Abstract: A fully autoclavable dental-hand-piece assembly which includes a unique, highly miniaturized, internally disposed, one-way check valve that effectively prevents microbial contamination from reaching the cooling fluid supply lines that provide cooling fluid to the unit. The one-way check valve is specially designed to be able to effectively withstand the high temperatures required in the autoclaving step to which the hand piece, including the check valve, is exposed. Uniquely, the one-way check valve can readily be installed either within the hollow handle of a conventional dental hand piece or within a conventional, universal dental-hand-piece coupler without the necessity of making any substantial modification to the design of the hollow handle or the universal coupler. Also disclosed is a novel coupler assembly for coupling together the hand piece and the air and water supply lines.