In general, there are two types of Dental indices.
The first type of index measures the ‘number’ or ‘proportion ‘ of people in a population with or without a specific condition at a specific point in time or interval of time.
The send type of Dental index measures the ‘number of people affected’ and the ‘severity’ of a specific condition at a specific time or interval of time.
1.Based upon the direction in which their scores can fluctuate:
An index that measures conditions whose scores will not decrease on subsequent examinations. Eg: DMFT index.
An index that measures conditions that can increase or decrease on subsequent examinations. Eg: Loe and Silness gingival index.
2.Depending upon the extent to which areas of oral cavity are measured
▪️Full mouth indices:
These indices measure the patient’s entire periodontium or dentition. Eg: Russell’s Periodontal Index
These indices measure only a representative sample of the dental apparatus. Eg: Greene and Vermillion’s Oral Hygiene index – Simplified
3.Indices may be classified under certain general categories according to the entity which they measure
The ‘D’ (decay) portion of the DMFT index best exemplifies a disease index.
The indices measuring gingival/sulcular bleeding are essentially symptom indices.
The ‘F’ (filled) portion of the DMFT index best exemplifies a treatment index.
4.Dental indices can also be classified under special categories as,
An index that measures the presence or absence of a condition. Eg: Silness and Loe Plaque Index
Am index that measures all the evidence of a condition, past and present. Eg:DMFT index for dental caries.
Textbook of Public Health Dentistry – Soben Peter 6th edition.