Finite element analysis of initial displacement and periodontal stress distribution for inverted impacted maxillary central incisor by multiple traction directions

Background: Maxillary incisors are frequently encountered impacted which affect oral function, facial esthetics, and psychological and physical health. Orthodontic traction is preferred for the cases of incomplete root development. This study was aimed to evaluate and compare the initial displacement and stress differences among traction directions during the traction of different root development stages of inverted impacted central incisor based on 3-dimensional finite element analysis (FEA). Methods: Accordingly, the finite element models including maxilla, dentition, labially inverted impacted central incisor, periodontal ligaments, and traction appliance were constructed. Three root development stages of impacted incisor (1/3, 1/2, 2/3) were simulated. Three traction directions for each root length were applied by adjusting traction hook lengths of modified Nance arch appliance. Results: The impacted central incisor exhibited similar initial displacement tendencies of crown lingually and root labially rotated in all nine models. The maximum initial displacement ranged from 0.00336 to 0.00644 mm, where all were located at the incisal edge. The stress concentrated around lingual button was 0.37972 to 0.51023 MPa. Furthermore, the periodontal ligament (PDL) stress value of impacted incisor ranged from 0.01538 to 0.02612 MPa. The initial displacement and PDL stress decrease with the increase in root length of impacted incisor. With the same root length, the initial displacement and PDL stress were increased as the traction hook extended more to labial. Moreover, the average maximum initial displacement and PDL stresses of anchorage molars were 0.00010–0.00011 mm and 0.00044–0.00052 MPa. Conclusions: The traction direction and root development stage influenced the biomechanical effect of impacted incisor during traction. Additionally, the biomechanical effect of anchorage teeth existed but was inconspicuous.

Inverted impacted central incisor; Modified Nance arch; Root development; Traction direction; 3-dimensional finite element analysis

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