AU695549B2

AU695549B2 - Sinterable lithium disilicate glass ceramic

Info

Publication number: AU695549B2
Application number: AU35305/97A
Authority: AU
Inventors: Martin Frank; Wolfram Hoeland; Volker Rheinberger; Marcel Schweiger
Original assignee: Ivoclar AG
Current assignee: Ivoclar AG
Priority date: 1996-09-05
Filing date: 1997-08-26
Publication date: 1998-08-13
Anticipated expiration: 2017-08-26
Also published as: ATE186286T1; AU3530597A; JPH10101409A; JP3093691B2; EP0827941B1; EP0827941A1; CA2213390C; CA2213390A1

Abstract

Sinterable lithium di:silicate glass ceramic contains (in wt.%): 57.0-80.0 SiO2; 0-5.0 Al2O3; 0.1-6.0 La2O3; 0-5.0 (esp. 0.1-5.0) Mg; 0-8.0 ZnO; 0-13.5 K2O; 11.0-19.0 Li2O; 0-11.0 P2O5; 0-8.0 colourants; and 0-6.0 additives. Al2O3+La2O3 = 0.1-7.0 wt.% and MgO+ZnO = 0.1-0.9 wt.%. The colourants comprise 0-5.0 wt.% glass-colouring oxides, and 0-5.0 wt.% coloured body. Also claimed is a process for forming a moulded dental product made of the glass ceramic.

Description

AUSTRALIA

Patents Act 1990 IVOCLAR AG

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Sinterable lithium disilicate glass ceramic The following statement is a full description of this invention including the best method of performing it known to us:- IPL---

I

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 La 2 0 3 and are formed in the usual manner by melting suitable starting materials, pouring into molds and subsequent heat treatment of the articles obtained.

15 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 i l 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. La 2

O

3 is not, however, contained in the glass ceramic.

Glass ceramics based on SiO 2 and Li 2 O which contain large 25 quantities of physiologically very harmful arsenic oxide are S 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 La 2 03 or MgO 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.

2- 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 necessarily contains CaO 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 25 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 I 1 i. 3 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.

The object of the invention is, therefore, to provide a lithium disilicate glass ceramic which exhibits optimum flow properties and at the same time little reaction with the investment material 15 when pressed in the plastic state to dental products, has high dimensional stability on heating, particularly in the range from 700 to 900°C, and has excellent chemical stability.

This object is achieved by the sinterable lithium disilicate 20 glass ceramic according to claims 1 to 6.

The invention also provides the process for the preparation of I shaped dental products according to claims 7 to 13, the use of the glass ceramic according to claim 14, and shaped dental 25 products containing the glass ceramic according to claims 15 and 16.

The sinterable lithium disilicate glass ceramic according to the invention is characterised in that it contains the following components: Component Wt.% SiO 2 57.0 to 80.0 A1 2 0 3 0 to LazO 3 0.1 to MgO 0 to -4 ZnO

K

2 0

L'

2 0 Color components Additional components particularly 0.1 to 0 to 0 to 13.5 11.0 to 19.0 0 to 11.0 0 to 0 to wherein A1 2 03 La 2

O

3 MgO ZnO amount to amount to 0.1 to 7.0 wt.% and 0.1 to 9.0 wt.% too.

to* Lot.toop to9 and wherein the color components ard formed from glass-coloring oxides and/or coloring bodies in the following quantities: glass-coloring oxides coloring bodies 0 to 5.0 and 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 S'0 2 A1 2 0 3 La 2

O

3 Wt. 57.0 to 75.0 0 to 0.1 to 4. 0

I

j 14g0 ZnO

K.,O

Li 2

O

P 20- Color components Additional components 0.2. to 0 to 6.0. particularly 0.1 to 0 to 9.0 particularly 0.5 to 13.0 to 19.0 0 to 8.0 particularly 0.5 to 0.05 to 0 to fira The glass ceramic according to the invention contains preferably color components, namely glass-coloring oxides and/or coloring bodies 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 TiO 2 CeO 2 and/or Fe 2

O

3 serve only to obtain a shading, the main coloration being brought about by the coloring bodies. It is to be noted that TiO 2 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 ZrO 2 The coloring bodies may be both non-fluorescing and fluorescing materials.

25 In addition to the components mentioned above, the lithium disilicate glass ceramic according to the invention may also contain additional components, for which B 2 0 3 F, Na 2 O, ZrO 2 BaO and/or SrO are particularly suitable. The viscosity of the residual glass phase of the glass ceramic may be influenced with

B

2 0 3 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

I

V

-6particular, 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 characterised in that a starting glass which contains the components according to any of claims 1 to 6 with the exception of coloring bodies is fused at temperatures of 1200 to 1650 0

C,

the glass melt is poured into water with the formation of glass granules, the glass granules are comminuted to a powder with an 'a average particle size of 1 to 100 gm, based on the number of particles, the coloring bodies optionally present are added to the powder, the powder is compacted to a starting glass blank of the desired geometry and heterogeneous structure, and the starting glass blank is subjected to one or more heat 400* *treatments under vacuum and in the temperature range from 400 to 1100 0 C in order to achieve a dense sintering and to give a dental product in the form of a blank.

In process stage 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 a -7process, since their effect would be lost at the high temperatures prevailing in the glass melt.

0 00 00 0 0*0 0 0000 0000 04 4, 00 0 00 9 000 0 00 *0 00 0 *0 411* Ii I 41 0 1 S 01 It,' 4 0044 0* 00 4 0000 4$ a

II

The glass melt obtained is then quenched in stage 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 and in particular milled to the desired particle size with conventional mills. An average particle size of the powder obtained of 10 to pin, based on the number of particles, is preferred.

The addition of optionally present coloring bodies then takes place in stage In stage 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 The heterogeneous structure of the starting glass blank 25 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 P 2 0 5 the heat treatment taking place in stage leads to the formation of a lithium disilicate gl~ass ceramic containing finely divided crystals. If P 2 0 5 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. in which no c-- 8 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 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 (gl) or 04 (g2) given below.

H 15 On the one hand, in stage the dental prodict taking the form of a blank is subjected to plastic deformation at a temperature of 700 to 1200 0 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 20 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.

o Oo The pressing furnace used for this purpose is marketed as the Empress furnace by Ivoclar AG, Liechtenstein.

S S: It was ascertained that conventional lithium disilicate glass ceramics do not satisfy various requirements for further 'i processing to dental products by plastic deformation. A requirement 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 La 2 0 3 and A1 2 0 3 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 L -9ceramic 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.

Ii *44p ft P4 4. Ph P 4 9 4

I.

*444 4 1*4 44, K*44 9 *4 It has proved to be particularly advantageous if the dental product in the form of a blank has a viscosity of 10 to 106 Pa.s during plastic deformation in stage (gi).

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 compute controlled milling machines are used.

15 In many cases it is advantageous that the dental 'product of the desired geometry obtained after stage (gi) or (g2) is provided with a coating in stage A suitable coating is, in particular, 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 3.0x10 -6K- f rom those of the substrate are particularly advantageous.

A coating is applied in particular by sintering on, f or 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 t.ieir dimensional stability on heating is too low. The dental product accor-ling to the invention, however, has an excellent dimensional stability on heating, for which in

L

^7 FSi 10 particular the La 2 0 3 and A1 2 0 3 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 A1 2 0 3 La20 3 MgO and ZnO 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: 4 4 o« S 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 MPaxm l The method of determination is explained in the Examples.

t A translucency comparable with that of the natural tooth, 25 although the production of the glass ceramic according to the invention takes place at least partially by the mechanism of surface crystallisation. This is surprising because opacity is often brought about in other glass ceramic systems due to surface crystallisation effects or initiation of surface nucleation, as in the case of the formation of surface distortion due to P-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 -11strength and toughness of the glass ceramic is not adversely 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- 15 duced in the surface region. As a result 6f a retentive 4. pattern of this kind, it becomes possible to fix the glass ceramic to the natural tooth with the aid of an adhesive bonding system.

20 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, a« 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 to of the process described.

i a 14la a *ao aC *t a an a a ad ag t C Table I Exp. SiO, A1 2 0, P 2 0 5 IK NaO LLO B 2 0 3 TiO, ZrO 2 CeO 2 F Lan,2 ZnO MgO FcO No.

1 65.0 4.8 3.7 4.0 14.2 0.1 4.6 3.6 2 66.9 1.1 3.8 3.4 14.8 1.8 7.9 0.3 3 66.6 1.0 3.4 3.7 15.1 0.6 6.0 3.5 0.1 4 66.2 0.7 2.5 13.4 14.7 0.85 0.6 0.2 0.7 0.15 73.1 4.3 15.8 1.0 5.5 0.3 6 65.0 4.7 3.6 4.0 14.3 0.3 3.3 4.8 7 75.3 1.0 3.7 4.1 11.0 0.6 4.3 8 79.8 0.5 2.1 2.0 12.1 1.5 1.8 0.2 9 70.1 0.7 2.5 2.8 18.9 1.7 3.0 0.3 69.5 1.1 3.8 4.3 15.4 0.55 0.3 4.9 0.15 _rLC i I C 4 r- e i 0 00 t 11 68.4 1.1 3.7 4.2 -15.1 1.7 0.8 4.8 0.2 12 619.8 1.0 3.8 4.3 15.5 0.25 0.3 -0.4 0.15 0.2 41.1 0.2 13 70.5 0.9 3.2 4.0 15.7 -0.5 1.25 0.4 3.4 0.15 14 57.2 2.8 10.8 3.7 2.1 14.5 3.2 0.5 0.3 4.9 71.4 1.1 4.0 4.4 15.9 0.5 2.7- 16 71.1 1.1 3.9 2.9 15.7 0.2 5.1 17 64.3 1.0 3.8 4.2 2.3 15.2 3.4 0.5 1.0 4.3 18 69.3 1.0 3.8 3.8 15.3 1.5 1.6 0.8 2.7 0.2- 19 72.6 4.1 16.1 0.9 0.5 3.2 2.2 0.4- 71.5 1.1 4.0 3.9 16.6 0.4 0.8 0.3 0.25 1.0 0.15 21 69.6 1.1 3.9 3.3 15.4 -0.5 0.3 0.3 5.2 0.2 0.2 14 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 multipleunit 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- P lnum/rhodium crucible at a temperature of 1500 to 1600 0 C for a homogenisation period of one hour. The glass melt was quenched .O in water, and the glass frit formed was dried and milled to an average particle size of 20 to 30 gm. Coloring by means of coloring bodies could be dispensed with due to the use of glasscoloring oxides, namely Ce02, TiO 2 and Fe20 3 2:The colored glass powder was then pressed by means of a uniaxial 4 dry press at room temperature and at a pressure of 750 bar to 20 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 0 C for 2 hours, the rate of heating being 30 0 C/min.

S.

A:

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 01 blanks from IVOCLAR AG, Liechtenstein.

Biaxial strenguth 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 o being introduced at one point by means of a punch with a diameter 0 1" of 1. 6 mm according to ISO 6872-1995 E "Dental Ceramic" The rate at which the load was applied was 0. 5 mm/mmn. 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 temperature of the pressing furnace was 700 0 C, and the rate of heating to the pressing temperature was 60 0 C/min; the pressing temperature was 920 0 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 A1 2 0 3 powder and glass beads.

The specimens obtained had the following properties: t4 S S $4 a 5 4 4. *4 4 4 4 16 Properties of glass ceramics subjlected 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 gn/mK, which was sintered in layers at 8001C under vacuum onto the crown or bridge structure having undergone 15 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 mm 3 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. mm/mmn. according to ISO 6872-1995 E Dental ceramic" The 3point bending strength determined under these conditions was 341 ±98 MPa.

Coefficient of linear thermal ex-pansion Cylindrical specimens with a diameter of 6 mm and a length of mm were pressed. The coefficient of expansion determined a. 4 eat.

94 o 4000 a i 111 -71 C 17 these specimens in the temperature range from 100 to 5001C was 10.6 pm/mK.

Fracture touqgmess K 1 3 Bars with the dimensions 1.5 x 4.8 x 20 mm 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 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 K 1 value determined was 4.0 0.2 MPa Vm.

o o a r* r or or a

P

or aO oP11

I

f i o o1 or r r w.

B

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 wetgrinding paper (grain size 1000). The loss of mass per unit area 20 of these specimens determined according to ISO 6872-1995 E UDental ceramic" was determined after 16 hours' storage in 4 vol.% aqueous acetic acid solution, and it was only 73 pg/cm 2 and was thus markedly below the required standard value for dental ceramic materials of 2000 Lg/cm 2 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 multipleunit bridge, onto which in addition a matching dental sintered ceramic has been fired on.

A starting glass with the chemical composition given in Table I, Example 18, was prepared initially. To this end, a batch of t c 18 oxides, carbonates and phosphates was melted in a platinuzm/rhodium crucible at a temperature of 1500 to 1600 0 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 pun. 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 I the glass ceramic according to the invention in the form of a blank. In a first phase, the green compact was fired at 500 0 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 Unless otherwise specified, the procedure used to determine the properties of the glass ceramic blank was the one ;Ij' given in Example 22.

Properties of the blanks Optical properties 25 The blanks obtained had optical properties such as translucency, 4 color and opacity comparable with conventional dental ceramic I commercial products, e.g. IPS Empress Dentin 24 blanks from IVOCLAR AG, Liechtenstein.

'*'WfWtassK- 11 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 furnaace was 700 0 C, the rate of heating to the pressing temperature was 601C/min, the pressing temperature was 9201 0 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 A1 2 0 3 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 I Optical prope ties Ip- The glass ceramic having undergone plastic def ormation 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 II' material and translucent to transparent dental sintered glass ceramic with a coefficient of expansion of 9.1 p.m/xmR which was sintered in layers at 8001C 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.

*C-

1 20 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 0 C was 10.7 pm/mK.

Fracture toughness K, The Ki, value determined was 3.8 0.5 MPa im.

f..

*ft@ f *a 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 gg/cm 2 t

Claims

1. Sinterable lithium disilicate the following components: Component SiO 2 A11203 La 2 03 MgO ZnO K 2 0 Li 2 O PzO 5 Color components Additional components glass ceramicr including Wt.%

57.0 to 80.0 0 to 0.1 to 0 to 5.0, particularly 0. l to 0 to 0 to 13.5 11.0 to 19.0 0 to 11.0 0 to 0 to Car, *t #4 4 4 4 .4,4 4 40 V a 4**V wherein A1 2 0 3 La 2 03 XgO ZnO amount to amount to 0.1 to and 0.1 to 9.0 wt.% and wherein the color components are formed from glass- coloring oxides and/or coloring bodies in the following quantities: glass-coloring oxides coloring bodies to 5.0 wt.% and to 5.0 wt.%. 2. Lithium disilicate glass ceramic according to claim 1, which consists of the components specified. 3. Lithium disilicate glass ceramic according to claim 1 or 2, wherein TiO 2 CeO z and/or Fe 2 0 3 are present as glass-coloring oxides. p. A 22 4. Lithium disilicate glass ceramic according to any one of claims 1 to 3, which contains doped spinels and/or doped ZrO 2 as coloring bodies. Lithium disilicate glass ceramic according to any one of claims 1 to 4, wherein the additional components are B 2 0 3 F, NazO, ZrO2, BaO and/or SrO. 6. Lithium disilicate glass ceramic according to any one of claims 1 to 5, wherein the quantities of the components, independently of one another, are as follows: Component Wt. SiO 2 57.0 to 75.0 SAlz,0 3 0 to Laz0 3 0.1 to MgO 0.1 to ZnO 0 to 6.0, particularly 0.1 to K 2 0 0 to 9.0, particularly 0.5 to Liz0 13.0 to 19.0 P205 0 to 8.0, particularly 0.5 to Color components 0.05 to Additional components 0 to 7. A process for the preparation of shaped dental products which contain the glass ceramic according to any one of claims 1 to 6, wherein: a starting glass containing the components according to any one of claims 1 to 6 with the exception of coloring bodies is fused at temperature of 1200 to 1650 0 C, the glass melt is poured into water with the formation of glass granules, -23- the glass granules are commninuted to a powder with an average particle size of 1. to 100 gin, based on the numbers of particles, the coloring bodies optionally present are added to the powder, the powder is compacted to a starting glass blank of the desired geometry and heterogeneous structure, and the starting glass blank is subjected to one or more heat treatments under vacuum and in the temperature 1' range from 400 to 1100'C. in order to achieve dense sintering and to give a dental product in the form of 0 a blank. 8. A process according to claim 7, wherein 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 bar to obtain a dental product of the desired geometry. A 9. A process according to claim 7, wherein (g2) the dental product in the form of a blank is machined to a dental product of the desired geometry. A process according to any one of claims 7 to 9, wherein the dental product of the desired geometry is provided with a coating. 24 11. A process according to claim 10, wherein the coating used is a ceramic, a sintered ceramic, a glass ceramic, a glass, a glaze and/or a composite. 12. A process according to claim 10 or 11, wherein the coating I has a sintering temperature of 650 to 950 0 C and a coeffi- cient of linear expansion which is lower than that of the dental product to be coated. 13. A process according to any one of claims 10 to 12, wherein the coating has a coefficient of linear expansion which deviates by no more than 3.0 x 10' 6 K l from that of the 4 dental product of the desired geometry. 14. A shaped dental product including the class ceramic according to any one of claims 1 to 6. I 15. A shaped dental product according to claims 14, which is San inlay, an onlay, a bridge, a post construction, a veneer, a crown or a partial crown. 16. Sinterable lithium disilicate glass ceramic as hereinbefore described with reference to any one of the examples. 17. A process for the preparation of a shaped dental product Sas hereinbefore described with reference to any one of Sthe examples. 18. A shaped dental product as hereinbefore described with reference to any one of the examples. DATED THIS 26 DAY OF AUGUST 1997 IVOCLAR AG Patent Attorneys for the Applicant:- F.B.RICE CO. t 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. I lo e9 4 9 iS II 9 9 9 9; o 9 *91t .ft 'C 9 l iiii I 99 I 49i