Initial force systems during bodily tooth movement with plastic aligners and composite attachments: A three-dimensional finite element analysis

Abstract

Objective: To describe, using a three-dimensional finite element (FE) model, the initial force system generated during bodily movement of upper canines with plastic aligners with and without composite attachments.

Materials and methods: A CAD model of an upper right canine, its alveolar bone and periodontal ligament, thermoformed plastic aligner, and two light-cured composite attachments were constructed. A FE model was used to analyze the effects of imposing a distal movement condition of 0.15 mm on the aligner (simulating the mechanics used to produce a distal bodily movement) with and without composite attachments.

Results: In terms of tension and compression stress distribution, without composite attachments a compression area in the cervical third of the distal root surface and a tension area in the apical third of the mesial surface were observed. With composite attachments, uniform compression areas in the distal root surface and uniform tension area in the mesial root surface were observed. Compression areas in the active surfaces of the composite attachments were also observed. In terms of movement patterns, an uncontrolled distal inclination, with rotation axis between the middle and cervical root thirds, was observed without composite attachment. Distal bodily movement (translation) was observed with composite attachment.

Conclusions: In a three-dimensional FE analysis of a plastic aligner system biomechanically supplementary composite attachments generate the force system required to produce bodily tooth movement; the absence of biomechanically supplementary composite attachments favors the undesired inclination of the tooth during the translation movements.

Keywords: Bodily movement; Finite element; Plastic aligners.

Figure 1.

Nonlinear properties of the periodontal ligament.

Figure 2.

CAD model assembly: (1) Alveolar bone, (2) Periodontal ligament, (3) Tooth, (4) Composite attachments, and (5) Plastic aligner.

Figure 3.

The effect of one treatment stage (aligner) was simulated by distally displacing the aligner segment 0.15 mm in the FE model.

Figure 4.

(a) Tension-compression patterns at PDL, in a model without composite attachments. (b) Tension-compression patterns at PDL, in a model with composite attachments.

Figure 5.

(a) Displacement patterns at the PDL in a model without composite attachments. (b) Displacement patterns at the PDL in a model without composite attachments.

Figure 6.

Equivalent stress patterns produced by aligner on active surfaces of attachments.

Figure 7.

Resultant force system acting on the tooth; 286 g net force (a) in distal direction, 3062 g × mm net counterclockwise moment (b).

Figure 8.

Bucco-lingual flaring of the aligner segment during distal displacement.