cement /siment″/ [L, caementum, rough stone] , 1. a sticky or mucilaginous substance that hardens into a firm mass and helps neighboring tissue cells stick together. 2. any of a variety of dental materials used to fill cavities or to hold bridgework or other dental prostheses in place. 3. a material, such as methyl methacrylate, used in the fixation of a prosthetic joint in adjacent bone.