A decrease in the number of teeth compared to normal. It is sometimes called partial anodontia. It is rare in the primary dentition but relatively common in the permanent dentition. The most frequent teeth to be missing are the mandibular second premolars, the maxillary lateral incisors, and the maxillary second premolars. It may be described as severe when six or more teeth are missing. Where the permanent tooth is missing, the primary tooth which it normally replaces is frequently retained into adult life but, having smaller roots, a retained primary tooth will usually be unable to survive many years of adult masticatory function. There may be a hereditary trait but in most cases the occurrence is sporadic. Hypodontia is often seen in a number of members of a family and may be associated with other conditions such as ectodermal dysplasia and orofaciodigital syndromes.
Gill D. S., Jones S., Hobkirk J., Bassi S., Hemmings K., Goodman J. Counselling patients with hypodontia. Dent Update 2008;35:344–52.