Patent ID: 7645138

Claim:
A dental tool assembly comprising: a housing body having a plurality of motorization means contained therein and a tool-holder head at one end thereof; a dental instrument or tool, said dental instrument being comprised of a shaft with an annular groove at one end thereof and having a flat surface in said annular groove parallel to a longitudinal axis of said shaft; a rotary spindle being comprised of a hollow spindle and a pinion, said hollow spindle having an open central bore traversing said hollow spindle longitudinally, the central bore receiving said dental instrument therein, said pinion being perpendicular to a central axis of said hollow spindle and meshing with said motorization means, said hollow spindle comprising: a cylindrical sleeve, being mounted below said pinion and cooperative with a bearing; a cylindrical lower part, being mounted above said pinion; a central part, being positioned above said cylindrical lower part, having a diameter smaller than a diameter of said cylindrical lower part, and forming a first peripheral shoulder on said cylindrical lower part; a cylindrical upper part, being positioned above said central part, having a diameter smaller than said diameter of said central part, and forming a second peripheral shoulder on said central part; and a slot, being located on the upper part and the central part, diametrically crossing the upper part and the central bore, and opening outward on each side of said hollow spindle, said slot continuing downward by two cuttings open outwardly along the central part, said two cuttings being aligned and having an identical width as said slot in the upper part, said slot having a concavely curved profile corresponding to curvature of the upper part; a locking spring, being comprised of a lower ring positioned around said hollow spindle and a plurality of elastic arms extending from one side of said lower ring, each arm being provided with a pin and having a rest position and a spaced-apart position, said pin engaging said annular groove of said dental instrument in said rest position, said pin being displaced away from said central axis of said hollow spindle in said spaced-apart position so as to release said dental instrument, each arm comprising: a central segment having one end attached to said lower ring and being inclined in a direction towards said central axis of said hollow spindle; and an upper segment parallel to said central axis at a terminal end of the arm, said central segment extending from said lower ring to said upper segment, each segment having an internal slope inclined by an angle towards the terminal end thereof; and a cap-shaped push-button comprising a center conical pressure head on an underside thereof, the pressure head having an external slope engaging the arms of said locking spring, the pins being moved from said rest position to said spaced apart position when the push-button is depressed towards said dental instrument such that the pins release said annular groove of said dental instrument.