Dental Fluorosis and Fluoride Exposure in Western Australia P.J. RIORDAN"', and J.A. BANKS' 'Community Dental Services, Health Department of Western Australia, P. O. Box 50, Como, WA 6152; and 'Dental School, University of Western Australia, 179 Wellington Street, Perth, WA 6000, Australia

Dental fluorosis in children is reported from many locations, and its prevalence may be increasing. This study aimed to measure fluorosis in 12-year-olds in fluoridated and non-fluoridated areas of Western Australia and to relate this to exposure. School dental clinics in Perth (F- 0.8 mg/L) and the Bunbury area (F- 1, but none was statistically significant, suggesting recall error. The findings suggest that supplement use by some children in 197882 provided too much fluoride, and that a small number of persons have undesirable fluorosis. J Dent Res 70(7):1022-1028, July, 1991

Introduction. Recent oral health literature has confirmed the presence of low levels of diffuse opacities-categorized by some authors as dental fluorosis or enamel defects-in children in communities in Canada (Osuji et al., 1988), the USA (Driscoll et al., 1983; Leverett, 1986; Beltran and Szpunar, 1988; Szpunar and Burt, 1988; Bagramian et al., 1989; Kumar et al., 1989), New Zealand (Cutress et al., 1985; de Liefde and Herbison, 1985), and several countries in Europe (Wenzel and Thylstrup, 1982; Levine et al., 1989; O'Mullane, 1990). Elevated tissue fluid fluoride levels during the secretary or maturation phases of enamel formation may produce such effects (Suckling, 1989; Fejerskov et al., 1990), and there is a tendency in the literature to ascribe them uniquely to ingestion of fluoride, as is implicit in the use of various fluorosis scales to measure such defects of enamel formation. Suckling (1989) has pointed out that the enamel organ has only a limited number of ways in which it Received for publication September 24, 1990 Accepted for publication February 22, 1991 1022

can

respond to environmental changes, so that diffuse opacities

such as those described in connection with high fluoride ingestion may also, on occasion, be due to other etiological factors. However, there is consensus that, while not all diffuse opacities are fluoride-induced, at least in areas of high fluoride availability, fluoride is an important etiological factor for diffuse opacities (Cutress, 1989). Fluorosis is not only seen in fluoridated communities; there are also reports of apparent fluorosis in non-fluoridated areas, implicating fluoride from sources other than water (Holm and Andersson, 1982; de Liefde and Herbison, 1985; Leverett, 1986; Osuji and Nikiforuk, 1988; Kumar et al., 1989; Levine et al., 1989). There is some evidence of a trend, since Dean's time, toward increasing prevalence of slight fluorosis in the United States (Leverett, 1986; Szpunar and Burt, 1987), reported to be greater in non-fluoridated cities than in fluoridated ones (Kumar et al., 1989). Horowitz et al. (1984) found fluorosis of increasing degree of severity with decreasing age in a study of children of different age groups. The same workers studied the same children again after five years and confirmed unchanged fluorosis severity, suggesting that children may be ingesting increasing amounts of fluoride (Heifetz et al., 1988). An increase in background levels of fluoride in some communities would elevate fluorosis prevalence (Leverett, 1982). An inverse relationship has consistently been reported between caries experience and increasing levels of mild fluorosis (Szpunar and Burt, 1988), which reverts as fluorosis becomes more severe.

Drinking water in the Perth metropolitan area and most larger regional centers in Western Australia (WA) is fluoridated; altogether, about 86% of the population (total 1.6 million) consumes adequately fluoridated water (Commonwealth Department of Health, 1987). The fluoridation of water supplies in almost all large cities in Australia ensures wide distribution of fluoride incorporated in manufactured foods and drinks. In addition, fluoride supplements are recommended (and are occasionally available free of charge) in non-fluoridated areas. Fluoride supplement use can lead to dental fluorosis (Larsen et al., 1985; Pendrys and Katz, 1989). Fluoride-containing toothpastes have accounted for at least 95% of toothpaste sales in WA for more than ten years (Stockwell et al., 1990) and probably contribute to total fluoride ingestion by children, as has been shown to occur elsewhere (Ericsson and Forsman, 1969; Hargreaves et al., 1972; Barnhart et al., 1974; Whitford et al., 1987; Pendrys and Katz, 1989). The bioavailability of such fluoride is high (Hargreaves et al., 1972; Ekstrand et al., 1983; Drummond et al., 1990). Fluoride has thus become ubiquitous in some populations. Leverett called for studies to evaluate the evidence for increasing levels of dental fluorosis and to identify factors that are causing fluorosis in children today (Leverett, 1986). The aim of this study was to ascertain the prevalence and severity of fluorosis-like defects of enamel formation in children in fluoridated and non-fluoridated areas of WA and to correlate the findings with each child's history of residence in fluoridated areas, use of fluoridated toothpaste, and ingestion of fluoride supplements.

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covered: areas of residence, type of regular water supply (piped, rain-, or well-water), and dates of changes since birth; periods Ethics review. -The study protocol was submitted to the and duration of use of fluoride supplements; use of fluoride Director of Epidemiology of the Health Department of Western toothpaste, including age at which use of toothpaste comAustralia, who gave it ethical clearance. menced; and parent's recollection of whether the child liked Participants. -About 77.3% of children aged six to 15 years and/or swallowed toothpaste. in WA attend government schools (Pink, 1989). In the Perth The questionnaire was accompanied by an explanatory letter metropolitan area (0.8 mg F-/L), there were 281 government from the Director of the CDS requesting cooperation. Those primary schools in 1989. The Community Dental Service (CDS) who had not the questionnaire within two weeks rereturned has a Dental Therapy Centre (DTC) at 71 of these. With a ceived a reminder letter. Children who had not returned a quescomputer, each DTC was assigned a random number, then they tionnaire by the time of the clinical examinations were examined were ranked in numerical order, and the first 14 were included. anyway, and a parent or guardian contacted by telephone to At each selected DTC, staff were asked to choose one class elicit the information required. A few parents stated that they of children attending their school in which most of the children did not wish their child to be included. This was respected. were born in 1978. At one larger DTC, two classes were choData on the water fluoridation status of areas in WA are sen. Only children born in 1978 were included. This generated held in the CDS. The fluoridation status of the former areas a sample of 376 children. In 1990, there were about 15,300 of residence of persons who had lived in other parts of Auschildren born in 1978 in the Perth metropolitan area (Ministry tralia was ascertained from various published sources (dental of Education, 1990). scientific or government literature) or by contacting the local In the region around the city of Bunbury, 200 km south of dental health or water authorities. Similar sources were used Perth, drinking water has never been fluoridated, and natural to confirm the fluoride exposure of participants who had mifluoride levels are low ( 0.05) from that for the metfication (Thylstrup and Fejerskov, 1978). If this tooth was ropolitan area. In the Bunbury region, the overall mean for 32 unavailable (due to anterior restorations or orthodontic applischools is 99.7 (S.D., 3.77); the mean for the five schools ances), the upper right central incisor was used. If both these with DTCs selected (99.0; S.D., 3.69) was not significantly teeth were unavailable, the lower anterior teeth were used. different (p >0.05). Although examinations were not conducted blind with respect The examinations in Perth were conducted in November and to area of residence, the examiner was not aware of the resiDecember, 1989, and in the Bunbury area in March, 1990. dence or fluoride supplement history of participants. As an aid Due to out-of-date class lists, seven children in Perth and three to reliability, written descriptions and color photographs (Fein Bunbury were included who were later found to have left jerskov et al., 1988) of TF-scored dental fluorosis were availtheir schools before the study commenced. A further two Perth able and consulted in cases of doubt. children could not be examined for clinical reasons (ameloAnalyses. -Fluorosis prevalence was defined as the proporgenesis imperfecta and orthodontic bands). These were extion of those examined who had TF scores > 0. Analyses were cluded from the sample, leaving 367 potential participants in carried out on personal computers with StatView II (Abacus Perth and 335 in Bunbury. Virtually all 11- to 12-year-old Concepts, Inc., Berkeley, CA 94704) and, for logistic analychildren in the areas of the study are regular patients of the sis, the EGRET package (Statistics and Epidemiology ReCDS. search Corp., Seattle, WA 98105). The t test and categorical Background information. -Before the clinical examinamethods were used to identify variables associated with the tions, each putative participant was provided with a questionprevalence of fluorosis. Variables thus identified were used as naire to be completed by the parents. Information requested independent predictors in logistic regression analysis; for diDownloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 23, 2015 For personal use only. No other uses without permission.

Materials and methods.

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RIORDAN & BANKS

J Dent Res July 1991

TABLE 1 EXPOSURE (BIRTH TO FOUR YEARS) TO FLUORIDATED WATER BY DURATION AND PLACE OF RESIDENCE AT TIME OF EXAMINATION Medium Long (2.5-4 yr) (1-2.5 yr) Short ( < 1 yr) n (%) n (%) n (%) 42 Perth Metropolitan 283 13 (83.7) (3.8) (12.4) 174 Bunbury Region 116 (36.1) 31 (9.7) (54.2) All 399 (60.5) 44 (6.7) 216 (32.8)

TABLE 2 TOTAL (WATER AND SUPPLEMENT) FLUORIDE EXPOSURE (BIRTH TO FOUR YEARS OLD) BY PLACE OF RESIDENCE AT TIME OF EXAMINATION Exposure Level 2 1 3 4-6 n (%) n (%) n (%) n (% Perth Metropolitan 39 (11.6) 13 (3.8) 283 (83.7) 3 (0.8) Bunbury Region 120 (37.4) 35 (10.9) 127 (39.6) 39 (12.1) All 159 (24.1) 48 (7.3) 410 (62.2) 42 (6.4) I~ I I I ~~~~ I

chotomized variables coded '0' for no exposure and '1' for exposure, the antilogarithm of the regression coefficient is the prevalence odds ratio of the subject having~the condition, given exposure. For non-dichotomous variables, the antilogarithm of the regression coefficient gives the multiplicative change in the odds ratio of the subject having the condition, for a unit change in the exposure variable (Kleinbaum et al., 1982; Rothman, 1986). All variables were coded so that increasing fluoride exposure was represented by increasing values. The statistical methods have been described by Szpunar and Burt (1988). Reliability. -In May, 1990 (five to six months after the first examinations), four metropolitan DTCs (chosen for practical reasons, such as availability of vacant dental units) were revisited, and examinations for fluorosis were repeated on 50 participants. This number is more than adequate for assessment of the reliability of a rating scale with four ordinal points (Cicchetti, 1976), which includes the TF classification used in this study. The same indicator tooth as previously used was cleaned and dried, and the examiner was unaware of the original scores. Reliability of fluorosis scoring, measured with weighted kappa with restricted weights (Cicchetti, 1976; Landis and Koch, 1977), was 0.78, representing "substantial" strength of agreement between the two examinations (Landis and Koch, 1977). Results. Participation. -At the 14 DTCs in the Perth metropolitan area, 338 children (163 girls, 175 boys; 92.1%) were examined. All were born in 1978 (mean age, 11 years seven months; S.D., 2.7 months). In Bunbury and environs, 321 children (151 girls, 170 boys; 95.0%) were examined, of whom two were born in 1976, 25 in 1977, 253 in 1978, and 41 in 1979 (mean age, 11 years ten months; S.D., 6.7 months). Nonparticipation was due to absence from school on the day of examination (25 persons), parental refusal (13 persons), or failure to supply information. There were no significant differences between boys and girls with regard to residence (X2 = 0.931, df = 1, p = 0.71), years of exposure to water fluoride from birth to age four (X2 = 1.627, df 2, p = 0.44), and TF score (X2 = 2.299, df = 3, p = 0.58), and in the following analyses, boys and girls are treated as one group. Fluoride exposure. -The principal source of fluoride was water fluoridation. Altogether, 399 children (60.5%) were "Long" residents (at least 2.5 years) of areas with fluoridated water, and a further 44 (6.7%) had had some exposure to fluoride from this source while aged under four years. The distribution of Perth- and Bunbury-region children by exposure =

to fluoridated water up to the age of four years is shown in Table 1. Use of fluoride supplements before the age of four years was not common: Only 79 children (12.0%) reported having used supplements. All supplementation occurred in the form of fluoride tablets. Use in the period between birth and four years was categorized as "Little" for 23 children, "Medium"

I

TABLE 3 DISTRIBUTION OF TF SCORES AMONG CHILDREN RESIDENT IN FLUORIDATED AND NON-FLUORIDATED AREAS All Perth Metro Bunbury region TF Score n n (%) n (%) (%) 0 417 202 (63.3) 215 (59.8) (67.0) 1 180 82 98 (27.3) (29.0) (25.5) 2 52 22 (7.9) 30 (8.9) (6.9) 3 10 (1.5) 8 (2.4) 2 (0.6) Totals 659 (100.0) 338 321 (100.0) (100.0)

for 26, and "Optimal" for 30. Altogether, 58 children had used supplements while aged under one year; three of these had been residents of fluoridated areas at the time. Total fluoride exposure from these two sources in the span between birth and four years was estimated for each person by addition of the scores. Since there were relatively few participants with aggregate scores greater than 3, scores 4 to 6 were collapsed to a single group; the data are presented in Table 2. Data on the age at which use of toothpaste commenced were available for only 622 participants. Of these, 14.6% had started by the age of one year, and a further 37.6% by the age of two years. The mean age at which toothbrushing started was 1.8 years (S.D., 1.36; range, 0-10 years; n = 622). Toothpaste was liked by 545 (86.6%) children and reportedly swallowed by 303 (49.1%). Children who liked toothpaste started toothbrushing at a younger age (n = 525; mean age, 1.8 years) than those who did not (n = 76; mean age, 2.3 years; t = 3.232; p = 0.0013). Similarly, children who swallowed toothpaste started toothbrushing at a younger age (n = 290; mean age, 1.6 years) than children who did not (n = 298; mean age, 2.1 years; t = 4.401; p = 0.0001). Fluorosis prevalence and TF scores. -Overall dental fluorosis prevalence was 0.37 (242 persons): In the Perth metropolitan area, it was 0.40 (136 persons), and in the non-fluoridated areas, it was 0.33 (106 persons). This difference was not statistically significant (X2 = 3.69, df = 1, p = 0.055). In 25 participants, assessment of fluorosis was based on the lower anterior teeth. The prevalence of fluorosis in this group was slightly higher than, but not significantly different from, that in the group whose upper teeth were used (X2 = 1.42, df = 1, p = 0.23). Similarly, the distribution of TF scores in the lower teeth was not significantly different from the distribution in the group whose upper teeth were assessed (X2 5.75, df = 3, p = 0.12). In the following analyses, these two groups are treated as one group. Distribution of the different TF scores is shown in Table 3. Although these data suggest that fluorosis was apparently somewhat more severe in the metropolitan area, the difference was not statistically significant (X2 = 5.893, df = 3, p = 0.12). However, there was a noticeable and strong relationship between total fluoride exposure (birth to four years) and TF score (Table 4); higher TF scores were associated with higher exposure levels (X2 = 50.55, df = 9, p = 0.0001). Fluorosis

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DENTAL FLUOROSIS IN WESTERN AUSTRALM

Vol. 70 No. 7 TABLE 4

DISTRIBUTION OF TF SCORES BY EXPOSURE (BIRTH TO FOUR YEARS OLD) TO FLUORIDE IN WATER AND SUPPLEMENTS Exposure Level All 2 3 4-6 1 TF (%) (%) n (%) n (%) n (%) n Score n 0 132 (83.0) 34 (70.8) 229 (55.9) 22 (52.4) 417 (63.3) 1 23 (14.5) 11 (22.9) 135 (32.9) 11 (26.2) 180 (27.3) 4 (2.5) 2 (4.2) 37 (9.0) 9 (21.4) 52 (7.9) 2 0 (0.0) 1 (2.1) 9 (2.2) 0 (0.0) 10 (1.5) 3 Totals 159 (100.0) 48 (100.0) 410 (100.0) 42 (100.0) 659 (100.0)

prevalence among persons who had had long (2.5 to four years) exposure to fluoridated water (n = 399) was 0.45, but among persons who had had short (< 1 year) fluoride exposure, it was 0.20 (X2 = 37.05, df = 1, p = 0.0001). Persons who had used supplements in accordance with recommendations (n = 30) had a fluorosis prevalence of 0.53. Children who commenced toothbrushing at an age younger than one year (X2 = 3.741, df = 3, p = 0.29) reported swallowing toothpaste (X2 = 2.145, df = 3, p = 0.54) and liking toothpaste (X2 = 1.926, df = 3, p = 0.59)-all statistically unrelated to TF score. This finding held when participants were grouped by present residence (Perth metro/Bunbury) or by fluoride exposure. There were 159 persons who had not been exposed to fluoridated water and had not used fluoride supplements. Of these, 27 had fluorosis. When these 27 were compared with the remaining 132 who did not have fluorosis, the children with fluorosis had not started brushing their teeth as early (t = 0.306, df = 146, p = 0.76); a somewhat greater proportion had swallowed toothpaste (57.7 vs. 42.3%), but the difference was not statistically significant (X2 = 1.12, df = 1, p = 0.29), and there was no difference in whether the children liked toothpaste (X2 = 0.144, df = 1, p = 0.70). There were 62 participants who had a TF score .2. When these persons were compared with those with TF score 1, the children with TF score .2 had started brushing their teeth slightly earlier, but the difference was not statistically significant (1.57 vs. 1.85 years, t = 1.411, df = 232, p = 0.16); a greater proportion swallowed toothpaste (X2 = 1.41, df = 1, p = 0.23), and a greater proportion did not like toothpaste (X2 = 1.92, df = 1, p = 0.17), but these differences were not statistically significant. The final multiple logistic regression model for fluorosis generally confirmed the contingency table analysis. The greatest risk of having fluorosis was associated with the optimal use of fluoride tablets, and almost as great a risk was to have lived in a fluoridated area for the first four years of life (Table 5). Lower levels of these two risk factors were associated with lower likelihoods of fluorosis. Liking toothpaste, swallowing toothpaste, and commencing the use of toothpaste at an early age were all associated with a slightly greater risk of fluorosis (OR > 1), but the 95% confidence intervals of these OR estimates included unity.

Discussion.

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TABLE 5 LOGISTIC REGRESSION COEFFICIENTS, ODDS RATIOS, AND 95% CONFIDENCE LIMITS FOR PREDICTING PREVALENCE OF DENTAL FLUOROSIS 95% Confidence Limits Upper Coefficient Odds Ratio Lower Exposure Term -1.98 Constant 4.42 0.54 1.55 0.44 Fluoride suppl. short* 2.52 0.30 0.87 -0.14 Fluoride suppl. medium* 10.90 1.97 4.63 1.53 Fluoride suppl. long* 6.42 1.42 3.02 1.11 F-area residence 1-2.4 yrt 6.44 2.55 4.06 1.40 F-area residence 2.5-4 yrt 2.15 0.75 1.27 0.24 Likes toothpaste* 2.55 0.72 1.35 0.30 Started toothpaste