A tooth is normally held within its socket by the periodontal ligament (PDL), a soft tissue structure that allows for minor movement and cushioning against biting forces. When a tooth becomes ankylosed, this natural connection is lost, and the tooth root fuses directly to the surrounding jawbone. This pathological fusion eliminates the PDL space, effectively making the tooth an unmoving part of the skeleton. Understanding the underlying biology of both the condition and orthodontic mechanics is necessary to determine if such a fused tooth can be moved using braces.
Understanding Dental Ankylosis
Dental ankylosis is a condition where the tooth becomes biologically welded to the alveolar bone. This process obliterates the periodontal ligament (PDL), the connective tissue layer that normally separates the root from the bone. Without the PDL, the tooth loses its ability to respond to pressure and tension, unlike a healthy tooth.
This fusion is a biological remodeling process, often involving replacement resorption where the root structure is absorbed and replaced with bone tissue. The most common causes include dental trauma, especially injuries involving the tooth being knocked out and replanted (avulsion), or severe intrusion into the socket. Genetic factors and chronic local infection can also play a role in the development of this condition.
While ankylosis can affect permanent teeth, it is more commonly observed in primary (baby) teeth. This often causes the affected tooth to appear sunken or submerged relative to its neighbors, a clinical sign known as infraocclusion. In a growing child, the jawbone continues to develop vertically around the ankylosed tooth, making the submerged appearance more pronounced over time.
Why Orthodontic Movement Fails
The fundamental principle of orthodontic tooth movement relies entirely on the presence and function of the periodontal ligament. When a force is applied to a healthy tooth, the PDL is compressed on one side and stretched on the opposite side. This differential pressure stimulates a cellular response in the bone.
On the compression side, specialized cells called osteoclasts break down the adjacent bone. Simultaneously, on the tension side, osteoblasts form new bone, a process called apposition. This coordinated destruction and creation allows the tooth to slowly glide through the bone, guided by the orthodontic appliance.
An ankylosed tooth lacks the PDL, meaning the root is a single, rigid unit fused with the bone. When orthodontic force is applied, the necessary biological cascade of bone resorption and apposition cannot occur. Instead of moving, the tooth acts as an unyielding anchor, resisting any force applied. The attempt to move the ankylosed tooth is biologically impossible because the mechanism of movement is absent.
Applying forces to an ankylosed tooth carries significant risks, primarily to adjacent, healthy teeth. Since the ankylosed tooth cannot move, it acts as a fixed point, transferring the entire force to surrounding structures. This can cause the healthy teeth next to it to move in unpredictable and undesirable ways, or even lead to root resorption. Force application can also be traumatic to the fused structure, potentially resulting in fracture of the compromised root or the surrounding alveolar bone.
Management Strategies and Alternatives
Since orthodontic movement is not a viable option, the management of an ankylosed tooth shifts to established clinical strategies. These strategies depend on the patient’s age and the severity of the infraocclusion. In milder cases, especially in young children with primary teeth, a “wait and see” approach may be taken. This involves careful monitoring of the tooth’s position relative to the continuous growth of the jaw.
When the infraocclusion is more severe or if the tooth is permanent, the most straightforward treatment is surgical extraction. However, removing an ankylosed tooth can be difficult and may result in the traumatic loss of surrounding alveolar bone. This bone loss creates a defect that complicates future restoration, especially in the aesthetically sensitive front of the mouth.
Decoronation
A preferred alternative, especially for ankylosed permanent incisors in growing patients, is a procedure called decoronation. This technique involves surgically removing the entire crown of the tooth at the bone level while leaving the root submerged within the socket. The retained root is then slowly resorbed and replaced by bone over time. This approach is designed to maintain the height and width of the alveolar ridge, promoting vertical bone growth as the patient matures. Preserving the bone volume through decoronation ensures the space can be managed with fixed prosthetic solutions, such as a bridge or a dental implant, without extensive bone grafting.