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Stephan Curve — MFDS Part 1 MCQ

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ModeratePhysiologyStephan CurveMFDS Part 1

Following a sucrose rinse, the pH within a patient's plaque biofilm falls from 6.8 to 5.2 within one minute and then returns towards baseline over the next 30 minutes. Which physiological process is represented by this Stephan curve?

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Correct answer: A — Rapid plaque acidification followed by slower salivary buffering and clearance

The correct answer is A. The Stephan curve records the change in plaque biofilm pH after exposure to fermentable carbohydrate. Oral bacteria rapidly metabolise sugar and produce acids, causing plaque pH to fall within minutes into a range favouring enamel demineralisation. Plaque pH then recovers more slowly as saliva buffers and washes away acids and the available sugar is depleted. Repeated sugar exposures prolong the cumulative time at low pH. The curve does not principally represent a change in salivary flow, systemic blood glucose or gingival crevicular fluid. Enamel demineralisation is favoured while plaque pH is sufficiently low; it does not necessarily continue once pH has recovered and conditions again favour remineralisation.

Reference: Department of Health and Social Care, Welsh Government, Department of Health Northern Ireland and NHS England. Delivering Better Oral Health: an evidence-based toolkit for prevention, Chapter 10: Healthier eating, section 'Sugar consumption and dental caries'. Updated 2025. https://www.gov.uk/government/publications/delivering-better-oral-health-an-evidence-based-toolkit-for-prevention/chapter-10-healthier-eating