Water fl uoridation and dental caries in 5- and 12-year-old children from Canterbury and Wellington

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1 18 10 NEW ZEALAND DENTAL JOURNAL MARCH 004 Wter fl uoridtion nd dentl cries in 5- nd 1-yer-old children from Cnterbury nd Wellington MARTIN LEE AND PETER J DENNISON New Zelnd Dentl Journl 100, No. 1: 10-15; Mrch 004. ABSTRACT Objectives Clims hve been mde tht the effectiveness of wter fluoridtion hs reduced due to the widespred vilbility of other sources of fluoride. This study exmines the differences in the orl helth of children living in fluoridted nd non-fluoridted res of Cnterbury nd Wellington, New Zelnd. Design The dt used in this cross-sectionl study hd been routinely collected into computerized dt-collection system by the School Dentl Services in the two study res. Subjects nd methods Records of dentl sttus (dmfs/dmfs), fluoridtion sttus, ethnicity, nd socio-economic sttus for yer-olds, nd yer-olds in 1996 were nlysed. Results Cries prevlence nd severity ws consistently lower for children in the fluoridted re for both ge groups, nd within ll subgroups. Five-yer-olds in the fluoridted re hd.63 dmfs (sd, 5.88), nd those in the non-fluoridted re 3.80 dmfs (sd, 6.79). For 1-yer-olds the respective figures were 1.39 DMFS (sd,.30) nd.37 DMFS (sd, 3.46). Multivrible nlysis confirmed the independent ssocition between wter fluoridtion nd better dentl helth. Conclusions This results of this study show children living in fluoridted re to hve significntly better orl helth compred to those not in fluoridted re. These differences re greter for Mori nd Pcific children nd children of low socio-economic sttus. INTRODUCTION In 1999, the United Sttes Centers for Disese Control nd Prevention (CDC) recognized wter fluoridtion s one of the ten gret public helth chievements in the United Sttes during the 0 th century (CDC, 1999). The CDC noted tht wter fluoridtion remins the most equitble nd costeffective method of delivering fluoride to ll members of most communities, regrdless of ge, eductionl ttinment, or income level. Despite these cknowledged benefits, little progress hs been mde since the 1970s in expnding the proportion of New Zelnd s popultion receiving fluoridted wter, nd the Ministry of Helth s trget of incresing the proportion of the popultion on reticulted wter supplies who receive fluoridted wter to 70 percent by the end of 000 ws not chieved, s the level is currently 6 percent (ESR Wter Group, 00). One of the resons for the lck of progress in extending wter fluoridtion in New Zelnd my hve been the perception tht becuse of the widespred vilbility of other sources of fluoride, nd declining dentl cries rtes, wter fluoridtion ws seen s providing little dditionl benefit (Colquhoun, 1984; de Liefde, 1998). However, lmost ll the studies crried out in New Zelnd tht hve exmined the effect of wter fluoridtion on orl helth hve shown wter fluoridtion to be ssocited with significntly lower dentl cries rtes. The most recent of these ws by Tresure nd Dever (1994); this study showed tht 14-yer-olds in fluoridted Ashburton hd DMFS scores tht were 49 percent lower thn their counterprts in non-fluoridted Omru. The sme uthors hd previously shown 5-yer-olds from fluoridted Dunedin nd Ashburton to hve dmfs scores 63 percent lower thn children from non-fluoridted Omru nd Timru (Tresure nd Dever, 199). Of the 15 studies on wter fluoridtion in New Zelnd published since 1980, nd reviewed in the Public Helth Commission s report Wter Fluoridtion in New Zelnd (Public Helth Commission, 1994), only two filed to report significnt benefits from fluoridtion. One of the mjor themes to emerge from recent work on wter fluoridtion hs been tht of the reltionship between wter fluoridtion nd socio-economic sttus. It hs been consistently observed tht individuls nd groups of low socio-economic sttus benefit to much greter extent from wter fluoridtion thn those of high socio-economic sttus (Fergusson nd Horwood, 1986; Stockwell et l, 1990; Tresure nd Dever, 1994; Slde et l, 1996; Jones nd Worthington, 1999; Riley et l, 1999). This suggests tht wter fluoridtion my be powerful mens of reducing inequlities in orl helth sttus cross the popultion. This study exmines the differences in dentl cries rtes between children living in fluoridted nd non-fluoridted res of Cnterbury nd Wellington, nd exmines the reltionships between dentl cries nd wter fluoridtion, gender, ethnicity nd socio-economic sttus. METHODS Dt on the dentl sttus of children from 5 to 1 yers of ge who hd dentl cre provided for them in 1996 were obtined from the Hospitl nd Helth Services providing school dentl services in the Cnterbury nd Wellington regions. These two Hospitl nd Helth Services (now the Cnterbury nd the Hutt Vlley District Helth Bords respectively) used the sme computer system, (Molris, E Pi Ltd, Lower Hutt, NZ) developed by one of the uthors (PJD), to cpture dt on the dentl cre nd orl helth sttus of individul children. This informtion ws entered into PSION Series 3 hnd-held computers (PSION Plc, UK) t school dentl clinics by dentl therpists nd ssistnts, nd included the sttus of ech tooth surfce following completion of course of routine dentl tretment. Detils included whether ech surfce ws present or bsent, or decyed, missing (extrcted), filled, or seled. Dt were extrcted from ech dtbse, nd merged to form single dtset for nlysis. For ech child, t the completion of their lst course of dentl cre in 1996, the number of decyed, missing nd filled deciduous nd permnent tooth surfces (dmfs nd DMFS respectively), nd ge (rounded down to whole number), were clculted. Clssifiction of ethnicity, wter fluoridtion sttus, nd socio-economic sttus ws lso mde using the computerized informtion. Ethnic origin ws ssigned s either Mori, Pcific,

2 MARCH 004 NEW ZEALAND DENTAL JOURNAL 1 11 or Other bsed on prent/cregiver selection when children were enrolled for school dentl services (the Other ctegory contined children identified s Europen, South Est Asin, nd Other ; Europens mde up 97 percent of this ctegory). Socio-economic sttus ws clssified ccording to the 1996 TFEA decile rnking of the school ech child ttended. The TFEA (Trgeted Funding for Eductionl Attinment) index is the Ministry of Eduction s socio-economic indictor for schools, nd is multidimensionl index of socio-economic disdvntge bsed prtly on school enrolment dt nd prtly on census dt from ech school s ctchment re. The six dimensions re: (1) equivlent household income; () prents occuption; (3) household crowding; (4) prents eductionl qulifictions; (5) income support pyments received by prents; nd (6) Mori nd Pcific Islnds ethnicity. On the bsis of their scores, schools re rnked into deciles. Decile one represents those schools drwing from the lowest socio-economic groups, nd decile ten the highest (Dt Mngement nd Anlysis Section, 1997). For this study, three groups were formed by ggregting those in Deciles 1-3, 4-7, nd 8-10 s low, medium, nd high socio-economic sttus groups respectively. The Significnt Cries Index (SiC) ws developed to refocus the efforts of countries which hd lredy chieved the WHO/FDI gol of three or less DMFT in 1-yer-olds by the yer 000, nd pply it to the third of the popultion with highest cries scores (Brtthll, 000). Individuls re sorted ccording to their DMFT vlues nd the one-third of the popultion with the highest cries score is selected. The men DMFT for this subgroup is clculted nd this vlue constitutes the SiC Index. In 1996, New Zelnd ws one of the countries which hd lredy chieved the originl WHO/FDI gol, nd so it ws of interest to pply this index to the 1-yer-olds living in res with nd without wter fluoridtion, nd nlyse the dt by gender, ethnicity nd socio-economic sttus. Whether or not children currently lived in n re with wter fluoridtion hd been recorded when orl helth sttus records were mde t school dentl clinics. No lifetime estimte of the length of ech child s residence in fluoridted re ws mde. In the res studied, two locl bodies hd cesed fluoridting wter supplies in the 1 yers prior to 1996 nd no new fluoridtion schemes hd been introduced. The res concerned were Timru city, in which fluoridtion stopped in 1985, nd Wimiri County (now prt of Christchurch City), which cesed fluoridtion in The fct tht the dt used in this study hd been collected by lrge number of dentl therpists, t lrge number of sites, s prt of providing routine orl helth cre, ment tht the exminers were not stndrdised, nor could the exminer relibility be ssessed. Ethicl pprovl ws not sought becuse this study utilised dt routinely collected for mndtory reporting to the Ministry of Helth, monitoring nd evluting orl helth, nd service plnning. No individuls were identified. While dt were vilble for ech ge-yer group, from 5 to 1 yers old, this study presents only nlyses of orl helth for 5- nd 1-yer-olds. This decision ws mde in order to reduce the mount of informtion presented, while mintining consistency with previous studies. Stndrd methods of tbulr nlysis, including the Chi squre test, nd clcultion of odds rtios were used to describe differences between groups for the ctegoricl cries prevlence vribles; the non-prmetric Kruskl-Wllis test ws used to test for differences between groups with continuous vribles (dmfs/dmfs nd SiC); nd liner nd logistic regression were used to exmine the ssocitions between multiple vribles simultneously. For the regression nlyses dummy vrible coding of ctegoricl independent vribles (fluoridtion, gender, ethnicity, nd socio-economic sttus) ws used. This entils the cretion of n-1 dummy vribles in ech ctegory, where n equls the number of groups in the ctegory, with ech dummy vrible representing membership of group (eg mle ). One group is not coded; this is designted the reference group, nd is not represented in the regression model. Levels of sttisticl significnce were set t p<0.05. Dt nlysis ws crried out using SPSS for Windows, Version 10 (SPSS Inc., Chicgo, Ill). RESULTS The smple. The two dtbses yielded records for yer-old nd yer-old children. Dt for some individuls were incomplete, nd their records were excluded from the nlysis to leve complete records for yerolds nd yer-olds. Tble I shows tht the principl reson for exclusion in both ge groups ws missing TFEA decile informtion. The reltively high rte of exclusion for this ctegory is becuse the 1996 version of the TFEA index did not include privte nd independent schools. For both ge groups, the excluded group hd higher proportion cries-free, nd lower men dmfs/dmfs scores. Of the children included in the study, there were significnt differences in the composition of the fluoridted nd non-fluoridted groups t both ges, with higher proportions of Mori nd Pcific children, nd children from decile 1-3 schools in the fluoridted group. TABLE I Summry of the numbers of records vilble, nd records excluded from nlysis for both 5- nd 1-yer-old children. 5-yer-olds 1-yer-olds Avilble records Records with missing dt elements dmfs/dmfs Fluoridtion TFEA decile Excluded records (percentge of vilble records)* (11.7) (1.) Complete records included in this study *Sum of records with missing dt is greter thn the number of excluded records becuse some records hve more thn one element missing This study compres those children in the Cnterbury region who were not receiving fluoridted wter, nd those from Wellington who were receiving fluoridted wter. Accordingly, the smll group of Cnterbury children tht hd received fluoridted wter ws not included, nd nor ws the still smller group of Wellington children who hd not received fluoridted wter. These numbers of children in ech group re shown in Tble II. Results for five-yer-olds. Tble III shows wter fluoridtion to be ssocited with 31 percent lower dentl cries severity scores in deciduous teeth (dmfs) mong 5-yer-old children. Fluoridted wter supplies were consistently ssocited with lower dmfs scores for mles nd femles seprtely, nd mong ll ethnic nd socio-economic groups. Liner regression nlysis (Tble IV) showed tht the presence of wter fluoridtion ws ssocited with significntly lower

3 NEW ZEALAND DENTAL JOURNAL Wter Fluoridtion LEE nd MARCH DENNISON 004 dmfs scores fter controlling for gender, ethnicity, nd socioeconomic sttus. In ddition to lower dentl cries severity, wter fluoridtion ws ssocited with lower proportions of children hving cries (Tble III). As with the dmfs scores, this difference ws seen consistently cross ll gender, ethnic, nd socio-economic sttus groups. Logistic regression ws used to clculte odds rtios, nd these showed children receiving fluoridted wter to hve 0.6 times the odds of hving cries thn those with non-fluoridted wter (Tble IV). TABLE II Numbers of 5- nd 1-yer-old children, by wter fluoridtion sttus for Cnterbury nd Wellington regions (percentge of children within regions). Fluoridted wter No Yes Totl Age 5 Cnterbury (95. percent) (4.8 percent) Wellington (.9 percent) (97.1 percent) Age 1 Cnterbury (95.8 percent) (4. percent) Wellington (.1 percent) (97.9 percent) Results for 1-yer-olds. The results for 1-yer-old children prlleled those for 5-yer-olds. Wter fluoridtion ws ssocited with 41 percent lower dentl cries severity scores in permnent teeth (DMFS) for the group s whole, nd similr differences were observed within ll sub-groups considered in this study (Tble V). Multivrible nlysis (Tble VI) showed wter fluoridtion to be independently ssocited with significntly lower DMFS scores, nd only 0.6 times the odds of hving cries. Differences between ethnic nd socio-economic groups. Although it ws not the intention of this study to exmine differences in orl helth between ethnic or socio-economic groups, it is cler tht Mori nd Pcific children, nd those from low socio-economic groups hve much worse orl helth thn children from the very lrgely Europen Other group, nd the more socio-economiclly dvntged groups. For exmple, in the non-fluoridted group, the men dmfs score of Mori five-yer-olds ws double tht for the Other group, nd tht for Pcific children, three times greter thn the Others. The dt in Tbles III nd V show mrkedly lower dentl cries severity scores t both ges for Mori nd Pcific children living in fluoridted res nd this fluoridtionssocited benefit is lso seen in the higher percentges of children cries-free. Signifi cnt Cries Index (SiC) The results of the SiC index clcultions (Tble VII) show tht cross ll sub-groups there re significnt (p<0.01) differences ssocited with wter fluoridtion in the dentl cries severity (DMFT) of the onethird of 1-yer-olds in the til of the distribution curve. It ws evident tht in the fluoridted res, the SiC index ws dfms 6 6 DMFS Non-Fluoridted Fluoridted FIG 1 - Men dmfs scores by ethicity nd socioeconomic sttus for 5-yer-olds from non-fluoridted nd fluoridted res. Non-fluoridted Fluoridted FIG - Men DMFS scores by ethicity nd socioeconomic sttus for 1-yer-olds from non-fluoridted nd fluoridted res. Tble III Five-yer-old children: men numbers of decyed missing nd filled deciduous tooth surfces (dmfs), nd percentge cries-free for children receiving nd not receiving fluoridted wter, nd bsolute nd percentge differences between the two groups. Non-fluoridted Fluoridted dmfs difference cries-free dmfs Percent dmfs Percent (NF to F) difference n men sd cries-free n men sd cries-free Absolute percent percent Femle b Mle b Ethnic group Mori b Pcific c Other b Low d Medium b High b All combined b dmfs: Kruskl-Wllis test: p < b cries-free: chi squre test: p < c cries-free: chi squre test: p < 0.01 d cries-free: chi squre test: p < 0.05

4 MARCH 004 NEW ZEALAND DENTAL JOURNAL 3 13 TABLE IV Results of liner nd logistic regression nlyses for 5-yer-old children. Independent vribles Liner regression Logistic regression dependent vrible: dmfs dependent vrible: dmfs > 0 B Stndrd Odds rtio 95 percent CI error of B Wter fluoridtion Fluoridted Mle 0.30 b Mori Pcific Low Medium Constnt p < b p < 0.05 Model sttistics - Liner regression: R = 0.07, ANOVA: p < 0.001; Logistic regression: R = 0.65, Chi squre: p < TABLE V Twelve-yer-old children: men numbers of decyed missing nd filled permnent tooth surfces (DMFS), nd percentge criesfree for children receiving nd not receiving fluoridted wter, nd bsolute nd percentge differences between the two groups. Non-fluoridted Fluoridted DMFS Cries-free difference difference DMFS Percent DMFS Percent (NF to F) n men Sd cries-free n men sd cries-free Absolute percent percent Femle b Mle b Ethnic group Mori b Pcific c Other b Low d Medium b High b All combined b DMFS: Kruskl-Wllis test: p < b cries-free: chi squre test: p < c cries-free: chi squre test: p < 0.01 d cries-free: chi squre test: p < percent less thn in the non-fluoridted res, nd lredy met the new WHO gol of SiC index score of 3.0 or less before 015. DISCUSSION With the exception of two studies by Colquhoun (1977, 1985), previous reserch into the effectiveness of wter fluoridtion in New Zelnd hs been crried out using trditionl orl helth survey methods, however the results of this study re bsed on routine dentl records mde following courses of dentl cre. The use of routinely-collected informtion in New Zelnd dentl epidemiology is incresing since 1990, three of the six published studies on dentl cries in New Zelnd children nd dolescents hve relied on routinely-collected dt source (Kngrtnm, 1997, Thomson, 1993, nd Thomson et l, 00, but not Anderson nd Tresure, 1994 nor Tresure nd Dever, 199, 1994). This study is the third to be bsed on informtion gthered using the Molris dt collection system (Thomson et l, 00; Wright et l, 001). There re potentil weknesses with this pproch, especilly when ecologicl mesures re used, such s the use of the school-bsed TFEA index s mesure of socio-economic sttus. These ecologicl mesures increse the likelihood of misclssifiction. For exmple, children from disdvntged fmilies cn ttend high-decile (more dvntged) schools nd be misclssified s hving high socio-economic sttus. Misclssifiction tends to mke intergroup differences less distinct, leding in turn to difficulties demonstrting differences (Type II error) rther thn finding differences tht do not exist (Type I error). However, this lck of precision is mitigted by the lrge numbers of prticipnts included when routinely-collected dt sources re used. Orl helth surveys re normlly crried out purposively, using trined dentist-exminers, nd often include repet

5 4 NEW ZEALAND DENTAL JOURNAL Wter Fluoridtion LEE nd MARCH DENNISON 004 TABLE VI Results of liner nd logistic regression nlyses for 1-yer-old children. Independent vribles Liner regression Logistic regression dependent vrible: DMFS dependent vrible: DMFS > 0 B Stndrd Odds rtio 95% CI error of B Wter fluoridtion Fluoridted Mle c Mori Pcific Low 0.3 b b Medium 0.1 c Constnt.9 b c p < p < 0.01 p < 0.05 Model sttistics Liner regression: R = 0.04, ANOVA: p < 0.001; Logistic regression: R = 0.0, Chi squre: p < TABLE VII Significnt Cries Index scores (SiC) for 1-yer-olds Non-fluoridted Fluoridted n SiC sd n SiC sd Femle Mle Ethnic group Mori Pcific b Other Low Medium High All combined Kruskl-Wllis test: p < b p < 0.01 These scores re the men DMFT of the one-third of individuls hving the highest DMFT scores in the group described; n refers to the number of individuls for whom the index ws clculted. exmintions of proportion of prticipnts to ensure tht both dignosis nd recording re relible (World Helth Orgniztion, 1987). Despite the fct tht the dentl therpists who recorded the dt used in this study hd not been trined s epidemiologicl exminers, nd there hving been no checks mde on the relibility of the records, we do not believe ny significnt bis hs ffected the results. Other studies hve shown tht in stndrdised conditions, dentl uxiliries re s cpble s dentists t detecting dentl cries (Kwn et l, 1996; Öhrn et l, 1996), nd Husen nd collegues (001) hve shown tht dt collected from ptient records is of comprble qulity to tht obtined directly by trined exminers. We consider tht one of the strengths of this study is the very lrge numbers of children involved yer-olds, nd yer-olds which resulted in reltively lrge numbers of Mori nd Pcific children. Lrge, routinely-collected dtsets my hve significnt dvntges in illustrting the orl helth sttus of the New Zelnd popultion, compred to conventionl survey methods tht utilise smller smples, s smller smples my lck sufficient sttisticl power to demonstrte ssocitions involving smll but importnt subgroups. These routinelycollected dtsets lso llow for longitudinl reserch, so tht chnges over time cn be exmined, such s the study crried out by Thomson et l (00). Erly studies on the effectiveness of wter fluoridtion found reductions in dentl cries severity scores in excess of 50 percent. However, the differences between fluoridted nd non-fluoridted res pper to hve decresed over time (Lewis nd Bnting, 1994), nd the UK Ntionl Helth Service review of wter fluoridtion (which involved met-nlysis of longitudinl studies) reported tht fluoridtion ws more recently ssocited with 15 percent improvement in DMFT (McDongh et l, 000). The results of this study show tht the benefits of fluoridtion in New Zelnd continue to be significnt. Lower cries prevlence nd severity in fluoridted res in excess of 30 percent for both 5- nd 1-yer-old children re importnt both from public helth perspective, nd for individul children. Mny of the children who hd received fluoridted wter would hve benefited from cliniclly meningful reductions in their dentl cries experience, nd the consequent reductions in the mount of dentl tretment they hd received. This study lso shows wter fluoridtion to be ssocited with mrked differences in orl helth inequlities between fluoridted nd non-fluoridted res, nd much lrger bsolute differences in

6 MARCH 004 NEW ZEALAND DENTAL JOURNAL 9 15 cries prevlence nd severity for Mori nd Pcific children, nd for socio-economiclly disdvntged children. An unexpected finding of the liner regression nlysis ws tht gender hd n independent effect on dmfs scores t ge five, with mles hving worse orl helth thn femles. We hd expected tht femles would hve worse orl helth t ge 1, becuse the permnent teeth of femles tend to erupt erlier (Mugonzibw et l, 00), nd re therefore more likely to hve experienced dentl cries, but we would not like to speculte on the resons for the differences t ge five. CONCLUSIONS This study provides evidence of rel differences in dentl helth for both 5- nd 1-yer-old children ssocited with wter fluoridtion, nd demonstrtes how fluoridted wter reduces orl helth inequlities mong children of different ethnic nd socio-economic bckgrounds. It is our hope tht n incresing number of New Zelnd communities will become wre of the benefits of wter fluoridtion, nd tke the necessry steps to implement the community wter fluoridtion schemes tht will help protect the orl helth of their locl popultion. REFERENCES Anderson RJ nd Tresure ET (1994). The prevlence of dentl cries in 5- nd 1-yer-old children resident in five loctions of South Otgo. New Zelnd Dentl Journl 90: Brtthll D (000). Introducing the Significnt Cries Index together with proposl for new globl orl helth gol for 1-yer-olds. Interntionl Dentl Journl 50: CDC (1999). Achievements in public helth, : fluoridtion of drinking wter to prevent dentl cries. Morbidity nd Mortlity Weekly Reports 48: Colquhoun J (1977). The influence of socil rnk nd fluoridtion on dentl tretment requirements. New Zelnd Dentl Journl 73: Colquhoun J (1984). New evidence on fluoridtion. Socil Science nd Medicine 19: Colquhoun J (1985). Influence of socil clss nd fluoridtion on child dentl helth. Community Dentistry nd Orl Epidemiology 13: Dt Mngement nd Anlysis Section (1997). Ministry of Eduction Socio-economic Indictor for Schools. Wellington: Ministry of Eduction. de Liefde B (1998). The decline of cries in New Zelnd over the pst 40 yers. New Zelnd Dentl Journl 94: ESR Wter Group (00). Register of Community Drinking Wter Supplies. Wellington: Ministry of Helth. Fergusson DM nd Horwood LJ (1986). Reltionships between exposure to dditionl fluoride, socil bckground nd dentl helth in 7-yer-old children. Community Dentistry nd Orl Epidemiology 14: Husen H, Kärkkäinen S, nd Sepp L (001). Cries dt collected from public helth records compred with dt bsed on exmintions by trined exminers. Cries Reserch 35: Jones CM nd Worthington H (1999). The reltionship between wter fluoridtion nd socio-economic deprivtion on tooth decy in 5-yer-old children. British Dentl Journl 186: Kngrtnm S (1997). Dentl cries ptterns nd the utilistion of dentl services mong 15-yer-old dolescents in the Southern Regionl Helth Authority region. New Zelnd Dentl Journl 93: Kwn SY, Prendergst MJ, nd Willims SA (1996). The dignostic relibility of clinicl dentl uxiliries in cries prevlence surveys - pilot study. Community Dentl Helth 13: Lewis DW nd Bnting DW (1994). Wter fluoridtion: current effectiveness nd dentl fluorosis. Community Dentistry nd Orl Epidemiology : McDongh MS, Whiting PF, Wilson PM, Sutton AJ, Chestnutt I et l (000). Systemtic review of wter fluoridtion. British Medicl Journl 31: Mugonzibw EA, Kuijpers-Jgtmn AM, Line-Alv MT, nd vn t Hof MA (00). Emergence of permnent teeth in Tnznin children. Community Dentistry nd Orl Epidemiology 30: Öhrn K, Crossner CG, Börgesson I, nd Tube A (1996). Accurcy of dentl hygienists in dignosing dentl decy. Community Dentistry nd Orl Epidemiology 4: Public Helth Commission (1994). Wter Fluoridtion in New Zelnd. Wellington: Public Helth Commission. Riley JC, Lennon MA, nd Ellwood RP (1999). The effect of wter fluoridtion nd socil inequlities on dentl cries in 5-yer-old children. Interntionl Journl of Epidemiology 8: Slde GD, Spencer AJ, Dvies MJ, nd Stewrt JF (1996). Influence of exposure to fluoridted wter on socio-economic inequlities on children s dentl experience. Community Dentistry nd Orl Epidemiology 4: Stockwell AJ, Medclf GW, Rutledge GJ, Holmn CDJ, nd Roberts M (1990). Dentl cries experience in school children in fluoridted nd non-fluoridted communities in Western Austrli. Community Dentistry nd Orl Epidemiology 18: Thomson WM (1993). nd child dentl helth sttus in the Mnwtu-Wngnui Are Helth Bord. New Zelnd Dentl Journl 89: Thomson WM, Willims SM, Dennison PJ, nd Pecock DW (00). Were NZ s structurl chnges to the welfre stte in the erly 1990s ssocited with mesurble increse in orl helth inequlities mong children? Austrlin nd New Zelnd Journl of Public Helth 6: Tresure ET nd Dever JG (199). The prevlence of cries in 5-yerold children living in fluoridted nd non-fluoridted communities in New Zelnd. New Zelnd Dentl Journl 88: Tresure ET nd Dever JG (1994). Reltionship of cries with socio-economic sttus in 14-yer-old children from communities with different fluoride histories. Community Dentistry nd Orl Epidemiology : World Helth Orgnizton (1987). Orl Helth Surveys - Bsic Methods. Genev: World Helth Orgniztion. Wright JC, Btes MN, Cutress T, nd Lee M (001). The costeffectiveness of fluoridting wter supplies in New Zelnd. Austrlin nd New Zelnd Journl of Public Helth 5: MARTIN LEE, BDS, MComDent School nd Community Dentl Service Cnterbury District Helth Bord Christchurch New Zelnd PETER J DENNISON, BDS, MComDent Fculty of Dentistry University of Sydney New South Wles Austrli Corresponding uthor: Mrtin Lee (E-mil: mrtin. lee@cdhb.govt.nz)