Referral & Clinical

Lingually Displaced Mandibular Canines

Often spotted at either the first puppy check or at six months of age. Either the deciduous or permanent lower canines occlude into the hard palate causing severe discomfort and, possibly, oral nasal fistulae. See our article from Vet Times 18 Dec 2006 or our new FAQ sheet for further information. The fact sheet answers many questions you may have about the cause of this problem and the various treatments available.

Puppies

Owners with young puppies identified with this problem at first presentation should be counselled to have the deciduous lower canines removed as soon as possible.

There are three reasopns for this. Firstly, and most importantly, these teeth are sharp and hitting the soft tissues of the palate. These pups cannot close their mouth without causing pain and often tend to hold the mouth slightly open to avoid contact. Secondly , the growth of the mandible is rostral from the junction of the vertical and horizontal ramus. If the lower canines are embedded in pits in the hard palate the normal rostral growth of the mandible(s) is translated into dorsal bowing. Thirdly, the permanent lower canine is located lingual to the deciduous canine. This means that if the deciduos lower canines are in a poor position it is a certainly the permanent teeth will be worse. For these three reasons it is advisable to surgically remove the lower canine teeth as soon as posible to allow maximum time between the surgery and the time the permanent teeth erupt at between 16 and 24 weeks of age

it is our opinion that it is necessary to remove these teeth surgically via wide based flaps. The deciduous tooth root is three to four times longer than the visible crown and curved. The root apex is often below the third premolar. The roots are also very fragile and will break easily if unduly stressed during removal. Finally, the permament successor tooth is located lingual to the deciduous tooth and wholly within the jaw at this stage. Any use of luxators or elevators on the lingual half of the deciduos tooth will cause permanent damage to the permanent tooth.

See our Powerpoint file for illustration of removal of deciduous lower canines.

Surgery to remove the deciduous canines may not prevent to need for surgery on the permanent canines - but without it few cases will resolve if left to nature. Occasionally we advocate the use of a soft rubber ball to assist tipping of the erupting permanent lower canines buccally. This must be done under veterinary supervision.

Adult Dogs

If the permanent teeth are lingually displaced the pup is usually older than 24 weeks. The trauma caused by the teeth on the sotf tiissues can be considerable with pain as a consequence.

These permanent teeth can be theoretically be treated by three options. Not all options are avilable to all casese. These are surgical removal of the lower canines teeth (and often incisors too), crown amputation and partial pulpectomy or by orthodontics via an inclined bite plane bonded to the upper canines and incisors. The latter option may not be available to all dogs if the diastema between the upper incisor and canine is too small for the lower canines to move into or if the lower canines are located behind (palatal) to the upper canines.

1. Crown Amputation and Partial Coronal Pulpectomy involves reducing the height of the lower canines to that of the adjacent incisors.

Left lower canine before surgery LL canine immediately after surgery

Clearly this surgery exposes the pulp and requires a partial coronal pulpectomy with a direct pulp dressing. This is a sterile procedure and carries a failure rate (the pulp dies) of less than 1% - in our hands - since Mineral Trioxide Aggregate has been used as the direct pulp capping agent from 2005.

Radiograph LL canine before (top) and LL canine after. Note immature morphology of tooth -thin walls and open root apices

In order to monitor this we require to radiograph these teeth at four to six months postop. This is mandatory check and we will not perform this surgery unless the owner agrees to this.

LL canine 18 weeks post op. Access filling intact

Left radiograph shows LL canine immediately after crown amputation and partial pulpectomy. Right radiograph is same tooth 18 weeks postop. Note thicker dentine walls, internal dentine bridge between pulp and direct pulp cap and the closed and matured root apex. These criteria indicate a successful procedure.

The advantage of this procedure is that the whole of the root and the majority of the crown remain. The strength and inegrity of the lowerr jaw is not weakened by the procedure and long term results are much better than previously due to the use of Mineral Trioxide Aggregate as a direct pulp dressing.

2. Surgical extraction is attractive to many clients as the problem is immediately dealt with without the uncertainties and post-op. checks that are part of any crown amputation procedure. Many clients are concerned (rightly) about the loss of the tooth and the weakness it may cause to the lower jaw(s). As these are elective procedures (i.e.clean) we can use a bone graft to fill the void created by the loss of the large canine tooth. The graft will promote new bone growth within a few weeks.

Lingually displace lower left canine and radiograph before surgery

Image left lower canine area folliwng surgival removal and radiographs showing deficit in mandible once toth no longer present.

Radiograph of socket once oesteoallograft placed.

3. Orthodontic Tipping

Orthodontic tipping is less invasive than surgery but does require careful case selection and management. Normally we place a composite resin bite plane (see below) on the upper teeth. The lower canine makes contact with the incline when the mouth closes and the force tips the tooth buccally. This takes around four weeks.

The lower canine may occasionally migrate back into a lingually displacd position. This can occur if the tooth height is too short (stunted). If the lower canine is not self-retained by the upper jaw when the mouth is shut further surgery may be required.

Orthodontic treatment will conceal a defect and will not be performed unless the patient is neutered. In addition we are required to inform the Kennel Club of a change in conformation.

The images below show a lingually displaced left lower canine before treatment and after application of a bite plane. The bite plane remains in the mouth as long as it takes for the power of the bite to tip the lower canine into the normal position by pushing it up the incline - about 4-6 weeks on average.