Dentin dysplasia type II, also known as coronal dentin dysplasia, is a rare genetic disorder that affects the teeth. It is characterized by abnormal development (dysplasia) of dentin. Dentin is the hard tissue found beneath the enamel that surrounds and protects the pulp and forms the major part of teeth. Affected children may exhibit brownish-blue discoloration of baby teeth (primary or deciduous teeth) and obliteration of the pulp chambers. Permanent teeth are usually unaffected or only mildly affected. Dentin dysplasia type II only affects the teeth. The disorder is caused by mutations of the DSPP gene.
Dentin dysplasia type II belongs to a group of disorders known as the hereditary dentin disorders. In 1973, a physician and his colleagues defined five disorders characterized by inherited dentin defects (Shields classification). Many physicians have noted that the Shields classification is out of date. As new research reveals genetic mutations and better defines these disorders, a new classification system will be warranted. Unfortunately, the current understanding of these disorders is insufficient to allow the creation of this updated classification.
Dentin dysplasia type II is a dental abnormality characterized by abnormal development (dysplasia) of dentin. Within the interior of a tooth is pulp – a specialized tissue that contains nerves, blood vessels, and lymphatic vessels. Pulp is surrounded by a hard dental tissue known as dentin, which forms the primary material of the tooth. The exposed region of the tooth above the gum (also known as the crown or “coronal region”) is covered by enamel, which is harder than dentin, while the root is covered by a bone-like rigid connective tissue known as cementum. Dentin protects the pulp chamber and provides support for enamel and cementum.
In individuals with dentin dysplasia type II, the baby teeth may be discolored appearing to be yellow, brown, grey-amber, or a brownish-blue color. The teeth are sometimes described as having a translucent “opalescence”. (Opalescence refers to a milky, opal-like display of colors in reflected light.) In most cases, the permanent (secondary) teeth have a normal color.
When the dentin layer beneath the enamel crown is too weak to support it, the enamel will tend to wear away (abrade) and fall out prematurely.
In addition to being normal in color, permanent teeth are also normal in shape and size. However, they also have characteristic abnormalities of the pulp chambers. More specifically, on dental x-rays, pulp chambers appear unusually “flame shaped” and often have abnormal extensions toward the roots (i.e., “thistle-tube” shaped pulp chambers). In addition, the pulp chambers often contain numerous pulp stones, which are abnormal deposits of calcium salts (calcifications). With age, the pulp chambers of the permanent teeth may become partially obliterated. Evidence suggests that root formation in the permanent teeth is usually normal.
In rare cases, some individuals with dentin dysplasia type II may develop mild tooth discoloration or abnormally rounded (bulbous) crowns. If these abnormalities are pronounced in the permanent teeth, then the diagnosis changes to dentinogenesis imperfecta type II (DGI-II).
Dentin dysplasia type II is caused by mutations of the dentin sialophosphoprotein (DSPP) gene. This mutation is inherited as an autosomal dominant trait.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother. Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Investigators have determined that the DSPP gene is located on the long arm (q) of chromosome 4 (4q21.3). Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 4q21.3” refers to band 21.3 on the short arm of chromosome 4. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Researchers have determined two classes of mutations that cause dentin dysplasia type II (and curiously, DGI-II & III). The first class involves missense mutations (i.e. changing one amino acid for another) in some of the first 18 amino acids of the DSPP gene (including the skipping of exon 3). The second class of mutations cause the amino acid repeat found in the second half of this large protein to change from being very acidic in character to very hydrophobic. Both classes apparently cause dentin dysplasia type II (as well as DGI-II & III) by disrupting the cell’s ability to make and/or mineralize the dentin matrix in as yet unknown ways. To date, the best evidence suggests that complete loss of a single copy of DSPP is unlikely to cause dentin dysplasia type II (or DGI) phenotypes although such a loss is predicted to cause some recessive forms of dentin diseases.
Dentin dysplasia type II affects males and females in equal numbers. The exact incidence and prevalence of dentin dysplasia type II is unknown. It occurs more frequently than dentin dysplasia type I, which is estimated to affect 1 in 100,000 people in the general population.
Abnormalities of dentin dysplasia have been known by many other names in the medical literature including rootless teeth, anomalous dysplasia of dentin, opalescent dentin, pulpless teeth, and thistle-tube teeth.
A diagnosis of coronal dentin dysplasia is made based upon identification of characteristic symptoms, a detailed patient history, and a thorough clinical evaluation. X-rays may reveal abnormal coronal pulp formation, obliteration of the pulp chambers, pulp stones or thistle-shaped deformity of the pulp chamber.
The treatment of coronal dentin dysplasia is directed toward the specific symptoms that are apparent in each individual. Because permanent teeth are often unaffected, no specific or unusually dental therapy is necessary. Recommended treatment may include regular monitoring by dental specialists and ongoing preventive dental care.
Genetic counseling may be of benefit for affected individuals and their families
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Contact for additional information about dentin dysplasia type II:
James P. Simmer, DDS, PhD
Professor, Dept. of Biologic and Materials Sciences
University of Michigan Dental Research Lab
1210 Eisenhower Place
Ann Arbor, MI 48108
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