John R. Lewis, VMD, DAVDC, discusses the phenomenon of tooth resorption in cats and dogs. Investigative studies indicate 20 percent to 70 percent of cats experience resorption. TR can be classified as internal resorption or external resorption.
Source: Veterinary Practice News, August 11, 2022. Link. Know there is a staging system developed to describe the severity of the resorption, but clinically this staging system need not be memorized. (It can be obtained at https://avdc.org/avdc-nomenclature.)
The important thing to remember is careful assessment of how close to the gingival margin the resorption is.” John R. Lewis, VMC, DAVDC
Also see: Name it to tame it, AHD, June 5, 2018. Link.