What Is a Cavity Between Teeth?
A cavity between teeth is tooth decay that develops on the side surface of a tooth where it contacts the neighboring tooth. Dentists call this an interproximal cavity. These cavities account for a large percentage of all cavities found in adults because the space between teeth is one of the hardest areas to keep clean.
Unlike cavities on the chewing surface of a tooth, which you or your dentist can sometimes see directly, interproximal cavities are hidden. They develop in a narrow gap that cannot be examined visually or reached by a toothbrush. This is why routine dental X-rays (bitewing radiographs) are so important for early detection.
What Causes Cavities Between Teeth?
Cavities between teeth form for the same reason as any cavity: bacteria in plaque produce acid that dissolves tooth enamel over time. The difference is location. The contact area between teeth traps food particles and plaque that a toothbrush cannot reach.
Plaque and Food Trapping
When food gets stuck between teeth, bacteria feed on it and produce acid. If plaque is not removed daily by flossing, the acid attack continues and eventually breaks through the enamel. Sticky and sugary foods are particularly harmful because they cling to tooth surfaces and fuel bacterial acid production for longer periods.
Risk Factors for Interproximal Cavities
- Not flossing daily or not flossing effectively
- Tight tooth contacts that make flossing difficult
- Dry mouth (reduced saliva), which decreases the mouth's natural ability to neutralize acid and wash away food
- Frequent snacking on sugary or starchy foods
- Orthodontic appliances or dental work that creates hard-to-clean areas
- Reduced enamel thickness from acid erosion or genetic factors
Symptoms of a Cavity Between Teeth
Early interproximal cavities often have no symptoms at all. This is one reason they are so problematic. By the time you feel something, the decay has usually progressed beyond the outer enamel layer.
Early Warning Signs
- Floss catches or shreds in a spot where it previously glided smoothly
- A faint white or brown spot visible on the side of a tooth (if you can see it at all)
- Mild sensitivity to sweet foods or drinks in a specific area
Signs of Advanced Decay
- Sensitivity to hot, cold, or sweet that lingers after the stimulus is removed
- A visible dark spot or hole between two teeth
- Food constantly getting stuck in one spot
- A dull ache or throbbing pain, which may indicate the decay has reached the nerve
- Bad taste in the mouth from a cavity that has become large enough to trap decaying food
How Dentists Detect Cavities Between Teeth
Bitewing X-rays are the standard diagnostic tool for finding interproximal cavities. These X-rays show the areas between teeth that cannot be seen during a visual exam. Most dentists recommend bitewing X-rays every 6 to 18 months, depending on your cavity risk.
On the X-ray, healthy enamel appears as a bright white layer. A cavity shows up as a dark shadow within that white layer. Your dentist can estimate the depth of the cavity based on how far the dark area extends toward the nerve.
Some dental offices also use laser cavity detection devices or transillumination (shining a bright light through the tooth) as supplemental tools. These can help detect early decay that may not yet be visible on X-rays.
Treatment Options for a Cavity Between Teeth
Treatment depends on how deep the decay has progressed. Catching a cavity between teeth early means simpler, less expensive treatment.
Very Early Decay: Fluoride and Monitoring
If the cavity is confined to the outer enamel and has not broken through to the softer dentin layer underneath, your dentist may recommend professional fluoride treatment, improved flossing habits, and monitoring at your next visit. At this stage, the enamel can sometimes remineralize and the cavity may not progress.
Small to Moderate Cavities: Filling
Once the cavity has penetrated through the enamel into the dentin, a filling is needed. The dentist removes the decayed portion and fills the space with composite resin (tooth-colored filling material) or another filling material. Interproximal fillings can be technically challenging because the dentist must shape the filling to recreate the natural contact point between the two teeth.
A well-placed filling restores the tooth's function and prevents further decay in that area. Composite fillings for interproximal cavities typically cost $200 to $400. Costs vary by location and provider.
Large Cavities: Inlay, Onlay, or Crown
If the cavity is large enough that a significant portion of the tooth structure is lost, a filling may not provide enough support. In these cases, an inlay (which fits inside the cusps), an onlay (which covers one or more cusps), or a full crown may be recommended. These restorations are fabricated in a lab or milled in-office and provide better structural support than a large filling.
Inlays and onlays typically cost $500 to $1,200. Crowns range from $800 to $1,500. Your dentist or a prosthodontist will recommend the best option based on how much tooth remains. Costs vary by location and provider.
When Decay Reaches the Nerve: Root Canal Treatment
If an interproximal cavity grows deep enough to reach the dental pulp (the nerve and blood supply inside the tooth), you will likely need root canal treatment to save the tooth. An endodontist, a specialist in treating problems inside the tooth, removes the infected pulp, cleans the canal system, and seals the tooth. After root canal treatment, the tooth typically needs a crown for long-term protection.
Root canal treatment typically costs $700 to $1,500 depending on the tooth. The crown adds $800 to $1,500. While this sounds like a lot, it is usually less expensive than extracting the tooth and replacing it with an implant or bridge. Costs vary by location and provider.
How to Prevent Cavities Between Teeth
Prevention is far simpler and less expensive than treatment. Because interproximal cavities form in areas a toothbrush cannot reach, flossing is essential.
Daily Flossing
Flossing once a day removes plaque and food from between teeth before bacteria can produce enough acid to damage enamel. Traditional string floss, floss picks, water flossers, and interdental brushes all work. The best tool is the one you will actually use every day. If you find string floss difficult, try a water flosser or soft interdental picks as an alternative.
Fluoride Protection
Fluoride strengthens enamel and can reverse very early decay before a cavity forms. Use fluoride toothpaste twice daily. If you are at high risk for cavities, your dentist may recommend a prescription-strength fluoride toothpaste or rinse, or apply professional fluoride varnish at your checkup visits.
Diet and Habits
Reducing the frequency of sugary and acidic foods and drinks lowers your cavity risk. Sipping sugary beverages throughout the day is especially harmful because it keeps the acid level in your mouth elevated for hours. Drinking water after meals and snacks helps rinse away food particles and neutralize acid.
When to See a Specialist
Most cavities between teeth are treated by a general dentist. However, if the decay has reached the nerve and you need root canal treatment, your dentist will likely refer you to an endodontist. Endodontists have 2 to 3 years of additional training focused on diagnosing and treating problems inside the tooth.
If the tooth needs a complex restoration after the cavity is treated, such as an inlay, onlay, or crown on a structurally compromised tooth, a prosthodontist can help. Prosthodontists specialize in restoring damaged teeth and can design restorations that rebuild both function and appearance.
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