The present invention concerns a method for making dental working models, wherein a moulding cup is used for securing a plaster cast of teeth, and a device for use in connection with the method.

Two methods are on the market to-day for manufacturing dental working models. A common feature of both systems is that they are based on a negative impression of the teeth taken by the dentist, which is subsequently filled with plaster by dental technicians. Finally the plaster cast together with the completed dental working model is sent to the dentist's office.

Method 1 , which comprises model pins with a plaster base, is the one which is most used and goes under the name of PinDex. In this case the plaster cast has to be surface ground before being split and then secured to a plaster base by means of pins. The work is time-consuming since the pins, which comprise a male and a female part, have to be fitted in pre-drilled holes in both the plaster cast and the base part. In addition to this the actual tooth which is to be replaced has to be provided with pins. The model is discarded after use. The method requires relatively expensive consumer materials, and the manufacture of the model requires relatively expensive equipment. Breakages also often occur in the working model. Ref. US patent no. 4 721 464 amongst others.

Method 2 comprises a moulding cup system, which permits the work involved in manufacturing working models for dental work to be performed more rapidly than in method 1 , the plaster impression being made directly in a moulding cup, thus avoiding the necessity of surface grinding and manufacturing the plaster base as well as attaching the plaster cast to the base. US 4 119 292 describes such a moulding cup. One drawback of this moulding cup is that the actual plaster cast has to be lifted out of the moulding cup for splitting and then returned to the cup. Moreover the moulding cup, which is designed for multiple use, is relatively expensive to purchase and leads to increased transport costs amongst other things in connection with the return of the moulding cups from the dentist's office, since the dentists seldom return them.

One object of the present invention is to provide a method which makes the manufacture of dental working models simpler and substantially less expensive in relation to existing manufacturing methods. A further object of the present invention is

to provide a device for use in connection with this method which avoids the above- mentioned drawbacks.

A further object of the invention is to provide a device for use in connection with the method which reduces the transport costs to and from the dentist's office.

Yet another object of the present invention is to provide a device which can be used in connection with existing material, such as, e.g., disposable articulators, special saws, etc.

These objects are achieved by a method and a device according to the type mentioned in the introduction, which are characterized by the features and advantages which are indicated in the attached claims.

By means of the invention a method is achieved by simple means, based on a moulding cup system, which enables the plaster cast to be split together with the moulding cup, and a device for use in connection with the method, consisting of a moulding cup which is designed in such a manner that it can be cut open. Thus the method according to the invention simplifies the manufacture of dental working models and substantially reduces the manufacturing costs.

The design according to the invention also reduces the transport costs in connection with the return of moulding cups from the dentist's office to the laboratory, the present moulding cup being intended for once-only use. With the design according to the invention a considerable simplification has also been achieved of the manufacture of the actual moulding cup, the moulding cup being moulded in one piece.

Furthermore the moulding cup according to the present invention is provided with a lower groove for additional attachment of the plaster cast in the moulding cup, especially in connection with antagonistic mounting of the moulding cups.

The moulding cup is also adapted to suit special tools and existing material, such as, e.g., articulators, which are employed in the manufacture of dental working models.

The invention will now be described in more detail by means of an embodiment which is illustrated in the drawing, in which:

Fig. 1 is a perspective view of the device according to the invention,

Fig. 2 is a side view of the device according to the invention,

Fig. 3 is a sectional view of the device according to the invention.

In the drawing the moulding cup is generally indicated by 1 , while the outer wall and the inner wall are indicated by 2 and 3 respectively. A plaster cast of teeth located in the moulding cup is indicated by 4 and a preparation model for manufacturing a crown or bridge is indicated by 5.

In the manufacture of dental working models according to the invention the following steps are employed:

The moulding cup 1 which is used to secure the plaster cast 4 is provided in the normal manner before splitting up of the preparation model begins. The splitting is performed by cutting grooves (figs. 2 and 3) on each side of the preparation model while it is still secured in the moulding cup, i.e. the preparation model is cut out together with the inner wall 3 and the outer wall 2 of the moulding cup 1 , after which the preparation model 5 can be removed for the manufacture of a crown or bridge.

As illustrated in figs. 2 and 3 there is provided in a rear wall 6 of the moulding cup 1 a groove 7 for attaching an articulator (not shown), e.g. a disposable articulator. There is further provided a pin 8 in the bottom of the moulding cup 1 in that part of the cup which is bounded by the inner wall 3 and the moulding cup's rear wall 6. The pin 8 is intended for use in the employment of a special saw for splitting the plaster cast 4 together with the moulding cup 1.

Between the outer wall 2 and the inner wall 3 there is further provided a sloping floor 9 which makes the actual sawing of the plaster cast 4 together with the moulding cup 1 much simpler, faster and more accurate compared to existing moulding cups.

A known method for securing the plaster cast in the moulding cup is to provide the outer wall 2 and the inner wall 3 with opposing ribs (not shown). This method has been shown to be inadequate for the securing process, especially when the moulding cup is employed antagonistically, i.e. when two opposing moulding cups are linked by means of an articulator for the formation of a complete dental working model. Consequently the device according to fig. 3 is provided at an upper edge of the outer wall 2 with a lower groove 10 in order to further secure the model cast 4.