Displacement and force distribution of splinted and tilted mandibular anterior teeth under occlusal loads: an in silico 3D finite element analysis

Abstract

Background: Fixed orthodontic retainers have numerous advantages, but it is not known whether they can exert pathological forces on supporting tissues around the splinted teeth. The purpose of this study was to investigate how the inclination of the lower anterior teeth can affect dental displacement and also change the direction of occlusal loads exerted to dental and its supporting tissues.

Methods: Four three-dimensional finite element models of the anterior part of the mandible were designed. All the models contained the incisors and canines, their periodontal ligament layers (PDLs), the supporting bone (both spongy and cortical), and a pentaflex splinting wire placed in the lingual side of the teeth. Teeth inclination was considered to be 80° (model 1), 90° (model 2), 100° (model 3), and 110° (model 4) to the horizontal plane. The lower incisors were loaded with a 187-N vertical force. Their displacement patterns and the stress in their PDLs were evaluated.

Results: In incisors with 80° of inclination, less than a 0.1-mm lingual displacement was seen on the incisal edge and a similar distance of displacement towards the labial was seen on their root apices. However, in models with 90°-110° of inclination, the incisal edge displaced labially between about 0.01 and 0.45 mm, while root apices displaced lingually instead. By increasing the angle of the teeth, the strain in the periodontal ligament increased from about 37 to 58 mJ. The von Mises stresses around the cervical and apical areas differed for each tooth and each model, without a similar pattern. Increasing the angle of the teeth resulted in much higher cervical stresses in the incisors, but not in the canines. In the lateral incisor, cervical stress increased until 100° of inclination but reduced to about half by increasing the angle to 110°. Apical stress increased rather consistently in the incisor and lateral incisors, by increasing the inclination. However, in the canines, apical stress reduced to about half, from the first to fourth models.

Conclusions: Increasing the labial inclination can mostly harm the central incisors, followed by the lateral incisors. This finding warns against long durations of splinting in patients with higher and/or patients with reduced labial bone thickness.

Keywords: Finite element method; Lower anterior teeth; Orthodontic treatment; Retention; Splinting; Tooth inclination.

Fig. 1

Meshed model 1 showing the inclination of the anterior teeth at 80° to the horizontal plane

Fig. 2

Meshed model 2 showing the inclination of the anterior teeth at 90° to the horizontal plane

Fig. 3

Meshed model 3 showing the inclination of the anterior teeth at 100° to the horizontal plane

Fig. 4

Meshed model 4 showing the inclination of the anterior teeth at 110° to the horizontal plane

Fig. 5

Total deformation in the teeth of the first model (the inclination of the anterior teeth at 80° to the horizontal plane)

Fig. 6

Total deformation in the teeth of the second model (the inclination of the anterior teeth at 90° to the horizontal plane)

Fig. 7

Total deformation in the teeth of the third model (the inclination of the anterior teeth at 100° to the horizontal plane)

Fig. 8

Total deformation in the teeth of the fourth model (the inclination of the anterior teeth at 110° to the horizontal plane)

Fig. 9

The von Mises stress in the cervical area of the PDL

Fig. 10

The von Mises stress in the apical area of the PDL

Fig. 11

The strain energy of the lower right central, lateral, and canine PDLs

Fig. 12

Max./Min. of strain energy in the lower right incisors and the canine

Fig. 13

Strain energy in the anterior teeth PDL