The present invention refers to adaptors and more specifically to an adaptor, which can be mounted on a drilling machine meant for drilling holes at right angles to a plane surface. The adaptor is especially suitable for dental technicians' work.

The invention of this adaptor was made to solve problems of preparing dentures, crowns, bridges and similar constructions made by dental technicians. But it is obvious that the invention can be used by other types of work including the same problems: To be able to drill any number of parallel holes anywhere at right angles to a plane surface.

Especially by preparation of crowns and bridges, which are to replace one tooth or more teeth, it is important that these are placed precisely on a level, partly because it must feel right to the patient, and partly because the bite has to be right. Furthermore, what is perhaps most important, the crown or the bridge must certainly fit the tooth or the teeth that are to support the crown or the bridge.

The starting point of the dental technicians is a cast of the patient's teeth, a negative cast. The tooth or the teeth that are to support the crown or the bridge are ground, so that the crown or the outermost teeth of a bridge can be fixed on them. Later the dental technicians prepare a positive cast out of the negative one. The positive cast is the model of the teeth. To prepare a crown or a bridge the dental technicians just need the model or the models of the ground teeth, so that the prepared dentures can be fixed on them. In this connection the other teeth are of no interest. However, the relation between the crown or the bridge and the other teeth are of importance, what will appear later.

The model cast of the teeth are ground on the side turning towards the teeth to a plane surface, which is treated with a remedy, making it resistant to any sticking to casting material. No less than two holes are drilled in the plane and prepared bottom, in each of the teeth that are to be separated to be used for the preparation of crowns or bridges. Protruding pins are glued into the holes. Some extra holes ar drilled in other places, and pins are glued into these holes to get the cast model into a fixed position. Small sleeves are mounted on the protruding ends of the pins , and then the plane and prepared surface is pressed against a casing material in a casting form, so that the pins including the sleeves penetrates it. When the casting material is cured, the model must be lifted up,

while the plastic sleeves are stuck in the casting material.

However, now the problem is, whether the drilled holes are parallel. If they are not parallel you cannot lift neither the entire model nor a single tooth or a group of teeth away from what is considered to be the base. But in this case the slanting pins will cause a locking. To solve this problem special machines for drilling of parallel holes have been developed. However, they have appeared to be difficult to handle and they are rather expensive. These special maschines can be used for nothing else and therefore they are doubtful investments. But as dental technicians are very often using a small drilling maschine, it should be desirable, if this drill could be used for the operation of drilling parallel holes as well.

The present invention is to fulfil this wish. This will be achieved by an adaptor of the type mentioned in the patent claims, from which the special characteristics of the invention appear as well.

A detailed description of the invention is following in addition to the enclosed drawings, of which:

Fig. 1 is a schematic cut through an adaptor similar to the invention.

Fig. 2 is a view from the under side of the adaptor of fig. 1.

Fig. 3 is a perspective view of an adaptor similar to the invention, mounted on a conventional drilling maschine for dental technicians. Fig. 1 shows a schematic cut of an adaptor (1) similar to the invention, which consists mainly of three elements, an inner sleeve (2), an outer sleeve (3) and a spiral spring (4). The inner sleeve (2) is tubular with a circular cross section, and at one outer end there is a thread (5) for screwing on the adaptor (1) to a drilling maschine equipped with a corresponding thread. Instead of threads other means of fastening can be used with machines having no tread but a conventional neck, such as clamps, screws etc. The outer tubular sleeve (3) slidingly surrounds the inner sleeve (2). The shape of the outer sleeve (3) is partly complementary to the inner sleeve (2), so that the outer sleeve (3) is gliding by control on to the inner sleeve (3). The outer sleeve (3) has an introverted shoulder, situated directly opposite of the inner end (7) of the inner sleeve (2). Two axially oriented grooves (8) with diametrically opposite levels are cut through the wall of the inner sleeve (2), and a screw or a pin (9) , which is radially directed towards the inside of the outer sleeve (3), is situated in each of these grooves. Thereby the length of the grooves (8) decides the

reach of which the sleeves (2) and (3) can be displaced axially in relation to one another. Thereby the spiral spring (4) is set between the screw and the inner bottom (7) of the inner sleeve (2). In this way the spring (4) presets the sleeves (2) and (3) to an extended level or a level opposite one another.

The outer sleeve (3) stretches from its shoulder to a foot or a support disk (10). One or more through-going holes (11) are situated in the wall of the area between the shoulder and the support disk (10). These holes are meant for outlet of chips from the invisible drilling machine.

Frqm fig. 2 it appears how two parts (12) and (13), shaped like pieces of tart, are made in the bottom of the support disk. The part (12) is hollow and meant for outlet of chips while the part (13) , which is cut through the support disk (10) and which is wider than the the one for outlet of chips, provides a view to the drills, which makes it possible to see where the drills hit the working area. In the centre of the round support disk (10) there is a through-going hole (14), through which the drills can be pulled out.

The adaptor 1), which is similar to the invention, is in fig. 1 mounted on a type of drilling machine (15) , which is often used in dental technicians' laboratories, so that it encloses the drill chuck including the fastened drills. In this case the thread (5) of the inner sleeve (2) is screwed into an opposite thread around the drill chuck of the drilling machine (15). The drills (16) fastened to the drill chucks are adjusted in a way that level their tips with the bottom of the support disk (10).

When drilling the dental technician places the support disk (10) against the surface, in which holes are to be drilled, that is the plane surface of the cast model, as mentioned in the introduction. Hereby the drill (16) is situated at a right angle to the plane surface and each hole to be drilled will be parrallel to any holes drilled in the same way in the plane surface of the cast model. Through the part (13) the dental technician is able to see precisely, to where the drill (16) can be displaced for drilling. Thereby the length of the groove (8) decides the maximum drilling-depth, which is adapted to the pins that are to be mounted in the parrallel holes.

With the present invention the in the introduction mentioned wish for drilling parrallel holes in a plane surface, using a conventional drilling machine, has been fulfilled. A professional realises that

various modifications of the invention makes it a tool with many applications, but such modifications must be within the framework of the invention, as defined in the following patent claims.