Anomolies 1-Hypodontia.txt

0.1 - 0.9% in Caucasian populations, most commonly in the maxilla, typically the lateral incisor.

3.5 - 6.5% EXCLUDING 3rd molars. In Caucasian populations 3rd molars are the most commonly missing teeth, occurring in 9 - 30% of individuals. Following this, other commonly missing teeth are mandibular 5, maxillary 2, and the maxillary 5, in this order

Most authors report a female predominance of hypodontia. - Small but insignificant [Muller 1970], [Rolling 1977], [Davis 1980], but significant in some studies [Brook 1974].

A strong correlation is seen. In patients with missing primary teeth, missing permanent teeth are seen in 30 - 50% of patients.

Often unclear, may be genetic in origin, or assoc with some environmental insult during development. Reports also associate missing teeth with multiple births, low birth weight, and increased maternal age. Also in children whose mother had used thalidomide during pregnancy.

Malignant disease. Irradiation produces more severe effects than chemotherapeutic agents.

MSX1 gene on chromosome 4. (If either Mum or Dad has a mutation, the child will have missing teeth)

PAX9 gene on chromosome 14.

A solitary median maxillary central incisor.

Is a congenital lack of more than 6 teeth, excluding 3rd molars. It has a prevalence of 0.08% in a Dutch study and 0.16% in a Danish study. Oligodontia, like hypodontia, is seen as an isolated trait or as part of a syndrome.

• Oligodontia and hypodontia have similar associated anomalies with a tendency toward
• 1. Delayed tooth formation and eruption
• 2. Reduced size of teeth (most striking example of crown-size reduction assoc with hypodontia is a peg shape upper later incisor)
• Other anomalies:
• 3. Ectopic maxillary canines have an assoc with hypodontia
• 4. Ectopic eruption of other teeth
• 5. Infraocclusion of primary molars - reciprocal assoc exists between infraocclusion of primary molars and aplasia of second premolars.
• 6. Short roots of teeth- Tooth agenesis has appeared in 46% of individuals with some short rooted permanent teeth (mostly maxillary central incisors and premolars)
• 7. Taurodontism

• All 1� teeth have erupted by 3yrs, and 2� teeth by 12-14yrs (excluding third molars). Therefore clinical Dx can be made after this age. Radiographic Dx can be made earlier.
• - All primary teeth and crypts of FPMs can be seen at birth.
• - Crowns of 4's, 5's and 7's start to mineralise near 2nd birthday.
• - By 6yrs all permanent tooth crowns have started to mineralise (except third molars)
• - Variation exists amongst mineralisation stages between individuals
• - First signs of third molars on a radiograph are usually at 8-10yrs, but occasionally very late appearance at 14-18yrs occurs [Pirinen and Thesleff 1995]
• - 5's may show late onset of mineralisation and give a false-positive Dx of hypodontia in rads
• - Therefore Dx of tooth agenesis in permanent dentition should be made after age 6, excluding third molars, and after age 10 if included.

ED 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.

Dx is usually by clinical observation often with the assistance of family MHx so that it can be determined whether transmission is autosomal dominant or recessive.

• ED can be classified by inheritance (autosomal dominant, autosomal recessive, and X-linked) or by which structures are involved (hair, teeth, nails, and/or sweat glands). There are several different types with distinct genetic causes, eg:
• Hypohidrotic ectodermal dysplasia (HED) can be associated with EDA, EDAR, and EDARADD
• Ellis-van Creveld syndrome is associated with EVC.

HED is inherited in an X-linked manner 95% of the time (EDA gene). The remaining 5% have either the autosomal recessive (EDAR and EDARADD genes) or autosomal dominant form (EDAR and EDARADD genes).

May be determined in some instances by family Hx and in others by molecular genetic testing. (Carrier testing is possible for the X-linked and autosomal recessive forms if the disease-causing mutation(s) in the family is (are) known. Prenatal testing is possible for pregnancies at increased risk for all forms if the disease-causing mutation(s) in the family is (are) known.)

• hypotrichosis - thin sparse scalp and body hair
• hypohidrosis - absence/reduced ability of sweating (therefore heat intolerance)
• hypodontia - multiple missing teeth
• dry skin, lightly pigmented hair, peg/pointed teeth.
• (If undiagnosed, children may die in infancy due to their inability to cool themselves.) Most commonly one or both maxillary lateral incisors and/or the second premolars are missing.

Down syndrome

Paediatric dentists, orthodontists, prosthodontists, as well as genetic counselling.

Partial dentures, with implants as part of the treatment protocol at a later age (until skeletal maturity occurs). Dentures will need to be replaced as the jaws grow (annual replacements during the school holidays, mimicking the developing dentition at the childs age can do much to minimize the stigma of these conditions. The lack of development of the alveolar bone may prove to be a limiting factor.