Mineralized pulp (MP) compromises tooth function and its causation is unknown. The Tresca failure criterion seems more suitable than other criteria for apical NVB and dental pulp. For the dental pulp, only the translation and rotation movements seemed to display a particular risk of ischemia, necrosis, and internal orthodontic-resorption for both coronal (0-8 mm of loss) and radicular pulp (4-8 mm of loss), despite the amount of stress being lower than the MHP. Rotation and tipping seemed to be the most invasive movements for the apical NVB. A force of 4.8 N was safely applied to apical NVB on the intact periodontium only. Forces of 0.6 N, 1.2 N, and 2.4 N had negligible effects on apical NVB and dental pulp up to 8 mm of periodontal breakdown. The Tresca failure criterion was applied, and the shear stress was assessed. Eighty-one (nine patients, with nine models for each patient) anatomically correct models of the periodontium, with the second lower-premolar reconstructed with its apical NVB and dental pulp were assembled, based on X-ray CBCT (cone-beam-computed-tomography) examinations and subjected to 0.6 N, 1.2 N, 2.4 N and 4.8 N of intrusion, extrusion, translation, rotation, and tipping. In addition, it examines whether the Tresca finite-element-analysis (FEA) criterion is more adequate for the examination of dental pulp and its apical NVB. This study examines 0.6 N-4.8 N as the maximum orthodontic force to be applied to dental pulp and apical NVB on intact and 1-8 mm reduced periodontal-ligament (PDL), in connection with movement and ischemic, necrotic and resorptive risk. The results indicate that traumatized teeth with total pulp obliteration have a higher susceptibility to pulpal complications during orthodontic intrusion than traumatized teeth without or only partial pulp obliteration. In addition, teeth in the OT group with total pulp obliteration showed a significantly higher rate of pulp necrosis than teeth without (p < 0.001) or only partial pulp obliteration (p = 0.025). Teeth in the OT group revealed a significantly higher rate of pulp necrosis than teeth in the C group (p < 0.001). According to the degree of initial pulp obliteration, the teeth were divided into three categories: teeth without, teeth with partial, and teeth with total pulp obliteration. Pulpal condition was examined in 269 traumatized maxillary incisors after orthodontic intrusion (OT group) and in 193 traumatized maxillary incisors without subsequent orthodontic treatment (C group). Limited information exists on the impact of pulp obliteration on pulpal vitality of orthodontically treated traumatized teeth.
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