Staged Orthodontic Movement of Mesiolinguoversion of the Mandibular Canine Tooth in a Dog

Introduction

Normal rostral occlusion occurs when the maxillary incisor teeth are rostral to the incisal edges of the mandibular incisor teeth and the mandibular canine teeth fit into the space between the maxillary canine and third incisor teeth.¹ Malocclusion is a common dental problem in dogs. Mesioversion of teeth occurs when the teeth become deviated in a forward direction. This condition can be easily observed in the maxillary canine teeth.^2,3 Lingual displacement of the teeth is termed linguoversion and is a common occlusal problem of the mandibular canine teeth.⁴

Several orthodontic treatment methods have been described to correct maloccluding mandibular canine teeth.^1,4–10 This case report describes the diagnosis and orthodontic correction of a class III malocclusion with an uncommon unilateral mesiolinguoversion of the mandibular canine tooth in a dog.

Case Report

A 10 mo old female Sapsaree weighing 15.8 kg was presented for evaluation and treatment of mesiolingually displaced 404. The referring veterinarian noted that the abnormally positioned 404 was impinging on the palatal mucosa between the 102 and 103.

A physical examination, including chest auscultation, heart rate, pulse, capillary refill time, and body temperature, was normal. Conscious oral examination revealed a class III malocclusion (mandibular mesiocclusion) with mesiolinguoversion of the right mandibular canine tooth (Figure 1A).¹¹ Enamel hypoplasia was also observed on 303 and 403. The left canines were normally occluded. A complete blood count and serum biochemical profile were performed for general anesthesia, and the results were unremarkable.

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Atropine^a (0.02 mg/kg), acepromazine^b (0.01 mg/kg), butorphanol^c (0.1 mg/kg), and tramadol^d (4 mg/kg) were administered intramuscularly as premedication for general anesthesia. Anesthesia was induced with the IV administration of propofol^e (4 mg/kg), and the dog was intubated with an 8.5 mm cuffed endotracheal tube that was inflated and secured. General anesthesia was maintained with isoflurane^f at 1.25–2.5% and O₂ at 1.5 L/min. A balanced electrolyte solution^g was administered IV at a rate of 10 mL/kg/hr throughout the procedure. A warm water circulating heating pad^h was placed under the dog and anesthesia was monitored using combination monitoring equipment, including a heart rate monitor, a thermometer, a pulse oximeter, capnometer, and a respiratory monitorⁱ. The systolic, diastolic, and mean arterial blood pressures were monitored noninvasively using an oscillometric blood pressure monitor^j.

A thorough oral examination was performed, and the enamel defects due to either hypoplasia or fracture were identified in the 302, 303, 403, 408, and the mesiobuccal and mesiolingual aspects of the 409. The mesiolinguoverted crown length of the 404 was shorter than that of the 304. A traumatic palate defect was noted on the mesiopalatal aspect of the 103 (Figure 1B). The defect extended 3 mm apically from the cementoenamel junction of the tooth, but no periodontal pocket was detected on periodontal probing. Full-mouth intraoral radiographs were obtained using a size 2 digital sensor^k. All of the teeth had closed apices and wide, thin-walled canals that were consistent with the age of the dog.¹² Vertical bone loss was noted between the 102 and 103 (Figure 1C). The root apex of the 404 was located more distally than was the 304. No apical pathology was noted on the 103 and 404. The bilateral mandibular second molar roots were fused. No other radiographic abnormalities were noted. A class III malocclusion with mesiolinguoversion of the right mandibular canine tooth and enamel hypoplasia was diagnosed based on the oral examination.

Correction of the malocclusion and enamel hypoplasia was indicated, and the treatment options were discussed with the owner. Orthodontic correction, crown reduction with vital pulp therapy, and extraction of the right mandibular canine tooth were offered as possible correction options of the malocclusion. Restoration of the enamel-defective teeth was also suggested. The owner elected orthodontic correction of the mesiolinguoverted tooth (404) and crown restoration of the enamel hypoplasia teeth (303, 403, 408, and 409). Multiple steps were needed for the orthodontic plan for a mesiolinguoverted 404. Following ultrasonic cleaning, the teeth were polished using a fine grit polishing pumice^l on a disposable oscillating prophy angle using a low-speed hand piece. The first step was the distal move, and the second was a buccal move. The 108 and 109 were used as anchor teeth to provide modified elastic traction.^3,5 The anchor teeth were etched with 37% phosphoric acid gel^m for 20 seconds. The etchant was rinsed off with distilled water for 50 seconds. The teeth were dried with oil and moisture-free air using an air/water syringe until a chalky appearance was noted. The bonding agentⁿ was then placed using an applicator brush and gently air-dried. The site was light-cured for 20 seconds/tooth using a portable LED curing light^o held 2–3 mm from the tooth surface. Two lingual buttons^p were placed on the apical third of the mesial crowns to minimize negative leverage forces on the anchor teeth using a flowable composite resin^q followed by light-curing for 20 seconds at multiple angles around the buttons, avoiding contact with the gingiva to prevent irritation to the gingival margin. A hook created by twisting 24-gauge wire^r was bonded in place using flowable composite resin to the coronal third of the mesiolinguoverted 404 that had been etched and treated with bonding agent.³ The hook placement was oriented to the intended movement. The sharp edges of the twisted wire were rounded by applying flowable composite resin to prevent tongue irritation. An elastic chain^s was cut at 90% of its resting length and stretched from the hook to the mesial lingual button of the anchor unit. For a single anchorage unit, an orthodontic tie wire was twisted from the mesial to the distal lingual buttons, connecting the teeth using a 26-gauge wire in a figure 8 pattern. The twisted sharp end was bent and flowable composite resin was applied to protect the buccal mucosa (Figure 2A).

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The diseased and unsupported enamel was debrided using a pear-shaped bur^t in a water-cooled, high-speed hand piece on the teeth with enamel defects. Acid-etching and bonding agents were applied following the previous technique. A flowable composite resin was placed in the prepared enamel defects with slight overflow, followed by light-curing for 20 seconds. The restoration was contoured using a variety of polishing discs^u on a low-speed hand piece, beginning with coarse and progressing to fine discs with composite polishing paste^v. A final layer of unfilled resin^w was applied and light-curing was performed to seal any margins that may have opened due to polymerization shrinkage (Figures 2B, C).¹³ The oral cavity was thoroughly rinsed with sterile water and inspected for foreign bodies prior to recovery. Recovery from anesthesia was uneventful and the dog was discharged the same day. The owner was instructed to feed softened food only and to avoid oral play while the appliance was in place. A 0.12% chlorhexidine rinse was dispensed for daily oral flushing.

The 1 wk postoperative examination following the initial correction revealed that the dog was eating well and was not experiencing any adverse effects from the orthodontic appliance. The target tooth (404) was moved distally. The owner was instructed to apply a daily oral rinse using 0.12% chlorhexidine solution and to remove food debris and fur from around the appliance. The dog was examined weekly for reassessment and adjustment of the elastic chain to maintain its resting length at 90% of the distance between the target tooth and the anchor unit.

The dog returned 5 wk following the initial orthodontic correction for a follow-up examination. The oral examination revealed that the 404 had moved more distally but was not sufficient to tip it the tooth into the appropriate position. It was concluded that the elastic chain and hook did not have sufficient tipping force and direction to move the mesiolinguoverted 404 distally. Another tipping force was needed to move the tooth correctly. The dog was sedated and intubated using a cuffed endotracheal tube. After a through oral examination, a mild plaque and calculus deposit was observed around the appliance. A tip of the twisted hook was deviated ventrally. Acid etching and bonding was performed as described previously on the coronal third of the lingual crown of the 404. A lingual button was bonded using flowable composite and then light-cured. An elastic chain was cut at 90% of its resting length and stretched from the lingual button to the anchor teeth unit (Figures 3A, B). The dog recovered from anesthesia without complication. Home care and maintenance were instructed to the owner as described previously.

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The dog was examined again 10 wk following the initial orthodontic correction. On conscious oral examination, the 404 was moved distally and displaced only lingually. It was in the appropriate position to insert the inclined plane to change the direction from mesiolinguoversion to linguoversion of the 404. Anesthesia was induced and maintained as described previously. There was no remarkable inflammation of the oral mucosa on oral examination. All of the appliances, including the elastic chains, hook, buttons, and wire, were removed using adhesive removing pliers^x. Dental cleaning, including ultrasonic scaling and polishing with flour pumice, was completed as described previously (Figure 4A). Intraoral dental radiographs were obtained to evaluate the radiographic changes of the anchor teeth (108 and 109) and of the target tooth. No abnormal radiographic changes of the anchor and target teeth were observed. The dentinal walls were thicker than on the initial radiographs. The maxillary incisors, 104, 105, and 106, were etched with 37% phosphoric acid gel for 20 seconds.

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The etchant was rinsed with distilled water, and the etched surfaces were air-dried until a frosty appearance was noted. The composite^y was applied continuously to the acid-etched teeth using an automix syringe. An additional layer of composite was applied to the interproximal space and the palatal aspect of the 104, 105, and 106. The composite was shaped roughly using an automix syringe tip to form a 60° inclined plane. After the composite hardened, the dog was temporarily extubated to assess the occlusion and reintubated for trimming and adjustments to the inclined plane. Unnecessary overfill and sharp composite were removed and smoothed using a #014 medium diamond round end taper bur^z on a low-speed hand piece.^4,14 The composite was finished from the coarse to fine grit sanding disc using a polishing paste on a low-speed hand piece (Figure 4B). The oral cavity was rinsed with distilled water. The dog was extubated again to verify the proper positioning of the 404 on the inclined plane and reintubated for anesthetic recovery. The recovery from anesthesia was uneventful. The owner was instructed in home care as described previously.

The dog returned 16 wk following the initial orthodontic correction (6 wk after the placement of inclined plane) for a follow-up examination. The owner reported that the rostral aspect of the dog's head had bumped into the ground 3 wk previously. On conscious oral exam, the 404 was repositioned buccally and had mild gingivitis adjacent to the composite (Figure 5A). The crown length of the 404 was still shorter than that of the 304. Anesthesia was induced and maintained for appliance removal and evaluation of the dental radiographic changes. The interproximal composite was cut using an ISO 199/016 diamond round end taper bur^aa on a water-cooled high-speed hand piece, and the bulk of the inclined plane was then removed using a pair of calculus forceps. The remaining composite was removed using adhesive removing pliers and an ultrasonic scaler, followed by polishing. The 104 was discolored on the coronal-third of the crown (Figure 5B). There was a widening of the interproximal space between the 403 and 404 compared to the initial presentation (Figure 5C). Intraoral dental radiographs of the discolored tooth revealed that the 104 pulp cavity size was similar to that of the contralateral canine tooth. The dentin was thicker than in the initial radiographs, indicating the presence of vital pulp. The 404 had no radiographic abnormalities, including both the periodontal ligament spaces and the periapical area of the tooth involved in the orthodontic correction. That orthodontic correction usually requires a retainer for at least 1 mo after appliance removal.⁶ In this case, the retainer was unnecessary because the orthodontic movement was relatively slow compared with similar cases reported in the literature. The owner declined restoration of the fractured enamel.

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The dog was re-examined 1 yr following the composite removal, and a dental prophy and dental radiographic examination were performed. A conscious oral examination revealed that the orthodontic correction of the 404 and the locally discolored 104 were intact and the occlusion was nearly normal. There was stage I plaque and calculus formation.¹⁵ The crown length of the 404 was longer than at the initial examination. A physical examination, complete blood count, and serum biochemical profile were unremarkable. Anesthesia was administered and dental cleaning was completed, including ultrasonic scaling and polishing with fine grit polishing paste containing fluoride^bb (Figure 6). Intraoral dental radiographs revealed that the 404 root apex was located more distally compared with the left mandibular canine root. There were no abnormal radiographic changes associated with the tooth involved in the orthodontic correction. In addition, the pulp cavity size of the local discoloration of the 104 was similar to that of the left tooth (Figures 7A–C). Orthodontic correction of the mesiolinguoverted 404 was successful based on the oral and radiographic examinations. The owner was advised that dental radiographs should be performed annually to verify the tooth vitality of the discolored 104.

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Discussion

Malocclusion is a common problem in dogs. A relatively common occlusal abnormality of the mandibular canine teeth is lingual deviation in a normal width jaw.^5,16 In that case, mesiolinguoversion is the malocclusion of the right mandibular canine tooth because the tooth is oriented abnormally forward and toward the tongue. Other patterns of malocclusion caused by palatal contact of mandibular canine teeth include an abnormally based narrow mandible, mandibular brachygnathism, and wry bite.⁵ Linguoversion of the mandibular canine teeth is considered to be a genetic problem. Common causes include persistent deciduous mandibular canine teeth, a malpositioned tooth bud, trauma to the tooth bud or tooth, a brachygnathic mandible, and excessively anisognathism.^4,14,16 Mesioversion is a relatively common orthodontic problem in dogs and generally occurs in combination with other genetic problems, such as dental and skeletal abnormalities.^2,16

Those malocclusions can cause secondary problems, including trauma, pseudopocket of the tooth, the failure of normal jaw interlock due to temporomandibular joint problem, excessive wear of canine teeth, and endodontic involvement of the teeth.^2,16 Those problems can result in mucosal ulceration, oronasal fistula, periodontal disease, endodontic disease, and concussive pulpitis due to contact of the canine crown tips, temporomandibular joint problems due to painful and nonfunctional mastication, and behavioral problems, such as an irritable temperament or head shyness.^3,5,6,8

The treatment of malocclusion of the mandibular canine teeth can be accomplished by extraction, crown reduction with vital pulp therapy, or orthodontic movement of the malpositioned tooth using a fixed or removable orthodontic device.^4,5 Extraction is a definitive treatment option that requires only a single administration of anesthesia; however, extraction may not be the best treatment option because it can be more invasive than other forms of treatment and involves the potential for serious complications, such as jaw fracture, osteomyelitis, bone sequestration, dry socket, hemorrhage, trauma to nearby structures, and loss of function (including support of the tongue and defense using the canine teeth).^3,4,16 Crown reduction with vital pulp therapy also requires only a single administration of anesthesia and has less of an effect on the supporting structures and tongue. Potential complications include a loss of the tooth function, pulpitis, and pulp necrosis, which can occur from a reduction of the crown height and pulpectomy.⁴

Orthodontic correction is a noninvasive method that precludes the need for extraction of important teeth, especially the mandibular canine teeth.¹⁶ The canine teeth can be moved atraumatically and predictably into the correct position using an orthodontic appliance. Although that method has the disadvantages of cost, multiple administrations of anesthesia, and plaque accumulation underneath the appliance, orthodontic correction is valuable for preserving the mandibular canine teeth.^5,16 Prior to the orthodontic correction of maloccluding mandibular canine teeth, the clinician should consider various factors, including patient age, the presence of adequate space to move the malaligned teeth into the correct position, and the mandibular length.^5,16 Other factors should be considered in consultation with the owner, such as the maintenance of regular oral hygiene and the ability to control the chewing behavior of the dog.⁴ Various orthodontic techniques have been described for the orthodontic movement of the mandibular canine teeth. The techniques involving orthodontic appliances include acrylic inclined plane, telescoping inclined plane, expansion screw, and w-wire.¹⁶

Orthodontic movement using an elastic chain and a composite inclined plane was considered for the dog described in this report based on the oral examination, evaluation of the occlusion, dental radiographic examination, and preference of the owner. In this dog, the deviated 404 required a move distobuccally to tip into the interdental space between the 103 and the 104. In the first step, the elastic chain was applied using a fixed dental attachment on the deviated tooth (404) and the anchor teeth (108 and 109) for correction of the mesioverted tooth. The force of this appliance was a distal tipping movement. The elastic chain appliance is clinically used to correct rostrally deviated maxillary canine teeth because it offers several advantages over other techniques.³ Ten weeks later, the composite inclined plane was applied on the interproximal space and the palatal aspect of the right maxillary incisor and canine teeth as well as the 105 and 106 after removal of the dental attachment and elastic chain to correct the linguoverted tooth. That appliance induced a buccal tipping movement of the crown and root of the mandibular canine tooth. Although the erupted crown of the 404 was shorter than that of the left tooth, the target tooth had moved sufficiently buccally to achieve normal occlusion. Orthodontic movement using light continuous pressure is most effective and results in faster tooth movement than do heavy forces. Excessively rapid movement or the use of heavy force can cause disruption of the apical blood supply to a tooth, loss of the periodontal ligament, and contact between the cementum and alveolar bone.⁶ The inclined plane technique provides intermittent forces to a particular tooth and minimizes complications.⁴ Additionally, the technique is easy to construct and less expensive than other techniques. After orthodontic movement was accomplished, local discoloration was observed at the crown of the 104. That local discoloration was thought to have an endodontic-traumatic origin.⁵ It was perhaps broken-down hemoglobin caused by a pulp hemorrhage that penetrated the dentinal tubules.^17,18 To ensure pulp vitality, radiographic examination was indicated for teeth with discoloration.⁵ In the dog described herein, the pulp of the locally discolored 104 appeared to be vital based on the 1 yr follow-up clinical and radiographic examinations.

An enamel defect of the crown can be either acquired or congenital. The underlying cause of the defect should be identified to determine the optimal treatment plan and to prevent recurrence of the lesion. The principles of restoration of an enamel defect are to remove the abnormal substance and the undermined and diseased enamel and dentin without weakening the tooth structure.¹⁹ Flowable composite material is appropriate for the restoration of enamel defects and the creation of a strong bond to the tooth because of its ability to flow into enamel defects.²⁰

Conclusion

This case report describes the diagnosis and orthodontic correction of a class III malocclusion with uncommon unilateral mesiolinguoversion of the mandibular canine tooth in a dog. Orthodontic manipulation using an elastic chain and composite inclined bite plane is an effective treatment option for the correction of malocclusion of a mandibular canine tooth.