<unk>  is a rare genetic disorder characterized by the congenital absence of all primary or permanent teeth. It is divided into two subsections, complete absence of teeth or only some absence of teeth. It is associated with the group of skin and nerve syndromes called the ectodermal dysplasias.<unk>  is usually part of a syndrome and seldom occurs as an isolated entity. There is usually no exact cause for<unk> . The defect results in the dental lamina obstruction during embryogenesis due to local, systemic and genetic factors. Congenital absence of permanent teeth can present as hypodontia, usually missing one or two permanent teeth, or oligodontia that is the congenital absence of six or more teeth. Congenital absence of all wisdom teeth, or third molars, is relatively common.<unk>  is the congenital absence of teeth and can occur in some or all teeth; whereas partial<unk>  (or hypodontia), involves two dentitions or only teeth of the permanent dentition (Dorland's 1998). Approximately 1% of the population has oligodontia. Many denominations are attributed to this anomaly: partial<unk> , hypodontia, oligodontia, the congenital absence,<unk> , bilateral aplasia.<unk>  being the term used in controlled vocabulary Medical Subject Headings (MeSH) from MEDLINE which was developed by the United States National Library of Medicine. The congenital absence of at least one permanent tooth is the most common dental anomaly and may contribute to masticator dysfunction, speech impairment, aesthetic problems, and malocclusion (Shapiro and Farrington 1983). Absence of lateral incisors represents a major stereotype. Individuals with this condition are perceived as socially most aggressive compared with people without<unk>  (Shaw 1981). The occurrence of<unk>  is less so than hypodontia which has a prevalence of 0.1-0.7% in primary teeth and 3–7.5% in permanent teeth.
Anodontia
Hypodontia
Maxillary hypoplasia
Hemifacial microsomia
Micrognathism
Macrodontia 
Oxycephaly
Iniencephaly