A PLASTIC DEGRADATION MODEL WITH EFFECT ON PERMEABILITY FOR THE ASSESSMENT OF INSTABILITY IN ABANDONED MINES

A toothbrush and replaceable brush head wherein the brush head is easily and positively inserted and removed by axial motion along the axis of the handle. The handle and head have cooperating tongue and groove configurations providing parallel guides to receive and retain the members in assembled relation by virtue of handle recesses and resilient catches on the brush head, while permitting ready disassembly to remove and replace the brush head. Further, the handle and brush head have cooperating wedge formations to insure positive centering of the brush head along the axis of the handle. The assembly is snug and leaves no room for dirt, thereby enhancing hygiene during repeated use.