DMFT and DMFS Indices (with DEF for Primary Dentition)

Core Review

DMFT Index: Definitions

The DMFT index was developed by Klein, Palmer, and Knutson (1938) for the U.S. Public Health Service. It counts the number of decayed, missing, and filled permanent teeth in a population:

D = Decayed: Teeth with clinically evident cavitated carious lesions. This includes:

• Teeth with a cavity that catches a #23 explorer (though tactile detection with an explorer is no longer universally recommended due to risk of cavitating non-cavitated lesions)
• Teeth with recurrent (secondary) caries around an existing restoration
• Teeth with both a restoration and a carious lesion are scored as D (the decay takes priority)

Teeth NOT counted as D:

• Incipient lesions (white spot lesions, non-cavitated) — these are not counted in DMFT
• Stained or discolored pits and fissures that do not catch an explorer and show no softness
• Teeth with arrested caries

M = Missing due to caries: Teeth that have been extracted because of caries. This is the trickiest component. Rule: ONLY count teeth missing due to caries. Do NOT count:

• Teeth missing due to orthodontic treatment
• Teeth missing due to trauma
• Teeth missing due to periodontal disease
• Congenitally missing teeth
• Unerupted teeth
• Teeth extracted for prosthetic reasons (e.g., full-mouth extraction for dentures)

In practice, distinguishing cause of tooth loss in adults is difficult — missing teeth are presumed to be due to caries unless there is a clear alternative explanation.

F = Filled: Teeth with one or more permanent restorations AND no evidence of current decay. If a filled tooth has recurrent decay, it is scored as D (not F). Teeth with crowns placed due to caries are scored as F.

T = Teeth: The denominator is permanent teeth (maximum 28, excluding third molars in most surveys; some surveys include third molars for a maximum of 32).

A tooth can only receive ONE score (D, M, or F). The hierarchy: D > M > F. If a tooth has both a filling and decay, score D.

DMFS Index: The Surface-Level System

DMFS counts affected surfaces rather than whole teeth, providing greater sensitivity for detecting caries experience. Each tooth is divided into surfaces:

• Posterior teeth (molars and premolars): 5 surfaces — occlusal, mesial, distal, buccal, lingual
• Anterior teeth (incisors and canines): 4 surfaces — incisal, mesial, distal, buccal, lingual (some systems count incisal edge as a single surface, resulting in 4 surfaces per anterior tooth)

Total surface count: 128 surfaces for 28 teeth (16 posterior × 5 surfaces = 80; 12 anterior × 4 surfaces = 48; total = 128). With third molars: 148 surfaces.

A surface is counted as D, M, or F under the same criteria as teeth, but:

• A filled tooth may have only 1, 2, or 3 surfaces filled — you count the specific involved surfaces
• A missing tooth causes loss of all its surfaces from the denominator (4 or 5 surfaces, depending on tooth type)
• DMFS is more sensitive to change than DMFT — a multi-surface restoration counts as one F in DMFT but multiple F surfaces in DMFS

DEF Index for Primary Teeth

The DEF index (Gruebbel, 1944) is the primary dentition analog of DMFS:

d = decayed (lowercase): Primary teeth with cavitated carious lesions. Same criteria as D in permanent teeth.

e = indicated for extraction: Primary teeth for which extraction is the indicated treatment due to extensive caries. This replaces "missing" because primary teeth may be missing due to normal exfoliation, and it can be difficult to determine whether an already-exfoliated primary tooth was lost early due to caries.

f = filled: Primary teeth with restorations and no current decay.

The DEF index is always computed per child (def per child), not per tooth count, because children have varying numbers of primary teeth depending on their stage of exfoliation and eruption. The defs index (surfaces) follows the same surface-counting rules as DMFS.

Worked Examples

Example 1 — DMFT calculation: A 14-year-old patient presents with:

• Tooth #3: occlusal caries (cavitated) → D
• Tooth #14: occlusal amalgam, no recurrent decay → F
• Tooth #19: MOD amalgam with recurrent mesial caries → D (decay takes priority over filling)
• Tooth #30: missing (extracted due to caries) → M
• All other teeth (excluding third molars): sound

DMFT = 4 (D = 2 [teeth #3 and #19], M = 1 [tooth #30], F = 1 [tooth #14]) DMFT = 4/28 (assuming 28 teeth assessed, third molars excluded)

Example 2 — DMFS calculation (same patient):

• Tooth #3: occlusal surface decayed → 1 D surface
• Tooth #14: occlusal surface filled → 1 F surface
• Tooth #19: MOD restoration with mesial recurrent decay → The mesial surface is D; the occlusal and distal surfaces are F → 1 D + 2 F surfaces
• Tooth #30: missing due to caries → 5 surfaces (posterior tooth)

DMFS = D surfaces (1 [tooth #3 O] + 1 [tooth #19 M]) = 2 D surfaces; M surfaces = 5; F surfaces (1 [tooth #14 O] + 2 [tooth #19 O, D]) = 3 F surfaces Total DMFS = 2 + 5 + 3 = 10

Example 3 — DEF calculation: A 4-year-old child with 20 primary teeth:

• Tooth #B (maxillary right primary first molar): occlusal caries → d
• Tooth #I (mandibular right primary first molar): grossly carious to the furcation, non-restorable → e
• Tooth #L (mandibular right primary second molar): occlusal amalgam, intact → f

def = d(1) + e(1) + f(1) = 3 defs = 1d (O surface) + 5e (all surfaces of a posterior primary tooth) + 1f (O surface) = 7

Limitations of DMFT/DMFS/def

1. Does not distinguish severity: A one-surface occlusal restoration and a full-coverage crown both count as one F tooth in DMFT. DMFS partially addresses this.
2. Irreversibility: Once a tooth is scored D, M, or F, it can never return to "sound." If a decayed tooth is restored, DMFT does not decrease — it converts from D to F (same count, different category). This means DMFT can only stay the same or increase over time, making it a measure of cumulative caries experience, not current disease activity.
3. Missing tooth ambiguity: Cannot always determine why a tooth was extracted in adults. Missing teeth are often presumed due to caries, which may overestimate the M component.
4. Does not capture non-cavitated lesions: White spot lesions and incipient caries, which may be reversible with fluoride and behavioral changes, are invisible to DMFT.
5. Equally weights all teeth: Losing a first molar (critical for occlusion) counts the same as losing a wisdom tooth in DMFT.
6. Does not account for treated vs. untreated decay: A population with DMFT = 4 comprising D=4 has untreated disease, while DMFT = 4 comprising F=4 has treated disease — identical scores, vastly different implications.
7. Excludes root caries: DMFT only captures coronal caries. Root caries (common in older adults) requires a separate Root Caries Index (RCI).

Clinical/Board Application

Board-style question: A public health hygienist screens 500 third-graders and finds: 120 teeth with untreated decay (D), 85 teeth extracted due to caries (M), and 340 teeth with fillings and no decay (F). The total of 28 teeth per child was examined (third molars excluded). What is the mean DMFT for this population?

Answer: Total D+M+F = 120 + 85 + 340 = 545. Number of children = 500. Mean DMFT = 545/500 = 1.09.

Common Traps

• Trap: Counting a tooth as both D and F. A tooth with a filling AND recurrent decay is D only.
• Trap: Counting orthodontic extractions or congenitally missing teeth in the M component.
• Trap: Using DMFT to evaluate a recent prevention program. Because DMFT is irreversible and cumulative, a new prevention program will not reduce existing DMFT scores — it will only slow the rate of new D/M/F.
• Trap: Confusing e (extraction indicated) in DEF with missing teeth. The "e" is for teeth still present but non-restorable.