In this longitudinal population-based study, we examined the effectiveness of physician-delivered preventive dental services for Medicaid-enrolled children in reducing treatments related to dental caries. Three important, age-related findings from this study of children who had ≥4 IMB visits include evidence for: (1) a preventive effect for caries-related treatments in children younger than 2 years; (2) a net referral effect for children aged 2 to 3½ years; and (3) a preventive effect for caries-related treatments for children aged 40 through 72 months. The observed small net referral effect of an IMB visit on caries-related treatments in children aged 2 to 3½ years most likely occurred because of increased detection of disease in teeth of children who received and benefitted from the program. Such dental treatment was considered to represent an improvement in oral health status compared with untreated disease. In total, the reduction in caries-related treatments from preventive dental services represents a substantial improvement in the oral health of Medicaid-enrolled children, who historically have had high rates of dental caries but poor access to care from dentists.2,22
The IMB program provided an opportunity for Medicaid-enrolled children to access preventive dental services at a crucial time when their first teeth were emerging and when oral health habits were being established. Previous research has established the effectiveness of fluoride varnish, applied 2 to 4 times per year, in preventing dental caries among children.9
A meta-analysis of 3 studies found a 33% (95% confidence interval: 19%–48%) reduction in decayed, missing and filled primary-tooth surfaces.9
More recently, in 2 community-randomized controlled trials conducted among Aboriginal children in Canada and Australia, fluoride varnish applied twice per year and provided in conjunction with health education was effective in preventing new caries (prevented fraction for Canada: 24.5%; for Australia: 31%).23,24
This evidence suggests that fluoride varnish is effective in a variety of clinical and community settings.
Our finding of a threshold effect wherein at least 4 visits are required to obtain a detectable preventive benefit from IMB services is not consistent with some previous studies on fluoride varnish use among preschool aged children. Results of those studies revealed that increasing benefit was incurred from every additional fluoride varnish application beginning with a single application.23,25
In 1 of these studies a caries preventive fraction of 53% over 2 years was observed after a single application of fluoride varnish in children who were free of caries at baseline.25
Our longer follow-up time of 6 years, and differences in study design (observational study versus randomized controlled trial) may account for the disparate results. Our results, however, are consistent with an observational study that found a 35% reduction in caries experienced among American Indian children who received ≥4 (versus no) fluoride varnish treatments at well-child visits beginning at age 9 months, but no effect with fewer applications.26
The variation in the benefit from a single fluoride varnish application may also be attributable to differences in the rates of ECC in the underlying population. In addition, we believe that using caries-related treatments as the outcome measure likely leads to underestimation of the benefit of the IMB intervention compared with a dental caries incidence measure. According to the results of 1 reported study, 31% of North Carolina Medicaid-enrolled children aged ~5 years had experienced dental caries during 2000–2001.22
However, only 23% of these children received any caries-related treatment during the same time period.
The initiation of preventive dental services early in life and shortly after tooth emergence seems to be important for maintaining good oral health. IMB benefits ended at the child's third birthday and were limited to only 1 application of fluoride varnish every 3 months and a maximum of 6 applications during the time of this study. Therefore, for children to have all 6 IMB visits they needed to start receiving IMB services early in life. The ideal time to counsel caregivers about establishing good oral hygiene and dietary habits as part of daily routines also occurs early in a child's life. Our finding that the effectiveness of the IMB program in reducing caries-related treatments varies over time is not surprising. Soon after a topical fluoride is applied to tooth surfaces, the level of fluoride released in the mouth is high, but its concentration tends to diminish over time.27
To maintain the preventive benefit from the fluoride varnish, especially among children at high risk, repeat applications of the varnish are necessary.28
Thus, we found a cumulative reduction in caries-related treatments of 49% at age 17 months when we simulated IMB visits at ages 12 and 15 months. Although the results are not directly comparable, this estimate yielded values similar to those reported in the literature for prevented-fraction values for cavitated and noncavitated carious lesions.23,25
The decrease in simulated effectiveness in children aged 2 to 3½ years possibly occurred because of physicians' referrals for treatment of existing disease. Although the purpose of the fluoride varnish is to reduce ECC, the screening and counseling components of the IMB program should result in referrals to dentists for follow-up of problems identified during the IMB visit. The analysis covered the period when the IMB program was being implemented statewide, so the analysis sample may have had a preponderance of children who already had ECC at the time of their IMB visits. Results of previous research showed that pediatricians and family physicians, once trained, are able to detect ECC and provide referrals to children in need of dental care.29
We believe this referral effect also likely reduced the estimated preventive effect for children who received fewer than 4 IMB visits, as well as children who were older and had many teeth emerging during the early implementation phase of the program. For example, children who received their first and only IMB visit at age 24 to 35 months may have been more likely to have ECC and more likely to be referred to a dentist for treatment than children seen at a younger age.
Although well-child visits provide a good opportunity for provision of preventive oral health services, low-income families face many challenges in adhering to the recommended well-visit schedule.30
Ultimately, the successful implementation of a medical office–based preventive dental program will rely heavily on caregivers' compliance with the well-visit schedule. During the very early stages of IMB implementation, children who received preventive dental services in medical offices had few repeat IMB visits or well-child visits (mean: 0.9 vs 1.3 visits, respectively), resulting in a recommendation that strategies to increase oral health visits in the medical setting would need to be tied to those directed at improving compliance with the well-visit schedule.31
In addition, barriers to implementation of preventive dental programs in primary care exist and need to be addressed to ensure successful implementation. The 2 most common barriers reported by IMB participants include difficulty in integrating the intervention into their practice routines and resistance from colleagues and staff.32
Policies to enhance program implementation have been instituted in North Carolina. For example, since November 1, 2007, the North Carolina Medicaid program has extended IMB benefits to children through age 3½ years and decreased the time interval required between visits. These policy changes have enabled more flexibility in providing IMB services by taking into account irregular well-child visits.
This study has 3 important limitations. First, we were unable to control for possible selection bias wherein physicians may have been more likely to provide IMB services to children with existing ECC or those considered at high risk for ECC. If physicians tended to select patients who would benefit most from IMB services, our estimates of IMB effectiveness might be biased upward. In preliminary investigations we used statistical techniques to help address selection bias in nonrandomized studies.33
Our investigations with these approaches did not provide evidence for selection bias but greatly reduced the precision of our estimates. We therefore relied on the use of observed control variables to offset the effects of any selection bias. Second, part of the analysis period coincided with the period when IMB was being implemented throughout North Carolina. Therefore, many children in the study did not have the opportunity to receive the full complement of 6 IMB visits starting at age 6 months. Nevertheless, this study provides estimates of effect for an entire statewide Medicaid population during implementation. Future studies will need to be performed to examine effects of the IMB program during its more mature stages. A third limitation was that we lacked any information about the child's actual clinical status. We therefore could measure only differences in treated disease, and the total reductions in dental caries could have been greater than what we estimated from the use of claims data.