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Associations between health insurance status and periodontal disease progression among Gullah African Americans with Type 2 diabetes after adjustments for glycemic control and other covariates
Dipankar Bandyopadhyay, Medical University of South Carolina 
Renata S. Leite, Medical University of South Carolina 
*Nicole Marguerite Marlow, Medical University of South Carolina 
Elizabeth H. Slate, Medical University of South Carolina 

Keywords: negative binomial regression, periodontal disease, diabetes, Gullah African Americans, access to healthcare, health insurance, glycemic control, income

AIM: To assess periodontal disease progression among Gullah African Americans with Type 2 diabetes-mellitus (T2DM) according to health insurance status. METHODS: From an ongoing clinical trial among Gullah with T2DM, we extracted subjects who were also in a previous cross-sectional study (N=92). Comparing the prior exam to trial initiation, total tooth-sites/person with disease progression (2+mm of clinical attachment loss [CAL], 2+mm increases in periodontal probing depths [PPD], and changes in bleeding on probing [BOP] from none to present, each separately) were evaluated according to health insurance status (private, Medicare, Medicaid, and uninsured) using regression techniques appropriate for count data with different numbers of potential events for different subjects (e.g., varying tooth-sites available for observation). After fitting univariable Poisson regression models according to health insurance, we determined it was necessary to account for overdispersion and used negative-binomial (NB) regression models (which allow greater flexibility in modeling the mean and variance of such outcomes). We then fit multivariable NB models that also included glycemic control (poor: glycylated hemoglobin (HbA1c) =7%, well: HbA1c<7%), age, gender, BMI, smoking history, annual income, and various oral health behaviors. Final models included health insurance, HbA1c status, and other significant predictors or determined confounders; these results were used to calculate adjusted rate ratios (RR). RESULTS: Privately-insured were most prevalent (43.5%), followed by uninsured (22.8%), Medicare (19.6%), and Medicaid (14.1%). Those with poorly-controlled diabetes (67.4%) were more prevalent than well-controlled (32.6%). CAL outcomes ranged 0-58.8% of tooth-sites/person (mean=11.5%, sd=12.3%), while PPD outcomes ranged 0-44.2% (mean=8.6%, sd=10.5%) and BOP outcomes ranged 0-95.8% (mean=23.7%, sd=17.5%). The adjusted rate of CAL outcomes among uninsured was significantly higher than that for privately-insured (RR=1.79, 95% confidence interval=1.14-2.81, p=0.0114), yet there were no significant differences for adjusted rates of PPD and BOP outcomes by insurance status. CONCLUSIONS: Significant associations between health insurance and CAL outcomes persisted after adjustment for HbA1c level and other factors. These results suggest that increased access to healthcare (including dental services) may reduce chronic periodontal progression for this study population.