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Dentinogenesis Imperfecta


What is Dentinogenesis Imperfecta? (DI)

Dentinogenesis imperfecta represents a group of hereditary conditions that are characterized by abnormal dentin formation. These conditions are genetically and clinically heterogenous and can affect only the teeth or can be associated with the condition osteogenesis imperfecta.The dentinogenesis imperfectas and dentin dysplasias were classified using clinical, radiographic and histopathologic features in 1973 and this nosology remains in use today [49]. Dentinogenesis imperfecta has been subdivided based on its association with osteogenesis imperfecta (OI) (Type I) (OMIM# 166240) or not (Type II) (OMIM# 125490), or being associated with the Brandywine triracial isolate and large pulp chambers (Type III) (OMIM# 125500).

Figure 20
The molecular defects in OI include numerous mutations in the pro-alpha chains of collagen type 1 that result in a phenotype characterized by increased bone fragility [50]. Although the dental phenotypes of DI types I and type II appear very similar, the latter disorder is not associated with any of the non-dental phenotypic features of osteogenesis imperfecta and is not caused by a collagen 1 defect. DI type II and type III are autosomal dominant conditions that have been linked to chromosome 4q12-21, suggesting these may be allelic mutations of the DSPP gene [51]. In several different families the gene responsible for DI type II has been identified as the DSPP gene that codes for the dentin sialophosphoprotein, the most abundant noncollagenous protein in dentin [52, 53].

Figure 21
 

In all three DI types the teeth have a variable blue-gray to yellow brown discoloration that appears opalescent due to the defective, abnormally colored dentin shining through the translucent enamel (Figure 20). Due to the lack of support of the poorly mineralized underlying dentin, the enamel frequently fractures from the teeth leading to rapid wear and attrition of the teeth. The severity of discoloration and enamel fracturing in all DI types is highly variable even within the same family. If left untreated it is not uncommon to see the entire DI affected dentition worn off to the gingiva.

Radiographs show pulpal obliteration in DI types I and II due to rapid and excessive deposition of dentin (Figure 21). The pulp chambers are large in DI type III.

Types of Dentinogenesis Imperfecta

The nomenclature for the different hereditary conditions that affect dentin is confusing at best and will need to be modified now that the molecular basis of these conditions is becoming understood. For example, it is now known that DI types II and III as well as DD type II can all be caused by allelic mutations.  Although there are subtle differences in the resulting phenotypes it is questionable whether the historical phenotype type based nosology is useful for delineating these phenotypically overlapping conditions that are all caused by mutations in the DSPP gene.  Adding to the confusion, there are numerous syndromes that have DI-like phenotypes associated with them other than OI such as sondylometaphyseal dysplasia (OMIM# 184260) Because these diverse conditions (e.g. OI and other collagen disorders) affecting the collagen-DSPP interaction and subsequent dentin formation and mineralization, they can have virtually idental phenotypes.  Although the Shields based classification has been used extensively since its introduction, the OMIM nomenclature is different (OMIM classification DGI1 is the same as Shields DI type II).  We show both the OMIM and Shields classifications and associated clinical an radiographic features in Table 4.

Heritable Conditions of Dentin

Condition Clinical Features Radiographic Features

Osetogenesis Imperfecta with DI (Shields DI type I)
(occurs in some forms of osteogenesis imperfecta)
(OMIM# 166240)

Variable blue-gray to yellow-brown teeth, enamel fracturing, excessive wear, primary teeth usually more affected than permanent Variable pulp obliteration,
bulbous crowns, altered
root morphology, increased risk of dentigerous cysts

Dentinogenesis imperfecta (Shields DI type II)
(OMIM# 125490)
Same appearance and variability as in DI type I. Often similar severity in primary and permanent dentitions

Pulp chamber obliteration that can begin prior to tooth eruption. Abnormal crown and root morphology
Dentinogenesis imperfecta type III
(OMIM# 125500)

Similar clinical phenotype as DI types I and II although typically severe expression with enamel loss and extensive wear occurring early

Large pulp chambers, Very thin dentin, bulbous crowns and diminished root structure
Dentin Dysplasia type I
(OMIM#125400)
Normal clinical crown morphology and coloration in primary and permanent dentitions, Mal-aligned teeth, frequent dental abscess

Pulp obliteration and short blunt roots in both primary and permanent dentitions

Dentin Dysplasia type II
(OMIM# 125420)
Primary dentition has same phenotype as DI, permanent dentition has normal to slight blue gray discoloration Pulp obliteration in primary dentition, abnormal pulp morphology and pulp stones in permanent dentition


Dentinogenesis Imperfecta Research

Numerous laboratories around the world are working to identify the different molecular defects associated with abnormal dentin development.  Becuase the genes epressed by odontoblasts during dentin formation also are expressed in many other tissues, it is not uncommon to have dentin defects associated with abnormalities in other tissues.  This is true not only for the different forms of osteogenesis imperfecta but many other conditions as well. An extensive review of the conditions associated with dentinogenesis imperfecdta can be searched at http://www.ncbi.nlm.nih.gov/O mim/

DI Associated with OI

Shields (DI Type I;OMIM# 166240)

The diverse mutations associated with the COL1A1 and COL1A2 genes and osteogenesis imperfeta are too numerous to review and can be searched at http://www.ncbi.nlm.nih.gov/O mim/. Mutations in these genes can cause the DI phenotype in association with osteogenesis imperfecta (DI type I).  Individuals with mutations in the type I collagen genes and in some genes involed in the formation of the collagen heterotrimer and its maturation (e.g. lysyl hydroxylase) can also be associated with dentin abnormalities.  The relationship between the different type I collagen mutations and the resulting bone and dental phenotype is not well understood. Why collagen mutations can result in a severe bone phenotype and only a mild or non-detectable dental phenotype is not known.  The range of severity of both bone and dental phenotypes in OI with DI type I are extensive.  Further studies will utimately help understand the mechanisms involved in producing these diverse clinical conditions and their dental manifestations.

DI (Shields DI type II; OMIM# 125490)  

DD Type II (OMIM# 125420)

Multiple mutations have been identified in the DSPP gene that are associated with DI type II and more recenlty have also been shown to be causative of DD type II.  In at least some families these conditions are allelic.  Indeed studies show that Shields DI type III is also caused by mutations in the DSPP gene.  These studies indicate that depending on the type of DSPP mutation and other, as yet unknown factors, there are a variety of resulting phenotypes that can occur.  Why the DD type II mutation affects the primary dentintion much more severely than the permanent dentition or why they young primary teeth can have enlarged pulp chambers in some cases (DI type III feature) is not known.  Future studies correlating these phenotypic variants with the specific DSPP mutations and how they alter the protein's function will utlimately help answer these important questions.

For additional information on the DI associated genes and molecular defects in DI see the OMIM Web site at http://www.ncbi.nlm.nih.gov/Omim/

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