Lithium silicate glass ceramic

DESCRIPTION

LITIO SILICATE VITROCERAMICS

The invention relates primarily to lithium silicate glass ceramic materials which can be easily mechanically molded and subsequently converted into high strength molded products.

There is a growing demand for materials that can be processed into dental restorative products such as crowns, inlays and bridges by computer controlled milling machines. Such CAD / CAM methods are very attractive as they allow the patient to be quickly restored to the desired restoration. A so-called office treatment is therefore possible for the dentist.

However, materials suitable for processing via computer aided design / computer aided manufacturing (DAC / MAC or CAD / CAM) methods must meet a very specific property profile.

First and foremost, they must ultimately have attractive optical properties in prepared restoration, such as translucency and shade, which mimic the appearance of natural teeth. They still need to show high strength and chemical durability so that they can

It is important to assume the function of the natural tooth material and to maintain these properties over a sufficient period of time, while being permanently in contact with fluids in the oral cavity which may even be aggressive as well as acidic in nature.

Secondly and most importantly, it should be possible to easily manufacture them mechanically to the desired shape without undue tool wear and within short time intervals. This property requires relatively low strength of the material and is therefore in contrast to the desired properties mentioned above for the final restoration.

The difficulty in combining the low strength properties in the phase of the material to be processed and the high strength of the final restoration is reflected by the known materials for CAD / CAM processing, which are in particular with regard to easy mechanical manufacture. , unsatisfactory.

DE-A-19750794 discloses lithium disilicate glass ceramics which are primarily intended to be molded to the desired geometry by a hot pressing process wherein the molten material is pressed into the viscous state. It is also possible for these materials to be molded by computer assisted milling processes. However, it has been shown that machine manufacture of these materials results in very severe wear and tear.

Alto1688398 high of tools and very long processing times. These disadvantages are caused by the high strength and toughness imparted to materials mainly by the crystalline phase of lithium disilicate. In addition, machine-made restorations have been shown to show only poor edge strength. The term edge strength refers to the strength of parts of the restoration having only a small thickness in the range of a few 1/10 mm.

Other approaches of realizing easy machine manufacturing capability in conjunction with a high strength of the final restoration have also been made. EP-B-774993 and EP-B-817597 describe Al2O3 or ZrO2 based ceramic materials which are manufactured in a non-sintered state which is also referred to as a green state. Subsequently, the green bodies are sintered to increase strength. However, these ceramic materials suffer from a drastic shrinkage of up to 50% by volume (or up to 30% as linear shrinkage) during the final sintering step. This leads to difficulties in preparing restorations with exactly the dimensions as desired. Substantial shrinkage poses a particular problem if complicated restorations such as a multipillary bridge are manufactured.

From

Photosensitive Glass

SD Stookey, Chemical Machining of Ind. Eng. Chem., 45 (1993) 115-118 and SD Stookey, Photosensitively Opacifiable Glass in

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US-A-2684911 (1954) is also known that in lithium silicate glass ceramics a metastable phase can first be formed. For example, in photosensitive glass ceramics (Fotoform®, FotoCeram®) Ag particles are formed using UV light. These Ag particles serve as a crystallizing agent in a lithium metasilicate phase. Areas that have been exposed to light are subsequently washed with diluted HF. This procedure is possible since the solubility of the lithium metasilicate phase in HF is much higher than the solubility of the parent glass. The remaining glass portion after said solubilization process (Fotoform®) may be transferred to a lithium disilicate glass ceramic (FotoCeram®) by an additional heat treatment.

Also Borom investigations, for example, M.-P. Borom, AM Turkalo, RH Doremus, Strength and

Microstructure in Lithium Disilicate Glass-Ceramics in J.

Am. Chem. Ceram. Soc., 58 (9-10) (1975) 385-391, and M.-P.

Borom, AM Turkalo, RH Doremus, Verfahren zum

Herstellen von Glaskeramiken in DE-A-2451121 (1974), show that a lithium disilicate glass ceramic can first crystallize in varying amounts as the metastable lithium metasilicate phase form.

However, there are also compositions which crystallize as the early disilicate phase and the metasilicate phase is not at all present. A systematic investigation of this effect has not become known. From Borom's investigations it is also known that the

ΡΕ1688398 vitroceramic which contains lithium metasilicate as the main phase has a reduced resistance compared to

<td colspan="2">of a glass ceramic lithium disilicate.</td><td>what</td><td>contains only</td><td>a phrase</td><td>in</td>

<td> 0</td><td>document</td><td>D3</td><td>(US 2002/0010063</td><td>) reveals</td><td>one</td>

process for the preparation of modeled translucent lithium disilicate glass ceramic products, which may be used in particular as dental restorations (summary). The process involves the preparation of a glass, followed by heat treatment (claim 1) to obtain the so-called blanks (paragraph 78). The glass ceramic composition comprises ZnO.

It has further been found that the presence of ZnO in prior art lithium silicate glass ceramics is undesirable especially when highly translucent dental restorations are to be produced. Under such circumstances, the strong opalescent effect caused by ZnO is apparent and results in unacceptable optical properties for a restoration that is to mimic the natural tooth material.

It is therefore an object of the present invention to eliminate these disadvantages and in particular to provide a material that can be easily shaped by computer aided shaping and shaping processes and can subsequently be converted into a high strength dental product which also exhibits high durability.

It has excellent chemical properties and excellent optical properties and exhibits drastically reduced shrinkage during said final conversion, and achieves all of these properties without the need for ZnO as a component.

This object is achieved by the process for preparing a dental restoration according to claims 1 to 23. The invention also relates to the use of a vitroceramic or lithium silicate glass according to claims 24 to 28.

It has been surprisingly shown that by using a starting glass of a very specific composition and a specific process, it is possible to provide in particular a glass ceramic having metastable lithium metasilicate (LI 2 SiO 3) as the main crystalline phase instead of lithium disilicate (Li 2 Si 2 O 5). This lithium metasilicate glass ceramic has a low strength and toughness and therefore can be easily manufactured with a machine in the form of even complicated dental restorations, but can after such machine manufacture be converted by heat treatment into a glass disilicate glass ceramic product. lithium with remarkable mechanical properties, excellent optical properties, in particular a strongly reduced opalescence, and very good chemical stability, therefore only suffering a very limited shrinkage.

The lithium silicate glass ceramic used according to the invention comprises the following components:

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% M / m component

SiO₂

Li₂O

K₂0

TO 1₂C&gt; 3

Nucleating Agent Me (11) 0

64.0-75.0, in particular 64.0-73.0 13.0-17.0

2,0-5,0 0,5-5,0 2,0-5,0

0-3.0 with Me (11) 0 to be selected from at least one of CaO, BaO, MgO and SrO, and comprises less than 0.1% w / w ZnO, and comprises lithium metasilicate as main crystalline phase.

It is preferable that the glass ceramic is essentially free of ZnO.

It is surprising that even without the presence of ZnO the glass ceramic used according to the invention fulfills the multiple requirements mentioned. This was made possible by selecting other components and their quantities, and preferably by the proportions of some of these components relative to others.

The vitroceramics used according to the invention comprise lithium metasilicate as the main crystalline phase. Such glass ceramics are also referred to herein as lithium metasilicate glass ceramics.

It has also been found to be beneficial for the glass ceramic to be from 0 to 2.0 and preferably from 0 to 1.5% w / w

ΡΕ1688398 to Me (II) O. Me (II) O is in particular selected from at least one of CaO and MgO. The vitroceramics particularly

<td colspan="6">Preferably, they comprise from 0.1 to 1.0% w / w MgO.</td>

<td></td><td> 0</td><td>agent</td><td colspan="2">nucleation is preferably</td><td>fur</td>

<td>any less</td><td>one of</td><td>P2O5 and</td><td>composed of elements Pt,</td><td>Ag, Cu</td><td>and W.</td>

<td>Him</td><td>it suits</td><td>for</td><td>induce the formation of</td><td>crystals</td><td>in</td>

lithium metasilicate and is preferably P2O5.

Furthermore, it has been shown that a specific molar ratio of SiO₂ to Li₂It serves to ensure that after the necessary heat treatment of a corresponding starting glass, mainly lithium metasilicate and lithium disilicate are produced, respectively. This is of particular importance. While an essentially lithium disilicate free lithium metasilicate vitroceramic in particular results in excellent machine-making capability, an essentially lithium disilicate free restoration of the easily dissolvable lithium metasilicate has very good chemical stability.

Thus, it was found to be preferable that the molar ratio of SiO₂: Li₂O is at least 2.2: 1, preferably

<td>at least 2.3: 1, and more</td><td>preferably</td><td>in the break</td><td>in</td>

<td>2.3: 1 to 2.5: 1.</td><td></td><td></td><td></td>

<td>In addition,</td><td>investigations</td><td>revealed that</td><td>The</td>

<td>molar ratio of A1₂O₂: K₂O is</td><td colspan="2">significant for obtaining</td><td>gives</td>

<td>desired translucency and</td><td>the crystallization</td><td>predominant</td><td>in</td>

<td>lithium metasilicate.</td><td></td><td></td><td></td>

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It is preferred that the molar ratio of A ^CqzKçO is in the range of 1: 0.5 to 1: 2.0 and preferably is 1: 1 to

1:2,0.

Preferred ranges also exist for the quantities of glass ceramic components used in accordance with the invention. These can be used independently of each other.

It is preferred that the glass ceramic comprises from 2.5 to 5.0% w / w ΑΙ2Ο3.

It is also preferred that the glass ceramic comprises 70.0 to 73.0% w / w SiCg.

It is also preferred that the glass ceramic comprises 0 to 4.0, preferably 0.1 to 4.0, more preferably 1.0 to 4.0 and most preferably 1.5 to 3.0% w / w. m from ZrCç. If the emphasis is on obtaining a high strength end-lithium disilicate ceramic, then 0 and 2.0% w / w ZrCC are advantageous.

It is further preferred that the glass ceramic comprises at least one of the following components in an amount of:

% M / m component

Li₂OK₂Dye and fluorescent metal oxides

14,0-16,0 3,0-4,5

0-7.5, preferably 0.5-3.5

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The metal of the dyeing and fluorescent metal oxides is preferably selected from the elements, and group f, in particular from the group Ta, Tb, Y, La, Er, Pr, Ce, Ti, V, Fe and Mn, is added. The coloring and fluorescent oxides ensure that the color of the final dental product matches that of the patient's natural tooth material.

In addition, glass ceramics may comprise as an additional component₂O in an amount from 0 to 2.0% w / w.

Additional components to increase the technical processing capacity of the glass may also be present. Such additional components may therefore be in particular compounds such as B₂C&gt; 3 and F in general quantity up to 0 to 5.0% w / w.

Generally, the amount of lithium metasilicate is from 20 to 80% v / v. It has been surprisingly shown that a specific volume portion of lithium metasilicate must be present to achieve excellent processing properties. Thus, it is further preferred that the crystalline lithium metasilicate phase forms from 20 to 50% v / v and in particular from 3 30 to 40% v / v of lithium lithium vitroceramics. Such a part of the volume causes the crystals to be present rather than spaced from each other and therefore avoids too high a resistance of the glass ceramic.

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If the emphasis is placed on obtaining a high strength lithium disilicate ceramic, then the lithium metasilicate phase preferably forms more than 50 and up to 80% v / v lithium silicate vitroceramics.

Lithium metasilicate crystals are preferably lamellar or platelet shaped. This leads to a very good manufacturing capability with lithium metasilicate glass-ceramic machine without the use of high energy and without uncontrolled breakage. The last aspect of uncontrolled breaking is for example known from glasses which are generally unsuitable for machine manufacturing. It is assumed that the preferred morphology of lithium metasilicate crystals is also responsible for the surprisingly high edge strength of the products, for example complicated dental restorations, can be made from the lithium metasilicate glass ceramics used in accordance with the invention.

The lithium silicate glass ceramic used according to the invention is preferably in the form of a blank. The blank usually takes the form of a small cylinder or a rectangular block. Exact form depends on the specific apparatus used for the desired white computer-aided manufacture.

After machine manufacturing, lithium silicate glass ceramic is preferably in the form of a dental restoration, such as an inlay, an onlay, a bridge, a pillar, a turning, an inlay, a

ΡΕ1688398 facet, a crown, a partial crown, a frame or an eyebrow.

A lithium silicate vitroceramic comprising lithium disilicate as the main crystalline phase may be formed in a process wherein the lithium metasilicate of a vitroceramic used according to the invention is converted to lithium disilicate crystals.

A dental product made from lithium disilicate glass ceramic may be formed in a process wherein the lithium metasilicate of a glass ceramic used according to the invention is converted to lithium disilicate crystals.

The lithium metasilicate glass ceramic used according to the invention is preferably prepared by a process comprising

<td>(a)</td><td>production</td><td>of a glass</td><td>of departure</td><td>containing the</td>

<td>components</td><td colspan="2">of glass ceramic,</td><td></td><td></td>

<td>(b) the</td><td>submission</td><td>from the glass of</td><td>departure to</td><td>one first</td>

<td>treatment</td><td>thermal a</td><td>a first</td><td>temperature</td><td>to give a</td>

<td>product of</td><td>glass the</td><td colspan="3">which contains cores suitable for</td>

<td>formation of</td><td colspan="3">lithium metasilicate crystals,</td><td></td>

<td>(c) the</td><td>submission</td><td>of product</td><td>glass to</td><td>one second</td>

<td>treatment</td><td>thermal a</td><td>a second</td><td>temperature</td><td>which is more</td>

higher than the first temperature to obtain lithium silicate glass ceramic with lithium metasilicate as the main crystalline phase.

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In step (a), generally a molten mass of a starting glass which is produced, which contains the glass ceramic components. For this purpose, a corresponding mixture of suitable starting materials, such as carbonates, oxides and phosphates, is prepared and heated to temperatures of in particular 1300 to 1600 ° C for 2 to 10 hours. In order to obtain a particularly high degree of homogeneity, the obtained molten glass can be poured into water to form glass granules and the obtained glass granules are melted again.

It is further preferred that the melting of the starting glass is cooled to room temperature before being subjected to step (b). The melting of the starting glass is also generally poured into a mold to form a starting glass blank.

In some cases it is convenient to control a cooling procedure such that it not only relaxes the glass but also performs the first heat treatment of step (b).

In step (b) the starting glass is subjected to a first heat treatment at a first temperature to cause the formation of lithium metasilicate crystal cores. Preferably, this first heat treatment comprises heating the starting glass to a temperature of 500 to 600 ° C over a period of about 10 minutes to 3 hours. This results in the formation of a large

881688398 number of cores to ensure very satisfactory crystal growth. It also ensures that in further processing after step (c) to give a lithium disilicate glass ceramic a very homogeneous lithium disilicate structure can be obtained.

It is also advantageous that the second heat treatment in step (c) comprises heating the glass product to a second temperature from 570 ° C to 750 ° C, preferably from 570 to 670 ° C, and more preferably at about 650 ° C. .

It has also been surprisingly shown that relatively high temperatures lead to high amounts of lithium metasilicate which in turn lead to a high amount of lithium disilicate in the third heat treatment. Such high amounts of lithium disilicate confer a high resistance to ceramics. Therefore, if the emphasis is on obtaining a high strength end product, then it is advantageous to carry out the second heat treatment at 680 ° C to 720 ° C, and preferably 690 ° C to 710 ° C and more preferably at about 700 ° C.

Depending on the specific composition of a selected starting glass, it is possible to one skilled in the art by means of differential scanning calorimetry (DSC) and X-ray diffraction analysis to determine the appropriate conditions in steps (b) and (c) to result in vitroceramics having the desired morphology and size of lithium metasilicate crystals. In addition, these analyzes

1688398 also permit the identification of conditions that prevent or limit the formation of other undesirable crystalline phases, such as high strength lithium disilicate, or cristobalite and lithium phosphate.

Usually, the starting glass of step (a), the glass product of step (b), or preferably the lithium metasilicate glass ceramic of step (c) is shaped to a desired geometry by machine manufacture or pressing. hot. Machine manufacturing is in particular performed by milling, trimming or milling and preferably controlled by a computer using CAD / CAM based milling devices. This allows for a so-called treatment in the patient's office by the dentist.

It is a particular advantage of the lithium metasilicate glass ceramic used according to the invention that it can be modeled by machine manufacture without the undue wear of tools observed with tenacious and high strength prior art materials. This is in particular shown by the easy possibility of polishing and trimming the glass ceramics used in accordance with the invention. Such polishing and trimming processes therefore require less energy and less time to prepare an acceptable product in the form of even very complicated dental restorations.

In addition, the lithium metasilicate glass ceramic used according to the invention can be advantageously processed to a high strength lithium disilicate glass ceramic, which generally has a content of 50 to 85% v / v and preferably 65 to 80% v. / v crystalline lithium disilicate phase.

This is preferably accomplished by a process wherein the lithium metasilicate glass ceramic of step (c) is subjected to a third heat treatment at a third temperature of 830 to 880 ° C for a period of 10 to 60 minutes. This heat treatment can also be performed when the hot pressing of the lithium metasilicate glass ceramic reaches a conformation.

Accordingly, lithium metasilicate glass ceramics can be further processed to lithium disilicate glass ceramics in the desired manner, for example not only by (i) CAD / CAM and heat treatment, but also by (ii) a hot pressing. This is very advantageous for the user.

A corresponding lithium silicate glass comprising cores suitable for the formation of lithium metasilicate crystals may also be used for these purposes. This glass is a precursor to the lithium metasilicate glass ceramic and the lithium disilicate glass ceramic used according to the invention. The invention is also directed to the use of such glass. It is obtainable by the above process in step (b). This lithium silicate glass used according to the invention comprises the following components:

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Component

SiO₂

Li₂O

K₂0

TO 1₂C&gt; 3

Nucleating Agent Me (11) 0% m / m

64.0-75.0, in particular 64.0-73.0 13.0-17.0

2,0-5,0 0,5-5,0 2,0-5,0

0-3.0 with Me (11) 0 to be selected from at least one of CaO, BaO, MgO and SrO, and comprises less than 0.1% w / w ZnO, and comprises nuclei suitable for formation of lithium metasilicate crystals.

For the manufacture of a dental restoration by the hot pressing technique, it is preferred to use a lithium silicate glass ingot used according to the invention having lithium metasilicate cores. This ingot is heated to about 700 to 1200 ° C to convert it to a viscous state. The heat treatment can be conducted in a special oven (EP 500®, EP 600®, Ivoclar Vivadent AG). The ingot is embedded in a special coating material. During heat treatment, the ingot will be crystallized. The main crystalline phase is then lithium disilicate. Viscous glass ceramic flows at a pressure of 1 to 4 MPa into the cavity of the coating material to achieve the desired shape of the dental restoration. After cooling of the coating mold to room temperature the lithium disilicate restoration may be sandblasted. The restoration may also be covered with glass or glass ceramic by

ΡΕ1688398 sintering or a hot pressing technique to achieve the finished dental restoration with natural aesthetics.

The same hot pressing technique can be applied to the lithium metasilicate glass ceramic used in accordance with the invention, which will be converted to lithium disilicate glass ceramic.

A preferred method for converting lithium metasilicate vitroceramics used in accordance with the invention for a dental restoration of lithium disilicate vitroceramics by the CAD / CAM technique utilizes lithium metasilicate vitroceramic blanks, for example blocks, having a strength from about 80 to 150 MPa. These can easily be machine manufactured on a Cerec 2® or Cerec 3® type CAM unit (Sirona, Germany). Larger milling machines such as DCS precimill® (DCS, Switzerland) are also suitable. The block is therefore positioned in the grinding chamber by a fixed or integrated support. The dental restoration CAD construction is done by a scanning process or an optical chamber in combination with a software tool. The milling process requires a unit of about 10 to 15 minutes. Copy milling units such as Celay® (Celay, Switzerland) are also suitable for block machine manufacture. First, a 1: 1 copy of the desired restoration is made of hard wax. The wax model is then mechanically scanned and mechanically transmitted 1: 1 to the wax.

ΡΕ1688398 grinding tool. The milling process is therefore not controlled by a computer. The dental restoration molds have to undergo the third heat treatment to obtain the desired high strength, tooth-like lithium disilicate glass ceramic. The product may be further coated with a glass or sintered glass ceramic or hot pressing technique to obtain the final restoration with natural aesthetics.

The lithium metasilicate glass ceramic used according to the invention may also be used for the coating of a dental restoration. The coating is preferably effected by hot pressing the lithium metasilicate glass ceramic on the restoration.

It has been surprisingly found that the easily machine-engineered lithium metasilicate glass ceramic used in accordance with the invention can be converted by another heat treatment to a lithium disilicate glass ceramic product also having excellent optical properties. Conversion to a lithium disilicate glass ceramic is associated with a very small linear shrinkage of only about 0.2 to 0.3%, which is almost negligible compared to a linear shrinkage of up to 30% when sintering ceramics. The lithium disilicate glass ceramics obtained have not only excellent mechanical properties such as high strength, but also exhibit other properties.

ΡΕ1688398 required for a material for dental restorations. It is noted that these properties are achieved without the need for ZnO as a component which may be detrimental to specific restorations in view of its strong opalescent effect.

Therefore, the product is finally obtained which has all the beneficial mechanical, optical and stability properties making lithium disilicate ceramics attractive for use as dental restorative materials. However, these properties are achieved without the disadvantages of conventional materials when molded using a CAD / CAM based process, in particular the undue wear of milling and trimming tools.

The invention is explained in more detail below based on the Examples.

EXAMPLES

Examples 1 to S

A total of 8 different lithium metasilicate vitroceramics used according to the invention with the chemical compositions indicated in Table I were prepared using the second indicated heat treatment. The obtained glass ceramics were then converted to the corresponding lithium disilicate glass ceramics using the third indicated heat treatment.

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First, the samples from the corresponding starting glasses were melted in a platinum rhodium crucible at a temperature of 1450 ° C and for a period of 40 minutes. The molten glass was poured into water and the granules obtained were, after drying, melted again at 1500 ° C. The obtained glass fusions were then poured into graphite molds to obtain blocks. After relaxation of the glass blocks at 500 to 600 ° C for 10 minutes to 3 hours, they were subjected to a second heat treatment. Prior to the third heat treatment, the blocks were checked for their machinability by milling on a CAD-CAM milling machine (ie CEREC 3®). Finally, the third indicated heat treatment was conducted. The crystalline phases present after the second and third heat treatment were identified by X-ray diffraction techniques and are given in Table I.

In addition, the opalescence of the products was visually assessed and the CR contrast value was determined according to BS 5612 (British Standard) using a spectral colorimeter (Minolta CM3700d). Chemical stability in acetic acid was determined as well as stability in artificial saliva. Corresponding data are to be found in Table II below and show in particular the surprising combination of a lack of opalescence together with high translucency and stability. The composition of artificial saliva is given in Table III.

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The data obtained show that the lithium metasilicate vitroceramics used in accordance with the invention combine very good machinability and high edge strength with the easy possibility of converting them by simple heat treatment to disilicate vitroceramics. lithium compounds which have very high flexural strength as well as excellent chemical durability and good translucency, all properties that make them very attractive as useful materials for the manufacture of dental restorations.

Examples 9 to 12

Four glass ceramics used according to the invention were prepared analogously to Examples 1 to 8. However, the heat treatment scheme was different. In addition, each material was subjected to the schemes referred to as Cycle A and Cycle B which differ in the temperature used for lithium metasilicate crystallization, namely 650 ° C and 700 ° C, respectively.

Details regarding prepared and tested materials as well as their properties are given in Table IV. It is evident that Cycle B treatment using a temperature of 700 ° C for crystallization of lithium metasilicate leads to lithium disilicate glass ceramics with excellent strengths.

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- 23 Table I

<td>Example</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td>

<td>Molar ratio</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>SiO₂: Li $</td><td> 2,39:1</td><td> 2,39:1</td><td> 2,4:1</td><td> 2,39:1</td><td> 2,39:1</td><td> 2,39:1</td><td> 2,39:1</td><td> 2,39:1</td>

<td>J1 &amp;: Kí</td><td> 1:1,0</td><td> 1:1,0</td><td> 1:1,2</td><td> 1:1,20</td><td> 1:1,35</td><td> 1:1,50</td><td> 1:1,70</td><td> 1:1,30</td>

<td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td>% m / m (% mol)</td><td>% m / m (% mol)</td><td>% m / m (% mol)</td><td>% m / m (% nol)</td><td>% m / ni (% nol)</td><td>% m / m (% mol)</td><td>% m / m (% mol)</td><td>% m / m (% nol)</td>

<td>SiO₂</td><td> 72,21 (66,12)</td><td> 70,64 (65,62)</td><td> 70,52 (65,52)</td><td> 70,78 (65,57)</td><td> 70,78 (65,56)</td><td> 70,78 (65,56)</td><td> 70,78 (65,55)</td><td> 70,78 (65,29)</td>

<td>K₂0</td><td> 3,16 (1,85)</td><td> 3,09 (1,83)</td><td> 3,81 (2,26)</td><td> 3,76 (2,22)</td><td> 3,96 (2,34)</td><td> 4,16 (2,46)</td><td> 4,36 (2,58)</td><td> 3,36 (1,98)</td>

<td>Li₂0</td><td> 14,99 (27,60)</td><td> 14,68 (27,43)</td><td> 14,64 (27,35)</td><td> 14,7 (27,38)</td><td> 14,7 (27,38)</td><td> 14,7 (27,37)</td><td> 14,7 (27,37)</td><td> 14, 7 (27, 26)</td>

<td>Alft</td><td> 3,45 (1,86)</td><td> 3,38 (1,85)</td><td> 3,35 (1,83)</td><td> 3,38 (1,85)</td><td> 3,18 (1,74)</td><td> 2,98 (1,63)</td><td> 2,78 (1,52)</td><td> 2,78 (1,51)</td>

<td>PAN</td><td> 3,28 (1,27)</td><td> 3,21 (1,26)</td><td> 3,2 (1,26)</td><td> 3,21 (1,26)</td><td> 3,21 (1,26)</td><td> 3,21 (1,26)</td><td> 3,21 (1,26)</td><td> 3,21 (1,25)</td>

<td>ZrO₂</td><td> 2,91 (1,30)</td><td> 3,00 (1,36)</td><td> 2,5 (1,13)</td><td> 1,8 (0,81)</td><td> 1,8 (0,81)</td><td> 1,80 (0,81)</td><td> 1,8 (0,81)</td><td> 1,8 (0,81)</td>

<td>CeO₂</td><td></td><td> 1,88 (0,61)</td><td> 1,86 (0,60)</td><td> 2,00 (0,65)</td><td> 2,00 (0,65)</td><td> 2,00 (0,65)</td><td> 2,00 (0,65)</td><td> 2,00 (0,65)</td>

<td>GO</td><td></td><td> 0,12 (0,04)</td><td> 0,12 (0,04)</td><td> 0,07 (0,02)</td><td> 0,07 (0,02)</td><td> 0,07 (0,02)</td><td> 0,07 (0,02)</td><td> 0,07 (0,02)</td>

<td>MnO₂</td><td></td><td></td><td></td><td> 0,03 (0,02)</td><td> 0,03 (0,02)</td><td> 0,03 (0,02)</td><td> 0,03 (0,02)</td><td> 0,03 (0,02)</td>

<td>Er₂O₃</td><td></td><td></td><td></td><td> 0,12 (0,017)</td><td> 0,12 (0,017)</td><td> 0,12 (0,017)</td><td> 0,12 (0,017)</td><td> 0,12 (0,017)</td>

<td>MgO</td><td></td><td></td><td></td><td> 0,15 (0,21)</td><td> 0,15 (0,21)</td><td> 0,15 (0,21)</td><td> 0,15 (0,21)</td><td> 0,15 (0,21)</td>

<td>Dog</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td> 1,00 (0,99)</td>

<td>Crystalline phases after:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>Second heat treatment: 20 7650 ^sÇ</td><td>Lithium3 Li₂Si₂O₅*</td><td>Lithium3 Li₂Si₂O₅*</td><td>Li2S1O3</td><td>Lithium3</td><td></td><td>Lithium3</td><td>Lithium3</td><td>Li2S1O3 LiSiO2 *</td>

<td>Third heat treatment: 10 7850 ⁵Ç</td><td>L12S12O5 L13PO4 *</td><td>L12S12O5 L13PO4 *</td><td>L12S12O5 L13PO4 *</td><td>LiSiO2 LIPPO4 *</td><td>LiSiO2 LIPPO4 *</td><td>LiSiO2 LIPPO4 *</td><td>LiSiO2 L13PO4 *</td><td>LiSiO2 LIPPO4 *</td>

ΡΕ1688398

4

Table II

<td>Example</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 6</td>

<td>CR value BS-5612 (1978)</td><td> 40,4</td><td> 37, 0</td><td> 50,0</td><td> 59,3</td><td> 58,8</td>

<td>Opalescence</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td>

<td>Chemical stability in acetic acid (24 h / 80 ° C, mass loss in pg / cm²)</td><td> 9</td><td> 18</td><td> 48</td><td> 3</td><td> 9</td>

<td>Chemical stability in Saliva (7d / 60 ° C, loss mass in μ / cm²)</td><td> 13</td><td> 17</td><td> 28</td><td> 27</td><td> 17</td>

Table III

<td></td><td>Artificial saliva composition</td>

<td>Component</td><td>Amount in mg totaling 500 mL of H₂O</td>

<td>NaCl</td><td> 125,64</td>

<td>KC1</td><td> 963,9</td>

<td>NH₄C1</td><td> 178,0</td>

<td>CaCl₂ · 2H₂O</td><td> 227, 8</td>

<td>KSCN</td><td> 189,2</td>

<td>CO (NH₂)₂</td><td> 200,0</td>

<td>At₂ONLY₄- 10am₂O</td><td> 336,2</td>

<td>NaHCO₃</td><td> 630,8</td>

<td>KH₂POWDER₄</td><td> 654,5</td>

ΡΕ1688398

Table IV

<td>Example</td><td> 9</td><td> 10</td><td> 11</td><td> 12</td>

<td colspan="5"></td>

<td>SiO₂</td><td> 74,37</td><td> 72,89</td><td> 72,21</td><td> 71, 40</td>

<td>K₂O</td><td> 3,26</td><td> 3, 18</td><td> 3,16</td><td> 3,13</td>

<td>Li₂O</td><td> 15, 44</td><td> 15,13</td><td> 14, 99</td><td> 14, 79</td>

<td>TO 1₂O3</td><td> 3,55</td><td> 3, 48</td><td> 3,45</td><td> 3,41</td>

<td>P₂0₅</td><td> 3,38</td><td> 3,31</td><td> 3,28</td><td> 3,22</td>

<td>ZrO₂</td><td> 0,00</td><td> 2, 01</td><td> 2,91</td><td> 4, 05</td>

<td></td><td colspan="4">All values ​​above in% m / m</td>

<td>SiO₂: Li₂O (mol% ratio)</td><td> 2,39</td><td> 2,40</td><td> 2,39</td><td> 2,40</td>

<td colspan="5"></td>

<td>Cycle A:</td><td colspan="4">(1) 500 ° C / 10 min + (2) 650 ° C / 20 min + (3) 850 ° C / 10 min *)</td>

<td>Flexural strength biaxial / MPa</td><td> 786+/-92</td><td> 515+/-54</td><td> 522+/-82</td><td> 479+/-36</td>

<td>Contrast Ratio</td><td> 0,80</td><td> 0, 56</td><td> 0,43</td><td> 0,36</td>

<td colspan="5"></td>

<td>cycle B:</td><td colspan="4">(1) 500 ° C / 10 min + (2) 700 ° C / 20 min + (3) 850 ° C / 10 min *)</td>

<td>Flexural strength biaxial / MPa</td><td> 828+/- 104</td><td> 659+/-75</td><td> 608+/-90</td><td> 694+/- 113</td>

<td>Contrast Ratio</td><td> 0,83</td><td> 0, 63</td><td> 0,53</td><td> 0,41</td>

<td> *)</td><td colspan="4">(1) Nucleation on glass (2) Metasilicate Crystallization from Li (3) Crystallization of Li from Li Metasilicate</td>

Lisbon, July 15, 2015