Dental restoration, method for its production and ingot

Abstract

The invention refers to a method for producing a dental restoration comprising a lithium silicate glass or glass ceramic as well as a dental restoration inself. The invention further refers to a ingot with the same composition having a defined strength.

Claims

1. A method for producing a dental restoration comprising a lithium silicate glass ceramic, wherein a) an amorphous glass with the composition 50 to 75 wt-% SiO.sub.2, 17 to 25 wt-% Li.sub.2O, 8 to 20 wt-% HfO.sub.2 or of a mixture of HfO.sub.2 and ZrO.sub.2, 0 to 8 wt-% Al.sub.2O.sub.3, 0 to 8 wt-% K.sub.2O, and 0 to 15 wt-% additives is provided as an ingot and b) the ingot is transformed to a dental restoration by at least one transformation process, wherein during the at least one transformation process at least a partial crystallisation occurs due to increased temperatures, wherein the transformation process is a lost wax process.

2. The method of claim 1, wherein the amorphous glass has the following composition: 55 to 64 wt-% SiO.sub.2, 17 to 22 wt-% of Li.sub.2O, 8 to 20 wt-% HfO.sub.2 or of a mixture of HfO.sub.2 and ZrO.sub.2, 0.1 to 5 wt-% of Al.sub.2O.sub.3, 0.1 to 5 wt-% of K.sub.2O, 2 to 8 wt-% P.sub.2O.sub.5, and 0 to 10 wt-% of additives.

3. The method of claim 1, wherein during the transformation process, thermal energy is conveyed to the ingot, with temperatures of at least 800° C.

4. The method of claim 1, wherein in a further step c) subsequent to the transformation process, the dental restoration is subjected to a heat treatment with temperatures from 850° C. to 1100° C.

5. The method of claim 1, wherein the additives are selected from nucleating agents, fluorescent agents, dyes, glass colouring oxides, coloured pigments, and mixtures thereof.

6. The method of claim 5, wherein the nucleating agents are selected from phosphorous oxide, titanium oxide, tin oxide, and mixtures thereof, and noble metals.

7. The method of claim 5, wherein the fluorescent agents are selected from oxides of strontium, bismuth, rare earth elements, and mixtures thereof.

8. The method of claim 5, wherein the glass colouring oxides are selected from oxides of iron, titanium, copper, chromium, cobalt, nickel, manganese, selenium, silver, indium, gold, vanadium, rare earth elements, and mixtures thereof.

9. The method of claim 1, wherein the additives are selected from boron oxide, fluorine, barium oxide, strontium oxide, magnesium oxide, zinc oxide, calcium oxide, yttrium oxide, titanium oxide, niobium oxide, tantalum oxide, lanthanum oxide and mixtures thereof.

10. The method of claim 1, wherein before the dental application, the dental restoration is subjected to a finishing process selected from polishing, glazing, sealing, coating, and veneering with a veneering ceramic or glaze.

11. The method of claim 6, wherein the nucleating agent is present in an amount of 1 to 10 wt-% of the dental restoration.

12. The method of claim 7, wherein the fluorescent agent is present in an amount of 0.1 to 5 wt-% of the dental restoration.

Description

(1) The subject according to the application is intended to be explained in more detail with reference to the subsequent figures and examples without restricting said subject to these variants.

(2) FIG. 1 shows a Scanning Electron microscope (SEM) micrograph of a glass according to the present invention after pre-crystallization.

(3) FIG. 2 shows a Scanning Electron microscope (SEM) micrograph of a glass according to the present invention after pressing at a temperature of 950° C.

(4) FIG. 3 shows a Scanning Electron microscope (SEM) micrograph of a glass according to the present invention after pressing at a temperature of 970° C.

EXAMPLE 1

(5) In Table 1, a fixed compositions given by way of example for different stabilizer is mentioned, from which high stabilizer-containing metasilicate glass ceramics can be produced for the dental field.

(6) TABLE-US-00002 TABLE 1 in % by weight SiO.sub.2 60.0 Li.sub.2O 19.0 P.sub.2O.sub.5 6.0 Al.sub.2O.sub.3 2.0 K.sub.2O 2.0 CeO.sub.2 1.0 Stabilizer SX* 10.0 *SX represent compositions of stabilizers S1 to S5 (s. table 2)

(7) Table 2 shows stabilizers used by way of example for dental applications with the composition of table 1.

(8) TABLE-US-00003 TABLE 2 Stabilizers SX S1 Zirconium oxide: 10% S2 Germanium oxide: 10% S3 Lanthanum oxide: 10% S4 Yttrium oxide: 10% S5 Zirconium oxide: 6% Titanium oxide: 4%

(9) The glasses were melted at 1.500° C. and poured into metal moulds to form blocks. The blocks were stress-relieved in the oven at 560° C. and cooled down slowly. For the various characterisation processes, the glass blocks were divided up and subjected to a first crystallisation treatment. For this purpose, the glasses were stored for 10 to 120 minutes at 600° C. to 750° C. As a result of this, glass ceramics with strength values of 150 MPa to 220 MPa were produced. Exclusively lithium metasilicate was hereby established as crystal phase. In this state, processing by means of CAD/CAM methods is possible very readily.

(10) In Table 3, compositions which are given by way of example are mentioned, from which high zirconium oxide-containing metasilicate glass ceramics can be produced for the dental field.

(11) TABLE-US-00004 TABLE 3 G1* G2* G3* G4* G5* G6* SiO.sub.2 63.5 63.5 59.0 59.0 63.5 63.5 Li.sub.2O 12.9 13.9 18.0 19.0 12.9 12.9 ZrO.sub.2 10.0 9.0 12.0 12.0 12.3 11.0 Al.sub.2O.sub.3 4.7 5.1 4.5 4.5 3.9 4.4 P.sub.2O.sub.5 4.5 4.5 3.5 3.5 3.7 4.2 K.sub.2O 4.4 4.0 3.0 2.0 3.6 4.0 *(Data in % by weight)

(12) The glasses were melted at 1.500° C. and poured into metal moulds to form blocks. The blocks were stress-relieved in the oven at 560° C. and cooled down slowly. For the various characterisation processes, the glass blocks were divided up and subjected to a first crystallisation treatment. For this purpose, the glasses were stored for 10 to 120 minutes at 600° C. to 750° C. As a result of this, glass ceramics with strength values of 150 MPa to 220 MPa were produced. Exclusively lithium metasilicate was hereby established as crystal phase. In this state, processing by means of CAD/CAM methods is possible very readily.

EXAMPLE 2

(13) An inventive dental restoration was produced according to the following process steps: 1. Melting of components to homogeneous liquid glass 2. Molding of glass blanks 3. Relief of stress within glass blank 4. Optional: Pre-crystallization of glass blank (process not necessary for high strength press result)

(14) The glass blanks are placed on firing trays, e.g. made of glass fibers. A thermal treatment 550-700° C., dwell time 10-60 min, heating rate 10-100° C./min and final temperature 800-850° C., dwell time 8-30 min in atmosphere.

(15) The microstructure shows a poly-crystalline state with crystals <5 μm (s. FIG. 1).

(16) XRD analysis shows phases of lithium silicate (Li.sub.2SiO.sub.3) and lithium phosphate (Li.sub.3PO.sub.4). 5. Modellation of the desired prosthesis in wax

(17) A full anatomical wax modellation of the prosthesis will be made out of residue free burning wax. The minimal thickness of the wax modellation should not be below 0.4 mm and should not exceed 2.0 mm on occlusal side. Wax sprues will be added to the modellation with a length of 5-6 mm and a thickness of 3-4 mm. 6. Investment of the wax modellation

(18) The investment mass will be stirred and poured bubble-free into the muffle under vibration where the wax modellation is fixed in until the wax modellation is completely covered by the investment mass. After this the muffle will be filled completely without applying vibration. The muffle with the liquid investment mass will now be stored to set the hardening process. 7. Heating of the muffle and burning off of the wax modellation

(19) After setting of the investment mass any of the auxiliary plastic parts will be removed and the surfaces (top/bottom) will be cleaned to obtain a plane surface.

(20) The muffle will be placed in the pre-heating furnace. The base temperature depends on the kind of used investment mass. By using the Dentsply investment mass the muffle can be placed directly after the setting of 15 min in furnace pre-heated to 850° C. 8. Pressing of the restoration

(21) The muffle then will be cooled down for 15 min to 700° C. The starting temperature of the pressing process is 600° C. Press-pellets of TW4 with a high strength are placed in the muffle. A non heated press rod made of alumina or investment mass now setting on the press pellets. The muffle with the pellets and the press rod will be placed now immediately into the pressing furnace and a press program with the following parameters will be started: Pre-heating temperature 600-850° C., heating rate 30-100° C./min, pressing temperature 890-995° C., dwell time 10-35 min, pressing time 1-20 min. After the pressing is completed the muffle will be put out of the furnace and will be cooled down at room temperature.

(22) After pressing the polycrystalline structure can be seen in FIG. 2.

(23) Due to a variation of the pressing temperature the crystal size can be changed. Pressing temperatures of 950° C. to 970° C. resulting in crystal sizes of 1500 nm to 3000 nm (median) (s. FIG. 3).

(24) 3-point-bending tests in accordance to DIN EN ISO 6872: 2008 shows a flexural strength of 370 MPa and the coefficient of thermal expansion at 25-400° C. is 10.6-10.9 μm/mK, for 25-500° C. 11.0-11.3 μm/mK and for 25-600° C. 11.4-11.8 μm/mK.

(25) XRD shows phases of lithium silicate (Li.sub.2SiO.sub.3) and lithium phosphate (Li.sub.3PO.sub.4). Different pressing temperatures do not show significantly different crystal phases. 9. Divesting of the pressed restoration

(26) The investment mass will be removed by blasting with glass beads having a diameter of 50 μm with a pressure of 2-4 bar or sandblasting with alumina (diameter 110 μm, 0.5-2 bar). 10. Removing of the reaction layer of the pressed restoration

(27) The residues of the reaction layer are removed in a ultrasonic bath with a hydrofluoric acid containing solvent for 30 min at 30° C. 11. Cutting off the sprues from the restoration

(28) The sprue will be cut-off with a water-cooled diamond saw and cleaned. The surface to be veneered or glazed will be sandblasted with alumina having a median diameter of 110 μm and a pressure of 0.5-1.5 bar. 12. Shading with glaze/stains and veneering technique, respectively

(29) The pressed restoration will be esthetically individualized either with glaze/stains using 2-3 firing cycles or will be finalized with veneering ceramic using the cut-back technique.

EXAMPLE 3

(30) An inventive dental restoration was produced according to the following process steps: 1. Melting of components to homogeneous liquid glass 2. Molding of glass blanks 3. Relief of stress within glass blank 4. Optional: Pre-crystallization of glass blank (process not necessary for high strength press result) 5. Modellation of the desired prosthesis in wax.

(31) A full anatomical wax modellation of the prosthesis will be made out of residue free burning wax. The minimal thickness of the wax modellation should not be below 0.4 mm and should not exceed 2.0 mm on occlusal side. Wax sprues will be added to the modellation with a length of 5-6 mm and a thickness of 3-4 mm. 6. Investment of the wax modellation

(32) The investment mass (gypsum or phosphate based) will be stirred and poured bubble-free into the muffle under vibration where the wax modellation is fixed in until the wax modellation is completely covered by the investment mass. After this the muffle will be filled completely without applying vibration. The muffle with the liquid investment mass will now be stored to set the hardening process. 7. Heating of the muffle and burning off of the wax modellation.

(33) When using a gypsum investment the maximum temperature of about 700° C. has to be taken into account.

(34) After setting of the investment mass any of the auxiliary plastic parts will be removed and the surfaces (top/bottom) will be cleaned to obtain a plane surface.

(35) The muffle will be placed in the pre-heating furnace. The base temperature depends on the kind of used investment mass. By using the Dentsply investment mass the muffle can be placed directly after the setting of 15 min in furnace pre-heated to 850° C. 8. Casting of the restoration

(36) The muffle then will be cooled down for 15 min to 700° C. For casting a suitable casting machine will be used for e.g. a Prestomat from DeguDent. The blank or pellet of TW4 produced as described before will be heated up to temperature of 1150° C. and then will be casted in the already preheated muffle (700° C.). After the casting is completed the muffle will be put out of the casting device and into a pre-heating furnace at 660° for 40 min for nucleation purposes. After this either the muffle will be heated up to crystallization temperature (e.g. 850° C., 5 min.) or the muffle will be cooled down at room temperature and the final crystallization takes place after being divested.

(37) Due to a variation of the nucleation and final crystallization temperature the crystal size can be changed. Different temperatures of nucleation of 600° C. to 850° C. and final crystallization from 750° C. to 850° C. resulting in crystal sizes of 100 nm to 3000 nm (median).

(38) 3-point-bending tests in accordance to DIN EN ISO 6872: 2008 shows a flexural strength of 370 MPa and the coefficient of thermal expansion at 25-400° C. is 10.6-10.9 μm/mK, for 25-500° C. 11.0-11.3 μm/mK and for 25-600° C. 11.4-11.8 μm/mK.

(39) XRD shows phases of lithium silicate (Li.sub.2SiO.sub.3) and lithium phosphate (Li.sub.3PO.sub.4). Different pressing temperatures do not show significantly different crystal phases. 9. Divesting of the cast restoration

(40) The investment mass will be removed either by blasting with glass beads having a diameter of 50 μm with a pressure of 2-4 bar or sandblasting with alumina (diameter 110 μm, 0.5-2 bar) or by using gypsum investment masses by dissolving in a water tank at room temperature. 10. Cutting off the sprues from the restoration

(41) The sprue will be cut-off with a water-cooled diamond saw and cleaned. The surface to be veneered or glazed will be sandblasted with alumina having a median diameter of 110 μm and a pressure of 0.5-1.5 bar. An advantage of the casting is a significantly reduced reaction layer or even no reaction layer. Therefore, reproduction of fine surface details (e.g. of thin margins) is superi- or especially if gypsum investment is used (easy to remove). 11. Shading with glaze/stains and veneering technique, respectively

(42) The pressed restoration will be esthetically individualized either with glaze/stains using 2-3 firing cycles or will be finalized with veneering ceramic using the cut-back technique.