In this work we investigate a scenario in which protected and unprotected services coexist in an elastic optical network under dynamic traffic. In the investigated scenario, unprotected services can reuse the reserved idle bandwidth to provide protection to the protected services. Under this scenario, we propose a new heuristic algorithm that enables such reuse as well as we define and introduce the new assignment problem in elastic optical networks named as Transmission Spectrum Assignment (T-SA) problem. We evaluated the proposed algorithm through simulations and we observed that it was able to reduce the network blocking probability by at least 6%, 7% and 10% depending on the investigated topology.