Cavities between teeth, called interproximal cavities, are fixed with dental fillings in most cases. The procedure is more involved than filling a cavity on the chewing surface because your dentist needs to rebuild the side wall of your tooth while keeping a proper gap between the two neighboring teeth. The specific fix depends on how deep the decay has spread and how much tooth structure remains.
Why Cavities Form Between Teeth
The contact points between your teeth are prime real estate for bacteria. Food particles and plaque get wedged into these tight spaces, and your toothbrush bristles can’t reach them effectively. Over time, the acid produced by bacteria eats through the enamel on the side of one or both neighboring teeth. These cavities often develop silently for months or even years before you notice any sensitivity or pain, which is why they’re frequently caught on routine dental X-rays rather than by symptoms.
How These Cavities Are Detected
Your dentist typically spots interproximal cavities on bitewing X-rays, the small images taken with the film held between your teeth. These remain the primary diagnostic tool for detecting decay between teeth, even though newer optical methods exist. Techniques like near-infrared transillumination (shining a special light through the tooth) show promise for deeper cavities that have reached the inner layer of the tooth, but they’re much less reliable for catching early-stage enamel decay. This is one reason skipping your routine X-rays can mean missing a cavity until it’s significantly larger and more expensive to treat.
What Happens During the Filling
Most interproximal cavities are treated with a two-surface composite (tooth-colored) filling. The process takes roughly 30 to 60 minutes per tooth and follows a specific sequence designed to restore the tooth’s original shape.
After numbing the area, your dentist removes the decayed portion of the tooth. Then comes the part that makes these fillings trickier than a simple surface cavity: a thin metal strip called a matrix band is placed around the tooth to act as a temporary wall. This band is held tightly in place with a small wedge pushed between the teeth at the gum line. Together, the band and wedge create a mold so the filling material can be shaped into a proper side wall with the right contour and a natural contact point against the neighboring tooth.
Once the band is in position, the remaining tooth surface is etched with a mild acid for about 20 seconds, rinsed, and coated with a bonding adhesive. Composite resin is then layered into the cavity in small portions, with each layer hardened using a curing light. After the matrix band is removed, your dentist shapes and polishes the filling to restore a natural bite and smooth contact with the adjacent tooth.
Getting that contact point right matters. If the filling is too flat, food will constantly pack between your teeth. If it’s too bulky, flossing becomes difficult or the filling puts pressure on the neighboring tooth. A well-placed filling should feel like your teeth fit together the way they did before the cavity.
Filling Materials and Cost
Composite resin is the standard choice for most interproximal fillings today because it matches your tooth color and bonds directly to the tooth structure. A two-surface composite filling (the type needed for a cavity between teeth) typically costs $130 to $220 without insurance. Amalgam (silver) fillings for the same type of cavity run $75 to $150, though fewer dentists offer them and they’re generally limited to back teeth where appearance is less of a concern.
Composite fillings do have a higher failure rate than amalgam over time. A meta-analysis in the International Dental Journal found average failure rates of about 14% for composite and 7.5% for amalgam over a six-year follow-up period. The most common reasons for failure are new decay forming around the edges of the filling, fractures in the tooth or filling, and the filling loosening or falling out. In practical terms, a well-placed composite filling between your teeth can last 7 to 10 years or longer, but the location makes it more vulnerable to wear and recurrent decay than fillings on chewing surfaces.
When a Filling Isn’t Enough
If the cavity has destroyed a significant amount of tooth structure, a standard filling may not provide enough support. Your dentist has a few options depending on the extent of damage.
- Inlays are custom-made restorations used when the cavity is too large for a filling but the outer walls of the tooth are still intact. They’re fabricated in a lab from porcelain or composite and cemented into the prepared cavity, offering more strength and durability than a direct filling.
- Onlays cover a larger area, extending over one or more of the tooth’s cusps (the raised points on the chewing surface). These are recommended when decay or fracture has compromised the top or sides of the tooth beyond what an inlay can address.
- Crowns cap the entire visible portion of the tooth and are reserved for severe damage. If the cavity between your teeth has undermined most of the tooth structure, a crown provides full coverage and protection against further fracture.
The progression from filling to inlay to crown generally follows the amount of healthy tooth that remains. Your dentist will recommend the most conservative option that still gives the restoration a reasonable lifespan.
Preventing Cavities Between Teeth
Since your toothbrush can’t clean the surfaces where these cavities form, daily interdental cleaning is the single most effective prevention strategy. Interdental brushes, the tiny bottle-shaped brushes you push between your teeth, outperform traditional floss by a wide margin. One study found interdental brushes reduced plaque by about 40% and gum inflammation by about 43% more than floss. Floss still reduced plaque to a statistically significant degree, but the difference in effectiveness was substantial.
The reason is simple: interdental brushes make better contact with the curved surfaces between teeth, scrubbing plaque off both sides of the gap in a single pass. Floss works well for very tight contacts where a brush won’t fit, but for most people with any space between their teeth, a properly sized interdental brush is more effective. Water flossers are another option and work well for reducing gum inflammation, though they haven’t shown the same plaque-removal benefit as interdental brushes.
If you’ve already had one interproximal cavity filled, you’re at higher risk for developing another. The edges of any filling create a microscopic seam where bacteria can accumulate, and the surfaces between your teeth remain just as vulnerable as before. Using an interdental brush or floss daily, keeping up with routine X-rays so new cavities are caught early, and limiting sugary or acidic foods between meals all reduce the chance of repeating the process.