Section 11. Unless each such payment is first authorized by a vote of its board of directors, no dental service corporation shall pay any salary, compensation or emolument to any officer, trustee or director thereof, or any salary, compensation or emolument to any person amounting in any year to more than five thousand dollars. No such corporation shall make any agreement with any of its officers, trustees or employees whereby it agrees that for any services rendered or to be rendered to it, they shall receive any salary, compensation or emolument for a period of more than three years from the date of such agreement.