Search Results (9)

Background/Objectives: Most orthodontic forces are absorbed–dissipated before reaching the dental pulp and its neuro-vascular bundle (NVB); nonetheless, no data are available about this issue during the periodontal breakdown. The current study’s objective was to investigate how much orthodontic force reaches the dental pulp and NVB during the orthodontic movements in periodontal breakdown. Methods: Herein, an assessment was performed on the second lower premolar of nine patients (72 3D models) and included 1440 numerical simulations. A gradual horizontal periodontal breakdown (1–8 mm loss) was simulated. Five orthodontic movements (intrusion, extrusion, rotation, translation, and tipping) under 0.5 N/5 KPa and 4 N/40 KPa were assessed. The numerical methods used were Von Mises/VM (overall homogenous) and Tresca (shear non-homogenous), suitable for the ductile resemblance of dental tissues. Results: Both methods showed similar color-coded projections for the two forces. Quantitatively, Tresca was 1.14 times higher than VM and lower than the maximum physiological hydrostatic circulatory pressure. During the bone loss simulation, the NVB stress was 5.7–10.7 times higher than the pulpal stress. A gradual tissue stress increase was seen, strictly correlated with the bone loss level. For 1 mm bone loss, only 2–3% of the applied force manifested at the NVB level (0.27–0.5% for pulp), while for 8 mm loss, the received stress was 4–10% for the NVB (0.6–0.9% for pulp) when compared to the applied force. Only translation displayed pulpal stress. Conclusions: When assessing NVB stress, the tooth absorption–dissipation ability of dental tissues varied between 90 and 93% (8 mm loss) and 97% (1 mm bone loss) and 99% when assessing pulpal stress. Full article

Background/Objectives: This study assessed the biomechanical behavior of dental pulp and the neuro-vascular bundle/NVB as well as the ischemic risks during orthodontic movements in a gradual horizontal periodontal breakdown, using five methods and aiming to identify the most accurate one. Methods: Seventy-two models of second lower premolar (from nine patients) were subjected to 3 N of intrusion, extrusion, rotation, tipping, and translation. Five numerical methods, Tresca, Von Mises/VM, Maximum and Minimum Principal, and hydrostatic pressure were used in a total of 1800 numerical simulations. The results were color-coded projections of the stress areas that were then correlated with maximum physiological hydrostatic pressure/MHP and known clinical biomechanical behavior. Results: During periodontal breakdown, all five methods displayed, for all movements, quantitative stresses lower than MHP, suggesting that 3 N are not inducing any local tissular ischemic risks for the healthy intact tissues. All five methods displayed rotation as the most stressful movement during periodontal breakdown, while translation was the least. The NVB was more exposed to ischemic risks than dental pulp during the periodontal breakdown due to constant tissular deformations. Only VM and Tresca methods showed translation as more prone to expose dental pulp (both coronal and radicular) to ischemic risks (than the other movements) during the periodontal breakdown simulation. However, all five methods showed intrusion and extrusion as more prone to expose the NVB to higher ischemic risks than the other movements during the periodontal breakdown simulation. Conclusions: During periodontal breakdown, Tresca and Von Mises were more accurate, with Tresca being the most accurate of all. Full article

Background/Objectives: There are few data about the ischemic risks induced by the large orthodontic forces during periodontal breakdown in dental pulp and neuro-vascular bundle (NVB) and none on the individual tissular stress distribution, despite their great importance for orthodontic treatment planning. Our aim was to assess, by a numerical analysis, the biomechanical behavior of dental pulp and the NVB during a simulated horizontal periodontal breakdown (1–8 mm), under 2–4 N of applied orthodontic forces and five movements (rotation, translation, tipping, intrusion, and extrusion). Additionally, the ischemic and degenerative-resorptive risks were assessed. Methods: The analysis involved 72 3D models of nine patients, totaling 720 simulations. The models were CBCT-based, having the second lower premolar and surrounding periodontium, and they suffered 1 mm of gradual horizontal periodontal breakdown (up to 8 mm loss). Results: Both forces displayed a similar qualitative stress distribution in all five movements, but with a quantitative increase (doubling of stress amounts for 4 N when compared with 2 N). The highest amounts of stress were displayed at 8 mm of periodontal loss, which is lower than the 16 KPa of the maximum hydrostatic pressure. The NVB stress was higher than the pulpal stress. Rotation was the most stressful, closely followed by tipping, intrusion, and extrusion. Conclusions: A total of 4 N of applied force seems to not induce any ischemic or degenerative-resorptive risks for healthy intact teeth, in up to 8 mm of periodontal breakdown. Intrusion and extrusion determined the highest visible tissular deformation in the NVB, with potential ischemic and resorptive-generative risks for previously traumatized/injured teeth (i.e., occlusal trauma). Rotation and translation (in particular) showed the highest coronal and radicular pulpal stress with potential ischemic and resorptive-generative risks for previously injured/traumatized dental pulp (i.e., direct-indirect pulp capping). It seems that 4 mm of periodontal breakdown could signal a clinical stress increase with potential ischemic and degenerative-resorptive risks for the previously traumatized/injured tissues. Full article

This numerical analysis, by employing Tresca and Von Mises failure criteria, assessed the biomechanical behavior of a trabecular bone component subjected to 0.6, 1.2, and 2.4 N orthodontic forces under five movements (intrusion, extrusion, tipping, rotation, and translation) and during a gradual horizontal periodontal breakdown (0–8 mm). Additionally, they assessed the changes produced by bone loss, and the ischemic and resorptive risks. The analysis employed eighty-one models of nine patients in 405 simulations. Both failure criteria showed similar qualitative results, with Tresca being quantitatively higher by 1.09–1.21. No qualitative differences were seen between the three orthodontic loads. Quantitatively, a doubling (1.2 N) and quadrupling (2.4 N) were visible when compared to 0.6 N. Rotation and translation followed by tipping are the most stressful, especially for a reduced periodontium, prone to higher ischemic and resorptive risks. In an intact periodontium, 1.2 N can be safely applied but only in a reduced periodontium for extrusion and intrusion. More than 0.6 N is prone to increasing ischemic and resorptive risks for the other three movements. In an intact periodontium, stress spreads in the entire trabecular structure. In a reduced periodontium, stress concentrates (after a 4 mm loss—marker for the stress change distribution) and increases around the cervical third of the remaining alveolar socket. Full article

Background and Objectives: Herein we used numerical analysis to study different biomechanical behaviors of mandibular bone subjected to 0.6 N, 1.2 N, and 2.4 N orthodontic loads during 0–8 mm periodontal breakdown using the Tresca failure criterion. Additionally, correlations with earlier FEA reports found potential ischemic and resorptive risks. Materials and Methods: Eighty-one models (nine patients) and 243 simulations (intrusion, extrusion, rotation, tipping, and translation) were analyzed. Results: Intrusion and extrusion displayed after 4 mm bone loss showed extended stress display in the apical and middle third alveolar sockets, showing higher ischemic and resorptive risks for 0.6 N. Rotation, translation, and tipping displayed the highest stress amounts, and cervical-third stress with higher ischemic and resorptive risks after 4 mm loss for 0.6 N. Conclusions: Quantitatively, rotation, translation, and tipping are the most stressful movements. All three applied forces produced similar stress-display areas for all movements and bone levels. The stress doubled for 1.2 N and quadrupled for 2.4 N when compared with 0.6 N. The differences between the three loads consisted of the stress amounts displayed in color-coded areas, while their location and extension remained constant. Since the MHP was exceeded, a reduction in the applied force to under 0.6 N (after 4 mm of bone loss) is recommended for reducing ischemic and resorptive risks. The stress-display pattern correlated with horizontal periodontal-breakdown simulations. Full article

This study assessed the stress distribution (in eighty-one 3D models of the second lower premolar) in a stainless-steel bracket and enamel crown under 0.5 N of intrusion, extrusion, rotation, translation, and tipping during a horizontal periodontal breakdown of 0–8 mm. The FEA simulations (totaling 405) employed five failure criteria and assessed the adequacy and accuracy of Von Mises (VM), Tresca (T), Maximum Principal (S1), Minimum Principal (S3), and Hydrostatic Pressure. T and VM criteria showed no change in stress display areas during the periodontal breakdown, seeming to be more correct and adequate than the other three (with unusual stress displays). Both VM and T (found to be more adequate) generated maximum stress areas on the attachment side and the entire base of the bracket, confirming the non-homogenous stress distribution areas and the risks of bond failure. Rotation, translation, and tipping were the most stressful movements and showed slightly lower quantitative values for 8 mm bone loss when compared with the intact periodontium, while intrusion and extrusion showed the opposite behavior (slight increase). Periodontal breakdown did not influence the stress display in the bracket and its surrounding enamel area during the five orthodontic movements. Full article

This Finite Elements Analysis (FEA) assessed the accuracy of Tresca failure criteria (maximum shear stress) for the study of external root resorption. Additionally, the tooth absorption–dissipation ability was assessed. Overall, 81 models of the second mandibular premolar, out of a total of 324 simulations, were involved. Five orthodontic movements (intrusion, extrusion, rotation, translation, and tipping) were simulated under 0.6 N and 1.2 N in a horizontal progressive periodontal breakdown simulation of 0–8 mm. In all simulations, Tresca criteria accurately displayed the localized areas of maximum stress prone to external resorption risks, seeming to be adequate for the study of the resorptive process. The localized areas were better displayed in the radicular dentine–cementum component than in the entire tooth structure. The rotation and translation seem prone to a higher risk of external root resorption after 4 mm of loss. The resorptive risks seem to increase along with the progression of periodontal breakdown if the same amount of applied force is guarded. The localized resorption-prone areas follow the progression of bone loss. The two light forces displayed similar extensions of maximum stress areas. The stress displayed in the coronal dentine decreases along with the progression of bone loss. The absorption–dissipation ability of the tooth is about 87.99–97.99% of the stress. Full article

The accuracy of five failure criterions employed in the study of periodontal ligaments (PDL) during periodontal breakdown under orthodontic movements was assessed. Based on cone-beam computed tomography (CBCT) examinations, nine 3D models of the second lower premolar with intact periodontium were created and individually subjected to various levels of horizontal bone loss. 0.5 N of intrusion, extrusion, rotation, tipping, and translation was applied. A finite Elements Analysis (FEA) was performed, and stresses were quantitatively and qualitatively analyzed. In intact periodontium, Tresca and Von Mises (VM) stresses were lower than maximum physiological hydrostatic pressure (MHP), while maximum principal stress S1, minimum principal stress S3, and pressure were higher. In reduced periodontium, Tresca and VM stresses were lower than MHP for intrusion, extrusion, and the apical third of the periodontal ligament for the other movements. 0.5 N of rotation, translation and tipping induced cervical third stress exceeding MHP. Only Tresca (quantitatively more accurate) and VM are adequate for the study of PDL (resemblance to ductile), being qualitatively similar. A 0.5 N force seems safe in the intact periodontium, and for intrusion and extrusion up to 8 mm bone loss. The amount of force should be reduced to 0.1–0.2 N for rotation, 0.15–0.3 N for translation and 0.2–0.4 N for tipping in 4–8 mm periodontal breakdown. S1, S3, and pressure criteria provided only qualitative results. Full article

Orthodontic treatment in patients with no periodontal tissue breakdown vs. horizontal bone loss should be approached with caution even though it can bring significant benefits in terms of periodontal recovery and long-term success. We used the finite element method (FEM) to simulate various clinical scenarios regarding the periodontal involvement: healthy with no horizontal bone loss, moderate periodontal damage (33%) and severe horizontal bone loss (66%). Afterwards, forces of different magnitudes (0.25 N, 1 N, 3 N, and 5 N) were applied in order to observe the behavioral patterns. Through mathematical modeling, we recorded the maximum equivalent stresses (σ ech), the stresses on the direction of force application (σ c) and the displacements produced (f) in the whole tooth–periodontal ligament–alveolar bone complex with various degrees of periodontal damage. The magnitude of lingualization forces in the lower anterior teeth influences primarily the values of equivalent tension, then those of the tensions in the direction in which the force is applied, and lastly those of the displacement of the lower central incisor. However, in the case of the lower lateral incisor, it influences primarily the values of the tensions in the direction in which the force is applied, then those of equivalent tensions, and lastly those of displacement. Anatomical particularities should also be considered since they may contribute to increased periodontal risk in case of lingualization of the LLI compared to that of the LCI, with a potential emergence of the “wedge effect”. To minimize periodontal hazards, the orthodontic force applied on anterior teeth with affected periodontium should not exceed 1 N. Full article