WO2003011168A1

WO2003011168A1 - Method for producing pressed ceramics for use in dentistry; ceramic press furnace, muffle and muffle mold therefor

Info

Publication number: WO2003011168A1
Application number: PCT/EP2002/008410
Authority: WO
Inventors: Kurt Zubler
Original assignee: Zubler Gerätebau GmbH
Priority date: 2001-07-28
Filing date: 2002-07-29
Publication date: 2003-02-13
Also published as: DE10136584A1

Abstract

In order to reliably execute a method for producing pressed ceramics for use in dentistry, involving the production of a muffle, the placement of the muffle in a ceramic press furnace, the heating of a ceramic pellet, and the pressing of a pressed ceramic object, the invention provides that the temperature inside the muffle (50) is measured and the pressing process is initiated once the pressing temperature inside the muffle (50) is attained.

Description

description

Process for the production of pressed ceramics in dental technology; Keramikpreßofen. Muffle and muffle gauge for this.

The invention relates to a method for producing pressed ceramics in dental technology, comprising the manufacture of a muffle, the introduction of the muffle into a press furnace, the heating of a ceramic pellet and the pressing of a press ceramic object. Furthermore, the invention relates to a ceramic press furnace and a muffle, in particular for carrying out the method according to the invention. Finally, the invention relates to a muffle gauge for producing a muffle according to the invention.

In the manufacture of dental pressed ceramic objects, for example bridges, crowns, veneers and inlays, a wax model of the object is first produced. This wax model is embedded in a muffle. The muffle is manufactured by assembling the muffle base, muffle gauge and sleeve into the muffle shape. The wax model is fixed with wax on the muffle base. The investment is then poured into the prepared muffle mold. After the investment has hardened, the muffle sleeve is removed and the muffle is reworked. Before the pressing process, the wax is first melted out and ceramic mass is introduced into the resulting cavity, so to speak, the positive shape of the future dental object. For this purpose, after the wax has melted out, a ceramic pellet of the desired color and the required size is introduced into the press ram channel and inserted together with the press ram into the combustion chamber of the press furnace. After the pressing temperature has been reached, the actual pressing process takes place, in which the now flowable ceramic mass is pressed into the melted-out mold with the help of the press ram. This is one of the most critical moments in the manufacture of dental press ceramics, since the pressing process of the ceramic is very sensitive to temperature. at

BESTATIGUNGSKOPIE known press furnaces, the press plate is not heated. The muffle is consequently only supplied with heat at the circumference, so that the temperature decreases towards the muffle base. Due to the decreasing temperature towards the muffle bottom, the flowability of the ceramic mass is reduced and can therefore no longer adequately fill the cavities formed by the wax flowing out. Especially for larger or angled objects, such as. B. with bridges, this means that the object is only insufficiently displayed. A completely warmed-up muffle is therefore a prerequisite for a mold to flow out completely. This means that the entire muffle, in particular in the area in which the objects are located, should have a temperature before pressing that corresponds to the optimum pressing temperature. The pressing process should therefore only be triggered when the required temperature in the area of the object shapes and pressing channels within the muffle is actually present.

In the known press ceramic furnaces, a temperature measurement is usually carried out in the combustion chamber. After reaching the target temperature in the combustion chamber, the pressing process is triggered based on empirical values, taking heating rates and holding times into account. This means that the dental technician must use his experience to estimate when the required temperature inside the muffle will be reached. Based on the size of the muffle and his experience with the furnace and the investment material, he must therefore estimate when this time could be reached and then enter the holding time and the target temperature to be achieved. Since the time factor usually plays a major role in dental technology laboratories, the pressing process should also be triggered as early as possible to avoid unnecessary downtimes.

DE 199 05 666 offers an approach to solving this problem. It describes a kiln which, in addition to the usual spiral, upper heating element, has an additional heating element in the base plate, as a result of which the muffle also heat is supplied from the bottom. This should ensure uniform heating and faster heating of the muffle. However, this approach also has the disadvantage that the time at which the pressing temperature is reached inside the muffle can only be roughly estimated.

The object of the present invention is therefore to provide a reliable method for producing pressed ceramic in dental technology which avoids the disadvantages described above. Furthermore, a ceramic press furnace and a muffle are to be provided, in particular for carrying out the method. In addition, a muffle gauge is to be made available for the production of said muffle.

This object is achieved by a method according to claim 1, a ceramic press furnace according to claim 7, a muffle according to claim 10 and a muffle gauge according to claim 15. Advantageous embodiments are the subject of the dependent claims.

The method according to the invention for the production of pressed ceramic objects in dental technology is based on the following steps, which are already known from the prior art: After producing a wax object and embedding it in a muffle, the muffle is introduced into a preheating furnace and the wax is melted out. After introducing the ceramic mass in the form of ceramic pellets and the press ram, the muffle, ceramic pellet and ram are heated in the press furnace. After the actual pressing process, the muffle with the ceramic object contained therein is cooled. According to the invention, the temperature is not measured in the environment, but directly inside the muffle. When the desired pressing temperature has been reached, the pressing process is triggered. In contrast to the prior art, the pressing process is no longer triggered as a function of the target temperature reached in the surrounding combustion chamber, but as a function of the temperature actually reached within the muffle. Since this actual temperature is determined inside the muffle, this takes place in the immediate vicinity the object shape, and thus in the immediate vicinity of the object position, at which the pressing temperature should be reached in order to ensure good flowability of the ceramic mass. Errors in the ceramic objects, which can be attributed to insufficient flowability of the ceramic mass and thus to a too low pressing temperature, are thereby avoided.

It is also advantageous that the warm-up time lasts only as long as is actually necessary by the method according to the invention. As a result, the time lapse in the manufacture of dental pressed ceramic objects can be further optimized. This also completely avoids unnecessary energy losses due to heating rates and holding times that are too long. In addition, overheating is avoided, which can damage the ceramic material and thus lead to a deterioration in the surface quality, as well as incorrect pressing.

It is preferred that the temperature is measured by means of at least one temperature sensor in at least one recess of the muffle pointing towards the object. This is preferably done by placing the muffle with said recess on a temperature sensor, which is preferably integrated in the base plate of the press furnace. This has several advantages. Placing the muffle on the temperature sensor ensures that the muffle is always precisely positioned for the pressing process. Furthermore, the simple handling of the method is of great advantage. Due to the fixed placement of the temperature sensor and the muffle placed on it, a permanently reliable temperature determination inside the muffle is easily possible.

Furthermore, a ceramic press furnace is provided with which the method according to the invention can be carried out. The press furnace according to the invention has a base plate in which at least one temperature sensor is integrated. This The temperature sensor preferably protrudes slightly from the base plate, so that a muffle can be placed on it. The muffle is explained in more detail below. It has a recess leading to the center, with which it can be placed on the temperature sensor of the base plate of the furnace. The inventive design of the press furnace in connection with the muffle according to the invention enables temperature measurement inside the muffle and thus in the immediate vicinity of the object shapes.

The muffle according to the invention is used in particular to carry out the method according to the invention. It contains the wax model or the corresponding object shape or the ceramic object itself. The muffle has a ram channel for inserting the ram and the ceramic pellet (s). Furthermore, the muffle has at least one z. B. 3 cm deep recess into which a temperature sensor can be inserted. In this way, the temperature inside the muffle can be measured, the recess and thus the temperature sensor being placed in such a way that the temperature in the immediate vicinity of the object or objects can be measured. This advantageous design enables the temperature within the muffle to be measured in the immediate vicinity of the press channels and the object shapes. The pressing process can therefore be triggered as a function of the actual temperature inside the muffle. The dental technician is therefore no longer dependent on any experience and does not need to include changed environmental and material conditions.

The recess is preferably located in the base of the muffle, the recess also being able to be designed as an annular groove all around. A plurality of recesses, in particular two or three recesses, are preferably provided in order to be able to insert the temperature sensor into the muffle in the manner of a probe. The recesses are still preferably cylindrical, but conical, frustoconical and rounded recesses are also possible. In order to achieve good heat transfer between the muffle and the temperature sensor, the recess is preferably designed to be form-fitting to the sensor.

Furthermore, a muffle gauge for producing a muffle according to the invention is proposed. The muffle gauge has at least one elevation with which a recess (as a "probe channel") can be formed in the muffle, into which a thermocouple or temperature sensor can in turn be inserted. After the investment has hardened, a channel-shaped recess remains in the finished muffle due to the increase. It is preferably provided that at least one projection is formed on the muffle gauge, since in this way the recess in the muffle is on the bottom of the finished muffle during the later pressing process.

The invention will be explained and described in more detail below with reference to the drawings. Show it:

Fig. 1 shows the elements of a muffle shape according to the invention in

Front view and partially cut (C); 2 shows a section through an assembled muffle shape. 3 shows a front view of an exemplary embodiment of a muffle gauge according to the invention; 4 shows a front view of a further exemplary embodiment of a muffle gauge according to the invention; Fig. 5 is a partial sectional view of an inventive

Ceramic press furnace with muffle; and FIG. 6 embodiments of details on the bottom of a press furnace according to the invention.

Fig. 1 shows the individual elements of a muffle shape. A muffle base 10 is shown in FIG. 1A, a muffle gauge 20 in FIG. 1B and a section through a sleeve 30 in FIG. IC. The muffle base 10 consists of the base ring 11, on the base ring 11 thereof Stop surface 15, the cuff 30 is placed. It also has a muffle base 12, the top 16 of which depicts the end face of the finished muffle. Furthermore, the muffle base 10 has a pin-shaped sprue or press ram channel 13 (more precisely: its negative shape as a placeholder) (cf. FIG. 2). At the upper end of the press ram channel 13 there is a growth surface 14 onto which the wax objects are waxed. The muffle gauge 20 (FIG. 1B) has a cover ring 21, on the stop surface 25 of which the sleeve 30 strikes. Furthermore, it has a muffle cover 22, the surface 26 of which depicts the bottom of the later muffle. Furthermore, the muffle gauge 20 has elevations 23 and 24, which form channel-shaped recesses in the later muffle. The pin-shaped elevations 23, 24 thus form negative forms of the later recesses.

1 and 2, the sleeve 30 is a rubber sleeve with a wall 31. The lower edge 32 of the sleeve 30 is placed on the stop surface 15 of the muffle base 10. The muffle gauge 20 with its stop surface 25 is then placed on the upper edge 33. The investment is introduced into the cavity or opening 34 of the muffle 30. Instead of a rubber sleeve, as in FIGS. 1 and 2, however, any other sleeve can also be used, in particular a paper sleeve using a casting ring (muffle ring).

Fig. 2 shows the muffle shape of Fig. 1 in the assembled state. The muffle shape 1 shown in section thus consists of the elements muffle base 10, muffle gauge 20 and sleeve 30. The section through the muffle shape 1 also shows two models 40 fixed on the growth surface 14 (see FIG. 1), each with a sprue 41 is fixed to a wax mountain 42. The finished investment ring is indicated by a dashed line and dotted filling and is identified by reference number 50. 3 and 4 show exemplary embodiments of muffle gauges 120 and 220 according to the invention. As already described for FIG. 1, the muffle gauges 120 and 220 each have a cover ring 121 or 221 and muffle cover 122 or 222. Furthermore, pin-shaped elevations 123 and 223, 224, 225 are provided, which depict the respective channel-shaped recess in the muffle 50, into which a temperature sensor is then inserted. In the exemplary embodiment in FIG. 3, the elevation 123 is designed in the form of a rounded cylinder. The elevations 223, 224, 225 of FIG. 4 have the shape of truncated cones. In FIG. 3, only one elevation 123 is provided, in contrast to FIG. 4, which shows three elevations 223, 224, 225. The number of increases provided should be adapted to the number of press objects, so that the temperature inside the muffle 50 in the vicinity of the respective object can be determined with sufficient accuracy. For this purpose, a recess in the finished muffle, which is also designed, for example, as a circumferential groove, is generally sufficient, but preferably two or three recesses are provided, which also results in a more uniform and rapid heating of the muffle. In addition, more than three recesses can also be provided. The shape of the recesses and thus the shape of the elevations 23, 24, 123, 223, 224, 225 can largely be chosen as far as a temperature sensor can preferably be inserted in a form-fitting manner into the recesses shown by these elevations in the finished muffle.

Fig. 5 shows a section of a ceramic press furnace. Temperature sensors 501 are integrated in the base plate 500. Their measurement signals are discharged via lines 502 and displayed, for example, on a display or fed to a computing unit. The temperature sensors 501 preferably have a cap-shaped cover 505 in the manner of a plug contact. As can be seen from FIG. 6, the cover 505 can have different shapes. It serves to transmit the temperature measured inside the muffle 50. The shape of the cover 505 is adapted to the shape of the recess 51 in the muffle 50 and can accordingly have different shapes. The recess can also be a circular groove, as is indicated by the dashed line (as a hidden edge) below the press ceramic object 140. A plurality of temperature sensors can then be inserted into this groove on the muffle base in a probe-like manner and with different pitch angles oriented towards the objects inside the muffle 50. 5 also shows how the muffle 50, which is now "turned upside down with respect to FIG. 2", is placed on the temperature sensors 501. For this purpose, the muffle 50 with its recesses 51 is placed on it and thus positioned exactly.

The method according to the invention for producing pressed ceramic objects in dental technology will now be described in more detail below, in particular with reference to FIGS. 2 and 5. The muffle mold 1 is assembled as described under FIG. 2 and the previously produced model for the object 40, 140 is fixed on the growth surface 14 of the muffle base 10. After the investment has been poured in, the muffle gauge 20 is put on. Due to the pin-like elevations 23 and 24, the channel-shaped recesses 51 are shown in the muffle 50. After the investment has hardened, the muffle base 10, muffle gauge 20 and sleeve 30 are removed. After the wax filling has melted out in the preheating furnace, ceramic mass in the form of ceramic pellets and the press die 60 are introduced into the press die channel 52. The muffle 50 is now placed in the press furnace and placed on the base plate 500 of the press furnace. For this purpose, the muffle 50 with its recesses 51 is placed over the temperature sensor 501 and plugged on. Now the muffle, ceramic pellet and press ram are heated until the press temperature is reached. In contrast to the prior art, the reaching of the pressing temperature is now measured with the aid of the 3 cm long temperature sensors 501 in the then approx. 3 cm deep recess 51 in the immediate vicinity of the object shape 140. Only after reaching the object 40, 140 or its directly Press channel 41 measured press temperature approximately in the center of the muffle, then the pressing process is triggered with optimal flowability of the ceramic mass. The temperature can be measured continuously as well as at short, regular intervals (eg every 3 seconds). The pressing process can then be triggered both manually and automatically.

Claims

claims

1. Process for the production of press ceramics in the

Dental technology, comprising the production of a muffle, the introduction of the muffle into a ceramic press furnace, the heating of a ceramic pellet and the pressing of a press ceramic object, characterized in that the temperature inside the muffle (50) is measured and the pressing process when the pressing temperature is reached inside the muffle (50) is triggered.

2. The method according to claim 1, characterized in that the pressing process is triggered automatically when the pressing temperature is reached.

3. The method according to claim 1 or 2, characterized in that the temperature is measured by means of at least one temperature sensor (501) in at least one recess (51) of the muffle (50).

4. The method according to claim 3, characterized in that the muffle (50) with its at least one recess (51) on the at least one temperature sensor (501), which is integrated in the base plate (500) of the ceramic press furnace, is placed.

5. The method according to any one of the preceding claims, characterized in that the temperature is determined continuously.

6. The method according to any one of claims 1 to 4, characterized in that the temperatures are measured at regular time intervals.

7. ceramic press furnace, in particular for performing the method according to claim 1, characterized in that in the bottom plate (500) at least one

Temperature sensor (501) is integrated.

8. Ceramic press furnace according to claim 7, characterized in that a plurality of temperature sensors (501), in particular two or three, are provided.

9. ceramic press furnace according to claim 7 or 8, characterized in that a muffle (50) with at least one recess (51) on at least one temperature sensor (501) can be placed.

10. muffle, in particular for performing the method according to claim 1, characterized in that the muffle (50) has at least one recess (51) into which at least one temperature sensor (501) can be inserted.

11. A muffle according to claim 10, characterized in that the recess (51) is arranged in close proximity to at least one press ceramic object (40, 140).

12. Muffle according to claim 10 or 11, characterized in that the recess (51) is formed in the bottom region of the muffle (50).

13. Muffle according to one of claims 10 to 12, characterized in that a plurality of recesses (51), in particular two or three are formed.

14. Muffle according to one of claims 10 to 13, characterized in that the recess (51) is cylindrical or designed as a circumferential ring groove.

15. Muffle gauge, in particular for producing a muffle according to claim 10, characterized in that the muffle gauge (20, 120, 200) at least one elevation (23,

24, 123, 223, 224, 225).

16. Muffle gauge according to claim 15, characterized in that the at least one elevation (23, 24, 123, 223, 224, 225) with the muffle gauge (20, 120, 220) is integrally formed.

17. Muffle gauge according to claim 15 or 16, characterized in that several elevations (23, 24, 123, 223, 224, 225), in particular two or three, are provided.