A cavity is a permanently damaged area in the hard surface of a tooth that develops into a tiny hole. It forms when bacteria in your mouth produce acids that dissolve tooth enamel over time. Cavities are one of the most common health problems worldwide, affecting about 26% of adults aged 20 to 44 in the United States and 13% of children aged 5 to 19.
How a Cavity Forms
Your teeth are coated in enamel, a mineral shell made mostly of a crystal called hydroxyapatite. This crystal is built from calcium, phosphate, and hydroxyl ions packed tightly together. Normally, your saliva keeps these minerals in balance, constantly bathing your teeth in just enough calcium and phosphate to keep enamel intact.
The trouble starts with plaque, a sticky film of bacteria that clings to your teeth. When you eat sugary or starchy foods, bacteria in plaque (primarily Streptococcus mutans and Lactobacillus species) feed on those carbohydrates and produce lactic acid as a byproduct. This acid lowers the pH at the tooth’s surface. When the pH drops below about 5.5, your saliva can no longer keep enamel saturated with minerals. At that point, calcium and phosphate ions start dissolving out of the enamel crystal and into the surrounding fluid. This process is called demineralization.
Your mouth naturally recovers between meals. Saliva neutralizes acids and delivers fresh minerals back to the enamel, repairing minor damage. But if acid attacks happen too frequently, or plaque isn’t cleaned away regularly, the mineral loss outpaces the repair. That’s when a cavity begins.
The Five Stages of Decay
Cavities don’t appear overnight. They progress through distinct stages, and catching them early makes a real difference in how they’re treated.
Stage 1: White spots. The earliest sign is a chalky white patch on the enamel where minerals have started to leach out. At this point, the surface is still intact. This stage is actually reversible with fluoride treatments and improved oral hygiene, because no physical hole has formed yet.
Stage 2: Enamel breakdown. If demineralization continues, the enamel weakens enough to form an actual hole. That white spot may darken to brown. This is what most people picture when they think of a cavity. Once the enamel is broken through, the damage can’t repair itself.
Stage 3: Dentin decay. Beneath enamel lies dentin, a softer, yellowish layer that makes up the bulk of the tooth. Dentin contains tiny tubes that connect to the nerve inside, which is why decay at this stage often brings noticeable sensitivity to hot, cold, or sweet foods. Decay spreads faster through dentin than through enamel because the tissue is less mineralized.
Stage 4: Pulp involvement. The innermost part of the tooth, the pulp, contains nerves and blood vessels. When bacteria reach this layer, the pulp becomes inflamed and swells. Because it’s trapped inside a rigid tooth, the swelling presses on nerves, causing significant pain that can be sharp, throbbing, or constant.
Stage 5: Abscess. If infection in the pulp goes untreated, a pocket of pus can form at the tip of the tooth root. An abscess can cause severe pain that radiates into the jaw, along with swelling of the gums or face, fever, and swollen lymph nodes in the neck. At this stage, the infection can spread to the surrounding bone and even to other parts of the body.
Three Types of Cavities
Not all cavities form in the same place. Dentists classify them into three types based on location:
- Pit and fissure cavities form in the grooves on the chewing surfaces of your back teeth. These grooves trap food and plaque easily, making them the most common site for decay, especially in children and teenagers.
- Smooth surface cavities develop on the flat sides of teeth, often in the tight spaces between teeth where floss is the only way to clean. They tend to progress more slowly than pit and fissure cavities.
- Root cavities appear on the exposed root surfaces of teeth, which lack the protective enamel coating. They’re most common in older adults whose gums have receded, leaving the softer root surface vulnerable to acid.
What a Cavity Feels Like
Early cavities often produce no symptoms at all. Many people have no idea they have one until a dentist finds it during a routine exam. As the decay progresses, though, the signs become harder to ignore.
Temperature sensitivity is typically the first thing people notice. A zing of pain when you drink something cold or sip hot coffee signals that enamel has thinned enough to expose the more sensitive layers underneath. Sensitivity to sweet, sour, or acidic foods follows the same pattern. Some people feel a twinge of pain just from the pressure of brushing.
Visually, you might spot a chalky white area, a dark brown or black stain, or an obvious hole in a tooth. But many cavities form between teeth where you can’t see them in a mirror, which is why dental X-rays are so important. Bitewing X-rays, the kind where you bite down on a small tab, are specifically designed to reveal decay hiding between teeth and below the gumline.
If you start feeling pain when biting or chewing, decay has likely reached deeper into the tooth or is irritating the surrounding tissue. Spontaneous pain that wakes you up at night, or a persistent dull ache in your jaw, usually signals that the pulp is involved.
How Dentists Find Cavities
During a routine checkup, your dentist examines each tooth visually and uses a thin metal instrument called an explorer to feel for soft spots on the enamel surface. But many cavities, particularly those between teeth or under old fillings, are invisible to the naked eye.
That’s where dental X-rays come in. Bitewing X-rays capture the upper and lower teeth together and are the standard tool for detecting cavities between teeth. Periapical X-rays show the full length of a tooth from crown to root tip, which helps identify decay near the roots, bone loss, and abscesses. These imaging methods let your dentist catch decay early, often before you feel anything.
Treatment Options by Stage
The right treatment depends entirely on how far the decay has progressed.
For the earliest white-spot stage, no drilling is needed. Fluoride treatments, whether in-office varnishes or prescription rinses, can help push minerals back into weakened enamel and halt the decay. The American Dental Association also recognizes silver diamine fluoride as a non-invasive option that can arrest active cavities, particularly useful for young children or patients who can’t easily tolerate traditional dental work.
Once an actual hole forms in the enamel or dentin, a filling is the standard treatment. Your dentist removes the decayed material and fills the space with a durable material like composite resin (tooth-colored) or amalgam. This is a straightforward procedure, usually done in one visit with local anesthesia. Most people feel fine within a few hours.
When decay is extensive enough to weaken the tooth’s structure, a filling alone won’t hold. In that case, a crown (a custom-fitted cap) replaces the entire visible portion of the tooth, restoring its shape and strength.
If decay reaches the pulp, a root canal becomes necessary. The infected pulp tissue is removed, the inside of the tooth is cleaned and sealed, and a crown is placed on top. Despite its reputation, a root canal relieves the intense pain caused by an infected pulp rather than causing it. Most people describe it as comparable to getting a large filling.
In the most advanced cases, where the tooth is too damaged to save or an abscess threatens surrounding bone, extraction is the only remaining option.
What Happens If You Ignore a Cavity
Cavities never heal on their own once they’ve progressed past the initial white-spot stage. Left untreated, they grow larger, move through deeper layers, and eventually reach the pulp. The infection can then spread beyond the tooth root into the jawbone, causing bone loss around the affected tooth and potentially damaging neighboring teeth.
A dental abscess is the most serious local complication. Beyond the intense pain, swelling, and fever it causes, the infection can spread to soft tissues in the face and neck, a condition called cellulitis. In rare but serious cases, the bacteria can enter the bloodstream. What started as a small, painless spot on a tooth can escalate into a medical emergency if left long enough.
Why Some People Get More Cavities
Cavity risk isn’t just about how well you brush. Several factors shift the balance between mineral loss and repair in your mouth. Frequent snacking or sipping sugary drinks keeps acid levels elevated for longer periods, giving enamel less recovery time between attacks. A naturally dry mouth, whether from medications, medical conditions, or breathing habits, removes the protective buffering effect of saliva.
The location and shape of your teeth matter too. Deep grooves in molars trap bacteria more easily, and crowded or overlapping teeth create tight spaces that are hard to clean. Receding gums expose root surfaces that are far more vulnerable to acid than enamel. Even the specific mix of bacteria in your mouth plays a role. People who harbor higher levels of acid-producing bacteria face a steeper uphill battle, regardless of their brushing habits.