Any member who has rendered service as a teacher, as defined under the provisions of chapters 16 and 17 of title 16, or as a state employee, as defined by the provisions of chapters 8 to 10 of title 36, is entitled to credit for that service for the various purposes of this system; provided, that the member was a contributing member for that period. All contributions made by the member for those periods of service shall be transferred in to this system and the retirement system shall calculate the full actuarial value of the accrued benefit with the former employer. If the full actuarial value of the accrued benefit with the former employer is greater than the total employee contributions transferred, the retirement system shall also transfer the difference between the full actuarial value of the accrued benefit with the former employer and the employee’s contributions from the account of the former employer to the account of the current employing municipality. In any case in which a member has received a refund or refunds of contributions made to the system, the allowance of the previously stated credit for service is conditioned upon the repayment of the refund or refunds, including regular interest from the date of refund to the date of repayment. Any service as defined in this section for which no contributions were made, may be granted; provided, that the member pays to the retirement system a lump sum payment equal to the amount had he or she been a member during that period, plus interest as defined in this section. Effective July 1, 2012, any purchase requested under this paragraph shall be made by a member at full actuarial cost. The retirement board shall fix and determine rules and regulations that are needed to govern the provisions of this section.