Preventive Dentistry and Community Dental Public Health
Caries prevention
The Stephan curve shows plaque pH falling below the critical pH (about 5.5 for enamel, 6.2–6.5 for root dentine) after sugar exposure, then recovering with saliva. Frequency of sugar exposure matters more than total amount. Fluoride acts mainly topically: it promotes remineralisation, forms fluorapatite, and inhibits demineralisation - small frequent exposures beat a single large dose. Know the vehicles: toothpaste (1,000–1,500 ppm; higher for high risk), varnish (5% NaF, 22,600 ppm), APF gel, silver diamine fluoride for arresting lesions, and water fluoridation at the optimal concentration (about 0.7 mg/L). Sealants prevent occlusal caries in deep fissures.
Epidemiology and indices
DMFT/dmft counts teeth; DMFS/dmfs counts surfaces - a classic distractor. Dean's index grades fluorosis from questionable to severe. CPI/CPITN records periodontal status by sextant. Distinguish prevalence (all cases at a point in time) from incidence (new cases over time), and know that screening programmes prioritise high sensitivity to avoid missing disease.
Prevention levels and programmes
Primary prevention precedes disease (fluoride, sealants, education), secondary detects and treats early (screening, restorations), tertiary limits disability (rehabilitation, prostheses). Community programmes rest on the Ottawa Charter: healthy public policy, supportive environments, community action, personal skills, reorientation of services. Planning requires a needs assessment, measurable objectives, implementation, and evaluation.
Rule of thumb
When asked why water fluoridation is effective, emphasise the constant low-level topical exposure at the plaque-enamel interface, not systemic incorporation into developing enamel.