Originally published in the March 2015 issue of Veterinary Practice News? Not a subscriber? Subscribe today!
If you extract enough firmly rooted mandibular canine teeth in your lifetime, basic anatomy suggests that you may find yourself to be the creator of an iatrogenic jaw fracture.
The root of the mandibular canine tooth of dogs and cats makes up a large portion of the rostral mandible and it is nearly twice as long as the crown of the tooth. Bone is very thin between the lingual surface of the root and the caudal symphysis.
Photos © 2014 John R. Lewis, NorthStar VETS.
Radiograph of an iatrogenic jaw fracture that occurred during attempted extraction of the left mandibular canine tooth in a cat. Iatrogenic jaw fractures that occur during canine tooth extraction tend to be parasymphyseal fractures rather than symphyseal separations.
Forces required to deliver this tooth root may also, in some cases, be sufficient to result in fracture of the bone. Here are some tips that I’ve learned on how to avoid iatrogenic fracture.
Take dental radiographs and adjust your therapeutic approach accordingly.
Dental radiographs are important from both diagnostic and therapeutic perspectives. For example, if I see radiographic evidence of loss of the dark thin line around a tooth root (the periodontal ligament space), I know that I need to elevate the tooth with less force when trying to deliver the root, because the lack of a periodontal ligament space suggests dentoalveolar ankylosis, or fusion of the tooth to the surrounding bone.
When dentoalveolar ankylosis is present, it is possible that either a portion of the root will break off, or the root will be attached to ankylosed bone when it comes out.
In some cases, dental radiographs will drastically shift your surgical approach, such as in cats with severe root replacement resorption. Sometimes radiographs will reveal that, despite a normal looking tooth crown, there is so much root replacement that there is literally no root to extract.
I have seen a case where a feline jaw was fractured in an attempt to extract a root that was no longer present radiographically, but since the practitioner who broke the jaw didn’t have dental radiography, he did not know that a crown amputation (coronectomy) would have been the desired approach.
Without dental radiography, proper treatment cannot be determined.
Proper equipment makes all the difference.
When a dental radiograph is suggestive of dentoalveolar ankylosis, I tend to lean towards a smaller dental elevator or luxator.
The smaller the elevator/luxator, the less force generated by the instrument when twisted.
I use almost exclusively winged elevators, but it is important to have a variety of different sizes and shapes of elevators to allow the elevator to pry the root from its alveolus without generating too much force.
How do you know how much force is too much? Trial and error. This is why attending multiple CE wet labs pays dividends.
Flaps Are Our friends!
If it is a firmly rooted tooth with no periodontal disease, I am raising a mucogingival flap from the start. This allows for use of a high-speed drill to create a window of bone to allow the tooth to be pried out of the alveolus with controlled lateral pressure.
It sounds counterintuitive, but it seems like the more bone you remove with your bur, the less likely you are to create an iatrogenic fracture (within reason, of course). This is because the further down the root surface your window extends, the less force you will need to generate with your dental elevators.
I often start with removal of a lateral window that extends approximately 50-60 percent of the length of the root, and if use of a dental elevator is not providing some loosening of the tooth, I will extend the window even further apically.
Removal of the lateral window of bone allows me to generate controlled forces in a lateral direction, rather than in an apical direction. Excessive forces in an apical direction tend to lead to trouble, such as an elevator that slips and causes damage to the adjacent hard or soft tissue structures.
Don't Be Afraid to Refer
Endodontics is a minimally invasive method for treating fractured teeth, and though the concept of performing root canal therapy on their pet seems novel to some owners, once you show them a clear dental model and how long the tooth roots are, they get it.
It is also totally acceptable to refer an extraction to a veterinary dentist if you don’t have experience with extraction of a particular tooth or if your practice does not have a high-speed dental drill and dental radiography.
Iatrogenic fractures are more likely to occur in cats than dogs due to the thin bone medial to the mandibular canine tooth root (Figure 1).
Iatrogenic fractures in dogs may also occur during extraction of a mandibular first molar tooth, especially in small breed dogs where the apices of the roots may extend to the most ventral aspect of the mandible.
In patients with severe periodontal disease, careful opening of the mouth during oral exam and intubation is warranted since a pathologic fracture may occur after placing minimal force on the diseased mandible.
How do we treat iatrogenic jaw fractures? On a case-by-case basis.
Sometimes, conservative treatment and soft tissue closure is all that is needed. Sometimes rigid fixation might be warranted. I’ll discuss symphyseal wiring for parasymphyseal fractures and symphyseal separations in next month’s column. Stay tuned!