The present invention relates to a method for producing a bridge structure with or for tooth-simulating parts from a ceramic blank body. An outer shape of the bridge structure is milled or formed in the body, together with sections retaining the bridge structure in the blank. The invention also relates to an arrangement at or for a bridge structure intended or provided for tooth-simulating parts of ceramic presintered material.

The bridge structure will be able to be provided with recesses for tooth remnants on which the bridge structure is to be applied. The bridge structure can be formed with outer parts which are applied to the tooth remnants and are to be machined, for example by milling, electroerosion, etc. Alternatively, the bridge structure comprises tooth simulations. It has been proposed that the bridge structure must assume a hard- sintered state during the machining, which imposes strict machining requirements, among other things from the point of view of time. There is also a need for the machining to be able to be performed with less specialized tools, for example drills, and with faster processing times. The object of the invention is to solve this- problem among others. In accordance with the concept of the. invention, the machining of the bridge structure will be able to be performed with the ceramic material in a semi-sintered state. In this connection, further measures are needed to be able to maintain the manufacturing precision, for example of 0.1 - 0.5 mm. The invention solves this problem too. There is also a need to be able to design the bridge structure in such ■ a way that any subsequent machining, when the bridge structure assumes a hard-sintered state, will be made easier. The invention solves this-problem too.

The feature which can principally be regarded as characterizing a method according to the invention is, inter alia, that the presintered bridge structure is released from the blank via the aforementioned sections and is placed in a machining arrangement with a support for the respective bridge structure part and/or tooth- simulating part, and that the bridge structure thus released and supported is machined in the presintered state.

In one embodiment, the tooth-simulating parts and/or bridge structure parts and/or ' blank are supported against one or more bearing surfaces included or used in or at the machining arrangement. The, central parts of the 'bridge structure and/or parts of the blank are in this way prevented from downward or upward bending tendencies of the parts of the bridge structure when the bridge structure and/or the blank are exposed to actuating forces during the machining. The sections are formed with material recesses or break markings at which the bridge structure is removed from the blank in its presintered state. The presintered bridge structure can be anchored to the blank only via a small number of sections, for example two sections. The blank body can be configured with a rod shape, and the bridge structure and the sections are milled with the aid of a milling tool which is applied in a single direction toward one side of the rod. The break markings can be arranged in close proximity to the bridge structure.

The feature which can be regarded as principally characterizing an arrangement according to the invention is that the bridge -structure in its presintered state can be retained in a first stage in the blank by means of retaining sections which extend between the blank and the bridge structure. The latter can be removed from the blank by cutting-off of the sections. The bridge structure in its presintered state can also be placed in a machining arrangement which supports the bridge structure and/or tooth-simulating parts during machining.

The bridge structure is assigned a manufacturing precision in the range of 0.1 - 0.5 mm despite the production being carried out in the ceramic material's presintered state. Further characteristics of the arrangement will become evident from the attached dependent claims.

By means of what has been explained above, the bridge structure can be produced and machined with the desired precision despite the ceramic material assuming only a presintered state.

Presently proposed embodiments of a method and an arrangement according to the invention will be described below with reference to the attached drawing, in which:

Figure 1 shows a side view of a blank and, profiled in the latter, a bridge structure which is retained in the blank by means of retaining sections,

Figure 2 shows a side view of a rod-shaped, blank,

Figure 3 shows an end view of the rod-shaped blank according to Figure 2,

Figure 4 shows the bridge structure removed from the blank and mounted on a bearing surface, and

Figure 5 shows, in a ' vertical cross section, the configuration of a retaining section.

A rod-shaped blank 1 is shown from the side in Figure 1. Profiled in the blank, for example by milling at right angles to the plane of the paper, there is, on the one hand, a bridge structure 2 and, on the other hand, retaining sections 3 which in a first stage retain the bridge structure in the blank. The number of sections may vary, for example between 2 and 6, preference being given to selecting a small number of sections, for example two, even though Figure 1 shows a greater number. The blank, the bridge structure and the sections are made of a ceramic material, for example zirconium oxide. The ceramic material assumes a presintered state, meaning that it has been sintered in a heating furnace at 8000C for 1 - 2 hours. Such presintering means that the original powder composition shrinks by ca. 30%. The milling groove in such presintered material is shown by reference number 4 in Figure 1 and can be produced by a milling tool in a relatively short time, for example a 50% shorter time, and exposes the milling tool to much less wear, for example 75% less wear. The bridge structure comprises a central part 2a and two outer parts 2b and 2c, and web parts 2d and 2e joining the parts 2a-2c together.

The blank 1 is mounted on a first bearing surface 5 before the milling takes place. The support and securing/clamping against the flat bearing surface 5 means that the rod is not bent downward or affected by the forces which the machining in question generates. The supporting surface or flat surface 5 is in the present case arranged at right angles to the machining direction, which is shown by the arrow 7 for a tool 6. The rod-shaped ceramic and presintered material is shown from one end in Figure 3. The sintering process, the milling process and the tool used can be of any type known per se and will therefore not be described in detail here. In Figures 2 and 3, a machining arrangement is indicated symbolically by reference number 8.

Figure 4 shows the bridge structure from one end . and released from the blank by cutting-off of said sections 3. The bridge structure can be placed on a support surface in said machining arrangement or in another machining arrangement 8' . The support surface 9 can consist of another support surface or, in an alternative embodiment, can be formed by .the first support surface 5. In the production of the bridge structure 2a - 2e, the latter can be machined, for example, by electroerosion of a type known per se. The anode of the latter equipment has been designated by 10 in Figure 4, and the direction of action of the anode on the bridge structure has been indicated by 11. The bridge structure is clamped and forced downward toward the surface 9 in Figure 4. The clamping member which cooperates with the top face of the bridge structure is indicated symbolically by reference number 12, and its direction of action on the bridge structure is indicated by reference number 13. The bridge structure is provided with cooperating parts 14, 15, 16, 17 and 18 which cooperate with the support surface 9. Forces F which attack the bridge structure during the machining cannot therefore cause any downward or upward bending tendencies in parts of the bridge structure. The corresponding force for the milling tool 6 in Figure 2 has been indicated by F' .

Figure 5 shows a . section 3 in detail. The section has a thickness t and a height H corresponding to the width of the groove 4. The thickness t of the section is chosen as a function of the number of sections and/or the positions of the sections. The section or the sections can be • provided with one or more break markings 19 which facilitate cutting of the section 3 when the bridge structure is removed from the blank. The break marking is placed a short distance L from the bridge structure 2a. This positioning of the break marking means that a remaining part 3a is easily removable upon finishing of the bridge structure, which can be hard-sintered at the finish. A cutting tool is indicated symbolically by 20 and the direction of the cutting tool during cutting of the section 3 in Figure 5 is shown by 21. In the case where the bridge structure is formed with a tooth simulation 22 (see Fig. 4), the tooth simulation in question has a support part that can cooperate with the support surface 9. The reference number 21 designates a grinding or polishing tool, and the arrows 22 and 23 indicate directions of movement for this tool. F'' represents actuating forces for these machining functions.

The invention is not limited to the embodiment described above by way of example, and instead it can be modified within the scope of the attached patent claims and the inventive concept.