18 Journal of Publi Health Dentistry Fluoride Exposure in Mihigan Shoolhildren Susan M. Szpunar MPH, DrPH Brian A. Butt BDS, MPH, PhD Program in Dental Publi Health Shool of Publi Health II The University of Mihigan Ann Arbor, MI Abstrat Reent trends in the prevalene of dental aries in hildren, as well as a possible inrease in the prevalene of dental fluorosis, have prompted some researhers to suggest the reassessment of water fluoride onentration standards. Instead of reduing water fluoride onentrations, an alternative approah would be to limit the use of, or redue the fluoride onentration of, dentifries, mouthrinses, and supplements. Information about the use of these other soures of fluoride, however, is sare. Using data from a 1987 survey of Mihigan shoolhildren, exposure to seleted fluoride soures as well as toothbrushing habits are desribed. Responses from questionnaires revealed that, overall, 98.5 perent of the hildren have used fluoride dentifries, 27 perent have used topial fluoride rinses, 72.5 perent have had at least one exposure to professionally applied topial fluoride, and 27 perent have used dietary fluoride supplements. Although the use of fluoride dietary supplements was appropriate for most hildren residing in fluoridedefiient Cadilla, the perentages of hildren in the other ommunities who have ingested these supplements suggest that these produts are being presribed improperly. Given the almost universal use of fluoride dentifries at an early age, it may be time to investigate the use of redued fluoride dentifries for hildren. In addition, ontinuing efforts to derease inappropriate dietary fluoride supplementation are required. Key Words: fluoride, dentifries, mouthrinses, supplements, fluoridation, dental fluorosis, toothbrushing. Reent studies of the prevalene of dental aries and fluorosis in US hildren (1-4) suggest that the widely reognized deline in aries may be aompanied by an Send orrespondene and reprint requests to Dr. Szpunar, Dental Dis ease Prevention Ativity, E09, Center for Prevention servies, Centers for Disease Control, Atlanta, GA 30333. Based on a dissertation submitted to the University of Mihigan shool of Publi Health, in partial fulfillment of the requirements for the DrPH degree. This study was supported by NIH National Researh Servie Award No. DE 07157. Manusript reeived: 5/31 /88; returned to author for revision: 11/14/88; aepted for publiation: 5/25/89. inrease in the very mildest forms of dental fluorosis. These trends have prompted some researhers (5,6) to all for the reassessment of the "optimal" water fluoride (F) onentration standards, in light of the inreased availability of multiple forms of fluoride, as well as possible environmental buildup. From a 1987 survey of Mihigan shoolhildren, Szpunar and Burt (2) onluded that the value of reexamining water fluoride standards should be balaned against the evidene that aries is still inversely related to water fluoride onentrations. In addition, beause water fluoridation requires no individual effort to obtain aries-preventive benefits and is available to individuals of all soioeonomi levels, it remains the most effiient and ost-effetive method of aries prevention available in the US today. If the risk of mild dental fluorosis is onsidered too high, one option might be to limit the use or redue the fluoride onentrations of other widely available soures of fluoride, suh as dentifries, mouthrinses, professionally applied topial fluorides, and fluoride supplements. Information about who uses these produts, as well as the frequeny and duration of use, however, is sare. Until a better understanding of the patterns of hildhood fluoride exposure in both fluoridated and nonfluoridated ommunities is gained, no pratial strategies for dereasing the risk of fluorosis an be developed. This artile desribes the reported use of seleted fluoride produts, as well as toothbrushing habits, in a group of 1,103 shoolhildren, aged six to 12 years, from four Mihigan ommunities with varying onentrations of fluoride in the publi water supply. In addition, the assoiation between the fluoride status of the ommunity water supply and the reported use of fluoride produts is also assessed. In the US, fluoride dentifries have been on the market sine about 1955. The sale of these dentifries amounts to about $700 million annually (7). Fluoride mouthrinsing programs have been reported to serve between 2 and 4 million hildren (Bedmarsh H, Connolly GN. Presented at APHA meeting, 1984), but the availability of over-theounter fluoride mouthrinses may have inreased the number of hildren using these produts.
Vol. 50, No. 1, Winter 1990 19 In 1983,for the first time,thenational HealthInterview Survey (NHIS) inluded questions on the use of fluoride mouthrinses, dietary fluoride supplements, and dentifries (8). Results from the survey indiated that about 89 perent of the dentate ivilian noninstitutionalized population reportedly used fluoridated dentifries; a p proximately 96.8 perent of hildren between the ages of five and 17 apparently used fluoridated dentifries. About 11 perent of dentate Amerians reportedly have used fluoride mouthrinses, with the highest perentageof usersamong thosefive to 17yearsof age(l7%). Over 14 perent of hildren younger than two years of age were reported to have used fluoride supplements, but the proportion dereased in older age groups. Only 3.9 perent of hildren aged 12 to 13 years have used these supplements. The inreased risk of fluorosis from the use of various ombinations of supplements, rinses, dentifries, and topial appliations of high onentration fluoride produts remains unknown. From an epidemiologi study of dental fluorosis and fluoride exposure, Forsman (9) determined that in infants, onsumption of 0.1 mg F/kg body weight was enough to result in dental fluorosis. This level of onsumption ould be reahed in a variety of ways, depending on the onsumption of water, infant formula, food, and the supplemental soures of fluoride (dietary fluoride supplements, rinses, dentifries). "About 50 perent of hildren in the fluoride-defiient area had reportedly used supplements, ompared to 28.2 perent of the hildren in the fluoridated areas." An inreased prevalene of fluorosis has been assoiated with the use of dietary fluoride supplements (10-12) and fluoride rinses (2). Houwink and Wagg (13), however, found no inreases in the prevalene of fluorosis in a group of hildren partiipating in a linial trial of a fluoridated dentifrie. Compliane in the use of the dentifries in the test and ontrol groups, however, was not assessed. Larsen (14) also deteted no inreased prevalene of fluorosis among hildren reeiving periodi topial fluoride gel treatments during tooth formation or prior to the end of mineralization, ompared to hildren reeiving the treatments only after tooth formation was omplete. Larsen did note, however, that the later a tooth was formed, the more enamel hanges were observed, and suggested that suh hanges may result from the use of dentifries during hildhood. The information presented here will desribe patterns in the reported use of multiple soures of fluoride by hildren residing in fluoridated and fluoride-defiient areas of Mihigan. These data may serve as a starting point in the assessment of exposure to multiple soures of fluoride in shool-aged hildren today. Methods The four ommunities surveyed were Cadilla, Hudson, Redford, and Rihmond, with ommunity water fluoride levels of approximately 0.0, 0.8, 1.0, and 1.2 ppm, respetively. Overall, 69.2 perent of the hildren reportedly reeived water from the publi water supply. By ommunity, the perentages were 65.8,57.8,99.3, and 47.4 for Cadilla, Hudson, Redford, and Rihmond, respetively. Although a question about fluoride assay of private water supplies was not asked, some parents in Rihmond indiated that their wells had been assayed for fluoride and found to have levels similar to that of the publi water supply (1.2 ppm). Details on the methods of subjet reruitment, questionnaire administration, and sreening used in this investigation have been desribed previously (2). The questionnaire form requested demographi information; residene history; information about the use of dietary fluoride supplements, professionally applied topial fluorides, over-the-ounter fluoride rinses, and dentifries; and information about toothbrushing habits, dental attendane patterns, and the method of feeding and soure of nutrition during the hild's first year of life. Parents also were asked about the highest level of eduation of the male and female heads-of-household and an open-ended question about their general opinion of the appearane of their hildren's teeth. The data used in these analyses are for the 1,103 hildren who both returned a questionnaire and partiipated in the sreening examination (Table 1). For the purposes of this analysis, hildren residing in Hudson (0.8 ppm), Redford (1.0 ppm), and Rihmond (1.2 ppm) were lassified as living in a fluoridated area, and hildren living in Cadilla (-0.0 ppm) as living in a fluoride-defiient area. The hi-squared statisti was used to test for assoiations in ontingeny table analyses. A P-value of.05 or less was onsidered to indiate statistial signifiane. Results Dietary Fluoride Supplements. Approximately 27 perent of all hildren were reported to have ever used dietary fluoride supplements. About 50 perent of hildren in the fluoridedefiient area had reportedly used supplements, ompared to 18.1 perent of the hildren in the fluoridated areas (P<.OOOl). When onsidering only those hildren who were lifetime ontinuous residents of their respetive ommunities, 58.5 perent of Cadilla hildren reported using supplements, ompared to 14.5 perent of hildren living in fluoridated areas (P<.OOOl). Using information on the reported agesat start and end of fluoride administration, the time period that a hild
20 Journal of Publi Health Dentistry TABLE 1 Number of Partiipants by Age, Sex, and Fluoride (F) Status of the Community Water Supply, Mihigan, 1987 Age (Years) FStatus/Sex <6 6-8 8-10 10-12 12+ Total Fdefiient Male 13 46 29 37 10 135 Female 12 35 48 62 21 178 Fluoridated Male 20 138 119 94 15 386 Female 30 144 121 90 19 404 Total 75 363 317 283 65 1,103 ould have reeived supplementation was omputed. For all subjets, over half of the hildren used supplements from less than one year to two full years. Among ontinuous residents only, over 50 perent of Cadilla hildren used supplements for one year or less, ompared to over 75 perent of the hildren residing in fluoridated ommunities. Cadilla residents reported slightly longer intervals of fluoride supplementation than residents of the fluoridated ommunities. In all areas, fluoride supplementation for most hildren did not our during the entire period of tooth mineralization, but rather for onsiderably shorter intervals of time. About 62 perent of all subjets and 69 perent of ontinuous residents reported that dietary fluoride supplements were given on a daily basis during the period of administration. Among the ontinuous resident subgroup, 83.3 perent of Cadilla hildren reported daily use, ompared to 57.6 perent of hildren in the fluoridated areas (P=.0037). Professionally Applied Topial Fluorides. Almost one-quarter of all hildren reportedly had never reeived a professional topial fluoride appliation. Children ontinuously residing in fluoridated areas were more likely to have had any exposure to topial fluoride. However, about one-quarter of the hildren in both fluoridated and fluoride-defiient areas reported frequent exposure (Figure 1). Toothpaste Use. Over 97 perent of all parents reported that they used a fluoride toothpaste when brushing their hild s teeth; 98.5 perent of all hildren were reported to use a fluoridated paste when brushing their own teeth. Overall, hildren in the fluoridated areas were more likely to use a fluoridated paste than hildren from Cadilla (P=.0141). However, no statistially signifiant differene was found among the ontinuousresident subgroups. Topial Fluoride Rinse Use. Overall, 73 perent of the hildren reportedly had never used a fluoride rinse. There were no signifiant differenes in the use of fluoride rinses by fluoridation status of the ommunity FIGURE 1 Perent Distribution of Continuous Resident Children by Fluoride Status of the Community Water and Exposure to Professionally Applied Topial Fluoride Treatments, Mihigan, 1987 e.- 0 S 0 u- V 0,.u 0 Y a 50 I 30 20 10 n = fluoride-defiient n=124 fluoridated n=380 4 or more 1-3 Yes, Freq. Never Treatments Treatments Unknown Frequeny of Exposure for either the full study group or the subset of ontinuous-resident hildren. Approximately 42 perent of all fluoride rinsers reported that they started using the rinse between the ages of four and five years, and 43 perent reported starting use at age six or older. Overall, hildren in the fluoridated areas tended to begin using these rinses at an earlier age than hildren in the fluoride defiient area (P=.0207), but no signifiant differenes were found for the subset of ontinuous resident hildren. From these data, it appears that the use of fluoride rinses generally began when the hild was nearing shool age, after some permanent teeth may have erupted and several had ompleted mineralization. Toothbrushing Habits. Over 50 perent of all hildren reportedly had their teeth brushed by a parent or guardian before the age of two years; there were no signifiant differenes by fluoridation status of the ommunity of residene. Figure 2 shows that about 45 perent of all hildren reportedly brushed one a day and about 43 perent brushed twie per day or more. Children in the fluoridedefiient area tended to brush less frequently than hildren in the fluoridated areas (P=.015), but the differenes among the groups were small. Assoiations with Age and Gender. Age in years was signifiantly assoiated with exposure to professionally applied topial fluorides (P<.OoOl) and with the use of topial fluoride rinses (P=.0244). As expeted, the proportion of hildren with exposure to those soures of fluoride was greater among older age groups. Sex was signifiantly assoiated with only one of the fators studied: a hild s usual frequeny of toothbrushing (P=.0256). A larger proportion of girls than boys reportedly brushed twie a day or more, and a smaller
Vol. 50, No. 1, Winter 1990 21 FIGURE 2 Perent Distribution of All Children by Fluoride Status of CommuNty Water and Usud Frequeny of Toothbrushing, Mihigan, 1987 e -.- 6 so _. - = I 40 E 50 e R 5 20 10 n Y Fluoride-defiient Less than One/day Twie/day One/day Usual Frequeny of Brushing proportion of girls than boys reportedly brushed less than one a day. Assoiations with Soioeonomi Status. Fators that were signifiantly assoiated with the highest level of eduation of the male head of household inluded the use of dietary fluoride supplements (P=.0238), the exposure to professionally applied topial fluorides (P=.OO34), the age at whih parents began brushing their hildren's teeth (P=.OO64), the age a hild began brushing his or her own teeth (P=.0369), and the usual frequeny of the hild's toothbrushing (P=.OOO9). As expeted, the frequeny of exposure to dietary fluoride supplements and professionally applied topial fluorides was greater in homes where the male parent had a ollege degree or some ollege than in homes where the male parent had fewer years of formal eduation. The majority of individuals with a high shool eduation or more began to brush their hildren's teeth before the hildren were two years old, but in homes where the male adult had only a grade shool eduation, parents were most likely to begin brushing their hildren's teeth when they were a bit older. Similarly, the majority of hildren from households where the male adult had a high shool eduation or more began to brush their own teeth between the ages of two and three years. In households where the male adult had only a grade shool eduation, the largest proportion of hildren began brushing between the ages of four and five years. In addition, the majority of hildren from households where the male adult had a grade shool eduation reportedly brushed one a day. However, in households where the male adult had a ollege degree or some ollege, the majority of hildren reportedly brushed twie a day or more. Bivariate Assoiations. A series of analyses was ompleted to assess the assoiation of one variable-for example, the use of dietary supplements-with another variable, suh as fluoride mouthrinses. In brief, the results from these analyses suggested that hildren who reeived one exposure on a frequent basis tended to reeive other exposures on a frequent basis also. For example, the reported use of over-the-ounter fluoride rinses was signifiantly related to the reported exposure to professionally applied topial fluorides. Over 38 perent of hildren who had reeived four or more professionally applied topial fluoride treatments were frequent users of fluoride mouthrinses, ompared to 28.7 perent of hildren who had reeived one to four professional fluoride treatments, and 18.8 perent of hildren who had never reeived a professional fluoride treatment (P.Ooo1). Disussion In this study, subjets were neither seleted randomly nor were the study ommunities seleted to be speifially representative of the state of Mihigan. The four ommunities were seleted purposely to have a range of water fluoride onentrations in the investigation. The information olleted on the questionnaire forms relied on parents' reall. With several hildren or a long interval of time, it is reasonable to assume that a parent's reall of an event, suh as the age a hild began toothbrushing, may have been inexat. Additionally, parents of younger hildren probably had more aurate reall of early events than parents of teenagers. In addition to possible reall bias, some parents may have answered a question in the way they thought the question should be answered, rather than what really ourred. For example, it is a widespread belief that people should brush after every meal. Some parents, then, may have indiated that their hild brushed more than one a day beause it is the "orret" answer, not the true frequeny. Beause only information about hildren who both returned a questionnaire and partiipated in the survey was used, there wasalso opportunity for seletion bias. Few differenes were noted among hildren who returned the questionnaire and agreed to be examined, and hildren who only returned the questionnaire. However, it was impossible to assess the differenes between hildren who returned a questionnaire and those who did not partiipate in any way (2). Another potential onfounding fator is that some hildren in eah ommunity were not using the publi water supply. Based on anedotal reports from these areas, however, it is unlikely that water from private wells in Cadilla, Hudson, or Rihmond had fluoride onentrations signifiantly greater than that found in the publi water supply. As disussed in the review, Ismail et al. (8) found that 96.8 perent of hildren aged five to 17 years used
22 Journal of Publi Health Dentistry fluoridated dentifries. Similarly, in this data set, 98.5 perent of hildren aged six to 12 used fluoride dentifries when brushing their own teeth. About 27 perent of hildren in the Mihigan investigation reportedly had used a topial fluoride rinse, ompared to 17 perent of hildren aged five to 17 in the NHIS data (8). The larger proportion of hildrenusing these rinses in the Mihigan study may have been a result of the differene in age groups and the inreased amount of advertising of these produts sine 1983. One reason to examine the differenes in the exposure to fluoride soures by ommunity is to see if hildren in the fluoride-defiient area were more likely to use other methods of fluoride exposure than hildren in the fluoridated areas. The data showed that the use of fluoride supplements was greater in the fluoride-defiient area than the fluoridated areas, as is appropriate. For the other fators that were examined, however, the small but statistially signifiant differenes among the ommunities were probably a result of soioeonomi and urbanhural differenes, not of an awareness of the fluoride onentration of the water supply. In optimally fluoridated areas... any additional aries protetion afforded from an inreased fluoride toothpaste ould be small ompared to a potential inrease in the risk of fluorosis. The proportions of ontinuous-resident hildren in the fluoridated areas who had ingested dietary fluoride supplements suggest that there were some physiians and dentists who were presribing these produts improperly. In this study, only hildren living in Cadilla (using the publi water supply or fluoride-defiient water from a private well) and hildren in the other three areas who were totally breast-fed should have reeived dietary sup plements. For those hildren using the ommunity water supply, over 55 perent of hildren living in the fluoridated areas who reeived fluoride supplements were bottle-fed. Aording to the ADA fluoride presription shedule, none of these hildren should have been reeiving fluoride supplements. In fluoridated ommunities, the inappropriate presription of dietary fluoride supplements may inrease a hild s risk of developing dental fluorosis. Other investigators (15-17) also have reported inappropriate fluoride presription praties in fluoridated and nonfluoridated ommunities. Levy et al. (18) found that in both fluoridated and nonfluoridated ommunities, most dentists presribed systemi fluoride supplements, but only a small number of pratitioners assayed water supplies before doing so. As demonstrated in this investigation and the 1983 NHIS data, over 95 perent of the individuals studied reportedly used fluoridated toothpastes. A portion of the deline in the prevalene of dental aries among hildren in the United States and other developed ountries sine the 1970s may be attributed to the use of suh dentifries. Beltran and Szpunar (19) onluded, from a review of the literature, that small hildren may swallow large enough amounts of dentifrie to produe levels of fluoride onsumption assoiated with an inreased risk of developing fluorosis. Bruun and Thylstrup (20) found that 55 perent of three-year-olds and 35 perent of seven-year-olds were ingesting fluoride from 1,OOO and 1,500 ppm dentifries in quantities exeeding reommended daily doses for their respetive age groups. In the Mihigan investigation, about half of the ontinuous resident hildren from the fluoridated areas had experiened dental fluorosis in the permanent dentition (2). Reently the manufaturers of dentifries in the US have begun to market two new types of produts: dentifries with an inreased onentration of fluoride (1,500 ppm F) and dentifries designed espeially for hildren. The hildren s dentifries are promoted as being less abrasive on tooth enamel than standard dentifries, as having an appealing taste for hildren, and as supplying the usual aries-protetive benefits. One dentifrie even inorporates sparkles in a blue gel. These good-tasting and appealing dentifries may promote exessive ingestion by hildren. Clinial trials omparing the antiaries effets of inreased fluoride toothpastes with the standard 1,000ppm onentration suggest relatively small inrements of additional aries protetion (21-23). In optimally fluoridated areas, therefore, any additional aries protetion afforded from an inreased fluoride toothpaste ould be small ompared to a potential inrease in the risk of fluorosis. With kiddy toothpastes already on the supermarket shelves, this may be the right time to investigate the use of lower onentrations of fluoride for hildren under the age of six years, in order to derease the risk of dental fluorosis. The questionnaire information olleted in this investigation demonstrates the widespread use of fluoridated toothpastes at an early age by hildren in four Mihigan ommunities. Other soures of fluoride, suh as professionally applied topial fluorides and over-the-ounter mouthrinses, are also used by a substantial number of individuals. However, these soures are used less frequently than dentifries, and are more likely to be used by hildren from higher soioeonomi bakgrounds. Along with the deline in dental aries that is being experiened by many Amerian hildren today, data suggest that the prevaleneof themildest forms of dental fluorosis may be inreasing in optimally and suboptimally fluoridated ommunities (1-4). To assess the role of various soures of fluoride in the etiology of dental
Vol. SO, No. 1, Winter 1990 23 fluorosis, more sensitive and reliable information on fluoride exposure will need to be olleted. Future investigators should onsider the use of personal or telephone interview of parents instead of the self-administered questionnaire that was used in this study. Personal interviews, although ostly and timeonsuming, would allow the researher to ask more speifi questions, to estimate quantity using models (for example, estimating the amount of dentifrie used per brushing), and to verify that the parents understand the meaning of the questions. Given urrent trends in the prevalene of aries and fluorosis, as well as the introdution of new dentifries to the onsumer market, it may be time to investigate the use of dentifries with a dereased onentration of fluoride for hildren under the age of six years to redue the possibility of future dental fluorosis. The use of professionally applied topial fluoride produts and topial fluoride rinses should perhaps be restrited to those hildren who appear to beat high riskof deay-for example, hildren with reent aries ativity, orthodonti bands, or poor oral hygiene. In addition, inreased efforts to derease the inappropriate presription of dietary fluoride supplements should be direted at dentists and physiians, perhaps through ontinuing eduation ourses, journal artiles and newsletters, and at professional assoiation meetings. Referenes 1. Szpunar SM, Burt BA. Trends in the prevalene of dental fluorosis in the United States: a review. J Publi Health Dent 1987;47(2):71-9. 2. Szpunar SM, Burt BA. Dental aries, fluorosis, and fluoride exposure in Mihigan shoolhildren. J Dent Res 1988 May;67802-6. 3. Leverett DH. Prevalene of fluorosis in fluoridated and nonfluoridated ommunities-a preliminary investigation. J Publi Health Dent 1986;46(4)184-7. 4. Segreto VA, Collins EM, Camann D, Smith CT. A urrent study of mottled enamel in Texas. J Am Dent Asso 1984 Jan;108:56-9. 5. Cutress TW, Sukling GW, Peare EIF, Ball ME. Defets of tooth enamel in hildren in fluoridated and nonfluoridated water areas of the Aukland Region. NZ Dent J 1985 Jan;81:12-9. 6. Leverett DH. Fluorides and the hanging prevalene of dental aries. Siene 1982 Jd;2172&30. 7. Sholle RH. Editorial: wil the manufaturers of the best fluoride dentifrie please stand. J Am Dent Asso 1981;102:958. 8. Ismail AI, Burt BA, Hendershot GE, Jak SJ, Corbin SB. Findings from thedental are supplement of the National Health Interview Survey, 1983. J Am Dent Asso 1987May;114617-21. 9. Forsman B. Early supply of fluoride and enamel fluorosis. %and J Dent Res 1977;85:22-30. 10. Aasenden R, Peebles TC. Effets of fluoride supplementation from birth on human deiduous and permanent teeth. Arh Oral Biol 1974;19:321-6. 11. Thylstrup A, Fejerskov 0, Brun C, Kann J. Enamel hanges and dental aries in 7-year-old hildren given fluoride tablets from shortly after birth. Caries Res 1979;13:265-76. 12. Granath L, Widenheim J, Birkhed D. Diagnosis of mild enamel fluorosis using two soring systems. Community Dent Oral Epidemiol1985;13:273-6. 13. Houwink B, Wagg BJ. Effet of fluoride dentifrie usage during infany upon enamel mottling of the permanent teeth. Caries Res 1979;13231-7. 14. Larsen MJ, Rihards A, Fejerskov 0. Development of dental fluorosis aording to age at start of fluoride administration. Caries Res 1985;19:519-27. 15. Margolis FJ, Burt BA, Work MA, Bashshur RL, Whittaker BA, Burns TL. Fluoride supplements for hildren. A survey of physiians' presription praties. Am J Dis Child 1980 Sept;134: 865-8. 16. Siegel C, Gutgesell ME. Fluoride supplementation in Harris Gunty, Texas. Am J Dis Child 1982 Jan;13661-3. 17. Kuthy RA, MTigue DJ. Fluoride presription praties of Ohio physiians. J Publi Health Dent 1987FaU;471R-6. 18. Levy SM, Rozier RG, Bawden JW. Use of systemi fluoride supplements by North Carolina dentists. J Am Dent Asso 1987 Mar;l14:347-50. 19. Beltran ED, Szpunar SM. Fluoride in toothpastes for hildren: suggestions for hange. J Pediatri Dent. 20. Bruun C, Thylstrup A. Dentifrie usage among Danish hildren. J Dent Res 1988 Aug671114-7. 21. Trio1 CW, Graves RC, Webster DB, Clark BJ. Antiaries effet of 1450 and 2000 ppm F dentifries [Abstrat]. J Dent Res 1987 Mar;66(Spe Iss):879. 22. Ripa L, Leske G, Forte F, Varma A. Caries inhibition of mixed NaF-Na2P03F dentifries ontaining lo00 and 2500 ppm F. Three year results. J Am Dent Asso 1988 Jan;11669-73. 23. Conti AJ, Lotzkar S, Daley R, Canro L, Marks RG, MNeal DR. A 3-year linial trial to ompare effiay of dentifries ontaining 1.14% and 0.76% sodium monofluorophospate. Community Dent Oral Epidemiol1988;16135-8. UNIVERSITY OF BRITISH COLUMBIA DEPARTMENT OF CLINICAL DENTAL SCIENCES ASSISTANT PROFESSOR Appliations are invited for a full-time, tenure-trak position as an assistant professor in the Department of Clinial Dental Sienes with a partiular interest in one or more of the disiplines of ommunity dentistry, operative dentistry, periodontis, or prosthodontis. The position involvesboth teahing and researhommitments and researh training at the PhD level, or its equivalent. Completion of an aredited graduate program in one of the disiplines is also preferred. A wide range of researh opportunities is available, as are exellent failities. One day per week is available for private pratie. The starting date is July 1,1990, or as soon as possible thereafter. Salary will be dependent on qualifiations and experiene and is subjet to final budgetary approval. The University of British Columbia is ommitted to the federal government's employment equity program and enourages appliations from all qualified individuals. In aordane with Canadian immigration requirements, priority will be given to Canadianitizens and permanent residents of Canada. Candidates are requested to forward a letter of appliation (inluding the names and addresses of three referees whom the seletion ommittee may ontat) and a urriulum vitae prior to February 15,1990. Appliations or further enquiries may be direted to Dr. Alan A. Lowe, Professor and Head, Department of Clinial Dental Sienes, Faulty of Dentistry, The University of British Columbia, 2199 Westbrook Mall, Vanouver, B.C. V6T 1Z