Community Dent Oral Epidemiol All rights reserved

Ó 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Exploring the determinants of secular decreases in dental caries among Korean children

Hye-Ju Lee1,2 and Dong-Hun Han1,2 1 Department of Preventive and Social Dentistry, School of Dentistry, Seoul National University, Seoul, Korea, 2Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea

Lee H-J, Han D-H. Exploring the determinants of secular decreases in dental caries among Korean children. Community Dent Oral Epidemiol 2015. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Abstract – Objective: The aim of this study was to determine the contributions of sealant and water fluoridation to the time trends in dental caries from 2003 to 2010. Materials and methods: Data were from three waves of the Korean National Oral Health Surveys between 2003 and 2010, including a total of 23 059 children (11 889 boys and 11 170 girls) aged 8, 10, and 12 years. The impacts of sealant and water fluoridation on dental caries were obtained by logistic regression for each age group of children. The contributions of sealant and water fluoridation to the time trends in the prevalence of dental caries were examined by a series of logistic regression models, and changes in the adjusted odds ratios for each survey year were also calculated. Results: Over the past 7 years, the prevalence of dental caries decreased dramatically. Although sealant had a significant impact on dental caries in each survey year, remarkable decreases in dental caries from 2003 to 2010 were not explained by the secular changes in the dental sealant or water fluoridation factor. Conclusion: We observed important population declines in dental caries in Korea in children aged 8–12 years; however, the likely causes for these secular trends remain to be determined.

Dental caries is the most common chronic disease in childhood. If not managed properly, it may result in significant acute and chronic conditions, of which the most severe include bacteremia and impaired development, not to mention high treatment costs and other consequences to their families and communities (1). However, the past several decades have seen a dramatic reduction in dental caries in many developed countries (2). Examining secular trends in childhood dental caries will help us better understanding populationlevel determinants of dental caries. Some prior studies reported secular changes in dental caries and examined the contribution of higher economic and social development (3), and numerous public health measures including community water fluoridation, better disease management, improved doi: 10.1111/cdoe.12160

Key words: caries; epidemiology; prevention; public health policy Dong-Hun Han, Department of Preventive and Social Dentistry, School of Dentistry, Seoul National University, 101 Daehak-ro, Jongno-gu, Seoul 110-749, Korea Tel.: +82-2-740-8780 Fax: +82-2-765-1722 e-mail: [email protected] Submitted 19 December 2013; accepted 25 January 2015

oral hygiene, and widespread use of fluoridated toothpaste (4). A previous study has reported on caries reduction trends in Korea (5). Dental caries prevention in children and adolescents involves a range of population- and individual-level strategies that may include oral health education, community water fluoridation, and topical fluorides such as fluoride varnish, dental sealants, antibacterial rinses, and dietary interventions. Other than community water fluoridation (6), the community-based prevention strategy best supported by evidence and feasibility is dental sealant (7). In 2000, the National Assembly of Korea passed the Oral Health Act, through which public oral health programs have gained a legal foothold for budgeting, and major projects have been planned.

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Lee & Han

To prevent dental caries, the main public oral health programs in urban and rural areas have been community water fluoridation and a public fissure sealant program (5). Examination of the trends for two major public oral health programs including water fluoridation and dental sealants may provide clues about the origin of the significant declines in childhood dental caries in Korea. In addition, understanding the relationships between public oral health programs and dental caries trends may provide evidence for better public oral health policy. Therefore, the aims of this study were (i) to trace the secular changes in childhood dental caries and two major dental public health programs including water fluoridation and dental sealants from 2003 to 2010 using nationally representative Korean data and (ii) to examine the potential contributions of trends in childhood dental caries.

Materials and methods Sampling Data were from three waves of the Korea National Oral Health Surveys (KNOHS) conducted in 2003, 2006, and 2010. Data are publicly available from the Korea Health Promotion Foundation (8). Information was collected with a stratified cluster sampling procedure. Oral health surveys for children aged 8, 10, and 12 years were conducted by visiting schools. In the 2003 survey which was made up of 60 survey districts, a classroom for all school grades was randomly selected, and every fifth student was examined (9). The 2006 and 2010 surveys were the same as that of the 2003 survey except for the number of survey districts and number of participants. The number of districts changed to 150 in the 2006 survey, and every fifth student was examined. 12-year-old children were oversampled by two times (10). In the 2010 survey, 6-, 8-, 10-, 12-, and 15-year-old children from 200 districts were selected, a classroom for each school age was randomly selected, and all the students in the classroom were examined (11). To analyze the effect of water fluoridation and dental sealants, 8-, 10-, 12-year-old children were chosen. The final samples of each survey were 1796 (2003 survey), 3518 (2006 survey), and 17 745 (2010 survey) children aged 8, 10, 12 years. The number of children by age were 599 (8 years), 600 (10 years), and 597 (12 years) in 2003, 875 (8 years), 888 (10 years), and 1755

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(12 years) in 2006, and 5732 (8 years), 5760 (10 years), and 6253 (12 years) in 2010.

Dental caries examination The dental caries in the permanent dentition was examined according to the WHO criteria (12). The subjects were examined in the classroom, sitting facing a window with natural lighting. Dental caries was detected at the D3 caries into the dentine threshold. The teeth showing sealed fissures, whether complete or incomplete, were recorded. The examination was performed using disposable instruments: plane mirrors, sharp explorers and CPITN probes. No radiographs were taken. Calibration exercises for the examiners were carried out before the survey. The first procedure consisted of dictation and discussion using slides to obtain validity. Then, the chief investigator and the examiners examined the same participants. Any discrepancies in the findings about untreated dental caries and caries experience were discussed. An examiner was acceptable to conduct the survey when interexaminer variability for untreated dental caries and caries experience was acceptable and good agreement for untreated dental caries and caries experience with the chief investigator was achieved (j ≥ 0.7). The prevalence of untreated dental caries was defined as the existence of untreated dental caries (yes versus no), and the prevalence of caries experience was defined as the existence of caries experience (yes versus no).

Sealants, water fluoridation, and resident area The prevalence of dental sealants was also defined as the existence of pit and fissure sealants (yes versus no). The survey district was linked to the information about community water fluoridation. The definition of water-fluoridated community was the community which was provided fluoridated tap water more than 3 years at the survey. Then, the water fluoridation variable was categorized into ‘fluoridated’ and ‘nonfluoridated’. The water-fluoridated period of fluoridated areas was at least 4 years in 2003 and 2010 surveys, and 7 years in 2006 survey. The demographic information including age, gender, and resident area (urban/rural) was obtained.

Statistical analysis We presented trends for the total and sex-specific untreated dental caries prevalence, dental sealant prevalence, percentage of residents with fluoridated water supply, and percentage of rural

Secular decrease in dental caries among Korean children

residents among each age group (8, 10, 12 years). Complex sample frequency analysis was performed after taking into account the district, stratification, and sample weights to obtain unbiased point estimates and robust linearized standard errors. We used logistic regression to test the association of dental sealant and water fluoridation with dental caries in each survey year controlling for gender and urban/rural area. Finally, we examined the contributions of dental sealant and water fluoridation to the time trends in the prevalences of dental caries by adjusting for each of those with dental sealant and water fluoridation in the baseline regression models and examining the changes in the adjusted odds ratios (ORs) for each survey year. The model adjusting for gender and urban/ rural area was the baseline model in this analysis. The roles of dental sealant and water fluoridation were evaluated with the percentage (%) excess odd explained, which can be calculated as

[(ORbaseline ORbaseline + dental sealant and/or water fluo1)] in this study (13). This perridation)/ORbaseline centage excess odd explained represents the degree to which dental sealant or water fluoridation explains the trends for the dental caries. The analyses were performed using SPSS 21.0 software (SPSS Inc., Chicago, IL, USA).

Results As shown in Table 1, a total of 23 059 children (11 889 boys and 11 170 girls) participated in the three waves of the surveys between 2003 and 2010. The prevalence of untreated dental caries substantially decreased from 22.2% to 7.6% in 8-year-olds, 34.0% to 11.4% in 10-year-olds, and 49.7% to 19.8% in 12-year-olds between 2003 and 2010. The prevalence of caries experience also decreased from 43.2% to 27.2% in 8-year-olds, 61.5% to 46.2% in

Table 1. Basic characteristics of Korean children from the Korean National Oral Health Surveys 2003–2010 Total Variables 8 years N Untreated caries, n (%) Caries experience, n (%) DT, mean FT, mean DMFT, mean F/DMFT, % Sealant, n (%) Water fluoridation, n (%) Rural residents, n (%) 10 years N Untreated caries, n (%) Caries experience, n (%) DT, mean FT, mean DMFT, mean F/DMFT, % Sealant, n (%) Water fluoridation, n (%) Rural residents, n (%) 12 years N Untreated caries, n (%) Caries experience, n (%) DT, mean FT, mean DMFT, mean F/DMFT, % Sealant, n (%) Water fluoridation, n (%) Rural residents, n (%)

2003

2006

2010

P for trend

599 133 (22.2) 259 (43.2) 0.44 0.60 1.03 58.3 206 (34.4) 80 (13.4) 90 (15.0)

875 92 (10.8) 267 (30.3) 0.16 0.51 0.67 76.1 338 (39.4) 48 (5.0) 86 (13.0)

5732 456 (7.6) 1591 (27.2) 0.12 0.45 0.57 78.9 3025 (52.9) 482 (8.5) 840 (13.3)

Exploring the determinants of secular decreases in dental caries among Korean children.

The aim of this study was to determine the contributions of sealant and water fluoridation to the time trends in dental caries from 2003 to 2010...
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