Tenn. Code § 49-1548
Should the medical board report and certify to the board of trustees that such disability beneficiary is engaged in or is able to engage in a gainful occupation, paying more than the difference between his retirement allowance and his average final compensation, and should the board of trustees concur in such report, then the amount of his state annuity shall be reduced to an amount which, together with his teacher annuity and the amount earnable by him, shall equal the amount of his average final compensation. Should his earning capacity be later changed, the amount of his state annuity may be further modified; provided, that the new state annuity shall not exceed the amount of the state annuity originally granted nor an amount which, when added to the amount earnable by the beneficiary together with his teacher annuity, equals the amount of his average final compensation. A beneficiary restored to active service at a salary less than the average final compensation shall not become a member of the retirement system.
T.C.A. § 49-1548