The Amount of Orthodontic Force Reaching the Dental Pulp and Neuro-Vascular Bundle During Orthodontic Movements in the Intact Periodontium.

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Background and Objectives: Most orthodontic forces are absorbed-dissipated before reaching the dental pulp and its neuro-vascular bundle (NVB); however, no data are available about their amounts. The objective of this study was to assess the amount of orthodontic force that reaches the dental pulp and its NVB during orthodontic movements in a healthy periodontium. Materials and Methods: This study involved the second lower premolars of nine patients and 180 numerical simulations. 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 included only two failure criteria suitable for dental tissue (of ductile resemblance): Von Mises (VM) (overall, homogenous) and Tresca (shear, non-homogenous). Results: Both forces displayed a similar color-coded stress display for the two methods. The Tresca quantitative results were 1.11 times higher than the VM but lower than the maximum physiological hydrostatic circulatory pressure. The biomechanical behavior of the pulp and NVB showed that, in the intact periodontium, the NVB-induced stress was 5.7 higher than in the pulp. Quantitatively, the rotation movement seemed to be the most stressful for the NVB, closely followed by intrusion and extrusion. For the dental pulp, rotation remained the most stressful, closely followed by tipping and translation. Tissue deformations were visible for NVB areas during intrusion and extrusion. The dental pulp showed pulpal stresses under translation and rotation. The numerical simulations with the two methods showed that, in the intact periodontium, only a small amount of the initial orthodontic load produced effects in the NVB and dental pulp. Only about 2.85% of the initial orthodontic load of 40 KPa/4 N applied at the bracket level induced stresses in the NVB, while the dental pulp was reached by 0.5% of the applied force. A similar distribution was seen at 5 KPa/0.5 N. Conclusions: The absorption-dissipation ability of the dental tissue varies between 97.15 and 99.98%.