The characteristics of wear in micro-beads were studied by focusing on projections on the surfaces of the micro-beads. Food safety associated with the presence of fine wear particles was studied by cytotoxicity tests reusing micro-beads with the projections weared away. It was shown that the smaller projections on the micro-beads surface were removed in a shorter time than the larger one and that if the beads diameter was less than about 60 mu m, the size of the projections reached the submicron-level. Also, it was shown that fine particles formed by wear in micro-beads made of yttria partially stabilized zirconia did not show cytotoxicity. (C) 2012 Elsevier B.V. All rights reserved.