Mo. Rev. Stat. § 340.256

Any person licensed under sections 340.200 to 340.330 who retires from any profession regulated by sections 340.200 to 340.330 shall file an affidavit stating the date of retirement and any other information required by the board in order to verify such retirement. Any person filing the affidavit as required by this section, does not need to renew his or her license as required by section 340.258. If such person decides to again practice his or her profession, the person must renew his or her license prior to performing any act or practice regulated by sections 340.200 to 340.330.