an oral orthosis includes a holder in the shape of a mouthpiece , including a curved arcuate trough - like upper section which receives a formable material . the formable material does not occupy the entire trough but rather includes voids between the formable material and the inner surfaces of trough of the holder to allow expansion of the formable material into the voids during the molding process when tooth pressure is placed on the formable material . this design results in elimination of the excess formable material which otherwise would require removal by trimming . additionally , the formable material is placed in the trough in a configuration which includes indexing indentations along the centerline of the material , such that , during the molding process , the mouthpiece containing the formable material is easily centered along the edges of the user &# 39 ; s teeth to provide a precise fitting .