Graymark Healthcare to close three sleep diagnostic centers in Oklahoma, Texas

Revenues from the company's sleep therapy business were down 6 percent from the same period in 2011, in part because of decreased insurance reimbursements for sleep apnea treatments, the company said.

The equity group Oklahoma Health Partners, led by investor Mike Horrell, purchased 1.4 million shares of Graymark stock in November for $650,000. Graymark said it would use that investment for operating expenses while it downsized its operations.

The Nasdaq Stock Market moved to delist Graymark's stock in November for failing to meet the exchange's minimum stock price requirements. The company's stock is trading on the over-the-counter market and closed at 23 cents a share, down two cents or 8 percent on Tuesday.