Abstract:
In a dental furnace that comprises a firing chamber ( 12 ) having a base and at least one receiving portion for dental restoration parts ( 40 ) it is provided that the receiving portion comprises a plurality of support elements ( 26 ) that are arranged adjacent to one another and in particular have the same thickness, wherein said support elements ( 26 ) support the dental restoration part ( 40 ) during the firing process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of European Patent Application No. 10 161 640.7, filed Apr. 30, 2010, which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF INVENTION 
     The invention relates to a dental furnace, and more particularly to a dental furnace having an effective firing base. 
     DE 26 32 846 and U.S. Pat. No. 4,139,341, which is hereby incorporated by reference, disclose a dental furnace in which a hood-shaped firing chamber comprises a bottom that is configured as a base for the material being fired. The base for the material being fired is approximately arranged at the same level as the surrounding areas, thus substantially simplifying the handling. 
     Dental furnaces of this kind have stood the test of decades. 
     A similar dental furnace for example is known from DE 199 05 666 and U.S. Pat. No. 6,252,202 which is hereby incorporated by reference. This dental furnace also comprises a hood-shaped firing chamber that may be moved vertically relative to a firing platform. The firing platform is supported on an insulation plate and is designed to receive the dental restoration part by means of a recess. 
     For the burning of dental ceramics it is very important that a precise temperature profile is complied with during the burning or firing process. A temperature profile of this kind is ensured by controlled heating via one or more heating coils, wherein one temperature sensor or more temperature sensors are destined for controlling the interior temperature of the firing chamber. For financial reasons it is desirable to limit the number of temperature sensors, in particular in the case of vacuum dental firing furnaces as the passageways always must be sealed in a particular manner. 
     Typically, the dental restoration parts are centrally arranged in the firing chamber. Often, however, the insertion does not exactly take place in the center, or several dental restoration parts are burned or fired at the same time in order to considerably increase the efficiency of the firing process in this manner. 
     To ensure a given and uniform temperature in the firing furnace though, it is frequent practice to produce the receiving section for the dental restoration parts, e.g. the base for the material being fired, according to above-mentioned DE 26 32 846 with a good thermal conductivity and solid design, as it is also provided for example in the firing furnace according to DE 195 42 984 and U.S. Pat. No. 5,788,485, which is hereby incorporated by reference. 
     In order to shorten the firing cycle it has become known to accelerate the cooling down by means of opening the hood of the dental furnace. In this way, a temperature gradient is frequently generated in the receiving section, which may also result in the breakage of the receiving section. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of providing a dental furnace that is improved with regard to durability without impairing the exact implementation of the desired temperature profiles within the entire firing chamber. 
     This object is inventively solved by the independent claims. Advantageous further developments emerge from the subclaims. 
     According to the invention it is intended to provide the receiving section with a plurality of support elements that are arranged next to one another, for example in the form of a matrix. Surprisingly, the support elements do not break even in the case of being very thin, for example 3-5 mm, as long as the diameter of the support elements is significantly smaller than the diameter of the firing chamber, so that for example more than 10 support elements may cover the base of the firing chamber. 
     It is particularly favorable, if several support elements together form a support plane and in particular support the dental restoration part during the firing or burning process. The support elements are preferably arranged next to each other and have the same thickness in case of the same base level. If the base, however, is slightly concavely arched for example, it is also possible to use slightly thicker support elements in the middle and thinner support elements towards the outside. The top side of the support elements then practically ends on the same level so that a support plane for the dental restoration part is possible. 
     It is particularly preferred if the support elements have a good thermal conductivity. Surprisingly, this also ensures a uniform temperature within the firing chamber, as long as the firing furnace is not open. The support elements obviously well conduct the heat by means of the abutment against each other, and also the firing chamber base permits a homogenization or equalization of the temperature profile. 
     At the same time, the support elements protect the firing chamber base, and surprisingly tests did not at all exhibit any damages through cracks, even if the hood of the dental furnace had been opened, what is probably attributed to the lowering and thus to a better protection of the firing chamber base. 
     According to the invention it is particularly favorable that a multi-point support is provided for the restoration part. Eventual non-planar top sides of the dental restoration parts are compensated in this manner, and the inclination of the dental restoration part having a non-planar bottom side, to a slight tilting movement is considerably smaller, so that the danger of unwanted vibrations is also reduced. 
     A particularly favorable embodiment of the invention provides that the substantially disc-shaped support elements cover the firing chamber base as much as possible, that is to say they fill the entire area to the maximum. In the case of using round discs, it is to be understood that clearances remain, even if the discs are arranged in close package next each other. 
     If an entire coverage of the firing chamber base with round discs is desired, it is also possible to use a second layer of support elements that is arranged offset relative to the first layer on top thereof, so that the remaining gaps of the first layer are covered. 
     It is also possible to use any other shape of support elements instead of the round discs, for example triangle-shaped, hexagonal-shaped, square-shaped, non-square rectangular shaped or for example cross-shaped support elements. 
     In particular cross-shaped support elements may be arranged next to one another in a positive-locking manner so that they fill the firing chamber base in the area of the support base for the material to be fired without gaps and are connected in a positive-locking manner. 
     A particularly favorable embodiment provides that each support element comprises a substantially plane surface. 
     A particularly favorable embodiment provides that the support elements in the top view have a geometric form, wherein the geometric shapes of adjacent support elements are identical. 
     A particularly favorable embodiment provides that at least a portion of the surface of the support elements ( 26 ) comprises a structure for generating a multi-point, multi-line or multi-area support plane. 
     A particularly favorable embodiment provides that the support elements in the top view have the same geometric shape, and in particular fit together or mate with one another. 
     A particularly favorable embodiment provides that each support element has a width and/or a length that amounts to more than twice the height thereof, in particular approximately to five times the height thereof. 
     In a particularly favorable embodiment it is provided that the support elements are arranged on the base of the firing chamber of the dental furnace in close package, if applicable leaving slots and/or gaps and in particular leaving a margin or edge distance to the walls of the firing chamber. 
     In a particular favorable embodiment it is provided that support elements adjacent to one another at least partially abut against each other, and wherein outer support elements are arranged with a clearance or margin to the walls of the firing chamber of the dental furnace, said clearance or margin at least corresponding to the difference between the added up expansion path of the support elements upon heating from room temperature to a maximum of 1800° C., and the expansion path or movement of the base of the firing chamber upon heating from room temperature to a maximum of 1800° C. 
     In a particularly favorable embodiment it is provided that the support elements are disc-shaped and in particular at least partially are formed of Al 2 O 3  and/or SiNi and/or Mullite and/or Cordierite and/or AIN and/or AlTi and/or SiC and/or SiO 2  and/or MgO and/or porcelain. 
     In a particularly favorable embodiment it is further provided that the support elements are arranged in a multiple arrangement of at least two support elements on the base of the dental furnace in a distributed manner. 
     In a particularly favorable embodiment it is provided that each support element has a point-symmetric shape such as a circle, a square, a hexagon, a cross or a star. 
     In a particularly favorable embodiment it is provided that at least one support element comprises a round shape or an outer contour that deviates from the circular shape. 
     In a particularly favorable embodiment it is provided that the support elements are formed in a disc-shaped manner from a solid and unfoamed material, in particular consist of ceramics whose softening temperature is higher than the maximum operating temperature of the dental furnace. 
     In a particularly favorable embodiment it is provided that at least two support elements engage positively one into the other. 
     In a particularly favorable embodiment it is provided that the receiving section comprises at least two layers of adjacent support elements, said layers being arranged one above the other. 
     In a particularly favorable embodiment it is provided that the support elements are of differing height, but at least end on same plane with respect to the top layer thereof in case several layers are arranged on top of each other. 
     In a particularly favorable embodiment it is provided that between the base of the dental furnace and the receiving section one at least one-piece disc having a high thermal conductivity is arranged. 
     In a particularly favorable embodiment it is provided that the disc is formed of SiC. 
     In a particularly favorable embodiment it is provided that the support elements substantially have a flat upper surface, if applicable slightly sloping towards their edges, and form a multi-point or multi-area support for dental restoration parts. 
     In a particularly favorable embodiment it is provided that the support elements are supported or applied on the firing chamber base that has a larger thermal conductivity than the heat insulating material of the dental furnace and in particular receives the support element in a positive-locking manner, said support elements in particular being formed of SiC. 
     In a particularly favorable embodiment it is provided that the support element for a dental furnace is characterized by the characterizing features of one of the preceding claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Further advantages, details and features emerge from the following description of several exemplary embodiments of the invention in conjunction with the drawings, in which: 
         FIG. 1  illustrates a schematic view of an inventive dental furnace in one embodiment; 
         FIG. 2  illustrates an enlarged view of one detail of  FIG. 1 ; 
         FIG. 3  illustrates a top view of one detail of a dental furnace according to the invention showing support elements and the firing chamber base; 
         FIG. 4  illustrates a modified embodiment of a dental furnace according to the invention in the representation of  FIG. 3 ; 
         FIG. 5  illustrates a modified embodiment of a dental furnace according to the invention in the representation of  FIG. 3 ; 
         FIG. 6  illustrates a modified embodiment of a dental furnace according to the invention in the representation of  FIG. 3 ; 
         FIG. 7  illustrates a modified embodiment of a dental furnace according to the invention in the representation of  FIG. 3 ; 
         FIG. 8  illustrates a modified embodiment of a dental furnace according to the invention in the representation of  FIG. 3 ; 
         FIG. 9  illustrates a modified embodiment of a dental furnace according to the invention in the representation of  FIG. 3 ; and 
         FIG. 10  illustrates a modified embodiment of a dental furnace according to the invention in the representation of  FIG. 3 . 
         FIG. 11  illustrates a modified embodiment of a dental furnace according to the invention in the representation of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     The dental furnace  10  of  FIG. 1  comprises a firing chamber  12  that is formed with the aid of side walls and a top wall forming a hood  14 . The base  16  of the firing chamber  12  is formed via a lower part  18  of the dental furnace  10 . In a manner known per se, the dental furnace  10  comprises a control panel  20 , and the lower part  18  and the hood-shaped upper part  14  are connected with one another via a hinge  22 . 
     In the illustrated embodiment, the dental furnace  10  comprises a vacuum connection  24  via which the firing chamber  12  with closed hood may be subjected to a vacuum. 
     According to the invention, the firing chamber base  16  is covered by support elements  26 , whose design becomes better apparent from  FIG. 2 . In this connection, the lower part  18  comprises a recess  28  in the area of the firing chamber base  16  and the height of the recess exactly corresponds to the height of a support element  26 . 
     From  FIG. 2  it becomes apparent that the support elements  26  are formed and arranged so that they practically completely fill the recess  28 . The support elements  26  may be formed in any suitable manner, however, they must be temperature-resistant up to a temperature that is clearly above the rated temperature of the firing furnace, e.g. 1600° C. They may entirely or partially consist of Al 2 O 3 . If the coefficient of thermal expansion of the firing chamber base  16  and the coefficient of thermal expansion of the support elements  26  differ from one another, this may be easily compensated by means of the clearance  30  between the support elements  26  and the edge  32  of the recess  28 . 
     It is to be understood that according to the invention the arrangement, number and shape of the support elements  26  may be adapted to the requirements in a wide range. The  FIGS. 3 to 10  illustrate examples thereof. Thus,  FIG. 3  shows circular, that is to say disc-shaped support elements  26  that may substantially be formed in a flat-cylindrical manner or that may comprise crowned roundings  34  at the edges thereof as shown in  FIG. 2 . 
       FIG. 4  shows a multiple arrangement of triangle-shaped arrangements of support elements  26 . In this embodiment it is favorable that primarily the central region  38  of the support element arrangement is covered in a gap-free manner, whereas at the edge area of the support element arrangement free spaces arise, that is to say the base  18  of the firing chamber is exposed at this position. 
       FIG. 5  shows cross-shaped support elements  26  that may even be arranged in a still more unconstrained manner as shown in  FIG. 6 , but that are partially hooked into one another so that they may be together displaced or twisted. 
       FIG. 7  provides a hexagonal design of the support elements  26  that exposes considerable edge regions  38  of the firing chamber base  16 , but fully covers the central area  38  of the firing chamber base. 
       FIG. 8  also illustrates cross-shaped support elements  26 . These support elements have longer and thinner cross arms so that altogether, the result is a slimmer design of the cross if compared to the embodiment according to  FIG. 5  and  FIG. 6 . 
     As can be seen in  FIG. 7  and  FIG. 8 , the dental restoration parts  40  that are illustrated as a schematic circle in a dotted line, may be centrally arranged in the firing chamber. For example, the dental restoration part  40  may also be accommodated and supported in a plaster muffle or the like. 
     By means of the close interlocking, especially in the embodiments according to  FIGS. 5 to 10 , a good heat transfer between the disc-shaped support elements  26  is achieved, said heat transfer providing for the homogenization of the temperature within the firing chamber. 
       FIG. 9  shows that the firing chamber base may also be covered partially, for example by square-shaped support elements  26 . 
     A further embodiment of the inventive support elements is illustrated in  FIG. 10 . In this embodiment, cross-shaped support elements  26  are positively connected with one another leaving gaps  42 . 
     Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.