A new report from the Urban Institute shows that 20 percent of Americans with health insurance say they can't afford proper dental care. It was the most commonly cited unmet need.

"Though the ACA has led to increased health insurance coverage for millions of nonelderly adults, and early signs indicate improvements in broad measures of access to care and affordability, we find that gaps in access to dental care remain even for insured adults and that low- and moderate-income adults in particular face challenges affording dental care," states the Urban Institute report.

Overall, 28 percent of adults between the ages of 18 and 64 reported a medical issue that could not be taken care of because of cost. Some reported multiple issues.

The next most-common unmet need relates to prescription drugs, which 13 percent of survey respondents said they have forgone out of financial concerns.

Eleven percent cited the cost of medical tests or follow-up care, while roughly 10 percent cited general medical care or visits to specialists as cost-prohibitive.

Perhaps surprisingly, despite widespread concerns that people are missing out on needed psychological treatment because it is an area of care traditionally not prioritized by health plans, only 5 percent of respondents reported forgoing mental health care due to cost.

Read: PPACA pushes dental further into voluntary

Insured people who are missing out on dental care are disproportionately low-income.

While 30 percent of those living below 139 percent of the federal poverty level report missing out on dental care, the percentage drops to 11 percent among those with 400 percent of the federal poverty level or more. Minorities are also more likely to forgo care than whites.

In a possible reflection of the shortcomings of the PPACA insurance marketplace, those with employer-backed insurance are far less likely to lack dental care (16 percent) than those who get coverage through other channels (30 percent).

Burton Edelstein, a Columbia University professor of health policy and dental medicine, told Medscape Medical News that the trends reflect the increasing costs of some dental procedures, as well as employers shifting dental costs onto employees.