I received a call from a referring veterinarian. He saw on his appointment book that a puppy was scheduled to have its four firmly rooted persistent deciduous canine teeth extracted. His 30-plus years of experience led him to conclude that firmly rooted deciduous canine teeth were among the most challenging extractions to perform. I agreed wholeheartedly.
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What causes persistent deciduous teeth? To answer, we need to know what causes deciduous teeth to be normally shed.
Resorption of permanent teeth is a pathological condition, but resorption of the deciduous tooth root is considered to be a physiologic process in which osteoclasts, osteoblasts and tooth-resorbing cells called odontoclasts work in concert to allow for resorption of the deciduous tooth root as the permanent tooth root moves into the area the deciduous root once occupied.
As a result, the deciduous crown is shed.
In cases where no permanent tooth is present, or if the permanent tooth is not in the correct location, the physiologic resorption of the deciduous tooth root does not occur at its regular time, and it may take years for the deciduous tooth root to resorb.
Note that I used the term “persistent” instead of “retained.”
For years, we referred to deciduous teeth that were not shed before eruption of their adult counterparts as “retained.” Actually, the appropriate term for a deciduous tooth not shed when its adult counterpart starts to erupt is a “persistent” deciduous tooth. “Retained” best describes things beneath the gingiva, for example, a retained tooth root.
Why are persistent deciduous teeth a problem? They can be a threat to both periodontal and orthodontic health. Crowding is the real concern for periodontal health; having both the deciduous tooth and permanent tooth competing for the same space often prevents both teeth from having a complete collar of gingiva around these teeth.
The crowding also makes for a great place for plaque and debris to accumulate. This results in the formation of periodontal pockets around both teeth at an early age.
Orthodontically, persistent deciduous teeth are a problem because they compete for space with erupting permanent counterparts, and this often results in permanent teeth being in the incorrect position.
If the permanent mandibular canine teeth erupt lingual (medial) to their normal position, this results in trauma to the hard palate every time the patient closes its mouth. We have seen cases where this trauma, over time, has resulted in formation of oronasal fistulae.
At a puppy’s four-month visit to a practice, it’s a good idea to show pet owners a picture of what the erupting permanent teeth look like so they can watch at home for signs of eruption of the permanent canine teeth. If persistent teeth are noted, they should be extracted (completely, including the unresorbed root) to provide every chance for the permanent tooth to move into its normal spot.
Here are a few tips for extracting deciduous canine teeth. After performing a regional nerve block, take a radiograph of the tooth to see if the root is showing signs of resorption.
Palpate the tooth to check mobility. If the tooth shows very little mobility and/or if the radiograph shows no signs of root resorption, create a mucoperiosteal flap with one or two releasing incisions. A periosteal elevator is used to raise the gingiva and mucosa with care to avoid perforation of the flap at the mucogingival junction.
After raising the flap, take a No. 2 round carbide bur and create a narrow window over the lateral surface of the deciduous tooth. Use a smaller bur, such as a 1/4 round carbide bur, to further expose root structure more apically.
The operator needs to be careful not to damage adjacent dental structures, such as the permanent canine or the first premolar teeth. Do not hesitate to remove bone directly over the lateral surface of the deciduous tooth to expose at least 60-80 percent of the tooth root’s length. These teeth are like eggshells, so the less force you use to elevate the tooth, the more likely it will be retrieved intact.
An 11 blade or periotome may be placed in the periodontal ligament space to break down the mesial and distal attachments to the tooth. I then use a No. 2 or No. 3 winged elevator on the palatal surface of the tooth to gently pry the tooth out of the window created laterally.
Recall that a larger elevator generates more force, and more force is not always better. Controlled force and patience will allow for delivery of the intact tooth.
If a root breaks off during elevation, remove more bone from the buccal surface and carefully expose the root tip with a 1/4 round bur, being careful not to damage the permanent teeth in this area. Use a smaller dental elevator or root tip elevator to pry the root through the buccal window. Root tip forceps are invaluable when grabbing onto the root tip.
Take a radiograph to confirm the entire tooth was extracted. The periosteum is released from the underside of the flap with a pair of Metzenbaum or Ragnell scissors, and the site is debrided and lavaged prior to closure. The site is closed with absorbable suture in a simple interrupted pattern.
Occasionally, deciduous teeth require extraction even when the permanent counterpart has not yet erupted, such as when there is a fractured deciduous tooth or a malocclusion.
With jaw length discrepancies where the deciduous teeth of the mandible are embedded into the soft tissue of the palate, an unfavorable dental interlock occurs that should be relieved by extraction of the deciduous teeth.
These extractions are even more challenging due to the potential for damage to the developing enamel of the unerupted permanent tooth. Whether the permanent counterpart is erupted or unerupted, avoid leveraging on the permanent tooth in an attempt to loosen the deciduous tooth, and pre-emptively warn pet owners that enamel hypoplasia of the forming adult tooth may occur if the deciduous teeth are extracted before eruption of the permanent counterpart.
Hopefully these tips will help to provide many peaceful, rather than problematic, persistent deciduous tooth extractions.
Dr. Lewis, FAVD, Dipl. AVDC, is a past president of the American Veterinary Dental Society and an assistant professor of dentistry and oral surgery at the University of Pennsylvania School of Veterinary Medicine.