第一大臼歯の頬舌的歯軸傾斜と歯列幅の成長パターンについて : 日本人と南太平洋諸国の2集団との比較  [in Japanese] A growth pattern of bucco-lingual inclination and arch width of first molar : A comparison with Japanese and 2 group of South Pacific populations  [in Japanese]

咀嚼機能と歯列弓形態の関係を探るため,南太平洋地域の2集団(フィジー人112名,サモア人101名)と日本人(122名)の口腔模型を用いて,集団の第一大臼歯の歯軸傾斜と歯列幅の成長パターンについて検討した.資料を採取時年齢によって6〜7歳の群(G1),11〜12歳の群(G2)および20歳以上の群(G3)の3群に分類し,接触型三次元形状測定装置から得られたデータの三次元画像解析を行った.3集団ともにG1からG3までの第一大臼歯歯列幅と頬舌的歯軸傾斜の成長パターンは同様の傾向をとるものの,おのおのの平均値には差が認められ,年齢が上がるにつれフィジー人とサモア人の上下顎歯列幅に関する項目は日本人より有意に広くなり,下顎第一大臼歯頬舌的歯軸は直立していた.上顎第一大臼歯頬舌的歯軸傾斜角と歯列幅との間に相関は認められなかったが,下顎第一大臼歯の頬舌的歯軸傾斜角と歯列幅に有意の負の相関関係が認められた.このことから,上顎歯列弓の主な成長は歯軸の変化によるものではなく口蓋の側方成長に起因しており,一方,下顎歯列弓は第一大臼歯の頬側への直立が歯列幅の増加に影響していることが示唆された.また,G1において既にフィジー人とサモア人の歯軸傾斜ならびに歯列幅がともに日本人より大きい値を示したことは,日本人よりフィジー人とサモア人の第一大臼歯の萌出が早く,早期から咀嚼に関与していた結果と考えられた.

The purpose of this study was to investigate the relationship between masticatory function and arch form using dental models of two South Pacific populations, Fijian (Melanesia), Samoan (Polynesia) and Japanese (Northeast Asia). The dental models of Fijian (n=112), Samoan (n=101) and Japanese (n=122) were used and grouped in G1 (6-7 years old), G2 (11-12 years old) and G3 (more than 20 years). The materials were measured three-dimensionally using contact type configuration measurement device. Dental arch width was increased and the buccolingual inclination of mandibular molar (LBLI) was straight from G1 to G3 in all three populations. However, arch width and LBLI were significantly greater in Fijian and Samoan than those in Japanese. A significant correlation was observed between mandibular arch width and LBLI in each population. In G1, both molar inclination and arch width of Fijian and Samoan were larger than those of Japanese. Early eruption of mandibular first molar in Fijian and Samoan may result greater inclination due to a longer exposure of masticatory forces than that in Japanese. It was suggested that mandibular molar inclination and molar arch width are influenced by masticatory function.