The present invention is directed to a dental turbine drive having a housing with a rotor or turbine space and a rotor having shafts extending from each side being mounted for rotation by bearings in the turbine space with one end of one shaft portion extending from the housing and having means for accepting a processing tool, the housing having an air drive channel for supplying and directing air onto the rotor and a return air channel for removing air from the turbine space.
A problem in present dental turbine drives is that the air and, thus, bacterially contaminated particles can be suctioned in from the immediate environment, such as the oral cavity of the patient after the drive air has been shut off. This is due to the continued rotation of the rotor or turbine in a run-down or run-out phase creating eddy currents or a suction which will be conveyed into the inside of the turbine handpiece. When the drive air is subsequently reactivated, these particles are then again conveyed outward from the handpiece by the pressure being built up within the drive air supply.
This event is extremely unhygienic and harbors the risk of transmitting morbific agents. In addition, the rotor bearings can be damaged due to the penetration of, in particular, humid air and/or superfine particles.
The suction effect is caused by the rotor that, after the drive air is shut off, requires several seconds due to its mass moment of inertia and due to the high speed to run down or come to a standstill. During this run-down phase, the decelerating rotor in the turbine housing acts like an impeller pump and radially centrifuges the air located in the rotor chamber or space radially outward into the return air channel that is arranged in the outer circumference of the rotor chamber in most known turbine handpieces. The under-pressure or suction will occur in the region of the rotor shaft, and this will result in the flow of the air from the outside through the existing bearing gaps or other openings.
A number of proposed solutions have been disclosed in order to prevent the above-mentioned aspiration effect. DE 11 47 003 and 11 07 891 both disclose that compressed air can be blown into the rotor chambers after the shut-off of the drive air feed until the rotor comes to a standstill. This method is extremely effective in and of itself, but is dependent on the supply of the dental apparatus to which the turbine drive is connected. Moreover, the technical outlay and cost for controlling the after-blowing is substantial.
EP-0 283 417 discloses a turbine drive wherein a mechanical brake acting on the rotor is intended to effect a rapid stopping of the rotor after deactivation of the drive air. Although such means for creating a rapid stop for the rotor is fundamentally desirable, it can be achieved only with relatively great technical outlay given the known turbine drive.
EP-0 471 961 discloses a turbine drive wherein a spin disc is put in place on the rotor shaft, only preceding the tool-proximate bearing, and this spin disc is intended to prevent the penetration of particles in that these are hurled radially outward when they impinge on the disc. Such an arrangement is, in fact, extremely simple but does not satisfactorily prevent the penetration of particles, since the suction effect at the rotor side is not eliminated.