Thursday, January 1, 2015

Veterinary Orthodontics

Orthodontics has a somewhat controversial place in veterinary dentistry. Malocclusions that we encounter in dogs may have a genetic (heritable) component. Therefore, it would be considered unethical to correct a dog's occlusion and then use that individual for breeding. On the other hand, it would be unethical to ignore a malocclusion that was the cause of discomfort for the dog. Veterinary dentists utilize orthodontic techniques to relieve or prevent oral pathology and pain, and promote longevity of the dentition. It is the client's responsibility to acknowledge that the dog should not be misrepresented in shows or used for breeding.

One of the more common malocclusions results from the failure of the persistence of the deciduous canine teeth. In this puppy, both the mandibular deciduous canine tooth (white arrow) and the maxillary deciduous canine tooth (black arrow) failed to exfoliate as the permanent canine teeth erupted.  Note that the permanent maxillary canine tooth has been deflected forward, and the permanent mandibular canine tooth has been deflected lingually. This results in the lower canine teeth impinging on the hard palate, which of course is painful for the dog.

 The first step in the treatment is surgical extraction of the persistent deciduous canine teeth. This requires general anesthesia, intraoral radiographs and careful extraction of the deciduous teeth so that no damage is done to the delicate permanent canine teeth. Notice in the radiographs that the persistent deciduous canine teeth have long, delicate roots, and that the adjacent permanent canine teeth have eggshell-thin enamel-dentin walls. Also note that after extraction, the permanent mandibular canine tooth is malpositioned and in traumatic contact with palate behind the 3rd incisor tooth.

When the persistent deciduous canine teeth are removed at an appropriate time, the permanent teeth will sometimes move into normal occlusion with no further treatment. The photos below show this puppy's occlusion 2 1/2 weeks after extraction of the deciduous canine teeth.


However, if the malocclusion does not self-correct after  extraction of the deciduous canine teeth, traumatic occlusion with the palate needs to be addressed.  There are three treatment options:
  1. Surgical: Extraction of the mandibular canine teeth.
  2. Endodontic: Shortening of the mandibular canine teeth.
  3. Orthodontic: Movement of the mandibular canine teeth.
Extraction of the mandibular canine teeth is an invasive surgical procedure that results in loss of the function of the mandibular canines in prehension, chewing and support of the tongue. Shortening of the mandibular canines in the immature individual (6-12 months old) is an endodontic procedure where a small portion of the pulp is surgically removed, and then "capped" with a composite restoration. This procedure, also called vital pulpectomy with pulp capping, is preferred by some veterinary dentists over orthodontic treatment. In some cases, the orthodontic movement of the mandibular canines is not feasible, and vital pulpectomy with pulp capping is elected.

There most common treatment of base narrow mandibular canines is the use of an incline plane. The mandibular canines are tipped into position by the light forces that are applied each time the mouth closes and the cusp of the tooth contacts the glide path of the incline plane. In this Bassett hound that had a short mandible and a traumatic occlusion of the mandibular canine on the palate, cast metal incline planes were fabricated in the dental lab and place on the maxillary canine teeth.

This is the initial examination. The mandible is short, with the lower canine teeth impinging on the palate adjacent to the upper canines.

The maxillary 1st premaolars were extracted to provide space for the incline planes and movement of the lower canines into an atraumatic position posterior to the maxillary canines. These incline planes were fabricated in a dental laboratory and cemented in place in a second procedure.

After 2 months, the canine teeth had been moved into position and the incline planes were removed. While not "normal" it is a comfortable occlusion.

Another method that is more commonly used is the fabrication of an acrylic incline plane in the patient. This has the advantage of fewer anesthetic procedures, but is not applicable to more complicated cases, as shown above. In this dog, the mandibular canine teeth required only lateral tipping into their proper location.

This acrylic incline plane was placed fabricated in the dog's mouth in one procedure. tipping movement of these canines takes about 2-4 weeks, at which time a 2nd anesthesia is required for removal of the appliance.