Factors associated with inter-municipality differences in dental caries experience among Danish adolescents. An ecological study

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1 Community Dent Oral Epidemiol All rights reserved Ó 009 John Wiley & Sons A/S Factors associated with inter-municipality differences in dental caries experience among Danish adolescents. An ecological study K.R. Ekstrand, M.E.C. Christiansen, V. Qvist and A. Ismail Department of Cariology and Endodontics, Dental Faculty of Copenhagen, Denmark, Department of Cariology, Restorative Sciences, and Endodontics, School of Dentistry, Temple s Maurice H. Kornberg School of Dentistry, Philadelphia, PA, USA Ekstrand KR, Christiansen MEC, Qvist V, Ismail A. Factors associated with inter-municipality differences in dental caries experience among Danish adolescents. An ecological study. Community Dent Oral Epidemiol 009. Ó 009 John Wiley & Sons A S Abstract Background: Caries on children and adolescents in Denmark has declined significantly over the last 30 years. Our first analysis in, however, disclosed huge inter-municipality disparities in mean DMFS values as well as in prevalence of caries on Danish children; that fluoride in the water supply and the length of the education of the mothers could explain up to 45% of the above-mentioned disparity and that very few municipalities were positive outliers, i.e. were providing significant better caries results than expected from the background variables. Three of the aims of this second analysis were to repeat the analyses done on the sample, but now on a 004 sample and then compare it with the results from. A fourth aim was by means of an interview of CDOs to determine their interpretation of relevant conditions in the public dental health service in relation dental health outcome. Methods: A total of 04 (99%) and 9 (93%) municipalities were involved in and 004, respectively. Unit of analysis were the municipalities. Mean DMFS of 5-year-olds was used as outcome variable. Eight background variables were accounted for during the analysis: For the fourth aim, a sample of CDOs representing municipalities with positive (n = 0), with no change (n = 0), or with negative change (n = 0) in mean DMFS, relative to all municipalities, between and 004 was selected. Results: The inter-municipality variation in mean DMFS was 0.88 to 8.73 and in 004 was 0.56 to 6.9. The analyses found that fluoride level of the drinking water and mothers length of education were significant variables explaining about 44% of the variations in mean DMFS in both years. Only one municipality was characterized as a positive outlier in as well as in 004. The dose-response relations between increasing fluoride concentrations in the water supply and DMF-S values diminished in both years at a level above 0.35 ppm. The structured interview disclosed that municipalities with significant improvement in mean DMFS from to 004 had established goals and were committed to the prevention of dental caries at the individual level. Instability in manpower; number of children in the service and economy was associated to municipalities with negative changes in caries experience. Key words: caries; disparities; epidemiology Kim Ekstrand, Department of Cariology and Endodontics, Dental Faculty, Copenhagen, Nörre Allé 0, 00 N, Denmark Tel.: Fax: kim@odont.ku.dk Submitted September 008; accepted 4 August 009 Over the last four decades, dental caries prevalence and severity have declined in Western Europe (, ). While there are several hypotheses explaining the reasons for the decline, there is no single reason that can uniformly be attributed to the significant improvement in dental caries experience (3). doi: 0./j x

2 Ekstrand et al. In some countries, like Denmark, significant investment has been allocated to build a national dental care system for children and adolescents (4, 5). The national program was established by the Act of the Child Dental Health Service, stated in 97 and modified in 988 (4). The program is organized at the municipality level; with public clinics in 06 municipalities, while in about 70 very small municipalities, private practitioners provide dental care (4, 6). Whether the service is done by public clinics or by private clinics the service is free of charge. Municipalities with public clinics are responsible for establishing dental clinics locally. The municipality engages the staff including a chief dental officer (CDO). The CDO is responsible for running the local dental service in accordance with the Act. The Act requires that each municipality provides oral care for children from the age of 0 to the age of 8 and this must include individual preventive measures, including guidance for each child and their parents, instruction to each child in oral health care and regular clinical examinations (4). Wang et al. (7) in their comparison of caries preventive services provided for children and adolescents in Denmark, Iceland, Norway and Sweden, reported that Danish dental care providers in the Child Dental Health service in fact have high focus on provision of preventive services (fluoride, oral hygiene and a focus on children with high risk). Denmark has developed a system for collecting standardized data on oral health status of children to evaluate its dental care program (4). The data are reported annually by each municipality using the same forms and criteria (4 6). Caries experience is expressed by means of the DMF index where D is cavitated caries, M is teeth extracted due to caries, and F is restorations made due to caries. The first valid Danish national data on caries experience in 5-year-olds were collected in 988 and the mean DMFS score was 6.7 (8), which declined to 3.0 in 003 (9). Expecting homogeneity in caries experience in Denmark, it was interesting that Ekstrand et al., in an ecological evaluation reported in (6), found large inter-municipality variation in caries experience. In one municipality the mean DMFS score was 0.9 among 5-year-olds, whereas in another it was 8.9. About 45% of the disparity in mean DMFS scores could be explained by variation in the fluoride concentration in the water supply and in the educational status of the mothers of 5-year-old children. Thus, >50% of the variation in mean DMFS on adolescents across Denmark is unexplained. Inter-municipality variation in mean DMFS was not significantly influenced by structural variables such as cost per child per year for the offered dental service, the ratio of children to dentists and the ratio of auxiliary staff to dentists and background variables as income-, number of immigrants- and size of the municipalities (6). The statistical analyses identified a few municipalities, with significantly lower mean DMFS or significant higher percentage of 5-year-olds with a DMFS = 0 than other municipalities, taking into account the influences of the caries relevant background variables mentioned above. The first aim of this study was to describe the level of inter-municipality variation in mean DMFS in 004 and compare the findings to those reported (6). The second aim was to replicate and extend the models using data collected in 004. The Danish public service is focusing on benchmarking (0), therefore, the third aim was to identify municipalities, which achieved significant better mean DMFS than expected from the background variables (positive outliers); in particular, municipalities which were positive outliers both in and 004 were of special interest. The fourth aim and an additional aim to those of the study was to assess, by means of a structured interview, whether organizational and professional factors in the dental services in the local municipality might influence on disparities in caries experience across Denmark. Methods Ecological study Sample selection. According to rules stated by the Danish National Board of Health (4 6) all municipalities are required to provide annual data on the dental caries experience of all residents aged 5, 7, and 5 years, and send these to the Danish National Board of Health, which then perform the data processing. For this study, caries data on 5-year-olds were obtained for each municipality from the databases of the Danish National Board of Health. However, to be included in this analysis, a municipality should provide data on dental caries experience of at least 60% of the 5-year-old children in 004. Similar threshold was used in. Of the 06 municipalities eligible for the analyses, 9 (93% coverage) and 04 (99% coverage) met the initial inclusion criteria in 004 and, respectively (Table, lines 3).

3 The influence of different variables on caries experience in Denmark Table. Data tree showing the number and reasons for municipalities excluded in this and the former study 004 Municipalities with public clinics Excluded due to <60% recorded 5 Total of municipalities eligible for analyses about caries 9 04 Number of municipalities eligible for comparing caries experience in 004 [06)(5 + )] = 89 and (Fig. ) Excluded due to lack of background variables 0 3 Total of municipalities eligible for analyses about caries and background 9 0 variables Number of municipalities eligible for comparing standardized residuals in 004 and (Fig. ) [06)( )] = 86 Outcome variables. To evaluate trends over time, the caries measures of 5-year-olds were used as unit in the analyses because caries had developed over a 9 0-year period (age from 5 to 5). Thus, outcome measure was the mean DMFS among 5-year-olds in 004 and. The number of municipalities eligible for comparing caries experience in 004 and were the 9 municipalities in 004 which matched the inclusion criteria, minus two other municipalities in which did not match the inclusion criteria (Table, line 5). Thus, comparison between mean DMFS in and 004 was based on 89 municipalities. Background variables. The eight variables that were used to model the differences among the municipalities are listed in Table. The municipality was the unit, not the individual child. All data used were based on the means or medians from the period to 004 in the present sample and from 987 to in the former sample (6, 7). There was information available about the background variables for all the 9 municipalities, which in 004 had reported acceptable caries data (Table, line 6 8). Concerning, information about background variables was available from 0 municipalities (Table, line 6 8). Data analysis. Scatter plots were prepared to illustrate correlation between the municipality mean DMFS scores in 004 and in (Fig., n =89 municipalities). Bivariate analyses in 004 (n = 9 municipalities) and in (n = 0 municipalities) were made (i) between the 8 background variables in order initially to test level of correlation between them (Table 3) and (ii) between each of the eight background variables and mean DMFS (Table 4). Spearman s correlation coefficients (r s ) were used to describe the correlations, as the data were not normally distributed. All analyses were conducted using spss Version (SPSS Inc., Chicago, IL, USA). Stepwise (backward elimination) regression models were developed to investigate the association between the mean DMFS and the eight background variables. The assumptions for doing multiple regression analysis were checked as in the study (6) and found adequate (8). As in, the data on fluoride concentration in the drinking water of the municipality were transformed using log 0 as this gave a more linear relationship with caries data. Data transformation representing the other independent variables to different scales of measurements did not give stronger linear relationships than the original data. The influence of collinearity between two or more of the background variables was expressed by means of The variance inflation factor (VIF), (8). A VIF higher than 0 is of concern (8). It was decided in this article to include multiple regression analyses, but stratified according to four levels of size of the municipalities; (i) < year-olds, (ii) between 94 and yearolds, (iii) between 965 and year-olds, and (iv) > year-olds (quartiles in Table ). To identify the outliers, multiple regression analyses were conducted to compute expected mean DMFS for each municipality. Residuals are defined as the difference between the observed and the expected value (8). The residual for each municipality, was standardized by dividing the residuals with the standard error of the estimate of the model (8). Outliers are in this paper defined as municipalities with standardized residuals less than ).96 (positive outlier) or higher than +.96 (negative outlier). The outliers (Table, line 9, 0) are illustrated on Fig. (coloured numbers) located outside the horizontal and vertical lines (indicating the threshold of ±.96). The relationship, in 004, between the fluoride concentration in the individual municipalities and 3

4 Ekstrand et al. Table. Characteristics of the study populations and a summary of selected statistics Variables Cost per child per year (mean) DKK Children dentist ratio (mean) Auxiliary personnel dentist ratio (mean) Concentration of fluoride in the water supply (mean) ppm Personal income (mean) DKK Mothers with 0 years education to 5-year-olds (Percentage) Statistics: Up till municipalities Data collected: from 995 to 004 Range: First quartile: 30 Median: 303* Third quartile: 40 Data collected: in 996,, 004. Range: First quartile: 79* Median: 86. Third quartile: 934 Data collected: in 996,, 004 Range First quartile:.8* median:.0 third quartile:. Data collected: from 995 to 004 Range 0. First quartile: 0. Median: 0.3 Third quartile: 0.4* Data collected: from 995 to 004 Range DKK: First quartile: 7 000* Median: Third quartile: Data collected: 004 Range: % First quartile: 4.% Median: 9.5% Third quartile: 33.5%* Immigrants (median) Data collected: from 995 to 004 Range.5 8.7% First quartile:.4%* Median: 3.% Third quartile: 5.4% Size of the municipalities in terms of number of 0 8 years (mean) Data collected: in, 004 Range First quartile: 94 Median: 965* Third quartile: 538 DMFS Range 0.56* 6.9 First quartile:.00 Median:.66 Third quartile: 3.37 National mean:.8 SD.03 *The position of the municipality of Nexö. Statistics: Up till 03 municipalities Data collected: from 995 to Range: First quartile: 5 Median: 4* third quartile:333 Data collected: in 987, 990, 993, 996, Range First quartile: 78* Median: 847 Third quartile: 93 Data collected: in 987, 990, 993, 996, Range. 3. First quartile:.8* Median:.0 Third quartile:. Data collected: from 989 to 998 Range: 0.4 First quartile: 0. Median: 0.3 Third quartile: 0.4* Data collected: from Range DKK: First quartile: * Median: Third quartile: Data collected: Range % First quartile: 34.5% Median: 39.%* Third quartile: 44% Data collected: from 989 to 998 Range: % First quartile:.6% Median:.3%* Third quartile: 4.% Data collected: In 989, Range First quartile: 967 Median: 89* Third quartile: 505 Range 0.88* 8.73 First quartile:.56 Median: 3.34 Third quartile: 4.4 National mean: 3.53 SD:.9 mean DMFS was illustrated by a scatter diagram (Fig. 3, n = 9 municipalities). Regression analyses were performed to confirm or disconfirm the dose response relationship between fluoride concentrations in the water supply and mean DMFS over the full range of fluoride concentrations (0.03. ppm fluoride in 004 and in ). For the final calculations, the slopes of the regression lines were used as statistics in terms of the slopes significantly different from 0. Interviews with the CDOs Appendix lists the questions, which were used to seek information from a selected sample of the CDOs. The interview evaluated four areas within the dental services in the municipalities: (i) stability 4

5 The influence of different variables on caries experience in Denmark Mean DMFS Mean DMFS Fig.. Each dot in the figure represents a DMF-S score from and 004 collected from the individual municipalities. The inter-municipality relationship between mean DMFS scores among 5-year-old children in 004 and can then be illustrated. The diagonal represents municipalities where the mean DMFS were the same in 004 and. concerning manpower, number of patients and economy (stability); (ii) continuing education in cariology of the dental staff (continued education); (iii) availability of stated goals for dental health in the municipality (goals); and (iv) the level of emphasis placed on prevention of caries in the operations of the clinics (prevention of caries). The questions used for the interview were initially sent to 0 very experienced CDOs for pretesting and comments. They had only few comments and found the questions relevant related to the purpose. Sample selection. Three groups of CDOs were targeted in this part of the investigation. Group included the 0 CDOs representing those municipalities with the most positive improvement in mean DMFS scores, based on the residuals, between and 004 (below or at the lower dotted line in Fig. ); Group involved the 0 CDOs representing the municipalities where the standardized residual were closest to 0, indicating no changes in mean DMFS between the two periods (located on or close to the diagonal in Fig. ); and Group 3 involved the 0 CDOs representing those municipalities with the most negative change between and 004 (above or at the upper dotted line in Fig. ). Thus, a total of 30 municipalities were included in this analysis. The first author (KE) phoned the CDOs in the selected municipalities and the aim of the interview was carefully explained to them. All agreed to participate. The questions were asked in the order given in the Appendix and the answers were noted by KE. The questions and the answers from the individual municipality were then sent to the CDOs for correction of misunderstandings, if any. Data analysis As shown in Appendix, points were assigned to each question. The points for each of the four areas were summed up for each CDOs. The sum of points ranged between 0 and 6 concerning stability, 0 and 5 concerning continued education, 0 and 6 on goals and 0 and 9 concerning prevention of caries. High cumulative points within each area indicated: Stable conditions in the dental services; strong focus on continued education in cariology; strong focus on goals; and strong focus on prevention of caries. Significant differences in cumulative points within each of the four areas of questions between the three groups of municipalities were tested by means of the Kruskal Wallis test (9) (Table 5). Significant differences; P-values below Results Mean DMFS scores in 004 and in From Table, it can be seen that in 004, the lowest mean DMFS among the municipalities was 0.56, the highest was 6.9 and the national mean was.8 (SD =.03). Corresponding measures in were 0.88, 8.73 and 3.53 (SD =.9). Figure presents the scatter diagram illustrating the relationship between mean DMFS in 004 and in [(r s = 0.69) (P < 0.00)]. A total of 80% of the municipalities had achieved a lower mean DMFS in 004 relative to their status (Fig., dots below the diagonal). In contrast, 6% of the municipalities had a higher caries level (mean DMFS) in 004 compared to (Fig., dots above the diagonal). About 4% of the municipalities had the same mean DMFS in and in 004 (Fig., dots at the diagonal). On the national level the improvement from to 004 was 8% (P < 0.0). Background variables associated with the change in caries experience Looking at Table it appears that the number of mothers with less than or equal to 0 years of education were markedly lower in 004 than in. Thus, the median, moved from 39% in to 5

6 Ekstrand et al. Table 3. Correlations between background variables Independent variables Year Cost child year Children dentist ratio Auxiliary personnel dentist ratio Concentration of fluoride in the water supply Personal income Length of education Proportions of Immigrants Size of the municipality Cost child year 0.0 ** )0.30 ** ** 0.5 * )0.483 ** 0.4 ** 0.69 * )0.483 ** 004 )0.438 ** )0.4 ** 0.8 ** 0.56 * )0.63 * )0.68 ** Children dentist ratio 004 )0.43 ** )0.4 ** 0.35 ** Auxiliary personnel ** ** 0.69 * dentist ratio 0.8 ** 0.35 ** Concentration of fluoride * 0.30 ** in the water supply 0.3 ** Personal income ** )0.63 * 0.3 ** )0.380 ** ** ** Length of education * Proportions of immigrants 004 Size of the municipality 004 )0.63 * 0.30 ** 0.3 ** 0.38 ** )0.30 ** )0.68 ** 0.4 ** )0.97 ** )0.380 ** )0.58 * 0.6 ** ** ** ** )0.58 * ** )0.97 ** 0.6 ** *P < 0.05; **P < 0.0; ***P <

7 The influence of different variables on caries experience in Denmark Table 4. The correlation a between mean DMF-S and selected variables for 004 and Independent variable. Municipality level Year Cost child year 004 Children dentist ratio 004 Auxiliary person-nel 004 dentist ratio Concentration of fluoride 004 in the water supply Personal income 004 Length of education 004 Proportions of immigrants 004 Size of the municipality 004 a Spearman s rank correlation coefficient. *P < 0.05; **P < 0.0; ***P < Standardized residuals DMFS Mean DMFS ) )0.6 *** )0.63 *** )0.5 *** )0.5 ** 0.7 * 0.6 *** )0.0 ** )0.3 ** % in 004. Also the mean personal income in the municipalities was higher in 004 ( DKK) than in ( DKK). However, the inflation rate estimated to % during the 5-year period has Standardized residuals DMFS Fig.. Inter-municipality relationship between standardized residuals based on mean DMFS scores in 004 and. The horizontal lines (bold) represent ±.96 threshold for 004. Outside are the outliers in 004, the green ( 4) are the positive outliers, while the red ( 9) are the negative outliers. The vertical full lines are the ±.96 threshold for. Outside are the outliers. The green underlined ( 3) are the positive outliers, while the red underlined are the negative outliers. The arrow points on the municipality of Nexö. The points encircled indicate municipalities, which are positive outliers in 004 and near to be a positive outliers in Mean DMF-S in the municipalities Fluoride concentration in the municipalities Fig. 3. Fluoride concentration in the water supply versus mean DMFS among 5-year-olds in the different municipalities in 004. Tendency line is presented. Table 5. Inter-group statistics related to the four areas of interest in the interview Mean rank (stability) Mean rank (education) Mean rank (goals) Mean rank (program) Group Group Group Chi-Square d.f. P-value to be taken into account (Statistics, Denmark). Only minor differences between versus 004 were noted concerning the other six variables which were cost per child per year; children dentist ratio; auxiliary personnel dentist ratio; concentration of fluoride in the water supply; proportion of immigrants and size of the municipalities in terms of number of 0 8 years. Table 3 presents an overview of the associations between the background variables in 004 and in, respectively. No figures are presented where the associations in terms of correlation coefficients between variables were very low and not significant. At best there were only moderate correlations between background variables (highest r s = 0.6) between size of the municipality and proportion of immigrants. Table 4 summarizes the associations between the background variables and the DMFS scores. The correlation coefficients values did not differ much between and 004, within each variable. There was no significant correlation between the variables cost child year-; children dentist ratio-; auxiliary personnel dentist ratio and size of the municipality and DMFS. In contrast, the remaining four variables were significantly correlated to 7

8 Ekstrand et al. DMFS, however, three of them weakly whereas the fluoride concentration in the water supply was moderately, negatively associated to DMFS. When all eight background variables were included in the statistical model, the explained part of the variation, the R -values in 004, were 0.45 for mean DMFS scores. When only the fluoride level in the water supply and the length of the education of the mothers in 004 were included in the models (final model), the R decreased to Corresponding R in for the full model with all eight variables were: The R -values decreased to 0.45 in the final model, which also only included the fluoride level and the length of the mothers education (P < 0.00). Analyses for level of collinearity between two or more of the background variables showed VIF values between and both in 004 and in, indicating low risk for collinearity. When the size of the municipalities were stratified into four levels and the multiple regression analyses were repeated using data from 004, the values of R in the final models within the four levels were as follows: 0.37; 0.39, 0.60 and The fluoride concentration in the water supply was a significant explanatory variable at all four levels (P-values <0.00), while the length of the mothers education were borderline significant explanatory variables (P = 0.08) at level and 3, and a significant explanatory variable in level 4 (P = 0.03). At level, the P-value was 0.6. Municipalities with significant change between and 004 The level of associations between the standardized residuals in 004 and in were both moderate, although statistical significant (mean DMFS; r s = 0.44; P < 0.00) (Fig. ). From Fig. it can be seen that four municipalities in 004 (green number 4, below or on the lower horizontal line) and three municipalities in (green underlined number 3, outside or on the left vertical line) were positive outliers. Thus, their standardized residuals calculated from mean DMFS scores were <).96). In contrast, nine municipalities were negative outliers (the residuals were >.96) in 004 (red number 9, above or on the upper horizontal line) and in (red underlined number 9 outside or on the right vertical line). Only one municipality (municipality of Nexö) was a positive outlier in the analyses in 004 as well as in (Fig., arrow). Detailed analyses between fluoride concentration in the water supply and DMFS The scatter diagram in Fig. 3 illustrates the association in 004 between fluoride level in the water supply in the individual municipalities and the corresponding mean DMFS scores. The data indicate a clear drop in mean DMFS as the fluoride concentration in the water supply increase from nearly nothing up to a level of about 0.35 ppm. After this level there is no clear trend, while the tendency line is parallel to the X-axis. Analyses of the data from showed similar trends (6). In order to elaborate further on the dose response effect between mean DMFS and fluoride concentration in the water supply, regression analyses were made using the fluoride data transformed to log 0 (see the data analysis paragraph). The models indicated that the slopes of the curves significantly differed from 0 in the interval ppm fluoride (P < 0.00) in 004 and in the interval ppm fluoride (P < 0.00) in. Above these intervals the slopes of the curves did not differ from 0; (P = 0.06 in 004; P = 0. in ). Interview with the CDOs For this analysis three groups were formed based on their standardized residuals values. The municipalities within the three groups can be seen in Fig., thus below or at the dotted line are those 0 municipalities, which have had the largest positive movement (in mean DMFS from to 004 Group ). The 0 municipalities in Group are located at or very close to the diagonal as they had achieved no changes during the 5-year period. Above or at the dotted line are those 0 municipalities (Group 3), which have had the largest negative changes (mean DMFS) from to 004. Table 5 presents the mean rank values and P-values for each of the four local variables related to the three groups when calculated by Kruskal Wallis test. There were significant inter-group differences concerning stability of manpower, number of patients and economy (P = 0.0); concerning availability of stated goals for dental health in the municipality (P < 0.00) and concerning the level of emphasis placed on prevention of caries in the operations of the clinics (P < 0.00). Further analysis disclosed that concerning stability, the difference was between Group and versus Group 3, while concerning stated goals and concerning prevention of caries, the differences were between Group versus Group and 3. 8

9 The influence of different variables on caries experience in Denmark Discussion The authors are aware of the shortcoming of using an ecological study design. However, the present study and its predecessor performed 5 years earlier agreed about the following, which in our view increase the impact of the findings; in both the study periods there was a great inter-municipality variation in mean DMFS in Denmark among 5-year-olds; the fluoride concentration in the water supply and the length of the mothers education explained about 45% of the inter-municipality variation in mean DMFS; the municipality of Nexö was a positive outlier. The fluoride concentration in the water supply was the single strongest factor both in and 004 and was moderately and negatively correlated to mean DMFS. The negative correlation was significant up till between 0.30 and 0.38 ppm fluoride level. In addition, the interview disclosed that CDOs who were more committed to goals and focused on caries prevention had achieved a positive influence on the caries experience, while instability in manpower; number of children in the service and economy was associated to municipalities with negative changes in caries experience. Outcome data and background variables In the former study (6), we used two outcome variables; mean DMFS and % children with a DMFS = 0. In order to reduce the amount of data we chose in this paper only to show data based on mean DMFS. However, the conclusions would have been the same if we had included the % children with a DMFS = 0 as outcome variables. In the former study (6), we also used both 5- and 8-year-olds. In this study, we chose to use data on 5-year-olds only, because more than 90% the municipalities with public clinics have reported on this age group, whereas only 60% of the municipalities reported outcome measures for 8-year-olds. Caries data, used in this paper, were collected by well-calibrated dentists in the municipalities and by using standardized protocols (4 6, 9) which have been provided by the Danish National Board of Health for decades. Mean DMFS scores are vulnerable to be used as outcome variable, in particular, if they are based on too few subjects (5, 6, 0). In our analyses, the lowest number of 5-year-olds recorded in one municipality in 004 were 8, however, the 5% quartile was 4 5-year-olds, meaning that in 75% of the municipalities the number of recorded 5-year-olds were >4 children. Thus, in general, an adequate number of subjects were recorded, indicating a low risk of being influenced by for example extreme DMF values on few children. Further, in order to control not to underscore overscore the mean DMFS in the individual municipalities, they were excluded if the number of 5-year-olds registered was less than 60% of the total number of 5-year-olds in the municipality. Thus, a total of 5 and two municipalities were omitted in 004 and in, respectively. Those municipalities (n = 5), which were omitted in 004 but were included in the analyses were characterized as follows in : Mean DMFS ranged from. to 4. with an average on 3.. None of the municipalities were outliers (Standardized residuals ranged from ).5.). Thus, in all relevant aspects the omitted municipalities were average municipalities. This indicates that the excluded municipalities would not have influenced the trends of 004 if they had been included. Another problem of concern could be movement of children between municipalities over time. Of interest in this study is how many of the 5-year-olds both in 004 and had moved from one municipality to another since the age of 5 years, where the permanent teeth start to erupt and they started to contribute to the outcome measure used in this analysis (mean DMFS). There are no data, neither at the national nor at municipality level dealing with this issue. However, published data (0) from five municipalities in Denmark indicates that movement to another municipality in that age interval is limited (<0%), perhaps related to the fact that parents don t wish their children to change schools. The background data were in general based on means or medians from the period to 004 in the present sample, and from in the former sample, resulting in an overlap of about 3 years. Such an overlap may influence the results. This risk was found to be of minor importance seen from the point of view of including a 0-year-period in both groups of 5-year-olds, corresponding to the period where the caries experience of the5-year-olds actually had developed (age from 5 to 5). When we compared the background data from 004 with the data from, small changes were observed for 6 out of the 8 background variables. Concerning municipality income Denmark has become slightly richer during the five period, but focus of attention in the Danish society has for a long time been on education, which explains the marked drop from to 004 in number of 9

10 Ekstrand et al. mothers with only 0 years of education. Internal analysis disclosed that nearly all municipalities (>95%) had a higher educational status, in terms of length of education of the mothers, in 004 compared with. Explanation for the inter-municipality variation in caries experience The analyses for correlation between the background variables showed corresponding trends in 004 and in and at best moderate correlation coefficient. This was also the case for correlation between the background variables and the outcome variable. The multiple regression analyses disclosed that only fluoride in the water supply and the length of the education of the mothers had a significant influence on the variation in the mean DMFS scores. The fact that the data provides similar trends in 004 as in strengthens the validity of the data and the analyses. The VIF analysis confirmed (values <) that collinearity between two or more background variables could not bias the above observation (8). Moreover, more complicated models for testing interactions between background variables as stratification of one of the background variables (the size of the municipality) did not come up with conflicting results to that obtained by the more simple model described above. The size of the municipality was chosen as the stratification variable because it was the variable with the greatest variation ranging from 474 to 79 0 young adults aged 8 years in 004 (Table ), and because that variable showed the strongest correlation to other background variables (Table 3). As this analysis did not improve the results compared with the more simple multiple regression analyses, we decided not to use stratification of any background variable. The large inter-municipality variations in mean DMFS observed in were, however, still present in 004. As only about 45% of this variation can be attributed to variations in fluoride concentration in the drinking water and in the level of education of the mothers, a significantly large proportion of the variation remains unexplained. The question is whether there are other caries relevant background variables not included in the analyses, keeping in mind that the other six background variables evaluated, all recognized as important factors in caries epidemiology ( 5), were insignificantly related in this ecological analysis to variation in mean DMFS. An interesting area is that data from the Geological Survey of Denmark and Greenland from where we got the data of fluoride level in the water supply, has also disclosed large inter-municipality variations in other ions in the water supply than fluoride. Analyses have shown that variations in ions in water can explain another 0% of the variation in mean DMFS in Denmark and, in particular, variation in Calcium s in the water supply is of importance (6). In this study, it is not possible to state the level of impact, variation in the uses of fluoridated toothpaste and variations in diet have had on the variation in mean DMFS among 5-year-olds in Denmark. However, the following can be stated concerning those two variables under Danish conditions: Nearly, all children in Denmark have been using a mixture of ppm fluoridated toothpaste on a daily basis since the late 60s. The amount of carbohydrate intake per individual has been steady, around 40 kg individual, the last 0 years in Denmark (7). Thus, the inter-municipality variation, concerning those two variables, would be very limited and had likely not explained a significant part of the observed intermunicipality variation in mean DMFS across Denmark. Outliers It was disappointing to learn that only the municipality of Nexö was characterized as a positive outlier in the analyses from 004 as well as from (Fig. ). The asterisks in Table indicate the position of Nexö concerning the individual background variables and the outcome variable. Thus, in favour for the results obtained in Nexö is the 0.84 ppm fluoride concentration in the water supply, against is the high number of mothers with 0 years of education (38% both in 004 and in ), and the low personal income ( DKK in 004 and DDK in ). Nexö also differs from the majority of the other municipalities concerning a relative low number of children per dentist (. quartile), but with a correspondingly low number of auxiliary personnel per dentist (first quartile). The caries preventive and management program used in Nexö, the scientific rationale of the program have been described before (0, 8). Two other municipalities (Broby and Ryslinge) were positive outliers in 004, but not in. Both municipalities have a lower ppm fluoride (0. and 0.3) in the water supply than Nexö, but are wealthier and have a higher proportion of mothers with longer education. The caries management program used in these two municipalities could also be of interest to learn in details and benchmark 0

11 The influence of different variables on caries experience in Denmark against (encircled in Fig. ). Unfortunately, their caries management programs have not yet been described in any publication. Benchmarking is a wide issue, eventually with the aim through best practice to increase some aspect of performance. It seems that municipalities providing the best practice concerning caries controlling for children and adolescents in Denmark can be identified through the methods used in this study. Thus, the Danish National Board of Health could in fact force the above three CDOs to publish nationally their caries preventive programs running in their municipalities, so other CDOs in other municipalities could learn from their experience. Fluoride in the water supply Both in and in 004 it was found that the fluoride concentration in the water supply remained the most important single factor explaining the variation in mean DMFS across Denmark. Further, the dose response effect between fluoride and mean DMFS, under Danish conditions, leveled out over 0.38 ppm fluoride in the water supply both in 004 and, which is much lower than previously considered as optimal (0.7. ppm, (9 3). The apparently lower optimal threshold (between 0.3 and 0.38 ppm fluoride) in Denmark shall among other factors be seen in the light of the fact that nearly all Danish children for more than 30 years have used fluoridated toothpaste and that children and adolescents in the same period have participated in the Child Dental Health Service, free of charge. This view is supported by studies from Finland (33). Like Denmark, Finland has also an organized Child Dental Health Service. The authors expect other thresholds in countries with other cultural and social backgrounds than in Denmark and Finland. Interviews with CDOs No earlier attempts have been made to test the impact different factors related to the service in the individual clinics has on the caries level in the municipality. So the initiative included in this study should be regarded as a kind of a pilot study in this regard. It was decided to conduct a structured interview with a number of questions, subsequently, for minimizing interviewer bias, letting the CDOs themselves check their answers a model suggested by Ekstrand et al., (0). Only dental officers of the 30 selected had changes to what they have answered over the phone. Ekstrand et al. (0) pointed to the fact that systematic use of guidelines, individualized toothbrushing instruction every time the children came to clinical examination and considering the eruption period of molar teeth as a risk factor for developing caries, were important factors to control caries development. Therefore, the last area of questions (prevention of caries) involved questions around these matters. The answers to the questions in area (stability) and area 3 (goals) are available at the municipality level, while the questions in area (continued education) is knowledge the individual CDO s has. The CDOs who initially were asked to comment on the interview apparently agreed to that the questions were of relevance for the matter to be investigated, as they had only very few comments. In order to avoid noise from the many municipalities (85% of the municipalities) which had only experienced minor positive or negative changes in mean DMFS scores from to 004, it was decided only to contact the municipalities which had improved most, worsened most, or which had not changed at all from to 004. To avoid also the influence of the background variables, it was decided to use the standardized residuals for both mean DMFS scores. The questionnaire was evaluated using a point system to generate a score for analysis. Two factors were found to be of significance in achieving better caries experience data in the municipalities; (i) that the CDO had stated goals, and (ii) that the CDO had a strong focus on caries prevention. Further, instability concerning manpower, etc., was also found to be important for those municipalities which had achieved worse results A confounding factor was, however, that both the observed caries experience and the predicted caries experience in in those municipalities, which had had the best improvement between and 004, was higher than in the other two groups. Some would therefore argue that it is easier for municipalities with high caries level to obtain a significant reduction. Those municipalities, which experienced a worsening in their caries status from to 004, had, however, also had on average higher mean DMFS scores than the national average in. Final remarks Although the Child Dental Health System in Denmark goes beyond what is typically available in many other countries, the findings in this paper may have dental public health relevance outside

12 Ekstrand et al. Denmark. Our data do support that fluoride in the water supply is important in caries prevention. In countries that would like to introduce water fluoridation and where the population already uses fluoridated toothpaste and where some organized dental health care system exists, a level of 0.5 ppm fluoride seems to be a relevant to add to the water supply. We have devised a method where outliers at the municipality level, or the best practice, can be found, which other providers should benchmark against, and finally we have established that stability of manpower and economy, implementation of goals in the dental service as well as modern focus on caries prevention are important factors, if improvement in caries status is wanted. References. Marthaler TM, Brunelle J, Downer MC, König KG, Truin GJ, et al. The prevalence of dental caries in Europe Caries Res 996;30: Petersen PE. 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13 The influence of different variables on caries experience in Denmark Appendix Questions used in the interview and points related to the answers Stability concerning manpower, number of patients and economy. Has there been more than two new chief dentist officers the last 8 years? Yes (0 point) No ( point). Has your dental health service been short of dentists within the last 8 years? Yes (0 point) No ( point) 3. Has your dental health service been short of auxiliary staff within the last 8 years? Yes (0 point) No ( point) 4. Has your municipality experienced a marked increase in the number of children Yes (0 point) and adolescents within the last 8 years (>0%)? No ( point) 5. Has your municipality experienced a marked increase in the number of Yes (0 point) children and adolescents with immigrant background the last 8 years (>5%)? 6. Has there been a marked drop in financial resources for the dental health service in your municipality (>% per year) within the last 8 years? Continuing education in cariology of the dental staff No ( point) Yes (0 point) No ( point). Does your dental health service review and apply current literature on caries prevention?. Do you expect that your dentists read International literature? 3. Do you expect that your dentists read their national trade magazines? 4. Do you expect that your dentists search on the internet for relevant cariological literature? 5. How often is caries on the agenda for your internal meetings? Often Always ( point) Seldom (0 point) Availability of stated goals for dental health in the municipality. Does your dental health service have any statement of goals?. Does your dental health service have cariologic goals regarding e.g. 5-years-olds? 3. Does your dental health service have mean DMFS scores as part of the statement of the goals? 4. If yes, which mean value should DMFS and or % DMFS = 0 be for 5-years-olds? In If stated point, if not 0 point In 004 If stated point, if not 0 point 5. Did you dental health care reach their goal, regarding either mean DMFS score or %DMFS = 0 In In 004 If stated point, if not 0 point If stated point, if not 0 point 3