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Linguoversion of the mandibular canine tooth/teeth is where one or both mandibular canines is lingually displaced from their normal position in the dental arch. The displaced tooth or teeth can cause indentations or trauma to the hard palate ranging from minor to significant, including penetration into the nasal cavity. The displaced teeth can also cause accelerated periodontal disease to the maxillary canine or incisor teeth. The trauma to the hard palate caused by these malpositioned mandibular canine teeth is not only painful to the animal (leading to head shyness or eating difficulties) but can also lead to eventual communication between the oral and nasal cavities (oronasal fistula).
It is a commonly seen malocclusion in puppies and young dogs. It can occasionally be seen in cats. Certain breeds may be more predisposed to the condition including Labradors and Staffordshire bull terrier breeds. It is also more common in dolichocephalic head types.
Apart from a true skeletal base malocclusion, sometimes dental malocclusions caused by either retained deciduous teeth or malpositioned teeth (i.e. maxillary third incisor reducing the diastema space between it and the maxillary canine tooth) can also lead to this “base narrow” condition.
This is where a FIRM rubber ball is used to apply an intermittent force to the permanent mandibular canine teeth to move them labially. The proviso is that the mandibular canine teeth should be in a favourable position (in the diastema between the maxillary 3rd incisor and canine tooth) to move labially (laterally) without any obstruction (usually the obstruction is from the maxillary canine tooth or maxillary third incisor tooth). One study3 showed that having young dogs with lingually displaced mandibular canine teeth hold an appropriately sized rubber device (e.g. a hard rubber chew ball, but not a tennis ball) in their mouths for a minimum of 15 minutes three times a day may correct mild forms of this malocclusion. The ball acts like an inclined plane, causing tipping forces to be placed on the affected teeth every time the dog bites down on the ball. However, in human orthodontics, forces usually need to be applied to a tooth or teeth for several hours per day to prevent rebound of the tooth back to its original position.
I rarely consider this removable orthodontic appliance technique unless the owner has financial constraints and wants to try it.
In mild cases, where there is minor trauma to the gingival tissues, a wedge of gingival tissue and/or alveolar bone is removed from the maxilla between the maxillary third incisor and the canine tooth. The permanent mandibular base narrow canine teeth must be in a favourable position for this procedure to work.
This procedure is relatively simple and requires only one general anaesthetic.
If the base narrow condition is diagnosed at an early age (ideally less than 10 weeks of age), sometimes the extraction of the deciduous mandibular canine teeth (and mandibular incisors if necessary) will prevent the problem from occurring when the permanent canines start to erupt (interceptive orthodontics). The term “adverse dental interlock” is used to describe this base narrow condition in puppies. As mentioned before, because base narrow condition usually occurs due to a skeletal base mismatch, extracting the deciduous canines often doesn’t alter the base narrow condition in the permanent dentition. However, it may in a small percentage of cases prevent base narrow condition occurring in the permanent dentition or may sometimes minimise the traumatic consequences of it. However, whether the deciduous canines are extracted with a simple or surgical approach there is a real risk of damaging the crown of the permanent mandibular canine tooth (owners need to be made aware of this). The damage to the crown usually manifests as an indentation or enamel defect in the permanent canine tooth. Extraction of any persistent deciduous tooth or teeth, or extraction of a malpositioned tooth (i.e. maxillary third incisor tooth) if diagnosed and treated early enough in the young animal may prevent or successfully treat “base narrow” condition.
Another method used to treat mild cases of linguoversion of the mandibular canines is the so-called tooth extensions. The linguoverted canine tooth needs to be in either the diastema between the maxillary 3rd incisor tooth and the maxillary canine tooth or the maxillary canine tooth and the maxillary first premolar tooth. The procedure involves building up the height and changing the shape of the mandibular canine tooth with composite resins. This build up allows orthodontic forces to act on the tooth when the dog closes its mouth causing a tipping into a more labial position. When the canine tooth is in its correct position, the composite built up crown tip can be removed, but only after a period of retention to prevent the teeth rebounding lingually.
Involves the manufacture of a fixed incline plane made usually of acrylic. These appliances act as a ramp to position the mandibular canine teeth into a better, non- traumatic position. The incline plane can be manufactured directly in the mouth usually with crown and bridge acrylics. The teeth are etched with 37% phosphoric acid, the acid is rinsed off and then a bonding agent is applied (this step may not be necessary). The self-curing (chemically cured) acrylic is then applied to the teeth (usually the maxillary canine and incisor teeth) in increments. An incline plane is formed with an acrylic bur in a straight handpiece. But once fabricated, the incline plane usually cannot be altered. Once installed, the inclined plane places tipping forces on the displaced canine tooth in a direction determined by the slope and direction of the fabricated incline. The correction usually occurs within four weeks, but a retention phase of another 4 weeks is recommended, prior to the appliance being carefully removed. Homecare with 0.12% chlorhexidine gluconate is imperative for good oral hygiene and to prevent mucositis.
This procedure is often the procedure that offers instant success, by eliminating the trauma to the hard palate of the maxilla. Pulpotomy involves the surgical amputation of the coronal pulp when combined with a crown reduction procedure to correct the oral trauma from ‘base narrow’ canines. The wounded surface of the amputated pulp is then treated with medicaments such as mineral trioxide aggregate; the high ph of the product stimulates odontoblasts (which line the pulp). These stimulated odontoblasts lay down reparative dentine.
This layer allows the remaining pulp to maintain its vitality and allows for continuing maturation of the tooth and deposition of more dentine with strengthening of the tooth. This is important when dealing with young immature teeth.
According to a retrospective study, vital pulpotomy has a high success rate (88%)4. In primates, there was a 21% failure rate for crown reduction of canine teeth (disarming procedure)5.
A 6 month old Labrador presented via referral to North Coast Veterinary Specialists and Referral Centre with moderately linguoverted mandibular canine teeth. There was associated trauma to the hard palate on both sides with approximately 4 mm indentations into the hard palate. Both mandibular canines were positioned in the diastema between the maxillary third incisor and the maxillary canine tooth, however the distal surfaces of both mandibular canines were starting to abrade against the mesial surface of both maxillary canines due to the moderate Class II malocclusion. (Figure 1)
Figure 1
After discussing treatment options, as mentioned previously in this article, it was decided to perform a crown extension procedure, by lengthening the mandibular canine teeth with composite resin as well as having a labial incline to the extensions.
Prior to performing the procedure, an alginate impression was taken of a normal occlusion dog skull of similar size to the Labrador. The alginate impression was poured up with a type 4 die stone, and after trimming the stone model, a vacuum forming machine and plastic blank former were used to create crown formers over the mandibular canine teeth. (video 1).
Click here to watch the Video: A vacuum forming machine and plastic blank former used to create crown formers over the mandibular canine teeth
Alternatively, the crown extensions can be made directly onto the enamel surface in the mouth. However, I like the above method because it creates the perfect canine tooth shape with the labial inclination built into it, which is required to push the crown of the tooth laterally.
Once the dog was anaesthetised, intraoral radiographs of all 4 canine teeth were taken, paying particular attention to the apical areas of these teeth (CR7 iM3). The mandibular canine teeth still had open apices (figure 2).
Figure 2
This indicates that there is still tooth development occurring and the crown should lengthen and erupt further into the mouth as the root continues to develop. This is important, because when the crown extensions are removed, the mandibular canines need to be retained in the diastema space, to prevent them from relapsing lingually.
The canine teeth were then prepared for bonding a composite resin (CR) to the enamel surface. The teeth were cleaned with pumice and then each tooth is etched for 30 seconds (Figure 3: iM3 Etchgel) and then the etch is rinsed off with copious water, air dried and a bonding agent applied (Figure 4: iM3 Bond).
The bonding agent is then thinned out with air from the 3-way syringe and finally light cured for about 10 seconds (Figure 5: LED curing light, iM3). A coloured CR material (Figure 6: iM3 colour flow) is then applied to the treated teeth surfaces of 304/404.
This material is light cured for 20 seconds in 1mm incremental build ups (figure 7). The colour allows one to differentiate the composite resin from the natural tooth, when it’s time to remove the crown extensions.
Figure 7
The bespoked canine crown formers (figure 8) from the model had composite resin (Figure 9: iM3 Create) packed into them and then the crown formers were placed over the dog’s canine teeth.
Prior to light curing the CR, a labial incline was made with the crown former, by pushing the crown former slightly laterally. Excess composite resin was removed from the base of the crown former prior to light curing the CR through the crown former. The CR was thoroughly light cured prior to removing the crown former.
After removal of the crown former, further light curing of the composite resin is carried out at different positions on the tooth, to make certain the material is fully cured. The CR is then polished, and any excess set CR removed from near the gingival margin with a combination of polishing burs and the ultrasonic scaler (iM3 42-12 ultrasonic scaler).
The endotracheal tube was then removed, to check that the crown extensions were in the correct position to tip the natural tooth labially (figure 10). Any adjustments were carried out at this point, prior to the dog being allowed to wake up.
Figure 10
The crown extensions will need to stay in place for at least 2 months, or until the apices of the mandibular canine teeth close (approx. 8-9 months of age).
This case is still mid- way through the treatment.
The owner needs to supervise the dog, especially with diet. No bones, no hard biscuits, rocks or sticks. No chew toys.
The success rate with this procedure is around 70%. However, case selection is important. The age of the dog is important. The apices of the mandibular canine teeth need to still be open, for this procedure to work. There are very few studies assessing the success rate of this procedure. One study7 showed a success rate of 77%.
In my opinion, the smaller the size of the dog, the higher the success rate, because fracture or loss of the crown extension is less likely to occur in small breed dogs.
Dr. Anthony Caiafa BVSc, BDSc, MANZCVS is the Adjunct Associate Professor, School of Veterinary and Biomedical Sciences at James Cook University, Townsville, Queensland, Australia. He is also a Consultant at North Coast Veterinary Specialists and Referral Centre, Tanawha, Sunshine Coast. You can contact Dr Caiafa at toothdoctor@optusnet.com.au
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Author: Denzie White, Senior Nurse, ARH Woollongong & Technical Support Officer, Vepalabs Ella, the 5-year-old yellow Labrador, presented to her regular general practice clinic unwell. Her recent history included eating a loaf of bread (bag and all), so there was...
