A Silver Spring dentist pleaded guilty today to a Medicaid fraud scheme in which Maryland prosecutors say he fleeced the state of thousands of dollars in phony Medicaid reimbursement claims in 1979 and 1980.

Roy L. Mitchell, 46, pleaded guilty to a single count of fraud before Baltimore Circuit Court Judge Elsbeth Bothe. He will be sentenced Sept. 27. Prosecutors recommended he be jailed for six months and given an "appropriate" fine.

The maximum penalty for the offense is five years in prison and a $10,000 fine.

Mitchell is the seventh dentist accused of fraud since the state attorney general's five-member Medicaid fraud control unit began tracking reimbursement claims by computer in 1982.

Five of the dentists were convicted and one was ordered to make restitution to the state in an administrative procedure.

In a statement of facts prepared for today's guilty plea, Assistant Attorney General Stefan D. Cassella said Mitchell received almost $100,000 in reimbursements from the state in fiscal 1979 and 1980 for work on low-income Medicaid patients, but more than $30,000 of the total was for work he did not do.

For example, according to the statement of facts, Mitchell submitted claims for 551 plastic fillings at $10 each on 38 patients.

"Yet when the patients were examined by a state dentist," the statement said, "only 150 fillings were found. The resulting overpayment to Mitchell was $4,010.

In other cases, according to the statement, Mitchell claimed he provided more expensive emergency service for patients, when in fact he gave routine service, bilking the state out of more than $22,000 in overpayments.

Since 1982, Cassella's Medicaid fraud control unit has been monitoring patterns of reimbursement claims by the state's 1,300 Medicaid dentists at the state health department with the use of computers.

Whenever investigators detect "statistically unusual" patterns, such as abnormally large numbers of fillings for individual patients, state dentists examine and interview the patients to see if, in fact, the claimed dental work was performed. "That's how we catch them," Cassella said.