Section 71. The board may refuse to grant a certificate of registration to any applicant found guilty of fraud in making application or taking an examination for registration. The board may revoke or suspend any certificate of registration for unprofessional conduct, for fraud, deceit or misrepresentation in practice or in advertising, for conviction of crime, for habitual drunkenness for six months immediately before the charges are made, for gross incompetence, or for violation of any rule or regulation made under section sixty-seven; provided, that before any action is taken the accused party shall have written notice of the charges against him and of the day appointed for a public hearing thereon, which shall be at least five days after the service of such notice. At such hearing the accused shall have an opportunity to produce testimony in his own behalf and to confront the witnesses against him. Three members of the board shall be a quorum for any such hearing. Witnesses at hearings before the board shall testify on oath, and may be sworn by any member thereof. The board may compel the attendance of witnesses and the production of documents at any such hearing. Whenever the certificate of any registered optometrist is revoked or suspended, such certificate shall be returned to the board, on demand, and the secretary of the board shall give notice of such revocation or suspension to the clerk of the town wherein the principal office of such optometrist is located, and the clerk shall record the revocation or suspension on the records of his office. Where the right of any person to practice has been revoked as herein provided, the board may, after the expiration of one year, receive an application for a renewal of the right to practice, and upon such new application it may grant such a renewal.