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Prognathism is the positional relationship of the mandible and/or maxilla to the skeletal base where either of the jaws protrudes beyond a predetermined imaginary line in the coronal plane of the skull. In general dentistry, oral and maxillofacial surgery and orthodontics, this is assessed clinically or radiographically (cephalometrics). The word "prognathism" derives from Greek ''pro'' (forward) and γνάθος ''gnathos'' (jaw). One or more types of prognathism may result in the common condition of malocclusion, in which an individual's top teeth and lower teeth do not align properly. ==Presentation== Prognathism in humans can be due to normal variation among phenotypes. In human populations where prognathism is not the norm, it may be a malformation, the result of injury, a disease state or a hereditary condition.〔(MedlinePlus Medical Encyclopedia: Prognathism )〕 Prognathism is considered a disorder only if it affects mastication, speech or social function as a byproduct of severely affected aesthetics of the face. Clinical determinants include soft tissue analysis where the clinician assesses nasolabial angle, the relationship of the soft tissue portion of the chin to the nose, and the relationship between the upper and lower lips; also used is dental arch relationship assessment such as Angle's classification. Cephalometric analysis is the most accurate way of determining all types of prognathism, as it includes assessments of skeletal base, occlusal plane angulation, facial height, soft tissue assessment and anterior dental angulation. Various calculations and assessments of the information in a cephalometric radiograph allow the clinician to objectively determine dental and skeletal relationships and determine a treatment plan. Maxillary prognathism is a protrusion of the maxilla, and is a common feature in Sub Saharan Africans. It is not to be confused with micrognathism, although combinations of both may be found. It affects the middle third of the face, causing it to jut out, thereby increasing the facial area, similar in phenotype of archaic hominids and apes. Mandibular prognathism is a protrusion of the mandible, affecting the lower third of the face. Alveolar prognathism is a protrusion of that portion of the maxilla where the teeth are located, in the dental lining of the upper jaw. Prognathism can also be used to describe ways that the maxillary and mandibular dental arches relate to one another, including malocclusion (where the upper and lower teeth do not align). When there is maxillary and/or alveolar prognathism which causes an alignment of the maxillary incisors significantly anterior to the lower teeth, the condition is called an overjet. When the reverse is the case, and the lower jaw extends forward beyond the upper, the condition is referred to as retrognathia (reverse overjet). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Prognathism」の詳細全文を読む スポンサード リンク
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