Root caries are cavities that form on the root surfaces of teeth, below the gum line or on areas where the gums have pulled back to expose the root. Unlike the cavities most people picture on the chewing surfaces of teeth, root caries attack a part of the tooth that lacks the hard enamel shell, making them faster to progress and harder to treat. They are especially common in older adults: national health data show that about 15.5% of older Americans have untreated root surface decay.
Why Roots Are Vulnerable
The crown of a tooth, the part you can see when you smile, is covered in enamel, the hardest substance in the human body. Tooth roots, by contrast, are covered in a much softer material called cementum. Under normal conditions this doesn’t matter because healthy gum tissue covers and protects the roots entirely. The problem starts when that protective gum tissue recedes.
Once root surfaces are exposed, they’re in direct contact with bacteria, acids from food, and everything else in the mouth. Cementum dissolves at a lower acid level than enamel does, so decay can begin under conditions that wouldn’t damage a tooth’s crown. The decay also spreads more quickly through the softer root structure, which is why root caries can go from a small spot to a serious problem in relatively little time.
What Causes Gum Recession
Gum recession is the gateway to root caries, and it has several causes. Periodontal (gum) disease is the most significant. When bacterial buildup along the gum line triggers a chronic inflammatory response, the body’s own immune reaction gradually destroys the bone and tissue supporting the teeth. As that support erodes, the gums pull away and root surfaces become exposed.
Mechanical trauma is another common cause. Vigorous toothbrushing, especially with a hard-bristled brush, can physically wear gum tissue away over time. Epidemiologic studies have found that gum recession correlates positively with toothbrushing frequency, a counterintuitive finding that underscores the importance of brushing technique over intensity. Tobacco use, misaligned teeth, and habits like chronically pressing foreign objects against the gums also contribute. Even certain dental procedures can trigger localized recession.
Dry Mouth: The Overlooked Risk Factor
Saliva is the mouth’s primary defense system. It rinses away food debris, neutralizes acids, and delivers minerals that help repair early tooth damage. When saliva production drops, every surface of the tooth becomes more vulnerable, but exposed roots suffer the most because they have less built-in protection to begin with.
Chronic dry mouth, known clinically as xerostomia, is extremely common in older adults, largely because of medications. The American Dental Association lists antihistamines, blood pressure medications, decongestants, pain medications, diuretics, muscle relaxants, GLP-1 receptor agonists (a class of diabetes and weight-loss drugs), and antidepressants as contributors to oral dryness. Many older adults take several of these simultaneously, compounding the effect. This overlap of gum recession, reduced saliva, and multiple medications is a major reason root caries cluster so heavily in people over 65.
What Root Caries Look and Feel Like
Root caries often appear as dark, soft spots along the gum line or just beneath it. They can be yellow, brown, or black. Unlike cavities on chewing surfaces, which tend to be pit-shaped, root caries frequently spread sideways along the root, creating a broad, shallow lesion that wraps around the tooth. In some cases, the decay can encircle the entire root, undermining the tooth’s structural integrity.
Symptoms vary. Some people notice sensitivity to hot, cold, or sweet foods in a specific area. Others feel a rough or sticky spot near the gum line when they run their tongue along their teeth. Root caries can also be completely painless until they’ve progressed significantly, which is one reason routine dental exams matter for catching them early.
Non-Invasive Treatment Options
Not every root cavity needs a drill. When root caries are caught early, before they’ve created a deep hole in the tooth, non-invasive approaches can stop the decay from progressing. The most effective of these is silver diamine fluoride (SDF), a liquid applied directly to the affected surface. In a randomized clinical trial of older adults, a single application of SDF arrested active root caries in 90% of cases, compared to 45% in the control group. Adding a follow-up application of potassium iodide pushed that success rate to 93%.
The tradeoff is cosmetic: SDF permanently stains decayed tooth structure black. For root surfaces near the gum line that aren’t highly visible, this is often acceptable. For more visible areas, other fluoride-based treatments or careful monitoring may be preferred. High-concentration fluoride toothpaste, typically prescribed by a dentist, is another tool for slowing or halting early root decay, particularly for people at ongoing risk.
Restorative Treatment for Advanced Decay
When root caries have progressed beyond what non-invasive methods can manage, the decayed tissue needs to be removed and the tooth restored with a filling. Root surface restorations present unique challenges compared to fillings on chewing surfaces. The location near or under the gum line makes moisture control difficult, and the softer root material bonds differently than enamel.
Glass ionomer cements are a popular choice for root surface fillings because they chemically bond to tooth structure and continuously release fluoride, which helps prevent new decay from forming around the edges of the filling. A recent systematic review confirmed that glass ionomer restorations inhibit secondary caries, a meaningful advantage in a high-risk area. Their main limitation is mechanical strength: they’re softer and less durable than composite resin fillings, which makes them a better fit for root surfaces (which bear less direct chewing force) than for the tops of back teeth. Modified versions that combine glass ionomer with resin aim to offer both the fluoride benefit and improved durability.
If the decay has destroyed too much of the root or reached the nerve inside the tooth, a crown, root canal, or extraction may be necessary. The goal of early detection is to avoid reaching that point.
Reducing Your Risk
Prevention centers on protecting root surfaces and maintaining a healthy oral environment. Brushing with a soft-bristled brush using gentle, circular motions reduces the mechanical damage that causes gum recession. Flossing or using interdental brushes keeps bacteria from accumulating between teeth and along the gum line where root caries typically start.
If you take medications that cause dry mouth, staying well hydrated, chewing sugar-free gum to stimulate saliva, and using saliva substitutes can partially compensate. Fluoride rinses or prescription-strength fluoride toothpaste add a layer of chemical protection to exposed root surfaces. People who already have gum recession or a history of root caries benefit from more frequent dental cleanings, typically every three to four months rather than the standard six, so early signs of new decay can be caught before they require invasive treatment.