Dental Public Health
What this domain tests
Measurement of oral disease, prevention at community level, study design and interpretation, and the planning of oral health services.
Core rules
- Indices: DMFT/dmft counts decayed, missing and filled teeth; DMFS counts surfaces. The Community Periodontal Index of Treatment Needs (CPITN) uses sextants and scores of 0–4. Plaque and gingival indices quantify oral hygiene and inflammation.
- Epidemiological measures: prevalence is the proportion affected at a point in time; incidence is new cases over a period. Sensitivity detects true positives; specificity detects true negatives; positive predictive value depends on prevalence.
- Study designs: cross-sectional for prevalence, cohort for incidence and risk, case-control for rare outcomes, randomised controlled trials for causation.
- Prevention: community water fluoridation at about 1 ppm is the most cost-effective population measure; fluoride varnish and toothbrushing programmes are targeted measures; the common risk factor approach links oral disease to diet, tobacco and alcohol.
- Service planning uses the basic package of oral care and the principle of progressive universalism - proportionate universalism targeted at need.
Worked example
A screening test for caries has sensitivity 90% and specificity 80% in a population with 20% prevalence. Reasoning: most positive results will still include many false positives because prevalence is modest; the positive predictive value is therefore lower than sensitivity alone suggests. Screening programmes must be judged on predictive value in the target population, not on test accuracy alone.
Traps
- Confusing incidence with prevalence in cohort studies.
- Assuming high sensitivity guarantees a high positive predictive value.
- Describing water fluoridation as a targeted individual measure.