Dentin Dysplasia, Type I
A number sign (#) is used with this entry because of evidence that a form of dentin dysplasia type I associated with extreme microdontia and misshapen teeth is caused by homozygous mutation in the SMOC2 gene (607223) on chromosome 6q27.
DescriptionIn dentin dysplasia type I, both primary and secondary dentitions are affected. The color and general morphology of the teeth are usually normal, although they may be slightly opalescent and blue or brown. Teeth may be very mobile and exfoliate spontaneously because of inadequate root formation. On radiographs, the roots are short and may be more pointed than normal. Pulp chambers are usually absent except for a chevron-shaped remnant in the crown (Witkop, 1975). Root canals are usually absent. Periapical radiolucencies may be present at the apices of affected teeth, for reasons unknown. On light microscopic examination of the permanent teeth, the coronal dentin is normal, but further apically becomes irregular, fills the pulp chamber, and has a 'sand-dune' morphology. Scanning electron microscopic studies of the deciduous and permanent teeth have been reported (Sauk et al., 1972; Melnick et al., 1980).
Subclassification of Dentin Dysplasia Type I
O Carroll et al. (1991) and O Carroll and Duncan (1994) reviewed dentin dysplasia and proposed 4 subtypes of dentin dysplasia type I, which they designated as DD1a-d. In DD1a, there is complete obliteration of pulp chambers and no root development, with many periapical radiolucent areas. In DD1b, there are horizontal crescent-shaped radiolucent pulpal remnants and a few millimeters of root development, with many periapical radiolucent areas. DD1c shows 2 horizontal crescent-shaped radiolucent lines and significant but incomplete root development, with or without periapical radiolucent areas. DD1d is characterized by visible pulp chambers and oval pulp stones in the coronal third of the root canal with bulging of the root around the stones and few if any periapical radiolucent areas. The authors noted that the distinctions between the subtypes of DD1 were primarily useful clinically in terms of treatment options.
Clinical FeaturesBrown (1944) described a 19-year-old boy with underdeveloped dental roots and early exfoliation of the teeth. The father and a paternal uncle were edentulous. Lind (1972) described hypoplasia of the teeth roots in 3 generations.
Morris and Augsburger (1977) reported a kindred in which dentin dysplasia type I was associated with generalized osteosclerosis and mild shortening of the distal ulna; see 125440.
O Carroll and Duncan (1994) studied a large 6-generation family in which 35 individuals were confirmed or reliably reported to have dentin dysplasia type I, and a further 6 were suspected of having it on the basis of the autosomal dominant nature of its transmission. Two affected family members had been reported by Duncan et al. (1991). The coronal size, shape, and color of most of the teeth were normal, but root size and shape were markedly altered. Panoramic radiographs revealed either complete pulpal obliteration or semilunar pulpal remnants, with no root structure present or roots that were either a few millimeters long or were 10 to 15 mm long. Some patients had only short roots and others exhibited a combination of both types. Periapical radiolucent lesions were found on almost all teeth in most affected individuals. Of 18 patients in whom panoramic radiographs were made, 8 were classified as having DD1a, the most severe form of dentin dysplasia, and the remaining 10 were classified as having DD1b.
Kalk et al. (1998) reported 5 affected individuals over 2 generations of a family with dentin dysplasia type I. The proband was an 8-year-old boy who was referred due to delayed eruption of upper central incisors. Examination revealed dentition with normal morphology and color, except for opacity of the incisional margin of the erupted incisors. All deciduous and permanent teeth were highly mobile. The dentition was free of caries, although oral hygiene was poor. Panoramic radiographs showed short, blunted, and malformed roots in both the deciduous and permanent teeth. The root canals were obliterated and appeared as small slits at the apices of the lower incisors; they were not visible in other teeth at all. The pulp chambers were obliterated as well, appearing as 2 crescent-shaped radiolucent lines, concave towards each other, in both deciduous and permanent molars. Periapical radiolucencies were present at the permanent lower incisors and first molars. The proband's father also had a history of delayed eruption, and stated that he had lost most of his teeth at an early age due to spontaneous exfoliation, requiring a full maxillary denture and partial mandibular denture by the end of adolescence. Panoramic radiographs showed obliterated root canals and pulp chambers, short roots, and periapical lucencies, confirming the diagnosis of DTDP1. The father had 2 sisters with the same history of delayed eruption and premature exfoliation, and 1 of the sisters had an affected 11-year-old daughter. Kalk et al. (1998) stated that the short root lengths in this family did not correlate with the radiographic pulp obliteration, and thus subclassification of patients into the previously proposed 4 distinct forms was not possible. In addition, root lengths varied from diminutive to intermediate, and cases could not be described as 'total' or 'subtotal.'
Dentin Dysplasia, Type I, With Extreme Microdontia and Misshapen Teeth
Bloch-Zupan et al. (2011) described a 10-year-old boy and his 5-year-old female first cousin, both born of consanguineous Turkish parents, who had extreme microdontia, oligodontia, dental shape anomalies, double permanent-tooth formation, thin enamel, and short roots with thin associated alveolar bone. Oligodontia was diagnosed due to missing permanent teeth, 14 in the boy and 13 in the girl. Anomalies of tooth size were observed, and extreme microdontia affected both the primary teeth, which were all present, and the permanent teeth; however, some of the permanent teeth were macrodontic. All existing teeth showed anomalies of shape, with extra cusps and tiny, globular, malformed crowns, especially in the primary dentition. Double tooth formation (notched and macrodontic) was visible on the permanent incisors. Temporary and permanent molars exhibited taurodontism; in addition, the molars had tooth-structure anomalies reminiscent of dentin dysplasia type I spectrum, with very short roots. Dental x-rays showed that the enamel was very thin and had limited contrast compared to the dentin. The alveolar bone associated with the primary teeth was underdeveloped, and the primary teeth were mobile and exfoliated prematurely. Psychomotor development was normal in both children; the girl was obese and had 'very mild bone abnormalities' that were not present in her male cousin. Bloch-Zupan et al. (2011) stated that the dental phenotype in the affected cousins resembled that of dentin dysplasia type I, but was distinct because of the extreme microdontia and dental shape anomalies.
AlFawaz et al. (2013) reported 3 sibs, aged 16, 10, and 8 years, from a consanguineous Pakistani family with oligodontia and microdontia. Some teeth also showed abnormal forms with buccal evagination, and there was an incisal notch in the central incisors of varying degrees. Radiographic examination revealed 10 to 15 missing adult teeth in each of the sibs, and there was evidence of taurodontism in some of their posterior permanent molars; the permanent molars also displayed a single root with a thistle-shaped pulp. Two of the sibs had an anterior open bite due to lack of upper anterior alveolar growth, and all 3 had increased amounts of calculus deposits in the lower central incisor region.
Population GeneticsO Carroll and Duncan (1994) stated that 190 cases of dentin dysplasia had been reported in the world literature, of which 128 represented dentin dysplasia type I.
Kalk et al. (1998) stated that the incidence of dentin dysplasia type I has been estimated at 1:100,000.
MappingIn a highly consanguineous Turkish family in which 2 first cousins had a form of type I dentin dysplasia associated with extreme microdontia and misshapen teeth, Bloch-Zupan et al. (2011) performed homozygosity mapping and identified a 3-Mb region of homozygosity on chromosome 6q27-qter that was shared between the 2 affected individuals but not was not present in unaffected members of the family.
Molecular GeneticsIn 2 affected first cousins from a consanguineous Turkish pedigree with a form of type I dentin dysplasia associated with extreme microdontia and misshapen teeth, mapping to chromosome 6q27-qter, Bloch-Zupan et al. (2011) identified homozygosity for a splice site mutation in the candidate gene SMOC2 (607223.0001). The unaffected parents and sibs were heterozygous for the mutation, which was not found in 112 ethnically matched controls.
In 2 affected sibs from a consanguineous Pakistani family with oligodontia, microdontia, and abnormally shaped teeth, AlFawaz et al. (2013) performed exome sequencing and identified homozygosity for a nonsense mutation in the SMOC2 gene (C227X; 607223.0002) that segregated with disease in the family. The authors noted that the previously reported Turkish patients with a splice site mutation in SMOC2 (Bloch-Zupan et al., 2011) had a similar clinical presentation.
HistoryKalk et al. (1998) stated that this disorder was first described as 'rootless teeth' in a dissertation by Ballschmiede in 1920, as cited by Herbst and Apffelstaedt (1930).