Korean J Orthod.  2016 Jul;46(4):242-252. 10.4041/kjod.2016.46.4.242.

Finite element analysis of maxillary incisor displacement during en-masse retraction according to orthodontic mini-implant position

• Song JW
• Lim JK
• Lee KJ
• Sung SJ
• Chun YS
• Mo SS

• KMID: 2392204
• DOI: http://doi.org/10.4041/kjod.2016.46.4.242

Abstract

OBJECTIVE
Orthodontic mini-implants (OMI) generate various horizontal and vertical force vectors and moments according to their insertion positions. This study aimed to help select ideal biomechanics during maxillary incisor retraction by varying the length in the anterior retraction hook (ARH) and OMI position.
METHODS
Two extraction models were constructed to analyze the three-dimentional finite element: a first premolar extraction model (Model 1, M1) and a residual 1-mm space post-extraction model (Model 2, M2). The OMI position was set at a height of 8 mm from the arch wire between the second maxillary premolar and the first molar (low OMI traction) or at a 12-mm height in the mesial second maxillary premolar (high OMI traction). Retraction force vectors of 200 g from the ARH (-1, +1, +3, and +6 mm) at low or high OMI traction were resolved into X-, Y-, and Z-axis components.
RESULTS
In M1 (low and high OMI traction) and M2 (low OMI traction), the maxillary incisor tip was extruded, but the apex was intruded, and the occlusal plane was rotated clockwise. Significant intrusion and counter-clockwise rotation in the occlusal plane were observed under high OMI traction and -1 mm ARH in M2.
CONCLUSIONS
This study observed orthodontic tooth movement according to the OMI position and ARH height, and M2 under high OMI traction with short ARH showed retraction with maxillary incisor intrusion.

Keyword

Finite element model; Tooth movement; Mini-implant

MeSH Terms

Bicuspid
Dental Occlusion
Finite Element Analysis*
Incisor*
Molar
Tooth Movement
Traction

Figure

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  Figure 1 Three-dimensional finite element models. A, Occlusal view of the model with extraction of the first premolar (Model 1, M1). B, Occlusal view of the model with residual extraction space of 1 mm (Model 2, M2). C, Lateral view of the model with extraction of the first premolar (M1). D, Lateral view of the model with residual extraction space of 1 mm (M2). ARH, Anterior retraction hook; OMI, orthodontic mini-implants; X, medio-lateral; +, lateral; -, medial direction; Y, anterio-posterior; +, anterior; -, posterior direction; Z, superio-inferior; +, superior; -, inferior direction.

• 

  Figure 2 Von Mises stress distribution (g/mm2). M1, Model 1; M2, Model 2; OMI, orthodontic mini-implants.

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  Figure 3 The axis changes of the maxillary central incisors according to the length of the anterior retraction hook under low and high orthodontic mini-implant traction in both models with extraction of the first premolar (Model 1, M1) and a residual extraction space of 1 mm (Model 2, M2). Solid line, original axis of the maxillary central incisor; dashed line, changed axis of the maxillary central incisor; ○, -1 mm hook; □, +1 mm hook; △, + 3 mm hook; ×, +6 mm hook.

• 

  Figure 4 The axis change in the maxillary central incisor retracted by low and high orthodontic mini-implant (OMI) traction with a 3-mm anterior retraction hook in both models with extraction of the first premolar (Model 1, M1) and a residual extraction space of 1 mm (Model 2, M2). Solid line, original axis of the maxillary central incisor; dashed line, changed axis of the maxillary central incisor; ○, low OMI retraction; □, high OMI retraction.

• 

  Figure 5 The axis change in the maxillary incisors retracted by high orthodontic mini-implant traction with a -1 mm anterior retraction hook in both models with extraction of the first premolar (Model 1, M1) and a residual extraction space of 1 mm (Model 2, M2). Solid line, original axis of maxillary incisors; dashed line, changed axis of maxillary incisors; ○, maxillary central incisor; □, maxillary lateral incisor; △, maxillary canine.

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  Figure 6 Movement pattern of the model with extraction of the first premolar (Model 1, M1). The rotation of the occlusal plane according to the length of anterior retraction hook used in the model with extraction of the first premolar (M1) under low and high orthodontic miniimplant traction. Solid line, original occlusal plane; dashed line, rotated occlusal plane; ○, -1 mm hook; □, +1 mm hook; △, +3 mm hook; ×, +6 mm hook.

• 

  Figure 7 Movement pattern of the model with residual extraction space of 1 mm (Model 2, M2). The rotation of the occlusal plane according to the length of the anterior retraction hook used in the model with residual extraction space of 1 mm (M2) under low and high orthodontic mini-implant traction. Solid line, original occlusal plane; dashed line, rotated occlusal plane; ○, -1 mm hook; □, +1 mm hook; △, +3 mm hook; ×, +6 mm hook.

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