When fabricating prostheses in a partially edentulous arch with some mobile teeth, it is important to minimize tooth displacement during the impression procedure. The present study examined the effect of custom tray designs on the displacement of a mobile central incisor in a mandibular simulation model with six anterior teeth. Twelve custom trays were designed according to the different spaces and perforated holes in the region of the remaining teeth. As a result, the degree of displacement of the mobile tooth could be reduced according to the size of spaces and the location of perforated holes in the custom tray.