Abstract: A dental investment material comprising a modified calcium sulfate which when hydrated possesses unique fracture properties of particular advantage when the material is used as a composition for making molds particularly for use in the lost wax process.

Abstract: A water recirculation system is described wherein the discharge of one or more dental cuspidors is rendered reuseable and continuously used in the operation of a water sealed vacuum pump in a dental vacuum discharge system.

Abstract: An electrosurgical device in which high frequency electrical energy powers a cutting electrode. Radio frequency energy is set up in a driver coil and a driven coil mounted in a handpiece. The driver coil energizes the driven coil to energize a surgical electrode connected to one end of the driven coil. Connection between the source of radio frequency energy and the driver coil includes a circuit in which condensers and impedances are so connected that, if there is a failure of the condensers, energy is dissipated.

Abstract: A base metal alloy primarily for jewelry use comprising a major portion of nickel and minor proportions selected from the group tin, chromium, silicon, aluminum, niobium and manganese.

Abstract: A chair of the type particularly adapted for use by dentists, ophthalmologists and the like but also useful for other purposes in which a back is pivoted relative to a seat and a leg rests extends outward from the seat. The seat with the back pivotally connected thereto is adapted to be moved about a vertical axis from a position in which the front to back axis of the seat is disposed in alignment with the longitudinal axis of the leg rest which projects laterally outward from one side of the base and a position in which said axis of the seat is transverse to said longitudinal axis of the leg rest in order to facilitate the seating of a person in the chair while the seat is in the latter position and then rotating the seat 90.degree. to permit the person to dispose his legs upon the leg rest which preferably is stationary relative to the base of the chair.

Abstract: An operatory-type chair having a seat to which a back rest is pivotably connected for movement between upright and rearwardly extending positions by an electric motor interconnected to said back rest by a rotatable screw driven by said motor. Movement of the back rest is controlled by limit switches which stop the motor when either limit of movement is reached, the invention comprising an adjustable program switch included in said control system which operates to stop the motor when the back rest reaches a desired position intermediately of the opposite limits of movement thereof, as controlled by said limit switches.