar stress distribution for both criterions. There were no differences in the stress display among the three loads. Quantitatively, the Tresca displayed amounts of stress that were 15% higher than Von Mises. For both criteria, the maximum shear and overall stresses doubled to 1.2 N and quadrupled to 2.4 N, when compared with 0.6 N. The highest amounts of stress were displayed by the rotation and translation, followed by the tipping, extrusion, and intrusion. The cervical third stress always displayed the highest amounts of stress, independently of the movements, bone loss levels, loads, and criteria. The amount of stress increase is directly correlated with the periodontal breakdown. The rotation and translation, followed by tipping, are the most stressful movements prone to higher ischemic and resorptive risks (exceeding the 16 KPa of MHP) than the extrusion and intrusion, especially after 4 mm of bone loss. The 0.6-1.2 N seems perfectly safe to be applied in both intact and reduced periodontium. However, after 1.2 N, the cervical third stress progressively increased, which correlated with load and bone loss levels, extending to the middle and apical thirds, thus increasing the ischemic and resorptive risks (especially for the rotation, translation, and tipping). However, it must be kept in mind that these are pure orthodontic movements, while clinically it is usually an association and combination that could lead to lower amounts of stress than here. These aspects were considered when the ischemic and resorptive risks were evaluated. The assumed boundary conditions (i.e., isotropy, homogeneity, linear elasticity, and perfectly bonded interfaces) that were acknowledged as being correctly applied from the physical mechanical point of view for up to 1 N of load, seemed to be correct up to 2.4 N of load, for both criteria. Since the Tresca algorithm was designed for non-homogenous materials, it seems better suited for the study of PDL, falling within the range specified in the literature of 15-30% (when compared with the VM). The Von Mises criteria seemed also suited for dental tissue FEA studies, despite its homogenous material mathematical algorithm design, if all the above-mentioned issues are acknowledged. Regarding extrusion (Figure 3, Table 2), qualitatively, the stress display areas were similar for both criteria, bone levels and loads, with an extension in the entire PDL (from apical to cervical thirds). Quantitatively, for both criteria, in an intact periodontium experiencing up to 2.4 N, the orthodontic loads were tolerable for the PDL, with the highest amount of stress concentrated in the cervical third. In a reduced periodontium, the stress increase was correlated with bone loss. 0.6 N was perfectly tolerable up to 8 mm bone loss. For 1.2 N, the cervical third stress progressively increased after 4 mm of loss, up to 40-45 KPa (2.8 times higher than MHP). However, both the apical and middle PDL thirds (with richer vascularity than the cervical third) displayed stresses lower than MHP. 2.4 N displayed overruns of the MHP in the entire PDL after 4 mm of loss.