Korean J Orthod.  2019 May;49(3):188-193. 10.4041/kjod.2019.49.3.188.

Palatal en-masse retraction of segmented maxillary anterior teeth: A finite element study

• Park JH
• Kook YA
• Kojima Y
• Yun S
• Chae JM

• KMID: 2450228
• DOI: http://doi.org/10.4041/kjod.2019.49.3.188

Abstract

OBJECTIVE
The aim of this finite element study was to clarify the mechanics of tooth movement in palatal en-masse retraction of segmented maxillary anterior teeth by using anchor screws and lever arms.
METHODS
A three-dimensional finite element method was used to simulate overall orthodontic tooth movements. The line of action of the force was varied by changing both the lever arm height and anchor screw position.
RESULTS
When the line of action of the force passed through the center of resistance (CR), the anterior teeth showed translation. However, when the line of action was not perpendicular to the long axis of the anterior teeth, the anterior teeth moved bodily with an unexpected intrusion even though the force was transmitted horizontally. To move the anterior teeth bodily without intrusion and extrusion, a downward force passing through the CR was necessary. When the line of action of the force passed apical to the CR, the anterior teeth tipped counterclockwise during retraction, and when the line of action of the force passed coronal to the CR, the anterior teeth tipped clockwise during retraction.
CONCLUSIONS
The movement pattern of the anterior teeth changed depending on the combination of lever arm height and anchor screw position. However, this pattern may be unpredictable in clinical settings because the movement direction is not always equal to the force direction.

Keyword

Segmented palatal en-masse retraction; Finite element study; Anchor screw; Lever arm

MeSH Terms

Arm
Mechanics
Methods
Tooth Movement
Tooth*

Figure

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  Figure 1 Finite element model for simulating overall orthodontic tooth movement. The alveolar bone was assumed to be a rigid body; the wire was fixed to the crowns; and symmetrical boundary condition was applied.

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  Figure 2 The center of resistance (CR) of anterior teeth, locations of anchor screws, and lever-arm height. Lines of action of force are drawn with red lines. A, Midpalatal anchor screw. B, Palatal slope screw.

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  Figure 3 Movement patterns at N = 800, when the line of action of the force passed through the center of resistance (CR) at the initial position. A, Midpalatal position (lever-arm height, 12 mm) and B, high position (lever-arm height, 10 mm); the anterior teeth translated upward. C, Low position (lever-arm height, 8 mm); the anterior teeth translated horizontally without upward movement.

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  Figure 4 Movement patterns at N = 800, when the line of action of force passed apical or coronal to the center of resistance (CR) at the initial position. A, Low position (lever-arm height, 10 mm); the anterior teeth tipped labially. B, Low position (lever-arm height, 6 mm); the anterior teeth tipped lingually.

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