The Effect of Larger Orthodontic Forces and Movement Types over a Dental Pulp and Neuro-Vascular Bundle of Lower Premolars in Intact Periodontium-A Numerical Analysis.

Background/objectives: This numerical analysis of stress distribution in the dental pulp and neuro-vascular bundle (NVB) of lower premolars assessed the ischemic and degenerative-resorptive risks generated by 2 and 4 N during orthodontic movements (rotation, translation, tipping, intrusion and extrusion) in intact periodontium.
Methods: The numerical analysis was performed on nine intact periodontium 3D models of the second lower premolar of nine patients totaling 90 simulations.
Results: In intact periodontium, both forces displayed a similar stress distribution for all five orthodontic movements but different amounts of stress (a doubling for 4 N when compared with 2 N), with the highest values displayed in NVB. In intact periodontium, 2 N and 4 N induced stresses lower than the maximum hydrostatic pressure (MHP) with no ischemic risks for healthy intact teeth. The rotation was seen as the most stressful movement, closely followed by intrusion and extrusion. Translation was quantitatively seen as the least stressful when compared with other movements.
Conclusions: Larger orthodontic forces of 2 N and 4 N are safe (with any expected ischemic or resorptive risks) for the dental pulp and NVB of healthy intact teeth and in intact periodontium. Nevertheless, rotation and translation movements can induce localized circulatory disturbances in coronal pulp (i.e., vestibular and proximal sides) generating ischemic and resorptive risks on previously treated teeth (i.e., direct and indirect dental pulp capping). The intrusion and extrusion movements, due to the higher NVB-induced deformation when compared with the other three movements, could trigger circulatory disturbances followed by ischemia on previously traumatized teeth (i.e., occlusal trauma).