Abstract: In a motorized handpiece (101), in particular for medical purposes, preferably for a medical or dental laboratory, with a clamping device (106) arranged in a sleeve-like casing (111) for the selective mounting of tools (105) which may be inserted into the handpiece (101) from the front, whereby for opening and closing the clamping device (106) a moveably mounted actuating part (104a) is provided which is accessible at the circumference of the motorized handpiece (101), whereby the clamping device (106) is arranged on a drive shaft (107), which is mounted by means of a casing (101) rotatable by means of a rear and a forward roller bearing (113, 114), whereby the actuating part (104a) is connected with the clamping device (106) by way of an actuating mechanism (108), and whereby a sealing system (146) is associated with the forward roller bearing (114) on the forward side of the roller bodies thereof, which has at least one sealing disk (146a) which is effective between the inner and the outer ring (114a, 114b)