Which of the following is a substrate-related factor in caries etiology?

• A. Age, fluoride exposure
• B. Oral clearance
• C. Carbohydrate frequency and intake
• D. Tooth morphology

Answer: (C)

Substrate-related factors are about the nutrients in the mouth that bacteria use to produce acid. Fermentable carbohydrates serve as that substrate, and when they’re present in the mouth in frequent, repeated exposures, plaque bacteria metabolize them to acid. This acid lowers the local pH, and when exposure is frequent, there isn’t enough time for remineralization, so demineralization accumulates. That’s why carbohydrate frequency and intake is the best answer—it directly describes the substrate that drives acid production and caries development.

Age and fluoride exposure relate more to host defenses and protective factors—age can influence enamel maturity and behavior, while fluoride enhances remineralization and resistance. Oral clearance affects how long sugars stay in the mouth, which modulates exposure but does not define the substrate itself. Tooth morphology influences where plaque accumulates, not the substrate input.