On the trial of anyone charged with the violation of this chapter or with the illegal practice of dentistry, it shall be incumbent on the defendant, upon proof that he or she practiced dentistry, to show that he or she had authority under the law to practice dentistry in order to exempt himself or herself from the penalty for such violation.
(Ga. L. 1920, p. 132, § 24; Code 1933, § 84-9911; Ga. L. 1999, p. 234, § 18.)