From Big Medical Encyclopedia

PROGNATHISM (Greek pro ahead, forward + gnathos a jaw) — a vystoyaniye of the lower (gnatichesky) part of the face, i.e. top and bottom jaws with their dentitions. The prognathism belongs to racial signs, it is characteristic of some tribes and the people living in Africa and in America. Among P. Europeans meets extremely seldom, the biprognatiya, i.e. a vystoyaniye of dentitions of both jaws with a vestibular deviation of all foreteeth a little more often is observed. Such type of a bite is considered as family feature of a structure of a facial skeleton. The prognathism is not subject to correction.

Vystoyaniye only of one upper jaw and its dentition is called a prognathism. The prognathism can be also carried to racial signs; it is characteristic, e.g., of Japanese. Such type of a bite occurs among Europeans as option of norm (see. Bite ). However at a considerable vystoyaniye of upper dentition the nibble and chewing of food is complicated, purity of a pronunciation of sounds of the speech and esthetic harmony of the person is broken. In such cases the prognathism is considered pathological and is subject to correction (see. Orthodontic methods of treatment ).