Caries is the clinical term dentists use for tooth decay. When your dentist says you have “caries” or “dental caries,” they’re telling you that acid-producing bacteria have damaged the mineral structure of one or more teeth. The word comes from Latin, meaning “rottenness” or “decay,” and it covers everything from the earliest invisible mineral loss on a tooth’s surface to a deep cavity that reaches the nerve.
Dental caries is one of the most common chronic diseases in the world. Oral diseases affect roughly 3.5 billion people globally, and in the United States alone, about 21% of adults aged 20 to 64 have at least one tooth with untreated decay. Understanding what caries actually is, how it develops, and what it looks like at each stage can help you catch problems early, when they’re easiest (and cheapest) to fix.
How Caries Forms Inside Your Mouth
Your teeth are covered in enamel, the hardest tissue in your body, built mostly from tightly packed mineral crystals. Caries starts when bacteria in dental plaque feed on sugars from your food and produce acid as a byproduct. That acid dissolves minerals out of the enamel’s crystal structure, a process called demineralization. This happens every time you eat or drink something sugary.
Your mouth has a natural repair system. Saliva carries calcium and phosphate ions that can rebuild the mineral surface of your teeth, essentially patching the damage before it becomes permanent. This is remineralization, and it happens constantly throughout the day. Caries develops when demineralization outpaces remineralization over weeks and months. The critical threshold is a plaque pH below 5.5. Below that level, minerals dissolve faster than your saliva can replace them, and the tooth structure starts breaking down.
This is why caries is described as a “multifactorial” disease. It’s not caused by any single thing. It requires bacteria, sugar, a vulnerable tooth surface, and enough time for the acid attacks to win out over your body’s repair process.
The Five Stages of Tooth Decay
Caries doesn’t appear overnight as a hole in your tooth. It progresses through distinct stages, and knowing them helps you understand what your dentist is seeing and why early action matters so much.
Stage 1: White Spot Lesions
The first visible sign is a chalky white spot on the tooth surface. This is a patch of enamel that has lost minerals but hasn’t broken down structurally. The spot looks white and matte because the demineralized enamel scatters light differently than healthy enamel. At this stage, the damage is reversible. Fluoride treatments, improved brushing habits, and reducing sugar intake can allow your saliva to rebuild the mineral surface without any drilling.
Stage 2: Enamel Decay
If the mineral loss continues, the white spot may darken to brown, and the enamel begins to physically break apart. Small holes, what most people call cavities, form in the tooth surface. Once the enamel has a hole in it, remineralization can no longer fix the problem. A dentist will typically place a filling at this stage.
Stage 3: Dentin Decay
Beneath the enamel sits dentin, a softer tissue threaded with tiny tubes that connect to the tooth’s nerve. Decay moves faster through dentin because it’s less mineralized than enamel. This is the stage where you’ll likely start feeling sensitivity to hot, cold, or sweet foods. A filling can still work here, though a larger one may be needed, and in some cases a crown is necessary to protect what’s left of the tooth.
Stage 4: Pulp Involvement
The pulp is the innermost part of your tooth, containing nerves and blood vessels. When decay reaches the pulp, it causes inflammation and swelling. Because the pulp sits inside a rigid shell of tooth, swelling creates intense pressure and pain. At this point, a root canal is usually required to remove the infected tissue and save the tooth.
Stage 5: Abscess
If untreated pulp infection spreads beyond the tooth root, it can form a pocket of pus called an abscess. This causes throbbing pain, facial swelling, and sometimes fever. An abscess requires urgent treatment, which may involve draining the infection, a root canal, or extraction of the tooth.
Where Caries Tends to Show Up
Not all surfaces of your teeth are equally vulnerable. Dentists classify caries partly by location because different spots carry different risks and need different approaches.
- Pits and fissures: The grooves on the chewing surfaces of your back teeth. These are the most common site, especially in children and teenagers, because food and bacteria settle into the narrow crevices where a toothbrush can’t easily reach.
- Smooth surfaces: The flat areas between teeth (called interproximal surfaces). Decay here often goes unnoticed because you can’t see it, which is why dental X-rays are so important. This is also the area flossing is designed to protect.
- Root surfaces: When gums recede with age or gum disease, the root becomes exposed. Root surfaces lack the thick enamel covering the rest of the tooth, making them especially vulnerable. About 13% of adults 65 and older have untreated decay, and root caries is a significant part of that.
How Dentists Detect Caries
Your dentist uses several tools to find decay, often before you notice anything wrong. The most basic is a visual exam, looking for discoloration, white spots, or obvious holes. For surfaces between teeth that can’t be seen directly, bitewing X-rays reveal dark shadows where mineral has been lost. These two methods catch the majority of cavities.
Some dental offices use newer technology for earlier detection. Laser fluorescence devices shine a light onto the tooth and measure how much fluorescence bounces back. Bacteria inside a developing cavity produce compounds that fluoresce differently than healthy enamel, so the device can flag decay that’s still too small to see or feel. Another tool, fiber-optic transillumination, shines a bright light through the tooth. Demineralized areas scatter the light and appear darker, highlighting damage that might not show up on an X-ray yet.
These tools are especially useful for catching caries at the white spot stage, when the damage can still be reversed without a filling.
Treatment Options by Stage
What your dentist recommends depends entirely on how far the decay has progressed.
For white spot lesions, the goal is to help your teeth remineralize. Professional fluoride varnish strengthens the enamel surface and encourages mineral uptake. A newer option called resin infiltration involves applying a liquid resin that soaks into the porous enamel, sealing the lesion without drilling. The resin has a similar light-bending property to healthy enamel, so it also restores the tooth’s normal appearance.
Once a true cavity has formed in the enamel or dentin, a filling is the standard treatment. Your dentist removes the decayed material and fills the space with composite resin (tooth-colored) or another restorative material. For larger areas of damage, a crown may be placed over the tooth to provide structural support. When decay reaches the pulp, a root canal removes the infected nerve tissue, and the tooth is sealed and usually crowned. If the tooth is too far gone, extraction followed by an implant, bridge, or partial denture replaces it.
Prevention and How Much It Helps
Fluoride is the single most effective tool for preventing caries. It integrates into the enamel crystal structure, making it more resistant to acid attack, and it accelerates remineralization. Studies show fluoride varnish applied twice a year reduces cavities by 37 to 41% in permanent teeth. When preventive care starts before any decay is present, reductions of 18 to 25% have been documented even with less intensive protocols.
Dental sealants, thin plastic coatings painted into the grooves of back teeth, physically block bacteria and food from settling into pits and fissures. They’re most effective in children whose permanent molars have recently come in, and research shows they outperform fluoride varnish alone for preventing decay on chewing surfaces in high-risk populations.
Beyond professional treatments, the basics matter enormously. Brushing twice daily with fluoride toothpaste, flossing to clean between teeth, and limiting how often you eat sugary or acidic foods all shift the balance toward remineralization and away from decay. It’s less about never eating sugar and more about reducing how many times per day your teeth face an acid attack. Sipping a soda over two hours is far worse for your teeth than drinking it in ten minutes, because each sip resets the acid clock.
Who Gets Caries Most Often
Caries affects people across every age group, but the rates vary. According to 2024 CDC data, about 11% of children aged 2 to 5 already have untreated decay in their baby teeth. That number climbs to nearly 18% for children aged 6 to 8. Among adolescents 12 to 19, about 10% have untreated permanent tooth decay. The peak is in working-age adults: nearly 21% of those aged 20 to 64 have at least one untreated cavity.
Risk factors include dry mouth (from medications or medical conditions), a diet high in sugar or refined carbohydrates, inconsistent oral hygiene, lack of access to dental care, and a history of previous cavities. Having had caries before is one of the strongest predictors of getting it again, because the underlying bacterial environment and habits tend to persist unless actively changed.