The invention is directed to largely improve reliability by surely protecting data on the basis of an emergency stop request even during a data transfer process. The disposable prophy angles and dental tool heads are designed with non circular input shaft endings, engaging a matching non circular power output driver of the handpiece. ; a fourth layer, which is an outer layer, the fourth layer comprising at least one member selected from the group consisting of polyester, polyamide and polyurethane. In other aspects, small cells coordinate handovers through the use of a controller, or by leveraging wireless connections created between the small cells.