**Core Concept**
Root fractures are serious injuries that occur in the root of a tooth, often as a result of trauma. The management of root fractures is crucial to prevent further complications, such as root resorption, infection, or tooth loss. In some cases, surgical intervention is necessary to repair the fracture.

**Why the Correct Answer is Right**
The least favourable form of attempted repair of the root fracture is **apical reimplantation**. This method involves removing the fractured root from the mouth and reimplanting it into the socket. However, this approach has a high risk of failure, as the blood supply to the root is often compromised, leading to necrosis and root resorption. Furthermore, apical reimplantation may also lead to infection and other complications.

**Why Each Wrong Option is Incorrect**
**Option A:** **Root canal therapy** may be performed on a tooth with a root fracture to remove infected pulp tissue and promote healing. However, this is not a form of repair and is not appropriate for all root fractures.
**Option B:** **Orthodontic movement** may be used to help align the fractured root and promote healing. However, this approach is not a definitive form of repair and may not be suitable for all cases.
**Option C:** **Surgical repair** using bone grafts and other materials can be an effective way to repair a root fracture. This approach allows for better control over the repair process and can promote healing and regeneration.

**Clinical Pearl / High-Yield Fact**
When managing root fractures, it is essential to assess the extent of the fracture and the vitality of the pulp. A thorough examination and imaging studies, such as radiographs and CT scans, can help guide treatment decisions.

**Correct Answer: C. Surgical repair**