Technical Field

The invention relates to an apparatus for making dental models for prosthesis work comprising a base plate having a groove extending essentially in accordance with the centre line of a row of teeth, the surfaces of said groove being provided with pairs of slots facing each other, said pairs of slots being adapted to receive the essentially complementary shaped parts of keys to be removeably retained in the groove, said keys each comprising an upper casting portion to be cast into a casting of a segment of a row of teeth and a lower keying portion to be inserted in the groove.

Background Art

PCT Application WO 93/24073 discloses an apparatus for making dental models for prosthesis work comprising a base plate for receiving a base key or separate segments thereof, e.g. in the form of individual keys to be inserted in a groove on said base plate. The base plate with inserted keys or larger or smaller seg¬ ments of a base key is used to cast gypsum dental models and later, during prosthesis work, dental models of fire-proof material. When using segments of a base key or individual keys, the uncovered portions of the groove have to be covered to prevent a casting material such as gypsum to run out of the form via the groove. There are several ways of covering the groove, such as by means of specially shaped groove-filling segments to be inserted into the groove, or tape arranged to cover the groove. A third possibility is to insert a piece of foam rubber into the groove on each side of a segment or key. Since there are intervals between the segments or keys because each segment has to have at least one key and to ensure that the upper casting portion of a key or segment is always com¬ pletely embedded in the casting material, the groove has to be covered on both sides by a plurality of keys or segments. This makes adjusting tape or foam

rubber demanding work.

Disclosure of the Invention

The object of the present invention is to provide an apparatus allowing easy covering of those parts of the groove of the base key which are not used.

The object of the invention is accomplished by an apparatus of the type stated in the introduction and characterised in that the keying portion of a key is an essentially U-shaped element to be inserted into the groove with the bottom of the U first and each leg engaging the corresponding surface of the groove, and that when the key is mounted in the base plate the casting portion of the key is an upwards projecting part forming an extension of one of the legs of the U.

As a result, the groove is readily filled over its entire length by means of a continuous strip of foam rubber having the same length as the groove and a width slightly larger than the groove. This facilitates casting considerably.

According to the invention, the upwards projecting part of the leg forming the casting portion of the key may be a linear extension of said leg, allowing for a particularly simple key.

Moreover, according to the invention, the upwards projecting part of the leg forming the casting portion of the key may extend essentially parallel to the leg and being connected to said leg by a short connecting piece extending essentially parallel to the bottom of the U. As a result, it is possible to adjust the keys to a row of teeth the shape of which deviates from the form of the groove on the base plate. This allows one base plate to be used for a comparatively large number of dental impressions.

Furthermore, according to the invention, the base plate may be transparent and

provided with at least one blind hole for each pair of slots on the surface facing

' away from the casting surface, said blind hole being adapted to receive a coloured marking. This embodiment facilitates the insertion of the keys in the correct position, as the impression of the row of teeth arranged on the upper side of the

5 base plate is visible through the base plate from the lower side. It is therefore easy to select insertion places for the keys. By affixing a coloured marking in the blind hole at said pair of slots, these places are easily found from the upper or front side of the plate, when the keys have to be inserted prior to casting with gypsum or for later handling, involving repeated removing and mounting of model

10 parts on the base plate.

In a particularly advantageous embodiment of the invention, the casting portion of the key may end in an easily broken-off part to be inserted and broken off in one of the blind holes at each pair of slots on the bottom surface of the base plate, thus facilitating the marking of the slots to a considerable degree, especially by 15 using keys of different colour.

According to another advantageous embodiment of the invention, the keys may be made of bent metal wire. Keys made of metal can be used for gypsum castings as well as for castings made of fire-proof material, which is subjected to high temperatures in a porcelain kiln.

20 According to the invention, the keys may be dimensioned in such a way that they are pre-stressed when inserted into the groove in order to obtain a particularly secure hold.

I Finally, according to the invention, the casting portions of the keys may be provided with recesses to facilitate fixation in the casting material.

25 Brief Description of the Drawings

The invention is described in greater detail below with reference to the accom¬ panying drawings, in which

Fig. 1 is a top view of a base plate,

Fig. 2 is a sectional view taken along the line I-I of Fig. 1 with one key inserted, and

Fig. 3-5 are different embodiments of the key.

Best Mode for carrying out the invention

The base plate of Fig. 1, having the general reference numeral 1, has a groove 2 extending essentially in accordance with the centre line of an average person's row of teeth. When seen in the direction of the upper surface 3 of the base plate towards the bottom surface 4, confer Fig. 2, the groove is provided with parallel surfaces, wherein pairs of parallel slots facing each other are formed, such as slots 5 and 6, into which individual keys 7, like the one shown in Fig. 2, are inserted.

In front of each pair of slots 5, 6 on each side of the groove 2 there are blind holes 8, 9 in the bottom side of the base plate. The blind holes 8, 9 are used for affixing a coloured marking at the pair of slots 5, 6 where the key 7 is to be inserted.

The key 7 is made of bent metal wire and comprises an upper casting portion 10 projecting above the upper surface 3 of the base plate 1 in the mounted condition and a lower keying portion 11 adapted to engage a pair of slots 5, 6 in the groove 2. The casting portion has a U-shaped part, each leg 12, 13 of the U being inserted in a slot of a pair of slots 5, 6. The keying portion 11 is dimensioned in such a way that the key 7 is pre-stressed when inserted in the slots 5, 6. One leg

12 of the keying portion 11 is directly connected to the casting portion 10 which in the embodiment shown in Fig. 2 is a direct linear extension of the leg 12.

As indicated by the dotted line in Fig. 2, the casting portion 10 may be provided with an easily broken-off extension 14 to be used for the above colour marking by inserting it in a blind hole 8 or 9 and breaking it off. The extension 14 can be formed in such a way that it is retained in a blind hole 8, 9 by friction or pre- stress. With suitable processing the key can be produced in different colours. When made of aluminium it can be advantageously anodized in various colours.

Fig. 3-5 show different embodiments of the key 7. The parts common to all the embodiments are shown with the same reference numeral as above. All the keys thus have a U-shaped keying portion 11 and a casting portion 10.

The embodiment shown in Fig. 3 corresponds largely to the embodiment shown in Fig. 2. The casting portion 10 is again a direct linear extension of the U-leg 12. The casting portion 10 is, however, provided with recesses 15, 16, 17 and 18 in order to facilitate interlocking between the casting portion 10 of key 7 and the casting material in question.

In the embodiment shown in Fig. 4, the casting portion 10 is provided with a short connecting piece 19, extending essentially parallel to the bottom 19 of the U between one leg 12 of the U and a section 21 parallel to said leg 12. Fig. 5 shows a similar embodiment. The difference between the embodiment in Fig. 4 and the embodiment in Fig. 5 is that the connecting piece of Fig. 4 extends away from the second leg 13 of the U, while in Fig. 5 the connecting piece extends towards said leg 13.

The embodiments of Fig. 4 and 5 allow the keys to be adjusted to rows of teeth considerably deviating from the one of an average person with respect to the extension of groove 2 on the base plate 1.

6

The base plate 1 can be manufactured in a manner known per se from various materials. Advantageously it is made by injection-moulding of plastics, for example acrylic, POM or ABS. As mentioned above, the base plate is advanta¬ geously made of a transparent material.

The keys are advantageously made of metal, such as steel, titanium or aluminium.

The invention has been described by means of the preferred embodiments, many modifications are, however, possible without departing from the scope of the invention. The keys may for example have another cross-section than the circular one shown or may be manufactured in a different way than by bending a wire, for example by casting or punching, since they only have to be shaped in such a way as to interact with the slots 5, 6 and to be provided with an essentially U-shaped keying portion 11.