Dentinogenesis imperfecta

Date: 2015-10-07; view: 550.

Genetically determined dentine defects

Dentinogenesis imperfecta is an autosomal dominant inherited condition. It may occur in isolation or in association with osteogenesis imperfecta. This represents two conditions, rather than a spectrum of effect. The term hereditary opalescent dentine is sometimes applied because of the typical opalescent hue of the teeth. Dentinogenesis imperfecta, both the typical variant and the 'Brandywine isolate' variant in the eastern United States, has been mapped to chromosome 4 and the DSPP gene has been shown to be mutated in several families (some of whom also have had hearing defects). In some of the Brandywine isolate families, occasional individuals have teeth which are indistinguished from the more typical form of dentinogenesis imperfecta; it is therefore likely that this represents an allelic variant of the same genetic condition. Similarly, the diagnosis of coronal dentinal dysplasia has been proposed but this also seems likely to be a variant of dentinogenesis imperfecta.

Dentinogenesis imperfecta type I in association with osteogenesis imperfecta is a result of mutations in one of the two collagen type 1 genes on chromosome 7 or 17. The dentine defects may be very apparent or rather subtle, in some cases requiring 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 (type II) 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. 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. 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. 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. 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.