© 2004 American Public Health Association
At the time of this investigation, Jessica Y. Lee was a PhD candidate in health policy and administration at the University of North Carolina, Chapel Hill, School of Public Health. R. Gary Rozier and Edward C. Norton are with the Department Health Policy Analysis and Administration, University of North Carolina, Chapel Hill. William F. Vann Jr is with the Department of Pediatric Dentistry, University of North Carolina, Chapel Hill. Jonathan B. Kotch is with the Department of Maternal and Child Health, University of North Carolina, Chapel Hill. Correspondence: Requests for reprints should be sent to Jessica Y. Lee, DDS, MPH, PhD, Department of Pediatric Dentistry, CB 7450 Brauer Hall, Carolina Campus, Chapel Hill, NC 275997450 (e-mail: jessica_lee{at}dentistry.unc.edu).
Objectives. We estimated the effects of the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) on dental services use by Medicaid children in North Carolina. Methods. We used linked Medicaid claims and enrollment files, WIC files, and the area resource file to compare dental services use for children enrolled in WIC with those not enrolled. We used multivariate models that controlled for child clustering and employed 2-step methodology to control for selection bias. Results. Children who participated in WIC had an increased probability of having a dental visit, were more likely to use preventive and restorative services, and were less likely to use emergency services. Conclusions. Childrens WIC participation improved access to dental care services that should lead to improved oral health.
Dental disease and access to dental care are major public health problems for young low-income children living in the United States. This national dilemma has recently come under close scrutiny by policymakers, health care providers, and researchers.1,2 Because of frequent interactions with low-income children and their families, several public health programs can help alleviate dental problems and improve access to dental care. An example of such a program is the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). WIC is administered by the Food and Nutrition Services of the US Department of Agriculture and serves more than 7.4 million individuals.3 Over one third of infants born in the United States are enrolled in the WIC program. It is often the first contact with the health care system for many poor women and children. The primary goal of WIC is to "improve the health of women and children by providing nutritious foods, nutrition education and good health care during pregnancy, the postpartum period, infancy and early childhood."4(p391) To achieve its goal, WIC agencies work to improve the linkage between clients and health care providers, including dentists, through referrals and networking.5
Several investigations have demonstrated the effectiveness of WIC in providing positive health outcomes. Among the benefits are a reduced frequency of low-birthweight deliveries,68 reduced Medicaid costs for newborns,9 reduced rates of anemia in children,6 and increased nutrient intake in children.10 The health effects of WIC participation are attributed to the direct nutrition-related benefits of the program rather than to the benefits of coordination of health and social services.11 However, the beneficial effects of the coordination of health services cannot be dismissed readily.12 Referral of children to health and social services is an important component of WIC programs. WIC counselors advise families about the location of clinics and programs, such as Medicaid and the State Childrens Health Insurance Program, that help pay for health care. Few studies have addressed the effects of WIC on the utilization of health care services.3,6,10 One investigation demonstrated that WIC participants used a childrens clinic more frequently than did nonparticipants.12 In a recently published study, Buescher et al. reported that "Medicaid-enrolled children participating in the WIC program use all types of health care services compared with Medicaid-enrolled children who were not WIC participants."13(p145) They concluded that "the health care needs of low-income children who participate in WIC may be better met than those of low-income children who were not WIC participants."13(p145)
Only 2 small, descriptive studies have investigated the relation between participation in WIC programs and referrals for oral health care. McCunniff et al.14 examined dental referral rates by WIC clinics in Missouri, reporting that of the 1850 participants seen during a 2-month period at a clinic site, 27% of children and 17% of infants were referred for services outside the WIC clinic. Using selfreported information from caregivers, McCunniff et al.14 also reported a statistically significant bivariate relation between WIC referral and having a dental visit. Dental referrals constituted 10% of these referrals made for infants and children. Sargent et al.15 used a survey of WIC employees in an inner-city clinic to examine referral patterns. WIC nutritionists at this site offered a variety of referrals to their clients. One fifth of WIC participants were referred to health services, and referrals for dental care constituted the majority of these referrals. Results of these 2 studies suggest that dental referrals do take place within WIC clinics, but the proportion of all referrals due to a dental problem varied considerably. Furthermore, the outcome of these referrals is largely unknown. Findings from previous WIC and health care utilization investigations are further limited because they do not control for the nonrandomized nature of WIC participation.13,16 We build on these past studies in an investigation of WIC participation and use of dental services by using claims data rather than self-reports and by employing multistage modeling to control for selection bias. Using these more sophisticated analytic techniques in our exploration of the effects of WIC on use of oral health services, we provide an estimate of the effectiveness of WIC programs in linking clients with dental providers. Specifically, we determined whether, compared with Medicaid children who did not participate in WIC, preschool-aged Medicaid children enrolled in WIC had an increased likelihood of having had a dental visit and whether it was of a certain type (preventive, restorative, or emergency.
We tested the hypothesis that children enrolled in WIC have better access to dental care than children not enrolled in WIC. For purposes of this investigation, we defined access as use of services that was represented by Medicaid claims data. We measured the effects of childrens WIC participation on the probability of a childs having had a dental visit and the different types of visits. Available sociodemographic variables were included as control variables in our analyses.
Data Sources and Study Cohort All children born in North Carolina in calendar year 1992 who were enrolled in the Medicaid program were eligible for inclusion in the study. Children were excluded if they had more than 1 Medicaid identification in their records (759 children) or if they had recorded periods of Medicaid enrollment indicated before the date of birth (1371 children). A Medicaid enrollment history was created for each child in which enrollment status was indicated for each month of life from birth to the age of 5 years (months 1 through 60).
Analysis Strategy Another important analysis consideration was the potential for selection bias. Because WIC participation was not randomly determined among Medicaid children, we anticipated that children who participated in WIC would more likely be users of health care services than other Medicaid children. This assumption suggests the potential for correlation between the WIC participation variable and the error term of our main analysis. Failure to account for this correlation could bias our results. To control for this potential bias, we incorporated a 2-stage multilevel model using instrumental variables as outlined by Bollen et al.17 We screened potential instrumental variables for their close association with WIC participation. Three instrumental variables (number of WIC clinics per county, number of full-time WIC workers per county, and WIC hours of operation per county) were correlated with WIC participation but not with dental utilization and were used in our analysis. The primary measure of oral health utilization was a 3-level variable defined as no visits, 1 visit, or 2 or more visits per year as represented by dental claims. These categories were used because the recommended number of dental visits is 2 per year.18 We did not distinguish among the number of visits greater than 2 per year because those differences are likely to depend on the severity of dental disease rather than basic issues associated with access to care. Because the measure of this dependent variable was coded as 0, 1, and 2, we used an ordered probit analysis with controls for clustering to examine WIC and oral health services utilization for each observation year (1 through 4). We used separate random effects logit analyses (logistic regression) for each type of oral health services used. Type of services received was classified as (1) diagnostic/preventive services, (2) restorative services, and (3) emergency services. The American Dental Association procedure codes were used to classify service categories.18 Additionally, if a child had a hospital emergency room claim with a primary diagnosis of dental caries19 it was included as an emergency visit. These visit types were coded 0 or 1 to represent each type of visit per year as indicated by Medicaid claims. Our major explanatory variable was childrens WIC participation measured as the number of months when any WIC voucher was redeemed during each year of life. We also incorporated relevant available sociodemographic control variables into our analysis. These included maternal educational level (years of school completed), maternal age (years), household income (actual dollar amounts), marital status (unmarried vs married), and minority status (non-White vs White). Many of these variables have been reported as important determinants of access to oral health care.2022 In addition, we used length of Medicaid enrollment (months) and dentists-to-population ratio in our analyses.
Descriptive Statistics Summary statistics for the study cohort are presented in Table 1
Analytic Results The analytic file consisted of 4 observations per child (n = 49 795) representing 1 for each year of life until the age of 5 years, for a total of 199 180 child-year observations. Because the first year of life represented the infant year and use of oral health services was extremely low, we omitted this year from our analysis, leaving 4 observation years for ages 1 through 4 years. Table 2
Table 3
Table 4
This investigation represents the first detailed examination of childrens WIC participation and oral health care utilization. Previous studies have substantiated that WIC participation has an effect on the use of prenatal care and childrens medical care.3,6,10 Our findings indicate that children who participate in WIC are more likely to have a dental visit, thus increasing their access to oral health care. Because children on Medicaid are a high-risk population who often need more frequent and extensive dental services than other children, the association between WIC and greater use of services suggests that children on both Medicaid and WIC are more likely to receive the care they need. Our results also showed that young children participating in the WIC program are more likely to use preventive and restorative services and are less likely to use emergency services than WIC nonparticipants. These findings suggest that children participating in WIC may have a better connection to the health care system that can lead to care that is more planned and less urgent. If further studies can confirm a causal link between activities of a WIC nutritionist, dental referral, and use of dental services, it would appear that an important facet of the mission of WIC programsappropriate referrals to health and social servicesis being addressed. Our study contributes to the literature in 2 major ways: by broadening the understanding of the effects of WIC participation to oral health care and by making a methodological improvement on the way WIC effects are examined.
Methodological Contributions Sporadic and continuously enrolled Medicaid children differ demographically, socially, and economically,23 so we did not limit the cohort to continuously enrolled children. Doing so would have biased the sample and threatened generalizability. Continuously enrolled children in our cohort had utilization rates for oral health services that were 3 times greater than those not enrolled continuously in Medicaid (30% vs 10%).24 Instead, we controlled for Medicaid enrollment with a variable for duration of months per year enrolled in the program. However this approach can create another bias because low-income children qualifying for Medicaid may receive dental care under private insurance, with fee for service, or at no cost during periods in which they are not enrolled in Medicaid. Although low-income children are likely to use medical care when not enrolled in public insurance programs, it is unlikely that they receive dental care, particularly young children in North Carolina, where excess demand for services exists and dentists participation in Medicaid is low.25 Furthermore, dental care is the most prevalent unmet need in uninsured children who are eligible for Medicaid.26 These findings underscore the difficulty young low-income children have in gaining access to oral health care regardless of insurance coverage.
Policy Contributions In the North Carolina Institute of Medicine report on access to dental care, it was reported that fewer than 13% of children aged 1 to 5 years received any dental services. Our findings indicated that WIC participation could increase to 23% the use of dental services for children at this age. This is an increase of almost 50% compared with findings of the North Carolina Institute of Medicine. Even with this rather dramatic percentage increase in use, the absolute utilization of 23% is still relatively low; more work needs to be done to address the access to dental care crisis among low-income young children. Medicaid alone is not enough to provide sufficient access to oral health care for young children, but when available in combination with another public health program such as WIC, access to oral care health can be greatly improved.
Limitations We do not have information on childrens oral health status in the study. It is well documented that Medicaid children and children living in poverty have disproportionately more dental disease.31 Thus, any dental visit is likely to be beneficial to this high-risk population. The association of WIC with higher use of services may mean that oral health care needs of the children on Medicaid who participate in WIC are being better met. The findings for number of visits and type of use support this conclusion. Also, the adjusted odds of a child on Medicaid with WIC participation having 1 or more dental claims during the year was 1.3 to 1.5 times greater than that of a child with no WIC participation, across the 4 age groups. Studies have suggested that dental care is a serious unmet need among children in poverty, and our study suggests that use of dental care is enhanced among children participating in WIC services.
This study was supported in part by the AAPD Foundations Omnii Fellowship, MCH Grant 5 T17 MC 0001511, AHRQ Grants T32-HS-00032 and 1-RO3-HS1160701, and NIDCR Grant 1K22DE1474301. The authors recognize Dr Paul Buescher, Stephanie Horton, and all the staff at the North Carolina State Center for Health Statistics for their help in obtaining the data and linkage. We also recognize Alice Lenihan and Sarah Roholt at the North Carolina WIC program for their assistance.
Human Participant Protection
Contributors All authors participated in the conception, design, data analysis, and interpretation of the study. J. Y. Lee and R. G. Rozier wrote the first drafts of the article, and E. C. Norton, J. B. Kotch, and W. F. Vann contributed to subsequent versions.
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