Dental caries experience in children of a remote Australian Indigenous community following passive and active preventive interventions

Abstract Objectives To report on changes in dental caries experience in children of a remote Indigenous community following 6 years of passive preventive intervention (PPI) and 2 years of active preventive intervention (API). Methods Five consecutive cross‐sectional surveys were conducted on 4‐ to 15‐year‐old school going children between 2004 and 2017 following phases of Community Water Fluoridation (CWF), post‐cessation of CWF and API. Following treatment of any cavities present, API included selective placement of fissure sealants (FS) and an annual application of povidone‐iodine (PI) and fluoride varnish (FV). The World Health Organization's (WHO) “Oral Health Surveys – Basic Methods (4th Edition)” methodology was used in the first two and the International Caries Detection and Assessment System (ICDAS‐II) in the latter three surveys. ICDAS‐II codes of 3‐6, representing advanced caries, were combined to allow comparison to the decayed component of the DMF caries index. Results Age‐weighted mean dmft decreased by 37.7% in the deciduous (DD) and DMFT by 35% in the permanent (PD) dentitions between the pre‐ and post‐CWF surveys, followed by increases of 25% and 7.7%, respectively, between the 1‐year and 4‐year post‐CWF surveys. After 2 years of API, mean dmft decreased by 14.3% and DMFT by 7.1%. Untreated dental caries however remained a concern in the DD and PD during both phases of PPI and of API. The decline in caries experience for both dentitions following 2 years of API exceeded that for the 6‐year period of PPI. Conclusions The annual reductions in caries experience of 7.2% (DD) and 8% (PD) during the phase of API exceeded annual decreases of 4.7% (DD) and 4.6% (PD) during the phase of PPI. Due to remoteness, cost and logistics in ensuring long‐term viability of API programmes, CWF remains necessary in this type of community.


| INTRODUC TI ON
Globally, between 1990 and 2015 the number of people with untreated oral disease is estimated to have increased from 2.5 to 3.5 billion. 1 Between 1990 and 2017, oral diseases remained one of the two most prevalent causes of the global burden of disease for all ages and sexes combined, despite decreasing by 5.5% over this time. 2 In the Australian National Child Oral Health Survey (NCOHS) 2012-14, 27.1% of 5-to 10-year-olds and 10.9% of 6-to 14-year-olds presented with untreated dental caries in their deciduous dentition (DD) and permanent dentition (PD), respectively. This was approximately 50% higher for Indigenous compared to non-Indigenous children and consistently higher again for remote/very remote communities. 3 A higher burden of dental caries has also been reported for adult Australian Indigenous people 4 as well as Indigenous communities globally. [5][6][7] Active and passive preventive measures are defined in terms of the amount of action required to produce benefit. Whereas passive preventive intervention (PPI) protects individuals without any cooperation or action on their part, active preventive intervention (API) not only requires individual action, but often trained personnel, facilities and resources. 8  Community Water Fluoridation is widely regarded as a safe and effective evidence-based intervention for the prevention of dental caries, as confirmed recently by a 2018 American Association for Dental Research (AADR) policy statement. 9 The Australian National Health and Medical Research Council (NHMRC) Information Paper on Water Fluoridation (2017) stated that CWF reduced tooth decay by between 26% and 44% in children, teenagers and adults. 10 A systematic review published in 2015 confirmed that CWF decreases tooth decay and increases the number of children free of caries in both dentitions, although the authors concluded that much of the evidence was of low quality and that many studies were conducted before 1975. 11 A critique of this review warned against concluding that CWF was of dubious benefit as all other authoritative reviews have found it to be effective at reducing dental caries in both dentitions. 12 A United States study including child and adolescent populations reported in 2018 that greater availability of CWF was associated with significantly lower levels of dental caries in both groups. 13 A consistent association between lifetime exposure to CWF and caries experience was found in both dentitions of Australian children 14 and a significant decrease in caries experience was reported for a low socioeconomic community in Queensland only 36 months after the introduction of CWF. 15 The York Report concluded that cessation of CWF resulted in a narrowing of the difference in caries experience between the fluoridated and nonfluoridated communities over time, 16 as confirmed by a recent systematic review. 17 Active preventive intervention such as FS, PI and FV has each been found to be effective in reducing dental caries. [18][19][20][21][22] In Australia, all of these require trained oral health workers and appropriate facilities. As the wider literature indicates that regular re-application is desirable, this is difficult to sustain in resource-constrained remote communities.
Following a 2004 survey of children in a remote Indigenous community consisting of five small towns, all within 20 km of each other, in the Northern Peninsula Area (NPA) of Far North Queensland (FNQ) Australia, dental caries experience of 6-and 12-year-olds was more than twice the Queensland average and more than four times greater than the Australian average. 23 The Bamaga Hospital has a 2-chair dental clinic with oral health staff from Thursday Island providing a dental service in this facility for a few days every fortnight. Children in need of emergency care are transported by ferry to Thursday Island.
The aim of this investigation was to report on changes in dental caries experience in children of this community following 6 years of PPI and 2 years of API, spanning 2004-2017.   20.4% of 6-to 14-year-olds (PD) presenting with untreated decayed teeth, compared to 28.4% (DD) and 11.7% (PD) for non-Indigenous children. 36 A 2018 report on the health of Q ueenslanders found dental decay to be higher than the state average in the TCHHS where F I G U R E 1 A timeline of surveys and the phases of PPI, post-cessation of CWF and API between 2004 and 2017 our study community is located. 37 In our study, the percentage of children with caries experience was similar to the QCOHS results in the DD, whereas lower mean dmft scores, and higher percentage of children with caries experience/mean DMFT scores were found in the PD. In line with other Australian studies in Indigenous populations, our findings confirm that dental caries, especially untreated decay, remains a significant burden of disease in our community as well.

| D ISCUSS I ON
Australian evidence suggests that longer lifetime exposure to CWF resulted in substantially lower caries experience in younger rural adults. 38  Evidence shows that over time cessation of CWF results in a narrowing of the difference in caries experience between fluoridated and nonfluoridated communities. 16 A recent systematic review concluded that an increase in dental caries occurs post-CWF cessation, but that the effect is not uniform or inevitable. 17 In our study we noted an increase in mean dmft/DMFT scores, percentage of children with caries experience and SiC for the phase of post-cessation of CWF (2012-2015), but less so in the PD compared to the DD. As the results presented were pooled for all ages with DD (4-12 years) and with PD (5-15 years), this difference can be explained by the PD of older children having been exposed to CWF for longer compared to the DD in younger children.
Fissure sealants, PI and FV have all been reported to have significant impact in preventing dental caries. A systematic review reported that FS reduced dental caries on permanent occlusal surfaces between 11% to 51% in children and adolescents 2 years after application 40 and that reductions in caries experience of between 37% (DD) and 43% (PD) could be achieved by regular application of FV in studies of a duration of between 1-5 years. 41 It is recommended that FV and PI should be applied 2-3 times a year to be most effective 22,40 with a combination of FV and PI reported to be more effective than FV alone. 20 In our study, the phase of API (2015-2017) consisted of treatment of dental decay including selective FS at baseline, followed by application of PI and FV on completion of treatment, with re-application of PI and FV at the 1-and 2-year follow-up visits. 24 API led to a decrease in mean dmft/DMFT, percentage of children with caries experience and SiC in both dentitions. However, the viability and sustainability of API in remote communities, such as that studied here, remain unanswered. A possible option would be to train other health workers, even members from the community, to apply FV and PI more frequently, if permitted by relevant legislation.
Untreated dental caries remained a concern in both dentitions during both phases of PPI and API. Whilst annual API was TA B L E 1 Caries experience for the phases of PPI, post-cessation of CWF and API effective, due to remoteness, cost and logistics in ensuring longterm viability of such programmes, CWF remains necessary in this type of community. Since substantial dental health disparities and inequalities in access to dental care currently exist in more regional and remote communities, such as the one we studied, there is justification for extending coverage to include all Australians, even when cost-effectiveness seems less favourable in more remote and smaller communities. 42 The savings in treatment are greater than the cost of CWF for communities with more than 1000 residents, with the benefit increasing for larger communities. 43 surveys was another limitation. Children who were not consented to treatment during the phase of API formed a natural comparison group.

| CON CLUS IONS
Dental caries remains a significant problem in this remote Indigenous community despite consecutive phases of PPI and API. Continuing efforts to lobby for the re-implementation of CWF are essential, as are addressing social determinants of health, especially related to diet.

ACK N OWLED G EM ENTS
The authors gratefully acknowledge the Elders, community members & community workers in the NPA of FNQ, as well as the principals, staff & children of the NPA State College. Our sincerest thank you to all chief and associate investigators, project managers and staff. The API phase of the study was funded by an Australian NHMRC Project Grant (APP1081320). The authors declare no potential conflicts of interest.

AUTH O R CO NTR I B UTI O N S
NWJ leads the project as PI. All authors contributed to conception and design, including participation in field work and data acquisition.
JK undertook initial data analysis supported by RL and ST. All authors participated in data interpretation. JK wrote the first draft of the paper which was critically reviewed by all authors, who accept joint responsibility for content.