Figure 1A (left) and Figure 1B (right): Small-breed dogs are at a higher risk of iatrogenic mandibular fracture during extraction of the mandibular first molar due to the height of the bone relative to the height of the tooth. A) Small-breed dog. B) Large-breed dog. Note the apex of the mesial root of the small-breed dog extends into the ventral-most aspect of the mandible.Photos courtesy John Lewis The clinical specialist plays many roles, including support of the general practitioner (GP). The former can be a valuable resource for the latter, offering advice when preoperative, intraoperative, and postoperative questions arise. He or she may provide guidance to a GP who is trying to decide which conditions are best referred. Further, the specialist is also asked to help when something goes wrong with a GP procedure. One example I’ve been increasingly called upon to intervene in recent months is iatrogenic fracture of the mandible (IFM). I addressed this topic in my March 2015 Veterinary Practice News column. However, a deeper discussion of the “whys” seems worthwhile, given what seems to be an uptick in occurrence of this complication of extractions.1 IFM occurs either in the hospital or shortly after extraction. If the bone density is already compromised due to periodontal disease or neoplasia, iatrogenic fracture can occur from something as basic as prying open a patient’s mouth during assessment in the exam room or during opening of the mouth during endotracheal intubation. More commonly, though, IFM occurs in veterinary patients during extraction procedures. There are certain teeth comprising a large portion of the alveolar bone height of the mandible, and an inherent risk is created when extracting these teeth. In humans, IFM is extremely rare; it is documented with a reported incidence of 0.0034 to 0.0075 percent. When it does occur in people, IFM most commonly happens at the site of an impacted mandibular third molar (wisdom tooth). Human adult male patients in their fifth decade appear to be at highest risk. Seventy-five percent of IFM cases occur postoperatively, rather than intraoperatively, usually within four weeks of extraction.2 In contrast to the human literature, nearly every veterinary case of IFM I’ve heard of has occurred intraoperatively. However, I recall a case that occurred one week postoperatively through the alveolus of an extraction site after a dog got into a scuffle with another dog. Who is at risk? Extraction of the mandibular canine tooth in both the dog and cat, and the mandibular first molar tooth in the small-breed dog are the ones with which we need to be most careful. One study that evaluated radiographic measurements of the first molar height and mandibular height found there was a statistically significant association between the measurement ratio of mandible: first molar tooth height and body weight (p < 0.0001) in all body weight groups. Small dogs had proportionally larger mandibular first molar teeth relative to mandibular height compared with larger dogs.3 As a result, small-breed dogs are often the ones that present with IFM in the first molar region (Figure 1). Figure 2: Iatrogenic rostral mandibular fracture in a cat between the symphysis and the alveolus of the left mandibular canine tooth. IFM in the mandibular canine region can occur in both dogs and cats, but it seems to be more common in the latter. Inherent risk of jaw fracture occurs due to the fact the canines comprise the majority of the rostral mandible. A distinction should be made between three different processes: IFM of the rostral mandible, symphyseal laxity, and bone loss of the rostral mandible due to severe periodontal disease. Symphyseal laxity may be present prior to an extraction procedure, and in the absence of recent trauma, is often an incidental finding that does not require treatment. Chronic bone loss of the rostral mandible due to severe periodontal disease can be identified on a preoperative radiograph as sometimes evidenced by complete loss of bone between the mandibular canine teeth. Where does it happen? IFM of the rostral mandible often occurs along the lingual aspect of the canine tooth when there is very little bone between the alveolus and the symphysis. Another condition that can increase risk of IFM in the rostral mandible is ankylosis of the canine tooth to the surrounding bone, as evidenced by loss of visible periodontal ligament space on dental radiographs. These teeth are basically spot-welded to the bone in multiple areas, making extraction a high-risk procedure. In cats, resorption and ankylosis can be prevalent with the mandibular canine tooth, so it is essential to take dental radiographs prior to developing a strategy for dealing with diseased mandibular canine teeth. In some cases, roots of the mandibular canine teeth may be so far along the resorption process, the root structure may have already been converted to a bone-cementum replacement material that does not require complete root removal. I’ve seen cases where IFM occurred during attempts to extract a root that was no longer present (i.e. fully resorbed by the body), but this was not known by the operator due to lack of dental radiography in the practice. The most common portion of the procedure that may induce an IFM is elevation with dental elevators. Force may be necessary to deliver a tooth from its alveolus, but it should always be controlled force, while simultaneously receiving feedback of the pressures being placed on the mandible that is cradled in the nondominant hand. This is the art of veterinary dentistry that sometimes only comes with experience—generating enough force to deliver the tooth without breaking the jaw in the process. How can those who perform dental procedures decrease the incidence of IFM? Education is a big part of the solution. One reason IFMs are on the rise is due to the fact that we, as a profession, no longer ignore firmly rooted teeth (which are difficult to remove) that require treatment. Many GP veterinarians are thrust into the role of oral surgeon within the walls of their practice, even though they have not received the necessary education. Hands-on training allows for complete understanding of the risks, the tools available to decrease the risk, and the realization that after radiographic assessment of risk, referral of certain cases is a win-win-win situation for the patient, client, and doctor. John Lewis, VMD, FAVD, DAVDC, practices dentistry and oral surgery at Veterinary Dentistry Specialists and is the founder of Silo Academy Education Center, both located in Chadds Ford, Pa. References 1 bit.ly/2ZjRFN4 2 Joshi A, Goel M, Thorat A. Identifying the risk factors causing iatrogenic mandibular fractures associated with exodontia: a systemic meta-analysis of 200 cases from 1953 to 2015. Oral Maxillofac Surg. 2016;20(4):391-396. 3 Gioso MA, Shofer F, Barros PS, Harvey CE. Mandible and mandibular first molar tooth measurements in dogs: relationship of radiographic height to body weight. J Vet Dent. 2001;18(2):65-68.
