Which index is used exclusively for the primary dentition?

Correct answer: C. deft / def

• A. DMFS is likewise a permanent dentition index, scored by surface rather than by tooth.
• B. DMFT, written in capitals, applies to the PERMANENT dentition.
• C. CORRECT. The deft index (decayed, extracted, filled teeth) is used only for PRIMARY teeth, and the lower case letters are the convention that signals this. The letter E is used for EXTRACTED rather than MISSING, because a missing primary tooth cannot be reliably attributed to caries — it may simply have exfoliated physiologically.
• D. The Simplified Oral Hygiene Index scores debris and calculus on six selected surfaces and is not a caries index at all.

Note: The distinction rests entirely on the M-versus-E problem. Third molars are conventionally EXCLUDED from DMFT, and both indices are IRREVERSIBLE — the score can never decrease, so they measure cumulative lifetime experience rather than current disease.