Modified Mandibular Lingual Arch for Orthodontic Traction of Impacted Mandibular Canine and Premolar: Case Reports
Article information
Trans Abstract
Impaction of the tooth can cause functional and esthetic problems, so early intervention is critical. This report describes two cases of orthodontic traction of impacted mandibular canine and mandibular premolar teeth using a modified mandibular lingual arch soldered with traction hooks rather than a conventional orthodontic appliance. By planning the position and shape of the traction hooks with consideration for the three-dimensional position and angulation of the impacted teeth, clinicians can apply the intended direction and magnitude of traction force. Furthermore, this appliance can be used for multiple impacted teeth in various locations within the mandibular arch by modifying the position and shape of the traction hooks.
Introduction
Impaction is defined as the disturbance of an eruption caused by a physical barrier in the eruption path. Impaction can be caused by either systemic or local factors [1]. Impaction is linked to systemic factors like endocrine disorders and genetic diseases. Local factors such as a mucosal barrier, space deficiency, cyst, odontoma, supernumerary teeth, prolonged retention of a primary tooth, and ectopic eruption have been identified as common causes of impaction [1,2].
Aside from the third molars, the maxillary canine, mandibular second premolar, and mandibular second molar were found to be the most commonly impacted teeth[3]. In mandibular dentition, impaction affected the mandibular canine, mandibular second premolar, and mandibular second molar more frequently [4-6].
Tooth impaction can cause problems with the stability of the dental arch, masticatory function, and appearance [7,8]. Therefore, the proper treatment strategy for aligning this impacted tooth into the dental arch and performing a reasonable occlusion is critical. There are four approaches to treating tooth impaction: observation, intervention, relocation with surgical exposure, and extraction [9]. Physical obstructions in the eruption pathway are removed as part of the intervention. If the tooth position or inclination remains unchanged after the physical barrier is removed, surgical exposure and orthodontic traction should be considered.
Various traction appliances have been used to treat impacted mandibular teeth [10-13]. Several factors, including the location and angulation of the impacted tooth, the need for space regaining, the patient’s age, and the degree of the patient’s compliance, should be taken into consideration when deciding on the types and specific designs of traction appliances.
This report presents two cases utilizing the modified mandibular lingual arch soldered with traction hooks for orthodontic traction of impacted mandibular canines and premolar teeth. Moreover, we provide the schematic diagrams of the appliances and explain how to design the traction hook based on the three-dimensional position and angulation of the impacted tooth, as well as the desired direction and magnitude of traction forces.
Case Reports
The patients’ legal guardians provided informed consent for the publication of this case report, as well as related clinical photographs and radiographic images of the patients.
1. Case 1
A 10-year-old boy came to Seoul National University Dental Hospital with an impaction of his mandibular left canine and mandibular left first premolar, as well as a cystic lesion. There was no major medical history. As shown on his initial panoramic radiograph, the mandibular left canine and mandibular left first premolar were dislocated by the radiolucent periapical cystic lesion arising from the mandibular left primary canine (Fig. 1A). Therefore, on the first visit, the mandibular left primary canine was extracted. However, after 3 months, the mandibular left canine impaction remained unchanged on the panoramic radiograph (Fig. 1B). Then, a cone-beam computed tomography (CBCT) was performed to show the relationship between the crown of the mandibular left canine and the roots of the mandibular left central and lateral incisors (Fig. 1C - 1E).
Radiographic images of case 1. (A) Panoramic radiograph taken at the initial visit, (B) Panoramic radiograph taken 3 months after the extraction of the mandibular left primary canine, (C) CBCT axial view taken 3 months after the extraction, (D) CBCT sagittal view taken 3 months after the extraction, and (E) 3D reconstruction of CBCT image taken 3 months after the extraction. The impacted mandibular left canine and first premolar related to the periapical cystic lesion of mandibular left primary canine were observed in the white dotted boxes. The yellow arrows point to the impacted mandibular left canine, which was in close proximity to the buccal side of the roots of the mandibular left incisors.
Given that the impacted mandibular left canine was unlikely to erupt spontaneously and that the roots of the neighboring anterior teeth may have resorbed, we decided to surgically expose and perform orthodontic traction of the mandibular left canine. Before surgery, an impression for a traction appliance was performed with alginate. On the day of surgery, a closed-eruption technique to expose the mandibular left canine was used. An orthodontic button was attached to the labial surface of the exposed crown. A ligature wire was threaded into the button. After one week, a modified mandibular lingual arch soldered with traction hooks was delivered, and traction of the mandibular left canine with elastic thread (TP orthodontics, La Porte, IN, USA) began. The impacted mandibular left canine and adjacent anterior teeth had to be separated to avoid unfavorable forces on the roots of neighboring teeth. For this reason, at first, both distal and buccal directional traction forces were applied to the mandibular left canine. The modified mandibular lingual arch featured two soldered traction hooks on the buccal side. The one in the mesial position provided disto-buccal force (Fig. 2A). Once the neighboring teeth have separated, the mesially inclined mandibular left canine should be forced in a more distal direction. The other traction hook in the more distal position provided more distal force than buccal force (Fig. 2B). Furthermore, both traction hooks exerted occlusal directional force simultaneously. The intraoral photograph of the appliance is shown in Fig. 2C.
A traction force diagram of the modified lingual arch in case 1. (A) First, disto-buccal force should be applied using a mesially located hook to separate the crown of the mandibular left canine from adjacent incisors’ roots, (B) Following separation, further distal traction was performed with a distally located hook. The orange arrows indicate the direction of traction forces, while the blue arrows indicate the vector components of those forces, (C) Intraoral photograph of the appliance.
Every month, the patient went to the hospital to replace the elastic thread and to change the direction of force. At the start of traction (Fig. 3), the mandibular left canine was tied to the mesially located traction hook with elastic thread. Following 4 months of traction (Fig. 4), additional distal traction of the mandibular left canine was initiated with a distal traction hook and an elastic thread. At the same time, the mandible’s left first premolar erupted with mesial angulation. To distalize the tooth, an orthodontic button was bonded to its buccal surface. The button was connected to a distally located traction hook with a power chain (Ormco, Brea, CA, USA). After 7 months of traction (Fig. 5), the crown of the mandibular left canine was visible in the oral cavity and positioned in the arch with adequate space, but it had not fully erupted to occlusion level. The traction hook, which was positioned mesially on the modified lingual arch, was removed because it could disrupt the proper alignment of the mandibular left canine. Given that the root development of the mandibular left canine was incomplete, we expected a spontaneous eruption of the tooth to the occlusion level. As a result, orthodontic traction of the tooth was discontinued, and a periodic recall check was scheduled. After 1 year and 3 months of traction (Fig. 6), the mandibular left canine had fully erupted to a level comparable to the adjacent premolar. Thus, the modified mandibular lingual arch soldered with traction hooks and orthodontic buttons were debonded. In this case, the impacted mandibular left canine and first premolar were well aligned, requiring no additional orthodontic treatment or complications such as root resorption.
Intraoral photographs of case 1 at the beginning of traction. (A) Occlusal view, (B) Lateral view. Using elastic thread, the impacted mandibular left canine was ligated to the mesially located traction hook, aiming to achieve distobuccal traction.
Intraoral photographs of case 1 after 4 months of traction. (A) Occlusal view, (B) Lateral view. The distally located hook was used to achieve the distal traction of the mandibular left canine and first premolar.
Intraoral photographs of case 1 after 7 months of traction. (A) Occlusal view, (B) Lateral view. The mandibular left canine emerged in the oral cavity, and the traction was discontinued.
Intraoral photographs of case 1 after 1 year and 3 months of traction. (A) Occlusal view, (B) Lateral view. The mandibular left canine and first premolar erupted to an acceptable occlusion level.
2. Case 2
An 11-year-old girl came to Seoul National University Dental Hospital for treatment of impaction of the mandibular right second premolar and prolonged retention of the mandibular right second primary molar. There was no significant medical history for the patient. Radiographically, the mandibular right second premolar showed no inclination but did have mild distal displacement and mesial-in rotation (Fig. 7).
Radiographic images of case 2. (A) Panoramic radiograph at the initial visit, (B) CBCT axial view at the initial visit, (C) CBCT sagittal view at the initial visit, and (D) 3D reconstruction of CBCT image at the initial visit. The yellow arrows point to the impacted mandibular right second premolar with mesial-in rotation and mild distal displacement.
Given the depth of impaction, we planned surgical exposure with the extraction of the retained primary tooth, followed by orthodontic traction of the impacted mandibular right second premolar. Before surgery, an impression for an orthodontic appliance was made with alginate. During surgery, the mandibular right primary second molar was extracted. Using the closed-eruption technique, the crown of the mandibular right second premolar was surgically exposed, and an orthodontic button was attached to the buccal surface. A ligature wire was threaded onto the button. After one week, a modified mandibular lingual arch soldered with a traction hook was delivered, and traction with elastic thread began. Every month, the patient went to the hospital to replace the elastic thread and change the direction of force. The traction force should be applied in the mesio-occlusal direction to separate the impacted mandibular right second premolar from the mesial root of the mandibular right first molar. Furthermore, it is critical to maintain the space required for the mandibular right second premolar to align. According to these specifications, the traction hook was placed on the mesial half of the extraction socket of the mandibular right primary second molar, in contact with the distal surface of the mandibular right first premolar (Fig. 8A, 8B). The U-shaped traction hook, parallel to the occlusal plane, provided effective occlusal traction. These mechanics applied forces from the hook’ s two points in the manner of a “slingshot” (Fig. 8C). After 6 months of traction, the mandibular right second premolar erupted in the occlusal direction. Therefore, the vertical distance between the impacted tooth and the traction hook became insufficient to generate adequate traction force. Consequently, the elastic thread needed to be knotted over the top of the U-shaped hook and extend to the hook’s lingual column (Fig. 8D, 8E). This method of tying resulted in a longer span of traction, which provided adequate occlusal traction force.
Intraoral photographs of a modified mandibular lingual arch, as well as diagrams of the “slingshot” method on the mesial view of a U-shaped traction hook and an impacted mandibular right second premolar from case 2. (A, B, C) At the beginning of traction, application of occlusal traction force over two points (a* and b*) on a U-shaped hook, (D, E) After 6 months of traction, when the impacted tooth was close to the hook, the elastic thread was extended to the hook’s lingual column (c*), but over the top of the U-shaped hook, increasing the span of traction. The blue arrows indicate the paths of elastic thread across the traction hook. “a*, b*, and c*” indicate the buccal and lingual points on the U-shaped hook, as well as the hook’s lingual column, respectively.
After 1 year of traction, the traction hook broke. Thus, after detaching the mandibular lingual arch, a buccal tube (Ormco) was welded to the mandibular right first molar band, and the appliance was re-delivered. A buccal sectional wire was made with 0.018 × 0.025 inch stainless steel wire (JISCOP, Gunpo, South Korea). The buccal sectional wire was inserted into the buccal tube of the mandibular right first molar and directly ligated to the ligature wire chain of the mandibular right second premolar. Additionally, for traction with the most occlusal vector, the sectional wire was folded once on the lingual side (Fig. 9A). After 1 year and 4 months of traction, the patient developed gingival impingement from the mandibular lingual arch, so the appliance was removed. A concurrent panoramic radiograph revealed eruption of the mandibular right second premolar up to the alveolar bone level. Consequently, a gingivectomy was performed on the mandibular right second premolar using a monopolar electrosurgical unit (Sensimatic® 700SE Electrosurgery, Parkell, Edgewood, NY, USA). The exposed tooth was rotated mesially by nearly 90°. To derotate, a new button was bonded to the more mesial part of the buccal surface than the previous one. The elastic thread was used to secure the new button to the buccal sectional wire with elastic thread (Fig. 9B). After 1 year and 8 months of traction (Fig. 9C), the distal button and buccal sectional wire were removed. To further derotate the tooth, the mesial button was ligated to the buccal tube of the mandibular right first molar with a power chain (Ormco). After 2 years and 5 months of traction (Fig. 9D), the mandibular right second premolar erupted to the marginal ridge of the mandibular right first molar. To keep the de-rotated position, the mandibular right second premolar and first molar were splinted for 6 months with 0.016-inch nickel-titanium wire (JISCOP). When the patient returned to the hospital 6 months after treatment ended, the mandibular right second premolar had normal occlusion and reasonable alignment (Fig. 9E, 9F).
Intraoral photographs taken during orthodontic traction and after 6 months of follow-up on case 2. (A) After 1 year of traction, the soldered traction hook broke, and the buccal sectional wire of the welded buccal tube on the molar band was directly connected to the ligature wire chain of the mandibular right second premolar, (B) After 1 year 4 months of traction, for de-rotation, a more mesially located button was bonded and then ligated to the buccal sectional wire, (C) After 1 year and 8 months of traction, for de-rotation, the mesial button was ligated to the welded buccal tube on the molar band using a power chain, (D) After 2 years and 5 months of traction, the mandibular right second premolar was splinted with 0.016-inch nickel-titanium wire for retention, (E, F) At 6 months of follow-up after the end of treatment, the mandibular right second premolar achieved functional occlusion and good alignment.
Discussion
For adolescent patients with impacted mandibular canines and premolars, various types of appliances can be used to achieve orthodontic traction. Removable appliances include conventional appliances with composite resin baseplates and clear aligners [14]. Fixed appliances are classified into four categories: traction on the main archwire of a full-fixed appliance, traction on the auxiliary archwire of a full-fixed appliance, mini-screws supported traction [10], and modified mandibular lingual arch. A removable appliance has several benefits [15]. First, traction and space regaining with an expansion screw can occur concurrently, shortening the duration of treatment. Second, by placing multiple traction hooks in various locations, a single appliance can gain traction in multiple directions. Third, removable appliances can reduce anchor unit loss because they use not only multiple teeth but also lingual coverage with a composite resin baseplate for anchorage [16]. Finally, patients can maintain better oral hygiene than when using a fixed appliance because they can remove and clean the appliances on their own. However, removable appliances have some disadvantages. First, a patient’s compliance is critical for treatment success. Second, achieving precise tooth movement other than tipping is difficult [17]. The appliance’s retention is determined by the number of remaining teeth, so the available time for use is limited. In late mixed dentition, which is when deciduous teeth are shedding, there are only a few teeth that serve as the anchors of the appliance. The first case in this report is a late mixed dentition, so orthodontic traction with a removable appliance is not recommended. Traction with a full-fixed appliance has the benefit of allowing for precise alignment of an impacted tooth, but it also has some drawbacks. First, to reduce the adverse reaction force on adjacent teeth, traction of the impacted tooth should be performed at least on the step of the rectangular main arch wire [18]. Therefore, it takes time to apply traction force, but there is an alternative technique that uses an auxiliary Piggyback NiTi arch wire. Second, bracket-induced inclination changes in adjacent teeth increase the risk of root resorption by the impacted tooth’s follicle [19]. Meanwhile, skeletal anchorage with mini-screws provides absolute anchorage for the traction of an impacted tooth, preventing unintended movements of neighboring teeth. Furthermore, this appliance requires minimal patient compliance [19]. However, due to adolescents’ lower bone qualities, the failure rate of mini-screws was higher in younger patients under the age of 15 compared to the older group [20]. A modified mandibular lingual arch soldered with traction hooks provides a stronger anchorage for traction, reducing the negative reciprocal effect on the adjacent teeth.
Also, this appliance serves as a space maintainer to help the impacted tooth align properly. It consists of bands on both first molars in the mandible. A 0.9-mm stainless steel wire sits on the cingulum of the mandibular anterior teeth, connecting the two first molars. The positions of mandibular first molars are thought to be stabilized against the cingulum of the lower incisors [21]. Therefore, extending the anterior segment of the mandibular lingual arch to include both canines, rather than just the central and lateral incisors, can more effectively prevent the mesial shifts of the mandibular first molars. This extension of the anterior wire to both canines was applied to the second case in this report. In contrast to the first case, the second case exhibited the loss of mandibular right primary second molar and the eruption of the mandibular second molar. Greater space loss has been observed with the loss of a primary second molar than with the loss of a primary first molar [22]. In addition, the erupted mandibular second molar could induce the forward movement of the mandibular first molar [23]. Thus, the second case was considered to need a more robust space maintenance strategy.
The mandibular lingual arch is effective in preserving the arch perimeter, but ensuring space for each tooth’s alignment is achieved by preventing tilting of adjacent teeth. An additional spur or horizontal loop in the edentulous region restricts the tilting of the adjacent tooth. These structures should be in contact with the proximal surface of the adjacent tooth just below its contact point. Likewise, in the second case described in this report, the mandibular lingual arch incorporated a horizontal U-shaped loop that made contact with the distal surface of the mandibular right first premolar, aiming to prevent its distal tilting.
Furthermore, the addition of multiple traction hooks provides different vectors and magnitudes of traction forces. As a result, it is possible to achieve simultaneous orthodontic traction of multiple teeth while lowering the overall appliance replacement cost and duration of treatment. However, the presence of multiple soldered traction hooks in the mandibular lingual arch reduces the appliance’s overall sturdiness due to the likelihood of the hooks becoming fractured. The exposure of the hook to saliva causes corrosion of the silver solder joint, increasing its vulnerability to repeated tensile stress [24]. Thus, reducing the stress on the solder joint is necessary to minimize the fracture of the hook. The stress and deformation of the hook increase as the total length of wire increases and its thickness decreases. In the second case discussed in this report, the broken U-shaped hook had a longer total length of wire, which resulted in higher deformation and stress when under load. To prevent such a fracture of the hook, it is advisable to employ a thicker wire when fabricating the hook with a complicated shape. Nonetheless, this appliance has a benefit in that the traction hooks can be easily and inexpensively repaired if they become deformed or fractured.
A buccal sectional wire can also be inserted into the welded buccal tube on the molar band, as shown in the report’s second case. The various lengths and loops of buccal sectional wire allow for controlled tooth movement of the impacted tooth. The free end of the buccal sectional wire was connected to the impacted tooth, creating cantilever-type orthodontic traction. The use of rectangular stainless steel wire as traction wire is appropriate due to its good stiffness and formability [25]. To increase the flexibility of the traction wire, helicoid can be added. The buccal sectional wire should include a U-shaped loop positioned ahead of the welded buccal tube to prevent it from sliding under traction force.
Finally, treatment outcomes with this appliance are independent on patient compliance.
However, orthodontic traction with this appliance is limited in terms of complete tooth leveling and alignment, necessitating the use of an additional full-fixed orthodontic appliance. In the first case described in this report, an impacted mandibular left canine and first premolar were simultaneously treated with several soldered traction hooks on a modified mandibular lingual arch without the need to replace the appliance. The second patient in this report had well-aligned mandibular teeth, except for the impacted mandibular right second premolar. Therefore, the modified mandibular lingual arch was the best option for the second case because it eliminated the need for additional orthodontic treatment to align the entire mandibular arch.
The “slingshot” method has been used to realign lingually or palatally displaced lateral incisors and canines [26,27]. This method applies two differential forces from the displaced tooth’s mesial and distal sections directly to the displaced tooth, using an elastomeric chain. These two-sided traction vectors help to effectively pull the displaced tooth back into the arch. In the second case in this report, the “slingshot” method was used for orthodontic traction of the impacted mandibular right second premolar. The “slingshot” method required a U-shaped traction hook that was placed on the occlusal plane. Tying elastic thread over the buccal and lingual portions of the U-shaped hook resulted in two differential force vectors, allowing for effective traction in the occlusal direction. The “slingshot” method of orthodontic traction has advantages over the traditional vertical elastic tie [28]. The conventional vertical tie reduces the distance between the elastic tie on the impacted tooth and the traction hook. A very short stretched range of a vertical elastic tie is associated with the risk of applying too much initial force. The traction directly applied to the impacted tooth is inefficient, with a very slow response and frequent elastic changes. Furthermore, the knot of the vertical tie is prone to becoming loose, causing the original force to decay. In contrast, in the “slingshot” method, the lateral displacement of a stretched elastic thread results in a wider range of tooth movement. The light and continuous traction forces in the “slingshot” last for a longer period.
As orthodontic elastics for traction of impacted teeth, thread-type elastics are preferred over elastic chains, because they allow for more precise control of initial force levels than elastic chains. This is because, unlike elastic chains, thread-type elastics allow the clinician to easily adjust the length of stretch based on their needs. In both cases in this report, nylon-coated latex threads were used instead of synthetic polymeric threads. Synthetic polymeric threads have high strength, stiffness, and modulus of elasticity. These properties make it difficult to apply precise force, and the initial force of elastics is rapidly lost even with very minor tooth movement [29]. In contrast, nylon-coated latex threads are softer and easier to tie. Several studies found that nylon-covered latex threads exhibited less force relaxation after initial loading than synthetic polymeric elastics [30,31]. This could be the result of reinforcement with a “nylon cover.” Furthermore, because synthetic polymeric threads have a much lower inherent frictional resistance, the material inside the knot had to be pre-tensioned for the knot to remain intact. In contrast, the relatively rough nylon covering prevents the knot from becoming loose [32]. However, nylon-covered latex threads should be replaced at least every six weeks due to hygienic concerns. Some debris and calculus will accumulate, particularly at bulky knots, and elastics’ mechanical behavior may be impaired as a result of deposits and chemical interactions with food and oral fluids [31,32].
Summary
The present case report describes the orthodontic traction of impacted mandibular canine and premolar teeth using a modified mandibular lingual arch soldered with traction hooks. It is a fixed appliance that does not require the patient’s cooperation and thus reduces treatment time. This appliance can apply traction forces in diverse directions and extents by positioning multiple traction hooks of varying shapes, depending on the clinician’s intentions. These multiple traction hooks are useful for multiple teeth’s simultaneous traction without having to replace the entire appliance. Furthermore, this appliance can play an important role in anchorage and space maintenance for the alignment of impacted teeth. In conclusion, the modified mandibular lingual arch soldered with traction hooks is an effective treatment option for orthodontic traction of impacted teeth in the mandible.
Notes
Conflicts of Interest
The authors have no potential conflicts of interest to disclose.