Dental Caries: Pathophysiology and Risk Factors

Keyes' three-circle model explaining how a cavity forms, the role of Streptococcus mutans, and why the critical pH of 5.5 is the number to remember.

Caries is a multifactorial infectious disease, and the simplest way to explain it — even to patients — remains the three-circle diagram proposed by Paul Keyes in 1960: for a carious lesion to form, a susceptible host (a tooth with vulnerable enamel), a cariogenic microflora, and a fermentable substrate, typically dietary sugars, must all be present simultaneously. Removing even just one of these three factors interrupts the cariogenic process.

The bacterium most directly involved in initiating the process is Streptococcus mutans, able to adhere to enamel and ferment sugars, producing organic acids as a byproduct of its own metabolism. When plaque pH drops below the critical threshold of 5.5, enamel hydroxyapatite begins demineralizing, releasing calcium and phosphate ions. This process, in its early stages, is reversible: saliva, rich in these same minerals and in fluoride if present, can promote remineralization if the enamel has time to recover between acid attacks.

It's precisely this dynamic balance between demineralization and remineralization that determines whether an early lesion regresses or progresses into a full-blown cavity. Each episode of sugar intake causes a drop in pH lasting roughly 20-30 minutes; the frequency of meals and snacks therefore matters at least as much as the total amount of sugar consumed over the day, because it determines how many "acid attacks" the enamel has to withstand.

Individual caries risk factors include, besides diet, poor oral hygiene, reduced salivary flow (xerostomia), the presence of orthodontic appliances or restorations that create new plaque-retention areas, and a prior history of caries, which remains one of the most reliable predictors of future risk. Assessing individual cariogenic risk, not just diagnosing the lesion already present, should guide recall frequency and the intensity of preventive measures proposed to each patient.

On Oralzon you'll find sealants, direct restorative materials, fluoride varnishes and gels to catch and manage the cariogenic process at every stage, from primary prevention to treating an established lesion.