Mo. Rev. Stat. § 337.090

The committee and division in issuing licenses and in publishing the directory as provided in section 324.032 shall not include or list the degree upon which the license or certificate was issued. Any person licensed on the basis of a master's degree who has then earned a doctoral degree may use the title "doctor" or hold himself out in his practice as a psychologist as having a doctoral degree so long as it is from an accredited institution of higher education and so long as the degree is relevant to the practice of psychology.