Conditions

Caries

Evidence: High Conditions Reading time: approx. 5 min. Reviewed: 11.08.2026 · KEERN Editorial Team

Caries is a biofilm-associated, multifactorial disease of tooth hard tissue that develops through the interaction of oral biofilm, fermentable carbohydrates, and individual risk factors. Acidogenic bacteria within the biofilm break down sugars into organic acids that demineralize enamel; with sustained imbalance, this can lead to permanent structural loss. Caries remains one of the most common chronic diseases worldwide, affecting approximately 27.5 percent of the global population, and is considered largely preventable.

Related terms:BiofilmDemineralizationRemineralizationpHFluorideHydroxyapatiteSalivaSalivary Buffer CapacityEnamelXylitolArginine

Definition

Caries is a biofilm-mediated, multifactorial disease in which acidogenic bacteria within the biofilm metabolize fermentable carbohydrates into organic acids. These acids lower the local pH below the critical range for enamel, often cited as around pH 5.5, though this threshold can vary with individual enamel composition, fluoride exposure, and saliva quality. Sustained low pH leads to demineralization of tooth hard tissue.

Caries is not a sudden event but a dynamic process. Phases of demineralization alternate with phases of remineralization, during which saliva minerals and supportive substances such as fluoride and hydroxyapatite can rebuild tooth structure. Whether caries ultimately develops depends on which side of that balance dominates over time.

Caries ranks among the most common chronic diseases worldwide. It is also considered largely preventable: consistent, individually tailored prevention can substantially reduce risk across all age groups.

Why caries matters

Caries affects people of every age and, left untreated, progresses in stages: from an early, reversible lesion to a cavitated defect and, eventually, to pulp involvement that can require extensive endodontic treatment or lead to tooth loss.

The burden is substantial. Caries affects chewing function, appearance, and quality of life, and it interacts in both directions with systemic conditions such as diabetes. At the same time, caries is among the best-studied diseases in dentistry: prevention, early detection, and non-invasive treatment approaches are well established and can preserve tooth structure over the long term.

How caries develops

Caries requires several factors to align: cariogenic bacteria in the biofilm, fermentable carbohydrates as substrate, a susceptible tooth surface, and enough time for the process to unfold. Removing or sufficiently limiting any one of these factors can substantially reduce risk.

The pH of the oral biofilm is the central regulator. Each exposure to sugar triggers a drop in pH. Saliva buffers that drop, shortening the duration of the acid attack, and initiates remineralization. Frequent sugar exposure is the real risk, because it does not give saliva enough time to recover between episodes.

In early stages, enamel can remineralize on its own, provided the lesion has not yet formed a cavity. Saliva supplies the calcium and phosphate ions needed for this. Fluoride and hydroxyapatite may support remineralization through different mechanisms, although the evidence base differs between them.

Caries as an ecological imbalance

Contemporary caries research increasingly frames caries as an ecological shift within the oral biofilm rather than the result of a single pathogen. Frequent sugar exposure favors acid-tolerant bacterial species, which further reinforce cariogenic conditions. This view has real consequences for prevention: the goal is not to eliminate specific bacteria, but to preserve the microbial balance in the first place.

Key takeaways

  • Caries is a dynamic process, not an irreversible event, in its early stages
  • Frequent sugar exposure is more damaging than total sugar intake
  • Saliva is the most important natural protective factor; both quantity and quality matter
  • Early lesions can remineralize; cavitated lesions cannot
  • Effective prevention relies on several measures working together, not a single intervention
  • Fluoride and hydroxyapatite may support remineralization through different mechanisms, with differing evidence behind each
  • Caries is largely preventable with consistent, individually tailored prevention

Frequently Asked Questions

Is caries really caused by sugar alone?

Sugar alone does not cause caries; it is the substrate that cariogenic bacteria metabolize. What matters most is how often sugar exposure occurs, not the total amount. Five small sugar exposures spread across a day are more cariogenic than the same amount consumed at once, because the pH drops repeatedly and saliva does not get enough time to support remineralization between exposures.

Can a cavity heal on its own?

No. Early, non-cavitated lesions, visible as a chalky white spot, can remineralize on their own. Once a true cavity has formed, the structure cannot heal itself and requires restorative treatment.

At what point does caries stop being reversible?

Early caries, visible as a chalky white spot on enamel, can remineralize if the triggering factors are reduced and remineralizing substances are available. Once a cavity has formed, spontaneous regeneration is no longer possible, and restorative treatment becomes necessary. This is why early detection matters.

Is it true that caries is contagious?

Cariogenic bacteria, particularly Streptococcus mutans, can transfer between people, for example through shared utensils or kissing. This does not mean caries automatically follows. Whether these bacteria become established in the biofilm long-term depends on additional factors, including oral hygiene, diet, and individual saliva composition. Transmissibility is one reason early caries control matters, especially in young children.

When should I see a dentist?

Early-stage caries typically causes no pain, which is one of the biggest diagnostic challenges. Regular checkups every six to twelve months allow for early detection and non-invasive treatment. Tooth pain, sensitivity to cold, or pressure sensitivity warrant a prompt dental visit, since these signs can indicate advanced caries with pulp involvement.

How common is caries worldwide?

Very common. Global Burden of Disease 2021 data estimate that approximately 27.5 percent of the world's population has untreated caries in permanent teeth, affecting more than 2 billion people, making it one of the most widespread chronic conditions globally.

KEERN Perspective

KEERN does not treat caries as an isolated, local disease. It treats it as a sign of a disrupted oral balance.

Traditional prevention strategies focus on reducing cariogenic risk and supporting remineralization, and this approach is well supported by evidence. KEERN also asks a broader question: why do cariogenic conditions arise in the first place, what shifts the microbial balance, and how can oral care shape the environment so that cariogenic dysbiosis is less likely to develop at all.

The goal is not only to treat existing lesions but to support conditions under which new lesions become less likely to form. Preserving tooth structure through prevention is the guiding principle: not repair, but preservation.

Professional perspective

Clinical relevance

  • Caries diagnosis and risk assessment (ICDAS system)
  • Non-invasive and micro-invasive caries management (infiltration, remineralization)
  • Fissure sealants for caries-susceptible molars
  • Caries prevention in pediatric dentistry
  • Caries prophylaxis in elevated-risk groups (xerostomia, diabetes, oncology patients, orthodontic patients)
  • Root caries in older adults

Clinical implications

Distinguishing active from arrested lesions is clinically important. Arrested lesions are brown, hard, and do not require intervention. Active lesions are white, chalky, soft, and progressive. The ICDAS system provides a standardized framework for this classification. In patients with xerostomia, caries risk is substantially elevated, and relevant guidelines recommend intensified fluoride use and saliva substitution.

Mechanisms

Caries development proceeds through stages: biofilm accumulation, acid production from bacterial metabolism, pH drop, demineralization of hydroxyapatite crystals in enamel, remineralization via saliva, and, when the balance tips, net mineral loss progressing to cavitation. The hydroxyapatite crystals in enamel exist in constant dynamic exchange with the surrounding oral environment.

Classification

The International Caries Detection and Assessment System (ICDAS), developed by an international consortium of caries researchers, provides a standardized, seven-point scale for classifying caries severity from sound tooth structure to extensive cavitation. Since its introduction, ICDAS has evolved into the broader International Caries Classification and Management System (ICCMS) and, more recently, CariesCare International, extending detection and classification into a structured framework for personalized caries management.

International guidelines

  • DGZ / DGZMK: S3 clinical guideline on caries prevention in permanent teeth, Version 2.0, AWMF registry number 083-021, valid until January 2030
  • DGKiZ / DGZ / DGZMK: S3 clinical guideline on fissure and pit sealing, AWMF registry number 083-002, 2024
  • EAPD: Guidelines on prevention of early childhood caries
  • WHO: Guideline on sugars intake for adults and children, 2015
  • American Dental Association: Evidence-based clinical practice guideline on nonrestorative treatments for carious lesions, 2018

Evidence summary

What current evidence supports

  • Caries results from the interaction of cariogenic biofilm, fermentable carbohydrates, a susceptible tooth surface, and time, not from sugar exposure alone
  • Frequency of sugar exposure is a stronger predictor of caries risk than total sugar intake
  • Early, non-cavitated lesions can remineralize; cavitated lesions require restorative treatment
  • Global Burden of Disease 2021 data estimate untreated caries in permanent teeth at approximately 27.5 percent age-standardized global prevalence, affecting more than 2 billion people

Why this matters

Because caries is dynamic rather than inevitable, early changes can often be managed before permanent tooth structure is lost. Understanding this process shifts the clinical focus from repairing cavities to preserving healthy tooth structure in the first place.

What remains uncertain

  • The precise individual threshold at which demineralization becomes irreversible, which varies with enamel composition, fluoride exposure, and saliva quality
  • The relative contribution of specific bacterial species versus overall biofilm ecology in individual caries risk
  • How consistently ecological, non-selective prevention strategies outperform targeted antibacterial approaches across different risk groups

DGZ and DGZMK (2025), in the German S3 clinical guideline on caries prevention in permanent teeth, screened over 1,100 publications and incorporated more than 230 studies into their evidence assessment.

Pitts, Zero, Marsh, et al. (2017), in Nature Reviews Disease Primers, published a comprehensive, widely cited overview of caries etiology, epidemiology, and prevention.

Ismail, Sohn, Tellez, et al. (2007), in Community Dentistry and Oral Epidemiology, introduced the International Caries Detection and Assessment System (ICDAS), now the internationally recognized standard for caries classification.

Slayton, Urquhart, Araujo, et al. (2018), in the American Dental Association's evidence-based clinical practice guideline, reviewed nonrestorative treatments for carious lesions, providing an independent international counterpart to the German S3 guideline.

A 2025 analysis of Global Burden of Disease 2021 data, published in BMC Oral Health, estimated the global age-standardized prevalence of untreated caries in permanent teeth at approximately 27.5 percent, corresponding to more than 2 billion cases worldwide.

Sources

Guidelines:
📋 DGZ / DGZMK: S3 Clinical Guideline on Caries Prevention in Permanent Teeth, AWMF 083-021, Version 2.0, valid until January 2030.
📋 DGKiZ / DGZ / DGZMK: S3 Clinical Guideline on Fissure and Pit Sealing, AWMF 083-002, 2024.
📋 World Health Organization (2015): Guideline: Sugars intake for adults and children. Geneva: WHO.
📋 American Dental Association (Slayton RL, Urquhart O, Araujo MWB, et al., 2018): Evidence-based clinical practice guideline on nonrestorative treatments for carious lesions. Journal of the American Dental Association, 149(10), 837-849.

Reviews and classification systems:
📚 Pitts NB, Zero DT, Marsh PD, Ekstrand K, Weintraub JA, Ramos-Gomez F, Tagami J, Twetman S, Tsakos G, Ismail A (2017): Dental caries. Nature Reviews Disease Primers, 3, Article 17030.
📚 Ismail AI, Sohn W, Tellez M, Amaya A, Sen A, Hasson H, Pitts NB (2007): The International Caries Detection and Assessment System (ICDAS): an integrated system for measuring dental caries. Community Dentistry and Oral Epidemiology, 35(3), 170-178.

Epidemiology:
📚 Global, regional, and national caries of permanent teeth incidence, prevalence, and disability-adjusted life years, 1990-2021: analysis for the Global Burden of Disease Study (2025). BMC Oral Health.

📚 Cochrane Oral Health

PubMed / NCBI: pubmed.ncbi.nlm.nih.gov
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The KEERN Lexicon provides evidence-based educational information about oral health. It is intended to support, not replace, individual advice from a dentist, physician, or pharmacist. Diagnosis and treatment decisions should always be based on a personal clinical assessment.