Final answer:
A vertical root fracture has the poorest prognosis for a traumatized tooth because it often leads to the tooth being non-restorable and requiring extraction, while other types of fractures may be treatable with restorative methods or endodontics if they do not extend below the gumline.
Step-by-step explanation:
When considering the prognosis for a traumatized tooth, various factors such as the type and location of the fracture play a crucial role. Among the options provided, A vertical fracture of the root generally has the poorest prognosis. This type of fracture often extends along the long axis of the root, making the tooth non-restorable and typically leading to tooth extraction. In contrast, a horizontal fracture of the apical third may have a more favorable prognosis if stabilization can be achieved, the fracture is clean and there is no significant displacement of the tooth fragments.
Coronal fractures involving dentin and the pulp chamber (E) or coronal fractures level with the gingiva (D) can often be treated successfully with restorative methods or endodontic treatment if the fracture does not extend below the gumline. Lastly a horizontal root fracture apical to the epithelial attachment can sometimes successfully heal if the segments are stable and proper endodontic therapy is initiated especially since the apical fragment is in a region with good blood supply which increases the potential for healing.