Introduction
Infraocclusion is a condition that occurs when the occlusal surface of a
tooth is located below the occlusal plane of the adjacent teeth.
Submergence is a synonymous term also used to describe this clinical
presentation, which most commonly affects primary molar
teeth.1-3 Infraocclusion of primary teeth is caused by
ankylosis of the cementum to the surrounding alveolar bone, thus
impeding its eruption.1-3 The incidence of ankylosis
is approximately 1.3-38.5% in primary molars.1Ankylosis can occur at any time and results in the primary tooth failing
to keep pace with the normal vertical alveolar bone height changes in a
growing individual. Therefore, ankylosis is the phenomenon which results
in the lack of tooth eruption and subsequently leads to the clinical
presentation of infraocclusion.
The prevalence of this condition is also affected by
age.1-4 Infraocclusion of the first primary molar is
reported to be more common in children under the age of nine and shows a
general increase in incidence after the age of
three.1-3 In comparison, the prevalence of
infraoccluded second primary molars increases after the age of five and
is more prevalent after the age of nine.1-3
The prevalence of infraocclusion is significantly higher in the primary
dentition compared to the permanent dentition and more commonly found in
the mandible as opposed to the maxilla, with no significant gender
dimorphism reported. The most commonly affected teeth are the mandibular
first and second primary molars, with no predilection between the left
and right sides. It has been reported that 1.3-8.9% of children are
affected by infraocclusion of one or more of their primary
teeth.1-3 In addition, it was found that 18-44% of
the affected children’s siblings also presented with infraoccluded
teeth, which appears to indicate a genetic contribution to this
condition.1-4
Infraocclusion can also be categorised as slight, moderate, or
severe.1,2 The Facile classification, as described by
Brearly5, defines infraocclusion as slight when the
occlusal surface of the tooth is one millimetre below that of its
neighbours, moderate when the occlusal surface of the tooth is level to
or below the contact point of the neighbouring teeth, and severe when
the occlusal surface of the tooth is below the interproximal gingival
tissue.1 Both the prevalence and severity of
infraocclusion increases with chronological age. Therefore, a younger
patient who experiences primary tooth ankylosis is likely to demonstrate
more severe infraocclusion due to the longer period of vertical alveolar
bone height development. Although most ankylosed primary teeth
eventually exfoliate with the ongoing eruption of the succedaneous tooth
underneath, delayed exfoliation is common. Despite the relative
infrequency of unfavourable outcomes, infraoccluded primary molars are
known to be associated with other dental anomalies, including
hypodontia.6 The eruption path of the successor tooth
must be monitored closely and periodically to avoid undesirable
permanent tooth impactions. In extreme cases, the ankylosed primary
tooth can submerge to the point of complete coverage by the surrounding
hard and soft tissues as detailed in this case
report.7
Despite the uncertainty, there is a general consensus that
infraocclusion is multifactorial in aetiology.1-3 It
has been postulated that infraocclusion may be genetic in nature as this
condition can be seen in families, however, there are several factors
such as altered local metabolism, local trauma and infection that may
also potentially result in the infraocclusion of
teeth.1-3
Hypodontia, also known as congenitally missing teeth, is another common
dental developmental anomaly that indicates that at least one permanent
tooth has failed to form and erupt into the oral
cavity.4,8-14
The current consensus is that the aetiology of congenitally missing
teeth is multifactorial, with genetic and environmental factors
potentially both playing a role.4,8-14 Heritability of
congenitally missing teeth has been established through familial studies
where parents and their offspring and/or siblings have presented with
the same or similar congenitally missing
teeth.4,6,8-18 Numerous developmental syndromes such
as Down, Book and Rieger are associated with congenitally missing teeth,
which suggests the influence of genetic factors on the development of
the dentition.6,13-15 It has been suggested that
missing anterior teeth have a stronger genetic contribution, while the
absence of posterior teeth may be more sporadic in
nature.13
When reporting on the prevalence of hypodontia, the inclusion or
exclusion of the third molars produces a distinct difference in the
data.4 This difference is due to the high frequency of
congenitally missing third molars across all genetic
populations.4,19 Excluding the third molars, the
prevalence of congenitally missing teeth in specific teeth appears to be
determined by the population demographics.4,19 The
prevalence of congenitally missing teeth in the primary dentition has
been reported to be less than 1%, however, the prevalence of missing
teeth in the permanent dentition ranges from 1.6-36.5%, when the
absence of third molars are included. When missing third molars are
excluded from the data, the prevalence of congenitally missing permanent
teeth is significantly lower and reported to range between
1.6-6.9%.13 It is also reported that congenitally
missing teeth occurs bilaterally in the mouth almost two to three times
more frequently than unilaterally. Excluding the third molars, the most
common congenitally missing teeth in the permanent dentition are the
mandibular second premolars followed by the maxillary lateral
incisors.13,14