Section 18. The board shall refuse to issue a certificate to a person, or may, after a hearing if requested by a person to whom a certificate has been issued, revoke such certificate if, in the opinion of the board, such person is intemperate in the use of alcoholic liquors or narcotic drugs, or has been guilty of misconduct involving moral turpitude, or has been convicted of an offence involving moral turpitude, or has violated any provision of sections thirteen to twenty-three, inclusive, or of section sixty-five relative to podiatry, or has been guilty of unprofessional conduct, or is in any other manner disqualified morally, mentally or physically to receive or hold such certificate, or has in his application therefor knowingly made any false statements or presented to the board a fraudulent diploma, certificate or other document.