Tooth decay (dental caries) is one of the most common oral diseases in humans. The World Health Organization (WHO) once ranked it as the third most significant disease affecting human health, following only cancer and cardiovascular diseases. Based on professional medical knowledge, this article clearly and concisely explains the formation mechanism of tooth decay from four aspects: etiology, progression, clinical manifestations, and preventive measures, helping readers establish a scientific understanding of prevention and treatment.

1. The Four Key Factors of Tooth Decay (The Four-Factor Theory)

The widely accepted etiology of dental caries in modern dentistry is the Four-Factor Theory proposed by Newbrun in 1976, which states that tooth decay results from the combined action of bacteria, diet, host (teeth and saliva), and time.

Bacterial Factors
Cariogenic bacteria (primarily Streptococcus mutans, Lactobacillus, and Actinomyces) form dental plaque biofilm on tooth surfaces. These bacteria metabolize sugars to produce acids (e.g., lactic acid), which demineralize tooth enamel. S. mutans is highly acidogenic and initiates decay, while Lactobacillus accelerates progression.

Dietary Factors
Carbohydrates (especially sucrose and refined sugars) are the primary energy source for cariogenic bacteria. Bacterial metabolism of sugars not only produces acid but also synthesizes extracellular polysaccharides that enhance plaque adhesion. The rise in caries prevalence in China over the past decade correlates directly with increased consumption of sugary foods.

Host Factors
These include tooth morphology (deep pits and fissures are more susceptible), mineralization level (poorly developed enamel has lower resistance), and saliva function. Saliva helps cleanse the mouth, inhibit bacteria, neutralize acids, and promote remineralization. Reduced saliva flow (e.g., in xerostomia or radiotherapy patients) significantly increases caries risk.

Time Factor
Dental caries is a chronic, progressive disease. It typically takes 1.5–2 years from initial demineralization to cavity formation. All four factors must interact over an extended period for decay to occur.

2. The Pathological Process of Tooth Decay

Tooth decay occurs when the balance between demineralization and remineralization is disrupted:

Enamel Stage
Acids from plaque dissolve hydroxyapatite crystals in enamel, initially appearing as white chalky spots (demineralization). As demineralization progresses, microporosities form, allowing bacterial invasion and cavity formation.

Dentin Stage
Once decay penetrates the enamel into dentin, bacterial proteolytic enzymes break down collagen fibers (due to dentin’s higher organic content), creating an "undermined" cavity. Symptoms like temperature sensitivity may occur.

Pulp Infection Stage
When decay nears the pulp, bacterial toxins cause pulpitis, leading to spontaneous or nighttime pain. Further progression may result in periapical abscesses or jaw infections.

Table: Characteristics of the Three Stages of Tooth Decay

3. Clinical Manifestations and Risks of Tooth Decay

Symptoms vary with progression:

Early stage: Dull white or brown spots on teeth, no discomfort

Moderate stage: Visible cavities, sensitivity to hot/cold/sweet foods (pain subsides after stimulus removal)

Late stage: Spontaneous pain (pulpitis), chewing difficulty, possible facial swelling (abscess)

Untreated complications include:

Severe tooth structure loss, eventual tooth loss

Pulpitis, periapical periodontitis, or osteomyelitis

Higher treatment complexity and cost (root canal therapy costs 3–5× more than early fillings)

Systemic health risks (e.g., increased cardiovascular disease risk)

4. Three Key Strategies for Preventing Tooth Decay

Based on the Four-Factor Theory, effective prevention requires comprehensive measures:

Control Cariogenic Bacteria

Brush twice daily (Bass technique) with fluoride toothpaste

Floss daily to clean interdental areas

Regular dental check-ups and cleanings every 3–6 months

Adjust Dietary Habits

Reduce frequency of sucrose intake (more critical than quantity)

Avoid sticky candies and carbonated drinks

Consume antibacterial foods like cheese and onions; black tea helps maintain oral pH

Strengthen Tooth Resistance

Pit-and-fissure sealants for children (primary molars at 3–4 years, permanent molars at 6–9 years)

Fluoride varnish for high-risk individuals

Treat underlying conditions like xerostomia

Special Note: Infants should avoid "baby bottle caries"—nighttime feeding without oral cleaning or sleeping with a milk bottle can cause severe decay in upper primary incisors.

Conclusion

Tooth decay results from prolonged interaction of multiple factors, with insidious onset and progressive development. Early intervention (at the small cavity stage) significantly reduces treatment difficulty and cost. Establishing proper oral hygiene habits and scheduling regular professional check-ups are key to lifelong dental health.