A claim sometimes circulates that owning a cat can cause internal tooth resorption in its owner. It is understandable why the idea sounds plausible: cats commonly develop a dental disorder called feline tooth resorption, while internal root resorption is a serious condition that can affect human teeth. The two conditions share part of a name, but current research does not support the conclusion that living with or owning a cat causes internal root resorption in humans.

What is internal root resorption?

Internal root resorption is a pathological process in which cells break down dentin from within the pulp chamber. It is not ordinary tooth decay, and it differs from the normal shedding of baby teeth. Often, it produces few early symptoms and is discovered on dental x-rays as an enlarged, rounded area within the root canal. In more advanced cases, a tooth may become discolored, painful, weakened, or infected.¹

The best available endodontic literature points instead to local dental factors. Reviews describe internal root resorption as progressive destruction of intraradicular dentin by resorptive cells.^1,2 Research consistently identifies previous dental trauma and inflammation or infection of the tooth pulp as the main contributors.^2,3 A childhood fall, sports injury, untreated deep decay, crack, or history of dental procedures may damage the protective layer lining the inside of the tooth. If inflammation persists and living tissue remains elsewhere in the pulp, cells capable of resorbing dentin can become active.

Other possible contributors discussed in the literature include orthodontic movement, bleaching-related injury, and certain restorative or pulp treatments.^1,3 However, the exact biology is not fully understood in every case. Some patients may not remember a relevant injury, particularly when it occurred many years earlier. That uncertainty is important, but it does not constitute evidence that a household pet is the cause.

Why, then, might the cat claim arise?

One source of confusion is feline tooth resorption. This common, painful disease in cats was formerly called feline odontoclastic resorptive lesions. In affected cats, tooth structure is progressively destroyed, often below the gumline. Veterinary research has not established a single definitive cause. Most importantly, it is a disease affecting the cat’s own teeth; there is no evidence that it passes from cat to person.

Another possible source of concern is Toxoplasma gondii, a parasite for which cats can be part of the life cycle. Cats may shed the parasite in feces for a limited period after infection, and people can become infected if they accidentally ingest contaminated material. However, the Centers for Disease Control and Prevention identifies exposure pathways such as contaminated food, water, soil, or cat litter—not internal root resorption.⁴ The leading dental reviews and professional guidance on human root resorption likewise do not identify cat ownership or toxoplasmosis as established causes.^1,3 Therefore, it would be inaccurate to claim that owning a cat causes this dental condition.

Basic hygiene around pets

This does not mean people should disregard oral health or basic hygiene around pets. Cat owners should wash their hands after handling litter, avoid feeding cats raw meat, and take special precautions during pregnancy or when immunocompromised, following advice from a health professional. These are sensible infection-prevention measures, but they should not be presented as treatment or prevention for internal root resorption.

The importance of dental history

For someone diagnosed with internal root resorption, the more useful questions concern dental history: Has the tooth been injured? Has there been deep decay, prior treatment, chronic inflammation, or an unnoticed crack? Dental radiographs—and, in selected cases, cone-beam computed tomography—help an endodontist distinguish internal from external resorption and determine whether the defect has perforated the root.^1,3 When identified early, root-canal treatment can remove inflamed or infected tissue and stop the active process; treatment becomes more complicated when damage is extensive.

In short, cat ownership and internal root resorption may appear linked because both cats and humans can experience forms of tooth resorption. That is an association of terminology, not evidence of transmission or causation. People who have cats can continue enjoying that relationship while focusing on well-supported dental risks: trauma, pulp inflammation, infection, and timely professional evaluation.

Editor’s note: This article first appeared in Clinical Insights newsletter, a publication of the Endeavor Business Media Dental Group. Read more articles and subscribe.

References

1. Patel S, Ricucci D, Durak C, Tay F. Internal root resorption: a review. J Endod. 2010;36(7):1107-1121. doi:10.1016/j.joen.2010.03.014
2. Nilsson E, Bonte E, Bayet F, Lasfargues JJ. Management of internal root resorption on permanent teeth. Int J Dent. 2013;2013:929486. doi:10.1155/2013/929486
3. Patel S, Krasti G, Weiger R, et al. ESE position statement on root resorption. Int Endod J. 2023;56(7):792-801. doi:10.1111/iej.13916
4. Toxoplasmosis: causes and how it spreads. Centers for Disease Control and Prevention. February 14, 2025. https://www.cdc.gov/toxoplasmosis/causes/index.html