The DMFT index was developed by Klein, Palmer and Knutson during a study of the dental condition and the need of children's treatment in elementary schools in Hagerstown, Maryland, USA, in 1935. It has been the most important index in the dental researches to quantify the prevalence of tooth decay (Katz et.al., 1997).
The caries experience (past and present) indicates the teeth damages and treatments received before by the count of teeth decays or natural history of the dental caries, which it expresses as decayed, missing and filled teeth (DMFT index) or decayed, missing and filled surfaces (DMFS index), both indexes express numerically the caries prevalence. The sum of these three points is the index (Sánchez & Sáenz, 1998; World Health Organization [WHO], 1997; WHO, 2011b).
For better analysis and interpretation it will be separate in each component and express it by percentage or mean. This is important to compare populations.
To obtain DMFT index in population, WHO recommended the next age groups: 5-6, 12, 15, 18, 35-44, 60-74 years. The index at 12 age is used to compare the oral health between countries.
The scientific evidences suggest that this is the most sensitive indicator to predict future risk, since if a subject does not establish the biochemical balance between demineralization-remineralization it will develop more caries lesions.
World Health Organization clearly established the methodology to obtain the index in the Oral Health Surveys. As increase the lesions number, increases the risk to develop caries, even in filled teeth (WHO, 1997).
The subjects are examined in the clinic area with the aid of a dental mouth mirror and periodontal probe, type E. The presence of caries was recorded using WHO's DMFS criteria.
For permanent dentition use the next codes:
2 Filled with caries
3 Filled without caries
4 Missing by caries
5 Missing by other reason
6 Sealant, coat
7 Bridge or crown
8 Non eruption
0: showing no evidence of either treated or untreated caries. A crown may have defects and still be recorded as 0. Defects that can be disregarded include white spots; discolored or rough spots that are not soft; stained enamel pits or fissures; dark, shiny, hard, pitted areas of moderate to severe fluorosis; or abraded areas.
1: indicates a tooth with caries. A tooth or root with a definite cavity, undermined enamel, or detectably softened or leathery area of enamel or cementum can be designated a 1. A tooth with a temporary filling, and teeth that are sealed but decayed, are also termed 1.
2: Filled teeth, with additional decay. No distinction is made between primary caries which is not associated with a previous filling, and secondary caries, adjacent to an existing restoration.
3: indicates a filled tooth with no decay. If a tooth has been crowned because of previous decay, that tooth is judged a 3. When a tooth has been crowned for another reason such as aesthetics or for use as a bridge abutment, a 7 is used.
4: indicates a tooth that is missing as a result of caries. When primary teeth are missing, the score should be used only if the tooth is missing prematurely. Primary teeth missing because of normal exfoliation need no recording.
5: a permanent tooth missing for any other reason than decay is given a 5. Examples are teeth extracted for orthodontics or periodontal disease, teeth that are congenitally missing, or teeth missing by trauma.
6: is assigned to teeth on which sealants have been placed. Teeth on which the occlusal fissure has been enlarged and a composite material placed should also be termed 6.
7: is used to indicate that the tooth is part of a fixed bridge. When a tooth has been crowned for a reason other than decay, this code is also used. Teeth that have veneers or laminates covering the facial surface are also termed 7 when there is no evidence of caries or restoration. A 7 is also used to indicate a root replaced by an implant. Teeth that have been replaced by bridge pontics are scored 4 or 5; their roots are scored 9.
8: this code is used for a space with an unerupted permanent tooth where no primary tooth is present. The category does not include missing teeth.
9: Erupted teeth that cannot be examined — because of orthodontic bands, for example — are scored a 9.
The "D" of DMFT refers to all teeth with codes 1 and 2. The "M" applies to teeth scored 4 in subjects under age 30, and teeth scored 4 or 5 in subjects over age 30. The "F" refers to teeth with code 3. Those teeth coded 6, 7, 8, 9, or T are not included in DMFT calculations.
The parameters to reference are:
Low 1 to 3 caries lesions
Moderate 4 to 6 caries lesions
High 7 to 9 caries lesions
Higher 10 or mores caries lesions (Fig. 1).
Fig. 1. Obtained DMFS index.
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