What Is a Cavity and How Do You Know If You Have One?

What is a cavity and how does one form?

Your mouth is home to bacteria that feed on sugars and carbohydrates from food and drinks. As they break down those sugars, they produce acids that attack tooth enamel in a process called demineralization. Saliva naturally neutralizes some of this acid and helps remineralize (re-harden) enamel between meals. When acid attacks happen too frequently — from frequent snacking, sugary drinks, or poor brushing — the remineralization process cannot keep up, and a cavity begins to form.

Cavities follow a predictable progression: 1. White spot lesion — early demineralization, visible as a chalky white patch; reversible with fluoride 2. Enamel cavity — the acid has broken through the enamel surface; usually no pain 3. Dentin cavity — decay has reached the softer inner layer; sensitivity may begin 4. Pulp involvement — bacteria reach the nerve; often painful and may require a root canal 5. Abscess — infection spreads to the root or surrounding bone

The CDC's 2024 Oral Health Surveillance Report documents dental caries as one of the most prevalent chronic conditions among adults 1Ref 1Centers for Disease Control and Prevention (2024).2024 Oral Health Surveillance Report: Dental Caries, Tooth Retention, and Edentulism.Dental caries is one of the most prevalent chronic conditions in adults.

What are the signs and symptoms of a cavity?

Many cavities produce no symptoms until they are well advanced. When symptoms do appear:

• Tooth sensitivity — a brief zing when eating something cold, sweet, or acidic
• Toothache — spontaneous aching or pain when biting, suggesting deeper involvement
• Visible discoloration — brown, gray, or black spots on the tooth surface (though not all discoloration is decay; staining can look similar)
• A visible pit or hole — you or your dentist can see or feel a depression
• Food getting stuck — floss frays or food catches in the same spot repeatedly
• Sensitivity to heat — a later sign that suggests deeper decay near the pulp

It bears repeating: the absence of symptoms does not mean the absence of decay. Early-stage cavities between teeth or under the gumline are essentially invisible without X-rays.

How does a dentist diagnose a cavity?

Dentists use several complementary methods:

• Visual exam and probing — checking for soft spots, color changes, or obvious holes
• Bitewing X-rays — the standard method for finding cavities between teeth where they cannot be seen directly
• Transillumination — shining a fiber-optic light through the tooth to detect density changes

Routine checkups allow cavities to be caught at the white spot or early enamel stage, when less invasive treatment — or even remineralization — is possible. This is why the American Dental Association emphasizes regular dental visits 2Ref 2American Dental Association (2013).American Dental Association Statement on Regular Dental Visits.Regular dental visits allow early cavity detection when treatment is less invasive.

How are cavities treated?

Treatment depends on how advanced the decay is:

• Remineralization (very early stage). Prescription fluoride varnish, silver diamine fluoride, or high-fluoride toothpaste can arrest a white spot lesion before it requires drilling. ADA evidence-based guidelines support non-restorative approaches for early lesions 3Ref 3Slayton RL, Urquhart O, Araujo MWB, Fontana M, Guzmán-Armstrong S, Nascimento MM, Nový BB, Tinanoff N, Weyant RJ, Wolff MS, Young DA, Zero DT, Tampi MP, Pilcher L, Banfield L, Carrasco-Labra A (2018).Evidence-based clinical practice guideline on nonrestorative treatments for carious lesions: A report from the American Dental Association.Non-restorative treatments (fluoride, silver diamine fluoride) are supported for early-stage carious lesions.
• Filling (most cavities). The decayed portion is removed and the space is filled with composite resin, amalgam, or another material. ADA guidelines provide evidence-based recommendations for restorative treatments depending on cavity depth and location 4Ref 4Dhar V, Pilcher L, Fontana M, González-Cabezas C, Keels MA, Mascarenhas AK, Nascimento M, Platt JA, Sabino GJ, Slayton R, Tinanoff N, Young DA, Zero DT, Pahlke S, Urquhart O, O'Brien KK, Carrasco-Labra A (2023).Evidence-based clinical practice guideline on restorative treatments for caries lesions: A report from the American Dental Association.ADA evidence-based guidelines direct restorative treatment choices based on cavity depth and location.
• Inlay or crown. Larger cavities that leave insufficient tooth structure for a filling may need a partial or full crown.
• Root canal treatment. If decay has reached the pulp, the nerve and infected tissue must be removed before the tooth can be restored.
• Extraction. When a tooth is too damaged to save.

Fluoride toothpaste, used consistently, helps prevent cavities from forming and supports remineralization of early lesions 5Ref 5Marinho VC, Higgins JP, Sheiham A, Logan S (2003).Fluoride toothpastes for preventing dental caries in children and adolescents.Fluoride toothpaste is effective for cavity prevention and supports remineralization.

How can I prevent cavities?

• Brush twice daily with a fluoride toothpaste.
• Floss once daily to clean between teeth where the brush cannot reach.
• Limit frequent snacking on sugary or starchy foods — the frequency of sugar exposure matters as much as the amount.
• Drink water (especially fluoridated water) rather than sugary or acidic drinks.
• See a dentist for regular checkups and professional cleanings.
• Ask your dentist about dental sealants if you have deep grooves in your back teeth.