MONOCHROME COMPOSITE MILLING BLOCKS AND METHOD FOR THE PRODUCTION THEREOF

Abstract

The invention relates to a method for the production of blocks of material of a polymerized dental composite material as well as to the blocks of material obtainable according to the method, in which (i) a polymerisable dental composite material is transferred into a pressure-resistant casting mould (100), (ii) a pressure in the range of 10 to 500 MPa is applied to the polymerisable dental composite material in the pressure-resistant casting mould, and (iii) at least a part of the casting mould and/or the polymerisable material is heated in a defined manner to a temperature of 90 to 150 C.

Claims

1. A method for the production of at least one block of material (3) of a polymerized dental composite material, in which (i) a polymerisable dental composite material is transferred into a pressure-resistant casting mould (100), (ii) a pressure in the range of 10 to 500 MPa is applied to the polymerisable dental composite material in the pressure-resistant casting mould, (iii) at least a part of the casting mould as well as the polymerisable material are heated in a defined manner to a temperature of 90 to 150 C. wherein the polymerisable dental composite material in the pressure-resistant casting mould is hot isostatically pressed and polymerized, wherein the polymerization front is substantially perpendicular to the vector of force (N).

2. The method according to claim 1, wherein the pressure-resistant casting mould (100) is formed in multiple parts and comprises at least a) a bottom part (0) having at least one integral center part (1) having at least one mould cavity (2), as well as at least one top cover (7) or b) a bottom part (0), at least one center part (1) having at least one mould cavity (2), as well as at least one top cover (7).

3. The method according to claim 1, wherein the pressure-resistant casting mould, the bottom part, the center part having at least one mould cavity and/or the top cover, each independently, are made of a metal, a metallic alloy, or a temperature-resistant plastic, or a temperature-resistant hybrid material.

4. The method according to claim 1, in which in (i.1) the polymerisable dental composite material being preheated to a temperature in the range of 25 to 50 C. is transferred into at least one mould cavity of the pressure resistant casting mould, and (i.2) at least one mould cavity filled with preheated composite material is obtained.

5. The method according to claim 1, in which a) in (i.3) a top cover of the pressure-resistant casting mould is put onto the at least one mould cavity filled with preheated composite material, wherein at least one press punch (8) is arranged at the top cover, and the press punch as being a male part gears into a mould cavity (2) as being a female part of the casting mould (100), or b) in (i.1) a top cover of the pressure-resistant casting mould is put onto the at least one mould cavity filled with composite material, wherein preferably at least one press punch is arranged at the top cover, and the press punch as being a male part gears into the mould cavity as being a female part of the casting mould.

6. The method according to claim 1, wherein (ii) a pressure in the range of 125 to 250 MPa is applied to the polymerisable dental composite material in the pressure-resistant casting mould.

7. The method according to claim 1, wherein (iii) at least a part of the casting mould or the polymerisable material is heated in a defined manner for 0.1 to 60 seconds to a temperature of 110 to 150 C.

8. The method according to claim 1, wherein the polymerisable dental composite material in the pressure-resistant casting mould is hot isostatically pressed and polymerized (HIPP).

9. (canceled)

10. The method according to claim 1, wherein the polymerisable dental composite material in the pressure-resistant casting mould is hot isostatically pressed and polymerized in a thermally-directed manner (HIPP).

11. The method according to claim 1, wherein the polymerisable dental composite material, comprises (i) 70 to 85% by weight of an inorganic filler component comprising at least one dental glass, as well as optionally at least one amorphous metal oxide, (ii) 10 to 30% by weight of a mixture of at least two different urethane (meth)acrylates, (iii) 0.01 to 5% by weight of at least one di-, tri-, tetra- or multi-functional monomer not being an urethane (meth)acrylate, (iv) 0.01 to 10% by weight of at least one initiator, of an initiator system, as well as optionally of at least one stabilizer, and optionally of at least one pigment, wherein the total composition of the composite material amounts to 100% by weight.

12. The method according to claim 1, wherein a block of material of a polymerized composite material is obtained, having a defect volume of 15.Math.10.sup.6% by volume to 14.Math.10.sup.4% by volume, based on the total block of material.

13. A pressure-resistant casting mould (100) for use in a method according to claim 1, wherein the pressure-resistant casting mould (100) is formed of multiple parts and comprises at least one bottom part (0), at least one center part (1) having at least one mould cavity (2), as well as at least one top cover (7).

14. The pressure-resistant casting mould according to claim 13, wherein the at least one mould cavity has a geometrical shape.

15. The pressure-resistant casting mould according to claim 13, wherein the at least one mould cavity (2) has an inner surface having a defined surface roughness with an average roughness value of R.sub.a N3 to N9.

16. A block of material (3) obtainable according to a method according to claim 1, wherein the block of material of a polymerized composite material has a defect volume of 15.Math.10.sup.6% by volume to 14.Math.10.sup.4% by volume, based on the total block of material.

17. The method according to claim 1, wherein the pressure-resistant casting mould (100) is formed in multiple parts and comprises at least a) a bottom part (0) having at least one integral center part (1) having at least two mould cavities (2), as well as at least one top cover (7) or b) a bottom part (0), at least one center part (1) having at least two mould cavities (2), as well as at least one top cover (7).

Description

[0049] In the following, FIGS. 1a to 1c, 2, 3 and 4 are illustrated without limiting the invention to the specific embodiment.

[0050] The pressure-resistant casting mould 100 may comprise three single components or may consist of three components, a planar bottom part 0 (see FIG. 1), a center part 1 with appropriate casting moulds (see FIGS. 1a, 1b and 1c) as well as a top cover 7 with integrated press punches 8 (see FIG. 2). The components are to be arranged relative to each other in just one position via appropriate construction elements, such as e.g. guide bolts 4 and appropriate blind holes 5. FIG. 1b shows a generalized cross section of the mould cavities by showing the inner surface 11 as well as also the sealing face 10 at the mould cavity 2 and the spillway 9.

[0051] Process sequence: At first, the center part 1 is put onto the bottom plate 0 and connected to each other via the guide bolts 4 in the provided blind holes 5. Subsequently, the mould cavities 2 are filled, preferably bubble-free, with a defined amount of preheated non-polymerized composite material having a temperature of approx. 35 C. After having filled the available mould cavities 2, the top cover 7 is put onto in such a way that the press punches 8 are exactly oriented above the mould cavities 2. Since the dimensions of press punch 8 and casting mould 2 are exactly coordinated, exact position of the press punches and casting moulds relative to each other is important for the production of high-quality blocks of material suitable for dental use. Due to this exact coordination, the remaining gap between casting mould and press punch is kept as small as possible with a defined clearance, preferably smaller than or equal to 5 1/100 mm, preferably smaller than or equal to 3 1/100 mm.

[0052] The pressure-resistant casting mould 100 is now transferred into a hot press 12 (see FIG. 3) and the pressure on the pressure-resistant casting mould 100 is raised to approx. 15-20 tonnes within approx. 5-10 sec. The slightly conical press punches 8 which improve the accuracy of fit and allow for better sealing of the casting mould, squeeze excess material out of the casting mould into a spillway 9 and then seal the casting mould with increasing press force by means of the appropriate sealing faces (6 sealing face at the press punch, 10 sealing face at the casting mould). Due to the chosen geometry of the casting moulds 2, the press punches 8 and the sealing faces 6/10, the press punch 8 may exert pressure to the composite material, by means of which polymerization shrinkage can be compensated and preferably minimized to avoided. At the same time, bubbles possibly being in the composite material may be isostatically grouted. After rendering the press pressure, the temperature is increased to start the polymerization. The press pressure is maintained and readjusted during the whole hot polymerization process. In the method according to the invention, at first, the press pressure is thus adjusted and optionally later the temperature is heated in a defined manner to 90 to 150 C., wherein preferably the press pressure is readjusted over the whole period of heating. Preferably, the press pressure is also maintained during cooling.

[0053] The whole mould 100 is advantageously made of an afore-mentioned steel to receive the high press forces, wherein the center part 1 is additionally hardened so that the mould cavity does not deform geometrically.

[0054] After closing the press plates 13 of the hot press 12 according to FIG. 3, the mould 100 is slowly heated by means of heat conduction to 120 C. within approx. 10 min to start the polymerization reaction. The pressure-resistant casting mould 100 is thereby kept under a pressure 14 of 125 to 250 MPa by an applied force at the top cover 7. In this context, it is preferred for just one press plate 13, here the bottom plate 0, to be heated, in order to control the polymerization in a directed manner from the bottom to the top cover 7. By this measure, the opposing press punch in the top cover 7 may be pressed until the end and the polymerization shrinkage can be compensated. Likewise, it is possible to heat the top cover plate 7 and to apply pressure 14 to the bottom plate 0 further.

[0055] After finishing the polymerization process, in order to avoid stresses, the mould is cooled in a directed manner to approx. 40 C. within 10 min, the mould is disassembled and the polymerized blocks are removed. Cooling is preferably carried out symmetrically from both sides via the top cover and the bottom part to avoid stresses.

[0056] The material blocks can be checked for invisible bubbles by means of X-ray CT. Cavities can be detected as defect volumes in defined incremental layers of a defined thickness in the illustration shown in FIG. 4. According to the invention, blocks of material of a polymerized composite material are obtainable, having a defect volume of less than or equal to 1.Math.10.sup.6%, by volume to 14.Math.10.sup.4%, by volume. The samples are analyzed using non-destructive X-ray CT method.

LIST OF REFERENCE NUMERALS

[0057] 0 bottom part, in particular bottom plate [0058] 1 center part [0059] 2 mould cavities [0060] 3 block of material [0061] 4 guide bolt [0062] 5 blind holes [0063] 6 sealing face at the press punch [0064] 7 top cover, in particular top cover plate [0065] 8 press punch [0066] 9 spillway [0067] 10 sealing face at the mould cavity [0068] 11 inner surface [0069] 12 hot press [0070] 13 press plates [0071] 14 pressure [0072] 15 temperature control [0073] 100 pressure-resistant casting mould