37.2 Oral Health Epidemiology and Indices

Measuring Disease in Populations

"Dental public health" is a named Paper B blueprint topic, and Preparing for Practice outcome 1.1.12 requires registrants to "explain the principles of epidemiology and critically evaluate their application to patient management". Outcome 2.1 requires discussion of demographic and social trends, UK and international oral health trends, determinants of health, inequalities, and the ways in which these are measured.

Prevalence and Incidence

• Prevalence is the proportion of a population with a condition at a point in time. It is what a cross-sectional survey measures, and it reflects both how often disease occurs and how long it lasts.
• Incidence is the number of new cases arising in a defined population over a defined period. It requires longitudinal follow-up, which is why cohort studies rather than surveys measure it.

Caries prevalence in a population of 12-year-olds tells you how much disease has accumulated; caries increment over two years tells you how fast it is arising. Preventive programmes are evaluated on increment, not prevalence.

Caries Indices

DMFT has well-known limitations. It weights a tooth lost to trauma the same as one lost to caries, gives equal weight to a small filling and a full-coverage crown, and cannot distinguish an arrested white spot from sound enamel. It also cannot be reversed: a remineralised lesion still counts. This is why the Significant Caries Index and ICDAS were developed.

Periodontal and Other Indices

• BPE in the UK, derived from the WHO CPITN, is a screening index rather than an epidemiological measure of attachment loss.
• Plaque and bleeding indices — Silness and Löe plaque index, Löe and Silness gingival index, and the full-mouth plaque and bleeding scores used as endpoints in the British Society of Periodontology framework.
• IOTN measures normative orthodontic treatment need and has both a dental health component and an aesthetic component.
• BEWE — the Basic Erosive Wear Examination — scores the worst affected surface in each sextant from 0 to 3 and sums them to stratify erosive risk.
• OHIP-14 measures oral health-related quality of life, capturing the functional, social and psychological impact that clinical indices miss.

UK Surveys

The UK has an unusually strong dental epidemiological tradition. The Adult Dental Health Survey and the Child Dental Health Survey are decennial national surveys, and routine epidemiological surveys of children are carried out by local authorities and national public health bodies. These are the data sources behind statements about the social gradient in caries, the decline in total tooth loss, and the persistent concentration of disease in a minority of children.

Normative Versus Perceived Need

• Normative need is need as defined by a professional, for example an IOTN dental health component of 4 or a DMFT above a threshold.
• Perceived (felt) need is what the patient believes they need.
• Expressed need is demand: the felt need that is actually acted upon by seeking care.
• Unmet need is normative need that is never expressed.

The gap between these categories is the reason that clinical indices alone cannot plan a service. A community may have high normative need and low expressed need because of access barriers, and an intervention aimed at supply will fail unless it addresses that gap.

Exam link. A question giving a mean DMFT of 0.8 in a group of 12-year-olds, with a Significant Caries Index of 2.6, is testing whether you recognise skew. The mean looks reassuring; the SiC shows that the worst-affected third carry more than three times that burden, and targeted prevention is indicated.

Reading the UK Survey Data

Epidemiological indices are examined through the surveys that use them. The Adult Dental Health Survey and the Child Dental Health Survey are the decennial national surveys, supplemented in England by the National Dental Epidemiology Programme oral health surveys of five-year-olds and other age groups, which provide the local-authority-level data that commissioners use. Candidates are expected to know the direction of the long-term trends rather than precise figures: total tooth loss in adults has fallen dramatically over recent decades, the proportion of children who are caries-free has improved, but inequality has widened, so that a small proportion of children carry most of the disease and the burden is concentrated in the most deprived communities.

The examinable limitation of the DMFT index is that it weights all components equally — a filled tooth counts the same as a decayed one — that it is irreversible and cumulative, so it cannot fall or reflect remineralisation, and that it gives no information about lesion activity, severity or the impact on the person. This is why measures of oral health-related quality of life, such as OHIP and OIDP, and measures of normative versus perceived need are used alongside it.