I recently saw a cat named Squishy that was presented to me after its primary care veterinarian performed crown amputations on its maxillary canine teeth due to tooth resorption. Squishy’s owner is a non-practicing veterinarian, and when the cat’s crown amputation sites dehisced, resulting in decreased appetite, she reached out to me. Squishy’s owner sent me a photo of the surgical sites and dental radiographs from the recent procedure (Figures 1 and 2). This case is a good refresher study regarding the decision-making process of treating teeth affected by tooth resorption. Figure 1. Dehiscence of crown amputation site of tooth 204. Photo courtesy Dr. John R. Lewis Radiographs are key Extractions should not be attempted without preoperative dental radiographs. This is particularly important in cats since the extent of root replacement resorption cannot be determined without radiographs. Proper treatment (extraction vs. crown amputation) cannot be determined without knowing the extent of root replacement resorption. Tooth resorption in cats is most commonly due to external tooth resorption, which starts on the root surface and results in focal tooth resorption near where the crown meets the root. The radiographic appearance of focal resorption near the cementoenamel junction is referred to as Type 1 resorption. Figure 2. Preoperative and postoperative radiographs of tooth 204 after a coronectomy. The tooth structure is more recognizable, and an endodontic system is easily visible so that the author would recommend extraction rather than crown amputation in this case. Photo courtesy Dr. John R. Lewis Teeth affected by Type 1 resorption require extraction, and these extractions can be challenging since, in some areas, the tooth may be “spot welded” to the surrounding alveolar bone. The radiographic appearance referred to as Type 2 resorption is seen on radiographs as root replacement resorption, in which the radiographic density of the root is much less than that of an unaffected root, approximating the density of bone rather than the normally dense root structure. In some cases, Type 2 root resorption can be so severe that the roots of a tooth are no longer present, making extraction impossible. In these cases, a technique referred to as “crown amputation” or “coronectomy” can be performed. Coronectomy is easier than an extraction, so the technique is prone to abuse. Below are the radiographic signs I use to decide on extraction vs. crown amputation. I like to use both the dental radiographs and the clinical appearance of the tooth’s hard tissue (as visualized with magnifying loupes) to determine if coronectomy is an acceptable option. Radiographic features that tell us if coronectomy is appropriate include: Radiographic density of the root structure approximating that of bone rather than normal root No radiographic evidence of an endodontic canal within the resorbing root No radiographic evidence of a pathologic periapical lucency No radiographic evidence of the normal periodontal ligament separating tooth from bone No evidence of periodontal disease Clinically, unless the root looks completely resorbed on dental radiographs, I err on the side of raising a flap to visualize the root structure after removing the buccal shelf of bone to expose the root. The normal root structure looks glassy tan/yellow, rather than a pinkish white color seen in roots that have been resorbed and replaced by bone. Additionally, a fully resorbed root will show no signs of pinpoint bleeding from a central endodontic system when assessed on the cross-section of where the root meets the crown. If all these criteria are met (both clinically and radiographically), coronectomy may be performed. Radiographic evidence of Type 3 root resorption will show the presence of Types 1 and 2 resorption in the same tooth. For example, Type 3 resorption may be seen in a mandibular third premolar tooth where the mesial root shows Type 1 resorption and the distal root shows complete root replacement resorption (Type 2). Each root is treated differently depending on its radiographic appearance. In the example above, the mesial root would need to be entirely extracted, whereas the distal root may be a candidate for coronectomy. Off with the crown: Coronectomy technique Coronectomy is often performed with a crosscut fissure bur, such as 699, 700, or 701, on a high-speed water-cooled handpiece. These burs are designed to cut on their sides rather than the end of the bur. Prior to using the bur, a small periosteal elevator is used to create an envelope flap, where the periosteal elevator releases the gingival attachments from the bone in a circumference around the tooth crown. The side of the tip of the bur is then used to remove the tooth crown by passing the bur along the neck of the tooth (where the crown meets the roots), which will result in separating the crown from any underlying root structure. A round diamond bur (such as a #10 diamond bur) may be used to remove any small spicules of the crown at the mesial or distal aspects of the tooth border. After the crown is removed, the cross-sections of the roots are evaluated from an “aerial” view. If discernable root structure or endodontic system is seen, a flap is raised (one or two releasing incisions) to allow for more exposure and further assessment. Further root structure is extracted until no evidence of clinical or radiographic root remains. Postoperative radiographs are necessary to ensure smoothness at the alveolar margin. Case in point: For extraction or coronectomy? Now, let’s use the above criteria to assess whether Squishy’s maxillary canine teeth would be best treated by extraction or coronectomy. This is no easy decision the primary care veterinarian had to make. There is radiographic evidence of the loss of the normal periodontal ligament space (ankylosis). When ankylosis is present, and extraction of the maxillary canine is attempted, the tooth root can bring with it alveolar bone, which can result in the creation of an iatrogenic oronasal fistula. However, since the endodontic canal is so visible in the tooth’s center and the root is still much denser than the surrounding bone, I would typically recommend extraction in a tooth similar to Squishy’s. Knowing how challenging these ankylosed extractions can be, it would not be wrong for a primary care veterinarian to refer a patient with this radiographic appearance to your local veterinary dentist to have the specialist treat these challenging resorbed teeth. Since Squishy’s dehisced sites showed improving granulation at recheck, and since its appetite has improved, we did not immediately place Squishy under anesthesia for a repeat procedure. However, we will be prepared to possibly extract any remaining root structure in the coming months, when repeat radiographs are done, to assess whether the resorptive process is progressing with no evidence of endodontic disease. Recommended reading DuPont GA. Crown amputation with intentional root retention for dental resorptive lesions in cats. J Vet Dent. 2002; 19 (2): 107-110. Lewis JR, Miller BR (Bassert JM, ed.). Veterinary Dentistry. In: Bassert JM, Thomas JA, eds. Clinical Textbook for Veterinary Technicians, 8th ed. St. Louis: Elsevier Saunders, 2014; 1299-1352. Lommer MJ. Special considerations in feline exodontics. In: Verstraete FJM, Lommer MJ, eds. Oral and Maxillofacial Surgery in Dogs and Cats. London: Saunders Elsevier, 2012; 141-152. John R. Lewis, VMD, DAVDC, FF-OMFS, practices and teaches at Veterinary Dentistry Specialists and Silo Academy Education Center in Chadds Ford, Pa.
