91

Vol. 51, No. 2, Spring 1991

Dental Fluorosis Following Downward Adjustment of Fluoride in Drinking Water R. Wendell Evans, MDS Department of Periodontology and Public Health Faculty of Dentistry University of Hong Kong, Hong Kong

John W. Stamm, DDS, DDPH, MScD Department of Dental Ecology University of North Carolina Chapel Hill, NC

Abstract Thedrinking water fluoride concentration in Hong Kong was reduced by about 0.2 ppm in June 1978. This study was undertaken to determine whether the prevailing level of dental fluorosis was affected by such a minor change. Cohorts of children (N= 1,062)aged seven to 12 years, who were born both before and after the fluoride reduction, were examined clinically using Dean's fluorosis index. Based on upper right central incisors, dental fluorosisprevalence decreased from 64 to 47percent and the community fluorosis index decreased from 7.01 to 0.75 (P3 mm) 9 2 percent of number selected. tll percent of number examined.

1,680 1,541* 172t 1,369 1,062

10 percent of the children were reexamined for monitoring diagnostic standards. Children were randomly selected for this purpose and an attempt was made to reexamine them in a single-blind fashion. In addition, the entire sample from one school was reexamined one month later and the sample obtained from another school was reexamined four months later for assessing withinexaminer reproducibility. The level of reproducibility was quantified by calculating the Kappa statistic (32). Results Of 1,680 children initially selected and invited to take part in the survey, 92 percent received parental consent and were clinically examined (Table 1). Subsequently, data in relation to 11 percent of children, who were not continuous Hong Kong residents, were excluded from the analysis. Altogether,there were 1,062children having erupted upper right central incisors in the cohorts relevant to this study. The children in the age seven cohort were born during the year commencing June 1, 1978; thus all older children were born at times prior to the date when the fluoride concentration was reduced (Figure 1 ). The level of reproducibility achieved in the duplicate fluorosis examinations conducted on the same day was excellent, attaining a Kappa of .86 on all teeth and -92on maxillary right central incisors only (Table 2). Duplicate fluorosis examinations conducted one and four months apart achieved Kappa scores of .68 and .57,respectively. The latter scores reflect substantial and moderate reproducibility, respectively, using the criteria elaborated by Landis and Koch (33). Dental fluorosis across the six cohorts decreased in direction from older to younger (Table3). The prevalence of fluorosis (very mild or greater) decreased from 64 to 47 percent. This trend is also evident by the declining CFI values in children under ten years of age. The results of a separate analysis of the data by gender are given in Table 4, where it is observed that the decline in the CFI gradient, from older to younger cohorts, is relatively more steep in males than in females. A multiple regression analysis of CFI on cohort and gender showed the decline in dental fluorosis to be highly significant (Table

TABLE 2 Kappa Values Indicating Within-Examiner Agreement in Scoring Dean’s Fluorosis Index Duplicate Examinations Conducted

Teeth

All Upper right central incisor only

Same Day

1 Mo. Later

4 Mos. Later

.86 .92

.68

.57

Journal of Public Health Dentistry

94

TABLE 3 Cohort-specific Frequency Distribution of Dean’s Fluorosis Scores and Community Fluorosis Index (CFI) Based on Upper Right Central Incisor Cohort Age in June 1985 Score

12

0 0.5 1 2 3 4

16 (12)* 34 (25) 50 (37) 30 (22) 6 (6) 10) 137 1.008 63.5

Normal Questionable Very mild Mild Moderate Severe Sum of frequencies

CFl Fluorosis prevalence ratet SE of prevalence

34 (15) 55 (24) 91 (40) 41 (18) 5 (2) 1(0) 227 0.967 60.8

4.1

9

8

7

39 (21) 54 (28) 69 (36) 24 (13) 4 (2)

44 (24) 50 (27) 61 (33) 27 (15) 2 (1)

28 (23) 37 (30) 42 (34) 14 (11) 1(1)

202 0.975 57.9

190 0.821 51.1

184 0.793 48.9

122 0.750 46.7

3.5

3.6

3.7

10

11

-

29 (14) 56 (28) 70 (35) 43 (21) 3 (1)

-

10)

3.2

4.5

‘Percents (may not total 100 due to roundmg) tPercent with very mild or higher.

TABLE 4 Community Fluorosis Index (CFI) and Fluorosis Prevalence (Based on Upper Right Central Incisor) by Cohort and Gender Cohort Age in June 1985 Gender Male CH Fluorosis prevalence rate* Female CFI Fluorosis prevalence rate

12

11

10

9

8

7

1.162 62.2 1.ooo 65.1

1.009 60.5 0.925 61.1

1.080 65.9 0.895 51.8

0.869 54.4 0.764 47.1

0.737 44.5 0.859 54.1

0.717 38.3 0.782 54.8

*Percent with very mild or higher.

TABLE 5 Regression of CFI on Cohort and Gender (N=1,062) Variable Cohort Gender Cohort x gender

Parameter Estimate

Standard Error

Probability

0.093 0.078 -0.053

0.019 0.084 0.028

.0001 .3491 .0532

Model F value=9.87, P

Dental fluorosis following downward adjustment of fluoride in drinking water.

The drinking water fluoride concentration in Hong Kong was reduced by about 0.2 ppm in June 1978. This study was undertaken to determine whether the p...
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