Tooth Decay (Cavities): How They Form, Their Stages, and the Right Treatment for Each

Tooth Decay (Cavities): How They Form, Their Stages, and the Right Treatment for Each

Medically reviewed by Dr. Telman İskender, Clinic Director, Stom Dental Centre Antalya

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Tooth decay is one of the most common chronic diseases worldwide, but it does not appear overnight — it moves through clearly defined stages, from the first white spot to a deep cavity. Understanding how decay forms and which stage a lesion has reached helps you and your dentist choose the gentlest treatment that still works, from fluoride remineralization to a filling. This guide explains the mechanism, the stages, the signs to watch for, and evidence-based prevention.

How Does Tooth Decay Actually Form?

Tooth decay begins when bacteria in dental plaque metabolize sugars and other fermentable carbohydrates from food into acids that demineralize the enamel. Clinically, caries is defined as a “biofilm-mediated, sugar-driven, multifactorial, dynamic disease that results in the phasic demineralization and remineralization of dental hard tissues.” As long as remineralizing phases — driven by saliva and fluoride — outweigh acid attacks, the tooth stays healthy. When frequent sugar intake, inadequate hygiene, or insufficient fluoride exposure tip that balance toward demineralization for long enough, visible decay begins. Below a critical pH, the enamel loses minerals — invisibly at first, beneath an intact surface, until the structure is weak enough for a white spot to appear.

The Stages of Tooth Decay in Detail

Dentists commonly classify decay using the internationally recognized ICDAS system (International Caries Detection and Assessment System), which scores severity from code 0 (sound surface) to code 6 (extensive cavity with visible dentin):

• Codes 1-2: The first visible enamel change — a chalky-white or brownish spot (“white spot lesion”); the surface itself is still intact.
• Code 3: A localized breakdown of the enamel surface, without visible involvement of the underlying dentin.
• Code 4: A dark shadow shows through the enamel — a sign that decay has already reached the dentin.
• Codes 5-6: A clearly visible cavity with exposed dentin, in advanced cases with extensive loss of tooth structure.

If left untreated at this point, bacteria can progress further toward the tooth’s nerve (the pulp) and trigger inflammation there (pulpitis) — a complication of untreated decay that sits outside the ICDAS scale itself.

Stages at a Glance

Which Treatment Fits Which Stage?

This is exactly where the modern, risk-based approach to caries management comes in, as described by the ICCMS (International Caries Classification and Management System): not every carious lesion needs a drill immediately — early, non-cavitated lesions (ICDAS 1-2) can often be arrested or even reversed through remineralization, while cavitated lesions require restorative treatment.

• Early stage (white spot, ICDAS 1-2): Fluoride varnish or gel at the dentist, consistent oral hygiene, and reduced sugar intake can arrest or remineralize the lesion — no drilling required.
• Intermediate stage (localized enamel breakdown to early dentin involvement, ICDAS 3-4): Depending on the individual finding, intensified prevention may still be enough, though a small filling is often already the sensible option to seal the cavity and stop progression.
• Advanced stage (dentin decay with a visible hole, ICDAS 5-6): A filling is generally needed here; material and technique differ depending on whether the tooth is in the front or back of the mouth — see our dedicated pages on anterior and posterior aesthetic fillings for details on those procedures.
• Pulp involvement (the tooth’s nerve is inflamed or has died): once decay reaches the nerve, a filling alone is no longer enough — root canal treatment is needed to save the tooth. Read more in our article on crowns and root canal treatment. Extraction is only considered when the tooth can no longer be structurally preserved.

This staging never replaces an individual dental examination, including probing and, where needed, an X-ray — only that can reliably confirm the actual stage.

Signs You Can Notice Yourself

Not every cavity hurts — early stages in particular often go unnoticed. Possible warning signs include: a chalky-white or brownish-black spot on the tooth surface, a patch that feels rough against the tongue, sensitivity to sweet, cold, or hot, a visible hole or a chipped piece of tooth structure, persistent bad breath despite good oral hygiene, and — in advanced stages with pulp involvement — ongoing or throbbing pain, sometimes with swelling. Because early stages are usually symptom-free, regular dental check-ups matter more than waiting for symptoms to appear.

Risk Factors for Tooth Decay

Several factors influence how quickly the demineralization-remineralization balance tips:

• Frequency and amount of sugar intake: the WHO recommends limiting free sugars to under 10% of daily energy intake, with additional benefit from a further reduction to under 5%.
• Oral hygiene: inadequate or irregular brushing lets plaque sit on the tooth surface longer.
• Fluoride exposure: little or no fluoride from toothpaste, water, or professional applications weakens saliva’s remineralizing capacity.
• Saliva flow: reduced salivary flow (dry mouth, for example from certain medications) weakens saliva’s natural buffering and clearing action, raising caries risk.
• Eating frequency: frequent snacking between meals keeps the mouth in an acidic state more often than a few clearly separated meals.
• Tooth position and surface: crowded teeth, deep fissures on chewing surfaces, or existing restoration margins can make plaque removal harder.

Everyday Prevention: Diet, Hygiene, Fluoride

The most effective preventive measures are well documented:

• Brush twice daily with fluoride toothpaste: A Cochrane review of 96 studies shows solid evidence that toothpastes with 1,000-1,500 ppm fluoride measurably reduce caries increment.
• Limit free sugars: following the WHO recommendation, keep free sugars under 10%, ideally under 5%, of energy intake.
• Clean between teeth: floss or interdental brushes remove plaque where a toothbrush cannot reach.
• Professional fluoride applications: A Cochrane review shows a clear caries-preventive effect of fluoride varnish in children and adolescents.
• Fissure sealants: for deep grooves on molars, Cochrane data show sealants reduce caries risk by roughly 11-51% compared with unsealed teeth at 24-month follow-up.
• Regular dental check-ups: the only reliable way to catch early-stage lesions before a filling becomes necessary.

What Happens If Tooth Decay Is Left Untreated?

Left untreated, decay generally keeps progressing — from the enamel surface through the dentin toward the tooth’s nerve. Once bacteria reach the pulp, pulpitis (nerve inflammation) can develop; initially reversible, it can become irreversible and lead to the nerve dying. From there, infection can spread into the jawbone and cause a painful abscess. At this stage, often only root canal treatment — or, if the tooth can no longer be preserved, extraction — remains an option. Globally, untreated decay of permanent teeth is, according to current Global Burden of Disease 2021 estimates, the single most common health condition worldwide, affecting an estimated 2.24 billion people (age-standardized prevalence 27.5%); for primary teeth the estimate is around 524.6 million children (7.6%). These numbers show that catching and treating decay early matters not just individually, but as a global health issue.

When Should You See a Dentist?

Ideally at the very first sign — not only once it hurts. Because white spot lesions are often hard to distinguish from harmless enamel marks with the naked eye, only a dental examination (visual, with a probe, and an X-ray if needed) can reliably confirm the actual stage. Check-ups every six to twelve months, depending on individual risk, let decay be caught while it is still in the remineralizable early stage — rather than only once a filling or more is already needed.

Frequently Asked Questions

Is tooth decay contagious?

Yes — the bacteria that cause decay can be transmitted, for example between close family members — but the disease itself only develops through the interplay of bacteria, sugar, tooth surface, and time.

Can a white spot (early decay) heal on its own?

Yes. At the early, non-cavitated stage (ICDAS 1-2), remineralization through better oral hygiene, fluoride exposure, and reduced sugar intake is possible — drilling is usually not needed at this stage.

How long does it take for a white spot to turn into a cavity?

This varies a great deal from person to person and depends on oral hygiene, diet, fluoride exposure, and saliva flow — progression can take anywhere from months to several years if nothing is done.

Does tooth decay always hurt?

No. Early and even intermediate stages are often painless. Pain usually appears only once decay reaches the dentin or the nerve.

Does every cavity need a filling?

No. Early, non-cavitated lesions can be remineralized. Restorative treatment such as a filling generally becomes appropriate only once a true cavity has formed (ICDAS 3 and above).

When is root canal treatment needed instead of a filling?

Once decay reaches the tooth’s nerve (the pulp) and causes inflammation or infection there, a filling alone is no longer enough — root canal treatment is then needed to save the tooth.

How often should I go for a check-up?

This depends on your individual caries risk; every six to twelve months is typical, more often if your risk is elevated.

Can tooth decay be treated with home remedies?

No. Home remedies can, at best, support oral hygiene, but they cannot replace a dental diagnosis and treatment — an existing cavity in particular will not reverse with home remedies.

Sources

• World Health Organization. “Oral health.” Fact sheet, who.int/news-room/fact-sheets/detail/oral-health (accessed September 2026).
• Alves-Costa S, Romandini M, Nascimento GG. “Lip and Oral Cancer, Caries and Other Oral Conditions: Estimates From the 2021 Global Burden of Disease Study and Projections up to 2050.” Journal of Periodontal Research. 2025;60(6):544–558. doi:10.1111/jre.13421.
• Pitts NB, Zero DT, Marsh PD, et al. “Dental caries.” Nature Reviews Disease Primers. 2017;3:17030. PMID: 28540937.
• Ismail AI, Sohn W, Tellez M, Amaya A, Sen A, Hasson H, Pitts NB. “The International Caries Detection and Assessment System (ICDAS): an integrated system for measuring dental caries.” Community Dentistry and Oral Epidemiology. 2007;35(3):170–178. PMID: 17518963.
• Pitts NB, Ismail AI, Martignon S, et al. “ICDAS and its International Caries Classification and Management System (ICCMS) – methods for staging of the caries process and enabling dentists to manage caries.” Community Dentistry and Oral Epidemiology. 2013;41. PMID: 24916677.
• World Health Organization. “Guideline: Sugars intake for adults and children.” Geneva: WHO; 2015.
• Walsh T, Worthington HV, Glenny AM, et al. “Fluoride toothpastes of different concentrations for preventing dental caries.” Cochrane Database of Systematic Reviews. 2019;3:CD007868. doi:10.1002/14651858.CD007868.pub3.
• Marinho VCC, Worthington HV, Walsh T, Clarkson JE. “Fluoride varnishes for preventing dental caries in children and adolescents.” Cochrane Database of Systematic Reviews. 2013;7:CD002279. doi:10.1002/14651858.CD002279.pub2.
• Ahovuo-Saloranta A, Forss H, Walsh T, Nordblad A, Mäkelä M, Worthington HV. “Pit and fissure sealants for preventing dental decay in permanent teeth.” Cochrane Database of Systematic Reviews. 2017;7:CD001830. doi:10.1002/14651858.CD001830.pub5.

This article is for informational purposes only and does not replace a dental examination. Treatment decisions for tooth decay should be made individually with your dentist, based on the individual finding and stage of decay. Figures are drawn from independent scientific publications and are not a guarantee of outcome at any specific clinic.