Removably fixing a dental instrument with a retractable catch relative to a drive shaft axis

A head assembly for attaching to a dental instrument in which the dental instrument has a shank formed of a cylindrical body and an annular latching groove, said shank having a drive flat extending parallel to a longitudinal axis of the instrument, the head assembly comprising:

• a rotary shaft having a pinion thereon, said rotary shaft being mounted in an upper bearing and a lower bearing, said rotary shaft having a central bore suitable for receiving the shank of the dental instrument therein;
• a body having said rotary shaft and said upper and lower bearings therein, said body having a circular opening closed off by a push button, said push button being cooperative with said rotary shaft so as to release the shank of the dental instrument therefrom;
• at least one retractable latching lever having a peg extending inwardly therefrom, said peg having a size suitable for fitting into the annular latching groove;
• and
• a retractable catch connected to said rotary shaft so as to rotate with said rotary shaft, said retractable catch having a positioning plane suitable for coinciding with the drive flat of the dental instrument, said rotary shaft being covered by a cap such that said cap rotates and translates therewith, said cap being positioned in one of said upper bearing and said lower bearing, said retractable catch resting on said pinion and held captive in said cap so as to be slidable therein.