Mass. Gen. Laws ch. 112, § 46A

If any applicant for registration, either by examination or under the provisions of section forty-eight, is registered and issued a certificate of registration by the board, and does not practice dentistry in the commonwealth within five years from the date of the certificate of registration, or does not maintain a current license to practice dentistry in the commonwealth for a period of five consecutive years, may be required by the board to be reexamined for competency.