Slides (PDF) · Student tasks · Български
Set aside about 15 minutes to read and reflect. The text follows the presentation “Epidemiology of dental diseases” and applies the measures of frequency from Class 8 to oral disease. Afterwards you should be able to calculate and interpret DMFT, SiC, the Care Index and Dean’s Community Fluorosis Index, explain why WHO uses index ages and a pathfinder sample, describe the burden of oral diseases worldwide and in Bulgaria, and link the main risk factors to specific diseases.
From measures of frequency to indices
The measures of Class 8 reappear in dental form. The share of people with untreated caries (D > 0) or of adults with a pocket of 6 mm or more is a prevalence; DMFT > 0 is the prevalence of caries experience. The share of caries-free children who develop caries within three years is a cumulative incidence; new carious surfaces per 100 person-years is an incidence rate; and a mean index value, such as mean DMFT, describes severity. Caries experience is cumulative: once affected, a tooth stays D, M or F, so mean DMFT describes the accumulated experience on the day of examination, and the DMFT increment shows newly accumulated experience. Every index needs three specifications: age, diagnostic threshold and examination protocol.
An index is a standardised numerical scale for a condition in a population. A good index is valid, reliable, simple and quick enough for field use, quantitative, sensitive to change and acceptable to those examined. Before a survey, examiners are calibrated: they assess the same subjects and their agreement is expressed as Cohen’s kappa, usually with a threshold of κ ≥ 0.60. An index does not replace the clinical diagnosis and treatment plan.
Caries indices
DMFT counts the permanent teeth that are decayed (D), missing because of caries (M) or filled (F) — 0 to 32, since WHO counts third molars. DMFS counts surfaces (up to 148), and dmft counts primary teeth (0–20). A tooth is counted once — a filling with secondary caries is D — and sealants, crowns and bridges placed for non-carious reasons and implants are not counted. Under the WHO rule for M, only teeth extracted because of caries count under the age of 30; from 30 years, all missing teeth count, so in adults M is not a pure measure of caries. DMFT has limitations: it has no denominator of teeth at risk (so it is always reported by age), D, M and F have equal weight, M and F depend on the dentist’s decisions, and DMFT = 0 does not mean caries-free if initial lesions are not recorded.
Means can hide polarisation. In a class of 12 twelve-year-olds with DMFT 0, 0, 0, 0, 1, 1, 2, 2, 3, 4, 5 and 7, the mean DMFT is 2.08 — below the old goal of 3 — and two thirds have caries experience. But the Significant Caries Index (SiC), the mean DMFT of the third with the highest caries experience (Bratthall, 2000), is 4.75. The Care Index (100 × ΣF / ΣDMFT) is 56%, and 40% of the caries experience is untreated.
ICDAS treats caries as a process rather than a hole, with codes from 0 (sound) through 1–2 (visual changes in enamel), 3 (localised enamel breakdown) and 4 (dark shadow from dentine) to 5–6 (distinct cavities with visible dentine) (Ismail et al., 2007). The D1 threshold includes initial enamel lesions; D3 includes only lesions into dentine. At D1, prevalence and DMFT are higher, so comparisons between countries and years are valid only with the same threshold and protocol.
Periodontal, hygiene and fluorosis indices
The historical CPITN (Ainamo et al., 1982) coded the worst finding in each of six sextants — 0 healthy, 1 bleeding, 2 calculus, 3 a pocket of 4–5 mm, 4 a pocket of 6 mm or more — and linked each code to a treatment need. The modified CPI of WHO (2013) records bleeding on all teeth present, and from age 15 pockets (0, 4–5 mm, ≥ 6 mm) and loss of attachment by sextant. Severe periodontal disease in WHO and GBD estimates means a pocket of 6 mm or more, CPI code 4 or loss of attachment over 6 mm.
The Plaque Index (Silness & Löe, 1964) and the Gingival Index (Löe & Silness, 1963) score six index teeth from 0 to 3; the OHI-S (Greene & Vermillion, 1964) adds a debris and a calculus score on six surfaces, giving a range of 0–6 (up to 1.2 good, 1.3–3.0 fair, above 3.0 poor hygiene).
Dean’s fluorosis index classifies each person, on the two most affected teeth, as normal, questionable, very mild, mild, moderate or severe. The Community Fluorosis Index weights these categories 0, 0.5, 1, 2, 3 and 4 and averages them. By Dean’s historical bands, a CFI of 0.4–0.6 is borderline and above 0.6 a public health problem. These weights are not the WHO codes (0–5).
The WHO survey methodology
The WHO manual Oral Health Surveys: Basic Methods (5th edition, 2013) standardises surveys through index ages: 5 years (primary teeth, school entry), 12 years — the global indicator age, the last age easily reached through schools, when most permanent teeth except third molars have usually erupted — 15 years, 35–44 years (the standard adult group) and 65–74 years. The pathfinder survey is a stratified cluster sample covering subgroups with different disease levels (urban and rural, regions), with 25–50 people per age group at each site — for example, 12 sites × 25 people = 300 for one age. Site selection determines generalisability; this is not a national probability sample. A single form, codes, the WHO probe, training, calibration and repeat examinations make the data comparable.
Goals have evolved: DMFT ≤ 3 in 12-year-olds by 2000 (FDI/WHO), reached in many countries in the 1990s; Bratthall’s proposed SiC < 3 by 2015, which turned attention to the most affected third; and the WHO resolution on oral health (2021), the global strategy (2022) and the Global Oral Health Action Plan 2023–2030, which put oral health into non-communicable disease programmes and universal health coverage. The goal shifts from “mean DMFT below 3” to equal access to prevention and treatment for all groups.
The burden: the world and Bulgaria
Oral diseases are the most widespread diseases of humankind. According to the WHO Global Oral Health Status Report (2022), based on GBD 2019, about 3.5 billion people are affected — roughly a billion more than the cases of the five main non-communicable diseases combined. Untreated caries of permanent teeth affects about 2 billion people (28.7% of those aged 5+), untreated caries of primary teeth 514 million children (42.7% of those aged 1–9), severe periodontal disease about 1 billion (18.8%) and edentulism 350 million (6.8%); the last two figures are age-standardised. Cases have grown by more than a billion since 1990, mainly because of population growth and ageing.
In Bulgaria (WHO country profile, 2022), untreated caries affects 48.1% of children aged 1–9 (European Region 39.6%, world 42.7%) and 38.2% of people aged 5+ (Region 33.6%, world 28.7%); these untreated-caries indicators are computed the same way in all three sources, so they can be compared. Severe periodontal disease affects 13.9% of people aged 15+ and edentulism 13.5% of those aged 20+. There were 455 new cases of lip and oral cavity cancer in 2020 (3.3 per 100,000, age-standardised); sugar availability was 74.4 g per person per day; 39.4% of people aged 15+ used tobacco (age-standardised); and there were 14.0 dentists per 10,000 population.
Bulgarian studies show who carries the burden. Among 12-year-olds in Plovdiv, mean DMFT was 1.57 in the city and 2.92 in the villages, and 38.4% vs 17.5% were caries-free (Onov & Beltcheva, 2020). Among 18-year-olds in two municipalities, mean DMFT was 7.48, of which untreated decay (D) was about 52% (Kondeva et al., 2026).