Which scenario presents the least favorable prognosis for endodontic treatment?

In assessing prognoses for endodontic treatments, the scenario involving a horizontal root fracture in the middle third of the root presents significant challenges that can lead to a less favorable outcome.

A horizontal root fracture often compromises the structural integrity of the tooth by creating two separate segments that may become non-viable. Depending on the location of the fracture and the vitality of the adjacent periodontal tissues, healing can be unpredictable. In addition, factors such as the degree of displacement of the fractured segments and the ability to maintain a seal during treatment can complicate the situation further.

Contrasting with other scenarios, conditions like an apical cyst or internal root resorption might be addressed with appropriate endodontic protocols and possibly surgical intervention, offering a path to repair and regain functionality. Unsuccessful endodontic treatment might also be corrected through retreatment or surgical measures for healing. Thus, while any of these conditions can pose challenges, the nature of a horizontal root fracture in the middle third typically yields the most significant hurdles for successful endodontic treatment and leads to a less favorable prognosis overall.