Production of dental shaped parts composed of porous glass

Abstract

The invention discloses a blank for producing dental shaped parts which consists entirely of porous glass without crystalline portions. The density of the blank is between 50% and 95% of its theoretical density. It has a discoidal shape with a diameter of at least 20 mm. The blank is produced by a process in which glass powder is first pressed at a pressure of between 10 MPa and 300 MPa and this green body is (pre-)sintered at a temperature of between 580 C. and 750 C. to form a blank of porous glass without crystalline portions. From the obtained blank, monolithic dental shaped parts can be obtained by mechanical processing followed by sintering, wherein a process according to the invention for stabilizing the shape of the shaped parts is used.

Claims

1. A blank for producing dental shaped parts, characterized in that it consists entirely of porous glass without crystalline portions, wherein the density of the porous glass blank is between 50% and 95% of the theoretical density of the blank when it is in its densely-sintered state, and in that it has a disc-like shape with a diameter of at least 20 mm, wherein the glass consists of the following components: TABLE-US-00007 SiO.sub.2 55-65 wt.-% Al.sub.2O.sub.3 17-24 wt.-% K.sub.2O 5-9 wt.-% Na.sub.2O 7-11 wt.-% Li.sub.2O 0-1 wt.-% B.sub.2O.sub.3 0-2 wt.-% F 0-1 wt.-% TiO.sub.2 0-1 wt.-% ZrO.sub.2 0-2 wt.-% P.sub.2O.sub.5 0-1 wt.-% SnO.sub.2 0-1 wt.-% MgO 0-4 wt.-% CaO 0-4 wt.-% BaO 0-4 wt.-% Sb.sub.2O.sub.3 0-4 wt.-% CeO.sub.2 0-8 wt.-%.

2. The blank according to claim 1, characterized in that the density of the blank is between 55% and 85% of the theoretical density of the blank when it is in its densely-sintered state.

3. The blank according to claim 1, characterized in that the diameter of the disc-like shape is at least 50 mm.

4. The blank according to claim 1, characterized in that the thickness of the disk-like shape is more than 5 mm.

5. The blank according to claim 1, characterized in that the blank has at least one recess for clamping the blank during the processing thereof to form a dental shaped part, wherein the at least one recess is provided on the outer circumference of the blank.

6. The blank according to claim 1, characterized in that the density of the blank is between 70% and 80% of the theoretical density of the blank when it is in its densely-sintered state.

7. The blank according to claim 1, characterized in that the diameter of the disc-like shape is at least 80 mm.

8. The blank according to claim 1, characterized in that the thickness of the disk-like shape is between 5 mm and 30 mm.

9. The blank according to claim 1, characterized in that the ratio of the diameter to the thickness is 4:1.

10. The blank according to claim 1, characterized in that the ratio of the diameter to the thickness is 20:1.

11. Process for producing the blank according to claim 1, characterized in that glass powder is pressed at a pressure of between 10 and 300 MPa to form a green body and said green body is pre sintered at a temperature of between 580 C. and 750 C. to form the blank that consists entirely of the porous glass without crystalline portions.

12. Process for producing the blank according to claim 1, characterized in that glass powder is pressed at a pressure of between 100 and 200 MPa to form a green body and said green body is (pre)sintered at a temperature of between 620 C. and 660 C. to form the blank that consists entirely of the porous glass without crystalline portions.

Description

(1) There are shown in the drawings:

(2) FIG. 1 the representation of an X-ray diffractogram of blanks according to the invention,

(3) FIG. 2 the schematic representation of an embodiment of the process according to the invention for stabilizing the shape of monolithic dental shaped parts.

EXAMPLE 1

(4) A first glass powder with the chemical composition corresponding to Table 2 and the particle-size distribution corresponding to Table 3 was uniaxially pressed by means of a hydraulic pressing machine to form circular discoidal blanks (green bodies) with a diameter of about 100 mm and a thickness of 18 mm. The pressing force was between 800 kN and 2000 kN, preferably about 1200 kN.

(5) During the production of such discoidal blanks, it is advantageous if the glass powder used for the production is granulated with a binder. As a rule, this is achieved by a so-called spray granulation. Here, the glass powder is processed to form a granular material accompanied by simultaneous mixing with the binder. Such processes are known to a person skilled in the art.

(6) Three groups of blanks were then sintered at atmospheric pressure at 640 C., at 660 C. and at 680 C., respectively, during a holding time of 2 hours (Table 1). The preferred sintering temperature was 640 C. Higher temperatures led to increasingly hard blanks which could only be milled with difficulty (high tool wear). Below 640 C. the blanks became increasingly soft, with the result that the blanks had to be processed and treated carefully. The density of the blanks was 1.79 g/cm.sup.3 after the sintering at 640 C., 1.82 g/cm.sup.3 after the sintering at 660 C. and 1.87 g/cm.sup.3 after the sintering at 680 C.

(7) As explained in the description, the thus-produced blank consists of porous glass without crystalline portions. This is shown in FIG. 1 for the blanks which were produced according to Example 1. FIG. 1 is an X-ray diffractogram which was obtained using the blanks pressed and sintered according to Example 1. The intensity is plotted against the angle in the usual way. FIG. 1 shows no diffraction intensity maxima which would be characteristic for crystalline solids or crystalline portions in such solids. Only the known diffuse dispersion which is characteristic for amorphous substances is shown.

(8) Accordingly, the blanks produced according to Example 1 are amorphous solids without crystalline content.

(9) The blanks sintered at 640 C. were clamped in a holding element and processed by means of CAD/CAM milling processing taking into account the sintering shrinkage. Enlarged crowns corrected for the sintering shrinkage were thus milled from the blanks as monolithic shaped parts. The results are shown in Table 1.

(10) As represented schematically in FIG. 2, the thus-milled crowns 1 (enlarged by the sintering shrinkage) were fitted onto a model die 2 made of non-shrinking refractory material (investing compound Wilavest Quick from the applicant) and sintered onto the die in form-fitting manner in a dental furnace. FIG. 2 shows arrangement 3 of die 2 with fitted crown 1 before the sintering and arrangement 4 of die 2 with fitted crown 1 after the sintering. The sintering shrinkage occurring during sintering, which is about 10% in the present case, is indicated (on the right) by the arrows in arrangement 4.

(11) For easy removal of the crown, the die of refractory material was thinly coated with a high-temperature release agent (BN powder, applied with a brush; alternatively also as a spray). Such a release agent is, however, not strictly necessary. The model die itself was produced by pouring the refractory compound into so-called duplicating moulds or by milling from the corresponding material. After the sintering, transparent and tooth-coloured sintered crowns were obtained which had adapted to the die contour and could easily be released from the die material.

(12) The CTE values of the shaped parts are 9.30.510.sup.6 1/K (25 C. to 500 C.).

(13) TABLE-US-00004 TABLE 1 Produced glass blanks from the first glass powder Press Pressing Sintering geometry pressure temperature Density No. [mm] [kN] [ C.] [g/cm.sup.3] 1 100 mm 18 mm 1200 640 1.79 2 100 mm 18 mm 1200 660 1.82 3 100 mm 18 mm 1200 680 1.87

(14) TABLE-US-00005 TABLE 2 Chemical composition of the first glass powder Substance Amount [wt.-%] SiO.sub.2 60.5 Al.sub.2O.sub.3 22.0 K.sub.2O 8.0 Na.sub.2O 9.0 B.sub.2O.sub.3 0.5

(15) The theoretical density of this glass powder is about 2.45 g/cm.sup.3.

(16) TABLE-US-00006 TABLE 3 Particle-size distribution of the first glass powder Distribution Diameter [m] d 10 1.5 d 50 9 d 90 45

(17) d 10, d 50, and d 90 means that 10%, 50% and 90%, respectively, of the particles present are smaller than the indicated value for the diameter.