This is the first study, to our knowledge, to examine dental visits by CKD status. Among a population of adult patients in a public healthcare setting in urban California, we found that the percentage of patients who had at least one dental visit during an average of > 4 years of observation was extremely low overall and that those with CKD had a 25% lower likelihood of having a dental visit than those without CKD. We found a similar difference in likelihood of having a dental visit by CKD status in the subgroup with diabetes, but no difference in the likelihood of having an eye visit by CKD status. Further, while the percentage having a dental visit was not significantly different between subgroups with or without diabetes, more than twice as many patients with diabetes than without diabetes had an eye visit.
These findings are important because of the emerging association between oral health and CKD. Though there have been no longitudinal studies to our knowledge examining the association of periodontal disease with incident or progressive CKD, cross-sectional associations have been reported [11–14] and its plausibility is supported in the cardiovascular literature where periodontal disease has been shown to be an independent risk factor for incident coronary heart disease , periodontal pathogens have been shown to be able to directly invade human coronary artery endothelial cells , and there is evidence of reversibility of effects on endothelial function . One proposed mechanism for how periodontal pathogens may induce kidney injury is through toll like receptor 4 (TLR4)--which is one in a group of transmembrane proteins that play a key role in the innate immune response. TLR4 is found throughout the kidney [24, 25] where it can recognize and bind bacterial lipopolysaccharide coating, and launch an inflammatory cascade that could lead to renal dysfunction [24, 25]. Because periodontal disease may contribute to the development and progression of CKD and because it is preventable and treatable with regular dental care, a paucity of dental care in the public healthcare setting may be contributing to the disparate burden of CKD among the poor and racial/ethnic minorities. Our finding that a periodontal disease diagnosis was common among those with a dental visit lends support for the scope of its possible past and future impact.
Several factors may explain our findings. A lack of public insurance coverage of dental services undoubtedly creates a significant barrier to dental care access among the poor. Those with dental insurance or the ability to pay out-of-pocket are significantly more likely to utilize dental services than those without such resources [26, 27]. Roughly 1 in 3 adults in the United States lacks dental insurance . A lack of dental insurance is higher among the poor and medically uninsured [26, 29]. Though the majority of our study population had Medicare (a federal health insurance program for adults over age 65 and those who are physically disabled or meet other special criteria) or Medicaid (a state-managed health insurance program for low income citizens and those with special disabilities), Medicare does not cover basic or routine dental care  and provision of adult dental services is optional for Medicaid programs . While the prevalence of dental insurance among medically insured adults in the San Francisco Bay area counties was 79% in the 2003 California Health Interview Survey , Denti-Cal--California's Medicaid fee-for-service dental program and primary public financer of dental care for more than 8 million low-income, elderly, and disabled people in California in 2007--eliminated most of its adult dental benefits in 2009 due to the state's budget deficit . Though Denti-Cal coverage was in place for most of our study period, the program's dental provider reimbursement rates are among the lowest in the nation and are significantly below the fees charged by most dentists. Because of these low reimbursement rates and elimination of adult dental benefits, only 24% of California's private dentists currently accept patients with Denti-Cal, down from 40% in 2003 .
Though fear of dental visits is commonplace  and may contribute to the marked differences in percentages of patients having a dental visit versus an eye visit, a lack of healthcare provider recommendation and referral for dental care may also contribute to this finding. In turn, healthcare provider recommendation may be in part influenced by guidelines. While the American Diabetes Association guidelines strongly recommend routine retinopathy screening for patients with diabetes, there is no such recommendation for routine dental care even though periodontal disease is known to worsen glycemic control . On the other hand, healthcare providers in public healthcare settings may not recommend routine dental care regardless of guidelines because accepted referrals may be limited to those with severe--and covered---dental problems such as oral abscess.
Our finding that having a dental visit varied by CKD status suggests that patients with CKD may be less likely to seek preventive dental care because of the burden of extra appointments and lifestyle modifications required for CKD management that their counterparts without CKD may not experience. Additionally, the finding may be partially attributable to out-of-pocket expenses associated with the extra appointments and medications specific to CKD management (such as phosphorus binders and vitamin D analogs). This burden would leave fewer resources for uncovered dental care expenses, but may not affect covered eye visits, for which we found no difference by CKD status. Future research should investigate the barriers to dental care specific to patients with CKD.
It is important to note that Healthy People 2010 goals for annual eye and dental examinations among people with diabetes were 76% and 71%, respectively. In 2005, 57.2% of Californians over age 18 with diabetes reported they had a dilated eye examination in the past year . In 2006, 66.7% of this population reported a dental examination within the past year . Our findings that only 58.3% and 14.7% of people with diabetes in our study had an eye and dental visit, respectively, over an average follow-up of > 4 years underscores the magnitude of barriers to standard of care in the public healthcare setting.
Our study is not without limitations. First, patients may have sought dental care outside of the Network. However, because of the low acceptance of private dentists of Medicaid and Medicare, we expect this was an uncommon occurrence. Also, we would not expect out-of-network care to differ by CKD status. Second, we did not have information on dentate status. Edentulous patients may have less need for dental services and are not at risk for periodontal disease. Finally, we do not have information if visits were for routine, preventive care or for problems requiring urgent attention. Given the barriers to dental care in the public healthcare setting, the rate of truly preventive dental care is likely considerably lower.