Dental cooling method and dental cooling device

Abstract

A dental cooling device is provided, comprising a muffle (12) and a medium (30) as cooling source. The medium (30), in particular a liquid medium (30), is stored at least in the outer region of the muffle (12) and has an evaporation temperature higher than the room temperature. The quantity of medium (30) is calculated in advance such that the enthalpy of evaporation of the medium is substantially destroyed or consumed when cooling the muffle (12) to the evaporation temperature.

Claims

1. A dental cooling method for cooling a muffle (12) comprising cooling the muffle with a cooling source (12) to a divesting temperature of less than 80° C., wherein the cooling source is a medium (30) having a melting or evaporation temperature higher than room temperature, wherein the medium (30) is fed to the muffle (12), wherein the cooling is effected by latent heat accumulators, wherein a quantity of the medium (30) is at least sufficient such that the muffle (12) is cooled to at least one phase transition temperature of the medium (30), and wherein the medium (30) is accommodated in a high-temperature-resistant, fibrous mass comprising a high-temperature thermal insulation fiber brought into contact with the muffle (12) for cooling the muffle.

2. The method according to claim 1 wherein the divesting temperature is less than 50° C., wherein the medium (30) comprises a solid or liquid medium (30), wherein feeding the medium to the muffle comprises bringing the medium into direct or indirect contact with the muffle, wherein the quantity of the medium (30) is calculated in advance.

3. The method according to claim 1, wherein during cooling to the at least one phase transition temperature, the thermal energy of the muffle is converted substantially into the enthalpy of vaporization and/or enthalpy of fusion of the medium (30), and is consumed.

4. The method according to claim 1, wherein the cooling of the muffle (12) by means of the cooling source is performed to a temperature below the phase transition temperature.

5. The method according to claim 1, wherein the muffle (12) is cooled by contacting from a temperature above a phase transition temperature to a temperature below the phase transition temperature.

6. The method according to claim 1, wherein the medium (30) is predominantly supplied to a lateral surface of the muffle (12) or is brought into direct or indirect contact with the lateral surface of the muffle.

7. The method according to claim 1, wherein the muffle (12) is at least partially surrounded by a sleeve (14) providing the medium (30) for cooling the outside of the muffle.

8. The method according to claim 7, wherein the muffle (12) is completely surrounded and circumferentially surrounded by the sleeve (14).

9. The method according to claim 1, wherein the high-temperature thermal insulation fiber that is brought into contact with the muffle (12) for cooling the muffle is performed by mutually rolling at selective locations of the muffle (12).

10. The method according to claim 9, wherein the high-temperature-resistant fibrous mass is brought into contact with the muffle (12) for cooling thereof by mutually rolling at all locations of the circumference of the muffle (12).

11. The method according to claim 1, wherein the medium (30), evenly distributed around the periphery of the muffle (12), is supplied to the muffle at the start of the cooling method by spraying or immersion in a suitable container or both by spraying and immersion.

12. The method according to claim 1, wherein the medium (30) is completely liquefied or evaporated in and at the muffle (12) at the end of the cooling method.

13. The method according to claim 1, wherein a moisture sensor or a plurality of moisture sensors detect the moisture content of the medium (30) or the muffle (12) or the temperature of the muffle (12) at the end of the cooling process, and wherein a control device initiates divesting of a dental restoration part from the muffle (12) when the moisture and/or temperature measured falls below a predetermined threshold value.

14. The method according to claim 1, wherein a pot-shaped container is provided for receiving the medium (30), an inner diameter of which pot-shaped container exceeds an outer diameter of the muffle (12) by a small amount, and wherein an annular gap resulting between the muffle (12) and the container is calculated with respect to a volume such that the volume corresponds to a quantity of the medium (30) of which an enthalpy of vaporization is to be consumed.

15. The method according to claim 1, wherein, when calculating an enthalpy of fusion and/or enthalpy of evaporation, addition or deduction for the mass of the cooling medium to be provided is included, depending on whether the divesting temperature is below the melting temperature or evaporation temperature (addition) or above (deduction).

16. The method according to claim 1, wherein, at the start of the cooling method, the temperature of the muffle (12) is detected, and wherein cooling is enabled by the cooling medium as soon as the temperature of the muffle (12), which is freely cooling down, falls below a predetermined threshold value.

17. The method according to claim 1, wherein after completion of the cooling method, a dental restoration part in the muffle (12) is divested.

18. The method according to claim 1, wherein after complete liquefaction or evaporation of the cooling medium, a dental restoration part in the muffle (12) is divested by sand blasting.

19. A dental cooling device comprising a muffle (12) and a medium (30) as cooling source, wherein the medium (30) is stored at least in an outer circumferential region of the muffle (12) and has an evaporation temperature exceeding room temperature, wherein the quantity of the medium (30) is calculated in advance such that the thermal energy of the muffle is substantially converted into enthalpy of vaporization and/or enthalpy of fusion of the medium (30) as a result of cooling the muffle (12), and the thermal energy is consumed, and wherein the medium (30) is accommodated in a high-temperature-resistant, fibrous mass comprising a high-temperature thermal insulation fiber brought into contact with the muffle (12) for cooling the muffle.

20. The dental cooling device according to claim 19, wherein the medium comprises a liquid medium (30).

21. The cooling device according to claim 19, comprising one or more of the following: wherein the muffle (12) is cylindrical, wherein the cooling medium is located on a lateral surface and in an upper or outer region of the muffle (12), and wherein a sleeve (14) impregnated or filled with the medium (30) surrounds the muffle (12).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, details and features will arise from the following description of an example of the invention, while making reference to the drawing, wherein:

(2) FIG. 1 is a schematic representation of a muffle including the dental restoration parts and a sleeve, which are indicated in dashed lines, to represent two embodiments of a cooling method according to the invention and a cooling device according to the invention;

(3) FIGS. 2a to 2d are schematic graphical representations of temperature gradients and temperatures of prior art and according to the invention;

(4) FIG. 3 is a diagram showing the specific enthalpy of fusion and specific enthalpy of vaporization of water; and

(5) FIG. 4 is a schematic representation of another embodiment of a dental cooling device according to the invention.

DETAILED DESCRIPTION

(6) FIG. 1 shows a schematic representation of a dental cooling device 10 according to the invention. It comprises a muffle 12, which is surrounded by a sleeve 14 on its circumferential surface 16, wherein in the example shown the sleeve 14 slightly protrudes over the muffle.

(7) At the beginning of the cooling, the medium is cooler than the muffle, thus forming a heat accumulator, i.e. a latent heat accumulator for controlled absorption of heat energy from the muffle.

(8) The muffle has a press aperture 18 known per se, in which an Al.sub.2O.sub.3 piston 20 is located, separating the press plunger from the blank prior to pressing. In addition, feeder channels 22 extend into the muffle, through which the material to be compressed may penetrate into mold cavities, in which, following pressing, there are dental restoration parts 24.

(9) As it may be seen, they extend slightly outside the channel of the press aperture 18, i.e. slightly more adjacent to the lateral surface 16.

(10) A spray device 26 is also schematically represented in FIG. 1, as is a dashed container 28, which accommodates the muffle 12 and the sleeve 14.

(11) In order to realize the method according to the invention, the muffle 12 is provided with the sleeve 14. The sleeve consists of a high-temperature thermal insulation fiber, such as that offered by Rath. The fiber is heat-resistant up to 1200 degrees Celsius, so that it can be laid over the hot muffle without any damage.

(12) The muffle 12 with the sleeve 14 is inserted into the vessel 28. In this condition, the drum 28 is empty when the muffle is hot, i.e. it is not filled with a medium, such as water.

(13) Following insertion of the muffle 12 into the vessel 28, the spraying device 26 is carefully operated for the first time. The spraying device 26 is filled with the medium 30, for example water or any other suitable cooling heat transfer medium.

(14) The medium 30 is sprayed and reaches the sleeve. Spraying occurs slightly above the center, i.e. at about 70% of the height of the muffle, and is distributed both vertically and horizontally.

(15) Then either the muffle or the spraying device is turned so far that a precedingly dry region of the sleeve 14 can be treated by the spraying device 26.

(16) This is continued until the medium 30 is applied to all circumferential regions of the sleeve 14 by the spraying device 26.

(17) The medium 30 is initially distributed both vertically and horizontally in the outer regions of the rather thick sleeve 14, so that there is uniform penetration of humidity.

(18) It also diffuses inwardly, i.e. towards the muffle 12.

(19) As soon as it meets the lateral surface 16 of the muffle, it evaporates, so that appropriate cooling of the lateral surface occurs.

(20) This is done evenly from all sides after the sleeve 14 has been evenly wetted.

(21) Wetting is maintained and increased, so that the cooling is comparatively more intensive.

(22) At the same time, the temperature difference between the cold medium 30, which, for example, is at room temperature, and the hot muffle 12 decreases.

(23) Finally, the vessel 28 can also be filled with the medium, but not before the cooling cycle is almost completed. This causes the muffle 14 to become intensively wetted across a large area, which is to further cool the muffle.

(24) Due to continuous and constantly increasing wetting the muffle 14, cooling efficiency will be increased. This results in that no exponential temperature gradient is created, but a temperature gradient with a constant slope, at least up to just above room temperature.

(25) This is shown in FIG. 2.

(26) FIG. 2a shows a natural cooling, as it is widely realized, according to which the temperature drops in the form of an e-function.

(27) The temperature gradient, as viewed from the inside to the outside direction, i.e. from the hot dental restoration part to the outside, at the cooling surface, is the first derivative of the temperature.

(28) It is initially large and then sharply declines from the maximum value of the temperature gradient, after the first derivative of an e-function in turn is an e-function.

(29) This is shown in FIG. 2b.

(30) The temperature gradient TG shown herein is the local temperature gradient, i.e. as measured at a point on the muffle just outside the dental restoration parts, but regarded over time.

(31) According to the invention, the temperature is not reduced in the form of an e-function, but as a constant time gradient TG.

(32) Accordingly, a constantly decreasing straight line results for the temperature according to the invention, until this in turn changes into an e-function near room temperature, cf. FIG. 2c.

(33) Accordingly, the local temperature gradient according to the invention, as represented over time, is the first derivative of this straight line, i.e. it is initially constant, up to the start of the e-function.

(34) This is shown in FIG. 2d.

(35) As can be seen from the comparison of FIGS. 2b and 2d, according to the invention, the maximum temperature gradient TG, which is responsible for the generation of stress cracks, is considerably lower than in prior art.

(36) According to the invention, it is provided to limit the quantity of medium used for cooling in such a way as specified herein- or to calculate it in advance such that the medium has been evaporated by the time when the cooling cycle is completed. This prevents the muffle from being impregnated with water, which would make it very hard and could only be removed using very high effort of sandblasting.

(37) It may as well be advantageous to provide a holding time of, for example, 1 minute, at the end of the cooling process according to the invention, during which residual water will be evaporated or vaporized.

(38) While cooling times between 60 min and 90 min, depending on the size of the muffle used, can be expected while using typical cooling, the cooling time could be reduced to 5 min to 15 min according to the invention, without compromising the quality of the dental restoration part, i.e. also without stress cracks.

(39) These cooling times are significantly lower than the cooling times achievable with a fan, reducing them, for example, to ⅓ thereof (10 min compared to 30 min).

(40) FIG. 3 shows the composition of the specific amount of heat to be applied. As can be seen, the specific enthalpy of evaporation, herein that of water, is the clearly predominant part. The amount of cold to be applied for cooling from 100 degrees to 15 degrees—or the corresponding amount of heat—is only a fraction, for example ⅛, of the enthalpy of evaporation.

(41) This explains the specific effectiveness of the method according to the invention.

(42) It is also evident that the enthalpy of fusion is significantly greater than a normally stored quantity of heat lacking phase transition, but significantly lower than the specific enthalpy of boiling.

(43) FIG. 4 shows how the muffle 12 can be rolled on a sleeve 14. The medium 30 is stored in the sleeve as a latent heat storage and is evaporated following rolling, so that it exits the sleeve as vapor 32. The heat energy of the muffle 12 transferred to the sleeve is represented by Q.sub.M in FIG. 4.

(44) The muffle 12 is rolled once completely to the right on the sleeve 14. The stored water 30 has evaporated to water vapor. The muffle 14 is in turn wetted again and the muffle 12 is unrolled across the muffle 14 to the left, i.e. in the opposite direction, again by at least one revolution.

(45) Herein, it is also possible to control the supply of medium 30, i.e. initially to supply a small amount of medium 30 and then to increase the amount supplied.

(46) The method according to the invention may also be performed in an automated manner. For example, it is possible to provide the spraying device 26 with a rotation guide according to FIG. 1 and to actuate it automatically, first to slightly actuate it and then to increase actuation.

(47) Alternatively, the vessel 28 or the muffle 12 may also be placed on a turntable and rotated continuously, while the medium 30 is fed gradually increasing.

(48) The vessel 28 and a support for the muffle 12 may also be configured such that the muffle 12 will first be slightly immersed and then will be immersed more and more, wherein a liquid level of the medium 30 exists in the vessel 28.

(49) The vessel 28 may also be considerably higher than shown in FIG. 1 and, for example, the muffle 12 may also be completely accommodated.

(50) Furthermore, it is also possible to spray or feed the medium 30 without using a sleeve 14. The spraying device 26 then sprays directly onto the muffle, and levelling is achieved by a more carefully spray distributing.

(51) It is also possible to automate the configuration according to FIG. 4. Rolling the muffle 12 on the sleeve 14 may occur in a controlled manner, for example by the muffle 12 being rotatably mounted on its axis and being rolled, whereby a back and forth movement in a horizontal direction occurs. Alternatively, the bearing of the muffle 12 may also be realized as being rotatable, and the sleeve 14 may be moved back and forth below the muffle. Herein, it is also possible to use any other suitable absorbent base or medium-receiving device instead of the sleeve 14, which makes it possible to absorb the medium 30 and release it again in the form of vapor.

(52) For example, a paraffin or a microcrystalline wax may also be used as a medium, which is dripped onto the base 14, while making use of the enthalpy of fusion of the paraffin.

(53) The paraffin may also be form-fittingly wrapped around or applied to a muffle, e.g. as a metallic sleeve still being elastically deformable but impermeable to liquid paraffin.