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Back to Journal »International Journal of General Medicine» Volume 14
Three-dimensional finite element analysis: lingual orthodontic micro-implant assisted maxillary dentition alienation
Author He Xin, Zhuang Wei, Zhang Delai
Published on November 18, 2021, the 2021 volume: 14 pages 8455-8461
DOI https://doi.org/10.2147/IJGM.S337212
Single anonymous peer review
Editor who approved for publication: Dr. Scott Fraser
Xin He,1 Wei-Hang Zhuang,2 Dong-Liang Zhang1 1 Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing, 100050; 2 Department of Stomatology, Beijing Ruitai Hospital of Stomatology, Beijing, 100024 [email protected] Purpose: On the tongue side With the aid of orthodontic micro-implants, the movement of the anterior teeth is analyzed by changing the height of the power arm and changing the force point, so as to set biomechanics to provide a reference for the clinical effective use of lingual orthodontic appliances. Methods: A three-dimensional finite element model of the maxillary teeth of the lingual appliance and related supporting tissues was established. Using the implant as the anchor, move the maxillary dentition far away with a force of 200g, and then analyze the movement edge of the anterior teeth by changing the length of the power arm (1mm, 3mm, 6mm, 9mm) and changing the position of the force from the lingual side to the buccal side . Results: In the process of total upper dentition displacement with the aid of lingual orthodontic implants: when the height of the power arm was 1mm, the front teeth rotated clockwise, and as the height of the power arm increased, the front teeth gradually rotated counterclockwise. When the height of the power arm is 9mm, all the front teeth rotate counterclockwise. When buccal force is applied, the central and lateral incisors rotate counterclockwise, and the canines rotate clockwise. Conclusion: As the height of the power arm increases, the movement of the upper anterior teeth is different. Compared with central incisors and lateral incisors, canine teeth are more sensitive to the height of the power arm. When the height of the power arm reaches 9mm, the upper anterior teeth show the crown tilting buccal movement. Compared with the lingual force, the buccal force does a better job in preventing the torque loss of the anterior teeth. If the upper front teeth are upright or the tongue is pointed before treatment, it is best to use a longer power arm or buccal traction. If the front teeth are already inclined to the buccal side, it is recommended to use a short power arm or lingual force. Keywords: lingual orthodontics, dynamic arm height, motion mode, 3-D finite element analysis, anterior teeth, maxillary dentition
With the widespread application of implant anchorage, orthodontists can incorporate a considerable number of marginal cases into the ranks of non-extraction treatments through the overall adduction of the upper dentition. 1-3 The position and angle of the upper and lower anterior teeth play an important role in facial beauty, normal function of the oral and maxillofacial system and orthodontic stability, thus becoming the focus of attention of patients and doctors. 4,5 Therefore, it is necessary to determine the reasonable position and angle of the upper jaw. The anterior teeth when formulating the orthodontic plan; in addition, the movement of the upper anterior teeth during the orthodontic process is also based on this design. 6 Due to the position of the brackets, the biomechanics of lingual orthodontics is very different from that of labial orthodontics. 5 According to reports, compared with the narrow and wide standard configuration of the platform, the switching configuration not only leads to a relatively lower stress level, but also leads to a significant shift of the stress field from the bone to the implant system, which may result in lower alveolar bone overload. 7 In this work, we analyzed the biomechanical mechanism of the combination of lingual orthodontics and micro-implant anchorage on the position of the upper anterior teeth in the overall adduction of the upper dentition when the height of the power arm and the point of force application are different.
This study was reviewed and approved by the Ethics Committee of Capital Medical University and was carried out in accordance with the Declaration of Helsinki. All participants provided written informed consent before being included in the study.
According to clinical indications, a 25-year-old female with maxillary protrusion was selected, and implant anchorage was needed to make the upper dentition adduct. The dentition is the normal teeth, arranged symmetrically on the arches of the left and right sides. The model is created symmetrically. The front teeth are not severely tilted forward. There was no hard tissue lesions in the teeth, and the periodontal tissues were healthy. Spiral computed tomography (CT) was performed after signing the informed consent form. Acquire DICOM (Medical Digital Imaging and Communication) data of the patient’s teeth and alveolar bone, and use MIMICS (Materialise Interactive Medical Image Control System) to convert the cross section into a three-dimensional mathematical model, export it to Geomagic Studio, and use Solidworks and 3-matic Research and modify. A 3D finite element model of upper dentition was established and analyzed using ANSYS Workbench, including upper dentition, periodontal ligament, maxilla, lingual appliance, implant and traction hook.
Hypermesh 0.7 is used to construct a finite element model, which consists of 1,682,386 nodes and 1,098,207 elements (Figure 1). A 0.018 inch × 0.025 inch (0.46mm × 0.64mm) stainless steel square wire is used as a straight lingual wire. A 9 mm (bottom of the mouth) stainless steel power arm model was constructed between the lateral incisors and the canines. The power arm extends to the gums according to the shape of the palatal arch. Four implant screws were constructed 8mm from the buccal and palatal sides of the first and second molars. Refer to related documents 8,9 to assign values to materials, including teeth, alveolar bone, alveolar process, and brackets/arch wires (Table 1). Table 1 The elastic modulus and Poisson's ratio of each material. Figure 1 (A and B) The three-dimensional finite element model of the lingual orthodontist’s implant-assisted upper dentition.
Table 1 Elastic modulus and Poisson's ratio of each material
Figure 1 (A and B) The three-dimensional finite element model of the lingual orthodontist's implant-assisted upper dentition.
Fixation constraints are applied above and behind the maxillary alveolar bone so that the maxillary alveolar bone remains absolutely still when force is applied. The contact relationship between the tooth and the bracket is defined as bonding, and the contact relationship between the bracket and the archwire is defined as non-separated contact. The arch wire can slide along the groove and will not separate in the vertical direction. The calculation results show that the axis of symmetry of the dental arch on the occlusal plane is the Y direction, the lip surface of the central incisor pointing to the tongue is Y, the occlusal plane is perpendicular to the Y direction is the X direction, and the XY plane is perpendicular to the Z direction. The direction to the gum is Z.
The design of the anterior teeth takes the midpoint and apex of the incisal edge as the reference point. The implant screw is located on the outer side between the first and second molars, 8mm from the plane of the arch wire, and the traction hook is set to four different heights of 1mm, 3mm, 6mm and 9mm. A 200g restoring force is applied between the top of the power arm and the head of the implant. These are four operating conditions. The fifth working condition is to apply 200g of restoring force between the head of the buccal implant and the lip of the lateral cervical canine. The analysis and comparison of the initial distance trend of the upper anterior teeth under five conditions.
After the force is applied, a cloud map of the distal upper dentition under four operating conditions is obtained, as shown in Figure 2. When the height of the power arm is 1mm, the horizontal component varies from 0.0019 cm to 0.0056 cm (Figure 2). 2A), similar to those under 3mm (Figure 2B), 6mm (Figure 2C) and 9mm (Figure 2D). Figure 2 Four working conditions ((A) power arm 1mm; (B) power arm 3mm; (C) power arm 6mm; (D) power arm 9mm long-distance cloud diagram.
Figure 2 Four working conditions ((A) power arm 1mm; (B) power arm 3mm; (C) power arm 6mm; (D) power arm 9mm long-distance cloud diagram.
Since the direction of force is sagittal, the change of the height of the power arm has little effect on the change of the horizontal force component. Therefore, we only studied the positional changes of the anterior teeth in the sagittal and vertical directions.
When the power arm height is 1mm, in the sagittal direction, the crown and root of the central incisor move to the lingual side, and the distance of the crown is greater than the root displacement; in the vertical direction, the crown and root of the tooth are extended far away, and the crown is farther. The distance is smaller than the root, indicating that the central incisor rotates clockwise at this time. As the height of the power arm increases, the distance between the crown and the root of the central incisor decreases in the sagittal direction. When the height of the power arm increases from 6mm to 9mm, the crown distance is less than the root displacement; in the vertical direction, the displacement of the upper root and crown increases, and the growth trend of the crown is greater than that of the root, indicating the length of the central incisor. The shaft rotates counterclockwise. See Figure 3. Figure 3 The trend of central incisor displacement when the height of the power arm is different. (A) Sagittal distal change; (B) Vertical distal change (unit: mm).
Figure 3 The trend of central incisor displacement when the height of the power arm is different. (A) Sagittal distal change; (B) Vertical distal change (unit: mm).
When the power arm height is 1mm, in the sagittal direction, the crown and root of the lateral incisor move to the lingual side, and the crown is much larger than the root; in the vertical direction, the crown and root extend distally, and the crown is much smaller than the root. , Indicating that the lateral incisor rotates clockwise. As the height of the power arm increases, in the sagittal direction, the distal distance between the crown and the root of the lateral incisor continues to decrease. When the height of the power arm increases from 3mm to 6mm, the crown distance is smaller than the root displacement, and the vertical distance between the root and the crown continues to increase; the growth trend of the crown is greater than the root, indicating that the lateral incisor rotates counterclockwise. See Figure 4. Figure 4 The trend of lateral incisor distalization with different hook heights. (A) Sagittal distal change; (B) Vertical distal change (unit: mm).
Figure 4 Distalization trend of lateral incisors with different hook heights. (A) Sagittal distal change; (B) Vertical distal change (unit: mm).
When the height of the power arm is 1mm, in the sagittal direction, the crown and root of the canine move to the lingual side, and the crown is longer than the root; in the vertical direction, the crown and root are longer and the crown is smaller than the root. , Which shows that the movement of the canine teeth is a sliding movement of the crown and tongue, which rotates clockwise. As the height of the power arm increases, the distance between the crown and the root of the central incisor decreases in the sagittal direction. When the height of the power arm increases from 1mm to 3mm, the crown distance is less than the root displacement. In the vertical direction, the distance between the tooth root and the tooth crown continues to decrease, and the reduction trend of the tooth crown is smaller than that of the tooth root. At this time, the canine teeth tilted counterclockwise. When the height of the power arm increases from 3mm to 9mm, the distance between the root of the tooth and the distal side of the tooth continues to decrease, and the lips of the canine are more inclined, as shown in Figure 5. Figure 5 The trend of the distal side of the canine, the height of the power arm is different. (A) Sagittal distal change; (B) Vertical distal change (unit: mm).
Figure 5 The trend of canine distalization when the height of the power arm is different. (A) Sagittal distal change; (B) Vertical distal change (unit: mm).
Apply buccal force to obtain a cloud image of the distal side of the upper dentition, as shown in Figure 6. Figure 6 Labial traction cloud map.
Figure 6 Labial traction cloud map.
In the sagittal direction, the central incisor is far more positive, the crown is far smaller than the root displacement, and the crown root is vertically elongated, and the crown is much larger than the root, showing a counterclockwise rotation.
In the sagittal direction, the lateral incisor is far forward, the crown is far smaller than the root displacement, and the crown root is vertically elongated, and the crown is much larger than the root, showing a counterclockwise rotation.
In the sagittal direction, the distal end of the canine is positive, the distal end of the crown is greater than the root displacement, the crown root is vertically elongated, and the distal end of the crown is greater than the root displacement, showing clockwise rotation. See Figure 7. Figure 7 The tendency of upper anterior teeth to become distal during labial traction. (A) Sagittal distal change; (B) Vertical distal change (unit: mm).
Figure 7 The tendency of upper anterior teeth to move far during labial traction. (A) Sagittal distal change; (B) Vertical distal change (unit: mm).
Compared with labial and tooth orthodontics, lingual orthodontics has the advantages of invisibility, beauty, and retention of posterior teeth anchorage. 10,11 However, the use of lingual appliances to retract the anterior teeth can easily cause torque loss12. This adverse effect can be achieved by changing the height of the power arm and the position of the force applied by the anchoring combination with the implant. Hedayati Z used the finite element analysis method to analyze the control method of changing the position of the implant screw to the torque of the anterior teeth. Hedayati believes that the higher the implant screw, the less likely it is to lose anterior torque. 13 Tominaga's research shows that increasing the height of the traction hook and matching the position of the implant nail can achieve root control movement during retraction. Anterior teeth 14
In this study, a finite element model of lingual orthodontics combined with upper dentition implant adduction was established. By changing the height of the extraction, the movement of the upper anterior teeth is analyzed, and it is shown that increasing the height of the power arm can effectively prevent the loss of torque of the anterior teeth.
As the height of the traction hook increases, the movement of the upper anterior teeth is also inconsistent. Compared with central incisors and lateral incisors, canine teeth are more sensitive to changes in the height of the power arm. But when the height of the power arm is 9mm, the upper front teeth rotate counterclockwise. This is roughly consistent with the results of previous studies. 5,15,16
Some scholars have also studied the position of the towing hook. Through finite element analysis, Feng believes that the placement of the traction hook at the distal end of the canine is not conducive to controlling the torque of the anterior teeth and the width of the dental arch. It will be better if it is placed between the canine and the lateral incisor, but it also requires additional control. 2 In this study, the traction force applied to the lip and neck was increased, and it was found that the lip force can prevent the torque loss of the anterior teeth better than the lingual force. It is worth noting that the force applied to the labial side of the canine teeth will cause the tongue of the canine teeth to tilt, which can be attributed to the excessive concentration of traction on the canine teeth. This phenomenon reminds us to avoid excessive force when the dentition is adducted as a whole. At the same time, the use of a harder arch wire makes the traction distribution more even.
There are still some limitations in this study. In order to clarify the deep-seated mechanism of anterior tooth movement, it is of great significance to study and summarize the stress distribution and size of the periodontal ligament, which will be our key research direction in the future.
In summary, during the overall adduction of the upper dentition, the longer the traction hook, the less likely the anterior teeth will be anchored. At the same time, no matter what force is used, a great stress concentration will be formed in the canine tooth area, causing the canine tooth to elongate and the tongue to tilt. Therefore, it is recommended to use lighter and harder arch wires to control the width between the canines to avoid the occurrence of the above phenomenon.
The authors report no conflicts of interest in this work.
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