Even if a fault occurs in the closing operation the upper and lower jaws and failure of engagement of the teeth of the challenge] up and down, and maintaining a good state to prevent loosening of the mounting of mouth breathing preventer, to close the opening of the mouth, I performed well to prevent mouth breathing. [MEANS FOR SOLVING PROBLEMS] Between the outer periphery and the buccolabial of the upper and lower teeth, the first plate portion in the transverse direction of the long arc that can be positioned so as to cover at least the labial side of the outer peripheral portion of the teeth, the upper and lower the inner periphery of the teeth, and can be positioned so as to cover at least the labial side of the inner periphery of the teeth, and the second plate portion in the transverse direction of the short of arc than the first plate portion, the 1 parallel to the plate portion and the second plate portion in the arcuate direction and a first connection portion which connects to. Gap between the facing surfaces of the first plate portion of the second plate portion is held between the teeth, the first plate portion labial side of the outer peripheral portion of the dentition, or the lip of the outer peripheral portion of the teeth and covers the cheek side, to close the opening in the mouth. [Selection Figure] Figure 1【課題】上下の歯の噛み合わせの不具合や上下顎を閉じ動作に不具合が生じた場合においても、口呼吸防止具の取り付けの緩みを防ぎ、口の開口部を塞ぐ状態を良好に維持し、口呼吸の防止を良好に行う。【解決手段】 上下の歯列の外周部と頬唇との間において、歯列の外周部の少なくとも唇側を覆うように位置させることができる横方向に長尺な弧状の第1のプレート部と、上下の歯列の内周部において、歯列の内周部の少なくとも唇側を覆うように位置させることができ、第1のプレート部よりも横方向に短尺な弧状の第2のプレート部と、第1のプレート部と第2のプレート部とを弧状方向で並列させて連結する第1の連結部とを備える。第1のプレート部と前記第2のプレート部の対向面の隙間は歯列を挟持し、第1のプレート部は歯列の外周部の唇側、又は、歯列の外周部の唇部および頬側を覆い、口の開口部を塞ぐ。【選択図】図1
