With instruments of this kind it is known to generate the light necessary for illuminating the treatment area by means of an electric lamp arranged in the instrument. The lamp may be arranged in the front region of the instrument so that its light is aimed directly on to the treatment area. In particular in the case of such instruments which are in two parts, so that it is possible to exchange different treatment tools and for the purpose of disinfection, wherein the front instrument part can be connected by a quick-fitting coupling to the rear instrument part and, in particular with regard to the latter, is held rotatably thereon, it is known to arrange the lamp in the region of the rear instrument part, preferably directly behind the separating point. The light generated by the lamp is guided by means of a light conductor extending longitudinally in the front instrument part to a light emission opening which is located in the front region of the front instrument part and is aimed towards the treatment area. The lamp may be arranged in the axis of rotation or the longitudinal centre axis of the instrument, as described in DE 31 04 239 C2, or the lamp may be arranged eccentrically, as described in DE 33 32 628 C2.
Owing to the motor drive for the treatment tool, which may be either a mechanical drive (DE 33 32 628 C2) or a turbine drive (DE 31 04 239 C2), vibrations are generated in the instrument which also act on the lamp. In the known constructions, in which the lamp is held immovably in the region of its plug-in foot and/or its lamp bulb, vibrations lead to premature failure of the lamp. With lamps having a spiral-wound filament the most common cause of failure is a break in the spiral-wound filament.
An instrument of the kind described in the introduction is in public use. In this known construction the lamp holder has a plug-in socket in the form of a hollow cylindrical bush, into which the lamp foot can be inserted, there being in the bush two contact elements which are spaced apart and formed by thoroughly bendable spring arms between which the lamp foot can be inserted. Owing to the fixed seating in the bush, the lamp is mounted rigidly. The contact elements serve only for electrical contacting. Furthermore the contact elements are supported laterally on a holding ring, with the intermediate arrangement of an insulating layer. In the contact position the contact elements are therefore practically immovable.