Oral status indicators DMFT and FS-T:reflections on index selection

Schuller AA, Holst D. Oral status indicators DMFT and FS-T: reflections on indexselection. Eur J Oral Sci 2001: 109: 155159. # Eur J Oral Sci, 2001

Oral status in a population has traditionally been described by the DMFT index(decayed, filled, and missing teeth). There seems to be contradicting and confusingevidence in the literature with regard to the usefulness of different indices.Limitations of the DMFT are recognised, and attempts have been made todevelop other indices. Two indices, DMFT and FS-T (filled and sound teeth) havebeen selected for analysis in the present paper. The purpose of this paper is toexamine the relationship between DMFT and FS-T in different populations, andto show consequences of choice of index exemplified in analytical analysis. Datastem from the Trndelag-83 and -94 studies that were follow-up studies of theNorwegian portion of the 1973 International Collaborative Study. Sunflowerscatter plots and regression analyses were used to describe the variation in DMFTand FS-T in different populations. DMFT was more suitable for describingvariation in populations with low levels of disease than FS-T, while FS-T wasmore suitable for describing variation in populations with high levels of disease.It may be concluded that both DMFT and FS-T should be presented whendescribing oral status in a population. However, choice of index depends first of allon the purpose of the investigation. If there are theoretical reasons to prefer oneindex instead of the other, the superiority of the alternative index in terms ofvariation must be disregarded.

Annemarie A. Schuller1,Dorthe Holst2

1Division of Public Health and Prevention, TNOPrevention and Health, Leiden,The Netherlands, 2Section for CommunityDentistry, Dental Faculty, University of Oslo,Oslo, Norway

Dr. Annemarie A. Schuller, TNO Prevention andHealth, P.O. Box 2215, 2301 CE Leiden,The Netherlands

Telefax +31715181920E-mail: AA.Schuller@pg.tno.nl

Key words: oral status indicators; DMFT;FS-T; epidemiology

Accepted for publication February 2001

Dental status in a population has traditionally beendescribed by the total number of decayed (D), missing(M) and filled (F) teeth (T) or surfaces (S) (DMFT andDMFS, respectively) (1). Several researchers have recog-nised limitations of the DMF (27). Attempts have beenmade to develop other indices or indicators to describethe oral status (2, 3, 811). One of these alternativeindices is FS-T, the number of filled and sound teeth (2).While DMFT represents disease and its consequences,FS-T represents health and functionality.

LEWIS (12) studied the validity of e.g. FS-T comparedto DMFT. The criterion for superior validity in LEWISstudy was the percentage of variance in the indexexplained by the same set of independent variables.The results showed that the percentage of the varianceexplained did not vary between the DMFT and FS-T.Regression analysis by JAKOBSEN & HUNT (13) showeda lower percentage variance explained by a specifiedmodel in DMFT than in FS-T. MARCENES & SHEIHAM(3) showed that the FS-T was more sensitive than theDMFS. BENIGERI et al. (6) showed that the proportionof variance explained was lower than shown in the studiesby SHEIHAM et al. (2), JAKOBSEN & HUNT (13) andMARCENES & SHEIHAM (3).

There seems to be contradicting and confusing evid-ence in the literature with regard to the usefulness of thedifferent indices. There would appear to be two majorstands in the discussion of indices of oral status. The first

question is related to validity: does the index of choiceactually measure the condition of interest? The otherquestion is related to describing variation in a popula-tion: which of the indices is most suitable for describingvariation in a given population.

The two indices, DMFT and FS-T, were selected foranalysis in the present paper. An analysis of the relation-ship between DMFT and FS-T may help to understandhow and why these indices behave differently in differentpopulations. The purpose of the present work was there-fore a) to examine the relationship between DMFT andFS-T in different populations; and b) to show the con-sequences of choice of index exemplified in an analyticalanalysis.

Material and methods

The DMFT index is the summation of the DT, FT and MT(decayed, filled and missing teeth). The FS-T index is thesummation of the number of FT and ST (filled and soundteeth). Both indices are based either on 32 teeth or 28 teethdepending on the inclusion or exclusion of wisdom teeth.The DMFT and FS-T indices are related numerically, sincethe total sum of D+M+F+S=28 or 32, and since theyshare the F component. Fig. 1A shows all theoretical com-binations of FS-T and DMFT based on 28 teeth. Scatterplots to describe the combinations of FS-T and DMFT indifferent populations will differ from each other, but all plots

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fall within the ABC area. A scatter plot visualises examplesof variation in data. The variation in DMFT and FS-T isequal when the plots are situated on the diagonal, the boldline in Fig. 1B. A population with a majority of plots in theBCX lower triangular area (Fig. 1B) shows more variationin the vertical direction (DMFT) than in the horizontaldirection (FS-T). A population with a majority of plotsin the AXB upper triangular area shows more variation inthe horizontal direction (FS-T) than in the vertical direction(DMFT).

For the present analysis, data from the Trndelag-83 andTrndelag-94 studies were used (7, 14, 15). The Trndelagstudy, named after the two participating counties ofNorth and South Trndelag in Norway, started in 1973 as

part of the World Health Organizations InternationalCollaborative Study-I (WHO-ICS-I) (16). The Norwegianpart of the study was followed up in 1983 and 1994(7, 1416). Random samples from selected age groups weretaken from population records from selected municipalitiesin 1983 and 1994 (7, 14, 15). The DMFT index and the FS-Tindex were calculated. DT is defined as the number of teethwith primary and secondary caries; FT is defined as thenumber of teeth filled, including all types of filling materialsand crowns; MT is defined as the number of teeth missing,irrespective of the reason; and ST as the number of soundteeth.

To show the relationship between DMFT and FS-T, thefive different age groups from the 1994 data set were used(2324 yr olds (n=454); 3334 yr olds (n=522); 35 44 yrolds (n=477); 4554 yr olds (n=439); and 5564 yr olds(n=449)). To visualise the relationship between DMFT andFS-T sunflower scatter plots were performed. To show theconsequences of choice of index in analytical analysis, datafrom 2324 yr olds from 1983 (n=797) and 1994 (n=454)and 4554 yr olds from 1983 (n=725) and 1994 (n=439)were used. The variable of socio-economic status was usedto analyse the impact of the choice of index. Cumulativefrequency distributions were performed with DMFT andFS-T as dependent variables and socio-economic status asindependent variable. Socio-economic status was measuredby the number of years of formal education. The number ofyears of education was broken down into low education(12 yr or less for 2324 yr olds, and 9 yr or less for 4554 yrolds) and high education (13 yr or more for 2324 yr olds,and 10 yr or more for 4554 yr olds). Multiple linearregression analyses were performed for each of the agegroups with DMFT and FS-T as the dependent variablesto illustrate the consequences of the choice of index. Gender,year of survey, and socio-economic status were used as theindependent variables.

Results

The relationship between DMFT and FS-T in theTrndelag data is shown in sunflower scatter plots inFig. 2AE. Depending on age, a shifting of the majorityof spots from area BCX to AXB was seen. The plots for2324 yr olds were mainly situated in the BCX area(Fig. 2A). More variation was found in DMFT (i.e. ina vertical direction) than in FS-T (i.e. in a horizontaldirection). The plots for the older age groups weresituated in both the AXB area and BCX area (Fig. 2D,E). More variation was found in FS-T (i.e. in a horizontaldirection) than in DMFT (i.e. in a vertical direction) eventhough this was not as distinct as in the younger agegroup. This means that most variation will be foundamong 2324 yr olds when DMFT is used as the index ofchoice to describe oral situation. Among for example5564 yr olds, most variation was found when FS-T wasused. Fig. 3AD show the cumulative frequency dis-tributions for the DMFT and FS-T indices accordingto socio-economic status in 2324 yr olds and 4554 yrolds. The figs. show that differences in oral status among2324 yr olds emerge clearly in the DMF graph, with thesame phenomenon being found for the 4554 yr olds inthe FS-T graph. Explained variance in the linear regres-sion analysis among 2324 yr olds was 33% for the

Fig. 1. A) Theoretical scatter plot FS-T DMFT (upper panel).B) Variation DMFT and FS-T (lower panel).

156 Schuller & Holst

DMFT and 3% for FS-T. Among 4554 yr olds,explained variance was 2% for DMFT and 8% for FS-T.

Discussion

The results showed how the scores for combinations ofDMFT and FS-T varied between samples of populationswith varying oral status. The position of the observationsin the scatter plots reflects the actual oral status. Eventhough the plots represent combinations of DMFT andFS-T scores, the values of each of the indices can also beread directly from the diagram. The results showed thatthe DMFT index is more suitable for describing variationthan the FS-T in populations with low levels of diseaseand treatment experience. In populations with high levelsof disease and treatment experience, FS-T is more suitablefor describing variation than DMFT. However, there areexceptions. When, e.g., plots are situated as shown inFig. 4. There is most variation seen in an unexpecteddirection. It should be noted that such populations arevery exceptional and are expected to be rare. However,a look at a scatter plot will reveal unexpected results.

In the present material, the conclusion is that socio-economic status was not clearly related to oral statusin young adults when expressed by the DMFT. Socio-economic status was clearly related to oral status inyoung adults when expressed by the FS-T. In olderadults, the conclusions were the other way round.

The variables of gender, socio-economic status andsurvey year showed more explained variation in DMFTthan in FS-T among 2324 yr olds. In 4554 yr olds,these independent variables explained more variationin FS-T than in DMFT. The regression model used inthis paper is a very simple model. Not all independentvariables that are important in explaining the varianceof dental health or dental disease were included in thesemodels. It should be noted that the regression modelswere used only to illustrate the consequences of the choiceof index, rather than to provide the most optimal explana-tion of variance in oral health or oral disease. Age isusually included in the regression analysis as an independ-ent variable. It could however be questioned whether thisis useful. As shown, indices could act different in differentage groups depending on the oral health status. Possibleeffects could be levelled out.

Both indices have limitations, and assumptions have tobe made. Both the DMFT and the FS-T depend on dia-gnostic thresholds for caries, which are registered as theD (decayed) in the DMF or as an S (not decayed, sound)in the FS-T. When considering the F component in theDMF index (as an expression for treated caries disease),it should be noted that fillings have been inserted bydental professionals, who vary greatly in their decisions

Fig. 2. Sunflower scatter plots FS-T DMFT according toage group. A) Sunflower scatter plots FS-T DMFT, 2324 yrolds. B) Sunflower scatter plots FS-T DMFT, 3334 yrolds. C) Sunflower scatter plots FS-T DMFT, 3544 yr olds.D) Sunflower scatter plots FS-T DMFT, 4554 yr olds.E) Sunflower scatter plots FS-T DMFT, 5564 yr olds.

Selection of oral status indicators 157

about intervention in the carious process and restorativeprocedures. In addition, it should be noted that 1)a restoration may be placed for reasons other than caries(5, 17); 2) exchange of restorations are not registered; and3) treatment criteria have changed dramatically, therebyhampering comparison of the DMFT index over time(18, 19). These considerations related to FT do not haveto be taken into account in the FS-T index, since FT isinterpreted as a functioning tooth (2). In the DMF index,a missing tooth should only be counted when the tooth ismissing due to caries. This is usually difficult to determine,and it could result in an overestimation of disease andtreatment experience.

The conclusion is that, when describing the oral statusin a population, both oral health status and oral diseasestatus should be described. It should be rememberedthat the DMFT and FS-T are expressions of differentunderlying dimensions. The FS-T represents health andfunctionality, and DMF represents disease and its con-sequences. The two indices supplement each other ratherthan competing with each other. By using both indices,a more complete picture of oral status and a broaderunderstanding of the underlying mechanisms will beobtained. The theoretical scatter plot in this paper

Fig. 3. Cumulative distributions of DMFT or FS-T in different age groups according to SES and year of survey. A) Cumulativedistributions of DMFT among 2324 yr olds according to SES and year of survey. B) Cumulative distributions of FS-T among2324 yr olds according to SES and year of survey. C) Cumulative distributions of DMFT among 4554 yr olds according to SES andyear of survey. D) Cumulative distributions of FS-T among 4554 yr olds according to SES and year of survey.

Fig. 4. Scatter plot where most variation is found in anunexpected direction (exceptions).

158 Schuller & Holst

indicates when either FS-T or DMFT recognisesthe variation in the data. If there are theoretical reasonsfor preferring the one index to the other, the superiorityof the alternative index in terms of variation must bedisregarded.

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