Final answer:
After replanting and splinting an avulsed tooth with nonsurgical endodontic therapy, ankylosis and root resorption are the most likely outcomes within two years due to bone fusing directly to the dentin and cementum and subsequent resorption of the root structure.
Step-by-step explanation:
When a tooth avulses and is later replanted, the tooth's long-term viability can be affected by several factors including the time elapsed before replantation and the conditions in which the avulsed tooth was stored. Replantation of an avulsed tooth within two hours is considered relatively prompt, yet the tooth may still be subject to several complications. The dentist's actions of replanting and splinting the tooth are correct for immediate management, with nonsurgical endodontic therapy being necessary to manage the health of the pulp.
The most likely outcome within two years after this treatment—given the avulsion and elapsed time before treatment—is ankylosis and root resorption. An avulsed tooth that has been out of the socket for an extended period is at higher risk for replacement resorption where the bone fuses directly to the dentin and cementum, leading to ankylosis, and ultimately the root structure can become resorbed. Other outcomes such as chronic periapical periodontitis, radicular cyst formation, and internal root resorption are possible but less likely in this scenario given the prompt intervention of the dentist.