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Abnormal Teeth
A number of tooth abnormalities can occur in development. These can relate to the shape, color, physical structure, or number of teeth.

Number of Teeth
Hypodontia: The lack of some tooth development.
Hypodontia can be caused by some of the same problems that cause delayed tooth eruption (eg, Down syndrome, ectodermal dysplasias, chemotherapy, radiation therapy). The prevalence of hypodontia is approximately 3% in the United States, excluding the absence of the third molars (wisdom teeth), which occurs in approximately 20% of individuals.

Anodontia: An especially congenital absence of teeth.
Anodontia is extremely rare and most often associated with hypohydrotic ectodermal dysplasia.

Hyperdontia: A congenital condition marked by a greater than normal number of teeth.
Hyperdontia prevalence ranges from 0.1% to 3.8% and can be associated with genetic disorders such as
Cleidocranial dysostosis: A rare condition inherited in an autosomal dominant fashion and characterized especially by partial or complete absence of the clavicles, defective ossification of the skull, and faulty occlusion due to missing, misplaced, or supernumerary teeth.
cleidocranial dysostosis and Gardner’s syndrome
Familial Adenomatous Polyposis: A disease of the large intestine that is marked by the formation especially in the colon and rectum of numerous adenomatous polyps which typically become malignant if left untreated; inherited as an autosomal dominant trait.
(Familial Adenomatous Polyposis).

Tooth Shape
Abnormal tooth shape can result from a variety of medical conditions. Some recognizable names of these abnormal teeth and their causes include Hutchinson incisors (congenital syphilis), mulberry teeth (congenital syphilis), and conical teeth (ectodermal dysplasias).
 
 
Hypodontia occurs in approximately 3% of the US population.
 
Anodontia, the complete lack of tooth development, is extremely rare.
 
The wisdom teeth do not develop in approximately 20% of people.
 
It is important to recognize medical conditions that affect the number or shape of an individual's teeth.

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