- Enamel defects;
- Hypoplasia⎯deficient matrix;
- Hypomineralisation⎯poor mineralisation.
Amelogenesis imperfecta
Amelogenesis imperfecta is the term applied to generalized enamel defects affecting
all (or predominantly all) of the teeth of both the primary and permanent dentitions. It
is of genomic origin and thus there may be a family history of similar defects in other
family members. Although the term strictly relates to enamel defects only, in some
patients there may be subtle or substantial changes in other dental tissues and cranio-
facial structures, or the condition may involve more widespread abnormalities as part
of a syndrome. Dentally, there may be failures of eruption with resorption of the
unerupted teeth. A case may be made for regular radiographic review of these patients
(825HFig. 13.21).
Amelogenesis imperfecta is seen in single gene mutations with autosomal dominant,
autosomal recessive, and X-linked patterns of inheritance. Apparently sporadic cases
are also seen⎯it is not clear whether these represent new mutations, or whether these
will then be passed on to future offspring (826HFig. 13.22). AI is relatively uncommon, but
there are marked population differences in prevalence. In parts of Sweden the
condition is relatively common (one in approximately 700 of the population). In one
study in the United States the prevalence was found to be approximately 1 in 14,000.
The classification of amelogenesis imperfecta has traditionally been based on the
phenotype⎯the clinical appearance. Following this system, patients are allocated
according to the perceived defect⎯hypoplasia, hypocalcification, or hypomaturation.
Some classifications have an additional category of hypomaturation-hypoplasia with
taurodontism to reflect the fact that some families show a combination of thin and/or
poorly mineralized enamel as well as taurodontism. However, it is important to
realize, both from a diagnostic and from a classification point of view, that not all
individuals within a family may show the same finding. As a result, phenotype
classifications become problematic when different members of the same family are
grouped into different categories. Furthermore, this classification system fails when
there is uncertainty as to which is the presumed predominant defect. It is possible that
the inheritance pattern will be forgotten in attempting to categorize individuals.
For this reason an alternative classification system has been suggested where the
mode of inheritance (autosomal dominant, autosomal recessive, X-linked or
apparently sporadic) is considered before the clinical phenotype. This classification
also allows for the fact that there may be some overlap between the clinical defects in
the same or different members of a family. The full classification scheme includes the
genomic and biochemical identity of the defect; however, for practical purposes, a
simplified use of this modern classification might, for example, define a patient's
presentation as 'autosomal dominant hypoplastic amelogenesis imperfecta'.
Autosomal dominant amelogenesis imperfecta
In autosomal dominant AI there is typically a clear pattern of inheritance with
individuals in successive generations being affected (827HFig. 13.23). Because the mutant