# Finite Element Analysis of Mandibular Anterior Teeth with Healthy, but Reduced Periodontium
## 5 Conclusions  
It was found that the maximum value of bone stress for the lateral incisor was in area 5, due to the minimal ligament thickness; it reached 448 KPa for the force of 1 N and 358 KPa for the force of 0.8 N. From a biomechanical point of view, a grade 2 lever was formed, due to the atypical root anatomy. The point of application of the resisting force (area 5, area with minimal PDL thickness) is between the fix point (tooth's root) and that of the active force (force applied to the tooth). Regarding the displacement of the lateral incisor, starting with area 5, the area with minimal ligament thickness, there was a decreasing tendency of the curve. In area 5, there was a risk of bone resorption occurrence due to increased stress, due to atypical root anatomy and longitudinal root depression. The increased displacement of the bone was determined by the minimal ligament thickness, as a result of the PDL's function, as the PDL optimizes the transfer of the forces and regulates orthodontic tooth movement. In the central incisor, the maximum bone stress was in area 1. In comparison, the maximum bone stress in the lateral incisor was in area 5, as a result of an atypical root anatomy. In areas 3, 4 and 5, areas with minimal ligament thickness, an increase in ligament tension was observed. Displacement was favored in areas 4-5 by the minimal ligament thickness; the curve had a constant horizontal appearance. This could determine root resorption. At the lateral incisor, the maximum stress in the bone in the area with the maximum increase for area 5 was 448 KPa, and in area 1, it was 128 KPa. In the canine, the maximum stress in the bone, in the area with the maximum increase, for area 4 was 89 KPa, and in area 1, it was 203 KPa. At the central incisor, the maximum stress in the bone, in the area with the maximum increase at the cervical margin for area 1 was 436 KPa. Comparing the two curves of the central and lateral incisor, it was observed that:  
1. The difference in increase is much higher at the lateral incisor (approx. 300 KPa), compared to the canine (approximately 100 KPa). 2. The difference in increase is explained by the specific mode of action of the force in the two cases. For the lateral incisor, the lever is of degree 2, with the force arm between zone 5 and zone 1; for the canine, the lever is of degree 1, and the arm of force between zone 1 and zone 4. 3. Due to the lever configuration, a compression force of the ligament appears in area 6-7 and this causes the PDL's increase. 4. In area 4, the risk of bone resorption due to increased stress is observed, as a result of atypical root anatomy. The minimal ligament thickness in area 4 causes increased displacement of the bone. This occurs as a result of the PDL's function, which optimizes the transfer of the forces and regulates orthodontic tooth movement. The displacement is a bodily movement with tipping. Considering that the stress is influenced by the tooth's morphology and the periodontal status, it can be concluded that the results obtained are similar to those from clinical practice. In addition, the outcome of this study demonstrates the correlation between the clinical results and FEA. Specific implications of orthodontic forces and biomechanical compression on the periodontal tissues are difficult to quantify; therefore, FEA is mandatory in order to achieve a treatment that is planned according to the patient's particular situation. This is even more important in patients with reduced periodontitis that are predisposed to recessions. Conceptualization, I-A.S. and M.A. ; methodology, S.M.S. and M.A. ; software, D.-C.K.-N.; validation, S.M.S. and N.C.; formal analysis, I-A.S.; investigation, S.T. and A.M.; resources, S.M., M.P. and N.C.; data curation, I.-A.S. and A.M.; writing--original draft preparation, I.-A.S. and M.A. ; writing--review and editing, I.-A.S. and N.C.; visualization, A.M., I.L. and M.A. ; supervision, S.M.S., M.A., N.C. and I.L. ; project administration, M.P. and S.M. ; funding acquisition, S.M.