Objective To evaluate the effect of Medicaid coverage on dental care outcomes, a major health concern for low‐income populations. Data Sources Primary and secondary data on health care use and outcomes for participants in Oregon's 2008 Medicaid lottery. Study Design We used the lottery's random selection to gauge the causal effects of Medicaid on dental care needs, medication, and emergency department visits for dental care. Data Collection Data were collected for lottery participants over 2 years, including mail surveys (N = 23,777) and in‐person questionnaires (N = 12,229). Emergency department (ED) records were matched to lottery participants in Portland (N = 24,646). Principal Findings Medicaid coverage significantly reduced the share of respondents who reported needing dental care (−9.8 percentage points, p < .001) or having unmet dental care needs (−13.5 percentage points, p < 0.001). Medicaid doubled the share visiting the ED for dental care (+2.6 percentage points, p = .003) and the use of anti‐infective medications often prescribed for dental care, but it had no detectable effect on uncovered dental care or out‐of‐pocket spending. Conclusions Expansion of Medicaid covering emergency dental care substantially reduced unmet need for dental care, increasing ED dental visits and medication use, while not changing patient use of uncovered dental services.