Hypodontia
Encyclopedia
In dentistry
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...

, hypodontia is the condition at which the patient has missing teeth as a result of their failure to develop. Hypodontia describes a situation where the patient is missing up to 6 teeth, excluding the 3rd molars. Missing third molars occur in 9-30% of population. In primary dentition the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

 is more affected, with the condition usually involving the maxillary lateral incisor
Maxillary lateral incisor
The Maxillary lateral incisor is a tooth that is located distally from both maxillary central incisors of the mouth and mesially from both maxillary canines. As with all incisors, their function is for shearing or cutting food during mastication, commonly known as chewing. There are no cusps on...

.

The condition of missing over 6 teeth, excluding 3rd molars or wisdom teeth, is called oligodontia. The condition for missing all teeth, either primary and/or permanent), is called anodontia
Anodontia
In dentistry, anodontia, also called anodontia vera, is a rare genetic disorder characterized by the congenital absence of all primary or permanent teeth. It is associated with the group of skin and nerve syndromes called the ectodermal dysplasias...

. A similar condition is hyperdontia
Hyperdontia
Hyperdontia is the condition of having supernumerary teeth, or teeth which appear in addition to the regular number of teeth.-Types:Supernumerary teeth can be classified by shape and by position...

, in which there are more than the usual number of teeth.

Many other terms to describe a reduction in number of teeth appear in the literature: oligodontia, anodontia, aplasia of teeth, congenitally missing teeth, absence of teeth, agenesis of teeth and lack of teeth.

Prevalence

In caucasians, the most common missing teeth are the wisdom teeth (25-35%), the upper lateral incisors (2%) the lower second premolars (3%), or the upper second premolar, with a 4:1 female to male ratio. The prevalence of missing primary teeth is found at 0.1-0.9%, with a 1:1 male to female ratio. Excluding the third molars, missing permanent dentition accounts for 3.5-6.5%.

30-50% of people with missing primary teeth will have missing permanent teeth, as well.

Etiology

The cause of isolated missing teeth remains unclear, but the condition is believed to be associated with genetic or environmental factors during dental development
Tooth development
Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans...

. Missing teeth have been reported in association with increased maternal age, low birth weight, multiple births and rubella virus
Rubella virus
Rubella virus is the pathogenic agent of the disease Rubella, and is the cause of congenital rubella syndrome when infection occurs during the first weeks of lunacy.Humans are the only known host of this virus....

 infection during embryonic life.

There is a possible correlation between tooth agenesis and innervation. A relationship was also postulated between abnormalities of the brainstem and the presence of agenesis.

Hypodontia is often familial, and can also be associated with genetic disorders such as ectodermal dysplasia
Ectodermal dysplasia
Ectodermal dysplasia is not a single disorder, but a group of syndromes all deriving from abnormalities of the ectodermal structures. More than 150 different syndromes have been identified. Despite some of the syndromes having different genetic causes the symptoms are sometimes very similar...

 or Down syndrome
Down syndrome
Down syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The condition was clinically described earlier in the 19th...

. Hypodontia can also been seen in people with cleft lip and palate.

Among the possible causes are mentioned genetic, hormonal, environmental and infectious.

Etiology due to hormonal defects: idiopathic hypoparathyroidism and pseudohypoparathyroidism
Parathyroid hormone
Parathyroid hormone , parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands as a polypeptide containing 84 amino acids...

. Exists the possibility that this defect depends on a moniliasis (candidiasis
Candidiasis
Thrush redirects here. For the hoof infection see Thrush .Candidiasis or thrush is a fungal infection of any of the Candida species , of which Candida albicans is the most common...

, candida endocrinopathy syndrome).

Environmental causes involving exposure to PCBs (ex.dioxin
Dioxin
Polychlorinated dibenzodioxins , or simply dioxins, are a group of organic polyhalogenated compounds that are significant environmental pollutants. They are commonly but inaccurately referred to as dioxins for simplicity, because every PCDD molecule contains a dioxin skeletal structure as the...

), radiation, anticancer chemotherapeutic agents, allergy and toxic epidermal necrolysis
Toxic epidermal necrolysis
Toxic epidermal necrolysis is a rare, life-threatening dermatological condition that is usually induced by a reaction to medications...

 after drug.

Infectious causes of hypodontia: rubella
Rubella
Rubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...

, candida
Candida (genus)
Candida is a genus of yeasts. Many species are harmless commensals or endosymbionts of animal hosts including humans, but other species, or harmless species in the wrong location, can cause disease. Candida albicans can cause infections in humans and other animals, especially in immunocompromised...

.

The Journal of the American Dental Association published preliminary data suggesting a statistical association between hypodontia of the permanent teeth and epithelial ovarian cancer
Ovarian cancer
Ovarian cancer is a cancerous growth arising from the ovary. Symptoms are frequently very subtle early on and may include: bloating, pelvic pain, difficulty eating and frequent urination, and are easily confused with other illnesses....

 (EOC). The study shows that women with EOC are 8.1 times more likely to have hypodontia than are women without EOC. The suggestion therefore is that hypodontia can serve as a "marker" for potential risk of EOC in women.

Also the increased frequency of hypodontia in twins and low birth weight in twins with hypodontia suggests that environmental factors during perinatal are responsible hypodontia.

Genetics

Genetic causes also involve the genes MSX1
MSX1
Msh homeobox 1, also known as MSX1, is a protein that in humans is encoded by the MSX1 gene. MSX1 transcripts are not only found in thyrotrope-derived TSH cells, but also in the TtT97 thyrotropic tumor, which is a well differentiated hyperplastic tissue that produces both TSHß- and a-subunits and...

 and PAX9
PAX9
Paired box gene 9, also known as PAX9, is a protein which in humans is encoded by the PAX9 gene. It is also found in mammals generally.- Function :This gene is a member of the paired box family of transcription factors...

. But MSX1
MSX1
Msh homeobox 1, also known as MSX1, is a protein that in humans is encoded by the MSX1 gene. MSX1 transcripts are not only found in thyrotrope-derived TSH cells, but also in the TtT97 thyrotropic tumor, which is a well differentiated hyperplastic tissue that produces both TSHß- and a-subunits and...

 and MSX2
MSX2
MSX2 may refer to:* Msh homeobox 2, a human gene* The second generation of the MSX home computers...

 are excluded as candidate genes for hypodontia.

Genetic associations for selective tooth agenesis ("STHAG") include:
Type OMIM Gene Locus
STHAG1 MSX1
MSX1
Msh homeobox 1, also known as MSX1, is a protein that in humans is encoded by the MSX1 gene. MSX1 transcripts are not only found in thyrotrope-derived TSH cells, but also in the TtT97 thyrotropic tumor, which is a well differentiated hyperplastic tissue that produces both TSHß- and a-subunits and...

4p16
STHAG2 ? 16q12
STHAG3 PAX9
PAX9
Paired box gene 9, also known as PAX9, is a protein which in humans is encoded by the PAX9 gene. It is also found in mammals generally.- Function :This gene is a member of the paired box family of transcription factors...

14q12
STHAG4 ? ?
STHAG5 ? 10q11
STHAG6 LTBP3
LTBP3
Latent-transforming growth factor beta-binding protein 3 is a protein that in humans is encoded by the LTBP3 gene.-Further reading:...

11q12
STHAGX1 ? X chromosome

Curiosity

In the 1960s and 1970s were conducted several studies sponsored the U.S. Atomic Energy Commission
United States Atomic Energy Commission
The United States Atomic Energy Commission was an agency of the United States government established after World War II by Congress to foster and control the peace time development of atomic science and technology. President Harry S...

, with the aim of finding a link between genetics and hypodontia.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK