Abstract: The dental prophylactic right angle hand piece of the knob type includes conventional driving and driven members, with the driven member including an integral collar and an integral serrated knob to which the dental application or cup is releasably secured for preventing the cup from slipping under pressure. The collar forms an effective seal between the head of the hand piece and the cup to prevent bacteria from entering the interior of the hand piece. With such a construction the hand piece can be operated forwardly or backwardly without the cup slipping or falling out of the hand piece.