The DMFT (Decayed, Missing, Filled Teeth) index, introduced by Klein, Palmer and Knutson in 1938, is the universal yardstick for measuring dental caries experience in permanent dentition. It is the WHO-recommended index for oral health surveys and forms the basis of every Indian National Oral Health Survey (NOHS) conducted by the Dental Council of India.

For primary dentition, lowercase dmft is used. DMFS extends the count to tooth surfaces — usually 5 surfaces for posteriors and 4 for anteriors — giving 128 total surfaces in a full adult dentition (excluding third molars).

• Very low: < 2.6
• Low: 2.7 – 4.4
• Moderate: 4.5 – 6.5
• High: 6.6 – 13.9
• Very high: ≥ 14.0

India's mean DMFT in the 35–44 age group hovers around 5.5 (NOHS 2003), placing the country in the moderate band — but with wide rural-urban variation.

• A tooth with caries AND a restoration counts only once — as D (decay takes precedence).
• Teeth lost to trauma, orthodontic extraction, or periodontal disease are NOT counted as M.
• Crowns placed for caries reasons = F. Crowns placed for fracture = not counted.
• Third molars conventionally excluded unless fully erupted and surveyed.
• Sealants on sound teeth are NOT counted as F.

DMFT is faster and sufficient for population screening. DMFS is more sensitive to early carious change and is preferred for longitudinal studies, MDS theses, and clinical trials of fluoride or sealant programmes. For routine clinic recall in India, DMFT alone is generally adequate.