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Editors
Developmental Defects in Teeth
Essentials
- The first teeth usually erupt at the age of six months. If no teeth have erupted by the age of 1.5 years, further examination is warranted.
- Complete loss of teeth, i.e. anodontia is usually associated with some syndrome and requires paediatric consultations.
- Many teeth are usually missing in ectodermal dysplasia syndromes.
- Severe familial tooth agenesis may be associated with colorectal cancer.
- Of the minor dental defects the following require attention:
- a supernumerary tooth, especially in the midline of the maxilla
- aesthetically disturbing enamel defects
- missing teeth.
- Tetracyclines may cause discolouration and other defects in the developing teeth, and they should be avoided throughout pregnancy and in children until puberty.
Tooth development
- The part of the tooth that is visible in the oral cavity, the tooth crown, is completely developed inside the jaw-bone.
- The development of most teeth starts prenatally.
- The development of the roots of teeth is completed after eruption of the teeth into the oral cavity.
- The calcification of permanent teeth starts several years before their eruption, and their development can be followed by radiographs.
Missing and supernumerary teeth
- The number, size and shape of teeth are almost completely genetically regulated.
- The lack of a single tooth is common. One or more wisdom teeth are missing in 25% and other teeth in 5-10% of the population.
- Small or (conically) peg shaped teeth are typically seen in association with missing teeth.
- The lack of several teeth or complete lack of teeth (extremely rare) is usually associated with some syndrome. These are often conditions where also hair and other ectodermal organs are affected.
- The most common of these is hypohidrotic (anhidrotic) ectodermal dysplasia (HED, picture ). The remaining teeth may be smaller than normal and have an abnormal conical shape.
- The syndrome may be diagnosed early when only few (conically) peg shaped teeth erupt (this is important since the hyperthermia caused by lacking sweat glands may be fatal).
- Female carriers of the gene mutation in X-linked HED have usually some missing and conical teeth.
- Missing teeth are also seen, for example, in Down's syndrome.
- Severe familial tooth agenesis may be associated with colorectal cancer when the gene AXIN2 is mutated. The lack of teeth may be an indication of predisposition of cancer in these patients and their relatives and therefore genetic consultation is indicated in patients with many missing teeth who have colorectal cancer in the family.
- A high proportion of cases of missing teeth are caused by mutations in the WNT10A gene.
- Supernumerary teeth are seen in less than 4% of individuals.
- Mild abnormalities in tooth shape are common. Extra cusps on the occlusal surfaces of teeth represent these abnormalities.
- Sometimes the crowns or roots of neighbouring teeth fuse during development.
- Missing or abnormally shaped anterior teeth in the upper jaw may be associated with cleft lip and palate Cleft Lip and Palate.
Enamel hypoplasia and hypomineralization
- Disturbances in the development of dental enamel are relatively common. Hypomineralization is usually seen as local enamel discoloration, whereas hypoplasia is seen as unevenness.
- Enamel hypomineralizations are usually caused by environmental factors (e.g. infections) that disturb the functions of enamel-producing cells. They are most often seen in the first permanent molars, the enamel of which is mineralized during the first years of life.
- Exposure to high concentrations of fluoride also causes hypomineralization, but this is rare in countries where the water for household consumption does not contain much fluoride. Fluoride deficiency is not visible in the structure of teeth, however, the enamel is more susceptible to caries.
- Tetracyclines may cause discolouration and other permanent defects in the developing teeth. They should be used neither by mothers during the latter half of pregnancy nor by children during the first seven years of life. If there is no special indication for the use of tetracyclines, they should be avoided throughout pregnancy and in children until puberty.
- Enamel hypoplasias in the permanent teeth, either over the whole tooth surface or as transverse streaks, may be associated with APECED (autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy) syndrome Apeced (Autoimmune Polyendocrinopathy - Candidiasis - Ectodermal Dystrophy) (picture ). To exclude the syndrome, a paediatrician should be consulted, especially if the patient has oral candidiasis.
- Transverse dental streaks caused by enamel hypoplasia are also seen in coeliac disease Coeliac Disease.
- Genetic conditions affecting the structure of the enamel or the dentin are rare. They always affect both the deciduous teeth and the permanent teeth and are manifested as enamel hypomineralization or hypoplasia.
Developmental defects requiring treatment
- Most developmental defects in teeth do not need treatment.
- A supernumerary tooth, particularly in the midline of the maxilla, may prevent the eruption of other teeth. It should therefore be extracted.
- Missing of permanent teeth should ideally be diagnosed early (8-10 years of age) when growth-adapted measures can be used to minimize the need for treatment.
- Missing teeth can usually be corrected by moving teeth orthodontically or surgically or by prosthetic treatment including implants (usually placed when growth is completed.)
- Aesthetically disturbing enamel defects can be corrected by modern composite materials making them almost invisible.
- Hypomineralization of the first molars often causes stabbing pain in the teeth, and the teeth easily become carious. The teeth are restored by filling.
References
- Järvinen E, Salazar-Ciudad I, Birchmeier W, et al. Continuous tooth generation in mouse is induced by activated epithelial Wnt/beta-catenin signaling. Proc Natl Acad Sci U S A 2006;103(49):18627-32. [PubMed]
- Thesleff I. Developmental biology and building a tooth. Quintessence Int 2003;34(8):613-20. [PubMed]
- Thesleff I, Mikkola M. The role of growth factors in tooth development. Int Rev Cytol 2002;217():93-135. [PubMed]
- Vaahtokari A, Aberg T, Jernvall J, et al. The enamel knot as a signaling center in the developing mouse tooth. Mech Dev 1996;54(1):39-43. [PubMed]