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Veterinary Forum February 2007 (Vol 24, No 2)

Dental Dilemma: "Treating Severe Malocclusion"

by Jan Bellows, Haydee Dabritz, PhD, Patricia Conrad, DVM, PhD

    A 7-month-old, 26-kg, spayed German shepherd presented for orthodontic consultation. Physical examination revealed a lean, robust dog with moderate mandibular brachygnathism, rostroversion of the maxillary canines (Figure 1), and lingually displaced mandibular canines . The rest of the clinical examination was normal.

    Click here to see Glossary.

    Case strategy

    The client was advised that a thorough oral examination and intraoral radiography would be necessary to determine an appropriate treatment plan. Results of the complete blood count and serum chemistry profile were within normal limits, as was the preanesthetic electrocardiogram. The patient was premedicated with 75 mg of clindamycin PO; 0.1 mg/kg of hydromorphone combined with 0.01 mg/kg of acepromazine IM and 0.5 mg/kg of diazepam and 10 mg/kg of ketamine IV were administered to induce anesthesia. The dog was intubated and maintained on 2% isoflurane. The patient's temperature was controlled with a warm air Bair Hugger (Arizant Healthcare).

    Oral examination performed while the dog was anesthetized revealed two impinged areas on the rostral hard palate secondary to the lingually displaced mandibular canines (Figure 2). Intraoral radio­graphs revealed enamel with minimal dentin and a large canal chamber typically normal for a 7-month-old dog. A dental stone model was prepared to preserve the occlusion for further study.

    The treatment plan began by moving the maxillary canines caudally with orthodontic buttons and elastics to enlarge the space between the maxillary third incisors and canines. This would give clearance to move the mandibular canines laterally with an inclined plane.

    The teeth were cleaned, and 36% phosphoric acid was applied to spot areas on the buccal surface of the maxillary canines, fourth premolar, and first molar for 20 seconds to etch the enamel and then was irrigated. C & B Metabond (Parkell) was applied to orthodontic buttons (Henry Schein) before being placed on the teeth. After allowing 10 minutes for the cement to dry, an orthodontic elastic power chain was applied between the buttons using moderate force (Figure 3).

    The patient was examined weekly to monitor tooth movement. Oral medication was given by the owner before each visit. New elastics were applied at each follow-up examination. Within 3 weeks, the maxillary canines had moved sufficiently to proceed to the second stage of treatment.

    The dog was anesthetized to obtain dental model impressions, which were sent to the laboratory to fabricate a telescoping inclined plane. The inclined plane was affixed to the maxillary canines to gently guide the mandibular canines buccally. Two weeks later while the dog was anesthetized, the inclined plane was cemented on the mandibular canines (Figure 4).

    Within 6 weeks, the mandibular canines had moved buccally and no longer were impinging on the rostral maxilla. While the dog was anesthetized, the inclined plane was removed, and the teeth were cleaned and air-polished to remove stains (Figure 5 and Figure 6).

    Four weeks later, the dog was examined, and the teeth remained in functional occlusion (Figure 7). The client was advised to return every 4 months for follow-up examination to evaluate the permanent teeth for damage.

    Discussion

    Teeth are anchored to the alveolar bone by the periodontal ligament fibers. Orthodontic tooth movement properly occurs as the result of light, persistent pressure resulting in bone remodeling. Orthodontic tooth movement involves at least three variables: magnitude, direction, and duration of force. In addition, there are five basic tooth movements:

    • Tipping occurs when a single force being applied to the crown causes the tooth to rotate around its center of resistance. The crown moves in one direction and the apex in the opposite direction.
    • Bodily movement (translation) occurs when two forces are applied simultaneously to the crown of a tooth causing the crown and apex to move in the same direction.
    • Rotation (torsion) moves the tooth around its long axis.
    • Extrusion moves the tooth outward.
    • Intrusion moves the tooth inward.

    Force must be applied at least 6 hours each day for proper orthodontic tooth movement. Orthodontic appliances apply different types of forces:

    • Intermittent force can be applied with rest periods characterized by an abrupt decline of force to zero every time the load is released. An inclined plane is an example of an intermittent force appliance.
    • Continuous force produces effective tooth movement with light force. Orthodontic buttons and elastics applied to an anchor and target tooth are examples of continuous force.

    Lingually displaced canines (base narrow, lingual inclined, lingual tipped, or linguoverted; see the box Lingually Displaced Mandibular Canine Teeth) occur when the mandibular canine teeth impinge on the maxilla. The condition can result from one of the following linguoversions:

    • Dental linguoversion can occur when the mandibular canine(s) appears upright and impinges on the gingiva between the maxillary third incisor and the canine or penetrates the palate. In cases of dental linguoversion, the rest of the occlusion is normal, including the incisor relationship, premolar alignment, and molar occlusion. The most common cause of linguoverted mandibular canines is persistent primary teeth.
    • Skeletal linguoversion can occur when the mandible is underdeveloped (mandibular brachygnathia or micro­gnathia), as occurred in this case. The mandible is too narrow and/or short, resulting in the mandibular canines traumatizing soft maxillary tissues.

    Ways to resolve lingually displaced canine teeth are extraction; gingivoplasty; crown reduction, pulp therapy, and restoration; or orthodontic movement (as was done in this case). In the case of persistent dental linguoversion of the primary mandibular canine teeth, extraction allows secondary canine teeth to erupt laterally (interceptive orthodontics). Extraction is also an option in cases in which the mandibular canine teeth are directed medially (palatally) to the maxillary canine teeth. Mandibular canines are more important for oral function than maxillary canines. When the maxillary canine teeth are removed, the mandibular canines usually fit into the existing void. The dog thus has use of the maxillary incisors, which occlude with the mandibular canines when picking up objects.

    Another option is gingivoplasty, in which a wedge of gingival tissue is excised between the permanent maxillary canine and lateral incisor. Gingivoplasty allows movement of the mandibular canines into a normal position if they are in the process of erupting and contacting the area between the lateral incisor and maxillary canine.

    The third option involves mandibular canine crown reduction, vital pulp therapy, and restoration, in which the affected tooth (or teeth) is reduced in height, thus eliminating palatal contact. After crown reduction, a partial coronal pulpectomy is performed and the tooth is restored. The main advantages of crown reduction are decreased therapy time, less aftercare, and reduced expense compared with procedures involving tooth movement. The treatment can be completed in one or two visits. When the tooth is restored with a laboratory-prepared crown, however, the patient needs to be anesthetized twice. Yearly follow-up radiographs are necessary. Disadvantages of crown reduction and restoration include exposure of the pulp and possible future restoration leakage. In this case, crown reduction was not an option because of the enlarged coronal pulp cavity.

    Orthodontic movement involves cementing an acrylic, composite, or cast metal telescoping incline plane on the maxillary canine teeth to move the mandibular canine teeth laterally. Orthodontic movement to treat lingually displaced canines should start when the dog is between 7 and 12 months of age before the roots are fully developed. Over time (weeks), gradual lateral pressure usually moves the canine(s) to a functional position. An acrylic inclined plane is useful for minor movements. The acrylic plane is either fabricated on a stone model and installed during a secondary anesthetic event (preferred) or fabricated directly on the patient's maxilla (not preferred because of exothermic gingival damage). Acrylic bite planes restrict maxillary growth because of their rigid nature. Food debris also can lodge under the bite plane, causing localized gingival pathology. Toothbrushing, twice-daily home care, and application of 0.12% chlorhexidine flushes are recommended.

    For mild-to-moderate cases, a modified incline plane can be formed by building composite on the tip of the mandibular canine to allow movement laterally with adequate diastemal space.

    Closing remarks

    The case presented here demonstrates how orthodontic movement can correct severe malocclusion. However, orthodontic care in companion animals involves thorough knowledge of anatomy and orthodontic principles. If a practitioner is unfamiliar with these principles, referral to a veterinary dental specialist is recommended. In addition, there is a strong genetic component to lingually displaced mandibular canines. Therefore, genetic counseling concerning offspring is highly recommended.

    Reviewer Comment

    The author has mentioned several important points:

    • A patient is entitled to a comfortable, pain-free occlusion, not necessarily a perfect one.
    • Orthodontic movement attempts can be complex, and most cases should be referred to a specialist.
    • Genetic counseling is imperative with all patients.

    The key point is that all animals should have a thorough oral examination — including occlusal assessment — at each visit, particularly as the patient is developing.

    Suggested reading

    • Barbour-Hill E: Lingual deviation of mandibular canine teeth in the dog: Treatment by distal tipping of the maxillary canine teeth. BVDA J 1996;1-2.
    • Guiton S, Fulford M: A review of treatment modalities for malocclusions involving the mandibular canine teeth of the dog. BVDA J 1991;4.
    • Hale FA: Orthodontic correction of lingually displaced canine teeth in a young dog using light-cured acrylic resin. J Vet Dent 1996;13(2):69-73.
    • Hale FA: Juvenile veterinary dentistry. Vet Clin North Am Small Anim Pract 2005;35(4):789-817.
    • Holmstrom S, Frost P, Gammon R: Dental orthodontics, in Veterinary Dental Techniques. Philadelphia, WB Saunders, 1992, pp 339-387.
    • Legendre L: The use of a telescoping inclined plane to correct a canine tooth malocclusion. Proc 5th Eur Congr Vet Dent 1996;38-40.
    • Ross D: Basic orthodontic techniques. Proc 10th Annu Vet Dent Forum 1996;29-35.
    • Vandenbergh L: The use of a modified quad-helix appliance in the correction of lingually displaced mandibular canine teeth in the dog. J Vet Dent 1993;10(3):20-25.
    NEXT: Diagnostic Dilemma: "Pseudohypoadrenocorticism "Keeping an 'Ion' the Worms"

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