The Influence of the Periodontal Breakdown over the Amount of Orthodontic Force Reaching the Dental Pulp and NVB During Orthodontic Movements-A Biomechanical Finite Element Analysis.

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.