Patent Number: 047926929
Section: summary

DESCRIPTION A dental irradiation apparatus comprising a lamp for producing a convergent beam of radiation and an optical waveguide having an entrance surface disposed wtthin the beam and an exit surface adapted to be oriented with respect to a location to be irradiated is known from German Offenlegungsschrift No. 2,507,601. The optical waveguide provided in that apparatus has a constant diameter over its substantial length which, in practice, is about 8 mm, and the waveguide is bent near its exit end by an angle of about 60.degree. and has at its tip a conical portion of decreasing diameter. A similar irradiation apparatus without such a tapering tip portion is disclosed in U.S Pat. No. 4,298,806. The known apparatus permit photopolymerizable tooth fillings to be cured in situ by occlusal irradiation. Radiation-settable materials are known to shrink during polymerization at a degree which increases with the polymerization temperature. Since the filling material always shrinks towards the source of radiation, there is a tendency for the material to lift off the bottom and/or the sides of the cavity in case of a purely occlusal irradiation. This tendency may be counteracted by irradiating the filling material disposed in the cavity from the bottom or sides of the cavity. To this end, it is necessary either to penetrate the tooth itself with radiation of a correspondingly high intensity or, in case of multi-facial fillings, to apply the radiation totthe filling material from an interdentalapical position Either way of irradiation is practically impossible with the conventional optical waveguides It is an object of the present invention to devise a dental irradiation apparatus with an optical waveguide which enaables irradiation of individual dental areas in situ from any desired direction at an intensity which is sufficient to cure photopolymerizable fillings starting from the cavity walls. To meet with this object, the dental irradiation apparatus according to the present invention includes an optical waveguide having an entrance surface disposed in a convergent beam of radiation produced by a lamp and an exit surface adapted to be oriented with respect to the location to be irradiated, the angle of convergence being smaller than approximately 30.degree. with respect to the optical axis defined by the lamp, and the waveguide being conically shaped over a substantial part of its length with a diameter decreasing from the entrance surface to the exit surfcce. On account of the angle at which the radiation enters the optical waveguide and also because of the taper of the waveguide and the increased radiation divergence resulting therefrom, a substantially semi-spherical lobe of approximately constant radiation intensity is achieved at the exit surface of the waveguide; as a consequence, the end of the waveguide may be placed in practically any desired orientation with respect to the location to be irradiated while the material is still reliably cured. This is of great significance in view of the limited space, particularly in interdental areas or in case of curing distal molar fillings. Because of the constant radiation density, there is no danger of the filling material being exposed to excessive radiation intensity and thus overheated, inspite of large irradiance. If transparent interdental wedges are used, a very large amount of radiation may be coupled into the small axial end face of the wedge which radiation is emitted by the lateral wedge surfaces to cure filling material starting from a proximal-apical region. While the entrance surface may have a sufficient cross-section to receive a corresponding amount of irradiance, the exit surface of the optical waveguide according to the present invention is comparatively small, thereby permitting direct irradiation of interdental areas which cnnnot be reached by conventional waveguides. Due to the decrease in diameter, high intensity radiation is obtained at the exit surface which penetrates even relatively thick dentin layers. In the interior of the tooth, starting from the cavity walls, an intensive curing of the filling material is achieved, which strongly adheres to the tooth wall. German utility model specification No. 8,504,351 discloses an optical waveguide for a dental irradiation apparatus which has a portion conically tapering from an entrance surface. This portion, however, is followed by a portion increasing in cross-section towards an exit surface which is larger than the entrance surface. This waveguide serves to irradiate larger surfaces with parallel light as uniformly as possible, and it is ipportant in the practical use of this waveguide that the exit surface be placed on the surface to be cured in a substantially flush manner. In a preferred embodiment of the invention, the material of the waveguide has a refractive index ratio with respect to the invironment of greater than about 1.3, preferably about .sqroot.2. The radiation emitted by the lamp may thus have a great angle of convergence without being totally reflected at the exit surface. A great angle of convergenee of the radiation beam emiteed by the lamp is advantageous in that, in case a substantially point-shaped source of radiation is used with an ellipsoidal reflector, the reflector may be comparatively short in the direction of the optical axis, while utilizing a given portion of the overall radiation produced. When the refractive index is about .sqroot.2, a substantially semi-spherical lobe of radiation is actually achieved at the exit surface. With a smaller refractive index the exit angle also decreases. In another preferred embodiment of the invention, the ratio of the diameter of the exit surface to that of the entrance surface ranges from about 0.5 to about 0.2 and is preferably about 0.3, with the diameter of the entrance surface being about 10 mm, that of the exit surface about 3 mm, and the length of the waveguide being about 100 mm. With these dimensions, a waveguide is achieved which is easy to handle in practice and which can be used in connection with available lamps and irradiation apparatus, while a reasonable portion of the overall amount of available radiation is utilized. Preferably, a portion of the waveguide close to its exit surface is bent about an angle of approximately 60 to 90.degree., preferably 75.degree.. With this shape, even such dental areas which are difficult to access can be sufficiently irradiated. In order to avoid radiation to exit from the peripheral surface of the bent waveguide portion, the diameter of that portion is essentially constant. In a furteer preferred embodiment of the invention, the exit surface of the waveguide is crowned, and the tapering of the waveguide in a portion immediately before the exit surface is more pronounced than over its remaining length to enable placing the radiation spill closer to fillings in interdental spaces. At the same time, a drop of radiation intensity in the vicinity of an angle of 90.degree. with respect to the optical axis is avoided near the exit surface, as far as possible.