The first molar fixed type Palatal Lever Arm System （PLAS） fixes the maxillary first molar via the PLAS from the mid-palatal miniscrews. It gives absolute anchorage to molars. In addition, it is possible to prevent side effects of the first molar and expand dental arch to unilateral side, which is considered to be difficult using conventional auxiliary devices. Case 1 : The patient was a 25-years-old Japanese woman. Her chief complaint was upper teeth protrusion. The degree of overjet was 11.3 mm. Mandibular left second premolar was positioned lingually due to crowding. Lateral cephalometric analysis showed a skeletal Class II jaw relationship. Maxillary both first premolars and mandibular left second premolar were extracted. Lingual orthodontic treatment was applied using mid-palatal miniscrews and the first molar fixed type PLAS. Absolute anchorage of the maxillary both first molars were obtained and proper overjet was achieved. Case 2 : The patient was a 20-years-old Japanese woman. Her chief complaint was crowding of upper teeth. The left molars showed crossbite, and the maxillary left lateral incisor was positioned lingually. The inter-canine Class II relationship was observed. Four first premolars were extracted. Lingual orthodontic treatment was applied using mid-palatal miniscrews and the first molar fixed type PLAS. By activating the left arm of the PLAS to the buccal side, the crossbite of the left molars were corrected.

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　矯正歯科医にとって開咬は，治療を行うことが難しい不正咬合の一つである．この理由は，開咬が歯性，骨格性，機能的な要因，習癖そして神経因性・外傷的要因などが複合的に重なった状態を呈しているためである．このため，適切な治療を行うためにはその発生要因を含めた正確な診査・診断を行い，矯正歯科治療メカニクスを含んだ十分な治療計画を立案することが非常に重要となる．すなわち，上下顎臼歯部の挺出と近心移動に配慮し，十分なバーティカルコントロールとアンカレッジコントロールを行うこと，前歯部には十分なトルクコントロールを行い，舌癖などの機能的要因を排除すべく筋機能療法を含んだ治療計画を作成することが必要となる． 　今回，成長期の前歯部開咬とハイアングル下顎後退型開咬成人症例に対し，トルクコントロールおよびバーティカルコントロール，アンカレッジコントロールに注意しながら，フルカスタムリンガルブラケット矯正装置に一部スケレタルアンカレッジシステムや歯科矯正用アンカースクリューを併用して治療を行った2症例を報告する．

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In orthodontic treatment of bimaxillary protrusion cases, it is often accompanied by extraction of upper and lower premolars in order to ensure the amount of retraction of upper and lower incisors. In recent years, in the lingual it has been reported that the horizontal and vertical bowing effect is different from the case of the labial side, since the bracket position exists on the lingual side. This time we experienced orthodontic treatment of cases of bimaxillary protrusion cases of adult male with similar skeletal and dental properties at our office, and I report on differences by therapy method, compared and discussed.

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