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Assessment of Dentist Participation in Public Insurance Programs for Children in the US

Key Points Question Are there disparities in dentist availability for delivering dental care to children within or between states? Findings In this cross-sectional study of 204 279 active dentists across the US, dentist participation in public insurance programs varied substantially across states, especially for states that manage the Medicaid program and Children’s Health Insurance Program (CHIP) separately and within states. Dentist participation was lowest among dentists with urban practices and highest among those with rural practices, and notably lower among general dentists vs pediatric dentists. Meaning The findings of this study suggest that limited availability of pediatric dental care services remains a challenge in the US, especially for Medicaid- and CHIP-insured children, those living in rural communities, and those receiving specialized care.


Introduction
The availability of dentists varies widely in the US, 1 with the rate of dentists per 100 000 people between 41.8 (Alabama) and 82.7 (Massachusetts) in 2019. 2 The Health Policy Institute of the American Dental Association (HPI-ADA) published state reports on dentist participation in public insurance programs 1,3 and patient geographic access to dental care. 4 The HPI-ADA reports used limited data, not differentiating by rurality vs urbanicity of the dental offices, accounting for the dentist's taxonomy (general, pediatric, or specialized), or differentiating between public insurance programs.
Evaluating the distribution of dentists by rurality vs urbanicity is important in targeting specific interventions for increasing the availability of dental care in rural communities, which are known to have limited access to care. 5 Dentists are needed to provide both preventive and specialized care; hence, it would be useful to evaluate the availability of all dental taxonomies, particularly when considering participation in public insurance programs.
Public insurance for children includes Medicaid and the Children's Health Insurance Program (CHIP), covering children from low-income families, with Medicaid also covering children with disability or in foster care. Medicaid has a larger enrollee population, and generally, higher minimum comprehensive coverage requirements than CHIP. 6 Each state decides on whether to manage Medicaid and CHIP separately, under Medicaid expansion CHIP, or through a combination of the 2 methods. 7 When the 2 insurance programs are not managed under a single program or administrator, states may apply differential fee schedules and policies for the 2 programs. These different policies in managing public insurance programs could result in variations in the dental care availability for Medicaid-and CHIP-insured children.
This study expands on existing research on the availability of dental care for children by reporting the distribution of the US dentist population characterized by taxonomy, urbanicity vs rurality of dental practices, and participation in public insurance programs. We present our analysis for 48 states and the District of Columbia (referred to in analysis hereinafter as a state); Hawaii and Washington were excluded because their Boards of Dentistry did not approve release of the dentistry licensure data. The summarized results of this article are available with a web data portal, providing outcome data on the availability of dental care for children for each state and maps by rurality/ urbanicity and taxonomy, further presented in individual state reports. The outcome data are also summarized in state reports available in the data portal and in eFigure 2 in the Supplement.

Study Population and Data Sources
The study population consisted of the dentist population stratified by state, taxonomy, rurality vs urbanicity of their practice, and participation in public insurance programs. The 3 data sets used in this study were from the Boards of Dentistry (BOD), the National Plan and Provider Enumeration System (NPPES), and InsureKidsNow.gov (IKN) (eTable 1 in the Supplement).
The BOD data set was acquired from each state and provides information on all licensed dentists, regardless of whether they are in private practice or safety-net care settings. We considered only active-licensed dentists.
The NPPES database comprises all dentists who have applied for a National Provider Index. 8 A National Provider Index is required by the federal Health Insurance Portability and Accountability Act for electronic transactions. The data provide each dentist's name, address, and taxonomy classified into general dentistry, pediatric dentistry, or specialist. The data were cross-referenced with BOD to derive the taxonomy.
InsureKidsNow.gov includes all dentists who report their participation in Medicaid and/or CHIP. 9 This database provides each dentist's name or that of their practice, address, and taxonomy. We used the data to derive the dentists' participation in Medicaid and/or CHIP and to cross-reference with BOD, differentiating by taxonomy. We assumed dentists included in the IKN data set participated in public insurance.
Institutional review board approval was not applicable because all data sources are publicly available and do not include health-protected information. The study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cross-sectional studies. The study was conducted from January 2019 to March 2022.

Matching and Classification
The NPPES and IKN databases provided consistent information for all states, and the BOD data presented differences in the data content across states. The data-matching process consisted of multiple steps, including NPPES and IKN processing and matching, providing an NPPES-IKN data merge, and BOD and NPPES-IKN matching, with average match rates of 94% for BOD and 79% for NPPES-IKN. Data matching was by first and last names. The addresses of the practice sites listed in IKN were used for dentists participating in Medicaid or CHIP. Match rate was not affected by addresses but potentially by name variations (eAppendix in the Supplement).
Because the IKN database provides data on the addresses of the participating dentist practices, we derived the portion of time spent by taxonomy at each practice address. For dentists with multiple practice offices, we assumed an equal amount of time spent across the practice offices; hence, only a proportion of a dentist's caseload was allocated to 1 office location (eAppendix in the Supplement).

Outcome Measures
The outcome measures included (1) number and percentage of dentists; (2) number and percentage of dentists participating in Medicaid, CHIP, or Medicaid and CHIP; and (3) number and percentage of dentists participating in public insurance (Medicaid or CHIP). The measures were aggregated at the dental office location, then stratified by rurality/urbanicity and taxonomy, and reported by state.

Data Analysis
To perform the analysis, Python, version 3.7.4 (Python Software Foundation) was used with the following packages: pandas, numpy, matplotlib, altair, and geopandas. In addition, R, version 4.0.2 (R Foundation for Statistical Computing) was used.

Results
eTable 1 in the Supplement presents the availability of various attributes of BOD. eTable 2 in the Supplement provides state-level statistics on the number of BOD-IKN-matched dentists. eTable 3 in the Supplement reports state-level percentages of dentists stratified by rurality/urbanicity and taxonomy. eFigure 1 in the Supplement presents dental participation rates in Medicaid, CHIP, and HPI-ADA by county. Demographic characteristics were not available.
Of 204 279 active dentists, the number of dentists per 100 000 people ratio varied widely, for example, 41 in South Dakota, 89 in California, and 111 in the District of Columbia. Across all states, most dentists practiced in urban communities (median, 84% [IQR, 23%]), followed by suburban (median, 11% [IQR, 11%]) and rural (median, 5% [IQR, 10%]) communities. Most were general dentists (median, 84% [IQR, 4%]), followed by specialists (median, 13% [IQR, 3%]) and pediatric dentists (median, 3% [IQR, 1%]). General dentists were noted in as much as 90% of a state's dentist population, whereas pediatric dentists were found in as little as 1% of the population.  program; however, according to federal law, Medicaid and CHIP are required to provide dental benefits; hence, we assumed the same participation rates for the 2 programs. We considered cases with these assumptions as expanded Medicaid and noted the same participation rates for the 2 programs even though they had different management practices. The remaining 21 states had differences in Medicaid and CHIP participation rates, with some as high as 70%. For some states, there was a large gap in Medicaid vs CHIP participation (eg, Alabama, 5% vs 75%; Iowa, 2% vs 51%;

JAMA Network Open | Pediatrics
and New Mexico, 42% vs 6%). Nine states had a higher participation rate in CHIP, with the largest difference in Alabama (70%). The remaining 12 states had a higher participation rate in Medicaid, with the largest difference in New Mexico (36%).
We report the public insurance (Medicaid or CHIP) rates to compare with those published by HPI-ADA. The rates in our study were a mean (SD) of 40% (16%) and a median of 38% ( HPI-ADA reported rates, and 1 state (Kentucky) displayed the same participation rate. The largest difference between the rates in our study and the rates reported by both HPI-ADA studies was for Iowa (53% in this study vs 89% in the 2018 HPI-ADA study and 86% in the 2015 HPI-ADA study). Table 2 presents dentist participation in Medicaid or CHIP, stratified by rurality for each state.
The greatest participation was found among rural dentists, and the lowest rate was among urban dentists. The median Medicaid rates were 39% (IQR, 29%) for rural dentists, 32% (IQR, 30%) for suburban dentists, and 26% (IQR, 16%) for urban dentists. The median CHIP rates were 40% (IQR, 30%) for rural dentists, 36% (IQR, 34%) for suburban dentists, and 29% (IQR, 22%) for urban dentists. Alabama presented the greatest differences in Medicaid vs CHIP participation among urban dentists (69%), suburban dentists (73%), and rural dentists (71%). Medicaid and CHIP participation reached as high as 82% for rural dentists in South Carolina vs the maximum of 68% among urban dentists in Wyoming. New Hampshire had the lowest participation in the 2 programs among urban (6%) and suburban (5%) dentists. California had the lowest participation among suburban (5%) and rural (3%) dentists, excluding Rhode Island, which had only 1 rural dentist. Alabama and Rhode Island presented the largest differences in Medicaid vs CHIP participation among general dentists (73%), specialists (57%), and pediatric dentists (92%). New Hampshire showed the lowest participation in the 2 programs among general dentists (6%) and specialists (7%), and California had the lowest participation among pediatric dentists (11%).

JAMA Network Open | Pediatrics
Dentists' Participation in Public Insurance Programs for Children in the US

Discussion
This cross-sectional study analyzed dentist availability for pediatric dental care and their participation in public insurance programs. The analysis allowed for comparisons across states with inferences on variations by rurality vs urbanicity and taxonomy. Our overall findings suggest the need for more detailed analysis on dentist availability in delivering dental care to children.
There was a wide variation in dentist availability in rural communities, with many states having almost no rural dentists and few having a similar share of dentists across the 3 urbanicity-rurality levels. These differences were also subject to the rurality vs urbanicity status of each state; for example, Vermont had a higher percentage of dentists with rural practices (41%) and is a mostly rural state (60% of total communities). 11 Overall, the percentage of dentists practicing in rural communities was low compared with the level of the state's rurality status, for example, only 3% of the dentists practiced in rural communities in Georgia, and 40% of the state is considered rural. 11 This finding suggests that the supply of dental care for children was insufficient in rural communities during the study period; interventions such as loan forgiveness programs 12,13 or school-based mobile care may help address such shortages. [14][15][16] The primary focus of this study was to derive dentist participation in CHIP or Medicaid Medicaid and CHIP participation rates reported by the IKN data, the difference in the participation rates for the 2 programs varied widely, suggesting that policies instating a single administrator for the 2 programs in those states could result in higher participation of dentists in public insurance programs, because burdensome administrative requirements are one of the most common reasons for dentists not participating in public insurance programs. 19 The difference in CHIP and Medicaid participation was also reflected in differences between the rates reported in this study vs those reported by the HPI-ADA. 1,3 Because the HPI-ADA reports overall public insurance (Medicaid or CHIP) participation, we computed those rates for comparison. There were differences in the reported rates, with both higher and lower HPI-ADA rates vs those reported in our study. Some states had large differences in the reported rates, for example, Iowa (53% in this study vs 89% in the 2018 HPI-ADA database). Alabama had the greatest difference in Medicaid and CHIP participation (5% vs 75%), with the 2018 HPI-ADA report presenting only the overall rate (75%). These differences could be because of different data sets and approaches used. The 2015 HPI-ADA analysis 1 used a similar approach as in this study with 2014 data, while the 2018 HPI-ADA analysis 3 used the 2017 Transformed Medicaid Statistical Information System data instead of the 2018 IKN data set; IKN is used for finding participating dentists by those seeking dental care, and so is a pertinent source for identifying participation in public insurance programs. The 2018 HPI-ADA analysis 3 was not complete, with data on only 41 states reported.
Although a low percentage of dentists practiced in rural communities, the greatest participation in Medicaid and CHIP was for rural dentists, followed by suburban dentists, then urban dentists.
When comparing Medicaid vs CHIP rates by rurality and urbanicity, this study found large differences for the 2 programs. This finding suggests wide inconsistency in the availability of dentists across communities and insurance programs, pointing to the need for granular analysis toward informing a targeted policy to improve access.
This study also noted that median participation of pediatric dentists in Medicaid and CHIP was nearly twice as high as that of general and specialist dentists, in contrast to the makeup of dentist populations throughout the states, with pediatric dentists consisting of low percentages (as low as 1% for some states). This low rate suggests that future policies aiming to improve dental care access for children should consider the association between dentists' taxonomy and participation in Medicaid and CHIP programs, for example, expansion of loan forgiveness programs for pediatric dentists. This difference in participation rates is particularly important because pediatric dentists commonly treat children with challenging conditions, eg, attention deficit/hyperactivity disorder or special needs.
This study also derived county-level dentist availability, with more detailed analysis available in a data portal. Nearly half of the states had counties with no participation as well as with 100% participation, most corresponding to small counties, with some states having very large differences in participation at the county vs state level. These variations may be associated with social and cultural preferences and regulatory and legal environments, possibly affecting the geographic distribution of dentists overall. This granular analysis noted wide disparities in the dentist participation in Medicaid and CHIP across communities, suggesting that interventions for increasing the availability need to be targeted to meet the demand at the community level.

Limitations
This study had limitations. BOD data are primarily intended to serve as contact information; thus, a dentist may use an address of their residence vs their practice. Exceptions are Florida and California, which keep both home and practice addresses in separate columns. Moreover, most states' BOD databases provided only 1 street address; however, most dentists practice at more than 1 location.
Neither the BOD nor National Provider Index listings differentiate between dentists who are retired and no longer have active licenses and those who are retired but still have active licenses. This lack of distinction possibly resulted in overestimation of dentist availability. The IKN data listed each dentist for all the locations that their practice owns, but does not reflect the time a dentist spends in each location. Dentists listed in IKN data, although reported as participating in Medicaid or CHIP, may not necessarily accept children with public insurance; this limitation could result in lower participation rates for Medicaid and/or CHIP. 20 Moreover, according to an HPI-ADA report, 1 4 states allow dentists to opt out of being included in publicly available lists, including Alabama, New Hampshire, North Carolina, and Oklahoma. These limitations could result in participation estimates that are different from the true values. In addition, the comparisons with the HPI-ADA were not for the same years; the more recent HPI-ADA estimates were also incomplete.

Conclusions
This cross-sectional study noted wide disparities in dentist availability for pediatric dental care, particularly for Medicaid-and CHIP-insured children, for children living in rural communities, and for those receiving specialized care. Because dentist availability varied greatly across states, there is not a single policy or intervention that could reduce these disparities. State-level policies targeting different dimensions of the dental care system could address these disparities, for example, adopting joint administration of CHIP and Medicaid, funding public-health school programs, or expanding loan forgiveness programs. [21][22][23][24] A complete analysis of the current availability of dental care in all states could provide a starting point on what each state may improve upon by benchmarking to other states.
Because of the wide disparities across communities within each state, local interventions are necessary; however, such interventions would best be targeted for the subpopulations in need of improved dentist availability. Existing measures for addressing the shortage of dentists focused primarily on the number of dentists within a community, discounting participation in public insurance for the child population. 25,26 Because many decisions on improving dentist availability (eg, loan forgiveness programs) are targeted using shortage areas identified by the Health Resources & Services Administration, it is important that existing measures incorporate more rigorous methods in identifying shortage areas.
Although dental care benefits for children are mandated for Medicaid and CHIP programs, 7 lack of dentist availability for children with public insurance deters access to such services. This finding eTable 3.