Patent GB-1409797-A (GB)
Title: Apparatus for generating ultrasonic oscillations
IPC: A61C17/20
Filed: 1972-09-14
Abstract: 1409797 Piezo-electric motors DURRDENTAL KG 14 Sept 1972 [14 Sept 1971 28 Aug 1972] 42686/72 Heading H2A [Also in Divisions A5 H4 and B6] An instrument particularly suited for descaling the teeth has a generator adapted to generate electrical oscillations for energizing a piezo-electric oscillator element, the generator and oscillator element being spatially separate but both disposed in an elongated handpiece, the generator being insulated from oscillations of the oscillator element; the instrument is provided with a rod adapted to be oscillated by the oscillator element and projecting from the handpiece. The oscillating rod may be constructed as a tool or have a tool attached to one end thereof. The instrument may have a power supply lead or it may be adapted for battery operation. In the embodiment shown the oscillator element 126 is an elongated flat ceramic bar mounted in a member 150 in the head 111 of the instrument. The member 150 has a concentration part 180 shaped to amplify the oscillations. The oscillating rod takes the form of a tube 112. The retaining part 185 of the member 150 is clamped in the casing 125 of the instrument and is disposed in an oscillating node so that no oscillations are transmitted to the casing. The oscillator element extends rearward through an aperture 190 in a casing support 129 also disposed in an oscillating node. Two energizing conductors 142 and 143 are mounted on vapour-deposited electrodes 130 and 141 in the zone of the support 129. The member 150 is provided with a coolant duct 212 connected to a tube member 213 which, in turn, is connected to a further tube member 123 by a resilient hose member 122 passing through the support 129. The generator 151 is mounted on a support plate 156 provided with a printed circuit, and includes a transistor 152, a load resistor (168), Fig. 11 (not shown), and an inductance (165). A feedback ring-electrode 250 is disposed around a front zone of the oscillator element. The transistor 152 is clamped to a heat sink 153 having a coolant bore 224. The casing 125 may be of plastics having a metal coating for screening purposes. A knob 114 operates a switch 166 for switching the generator and the coolant supply. The rear end of the instrument is provided with a plug 231 which permits connection of a coolant duct 116 and electrical supply and control conductors 216. In use, the tube 112 performs combined longitudinal and transverse oscillations. In the alternative embodiment of Figs. 1-5 (not shown), the piezoelectric oscillator element takes the form of a crystal (26), Fig. 3, in the shape of a round plate and is clamped between a support member (29) and a spring (30). A free member (33) of the spring (30) bears on a lateral surface (28) of the crystal. The crystal is energized through a U- shaped conductor (40) and through the spring (30). The oscillating rod takes the form of a tube (12) joined to the spring (30). The spring (30) and the tube (12) act as a transmission lever to increase the amplitude of the oscillations. The head (11) of the instrument is insulated from the oscillations of the tube (12) by silicon rubber (50). The head and tubular casing (25) are of large mass relative to the crystal (26) and tube (12), and the casing (25) is therefore substantially free of oscillations. The tube (12) is connected to a further tube (23) by a resilient hose member (22). A plate (53) is soldered on the tube (23) to function as a heat sink for a transistor (52) of the generator (51). A thin mica plate (55) providing a low capacitance is mounted between the transistor and the plate (53). A low-coolant safety device may be incorporated into the hose (16) supplying coolant to the tube (23). The generator (51) includes the transistor (52), a capacitor (63), Fig. 4, inductors (64, 65), and a voltage divider comprising resistors (68, 69). The components of the  generator may be encapsulated in epoxy resin as indicated by the lines (73), Fig. 3. In use, a tool (18), Fig. 1, is mounted on the tube (12) and performs oscillations (75, 76, Fig. 5. The crystal (26) may be cut from a quartz crystal (74), Fig. 6 (not shown); two possible Y-cuts (77, 78) are indicated.