Indices in Oral Epidemiology
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Direct answer
An index, epidemiologically, is a graduated numerical expression of a population's disease status, scored by defined criteria — and an ideal one is valid, reliable, objective, sensitive to change and simple enough for field use. The examination-ready battery: DMFT (Klein, Palmer and Knutson, 1938) for caries; OHI-S (Greene and Vermillion, 1964) for hygiene on six scored surfaces; the gingival index of Löe and Silness (1963) and the plaque index of Silness and Löe (1964) — note the mirrored authorship that examiners exploit; Dean's fluorosis index with its community fluorosis index weighting, where a CFI above 0.6 signals public health significance; CPITN and its successor CPI for periodontal status; Katz's root caries index; and the dental aesthetic index for orthodontic need, where a score of 36 or more defines handicapping malocclusion.
What you must remember
- DMFT and its primary-dentition counterpart defs (Gruebbel, 1944): each tooth scores 1 whether it carries an early lesion or gross caries — the acknowledged limitation, alongside the 'M' counting orthodontic extractions as caries and the index conveying no treatment need; DMFS gives finer resolution.
- OHI-S: six surfaces — buccal of 16 and 26, labial of 11 and 31, lingual of 36 and 46 — debris and calculus each scored 0-3, each total divided by 3 (not 6), giving DI-S and CI-S from 0 to 3 and OHI-S up to 6; bands: good 0-1.2, fair 1.3-3.0, poor 3.1-6.0.
- Gingival index (Löe and Silness, 1963): 0-3 per site, anchored on bleeding on probing; scores 0.1-1.0 mild, 1.1-2.0 moderate, 2.1-3.0 severe. Plaque index (Silness and Löe, 1964) scores thickness without disclosing solution — the author-order flip is the classic MCQ.
- CPITN (Ainamo and colleagues, 1982): index teeth in those over 20 scored by sextant, codes 0-4 plus treatment needs — the system WHO used through the fourth edition, criticised for ignoring attachment loss, hence the CPI-plus-LOA replacement.
- Dean's fluorosis index (1934, modified 1942): normal 0, questionable 0.5, very mild 1, mild 2, moderate 3, severe 4; the community fluorosis index = the weighted sum divided by those examined, with 0.4-0.6 borderline and above 0.6 a public health problem.
- Root caries index (Katz, 1972): decayed or filled root lesions divided by root surfaces with gingival recession, times 100.
- Dental aesthetic index (DAI): regression-weighted aesthetic and occlusal measurements into one score; 36 or more defines handicapping malocclusion needing treatment — the cut-off the objective tests quote.
- Modern research criteria: ICDAS (0-6 visual caries codes) gives the graded detection DMFT cannot; useful to name when asked how indices evolve.
Working a score from surface to summary
Score a survey subject to see the arithmetic examiners probe. OHI-S first: debris on 16 buccal scores 2, on 26 buccal 1, on 11 labial 2; debris on 31 labial 1, calculus-free lingual of 36 scores 1, and 46 lingual carries calculus 2. Debris index = (2+1+2)/3 = 1.7; calculus index = (0+1+2)/3 = 1.0; OHI-S = 2.7 — "fair", one decimal from "poor", which immediately argues for hygiene intervention before the survey team leaves the school. Dean next: in a village of 200 examined, 90 score normal (0), 40 questionable (0.5), 40 very mild (1), 20 mild (2) and 10 moderate (3). CFI = (90×0 + 40×0.5 + 40×1 + 20×2 + 10×3) / 200 = 130/200 = 0.65 — above 0.6, a slight public health problem demanding water-supply investigation and defluoridation planning, whereas 0.55 would have kept the village in the borderline watch category. The lesson generalises: indices are only worth memorising because each number, correctly assembled, is a decision.
Where students slip
The flip-flop facts decide marks: the gingival index is Löe and Silness (1963), the plaque index Silness and Löe (1964) — reversed authorship, paired years, endlessly recycled as a matching item. The OHI-S divisor is the arithmetic trap: six surfaces are scored but each index divides by three, and the interpretation bands (1.2/3.0) hang on that half-remembered fact. Dean's weights are the third loss — questionable carries 0.5, not 0 — and the CFI threshold of 0.6 is quoted as 1.6 by candidates who never performed the division. The CPITN-to-CPI transition is the fourth: candidates attach treatment-need codes to CPI, which no longer records them.
Frequently asked questions
Which surfaces and divisor make up the OHI-S?
Buccal of 16 and 26, labial of 11 and 31, lingual of 36 and 46; debris and calculus each averaged over three surfaces (divided by 3), each index 0-3, total OHI-S 0-6.
Who described the gingival and plaque indices?
Gingival index: Löe and Silness, 1963 — scored 0-3 with bleeding as its anchor; plaque index: Silness and Löe, 1964 — scored on thickness without a disclosing agent.
How is the community fluorosis index computed and interpreted?
Each subject is weighted (questionable 0.5, very mild 1, mild 2, moderate 3, severe 4); the weighted sum over those examined gives CFI, where 0.4-0.6 is borderline and above 0.6 a public health problem.
Which index defines handicapping malocclusion?
The dental aesthetic index — a score of 36 or more defines handicapping malocclusion requiring mandatory treatment.