electron-microscopy for their identification.
Dentine (sometimes with enamel) changes can also be seen in some types of Ehlers
Danlos syndrome involving mutations in the collagen 1 genes.
Dentinogenesis imperfecta occurring in the absence of osteogenesis imperfecta is
inherited as an autosomal dominant trait. The primary and permanent dentitions are
usually affected. The teeth are opalescent with a greyish or brownish colour (862HFigs.
13.37, 863H13.38). There may be some variation in the severity of the appearance in
different members of the same family. Some variability may also be seen in the
severity of affliction of individual teeth in any one individual (864HFig. 13.39). The
enamel may chip away from the dentine to expose the dentine and the crowns may
suffer from attrition so that the teeth are worn down to the level of the gingivae (865HFig.
13.40). This situation is most commonly seen to affect the primary dentition. In the
primary dentition the pulps may be large and hence pulpal exposure may occur early.
In many cases, the pulps of the teeth tend to be obliterated, hence pulpal exposure and
abscess formation tend to occur later than might otherwise be expected. The chipping
of the enamel has often been claimed to result from a smooth enamel-dentine junction
but some studies have demonstrated that the contour of the enamel-dentine junction is
not a factor, with the weakness being within the dentine.
Radiographically the crowns appear relatively bulbous, the roots are shortened and
may be thinner than normal. The pulp chambers may be large initially, particularly in
the primary dentition, but more typically the pulps are obliterated as a result of
deposition of dentine in a rather haphazard manner (866HFig. 13.41 (a) and (b)). This can
be seen in histopathological sections where the mantle dentine adjacent to the enamel-
dentine junction is essentially normal but the deeper dentine is grossly abnormal.
OSTEOGENESIS IMPERFECTA
Osteogenesis imperfecta arises as a result of a mutation in one of the two collagen
type 1 genes. Although it used to be regarded as having autosomal dominant and
autosomal recessive modes of inheritance, it is now believed that autosomal dominant
mutations are the norm but that the severity varies in different individuals and
families. Cases such as those previously thought to be autosomal recessive are now
considered most likely to arise as a result of gonadal mosaicism.
The condition is characterized by bone fragility so that children may have a history of
fractures (from such mild trauma as walking into furniture), blue sclera, deafness
(though this does not usually develop until the third decade of life), and lax ligaments
around joints. There may or may not be dentinal changes, or these may be so subtle
that they are not apparent clinically or radiographically.
Key Points
Dentinogenesis imperfecta
- Autosomal dominant condition⎯isolated trait or associated with osteogenesis
imperfecta or other collagen abnormalities.
DENTINAL DYSPLASIA
Dentinal dysplasia was first described in the 1920s; 'rootless teeth' is an alternative,