CA2213390C

CA2213390C - Sinterable lithium disilicate glass ceramic

Info

Publication number: CA2213390C
Application number: CA002213390A
Authority: CA
Inventors: Martin Frank; Wolfram Hoeland; Marcel Schweiger; Volker Rheinberger
Original assignee: Ivoclar AG
Current assignee: Ivoclar AG
Priority date: 1996-09-05
Filing date: 1997-08-20
Publication date: 2002-07-23
Anticipated expiration: 2017-08-20
Also published as: ATE186286T1; EP0827941A1; AU695549B2; CA2213390A1; AU3530597A; JPH10101409A; EP0827941B1; JP3093691B2

Abstract

High-strength sinterable lithium disilicate glass ceramics are described which can be further processed in particular by pressing in the viscous state to shaped dental products.

Description

Sinterable lithium disilicate Qlass ceramic The invention relates to sinterable lithium disilicate glass ceramics and in particular those which, by virtue of their properties, are suitable for the production of shaped dental products by plastic deformation with the action of pressure and heat.
Lithium disilicate glass ceramics are known from the prior art.
EP-B-536 479 describes self-glazed lithium disilicate glass ceramic articles which are not, however, intended for dental applications . The glass ceramics are free from La203 and are formed in the usual manner by melting suitable starting materials, pouring into molds and subsequent heat treatment of the articles obtained.
Lithium silicate glass ceramics are also disclosed in EP-B-536 572. They are given structure and color by the dispersion of a finely divided colored glass onto their surface, and they are used as lining units for building purposes . They are manufactured in a conventional manner in that suitable starting materials are melted, the melt is molded to a desired body and the body is heat-treated together with dispersed colored glass . Laz03 is not, however, contained in the glass ceramic.
Glass ceramics based on SiOz and Li20 which contain large quantities of physiologically very harmful arsenic oxide are known from DE-C-1 421 886.
Moreover, the use of lithium disilicate glass ceramics in dental technology is also disclosed in the prior art, but said glass ceramics contain no Laz03 or Mg0 whatsoever and only conventional methods are used to process them to dental products, wherein a heat treatment is carried out to precipitate crystals only on homogeneous bodies, namely monoliths formed from a glass melt, such as small glass blocks or slabs . Conventional methods of this kind, however, only allow volume crystallisation to take place, not surface crystallisation.

Examples of such glass ceramics and conventional methods for the production thereof are described in following documents.
A lithium disilicate glass ceramic with high strength suitable for the preparation of dental crowns and bridges is described in US-A-4,515,634.
A high-strength lithium disilicate glass ceramic is also described in US-A-4,189,325 wherein said glass ceramic necessar-ily contains Ca0 to improve the flow and also platinum and niobium oxide to produce very fine and uniform crystals.
Glass ceramics containing lithium oxide and silicon oxide for the preparation of dental prostheses, which contain very large quantities of MgO, are described in FR-A-2 655 264.
Finally, US-A-5,507,981 and WO-A-95/32678 describe lithium disilicate glass ceramics which may be further processed to formed dental products by special methods, wherein pressing in the viscous, flowable state at elevated temperatures to the desired dental product takes place. No further details are given regarding the production of the slabs or buttons used during this process. A conventional method is also used to produce the glass ceramic in that homogeneous glass bodies, such as slabs, for example, are heat-treated. A disadvantage of these methods is that they are very elaborate for a dental technician as a result of the use of a special heat-pressure deformable crucible.
Moreover, the glass ceramic materials are heated to such an extent that crystals are no longer present in the molten material since the viscosity would otherwise be too high for pressing to the desired dental product. Consequently, the product processed is glass, not a glass ceramic.
The known lithium disilicate glass ceramics have shortcomings, particularly when they are to be processed further in the plastic state to shaped dental products. Their viscosity is not ideally adjusted for such processing, so a controlled flow is not possible and the reaction with the investment material is undesirably high. Moreover, conventional glass ceramics have only poor dimensional stability on heating, so that dental restorations produced from them may be provided with a sintered-on glass or glass ceramic layer only with deformation. Finally, conventional lithium disilicate glass ceramics also frequently lack the necessary chemical stability for use as dental material, which is permanently being flushed with fluids of various kinds in the oral cavity.
An object of the invention is, therefore, to provide a lithium disilicate glass ceramic which exhibits cptimum flow properties, and, at the same time, little reaction with the investment material when pressed in the plastic state to dental products, has high dimensional. stability on heating, particularly in the range from 700°C to 900°C, and has excellent chemical stability.
This object is achieved by the sinterable lithium disilicate glass ceramic of the present invention.
The invention also provides a process for the preparation of shaped dental products using the glass ceramic, the use of the glass ceramic, shaped dental products con~~aining the glass ceram=c, and the starting glass used to produce the glass ceramic.
The sinterable lithium disilicate glass ceramic according to the inver.t~_or_ is preferably characterised in that it contains the following components:
Component Wt.o SiO~ 57.0 to 80.0 A1~03 0 to 5.0 La~03 0.1 to 6.0 Mg0 0 to 5.0, particularly 0.1 to 5.0 Zn0 0 to 8.0 KZO 0 to 13.5 Li20 11.0 to 19.0 PZOS 0 to 11.0 Color components ~ 0 to 8.0 Additional components 0 to 6.0 wherein ( a ) A1z03 + La203 amount to 0 .1 to 7 . 0 wt . ~ and (b) Mg0 + Zn0 amount to 0.1 to 9.0 wt.~
and wherein the color components are formed from glass-coloring oxides (c) and/or coloring bodies (d) in the following quan tities:
(c) glass-coloring oxides 0 to 5.0 wt.~ and (d) coloring bodies 0 to 5.0 wt.~.
It is preferred that the glass ceramic essentially consists of the components mentioned above.
Lithium disilicate was detected by X-ray diffraction analyses as the main crystalline phase of the glass ceramic according to the invention.
There are preferred quantity ranges for the individual components of the lithium disilicate glass ceramic according to the invention. These may be chosen independently of one another and are as follows:
Component Wt. ~
Si02 57.0 to 75.0 A1203 0 to 2.5 La203 0.1 to 4.0 Mg0 0.1 to 4.0, Zn0 0 to 6.0 particularly 0.1 to 5.0 KZO 0 to 9.0 particularly 0.5 to 7.0 LizO 13.0 to 19.0 P205 0 to 8.0 particularly 0.5 to 8.0 Color components 0.05 to 6.0 Additional components 0 to 3Ø

The glass ceramic according to the invention contains preferably color components, namely glass-coloring oxides (c) and/or coloring bodies (d) in order to obtain a color match between a dental product produced from the glass ceramic and the natural dental material of the patient. The glass-coloring oxides, particularly TiOZ, Ce02 and/or Fe203 serve only to obtain a shading, the main coloration being brought about by the coloring bodies. It is to be noted that TiOZ does not act as a nucleating agent but, in combination with the other oxides, as a color component. The coloring bodies are metal oxides conventionally used in dental glass ceramics and, in particular, commercial isochromatic coloring bodies, such as doped spinels and/or doped Zr02. The coloring bodies may be both non-fluorescing and fluorescing materials.
In addition to the components mentioned above, the lithium disilicate glass ceramic according to the invention may also contain additional components, for which B203, F, NazO, Zr02, Ba0 and/or Sr0 are particularly suitable. The viscosity of the residual glass phase of the glass ceramic may be influenced with B203 and F, and it is assumed that they shift the ratio of surface to volume crystallisation in favour of surface crystallisation.
To produce the glass ceramics according to the invention, the process described in more detail below for the production of shaped dental products containing the glass ceramic is used in particular, wherein the forming of special shapes is not necessary.
The process according to the invention for the production of shaped dental products containing the sinterable lithium disilicate glass ceramic according to the invention is characterized in that (a) a starting glass which contains the components of the lithium disilicate glass ceramic as discussed above, with the exception of coloring bodies, is fused at temperatures of 1200 to 1650°C to form a glass melt, (b) the glass melt is poured into water with the formation of glass granules, (c) the glass granules are comminuted to a powder with an average particle size of 1 to 100 um, based on the number of particles, (d) the coloring bodies optionally present are added to the powder, (e) the powder is compacted to a starting glass blank of the desired geometry and he=erogeneous structure, and the starting glass blank is subjected to one or more heat treatments under vacuum and ;~n the temperature range from 400 to 1100°C in order to achieve a dense sintering and to give a dental product in the form cf a blank.
In process stage (a), a starting glass is melted, for which purpose suitable starting materials such as, for example, carbonates, oxides and fluorides, are intimately mixed with one another and heated to the specified temperatures, as a result of which the starting glass forms. If color-imparting oxides are to be used, these are added to the batch. The addition of optionally present coloring bodies takes place in a later stage of the process, since their effect would be lost at the high tempera-tures prevailing in the glass melt.
The glass melt obtained is then quenched in stage (b) by being poured into water and is thereby converted into glass granules.
This procedure is usually also referred to as fritting.
The glass granules are then comminuted in stage (c) and in particular milled to the desired particle size with conventional mills. An average particle size of the powder obtained of 10 to 50 um, based on the number of particles, is preferred.
The addition of optionally present coloring bodies then takes place in stage (d).
In stage (e), the powder is then compacted to a glass blank of the desired geometry and heterogeneous structure. This is carried out, in particular, at room temperature and pressures of, in particular, 500 to 2,000 bar are used. This process stage of pressing to a blank with a heterogeneous structure is important so that, in contrast to the procedures known from the prior art, surface crystallisation takes place in addition to volume crystallisation during the subsequent heat treatment in stage (f). The heterogeneous structure of the starting glass blank composed of starting glass powder particles pressed together thus allows controlled surface crystallisation on the inner surfaces of the glass powder. This surface crystallisation is identifiable by the fact that even without conventional volume nucleating agents, such as metals or P2O5, the heat treatment taking place in stage ( f ) leads to the formation of a lithium disilicate glass ceramic containing finely divided crystals. If PZOS is used as a component of the starting glass, the heat treatment in stage (f) causes both surface crystallisation and volume crystallisation to take place. In conventional processes, on the other hand, blanks with a homogeneous structure are used, i.e. iri which no - g -particles of starting glass powder are present. The result of this is that surface crystallisation is not possible.
The purpose of the heat treatment taking place in stage (f) is to initiate the crystallisation of the starting glass blank and hence to form the glass ceramic which, after this process stage has ended, takes the form of a densely sintered glass ceramic blank. This blank usually has the shape of a small cylinder or a small slab.
The options for producing the final dental product, such as a bridge or a crown are, in particular, the two options (g1) or (g2) given below.
On the one hand, in stage (g1), the dental product taking the form of a blank is subjected to plastic deformation at a temperature of 700 to 1200°C and by the application of a pressure of 2 to 10 bar to form a dental product of the desired geometry.
To this end, in particular the process described in EP-A-231 773 and the pressing furnace disclosed therein are used. In this process, the blank in the plastic state is pressed into a die cavity conforming with the dental product of the desired shape.
The pressing furnace used for this purpose is marketed as the Empress~ furnace by Ivoclar AG, Liechtenstein.
It was ascertained that conventional lithium disilicate glass ceramics do not satisfy various requirements for further processing to dental products by plastic deformation. A require-ment of this further processing is that the blank in the plastic state should flow in a controlled manner and at the same time react only to a small extent with the investment material.
Surprisingly, these two properties are obtained with the glass ceramic according to the invention by the use of La203 and A1203 in the specified quantities. It is very surprising that the dental product in the form of a blank is free flowing and can be pressed in the plastic state although it is already a glass ceramic material. In contrast to this, the prior art teaches always use of a glass as a liquid melt, since otherwise pressing in the plastic state is not possible because the viscosity is too high.
It has proved to be particularly advantageous if the dental product in the form of a blank has a viscosity of 105 to 106 Pa.s during plastic deformation in stage (g1).
On the other hand, the dental product in the form of a blank may also be machined in stage { g2 ) to a dental product of the desired geometry, for which purpose in particular computer-controlled milling machines are used.
In many cases it is advantageous that the dental product of the desired geometry obtained after stage (g1) or (g2) is provided with a coating in stage (h). A suitable coating is, in particu-lar, a ceramic, a sintered ceramic, a glass ceramic, a glass, a glaze and/or a composite. Coatings which have a sintering temperature of 650 to 950°C and a coefficient of linear expansion that is smaller than that of the dental product to be coated are advantageous. Coatings whose coefficients of linear expansion do not differ by more than t 3.Ox10-6K-1 from those of the substrate are particularly advantageous.
A coating is applied in particular by sintering on, for example, a glass, a glass ceramic or a composite. During this sintering process, the dental product containing lithium disilicate glass ceramic is, however, brought into a temperature range which is above the transformation point of the residual glass matrix of the glass ceramic. Conventional lithium disilicate glass ceramics are often deformed in an undesirable manner during this process since their dimensional stability on heating is too low. The dental product according to the invention, however, has an excellent dimensional stability on heating, for 'which in particular the Laz03 and A1z03 content in the specified quantities is responsible.
Apart from sintering on, other processes of the kind that are customary for the manufacture of material composites, e.g.
bonding or soldering, may also be used.
Moreover, the glass ceramic according to the invention also has very good chemical stability, which is brought about by the use of A1203, La203, Mg0 and Zn0 in the specified quantities .
Apart from the above-mentioned properties of the lithium disilicate glass ceramics according to the invention, these also have the following other important properties, as a result of which they are particularly suitable for use as dental material or component thereof:
- High bending fracture strengths of 200 to 400 MPa. The method of measurement is explained in the Examples.
- High fracture toughness values of 3 to 4.5 MPa~anl~2. The method of determination is explained in the Examples.
A translucency comparable with that of the natural tooth, although the production of the glass ceramic according to the invention takes place at least partially by the mechan-ism of surface crystallisation. This is surprising because opacity is often brought about in other glass ceramic systems due to surface crystallisation effects or initi-ation of surface nucleation, as in the case of the forma-tion of surface distortion due to j3-quartz mixed crystal formation.
- Ability of the color to be matched to that of a natural tooth by using color components. It is surprising-that in spite of the color components that can be used, the strength and toughness of the glass ceramic is not adverse-ly impaired. For example, it is known that the crystallisation of leucite glass ceramics, which are likewise produced by the mechanism of surface crystallisation, is greatly influenced by such additives and that their strength is often very much reduced thereby.
- Ease of etching of the glass ceramic if this is used as dental restoration. For example, a retentive pattern is produced on the inner side of a dental crown according to the invention by controlled etching. When a retentive pattern is produced, no layer-like erosion of the glass ceramic takes place, as is the case, for example, with mica glass ceramics, but small open-pored structures are pro-duced in the surface region. As a result of a retentive pattern of this kind, it becomes possible to fix the glass ceramic to the natural tooth with the aid of an adhesive bonding system.
Suitable shaped dental products according to the invention which contain the glass ceramic according to the invention are, in particular, dental restorations, such as, for example, an inlay, an onlay, a bridge, a post construction, a facing, jackets, veneers, facets, connectors, a crown or a partial crown.
The invention will be explained in more detail below on the basis of examples.
Examples Examples 1 to 21 A total of 21 different glass ceramics according to the invention and shaped dental products with the chemical composition given in Table I were prepared by carrying out stages ( a ) to '( f') of the process described.

O

N

w , , , . , , , , , , ' ~ ~

V M r-1 M 00 N M -I
' ~

M O O O O d , O O O

O

C V Os vp ~ In M M 00 O G~

N ~t h M O V1 , ~ .-i M ~Y
M

O

c~ ~ 00 O N O M ~O ~ h M

a o .-i ~ o .-io o .-a ,-ic w , , , . , , , , , N

O Ir , ~.''~

U , , , , o c , , . o N

O ~n L !)Q

N , . , c , . , . . , H O

H , . . , , , , , r-I

E O

N

I 1 n t , n n 1 , 1 0 N CO .~-~h Op M O r1 O~ ~Y

O

N

z , , , , , , , , , , O ~t h M M O .-~O 00 M

, M M ~-- W ~t et (V N ~t 'ct t r C4 M M M (V , M M N N M

n O

00 ~--~O h h O V'~ h Q et .-i .-iO , ~ r-iO O r-i N

O O~ ~ N v-1O M o0 ~ V'7 r O

W z .-aN M ~t V O

W h 00 Ov N

, , , , . , , O

N N ~ h N d N

O O O . (V , . O O . O

op .-a 'ctC; ~ M I~ N .~-;N

~t ~Y M ~ , v~ et (V N O v7 00 N wt M ~ N O 00 N O M

O O O O O O .~ O M .-iO

~-~ ~ V7 v~ N

O ~ D , , O , , O , '~ W C h M M

O O , , , , r.i O O C

i N I
t 0 i M , , M , , C , i i M I
n ~ tn n O n , n , m -I O n O

O . , , , . , , C , ~ h tn Cs h N M r-r~O et ~i ~n ~i ~ ~n ~i ~ Vi vG ~ ~i H ~

Ov M

, , , (V , (V fV , , , , N M O h ~t N o0 ~ GI M

~ 'ch et'M ~t , et M ~ M M

h 00 N ~ O Oy 00 00 O Oy M M M .~ ~ M M M , V M

O G1 00 .-a.-1 O O r1 .-a r-i .-i O CV .-ie-i .-ir-i m --i 'ct 00 v1 N et .-i M M v0 y 0 h r h I
N M ~t V1 ~O h 00 Ov O N
H ~--W--i~ .-~.--i~ ~ ~ N

Example 22 This Example describes the preparation of a glass ceramic according to the invention and the potential use thereof as a framework material for the preparation of a fully ceramic product which can be formed individually, such as a crown or a multiple-unit bridge, on which in addition a matching dental sintered ceramic is fired on.
A starting glass with the chemical composition given in Table I, Example 21, was prepared initially. To this end, a batch of oxides, carbonates and phosphates was melted in a plati-num/rhodium crucible at a temperature of 1500 to 1600°C for a homogenisation period of one hour. The glass melt was quenched in water, and the glass frit formed was dried and milled to an average particle size of 20 to 30 um. Coloring by means of coloring bodies could be dispensed with due to the use of glass-coloring oxides, namely Ce02, Ti02 and Fe203.
The colored glass powder was then pressed by means of a uniaxial dry press at room temperature and at a pressure of 750 bar to form cylindrical starting glass blanks, hereinafter referred to as green compacts, with a mass of about 4 g. The green compacts were sintered in a furnace under vacuum to produce the glass ceramic according to the invention in the form of a blank. In a first phase, the green compact was fired for one hour at 500°C.
The blank was then densely sintered in a second sinter treatment at 850°C for 2 hours, the rate of heating being 30°C/min.

Properties of the blanks Optical properties The blanks obtained had optical properties, e.g. translucency, color and opacity comparable with conventional dental ceramic commercial products, such as IPS Empress OI blanks from IVOCLAR
AG, Liechtenstein.
Biaxial strength To determine the biaxial strength, sintered blanks were sawn into discs with a diameter of 12 mm and a thickness of 1.1 mm. The biaxial strength was determined with three-point bearing test apparatus (steel balls with a diameter of 3.2 mm) with a force being introduced at one point by means of a punch with a diameter of 1.6 mm according to ISO 6872-1995 E "Dental Ceramic" . The rate at which the load was applied was 0.5 mm/min. The biaxial strength determined under these conditions was 261 ~ 31 MPa.
The glass ceramic blanks obtained were finally pressed under vacuum in the viscous state using the pressing method and pressing furnace according to EP-A-0 231 773 to obtain the sample geometry required for the test in question. The standby tempera-ture of the pressing furnace was 700°C, and the rate of heating to the pressing temperature was 60°C/min; the pressing tempera-ture was 920°C, the retention time at the pressing temperature was 10 min and the pressure was 5 bar. After the pressing process, the die was air-cooled and the specimens were removed from the die by sand-blasting with A1203 powder and glass beads.
The specimens obtained had the following properties:

Properties of glass ceramics sub-~ected to plastic deformation Optical properties The glass ceramic having undergone plastic deformation had translucence properties which enable the dental technician to prepare fully ceramic dental products from it, e.g. crowns or multiple-unit bridges which meet the optical requirements of a natural tooth. Due to the use of glass-coloring oxides in the basic glass, the hot-pressed glass ceramic was tooth-colored.
The color intensity could be adjusted by controlling the concentration of the coloring oxides or by the additional use of coloring bodies.
The combination of translucent framework material and translucent to transparent dental sintered glass ceramic with a coefficient of expansion of 9.1 ~m/mK, which was sintered in layers at 800°C
under vacuum onto the crown or bridge structure having undergone plastic deformation led to translucent, fully ceramic dental restorations which meet the stringent aesthetic requirements for such products.
3-point bending strength Bars with the dimensions 1.5 x 4.8 x 20 mm3 were pressed and these were ground on all sides with SiC wet-grinding paper (grain size 1000). The bending strength was determined with a test specimen span of 15 mm and a load applied at a rate of 0.5 mm/min. according to ISO 6872-1995 E ° Dental ceramic" . The 3 point bending strength determined under these conditions was 341 98 MPa.
Coefficient of linear thermal expansion Cylindrical specimens with a diameter of 6 mm and a length of 20 mm were pressed. The coefficient of expansion determined for these specimens in the temperature range from 100 to 500°C was . 6 ,~m/mK .
Fracture touqhness K, Bars with the dimensions 1.5 x 4.8 x 20 mm3 were pressed and these were ground on all sides with SiC wet-grinding paper ( grain size 1000). Using a diamond wheel (0.1 mm thick), the specimens were notched on one side to a depth of 2.8 mm and then tested for 10 their 3-point bending strength. The bending strength was determined with a test specimen span of 15 mm and a load applied at rate of 0.5 mm/min. The K1~ value determined was 4.0 ~ 0.2 MPa dm.
Acid resistance Disc-shaped specimens with a diameter of 15 mm and a thickness of 1.5 mm were pressed and then ground on all sides with SiC wet-grinding paper (grain size 1000). The loss of mass per unit area of these specimens determined according to ISO 6872-1995 E
"Dental ceramic" was determined after 16 hours' storage in 4 vol . ~ aqueous acetic acid solution, and it was only 73 ug/cmz and was thus markedly below the required standard value for dental ceramic materials of 2000 ug/cmZ.
Example 23 This Example describes the preparation of a glass ceramic according to the invention and the potential use thereof as a framework material for the preparation of a fully ceramic product which can be formed individually, such as a crown or a multiple-unit bridge, onto which in addition a matching dental sintered ceramic has been fired on.
A starting glass with the chemical composition given i~ Table I, Example 18, was prepared initially. To this end, a batch of oxides, carbonates and phosphates was melted in a plati-num/rhodium crucible at a temperature of 1500 to 1600°C for a homogenisation period of one hour. The glass melt was quenched in water and the glass frit formed was dried and milled to an average particle size of 20 to 30 Vim. Commercial coloring bodies and fluorescing agents were added to the glass powder and homogenised.
The colored glass powder was then pressed by means of a uniaxial dry press at room temperature and at a pressure of 750 bar to form cylindrical green compacts with a mass of about 4 g. The green compacts were sintered in a furnace under vacuum to obtain the glass ceramic according to the invention in the form of a blank. In a first phase, the green compact was fired at 500°C for 20 minutes. The blank was then densely sintered for 30 minutes at 850°C in a second sinter treatment, the rate of heating being 30°C/min. Unless otherwise specified, the procedure used to determine the properties of the glass ceramic blank was the one given in Example 22.
Properties of the blanks Optical properties The blanks obtained had optical properties such as translucency, color and opacity comparable with conventional dental ceramic commercial products, e.g. IPS Empress Dentin 24 blanks from IVOCLAR AG, Liechtenstein.

Biaxial strength The biaxial strength was 270 ~ 38 MPa.
The glass ceramic blanks obtained were finally pressed under vacuum in the viscous state to the desired specimen geometry for the test in question using the pressing process and pressing furnace according to EP-A-0 231 773. The standby temperature of the pressing furnace was 700°C, the rate of heating to the pressing temperature was 60°C/min, the pressing temperature was 920°C, the retention time at the pressing temperature was 10 min.
and the pressure was 5 bar. After the pressing process, the die was air-cooled and the specimens were removed from the die by sand blasting with A1z03 powder and glass beads.
The properties of the specimens obtained were determined according to the procedure described in each case in Example 22.
Properties of glass ceramic subjected to plastic deformation Optical properties The glass ceramic having undergone plastic deformation had translucence properties which enable the dental technician to prepare fully ceramic dental products from it, e.g. crowns or multiple-unit bridges, which comply with the optical requirements of a natural tooth. The combination of translucent framework material and translucent to transparent dental sintered glass ceramic with a coefficient of expansion of 9.1 ~m/mK which was sintered in layers at 800°C under vacuum onto the crown or bridge structure which had undergone plastic deformation led to translucent, fully ceramic dental restorations which meet the stringent aesthetic requirements of such dental products.

3-point bending strength The 3-point bending strength was 347 ~ 37 MPa.
Coefficient of linear thermal expansion The coefficient of expansion determined in the temperature range from 100 to 500°C was 10.7 um/mK.
Fracture toughness K, The K1~ value determined was 3.8 ~ 0.5 MPa dm.
Acid resistance The loss of mass per unit area determined according to ISO 6872-1995 after 16 hours' storage in 4 vol.~ aqueous acetic acid solution was markedly below the standard value for dental ceramic materials of 2000 ~g/cm2.

Claims

1. Sinterable lithium disilicate glass ceramic, which contains the following components in the following quantities:

Component Wt.%

SiO2 57.0 to 80.0 Al2O3 0 to 5.0 La2O3 0.1 to 6.0 MgO 0 to 5.0 ZnO 0 to 8.0 K2O 0 to 13.5 Li2O 11.0 to 19.0 P2O5 0 to 11.0 wherein Al2O3 + La2O3 equals 0.1 to 7.0 wt.% and MgO+ZnO equals 0.1 to 9.0 wt.%.

2. Sinterable lithium disilicate glass ceramic according to claim 1 wherein the quantity of MgO is 0.1 to 5.0 wt%.

3. Sinterable lithium disilicate glass ceramic according to claim 1 wherein the quantity of MgO is 0.1 to 4.0 wt%.

4. Sinterable lithium disilicate glass ceramic according to claim 1 which contains 0 to 8.0 wt.% color components, said color components being formed from glass-coloring oxides (c) and/or coloring bodies (d) in the following quantities:

(c) glass-coloring oxides 0 to 5.0 wt.% and (d) coloring bodies 0 to 5.0 wt.%

5. Lithium disilicate glass ceramic according to claim 4, wherein TiO2, CeO2 and/or Fe2O3 are present as glass-coloring oxides.

6. Lithium disilicate glass ceramic according to claim 4, which contains doped spinets and/or doped ZrO2 as coloring bodies.

7. Lithium disilicate glass ceramic according to any one of claims 1 to 6 which contains 0 to 6 wt.% additional components, said additional components being selected from B2O3, F, Na2O, ZrO2, BaO and/or SrO.

8. Lithium disilicate glass ceramic according to any one of claims 4 to 6 which contains 0 to 6 wt.% additional components, said additional components being selected from B2O3, F, Na2O, ZrO2, BaO and/or SrO.

9. Lithium disilicate glass ceramic according to claim 8, wherein the quantities of the components, independently of one another, are as follows:

Components Wt.%

SiO2 57.0 to 75.0 Al2O3 0 to 2.5 La2O3 0.1 to 4.0 MgO 0.1 to 4.0 ZnO 0 to 6.0 K2O 0 to 9.0 Li2O 13.0 to 19.0 P2O5 0 to 8.0 Colour components 0.05 to 6.0 Additional components 0 to 3.0

10. Lithium disilicate glass ceramic according to claim 9 wherein the quantities of ZnO, K2O and P2O5 independently of one another are as follows:

Components Wt.%
ZnO 0.1 to 5.0 K2O 0.5 to 7.0 P2O5 0.5 to 8.0

11. A process for the preparation of shaped dental products which contain the glass ceramic according to any one of claims 1 to 10, wherein:

(a) a starting glass containing the components according to any one of claims 1 to 10 with the exception of coloring bodies is fused at temperatures of 1200 to 1650°C to form a glass melt, (b) the glass melt is poured into water with the formation of glass granules, (c) the glass granules are comminuted to a powder with an average particle size of 1 to 100 µm, based on the numbers of particles, (d) the coloring bodies optionally present are added to the powder, (e) the powder is compacted to a starting glass blank of the desired geometry and heterogeneous structure, and (f) the starting glass blank is subjected to one or more heat treatments under vacuum and in the temperature range from 400 to 1100°C in order to achieve dense sintering and to give a dental product in the form of a blank.

12. A process according to claim 11, wherein (g1) the dental product in the form of a blank is subjected to plastic deformation at a temperature of 700 to 1200°C and by the application of a pressure of 2 to 10 bar to obtain a dental product of the desired geometry.

13. A process according to claim 12, wherein (g2) the dental product in the form of a blank is machined to a dental product of the desired geometry.

14. A process according to any one of claims 11 to 13, wherein the dental product of the desired geometry:
(h) is provided with a coating.

15. A process according to claim 14, wherein the coating used is a ceramic, a sintered ceramic, a glass ceramic, a glass a glaze and/or a composite.

16. A process according to claim 14 or 15, wherein the coating has a sintering temperature of 650 to 950°C and a linear coefficient of thermal expansion which is lower than that of the dental product to be coated.

17. A process according to any one of claims 14 to 16, wherein the coating has a linear coefficient of thermal expansion which deviates by no more than ~ 3.0 x 10-6 K-1 from that of the dental product of the desired geometry.

18. The use of the glass ceramic according to any one of claims 1 to 10 as a dental material or a component of dental material.

19. A shaped dental product which contains the glass ceramic according to any one of claims 1 to 10.

20. A shaped dental product according to claim 19, which is an inlay, an onlay, a bridge, a post construction, a veneer, a crown or a partial crown.

21. Glass comprising the components of the glass ceramic according to any one of claims 1 to 3.