The ankylosis of a tooth is defined as an anatomical fusion of alveolar bone with cementum and can occur any time during eruption, either before or after the tooth erupts into the oral cavity. Essentially, the periodontal ligament is obliterated by a 'bony bridge' and the root becomes fused to the alveolar bone.
An ankylosed tooth can be diagnosed multiple ways:
- A lack of mobility or a sharp, solid sound upon percussion with a hand instrument (typically only reliable when at least 20 percent of the root is affected)
- The incisal or occlusal edge is below the incisal/occlusal plane
- The gingival margin or, more accurately, the CEJ is at a more apical position compared to the adjacent teeth
- Radiographic examination reveals obliteration of the periodontal ligament space
So what is the concern with ankylosed teeth?
The first concern is that the ankylosed root is continually resorbed and replaced with bone, thereby diminishing the support of the crown of the tooth – although the rate of the resorption may be extremely variable.
The second is the impact on normal alveolar development if an ankylosed tooth is present while the patient is undergoing growth. The ankylosed tooth will appear as if it is becoming submerged as the adjacent teeth erupt.
Several theories have been proposed on the different etiologies that may cause ankylosis:
- A disruption of local metabolism of the PDL (Biederman: 1962)
- Genetics (Kural, Magnusson: 1984)
- Deciduous teeth without a permanent successor (Brearly, McKibben: 1972)
By far, the most common theory that is known to cause ankylosis is traumatic injury of the periodontal ligament (Kracke: 1975, Henderson: 1979, Andreasen: 1981). Risk of ankylosis is highest for teeth with subluxation or avulsion injuries because of the nature and severity of damage to the periodontal ligament.
Deciduous teeth become ankylosed far more frequently than do permanent teeth, the ratio being greater than 10-to-1, and lower teeth are ankylosed more than twice as often as upper teeth.
Although the initial treatment thought when an ankylosed tooth is encountered is often to immediately extract the ankylosed tooth, the actual treatment decision should be made only after evaluating multiple different factors:
- Whether the ankylosed tooth is deciduous or permanent
- The time/age of the onset of ankyloses
- The time/age at diagnosis; patient gender
- The location of the affected tooth
- The smile line
In the subsequent posts, I will look deeper into the different treatment recommendations and options given the variety of clinical findings that may be present.
(Click this link for more dental articles by Dr. Gregg Kinzer.)
Gregg Kinzer, D.D.S., M.S., Spear Faculty and Contributing Author