American Board of Orthodontics (ABO) Practice Exam

In replacement resorption, what happens to ankylosed teeth?

1. They become mobile

2. They fuse with the bone

3. They exhibit pulp necrosis

4. They undergo root resorption

The correct answer is: They fuse with the bone

Ankylosed teeth are those that have lost their periodontal ligament due to injury or a developmental issue, resulting in the teeth fusing directly to the surrounding alveolar bone. This fusion prevents normal tooth mobility and creates a stable yet problematic condition. In the context of replacement resorption, the ankylosed tooth does not resorb normally like a healthy tooth would, but rather, it becomes integrated into the bone structure. This fusion leads to a situation where the tooth's root structure is replaced by bone over time, which is the hallmark of replacement resorption. In this process, instead of the tooth being considered mobile or experiencing typical root resorption, it becomes bonded to the bone, thus losing its individual mobility and requiring careful management, especially when considering orthodontic treatment. The other options, while they may relate to different conditions of the tooth, do not accurately describe the outcome for ankylosed teeth in replacement resorption cases. For instance, mobile teeth indicate healthy periodontal support, while pulp necrosis would involve different pathological processes unrelated to ankylosis and fusion. Therefore, the correct understanding of what happens to ankylosed teeth during replacement resorption emphasizes their fusion with the bone.