Definition And Classification of Indices
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Definition And Classification of Indices


Community Dentistry


Russell defines index as:

“A numerical value describing the relative status of a population on a graduated scale with definite upper and lower limits, which is designed to permit and facilitate comparison with other populations classified by the same criteria and methods”



1. Based on the direction in which their scores can fluctuate:

  1. Irreversible index: Measures conditions that will not change scores once established cannot decreases in value on subsequent examination, e.g. Dental caries indices, Fluorosis index.
  2. Reversible index: Measures conditions that can be changed and scores can increases or decreased in subsequent examinations, e.g. periodontal indices.

2. Depending on extent to which areas of oral cavity are measures:

  1. Full mouth indices: measure the patient’s entire periodontium or dentition, e.g. Russell’s periodontal index.
  2. Simplified indices: Measure only a representative sample of the dental apparatus, e.g. OHI-S


3. According to the entity which they can measure:

  • Disease index
  • Symptom Index
  • Treatment Index
The D portion of the DMF index best exemplifies the disease index. The index measuring gingival or sulcular bleeding are essentially symptom indices. The F portion of the DMF index best exemplifies a treatment index.


In general there are 2 types of index:

  1. Measures the number or proportions of people in a population with or without a specific condition at a specific point in time or interval of time.

     2.  Measures the number of people affected and the severity of the specific condition at a specific time or interval of time.


Classified under special categories as:

  1. Simple index: Measures presence or absence of a condition, eg. An index that measures the presence of dental plaque without an evaluation of its effect on gingiva
  2. Cumulative index: Measures all the evidence of a condition , past and present , e.g. DMF index for dental caries.


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