1. IN A DENTAL TOOL DRIVING MECHANISM THE COMBINATION OF: A BODY MEMBER OF GENERALLY CYLINDRICAL SHAPE HAVING A CYLINDRICAL AXIAL BORE, AN AIR DRIVEN FREE POSITION RECIPROCABLE VIBRATORY MOTOR WITHIN SAID BODY ADAPTED TO IMPART VIBRATORY MOTION TO SAID BODY AS A WHOLE ALONG THE LONGITUDINAL AXIS THEREOF, THE CYLINDRICAL BORE OF SAID BODY CHARACTERIZED BY A SECTION OF UNIT DIAMETER INCLUDING A SECTION OF LIMITED LENGTH OF LARGER DIAMETER LOCATED BETWEEN A SEALING END CAP AND AN AIR INLET THROUGH THE CYLINDER WALL, BY A SECTION OF REDUCED DIAMETER BUT LIMITED LENGTH ADJACENT TO AND ON THE OPPOSITE SIDE OF SAID AIR INLET, AND BY A FURTHER SECTION OF ENLARGED DIAMETER, INCLUDING AN AIR EXHAUST PASSAGE THROUGH THE CYLINDER WALL, LOCATED BEYOND THE SECTION OF REDUCED DIAMETER, THE PISTON OF THE SAID MOTOR CHARACTERIZED BY A HEAD SECTION OF A DIAMETER FOR SLIDING FIT WITHIN THE CYLINDER BORE OF UNIT DIAMETER AND BY A SECOND SECTION OF REDUCED DIAMETER, FORMING A STEP ON SAID PISTON, FOR SLIDING FIT WITHIN THE BORE SECTION OF REDUCED DIAMETER, THE PISTON DIAMETERS PROPORTIONED TO GIVE EQUAL THRUST IN EACH DIRECTION, A BORE WITHIN THE PISTON EXTENDING FROM THE HEAD END TO INTERSECTION WITH RADIAL EXHAUST PORTS THROUGH THE PISTON WALL IN THE SECTION OF REDUCED DIAMETER AND ADJACENT THE OUTER END THEREOF, RADIAL INLET PORTS THROUGH THE PISTON WALL IN THE SECTION OF LARGE DIAMETER ALSO INTERSECTING SAID PISTON BORE, THE SAID INLET PORTS COOPERATING WITH THE PISTON STEP SAID THE CYLINDER SECTION OF INCREASED DIAMETER TO DETERMINE THE INLET AND CUTOFF EVENTS OF THE AIR MOTOR AND THE PISTON EXHAUST PORTS COOPERATING WITH THE CYLINDER SECTION OF REDUCED DIAMETER TO DETERMINED THE SEALING AND EXHAUST EVENTS OF THE MOTOR, TOGETHER WITH FIXED TOOL MOUNTING MEANS AT THE OUTER EXTREMITY OF SAID BODY ADAPTED TO HOLD A TOOL IMMOVABLE WITH RESPECT TO SAID BODY, THE SAID MOUNTING MEANS BEING DRIVEN IN A USEFUL WORK PATH SOLELY AS A RESULT OF THE REACTIVE VIBRATORY MOTION OF SAID CYLINDRICAL BODY MEMBER OF THE VIBRATION OF THE FREE PISTON THEREWITHIN.