The board shall conduct periodic checks to determine if participating employees who are drawing a total permanent disability benefit remain totally and permanently disabled. Such checks may consist of periodic examination by a physician or physicians appointed by the board, requiring the employee to submit evidence of continuing disability or absence of gainful employment and such other investigations as the board may deem appropriate. A written report by a physician appointed by the board stating that the employee is no longer totally and permanently disabled shall constitute prima-facie evidence of termination of total and permanent disability, except as provided in subsection (f) of Section 7-152.