BURR

Abstract: A burr comprises a shaft (7) and a conical head (8). The circumferential surface of the head of the burr is of a material-removing design merely within a circumferentially limited area (9). The sum of the angle which is occupied by the circumferentially limited area relative to the centre axis of the head of the burr and a rotary angle, through which the burr during operation is adapted to oscillate, is less than 360 DEG .

Description: BURR The present invention relates generally to a burr and more specifically to a burr having a shaft and a conical head. SE-C-9202428 discloses, among other things, a direct dental restoration, in which a cavity is first formed in a tooth. The mouth of the cavity is prepared by means of a conical burr to give it a corresponding conical shape. A conical insert having the same cone angle as the coni¬ cal burr is applied and finally fixed in the cavity. This technique is advantageous by the mouth of the cavity being filled completely by the conical insert, which suitably consists of ceramic material. The risk of shrinkage and gap formation is thus eliminated almost completely. The prior-art technique may, however, be difficult to apply in the cases where the cavity is located in the proximal area of a tooth, i.e. the part of the tooth that is located closest to a neighbouring tooth in the same jaw. Then the design of the cavity and especially the mouth thereof may in fact result in also the neighbouring tooth being affected by grinding, which, of course, is not desirable. The object of the present invention is to eliminate the above-mentioned drawback to the greatest possible extent. According to the invention, this object is achieved by the burr of the type mentioned by way of introduction being given the features that appear from claim 1. Advan¬ tageous embodiments of the burr are defined in the sub- claims. Thus, the circumferential surface of the head of the burr is given a material-removing design within a circumferentially limited area. By letting such a burr oscillate in smaller movements than a revolution when forming the cavity or at least the mouth thereof, a cavi- ty having a conical mouth can be accommodated in a tooth in its area adjacent to a neighbouring tooth with no risk that any material is removed from the neighbouring tooth. The limit to how close a cavity can be formed in a tooth without a neighbouring tooth being affected can then be defined by means of the conical surface, of which the mouth of the cavity constitutes a part. More speci¬ fically, a cavity can be formed such that said conical surface merely touches upon a point on the neighbouring tooth. The size of the oscillating motion of the burr and the size of said circumferentially limited area should thus be such that the material-removing part of the cir¬ cumferential surface of the burr does not run the risk of reaching the point of contact between the conical sur¬ face of the intended cavity and the neighbouring tooth. In fact, the sum of the rotary angle of the oscillating motion in either direction and the angular size of the limited area relative to the centre axis of the head of the burr should be less than one revolution (360°). If the oscillating motion consists of rotations back and forth by half a revolution, the circumferentially limited area should therefore according to the invention occupy a smaller angle than about 180° relative to the centre axis of the head of the burr. Preferably, the angle is however in the range 90-145°. The invention will now be described in more detail with reference to the accompanying drawings, in which: Fig. 1 is a schematic side view of two teeth, Fig. 2 is a view along line II-II of part of the teeth in Fig. 1, Fig. 3 is a side view of an embodiment of a burr according to the invention, Fig. 4 is an end view of the burr in Fig. 3, and Fig. 5 is an end view, corresponding to Fig. 4, of another embodiment of the inventive burr. Figs 1 and 2 show two teeth 1 and 2, which are jux¬ taposed in one and the same jaw. In the tooth 1, a cavity 3 is schematically shown, the mouth 4 of which is coni- cal. The actual mouth surface is more precisely part of a conical surface 5, which is indicated by dashed lines in Fig. 1. As illustrated in Fig. 1, this conical surface 5 is positioned such that it touches the surface of the tooth 1 in a point 6. The above implies that if the mouth surface 5 should be formed by means of a conventional conical burr, there is a great risk that the tooth 1 will be ground down in and around the point 6. By using a burr according to the present invention, this risk can be practically eliminated. The embodiment of an inventive burr as shown in Fig. 3 consists of a shaft 7 and a head 8. The shaft 7 is rotationally symmetrical and formed with an inner cylindrical part and an outer spherical part. Thus, the shaft can be mounted in an optional angu¬ lar position in a chuck, which is adapted to carry out an oscillating motion having in any case smaller rotary angles in each direction than 360°. The head 8 of the burr has the form of a truncated cone. For removing material, it preferably has a coat¬ ing of diamond powder, but some other material-removing design is of course also possible. The specific feature of the head 8 of the burr according to the invention is that on the circumferential surface thereof, the mate¬ rial-removing design is to be found merely within a cir¬ cumferentially limited area 9. In the embodiment according to Fig. 4, the limited area 9 occupies an angle of about 180° relative to the centre axis of the head 8 of the burr. In the embodiment according to Fig. 5, the limited area 9' occupies an angle of about 90°. A general condition to make it possible to give a cavity in a tooth a conical mouth without grinding down a neighbouring tooth in or around such a point as the point 6 in Figs 1 and 2 is that the sum of the angular size of the limited area 9 relative to the centre axis of the head 8 of the burr and the angular size of the oscillat¬ ing motion of the burr in either direction about the same centre axis is less than 360°. If the chuck, in which the burr is adapted to be fixed, is designed to oscillate half a revolution back and forth, the limited area of the burr must thus occupy a smaller angle than about 180°. If instead it occupies an angle of about 90°, an area having an angle of about 90° relative to the centre axis of the burr will not be worked by the burr while using the same chuck motion. To make it possible for the burr, which preferably has a truncated conical head 8, to remove material also in the bottom of a cavity, also the surface of the free end 10, 10' of the head 8 of the burr has a material- removing design of the same kind as the limited area on the circumferential surface of the head 8 of the burr. When preparing a cavity for filling by means of a conical insert preferably made of ceramic material, first the requisite material is removed, in which operation other kinds of burrs can be used, whereupon the mouth of the cavity is formed by means of an inventive burr. Finally, a suitably truncated conical insert is applied and fixed in a per se known manner.

Claims: CLAIMS 1. A burr comprising a shaft (7) and a conical head (8), c h a r a c t e r i s e d in that the circumferen¬ tial surface of the head ( 8 ) of the burr is of a mate¬ rial-removing design merely within a circumferentially limited area (9, 9' ). 2. The burr as claimed in claim 1, c h a r a c - t e r i s e d in that the sum of the angle which is occupied by the circumferentially limited area (9, 9' ) relative to the centre axis of the head ( 8 ) of the burr and a rotary angle, through which the burr during ope¬ ration is adapted to oscillate, is less than 360°. 3. The burr as claimed in claim 1 or 2, c h a r ¬ a c t e r i s e d in that the circumferentially limited area (9, 9' ) occupies an angle which is less than about 180° relative to the centre axis of the head (8) of the burr. 4. The burr as claimed in claim 3, c h a r a c ¬ t e r i s e d in that the angle is in the range 90-145°. 5. The burr as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that the head (8 ) of the burr has a truncated conical shape. 6. The burr as claimed in claim 5, c h a r a c ¬ t e r i s e d in that also the free end (10, 10' ) of the head (8) of the burr is of a material-removing design. 7. The burr as claimed in any one of claims 1-6, c h a r a c t e r i s e d in that the free end of the shaft (7) of the burr is rotationally symmetrical to permit mounting at an optional angle in a chuck. 8. The burr as claimed in any one of claims 1-7, c h a r a c t e r i s e d in that the material-removing design (9, 9', 10, 10' ) consists of a diamond coating.

Inventors: HAGNE LEIF, HAGNE, LEIF
Applicants: HAGNE LEIF, NORDISKA DENTAL AB, HAGNE, LEIF
Application year: 1996
Main classification: A61C3
IPC codes: A61C3