Method for the production of a dental restoration

Abstract

The invention relates to a method for the production of a restoration from a blank consisting of, or containing, a lithium silicate glass ceramic, wherein at least two layers of ceramic material of different compositions are filled into a mold layer-by-layer and after filling of the layers they are then pressed and sintered, wherein after filling of a first layer this is structured on its surface in such a way that the first layer, viewed across its surface, differs in its height from region to region, and then a layer with a composition that differs from the first layer is filled as a second layer into the mold. After sintering the dental restoration is produced from the blank by mechanical working.

Claims

1. A method for the production of a restoration from a blank that includes a lithium silicate glass ceramic, the method comprising the steps of: filling into a mold layer-by-layer at least two layers of powders, each powder being produced from starting lithium silicate glasses of different compositions, including the steps of: filling the mold with a first layer of a first powder material, the first layer having a surface that is structured in such a way that when the first layer is viewed across, the surface varies in height from one region to another region; after introduction of the first layer, filling the mold with a second layer of a second powder material that differs from the first powder material of the first layer in terms of composition, wherein a portion of the second powered material of the second layer is displaced within the surface of the first layer that varies in height from one region to another region to form an intermediate layer of the first powder material from a portion of the first layer that is mixed with the second powder material from a portion of the second layer; after introduction of the at least two layers, the at least two layers are pressed to form a body and then sintered to form a blank; and mechanically working the blank to form the restoration.

2. The method according to claim 1, wherein the surface of the first layer is structured such that elevations separated by depressions are formed.

3. The method according to claim 1, wherein a ring structure is formed in the surface in top view which has the elevations separated by the depressions.

4. The method according to claim 1, wherein the structure is created by an element that moves relative to the first layer through a wave-like, comb-like or saw-tooth-like region.

5. The method according to claim 1, wherein the structure is created by a pressure element acting in the direction of the surface of the first layer.

6. The method according to claim 5, wherein a pressure element is used which results in concentrically extending or parallel-extending elevations with depressions extending between them being pressed into the surface of the first layer.

7. The method according to claim 1, wherein the structure is formed such that the volume of the elevations is equal to, or approximately equal to, the volume of the depressions.

8. The method according to claim 1, wherein the material of the second layer is mixed with that of the first layer commencing from the free surface of the second layer over a height that corresponds to twice, or approximately twice the height of the second layer.

9. The method according to claim 1, wherein the body is fully sintered.

10. The method according to claim 1, wherein the starting glass used has a composition which includes, in percentage by weight: TABLE-US-00006 SiO.sub.2 57.5-60.5 Li.sub.2O 13.5-20.5 ZrO.sub.2 8.5-11.5 P.sub.2O.sub.5 3.0-7.5 Al.sub.2O.sub.3 0.5-6.0 K.sub.2O 0.5-3.5 CeO.sub.2 0.5-2.5 B.sub.2O.sub.3 .sup.0-3.0 Na.sub.2O .sup.0-3.0 At least one additive 0-4.

11. The method according to claim 1, wherein the starting glass used has a composition that includes, in percentage by weight: TABLE-US-00007 SiO.sub.2 57.5-60.5 Li.sub.2O 14.0-16.0 ZrO.sub.2 9.0-10.5 P.sub.2O.sub.5 5.0-6.0 Al.sub.2O.sub.3 2.5-3.0 K.sub.2O 1.0-1.5 CeO.sub.2 0.5-1.0 B.sub.2O.sub.3 2.5-3.0 Na.sub.2O 0.1-2.0 V.sub.2O.sub.5 0.1-0.7 Er.sub.2O.sub.3 .sup.0-1.0 Y.sub.2O.sub.3 0.3-0.5 MnO.sub.2 0-0.2.

12. The method according to claim 1, formation of a frit from the powder through quenching and/or the powder prior to pressing and/or the pressed powder are subject to at least one crystallization step.

13. The method according to claim 1, wherein the powder is pressed without binding agents.

14. The method according to claim 1, wherein the powder to be pressed is sieved through a sieve with a mesh size between 50 m and 250 m to obtain a mean grain size between 1 m and 150 m.

15. The method according to claim 1, wherein to influence the color of the dental restoration at least one oxide of the rare earth metals is added to the starting glass material.

16. The method according to claim 1, wherein to influence opalescence crystals of the crystal phases have a maximum length between 10 nm and 800 nm.

17. An use of a blank to manufacture a dental restoration through mechanical working of the blank according to claim 1, wherein the blank comprises a sintered body of pressed lithium silicate glass ceramic powder.

18. The use according to claim 17, in which the body and/or the blank is subject to at least one crystallization step.

19. The use according to claim 17, wherein the lithium silicate glass is present in the blank in the range 20 to 80% by volume.

20. The use according to claim 17, wherein the blank includes crystal phases, wherein the lithium metasilicate phase of the crystal phases of the blank is in the range 10 to 70 percent by volume and/or the lithium disilicate phase of the crystal phases of the blank is in the range 10 to 95 percent by volume.

21. The use according to claim 17, wherein the mechanical working includes at least grinding and/or milling.

22. The use according to claim 17, wherein the blank is a pressed body that is free of binding agents.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details, advantages and characteristics of the invention result not only from the claims and their features, both by themselves and/or in combination, but also from the following description of the preferred example embodiments and from the drawings.

(2) FIG. 1 A schematic of an assembly and the method steps that can be carried out using it,

(3) FIG. 2 An enlarged view of FIG. 1b),

(4) FIG. 3 A schematic of a bridge to be produced from a blank, and

(5) FIG. 4 A schematic of an alternative method

DETAILED DESCRIPTION OF THE INVENTION

(6) The teaching according to the invention is described with reference to FIG. 1, in which the same elements are given the same reference numbers, on the basis of which the dental restorations are produced from lithium silicate glass ceramic, and have a monolithic structure such that after full sintering a monolithic tooth prosthesis is available that can be used directly. For this purpose it is provided according to the invention for a blank to be produced that consists of a number of layers of powders that are derived from a starting lithium silicate glass, with compositions that differ from one another, through which in particular desired optical characteristics can be achieved which correspond to the dental restoration to be produced, leading to a direct use of the tooth prosthesis without it being necessary, for example, for an incisal layer to be manually applied and burned after full sintering.

(7) A first ceramic material 14 is initially produced that is made from a lithium silicate glass ceramic. For this a starting glass powder with a composition in percentage by weight given below is melted:

(8) TABLE-US-00003 SiO.sub.2 57.5-60.5 Li.sub.2O 13.5-20.5 ZrO.sub.2 8.5-11.5 P.sub.2O.sub.5 3.0-7.5 Al.sub.2O.sub.3 0.5-6.0 K.sub.2O 0.5-3.5 CeO.sub.2 0.5-2.5 B.sub.2O.sub.3 .sup.0-0 3 Na.sub.2O 0-3
At least one additive 0-4.

(9) The minimum of one additive is at least one additive from the group color pigments and/or fluorescence agents. It is in particular provided for the additive to be at least one oxide from the group of rare earth metals or for it to contain one such oxide.

(10) The corresponding mixture of starting materials is then melted in a suitable crucible of fire-resistant material or noble metal alloy at a temperature between 1350 C. and 1600 C. for a time period between 1 hour and 10 hours, in particular for a time period between 4 hours and 7 hours at a temperature of 1540 C. Homogenization is carried out either at the same time or thereafter, for example through stirring. The liquid glass so derived is then quenched in a suitable medium such as water or high-temperature wool. The quenched glass frit so produced is then dried. It is then milled, for example in a ball mill. It is then sieved, for which a sieve with a mesh size between 50 m and 250 m can be used. If necessary it can be milled further, for example using a jet mill or an attrition mill (Attritor).

(11) From the glass powder or glass particle powder so produced, those particles with a grain size between 1 m and 150 m are removed by sieving.

(12) To allow the blank to be worked without difficulty, without the molded part produced from the blank being unstable upon full sintering, a crystallization step is performed either for the frit obtained after melting or for the powder after pre-milling or final milling. Thereby in a first heat treatment step the frit/the powder is subjected to a temperature T.sub.1 between 500 C. and 750 C. for a time t.sub.1 between 5 minutes and 120 minutes. The first heat treatment step can also be carried out in two stages, i.e., initially at 640 C. and preferably 660 C. for 60 minutes and then at 750 C. for 40 minutes.

(13) In a preferred manner this is followed by a further heat treatment in the form of tempering, whereby the chosen temperature T.sub.3 should lie between 750 C. and 900 C. The temperature step is carried out over a time t.sub.3 in particular for between 5 and 30 minutes.

(14) There is naturally no departure from the invention if a binding agent is added to the starting powder. It is, however, preferred if no binding agent is used.

(15) The production of a blank, from which a dental restoration can be produced, is now described with reference to FIGS. 1 and 2. Thus a first powder 14 is initially filled into a mold 10 of a press 12 in accordance with FIG. 1a).

(16) A second layer 24 of a second powder is then produced as described before, but with a composition that differs from that of the first powder, and is filled into the mold 10 (FIG. 1 c)), wherein the total height of the layers 14 and 24 is twice the height of the layer 14 in an unstructured state, without any resultant limitation of the teaching according to the invention.

(17) If the first layer 14 preferably has a height that corresponds to half the total height H of the first and second layers 14, 24, then the height of the first layer 14 can also be H to H and thus that of the second layer 24 can be H to H.

(18) The smoothed surface is then structured in accordance with step b). For this purpose an element 16 that is disc-shaped, plate-shaped or web-shaped is used, which in the example embodiment on the layer side has a serrated geometry, so that a corresponding negative structure is formed in the surface 18 of the layer 14 through the displacement of material. This structure takes the form of concentrically extending elevations and surrounding valleys. The distance between an elevation (peak) and valley (depression), i.e., the clearance between projection 20 and valley base 22 according to FIG. 2 is approximately of the height of all layers.

(19) The invention in particular provides for the structure to be formed in such a way that the volume of the elevations is equal to, or approximately equal to, the volume of the depressions/valleys.

(20) Because the material of the second layer 24 penetrates into the base of the valleys 26 in the surface 18 of the layer 14, there is a continuous transition between the properties of the layer 14 and the layer 24, after the layers 24, 14 have been pressed according to FIG. 1d). The transition layer or intermediate layer is indicated by the reference number 28 in FIG. 1d).

(21) The layer 24 is made of a material that differs from that of the layer 14. The difference is due in particular to the color additives.

(22) The percentage of color oxides in the layer 24 is reduced compared to layer 14. As a result of this measure there is a continuous color transition between the layers 14 and 24.

(23) The layers 14, 24 are pressed by means of a stamp, with pressing carried out at a pressure between 50 MPa and 400 MPa.

(24) The blank 33 produced is forced out of the mold 10 after pressing and is then pre-sintered or fully sintered in the usual manner.

(25) If a dental prosthesis is milled from the blank 33in the example embodiment a bridge 34then the milling program is designed such that the lower region of the bridge 34 extends in the layer 14 and the cutting region 40 of the bridge extends in the layer 24.

(26) In the transition region, i.e., in the central layer 28, in which there is a virtually constant/continuous transition between the layers 14 and 24, there is the transition between dentine and incisal region. The dentine extends in the region 14.

(27) An alternative method is described with reference to FIG. 4 which follows the teaching according to the invention, to enable production of a blank or dental restoration that offers a substantially continuous transition between a first layer and a second layer or in the case of a restoration between the dentine and incisal regions in terms of translucency and strength.

(28) Thus in accordance with FIG. 4a a first powder is filled into a mold 10, which can correspond to that of layer 14 according to FIG. 1. The corresponding layer in FIG. 4a is indicated by the number 114. The height of this layer 114 can correspond to half the height of the total layers that are filled into the mold 10. A layer 127 is then laid on to the layer 114 with a thickness that in the example embodiment is 1/10 of the total height of the layers. The material of the layer 127 can correspond to that of the second layer 24 according to FIG. 1. There is then a mixing of the layer 127 with a surface region of the layer 114 over a depth that corresponds to the thickness of the layer 127. As a result, an intermediate layer 128 is formed that has a thickness that is 2/10 of the entire height of the layers. A further layer 124, which corresponds to the second layer 24 according to FIG. 1, is then applied to the intermediate layer 128. The height of the layer 124 in the example embodiment is thus 4/10 of the total height H. Then, in accordance with the example embodiment of FIG. 1, all the layers 124, 128, 114 together are pressed so that the method steps of pre-sintering, working and full sintering are then carried out, as has been explained. Naturally, working can also be carried out after sintering to full density.

(29) The present invention may include one or more of the following features and/or combinations:

(30) 1. A method for the production of a restoration (34) from a blank (33) consisting of, or containing, a lithium silicate glass ceramic, wherein at least one starting lithium silicate glass is melted, the glass melt is cooled rapidly and is comminuted to a powder,

(31) characterized in that

(32) at least two layers (14, 24) of powders, which are produced from starting lithium silicate glasses of different compositions, are filled into a mold layer-by-layer, wherein after filling of a first layer (14) its surface is structured in such a way that the first layer (14) viewed across its surface (18) varies in its height from one region to another and then as the second layer (24) a layer with a composition that differs from that of the first layer is filled into the mold, or that after introduction of the first layer (114) a further layer (127) of a powder is filled onto it in the mold (10) that differs from the first layer in terms of composition, that the material of the first layer is mixed with the material of the further layer to form an intermediate layer (128) and that the second layer (124) is then filled into the mold (10),
and that after introduction of the layers they are pressed and then sintered to form a blank, and that the dental restoration is produced from the blank by mechanical working.

(33) 2. The method according to claim 1,

(34) characterized in that

(35) the surface (18) of the first layer (14) is structured such that elevations separated by depressions are formed.

(36) 3. The method according to at least claim 1 or 2,

(37) characterized in that

(38) a ring structure is formed in the surface (18) in top view which has the elevations separated by the depressions.

(39) 4. The method according to at least claim 1,

(40) characterized in that

(41) the structure is created by an element (16) that moves, in particular rotates, relative to the first layer (14), that in particular structures the surface region of the first layer (14) through a wave-like, comb-like or saw-tooth-like region.

(42) 5. The method according to at least claim 1,

(43) characterized in that

(44) the structure is created by a pressure element acting in the direction of the surface (18) of the first layer (14).

(45) 6. The method according to at least claim 5,

(46) characterized in that

(47) a pressure element is used which results in concentrically extending or parallel-extending elevations with depressions extending between them being pressed into the surface (18) of the first layer (14).

(48) 7. The method according to at least claim 1,

(49) characterized in that

(50) the structure is formed such that the volume of the elevations is equal to, or approximately equal to, the volume of the depressions.

(51) 8. The method according to at least claim 1,

(52) characterized in that

(53) the material of the further layer (127) is mixed with that of the first layer (114) commencing from the free surface of the further layer over a height that corresponds to twice, or approximately twice the height of the further layer.

(54) 9. The method according to claim 1,

(55) characterized in that

(56) the body is fully sintered.

(57) 10. The method according to at least claim 1,

(58) characterized in that

(59) the starting glass used has a composition which contains, or consists of, in percentage by weight:

(60) TABLE-US-00004 SiO.sub.2 57.5-60.5 Li.sub.2O 13.5-20.5 ZrO.sub.2 8.5-11.5 P.sub.2O.sub.5 3.0-7.5 Al.sub.2O.sub.3 0.5-6.0 K.sub.2O 0.5-3.5 CeO.sub.2 0.5-2.5 B.sub.2O.sub.3 .sup.0-3.0 Na.sub.2O .sup.0-3.0
At least one additive 0-4.

(61) 11. The method according to at least claim 1,

(62) characterized in that

(63) the composition contains, or consists of, in percentage by weight:

(64) TABLE-US-00005 SiO.sub.2 57.5-60.5 Li.sub.2O 14.0-16.0 ZrO.sub.2 9.0-10.5 P.sub.2O.sub.5 5.0-6.0 Al.sub.2O.sub.3 2.5-3.0 K.sub.2O 1.0-1.5 CeO.sub.2 0.5-1.0 B.sub.2O.sub.3 2.5-3.0 Na.sub.2O 0.1-2.0 V.sub.2O.sub.5 0.1-0.7 Er.sub.2O.sub.3 .sup.0-1.0 Y.sub.2O.sub.3 0.3-0.5 MnO.sub.2 0-0.2.

(65) 12. The method according to at least claim 1,

(66) characterized in that

(67) the frit formed through quenching and/or the powder prior to pressing and/or the pressed powder are subject to at least one crystallization step.

(68) 13. The method according to at least claim 1,

(69) characterized in that

(70) the powder is pressed without binding agents.

(71) 14. The method according to at least claim 1,

(72) characterized in that

(73) the powder to be pressed is sieved through a sieve with a mesh size between 50 m and 250 m to obtain a mean grain size between 1 m and 150 m, in particular between 10 m and 30 m.

(74) 15. The method according to at least one of the above claims

(75) characterized in that

(76) to influence the color of the dental restoration at least one oxide of the rare earth metals is added to the starting material.

(77) 16. The method according to at least one of the above claims

(78) characterized in that

(79) to influence opalescence crystals of the crystal phases have a maximum length between 10 nm and 800 nm.

(80) 17. An use of a blank (33) to manufacture a dental restoration (34) through mechanical working of the blank, wherein the blank consists of, or contains, a sintered body of pressed lithium silicate glass ceramic powder.

(81) 18. The use according to claim 17, in which the body and/or the blank (33) is subject to at least one crystallization step.

(82) 19. The use according to claim 17 or 18, wherein the lithium silicate glass is present in the blank (33) in the range 20 to 80% by volume.

(83) 20. The use according to at least one of claims 17 to 19, wherein the blank (33) contains crystal phases, wherein the lithium metasilicate phase of the crystal phases of the blank is in the range 10 to 70 percent by volume and/or the lithium disilicate phase of the crystal phases of the blank is in the range 10 to 95 percent by volume.

(84) 21. The use according to at least claim 17, wherein the mechanical working includes at least grinding and/or milling.

(85) 22. The use according to at least claim 17, wherein the blank (33) is a pressed body that is free of binding agents.