Finite element simulation of first molar movement during orthodontic treatment.

Szuhanek, Camelia Alexandrina ; Cernescu, Anghel ; Faur, Nicolae 等

1. INTRODUCTION

The evaluation of tooth movement is crucial in achieving the goals of orthodontic treatment.

Previously, animal studies have been performed in order to analyse the characteristics of dental movement consecutive to orthodontic treatment. The advantage of finite elements method is the possibility of unlimited loading simulation that can provide answers to complex clinical situations (Faur, 2002). The application of finite elements method in orthodontics are frequently related to the effect of orthodontic treatment in frontal area (Liang et al., 2002; Szuhanek, 2006) or to the bone/implant interface during orthodontic implants use (Motoyoshi, 2009; Szuhanek et al., 2009).

Starting from these experimental studies, our objective is to provide a new experimental model that can simulate the displacement of first molar during the retraction phase of orthodontic treatment.

2. MATERIALS AND METHODS

The experiment was done in the Department of Strenght of Materials, from the Poltehnica University of Timisoara. The geometrical model was constructed from 3D scans of three extracted teeth (a canine, a second premolar and a molar), using a Ronald PICZA 3D Laser Scanner LPX--1200. Periodontal ligament was simulated as a 0.25 mm membrane around the teeth. COSMOSM software was used in this numerical study.

The numerical model was subjected to forces similar to those used during the orthodontic treatment. The loading was applied on the labial/lingual area of the teeth, and in the molar area was inserted an orthodontic implant. Three molar was ligated to the implant, therefore the implant role was to prevent unwanted movements of this tooth. Our study evaluated the initial displacement in the first molar in the situation of labial/lingual loadings and also in the situation with/without orthodontic implants.

The model with orthodontic implant was formed by 27526 elements and 41781 nodes. The intensity of applied force was 1 N, 1.5 N and 2 N (see fig. 1, fig. 2). Material properties used are shown in the table 1.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Anchorage was evaluated by means of initial displacements values measured in the first molar, in all three directions: Ox, Oy, and Oz. An increased value of initial displacement in the molar was considered similar to a low resistance to movement, therefore a decreased level of anchorage

3. RESULTS

The amounts of initial displacement were lower in the lingual technique model, suggesting that the anchorage values are much higher in this group.

The resistance to anchorage loss was greater in lingual force application, especially in horizontal direction (fig. 3, fig. 4). The force system used in the two situations is shown in the figure 5.

The introduction of the orthodontic implant decreased dramatically the anchorage loss, both in lingual and labial model (tab. 2, tab. 3).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

The lingual technique model demonstrated better values of anchorage comparing to the labial technique group.

4. CONCLUSIONS

Orthodontic implants and lingual force application provide better anchorage, especially during space closure. The unlimited possibility of evaluation recommends the finite elements method as a powerful tool for investigating dentoalveolar reactions after orthodontic loading.

5. FUTURE WORK

Future work is required in order to investigate the dentoalveolar reactions in more complex situations.

6. REFERENCES

Faur, N. (2002). Finite elements: fundament (Elemente finite: fundamente). Publisher Politehnica, ISBN ..., Timisoara, Romania

Liang, W; Rong, Q; Lin, J & Xu, B. (2009). Torque control of the maxillary incisors in lingual and labial orthodontics: a 3-dimensional finite element analysis. American Journal of Orthodontics and Dentofacial Orthopedics, Vol. 135, No. 3, (March 2009) 316-322

Motoyoshi, M.; Ueno, S.; Okazaki, K. & Shimizu, N. (2009). Bone stress for a mini--implant close to the roots of adjacent teeth--3D finite element analysis. International Journal of Oral and Maxillofacial Surgery, Vol. 38, No. 4, (April 2009) 363-368

Szuhanek, C. (2006). Periodontal implications in orthodontics. PhD thesis. (Implicatii parodontale in anomaliile dentomaxilare. Teza de doctor at). Publisher Politehnica, Timisoara, Romania

Szuhanek, C.; Faur, N. & Cernescu, A. (2009). Biomechanical 3D analysis of stress induced by orthodontic implants. Key Engineering Materials, Vol. 399, (2009), 194-204, ISSN 1662-9795

Tab. 1. Material properties taken into this study

Material Young's modulus Poisson's
 (daN/[mm.sup.2]) ratio

enamel 8400 0.33
dentin 1890 0.31
cement 2000 0.16
Alveolar bone 2000 0.16
Periodontal
 ligament 100 0.45

Tab. 2. The initial displacement in the first molar after labial
force application

 Implant anchorage [mm]
 Initial displacements--labial
Force applications--
value X Y Z

1 N -0,00129 -0,00096 -0,00136
1,5 N -0,000755 0,00051 -0,00105
2 N -0,001 0,00068 -0,0014

Tab. 3. The initial displacement in the first molar after lingual
force application

 Implant anchorage Initial
 displacements--lingual
 application--
Force
value X Y Z

1 N -0,00125 -0,0014 0,00201
1,5 N -0,00302 0,000654 0,00151
2 N -0,00173 0,000872 0,0020