Problem to be solved: to provide a mouthpiece excellent in polishing processability, a sheet for manufacturing a piece portion of a mouthpiece capable of manufacturing a mouthpiece excellent in formability and excellent in machinability, and a method of manufacturing a mouthpiece excellent in polishing ability.Solution: the mouthpiece 10 includes an olefinic polymer (a) having a repeating unit of 2 or 3 and having a configuration (x) having a shore a hardness of 80 to 86 or less.Diagram【課題】研磨加工性に優れたマウスピース、成形性に優れ、かつ研磨加工性に優れたマウスピースを製造可能なマウスピースのピース部製造用シート、及び研磨加工性に優れたマウスピースの製造方法を提供する。【解決手段】炭素数が２又は３の繰り返し単位を有するオレフィン系重合体（Ａ）を含み、かつ、ショアＡ硬度が８０超８６未満を満たす構成部位（Ｘ）を備えるマウスピース１０。【選択図】図１
