GB2064737A - Dental furnace furniture - Google Patents

Abstract

A saggar for supporting artificial teeth during furnace treatment comprises a refractory base plate 10 and a plurality of separate tooth- supporting pins 20 which each mount on the base 10 by co-operative engagement between a hemi- spherical protrusion 24 at the lower end and a complementary spherically curved surface of a recess 18 in the base forming a ball-and- socket joint. The parts are made of silicon nitride and sufficient frictional resistance is provided to enable each mounted support pin 20 to remain stationary in an upright position while permitting a limited extent of angular movement to accommodate dimensional variations and movement of the teeth during furnace treatment. <IMAGE>

Description

SPECIFICATION Dental furnace furniture This invention relates to dental furnace furniture, in particular saggars or support devices for supporting artificial teeth, composed of porcelain or metal for example, during firing or heat treatment which may be carried out in a furnace, for instance an atmospheric furnace or a vacuum furnace, in the manufacture either of individual teeth or of teeth incorporated into a dental bridge fitting which may be made of metal.

For carrying out such firing or heat treatment a saggar or support device is commonly provided which comprises a refractory base upon which there is a plurality of upstanding support pins and/or other support elements each adapted to support an individual tooth.

In the case of dental bridges or parts thereof, however, even if the number and distribution of such support elements provided is sufficient to give a wide range of spacings as will generally be required for accommodating bridges of different sizes, if the support elements are rigid and at fixed spacings on a one piece base plate dimensional changes occurring during firing, especially with metal bridge frames which have a high expansion coefficient, give rise to stresses that can easily result in facture of the base.

To overcome this problem it has hitherto been proposed to mount one or more of the support elements in the form of support pins on arms pivoted on the base so permitting some relative movement and/or to make up the base from separate relatively movable parts. Another proposal has been to fit such support pins to the base by flexible wire mountings.

An object of the present invention is to provide an improved form of dental saggar or support device embodying a simplified solution to the above-mentioned problem of accommodating dimensional changes during firing.

According to the invention, in a saggar or support device comprising a refractory base and a plurality of upstanding tooth support elements for supporting artificial teeth during firing or heat treatment in a furnace, at least some of the support elements mount in preselected locations on the base by co-operative engagement between complementary spherically curved mounting surfaces which in effect form ball and socket joints having sufficient frictional resistance to enable these respective elements to remain stationary in an upstanding vertical position but which permit a limited extent of angular movement away from the vertical.

The support elements may be in the form of pins of various shapes and sizes-commonly they will be of generally conical shape or of rod-like form. One or more of the support elements may be fixed, but in preferred embodiments each said movable support element terminates at the lower end in a spherically curved convex surface and the base, in its top face, is formed with a plurality of sockets each having a complementary spherically curved concave surface for receiving the lower end of a respective movable support element.The converse arrangement could also be adopted, however, in which the top face of the base is formed with a plurality of protrusions having a spherically curved convex surface and the movable support elements are formed at their lower ends with a socket or recess having a spherically curved concave surface adapted to fit upon the protrusions of the base.

The invention and practical embodiments thereof will be further described with reference to the accompanying drawings, in which: Figure 1 is a plan view of a typical base of a dental saggar in accordance with the invention; Figure 2 is a side elevational view of the base of Fig. 1 showing one possible configuration; Figure 3 is a view similar to Fig. 2 but showing an alternative configuration; Figure 4 is a fragmentary vertical crosssectional view through a socket of the base which corresponds to the configuration of Fig.

2 showing a tooth support pin mounted therein; and Figure 5 is a view similar to Fig. 4 where the base has the configuration of Fig. 3 and showing the modified form of tooth support pin provided in this case.

Referring first to Figs. 1, 2 and 4, the dental saggar illustrated therein has a base 10 consisting of a flat rectangular plate of moulded ceramic refractory material having flat upper and lower faces, 12 and 14 respectively, which are each formed at the middle of each edge with a shallow recess 1 6 to facilitate handling and gripping, by tongs for example, during manipulation in and out of the furnace.

As indicated, the upper face 1 2 is formed with an array of shallow holes or recesses forming sockets 1 8 each having a spherically curved concave surface adapted to receive the lower end of a tooth support pin 20 as shown in Fig. 4.

The support pin 20 is also formed of moulded ceramic refractory material and has a generally conical configuration terminating at its lower end in an annular shoulder 22 and a substantially hemispherical convex protrusion 24 having a curvature matching that of the sockets 1 8 in which it seats as shown.

The convex protrusion 24 and complementary socket 18 thus in effect forms a ball and socket joint for mounting the pin 20 on the base, permitting the pin to move angularly and tilt to a certain extent. Sufficient frictional resistance is provided by the area and nature of the interengaging surfaces of socket 18 and protrusion 24 to permit the pin 20 to seat in stable relationship and remain stationary in an upstanding vertical position whiie dental forms are positioned prior to firing. During use, however, for supporting an artificial tooth forming part of a bridge the pin can tilt to accommodate dimensional changes of the bridge during the heating and cooling associated with the furnace firing process, thereby protecting the base from serious mechanical stress.

It will be understood that a number of similar support pins 20 are provided for use with the base 10 and these are each mounted as required in appropriate sockets 1 8 selected to provide, in the case of a dental bridge, the desired spacing.

With the configuration shown in Fig. 4 it should be noted that the amount of angular movement or tilting is restricted by the annular shoulder 22 which will bear against the top face 1 2 of the base at the limit of the range of movement of the pin 20.

Referring now to the modification of Figs. 3 and 5, in this case the base, designated here by the reference 1 Oa, is formed on its underside 1 4a with a series of protrusions 30 located directly beneath the socket recesses which are each denoted by reference 1 8a As seen most clearly in Fig. 5, each recess 1 8a is deeper than the recesses 18 of the first embodiment and includes an outermost cylindrical portion and an innermost hemispherical portion. The corresponding tooth support pins are also modified- in shape and as shown at 20a in Fig. 5, each has a conical configuration which terminates at its lower end in a hemispherical protrusion 24a without any intermediate annular shoulder. Consequently, when the modified pin 20a is seated in the deeper form of socket 1 8a as illustrated, the maximum extent of angular tilting movement is limited by the conical surface of the pin contacting against the cylindrical wall of the outermost portion of the socket 1 8a Apart from the modifications illustrated and mentioned above, the saggar of this second embodiment is similar and is used in the same manner as that of the first described embodiment.

Various ceramic refractory materials are suitable for making both the base and the support pins, but a particularly advantageous material for this purpose is silicon nitride, especially reaction bonded silicon nitride, which has an excellent thermal shock resistance, low heat capacity and does not tend to react with the dental materials commonly used in making artificial teeth and dental bridges.

Claims (8)

1. A saggar or support device comprising a refractory base and a plurality of upstanding tooth support elements for supporting artificial teeth during firing or heat treatment in a furnace, wherein at least some of said support elements mount in preselected locations on the base by co-operative engagement between complementary spherically curved mounting surfaces, respectively on said support elements and base, which in effect provide ball and socket joints or mountings having sufficient frictional resistance to enable these respective movable support elements to remain stationary in an upstanding vertical position while permitting a limited extent of angular movement away from the vertical.

2. A device as claimed in Claim 1 wherein each said movable support element terminates at its lower end in a spherically curved convex surface and the base, in its top face, is formed with a plurality of sockets each having a complementary spherically curved concave surface for receiving the lower end of a respective said movable support element.

3. A device as claimed in Claim 2 wherein said sockets in the base have an outermost cylindrical portion and an innermost hemispherical portion and wherein the movable support elements each have a body portion terminating at the lower end in a hemispherical protrusion which provides said spherically curved convex surface and which is received wholly within a said socket when mounted in place.

4. A device as claimed in Claim 3 wherein the body portion of each said movable support element has a tapering configuration of which the surface profile merges smoothly into that of the hemispherical protrusion at the lower end.

5. A device as claimed in Claim 4 wherein the maximum extent of angular tilting movement of each said movable support element is limited by conically tapering surface areas of the body portion contacting against the wall of the outermost cylindrical portion of the base socket in which the support element is mounted during use.

6. A device as claimed in Claim 2 wherein the movable support elements each have a radially projecting portion or shoulder above the spherically curved convex surface at the lower end which projecting portion or shoulder is arranged so as to contact and bear against the top face of the base when, in use, the support element is tilted angularly on its mount thereby to limit the range of such angular movement of said element.

7. A device as claimed in any of the preceding claims wherein the base and the support elements are made of silicon nitride ceramic refractory material.

8. A saggar or support device forming an article of dental furnace furniture with a refractory base and separate support elements for artificial teeth, said base and elements being constructed substantially as herein described and as illustrated with reference to Figs. 1, 2 and 3 or as modified in Figs. 3 and 5 of the accompanying drawing.