# DMF Index > DMF index notes for BDS Community Dentistry: Klein, Palmer and Knutson 1938, WHO codes, DMFT versus DMFS, primary tooth def index, SiC index and limitations. - Canonical URL: https://prepelephant.com/topics/bds/community-dentistry/dmf-index - Exam / course: BDS · Subject: Community Dentistry - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "DMF Index", PrepElephant, https://prepelephant.com/topics/bds/community-dentistry/dmf-index ## Direct answer Klein, Palmer and Knutson gave dental public health its workhorse in 1938: the DMF index counts permanent teeth that are Decayed, Missing or Filled due to caries, so DMFT of 3 means three teeth affected by the caries process in any of its treated or untreated forms. It is an irreversible, cumulative index — a tooth once counted stays counted — which is precisely why it suits surveys and why it cannot measure gum health or treatment quality. For primary teeth the lowercase def index is used, and the surface-counted DMFS version detects change more sensitively than the tooth-counted DMFT. ## What you must remember - Origin: Klein, Palmer and Knutson, 1938, for permanent teeth; Gruebbel proposed the def index for primary teeth in 1944, where e stands for indicated for extraction, since a missing primary tooth may simply have exfoliated. - WHO codes for crown status on the oral health assessment form: 0 sound, 1 decayed, 2 filled with decay, 3 filled without decay, 4 missing due to caries, 5 missing for other reasons, 6 fissure sealant, 7 bridge abutment or special crown, 8 unerupted, 9 not recorded. - DMFT counts teeth; DMFS counts surfaces (five surfaces per anterior tooth, eight per posterior tooth) and is the more sensitive instrument for detecting small changes. - Interpretation scale for 12-year-olds: DMFT below 1.2 very low, 1.2–2.6 low, 2.7–4.4 moderate, 4.5–6.5 high, above 6.5 very high. - The old WHO/FDI global goal was DMFT of no more than 3 at age 12; the Significant Caries index (Bratthall, 2000) highlights the one-third of a population with the highest DMFT, targeting hidden inequality behind a good mean. - Strengths: simple, quick, universally comparable, valid for irreversible caries experience; limitations: assumes a missing tooth equals a one-surface filling in severity, ignores treatment need, cannot fall, and the M component becomes unreliable in older adults whose teeth were lost to periodontal disease. - Root caries is measured separately, classically with Katz's Root Caries Index, in older age groups. ## Scoring a mouth from code to conclusion Score a 12-year-old boy tooth by tooth, which is how the viva and the survey both actually run. Tooth 16 has an occlusal cavity: code 1, one D. Tooth 26 has an intact amalgam on the occlusal surface: code 3, one F. Tooth 36 was extracted for pain last year: code 4, one M. Tooth 46 carries a fissure sealant: code 6 — not an F, a classic scoring trap. Tooth 38 is unerupted: code 8, excluded from any count. Everything else is sound. His DMFT totals 3, placing him in the moderate band for his age; the untreated component D is 1, so the care index F/(D+F) works out at one-half. Now translate: in a class of forty, if the mean DMFT is 2.1 but the SiC index is 5.8, the classroom mean hides a high-caries third who need targeted care — exactly the inequality argument the SiC index exists to make. Finally, if the same cohort is re-examined at 15 and the mean has risen to 2.9, that rise is genuine disease progression, because the index cannot decline with time. ## Where students slip The recurring mark-losers are coding decisions, not arithmetic. A filled tooth with recurrent caries at the margin is code 2 — it counts once, under D, never under both. A missing tooth in an adult over about 30 is not automatically caries-related; periodontal loss confounds the M component, which is why WHO scoring forces a judgement of reason for loss. A tooth missing because it was extracted for orthodontics or trauma is code 5 and scores nothing. On the primary side, an absent lower central incisor in a six-year-old is almost always exfoliation, not extraction, so it never enters def. And when asked "what does a DMFT of 2 tell you about treatment need?", the honest answer is nothing on its own — a filled tooth and a cavitated tooth both score 1 — a limitation examiners love because it separates reciters from thinkers. ## Frequently asked questions ### Who introduced the DMF index and when? Klein, Palmer and Knutson in 1938 for permanent teeth; Gruebbel adapted it as the def index for primary teeth in 1944. ### What is the difference between DMFT and DMFS? DMFT counts affected teeth while DMFS counts affected surfaces, making DMFS more sensitive to small increments of new disease. ### How does WHO code a fissure-sealed tooth? Code 6 — a sealed tooth is neither decayed nor filled and contributes nothing to the DMF count. ### What is the Significant Caries index? Bratthall's 2000 measure: the mean DMFT of the one-third of the population with the highest DMFT, designed to expose inequality hidden by a favourable population mean. ### Why does DMFT perform poorly in older adults? Because teeth missing past middle age cannot reliably be attributed to caries, periodontal disease being a competing cause of tooth loss.