What Are Dental Caries? Stages, Causes & Treatment

Dental caries is the scientific term for what most people call cavities or tooth decay. It describes a process, not just a hole: bacteria on the tooth surface feed on sugars and starches, produce acid, and gradually dissolve the mineral structure of enamel and, eventually, the softer dentin underneath. The disease is one of the most common chronic conditions in humans, affecting children and adults alike, and its progression can range from a faint white spot that reverses on its own to deep destruction that kills the nerve inside the tooth.

How a Cavity Actually Forms

Your mouth is home to hundreds of bacterial species, but one in particular has long been singled out as the primary troublemaker. Streptococcus mutans lives in the sticky film that coats your teeth, known as dental plaque or biofilm. It thrives on dietary sugars, especially sucrose, and produces enzymes that help it glue itself and other bacteria firmly to enamel surfaces. Once anchored, it and its neighbors metabolize carbohydrates and churn out lactic acid and other organic acids that eat away at tooth mineral.

That said, the picture is broader than a single villain. Molecular studies have shown that even in a sugar-rich diet, a wide spectrum of acid-producing microbes populates plaque, not just S. mutans.¹ Other organisms, including the yeast Candida albicans, can team up with S. mutans to make biofilms more aggressive. When both are present, the biofilm produces more of the sugary glue that holds it together, shelters more bacteria, and leads to more severe decay than either organism would cause alone.²

The biofilm itself is the key structure. It is not just a coating of germs; it is a complex community embedded in a matrix of sticky polysaccharides that the bacteria manufacture from dietary sugars. This matrix shields the bacteria from saliva, from antimicrobial agents, and from your immune system. Acid produced inside the biofilm stays concentrated against the tooth surface, which is why plaque that sits undisturbed in the grooves of molars or between teeth does far more damage than bacteria floating freely in saliva.³

The Demineralization-Remineralization Tug of War

Tooth enamel is the hardest substance in the human body, but it is not indestructible. It is made mostly of a crystalline mineral called hydroxyapatite. Every time you eat something that feeds the bacteria in plaque, acid lowers the pH at the tooth surface and minerals start dissolving out of the enamel crystals. This is demineralization. Between meals, saliva gradually washes away food particles, neutralizes acid, and delivers calcium and phosphate ions back to the enamel surface, rebuilding what was lost. This is remineralization.

Caries develops when this balance tips toward demineralization. That can happen because you eat sugary or starchy foods frequently, because your saliva flow is low, because the plaque on your teeth is thick and undisturbed, or some combination of all three. Teeth have evolved a remarkable resistance to this kind of localized acid attack, but they have limits.⁴ If acid exposure is frequent enough and long enough, the enamel surface breaks down and a cavity forms.

Stages of Decay, from White Spot to Abscess

Dental caries does not go from healthy tooth to gaping hole overnight. It progresses through distinct stages, and knowing where you are on that timeline matters because the earliest stage is entirely reversible without a drill.

White spot lesion. The first visible sign of caries is a chalky white patch on the enamel. This is a zone where minerals have been lost from beneath the surface, but the enamel has not yet broken through. At this point, the process can be halted and even reversed with fluoride treatments and improved oral hygiene. A clinical trial in children found that fluoride varnish combined with a remineralizing agent (casein phosphopeptide–amorphous calcium phosphate) was effective at reversing these white spot lesions.⁵ This stage is your best opportunity to avoid a filling entirely.

Enamel cavitation. If demineralization continues, the surface layer of enamel collapses and a small cavity forms. Bacteria can now shelter inside the defect, making it harder for saliva and brushing to reach them. This is the stage at which most dentists recommend placing a restoration.

Dentin involvement. Beneath the enamel lies dentin, a softer, more porous tissue. Once caries reaches dentin, it can spread faster because dentin contains tiny tubules that bacteria and acid can travel along. The tooth has a built-in defense here: living cells called odontoblasts detect the threat and lay down a layer of reactionary dentin to slow the advance. When decay moves slowly, this defensive dentin looks much like normal tooth structure. When it advances fast, the defensive response may be disorganized or absent altogether.⁶ The pace of progression, in other words, shapes how well the tooth can protect itself.

Pulp involvement and beyond. At the center of every tooth sits the pulp, a soft tissue packed with nerves and blood vessels. When bacteria reach the pulp, infection sets in. This is the stage that brings sharp or throbbing toothache, and the immune system mounts a response that can include nerve sprouting and an influx of immune cells into the area.⁷ If left untreated, infection can spread beyond the root tip and form an abscess, which can damage surrounding bone and, in rare cases, become a serious systemic health threat.

What Drives Your Risk

Caries is not caused by a single factor. It takes a convergence of susceptible tooth surfaces, acid-producing bacteria, a carbohydrate source, and time. But several things tip the odds significantly.

Diet

Sugar has been linked to caries for centuries, and the evidence remains strong. A study of U.S. adults found that higher amounts of added sugar intake were positively associated with both the number of decayed tooth surfaces and overall caries experience.⁸ Frequency matters as much as total quantity: more sugar episodes per day meant more decay, following a curvilinear pattern rather than a straight line.

But sugar is not the only culprit. Cooked starches, like bread, crackers, and chips, tend to cling to tooth surfaces far longer than sugary liquids and can produce a sustained acid challenge, especially in the grooves and pits where plaque collects.¹ A food does not have to taste sweet to feed the bacteria that cause decay.

Saliva

Saliva is your teeth’s natural defense system. It rinses food away, buffers acid, and carries the mineral building blocks for remineralization. Studies comparing children with active cavities to cavity-free children consistently find that the cavity-free group has higher salivary flow rates and better buffering capacity.⁹ Anything that dries your mouth out, whether it is medication side effects, radiation therapy, mouth-breathing, or autoimmune conditions affecting salivary glands, raises caries risk substantially.

This is especially relevant for older adults. Self-reported dry mouth was a significant risk factor for root caries in a study of people with a mean age of about 74, roughly doubling the odds of having root cavities compared to those without dry mouth. Visible plaque was an even stronger predictor, while daily fluoride exposure cut the risk nearly in half.¹⁰

Age and Tooth Anatomy

Children and teenagers are at high risk because their newly erupted permanent teeth have deep grooves that are hard to keep clean. Older adults face a different vulnerability: gum recession exposes the root surfaces of teeth, which are covered by cementum rather than enamel and are far less resistant to acid. Root caries can progress quickly and is a leading cause of tooth loss in people over 65.

Prevention That Actually Works

Brushing and flossing get the most airtime, and they do matter because they physically disrupt the biofilm before it can cause sustained acid damage. But several other strategies have strong evidence behind them.

Fluoride

Fluoride works on multiple fronts. When it is present in the fluid surrounding a tooth, it promotes the formation of a tougher mineral called fluorapatite, which resists acid attack better than the natural hydroxyapatite in enamel.¹¹ At low concentrations, fluoride speeds up remineralization and slows down dissolution, tipping the balance back in the tooth’s favor.¹² This is why fluoride toothpaste, fluoridated water, and professional fluoride treatments all reduce cavities. The effect is topical, meaning the fluoride needs to be in contact with the tooth surface to work. Swallowing it during tooth development has some benefit, but the main protective action comes from direct contact.

Dental Sealants

Sealants are thin resin coatings painted into the pits and fissures of back teeth, creating a physical barrier that keeps bacteria and food out of the spots where a toothbrush cannot reach. A Cochrane review found moderate-quality evidence that resin-based sealants reduced caries on permanent molars by between 11% and 51% at two years compared to no sealant.¹³ Other analyses report preventive fractions as high as 61% at five years.¹⁴ Sealants are typically applied shortly after permanent molars come in, around ages 6 and 12, but they can also be placed on primary teeth at risk.

Silver Diamine Fluoride

Silver diamine fluoride, or SDF, is a liquid that a dentist paints directly onto a cavity. It kills bacteria, hardens softened dentin, and stops or slows decay without any drilling. A controlled trial in children with weakened molars found that teeth treated with SDF had a lower incidence of new caries and a higher rate of caries arrest than teeth treated with another remineralizing agent.¹⁵ The trade-off is cosmetic: SDF stains decayed tooth structure black, which is noticeable on front teeth. For back teeth and baby teeth in young children, the staining is often considered an acceptable price for avoiding sedation or complex treatment.

How Dentists Detect Cavities

The traditional approach to finding caries involves a visual exam, a sharp explorer instrument, and dental X-rays. But the field has been shifting. Modern detection systems like the International Caries Detection and Assessment System (ICDAS) use standardized visual criteria to score the severity of lesions, from the earliest white spot all the way through to extensive cavitation. A study comparing ICDAS visual examination to standard bitewing X-rays found that the visual system was more sensitive at picking up early enamel caries, while X-rays were more specific, meaning they produced fewer false positives for deeper dentin decay on certain tooth types.¹⁶

In practice, this means that your dentist is likely using both methods, plus professional judgment. X-rays remain essential for detecting decay between teeth, where visual inspection cannot reach. But for the chewing surfaces of molars, a careful visual examination may actually catch very early lesions that X-rays miss. Newer technologies like laser fluorescence and infrared imaging are also entering dental offices, though they supplement rather than replace the exam-plus-X-ray approach.

Treatment When Prevention Is Not Enough

Once a cavity has progressed past the white-spot stage and the enamel surface has broken through, some form of restoration is usually needed. What that looks like depends on how deep the decay goes and how much tooth structure remains.

Fillings and the Selective Removal Approach

For decades, the standard approach was to drill out every trace of decayed tissue before placing a filling. That philosophy has shifted. A technique called selective caries removal aims to leave some softened dentin near the pulp rather than risking a breach into the nerve. A five-year randomized trial found that leaving decayed tissue beneath a restoration in deep lesions did not hurt the filling’s survival, and both amalgam and resin composite fillings performed similarly regardless of whether all decay was removed.¹⁷ A separate study confirmed that selective removal produced the same filling longevity as complete removal but with far fewer instances of accidentally exposing the pulp.¹⁸

This is genuinely good news. It means that in deep cavities close to the nerve, a more conservative approach protects the pulp without sacrificing the filling’s durability. The shift reflects a broader trend in dentistry toward preserving as much natural tooth structure as possible.

Root Canal Treatment Versus Extraction

When decay reaches the pulp and infection takes hold, the two main options are root canal treatment (removing the infected pulp, cleaning the canals, and sealing the tooth) or extraction. Root canal treatment saves the tooth but costs more upfront. Extraction is cheaper in the short term but often leads to costs later if the missing tooth needs to be replaced with an implant, bridge, or denture. A cost-effectiveness analysis estimated that a root canal with a crown on a lower molar needs a tooth survival probability in the range of about 83% to 93% to justify the cost over extraction followed by an implant-supported crown.¹⁹ A Swedish study reached a similar conclusion from a different angle: extraction was cost-effective in the short term, but the likely need for future tooth replacement shifted the calculation in favor of root canal treatment over time.²⁰

For people with very high caries risk who do not follow preventive recommendations, the math can flip. When the same conditions that destroyed one tooth are likely to damage any restoration placed on it, extraction may be the more realistic choice, and efforts shift toward preventing further losses rather than trying to save a tooth with a poor long-term outlook.²¹

Root Caries in Older Adults

Most discussion of dental caries focuses on children and teenagers, but older adults face a distinct form of the disease. As gums recede with age, the roots of teeth become exposed. Root surfaces lack the hard enamel covering that protects the crown, so they dissolve at a higher pH and decay faster once the process starts. A study of adults averaging about 74 years old found that roughly one in four had active root caries lesions. The strongest predictors were visible plaque buildup and self-reported dry mouth, while daily fluoride use cut the risk roughly in half.

Dry mouth is extremely common among older adults because many medications list it as a side effect, including antidepressants, blood-pressure drugs, antihistamines, and drugs for urinary incontinence. When a person is on several of these at once, the cumulative effect on saliva production can be dramatic. That makes prescription reviews, saliva substitutes, and more frequent fluoride exposure especially important in this age group.

An Unexpectedly Old Disease

Caries is sometimes imagined as a modern problem caused by processed sugar, but it long predates candy bars. Archaeological analysis of early Neolithic farming communities in central Germany, dating to roughly 5,000 years ago, found that about two-thirds of adults had at least one carious lesion, with roughly 10% of all teeth affected.²² Children in those same communities had much lower rates, which tracks with modern patterns: kids have fewer teeth and less exposure time. Isotope analysis of the bones linked the decay to starchy cereal grains rather than refined sugar, which would not exist for thousands of years.

The transition from hunting and gathering to farming is widely considered a turning point for human dental health. Hunter-gatherer populations consistently show lower caries rates than farming populations, largely because their diets contained fewer fermentable carbohydrates. The modern diet simply accelerated a problem that grain agriculture set in motion millennia ago. Understanding that history underscores a practical point: caries is fundamentally a disease of sustained acid exposure from carbohydrate metabolism, not merely of candy and soda. Reducing frequency of all fermentable carbohydrates, including refined starches, is part of effective prevention.