Korean J Orthod.  2023 Nov;53(6):420-430. 10.4041/kjod23.035.

Biomechanical analysis for different mandibular total distalization methods with clear aligners: A finite element study

• Oh S
• Choi YK
• Kim SH
• Ko CC
• Kim KB
• Kim YI

• KMID: 2548485
• DOI: http://doi.org/10.4041/kjod23.035

Abstract

Objective
The purpose of this finite element method (FEM) study was to analyze the biomechanical differences and tooth displacement patterns according to the traction direction, methods, and sites for total distalization of the mandibular dentition using clear aligner treatment (CAT).
Methods
A finite element analysis was performed on four FEM models using different traction methods (via a precision cut hook or button) and traction sites (mandibular canine or first premolar). A distalization force of 1.5 N was applied to the traction site by changing the direction from –30 to +30° to the occlusal plane. The initial tooth displacement and von Mises stress on the clear aligners were analyzed.
Results
All CAT-based total distalization groups showed an overall trend of clockwise or counterclockwise rotation of the occlusal plane as the force direction varied. Mesiodistal tipping of individual teeth was more prominent than that of bodily movements. The initial displacement pattern of the mandibular teeth was more predominant based on the traction site than on the traction method. The elastic deformation of clear aligners is attributed to unintentional lingual tipping or extrusion of the mandibular anterior teeth.
Conclusions
The initial tooth displacement can vary according to different distalization strategies for CAT-based total distalization. Discreet application and biomechanical understanding of traction sites and directions are necessary for appropriate mandibular total distalization.

Keyword

Finite element method; Clear aligner; Distalization

Figure

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  Figure 1 Four finite element method models. A, Group C1: distalization with a button on canine; B, Group C2: distalization with a precision cut hook on canine; C, Group P1: distalization with a button on first premolar; D, Group P2: distalization with a precision cut hook on first premolar.

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  Figure 2 Direction and magnitude of the distalization force. A, lateral and B, occlusal view.

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  Figure 3 Displacement pattern of dentition. A, B, Displacement (μm) of the dentition for +30°and –30° traction in Group C1, respectively. C, D, Displacement (μm) of the dentition for +30° and –30° traction in Group C2, respectively. E, F, Displacement (μm) of the dentition for +30° and –30° traction in Group P1, respectively. G, H, Displacement (μm) of the dentition for +30° and –30° traction in Group P2, respectively.

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  Figure 4 Pattern of tooth movement at the mandibular central incisor. A, Crown-centered medio-distal displacement (μm); B, crown-centered bucco-lingual displacement (μm); C, crown-centered apico-coronal displacement (μm); D, buccolingual inclination change (°); E, mesiodistal inclination change (°); F, occlusal rotation (°).

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  Figure 5 Pattern of tooth movement at the mandibular canine. A, Crown-centered medio-distal displacement (μm); B, crown-centered bucco-lingual displacement (μm); C, crown-centered apico-coronal displacement (μm); D, buccolingual inclination change (°); E, mesiodistal inclination change (°); F, occlusal rotation (°).

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  Figure 6 Pattern of tooth movement at mandibular first premolar. A, Crown-centered medio- distal displacement (μm); B, crown-centered bucco-lingual displacement (μm); C, crown-centered apico-coronal displacement (μm); D, buccolingual inclination change (°); E, mesiodistal inclination change (°); F, occlusal rotation (°).

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  Figure 7 Pattern of tooth movement at mandibular first molar. A, Crown-centered medio distal displacement (μm); B, crown-centered bucco-lingual displacement (μm); C, crown-centered apico-coronal displacement (μm); D, buccolingual inclination change (°); E, mesiodistal inclination change (°); F, occlusal rotation (°).

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  Figure 8 Total displacement pattern of aligners. A, B, Total displacement (μm) of the dentition for +30° and –30° traction in Group C1, respectively. C, D, Total displacement (μm) of the dentition for +30° and –30° traction in Group C2, respectively. E, F, Total displacement (μm) of the dentition for +30° and –30° traction in Group P1, respectively. G, H, Total displacement (μm) of the dentition for +30° and –30° traction in Group P2, respectively.

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  Figure 9 Elastic strain (mm/mm) of clear aligners. A, B, For +30° and –30° traction in Group C1, respectively. C, D, For +30° and –30° traction in Group C2, respectively. E, F, For +30° and –30° traction in Group P1, respectively. G, H, For +30° and –30° traction in Group P2, respectively.

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  Figure 10 Force diagram showing aligner deformation during distal retraction with a precision cut hook. A, The force system with –30° posteroinferior distalization force on a precision cut hook (black dot: center of resistance of mandibular dentition, red arrow: distalization force). B, Equivalent force system assuming CA as an ideal rigid body. Rotation occurred following the translation in the whole. C, Mesiodistal tipping of individual tooth rather than bodily movement occurred with lingual tipping and extrusion of the anterior teeth due to the deformation as the aligner is an elastic body (black dashed arrow: deformation of CA due to distalization force, black lined arrow: lingual tipping of the anterior teeth). CA, clear aligner.

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