Disorders of human dentin

Abstract

Dentin, the most abundant tissue in teeth, is produced by odontoblasts, which differentiate from mesenchymal cells of the dental papilla. Dentinogenesis is a highly controlled process that results in the conversion of unmineralized predentin to mineralized dentin. By weight, 70% of the dentin matrix is mineralized, while the organic phase accounts for 20% and water constitutes the remaining 10%. Type I collagen is the primary component (>85%) of the organic portion of dentin. The non-collagenous part of the organic matrix is composed of various proteins, with dentin phosphoprotein predominating, accounting for about 50% of the non-collagenous part. Dentin defects are broadly classified into two major types: dentinogenesis imperfectas (DIs, types I-III) and dentin dysplasias (DDs, types I and II). To date, mutations in DSPP have been found to underlie the dentin disorders DI types II and III and DD type II. With the elucidation of the underlying genetic mechanisms has come the realization that the clinical characteristics associated with DSPP mutations appear to represent a continuum of phenotypes. Thus, these disorders should likely be called DSPP-associated dentin defects, with DD type II representing the mild end of the phenotypic spectrum and DI type III representing the severe end.

Fig. 1

Clinical and radiographic features of DI types I–III (a–g) and DD types I and II (h–j). a–c Individuals with DI type I. In this family, affected members also had OI type I due to a missense alteration in COL1A1 (p.Gly559Cys). a, b The constriction of the crown in the cervical region and almost complete obliteration of the pulp chambers. c The enamel has fractured from the central and lateral incisors, exposing the underlying yellow-brown dentin. d, e An individual with DI type II. f, g An affected male from the Brandywine cohort. h The extremely short roots characteristic of DD type I. i The phenotype in deciduous teeth that resembles DI type II, but the permanent teeth are normal in color. j The thistle-tube deformity commonly seen in DD type II.

Fig. 2

Diagram of the DSPP gene and corresponding protein structure. Mutations are shown above the ge-nomic structure. Gray areas correspond to untranslated regions. The white box corresponds to the signal peptide [amino acids (aa) 1–15]. DSP is shown as black regions (aa 16–382). DGP, represented by a stippled box, corresponds to aa 383–462. The highly repetitive protein, DPP, is shown as a striped box (aa 463–1253).