Newfane dentist Scott D. Geise has long insisted federal prosecutors made “a terrible mistake” in accusing him of defrauding health insurance providers and the government.

Friday, two days after the start of what was expected to be a monthlong trial in federal court, Geise pleaded guilty to felony charges. He now faces up to five years in prison and a $250,000 fine when he is sentenced June 14 by U. S. District Judge Richard J. Arcara. Geise, 48, admitted to filing a false health care claim and filing a false tax return, in entering his guilty plea in the case against him, U. S. Attorney Kathleen M. Mehltretter reported late Friday afternoon.

Geise is a former star athlete, U. S. Army veteran of the Persian Gulf War and civic leader in his Niagara County town.

By pleading guilty, he admitted “to devising a scheme that defrauded insurance companies by submitting false claim forms to and receiving unearned payments” from insurance providers, according to Assistant U. S. Attorneys Timothy C. Lynch and John E. Rogowski.

Prosecutors Friday detailed a multifaceted scheme that allowed Geise to collect money from insurance companies that he was not entitled to, including:

Billing patients’ insurance companies for “an occlusal guard” — a mouth guard used to treat night-time teeth grinding — when patients asked for a cosmetic bleach whitening kit. The guards, which serve a medical purpose, were covered by insurance; the whitening kits were not.

Defrauding the self-insured dental insurance plan of General Motors and Delphi Corp. by billing insurance companies for amalgam fillings for several patients on occasions when he only applied sealants to their teeth. The insurance covered amalgams but not sealants.

Prosecutors said Geise additionally admitted to helping someone else “with submitting a fraudulent claim for health care benefits to the Laborers Local 91 Welfare Fund” and also pleaded guilty to filing a false tax return.

He admitted that he failed to list more than $188,000 in income by omitting cash receipts for his business, Newfane Family Dentistry, in corporate tax returns from 2003 to 2005. That allowed Geise to avoid $58,254 in taxes, federal authorities said.

Geise also agreed Friday to repay $29,527 in taxes owed on his personal returns from 2002-05.

Geise, who was represented by Joel L. Daniels and George V. C. Muscato, was first indicted on 57 felony counts in 2007.