Dentin dysplasia type I is an inherited disorder characterized by atypical development of the “dentin” of a person’s teeth. Dentin makes up most of the tooth and is the bone-like material under the enamel. It serves to contain the pulp of the tooth. The pulp is a soft tissue that is well supplied with blood vessels and nerves. This disorder is also known as radicular dentin dysplasia because the underdeveloped, abnormal pulp tissue is predominately in the roots of the teeth. The teeth lack pulp chambers or have half-moon shaped pulp chambers in short or abnormally shaped roots. The condition may affect juvenile as well as adult teeth and, since the roots are abnormally short, usually leads to the premature loss of teeth. The color of the teeth is usually normal.
Some people with dentin dysplasia type I have teeth with a bluish-brown shine. In most instances, however, the teeth have normally colored enamel. It is clear from X-ray photos that the tooth pulp chambers in the roots are unusually small, half-moon shaped or lacking altogether. The roots are very short and may appear to be dark (radiolucent) on X-rays.
Both the baby teeth and the permanent teeth are affected. The teeth are often poorly aligned and can be chipped easily. Without treatment, persons with dentin dysplasia type I may lose their teeth by age 30-40.
Dentin dysplasia is inherited as an autosomal dominant trait. The defective gene has not been identified or traced to a particular site on a particular chromosome.
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 11p13” refers to band 13 on the short arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
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.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Dentin dysplasia type I appears to affect about 1 in 100,000 persons. Males and females are apparently equally at risk.
The affected teeth are usually treated by a dentist specializing in the care o. the roots and pulp of the teeth (endodontists). Filling the tips of the root canals may extend the period of time that the affected teeth remain fixed to the jaw. Sometimes, the affected teeth must be extracted and replaced with dentures.
Genetic counseling is recommended for families of children with dentin dysplasia type I.
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FROM THE INTERNET
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