DE10362377C5 - Lithium silicate blank and its use - Google Patents

Abstract

Use of a lithium silicate latent material containing lithium metasilicate as a main crystal phase for making a dental restoration, the blank having a holder for mounting in a machine and being machined to a desired geometry to produce a shaped one Lithium silicate product, and the shaped lithium silicate product of a heat treatment at a temperature of about 820 to 950 ° C for a period of about 5 to 20 minutes. wherein the shrinkage occurring during the heat treatment is less than 0.5% by volume.

Description

The invention relates to a lithium silicate blank which can be easily shaped by machine processing and subsequently converted into molded products of high strength, and its use.

There is an increasing demand for materials associated with dental restorative products, such as As crowns, inlays and bridges, can be processed by means of computer-controlled milling machines. Such CAD / CAM methods are very attractive because they allow the patient to quickly provide the desired restoration. Thus, a so-called chair treatment for the dentist is possible.

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

First, they have in the final restoration produced appealing optical properties, such. As translucency and coloration, which mimic the appearance of natural teeth. They must also exhibit high strength and chemical resistance so that they can take over the function of the natural tooth material and maintain these properties for a sufficiently long period of time while being permanently in contact with fluids in the oral cavity that are even aggressive, such as z. B. sour, can be.

Second, and most importantly, it should be possible to easily machine them to the desired shape without undue wear on the tools and within a short time. This property requires a relatively low strength of the material and thus is contrary to the above-mentioned desired properties for the final restoration.

The difficulty of achieving the low strength properties at the stage of the material being processed and high strength of the final restoration is reflected by the known materials for CAD / CAM processing, which are unsatisfactory particularly in terms of ease of machinability.

DE-A-197 50 794 discloses lithium disilicate glass-ceramics primarily intended to be formed into the desired geometry by a hot pressing process wherein the molten material is viscous pressed. It is also possible that these materials are deformed by computer-aided milling techniques. However, it has been found that the machining of these materials results in very high tool wear and very long processing times. These disadvantages are caused by the high strength and toughness imparted to the materials primarily by the crystalline lithium disilicate phase. It has also been shown that the machined restorations show only a low edge strength. The term "edge strength" refers to the strength of parts of the restoration that have only a small thickness in the range of a few 1/10 mm.

Other attempts to achieve ease of machinability along with high strength of the final restoration have also been made. EP-B-774 993 and EP-B-817 597 describe ceramic materials based on Al ₂ O ₃ or ZrO ₂ , which are machined in an unsintered state, also referred to as "green state". The green bodies are then sintered to increase strength. However, these ceramic materials suffer a drastic shrinkage of up to 50% by volume (or up to 30% linear shrinkage) during the final sintering step. This leads to difficulties in the production of restorations with exactly the desired dimensions. The significant shrinkage is a particular problem when making complex restorations, such as. B. a multi-membered bridge.

Out SD Stookey: "Chemical Machining of Photosensitive Glass", Ind. Eng. Chem., 45, 115-118 (1993) and SD Stookey: "Photosensitively Opacifiable Glass" US-A-2 684 911 (1954) it is also known that a metastable phase can first be formed in lithium silicate glass-ceramics. For example be in photosensitive glass ceramics (Fotoform ^®, Fotoceram ^®) Ag-particles are formed using UV-light. These Ag particles serve as crystallizers in a lithium metasilicate phase. The areas exposed to light are washed out with dilute HF in a subsequent step. This method is possible because the solubility of the lithium metasilicate phase in HF is much higher than the solubility of the starting glass. The method according to the resolution (photo form ^®) glass remaining part can be converted by means of an additional heat treatment in a lithium disilicate glass ceramic (Fotoceram ^®).

The investigations of Borom, z. BM-P. Borom, AM Turkalo, RH Doremus: "Strength and Microstructure in Lithium Disilicate Glass-Ceramics", J. Am. Ceream. Soc., 58, no. 9-10, 385-391 (1975) and M.-P. Borom, AM Turkalo, RH Doremus: "Process for the production of glass-ceramics" DE-A-24 51 121 (1974) show that a lithium disilicate glass-ceramic can initially crystallize in different amounts as a metastable lithium metasilicate phase. However, there are also compositions which crystallize from the beginning in the form of the disilicate phase and in which the metasilicate phase does not exist at all. A systematic investigation of this effect has not yet become known. It is also known from the investigations of Borom that the glass-ceramic containing lithium metasilicate as the main phase has a reduced strength compared to a glass-ceramic containing only a lithium disilicate phase.

Thus, the materials known from the prior art show a number of disadvantages. It is therefore an object of the present invention to overcome these drawbacks and, more particularly, to provide a material which, above all, can be easily formed by computer-aided milling and grinding processes and subsequently converted into high strength dental products, which also have high chemical resistance and excellent performance show optical properties and show drastically reduced shrinkage during the final transformation.

This object is achieved by the lithium silicate blank according to claims 1 to 16 and its use according to claims 17 to 30. The invention thus provides a lithium silicate blank in the form of a lithium silicate material containing lithium metasilicate as a main crystal phase, or in the form of a lithium silicate glass containing nuclei suitable for forming lithium metasilicate, the blank having a holder for mounting it in a machine. The invention also provides the use of this lithium silicate blank for the production of a dental restoration.

It has surprisingly been found that by using a starting glass with a very special composition and a special process, it is possible to provide a glass-ceramic containing metastable lithium metasilicate (Li ₂ SiO ₃ ) as the main crystal phase instead of lithium disilicate (Li ₂ Si ₂ O ₅ ). Has. Accordingly, this lithium metasilicate glass-ceramic has a low strength and toughness, and thus can be easily machined to the shape even of complicated dental restorations, but can be converted into a lithium disilicate glass-ceramic product by such a heat treatment, which has excellent mechanical properties. has excellent optical properties and very good chemical stability and is subject to only a very limited shrinkage.

The lithium silicate material of the blank according to the invention contains lithium metasilicate as a main crystal phase. In another embodiment, the lithium silicate material contains suitable nuclei to form lithium metasilicate. It may be formed from a mixture containing the following initial components component Wt .-% SiO ₂ 64.0 to 73.0 Li ₂ O 13.0 to 17.0 K ₂ O 2.0-5.0 Al ₂ O ₃ 0.5-5.0 P ₂ O ₅ 2.0-5.0.

It is preferable that the lithium silicate material of the blank of the present invention further contains the following additional starting components independently of each other component Wt .-% ZnO 2.0-6.0 Na ₂ O 0.0-2.0 Me ^II O 0.0-5.0 ZrO ₂ 0.0-2.0 coloring and fluorescent metal oxides 0.5-7.5, wherein Me ^II O is one or more members selected from the group consisting of CaO, BaO, SrO and MgO.

Particularly preferred is a lithium silicate material as described above, which is formed from a mixture containing the following starting components independently in the following amounts: component Wt .-% SiO ₂ 65.0 to 70.0 Li ₂ O 14.0 to 16.0 K ₂ O 2.0-5.0 Al ₂ O ₃ 1.0-5.0 P ₂ O ₅ 2.0-5.0 ZnO 2.0-6.0 Na ₂ O 0.1-2.0 Me ^II O 0.1-5.0 ZrO ₂ 0.1-2.0 coloring and fluorescent metal oxides 0.5-3.5, wherein Me ^II O is one or more members selected from the group consisting of CaO, BaO, SrO and MgO, and
wherein the metal of the one or more coloring and fluorescent metal oxides is selected from the group consisting of Ta, Tb, Y, La, Er, Pr, Ce, Ti, V, Fe and Mn.

The passage "... independent of each other ..." means that at least one of the preferred amounts is selected and, accordingly, that it is not necessary that all components be present in the preferred amounts.

As coloring components or fluorescent components z. B. oxides of f-elements are used, d. H. the list of the above mentioned metals is not to be considered exhaustive.

The coloring or fluorescent components ensure that the color of the final dental product matches that of the natural tooth material of the patient in question.

In the above composition, P ₂ O ₅ acts as a nucleating agent for the lithium metasilicate crystals, and a concentration of at least 2% by weight is required for necessary nucleation. Instead of P ₂ O ₅ are also other nucleating agents such. B. compounds of the elements Pt, Ag, Cu and W possible.

In addition to the above-mentioned components, the glass-ceramic may also contain other additional components to improve the glass processability. Such additional components can therefore in particular compounds such. B. B ₂ O ₃ and F, which generally account for 0 to 5.0 wt .-%.

A lithium silicate material as described above, which is formed from a mixture initially containing 67.0 to 70.0 wt% of SiO ₂ , is particularly preferable.

It is further preferable that the lithium metasilicate crystal phase forms 20 to 50% by volume, and more preferably 30 to 40% by volume, of the lithium silicate material. Such a part of the volume causes the crystals are quite remote from each other and thus prevents too high strength of the lithium silicate material.

The lithium metasilicate crystals are preferably of a lamellar or platelet-like form. This leads to a very good machinability of the lithium silicate material without the use of high energy and without uncontrolled breaking. The last aspect of uncontrolled breaking is z. B. in glasses known, which are therefore unsuitable for a machine processing. It is believed that the preferred morphology of the lithium metasilicate crystals is also responsible for the surprisingly high edge strength of the products, e.g. B. of complicated dental restorations, is responsible, which are made from the blank according to the invention.

According to the invention, the lithium silicate material has the shape of a blank, the blank having a holder to fix it in a machine. The blank usually takes the form of a small cylinder or a rectangular block. The exact shape depends on the particular apparatus used for the desired computer-aided machining of the blank.

After machining, the lithium silicate material preferably has the form of a dental restoration, e.g. As an inlay, an onlay, a bridge, a pin structure, a veneer, a shell, a facet, a crown, a partial crown, a scaffold or a cap.

A lithium disilicate material may be formed in a process which includes a step of forming a phase containing mainly crystalline lithium metasilicate, the lithium metasilicate subsequently being converted to lithium disilicate.

A dental product made of lithium disilicate can be formed in a process which includes a step of preparing a phase containing mainly crystalline lithium metasilicate, and then converting the lithium metasilicate to lithium disilicate.

1. (a) eine Schmelze eines Ausgangsglases hergestellt wird, die die Anfangskomponenten SiO₂, Li₂O, K₂O, Al₂O₃ und P₂O₅ als die Hauptkomponenten enthält,
2. (b) die Schmelze des Ausgangsglases in eine Form gegossen wird, um einen Ausgangsglasrohling zu bilden, und der Glasrohling auf Raumtemperatur abgekühlt wird,
3. (c) der Ausgangsglasrohling einer ersten Wärmebehandlung bei einer ersten Temperatur unterworfen wird, um ein Glasprodukt zu ergeben, welches Keime enthält, die zur Bildung von Lithiummetasilicatkristallen geeignet sind,
4. (d) das Glasprodukt aus Schritt (c) einer zweiten Wärmebehandlung bei einer zweiten Temperatur unterworfen wird, die höher als die erste Temperatur ist, um den Lithiumsilicatrohling mit Lithiummetasilicatkristallen als Hauptkristallphase zu erhalten.

A blank according to the invention is preferably produced by means of a method in which

1. (a) preparing a melt of a starting glass containing the starting components SiO ₂ , Li ₂ O, K ₂ O, Al ₂ O ₃ and P ₂ O ₅ as the main components,
2. (b) pouring the melt of the starting glass into a mold to form a starting glass blank and cooling the glass blank to room temperature,
3. (c) subjecting the starting glass blank to a first heat treatment at a first temperature to yield a glass product containing seeds suitable for forming lithium metasilicate crystals,
4. (d) subjecting the glass product of step (c) to a second heat treatment at a second temperature higher than the first temperature to obtain the lithuanosilicate blank having lithium metasilicate crystals as the main crystal phase.

Preferred is a method as described above, wherein the starting glass of step (a) further contains ZnO, Na ₂ O, Me ^II O, ZrO ₂ , and coloring and fluorescent metal oxides, wherein Me ^II O is one or more members selected from the group consisting of CaO, BaO, SrO and MgO.

Particularly preferred is a method as described above, wherein the starting glass of step (a) contains the following starting components independently in the following amounts component Wt .-% SiO ₂ 65.0 to 70.0 Li ₂ O 14.0 to 16.0 K ₂ O 2.0-5.0 Al ₂ O ₃ 1.0-5.0 P ₂ O ₅ 2.0-5.0 ZnO 2.0-6.0 Na ₂ O 0.1-2.0 Me ^II O 0.1-5.0 ZrO ₂ 0.1-2.0 coloring and fluorescent metal oxides 0.5-3.5, wherein Me ^II O is one or more members selected from the group consisting of CaO, BaO, SrO and MgO, and
wherein the metal (s) of the one or more coloring and fluorescent metal oxides is selected from the group consisting of Ta, Tb, Y, La, Er, Pr, Ce, Ti, V, Fe and Mn.

In step (a), a melt of a starting glass containing the components of the glass-ceramic is produced. For this purpose, an appropriate mixture of suitable starting materials, such. As carbonates, oxides and phosphates, 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 glass melt obtained can be poured into water to form glass grains, and the resulting glass grains can be remelted.

In step (b), the melt of the starting glass is cooled to room temperature to give a glass product. This cooling step also usually involves the formation of a blank of the desired shape by melting the melt of the starting glass into a suitable mold, e.g. As a steel mold is poured.

The cooling is preferably carried out in a controlled manner to allow for relaxation of the glass and to avoid stresses in the structure associated with rapid temperature changes. In general, the melt is therefore in preheated forms z. B. at a temperature of 400 ° C or slowly cooled in an oven.

In step (c), the starting glass product is subjected to a first heat treatment at a first temperature to effect the formation of nuclei for lithium metasilicate crystals. This first heat treatment preferably involves heating the glass product for a period of 5 minutes. to 1 hour to a first temperature of 450 to 550 ° C. In some cases, it is convenient to combine step (b) and step (c) to relax the glass article and nucleate the lithium metasilicate crystals in a single heat treatment. Accordingly, step (c) may be replaced by changing step (b) such that during the cooling process a temperature of about 450 to 550 ° C for a period of about 5 to 50 minutes is maintained to produce the glass product containing nuclei suitable for the formation of lithium metasilicate crystals during step (b).

According to another preferred embodiment, in step (c), the first heat treatment includes heating the starting glass blank to a temperature of about 450 to 550 ° C for a duration of about 5 minutes. up to 1 hour

In the subsequent step (d), the glass product having the desired nuclei of Li ₂ SiO _{3 is} subjected to a second heat treatment at a second temperature higher than the first temperature. This second heat treatment results in the desired formation of lithium metasilicate crystals as the predominant and preferably the single crystal phase, thus yielding a lithium metasilicate glass-ceramic. Preferably, this second heat treatment of step (d) includes heating the glass product containing seeds suitable for formation of lithium metasilicate crystals to a second temperature of about 600 to 700 ° C for a period of about 10 to 30 minutes.

The basic temperature profile of such a process is in 1 exemplified. Already starting from the melt (1), ie at the end of step (a), the temperature for the relaxation of the product in a temperature range of 500 to 450 ° C lowers (2). The temperature can then be brought to room temperature (solid line), step (b), and then brought to a temperature of about 450 to 550 ° C, or it can be maintained in the temperature range of 450 to 500 ° C (dotted line). In the region indicated by (3), step (c), nucleation occurs at a temperature of 450 to 550 ° C, and it is affected by P ₂ O ₅ . Subsequently, the glass material is heated to a temperature in the range of 600 to 700 ° C and held at this temperature (4), and during this time forms lithium metasilicate, step (d). Then the material can be cooled down (solid line) to z. Room temperature for grinding, milling or CAD / CAM Processing and then brought to a temperature of about 700 to 950 ° C, or it can be brought directly to 700-950 ° C (dotted line), and at this temperature (5), the second crystallization, which forms lithium disilicate, and An additional heat treatment or a hot pressing can be carried out.

Depending on the particular composition of a selected starting glass, it will be possible for one of ordinary skill in the art, using differential thermal analysis (DSC) and X-ray diffraction analyzes, to determine appropriate conditions in steps (c) and (d) to yield materials having the desired morphology and Have size of lithium metasilicate crystals. To further illustrate this process, the 2 to 5 together with Tables I and II in the examples how relevant data was obtained using the above measurements for Example 13, and thus are generally available. In addition, these analyzes allow the identification of conditions that avoid or limit the formation of unwanted other crystal phases, such as, for example, As the high-strength lithium disilicate or cristobalite and lithium phosphate.

Following step (d), it is preferable to form the obtained glass-ceramic. This is preferably accomplished by step (e), in which the lithium metasilicate glass-ceramic is machined to a glass-ceramic product of desired shape, in particular the form of a dental restoration. The machining is preferably carried out by grinding or milling. It is also preferred that the machine processing be controlled by a computer, particularly by using CAD / CAM based milling equipment. This allows a so-called chair treatment of the patient by the dentist.

It is a particular advantage of the glass-ceramic described above that it can be formed by machining without the excessive tool wear being observed by the tough and high-strength materials of the prior art. This is shown in particular by the simple possibility of polishing and grinding the glass ceramics described above. Such polishing and grinding processes thus require less energy and less time to produce an acceptable product which takes the form of even very complicated dental restorations.

Lithium disilicate dental restorations can be made in many different ways. Usually, the CAD / CAM and the hot press technique are used. Dentists can use a CAD / CAM method (Cerec 2 ^®, Cerec 3 ^®, Sirona ^®) to produce a fully ceramic Lithiumdisilicatrestauration the chair. The final result is always a dental restoration with lithium disilicate as the main crystal phase. The microstructure of the starting blank may be different. The blank may be a lithium silicate glass, a lithium metasilicate glass ceramic, a lithium disilicate glass ceramic, or a glass ceramic consisting of lithium meta and disilicate.

For the preparation of a dental restoration by the hot press technique, the lithium silicate glass ingot or lithium metasilicate ingot is subjected to a heat treatment at about 700 to 1200 ° C to make it viscous. The heat treatment is carried out in a special oven (EP ^500® , EP ^600® , Ivoclar Vivadent AG). The ingot is embedded in a special embedding material. During the heat treatment, the ingot crystallizes. The main crystal phase is then lithium disilicate. The viscous glass ceramic flows under a pressure of 2 to 12 bar into the recess of the embedding material to obtain the desired shape of the dental restoration. After cooling the embedding mold to room temperature, the lithium disilicate restoration can be demolded by sandblasting. The framework can be further coated with a glass or a glass ceramic by sintering or hot pressing technique to obtain the final dental restoration with natural aesthetics.

The ingot containing lithium metasilicate and lithium disilicate is subjected to a heat treatment at about 700 to 1200 ° C to make it viscous. The heat treatment is carried out in a special oven (EP ^500® , EP ^600® , Ivoclar Vivadent AG). The glass ceramic ingot is embedded in a special embedding material. During the heat treatment, the glass ceramic continues to crystallize. The main crystal phase is then lithium disilicate. The viscous glass ceramic flows at a pressure of 2 to 12 bar into the recess of the embedding material to obtain the desired shape of the dental restoration. After cooling the embedding mold to room temperature, the lithium disilicate restoration can be demolded by sandblasting. The framework can be further coated with a glass or a glass ceramic by sintering or hot pressing technique to obtain the final dental restoration with natural aesthetics.

For the preparation of a dental restoration by the CAD / CAM technique, the lithium silicate or lithium metasilicate blocks having a possible subordinate crystalline phase with a strength of about 80 to 150 MPa can be readily machined in a CAM unit such as Cerec ^2® or Cerec ^3® (Sirona, Germany). Larger milling machines such. B. DCS precimill ^® (DCS, Switzerland) are also suitable. The block is thus positioned in the milling chamber by means of a fixed or integrated holder. The CAD design of the dental restoration is performed by means of a scanning method or an optical camera in combination with a software. The milling process requires 10 to 15 minutes for one unit. Kopierfräseinheiten as Celay ^® (Celay, Switzerland) are also suitable for machining the blocks. First, make a 1: 1 copy of the desired restoration in hard wax. The wax model is then mechanically scanned and transferred 1: 1 mechanically to a grinding unit. The grinding process is accordingly not controlled by a computer. The milled dental restoration must be subjected to a heat treatment in order to obtain the desired lithium disilicate glass ceramic with high strength and tooth-like color. The heat treatment is carried out in a range of 700 to 900 ° C for a period of about 5 to 30 minutes. carried out. The framework may be further coated with a glass or glass ceramic by sintering or hot pressing technique to obtain the final dental restoration with a natural appearance.

Due to the high strength and toughness of the glass ceramic, blocks having lithium disilicate as the main crystal phase can only be used in a large milling machine, such as a milling machine. B. DCS precimill ^® (DCS, Switzerland) are milled. The block is thus positioned in the milling chamber with a fixed metal holder. The CAD design of the dental restoration is performed by means of a scanning method in combination with a software. An additional heat treatment in the range of 700 to 900 ° C can be performed to close surface defects caused by the milling process. The framework may be further coated with a glass or a glass ceramic by means of sintering or hot pressing technique to obtain the final dental restoration with a natural appearance.

It has further been found that the easily machinable lithium metasilicate glass-ceramic described above can be converted to a lithium disilicate glass-ceramic product by means of a further heat treatment. The obtained lithium disilicate glass-ceramic not only has excellent mechanical properties, such as. B. high strength, but also shows other properties that are required for a material for dental restoration.

• (f) die oben beschriebene Lithiummetasilicat-Glaskeramik einer dritten Wärmebehandlung unterworfen wird, um Lithiummetasilicatkristalle in Lithiumdisilicatkristalle umzuwandeln.

Accordingly, a method for producing a lithium disilicate glass-ceramic product further comprises

• (f) subjecting the lithium metasilicate glass-ceramic described above to a third heat treatment to convert lithium metasilicate crystals to lithium disilicate crystals.

In this step (f), conversion of the metastable lithium metasilicate crystals to lithium disilicate crystals is effected. Preferably, this third heat treatment involves complete conversion to lithium disilicate crystals and is preferably carried out by heating at 700 to 950 ° C for 5 to 30 minutes. carried out. The appropriate conditions for a given glass-ceramic can be determined by performing XRD analyzes at different temperatures.

It has also been found that conversion to a lithium disilicate glass-ceramic is associated with only a very small linear shrinkage of only about 0.2 to 0.3%, compared to a linear shrinkage of up to 30% on sintering Ceramics is almost negligible.

A method as described above in which the lithium silicate blank has a biaxial strength of at least 90 MPa and a fracture toughness of at least 0.8 MPa ^0.5 is preferred.

Also preferred is a process as described above, wherein the starting glass blank of step (b), the glass product containing nuclei suitable for the formation of lithium metasilicate from step (c) or the lithium silicate with lithium metasilicate as the main crystal phase of step (d) a desired geometry by machining or hot pressing to form a shaped lithium silicate product.

Particularly preferred is such a process wherein the shaped lithium silicate blank is a dental restoration, and most preferred is a method wherein the dental restoration is an inlay, an onlay, a bridge, a post assembly, a veneer, a shell, a facet , a crown, a partial crown, a scaffold or a cap.

A method as described above, in which the machining is performed by grinding or milling, constitutes a preferred embodiment, and a method in which the machining by means of a computer is controlled is most preferable.

A method as described above, further comprising causing the shaped lithium silicate product to undergo a third heat treatment at a third temperature of about 700 to 950 ° C for a period of about 5 to 30 minutes. is another aspect and this method is particularly preferred when the lithium silicate product subjected to the third heat treatment contains lithium metasilicate as the main crystal phase and the third heat treatment converts the lithium metasilicate crystals to lithium disilicate crystals as the main crystal phase of the dental restoration.

Also preferred is a method as described above, wherein the lithium silicate product subjected to the third heat treatment contains the glass product having nuclei suitable for formation of lithium metasilicate crystals, and wherein the crystals of lithium disilicate are directly crystallized from the nuclei suitable for the formation of lithium metasilicate crystals.

Another preferred embodiment is a method as described above, wherein the shrinkage occurring during the third heat treatment is less than 0.5% by volume.

A lithium silicate material may also be deformed to the desired geometry by hot pressing to produce the dental restoration. Here, a method of manufacturing a dental restoration as described above, wherein the hot pressing involves subjecting the lithium silicate material to a heat treatment at a temperature of about 500 to 1200 ° C to make the lithium silicate material viscous, is preferred viscous lithium silicate material is pressed at a pressure of about 2 to 12 bar in a mold or a press die to obtain the dental restoration with a desired geometry.

A method as described above in which the lithium silicate material subjected to the heat treatment and pressing contains lithium metasilicate crystals which are converted to lithium disilicate crystals during the heat treatment and the pressing is particularly preferable.

Another preferred embodiment is a method as described above which comprises increasing the strength and fracture toughness of the lithium silicate material.

Preferred is a method for the preparation of a dental restoration as described above, wherein the dental restoration has a biaxial strength of at least 250 MPa and a fracture toughness of at least 1.5 MPa ^0.5 .

A method of manufacturing a dental restoration as described above, further comprising the step of finishing the dental restoration to obtain a natural appearance, wherein the finishing step includes applying a coating to the dental restoration by stacking powdered materials or coating a coating material on the dental restoration Non-finished dental restoration is also hot-pressed.

A method as described above, wherein the third heat treatment is carried out during firing of the coated materials or during the hot pressing of the coating material onto the unfinished dental restoration is particularly preferred.

Thus, a product is finally obtained which has all the advantageous mechanical, optical and stability properties which make lithium disilicate ceramics attractive for use as dental restorative materials. However, these properties are obtained without the disadvantages of conventional materials in forming using a CAD / CAM based process, especially the excessive wear of the milling and grinding tools.

Accordingly, by the above method, a lithium disilicate glass-ceramic product having lithium disilicate as the main crystal phase can be obtained. Preferably, the lithium disilicate glass-ceramic product is in the form of a dental restoration. It is further preferred that in the lithium disilicate glass-ceramic, the lithium disilicate crystals constitute 60 to 80% by volume of the glass-ceramic.

The conversion of the lithium metasilicate glass-ceramic described above to a lithium disilicate glass-ceramic product involves a surprisingly high increase in strength by a factor of up to 4. Typically, the above-described lithium metasilicate glass-ceramic has a strength of about 100 MPa, and the conversion results in a lithium disilicate glass-ceramic having a strength of more than 400 MPa (measured as biaxial strength).

In the case of the lithium silicate blank according to the invention, the holder can be attached and connected to the blank.

A lithium silicate blank as described above, in which the holder is made of a different material than the blank, forms an embodiment of the invention.

A lithium silicate blank as described above, in which the holder is made of an alloy, a metal, a glass ceramic or a ceramic, forms a preferred embodiment of the invention.

A lithium silicate blank as described above in which the holder is of the same material as the blank and is integral with the blank forms another embodiment of the invention.

A lithium silicate blank as described above in which the blank is provided with information, the information on the blank relating to the material, size and type of the mold to be machined from the blank, constitutes a preferred embodiment.

Another aspect relates to a process for producing a lithium silicate restoration in which a lithium silicate blank as described above is prepared and then a dental restoration is coated with the lithium silicate blank.

A method of manufacturing a dental restoration as described above, in which a dental framework is coated by hot pressing the lithium silicate blank onto the dental framework, is preferred.

Particularly preferred is a method for producing a dental restoration as described above, wherein the dental framework is a crown, a partial crown, a bridge, a cap, a shell, a veneer or a pin structure, and very particularly preferred is a method the dental framework is made of a metal, an alloy, a ceramic or a glass ceramic.

A method of making a dental restoration as described above wherein the ceramic contains zirconia, alumina, a zirconia mixed oxide, an aluminum mixed oxide, or a combination thereof forms a most preferred embodiment.

A further preferred article is a method of making a dental restoration as described above, wherein the lithium silicate blank coated on the framework contains lithium metasilicate crystals which are converted to lithium disilicate crystals during the hot pressing of the lithium silicate blank onto the dental framework or wherein Lithium Silicate Blank contains seeds suitable for the formation of lithium metasilicate crystals which crystallize as lithium disilicate crystals during the hot pressing of the lithium silicate blank onto the dental framework.

The invention will be explained in more detail below based on examples.

Examples

Examples 1 to 18 (invention) and 19 to 20 (comparison)

A total of 18 different lithium metasilicate glass ceramic products as well as two ceramics for comparison with the chemical compositions shown in Table III were prepared by performing steps (a) to (d) of the above-described process and finally by step (e) of the process described above To this end, samples of the respective starting glasses were melted in a platinum-rhodium crucible at a temperature of 1500 ° C and for a period of 3 hours (a).

The resulting glass melts were poured into steel molds preheated to 300 ° C. After 1 min. The glass blanks were transferred to an oven preheated to a temperature between 450 and 550 ° C. The exact values KB T [° C] and KB t [min] are given for each sample in Table III. After this relaxation and nucleation process (b) and (c), the blocks were allowed to cool to room temperature. The germinated samples were homogeneous and transparent.

The glass blanks were then subjected to step (d), i. H. the second heat treatment to crystallize lithium metasilicate, which means that the glass blanks have a temperature of about 650 ° C for a period of about 20 min. with the exception of Example 3, which was crystallized at 600 ° C,

The course of crystallization was examined by DCS measurements and the crystal phases obtained were analyzed by XRD to determine the ideal conditions for this heat treatment. "Ideal conditions" for the purposes of the invention are when the two crystallization peaks of the meta and the disilicate phase differ to such an extent that a clear distinction can be realized in a production process, that is, when heating a sample to ensure the first crystallization temperature that when reaching the desired temperature within the sample, the temperature in outer regions of the sample does not reach the second crystallization temperature, d. H. the larger the temperature difference of the first and second crystallization temperatures, the larger the sample mass can be.

To further illustrate the process, shows 2 a DSC plot of one of these examples, Example 13, of a quenched and powdered glass sample heated at a heating rate of 10 K / min. The crystallization of lithium metasilicate (1), the crystallization of lithium disilicate (2) and the glass transition temperature (3) and the temperature for the first crystallization (4) are clearly recognizable from the DSC plot.

Also, an example of the phase evolution analysis by high-temperature XRD for the same Example 13 is given. 3 shows accordingly the measurement of a glass sample at a constant heating rate of 2 K / min. It can be seen from the measurement that in this case the crystallization of the lithium metasilicate (1) takes place at a temperature of 510 ° C and that in this case the dissolution of the lithium metasilicate and the crystallization of the lithium disilicate (2) at a temperature of 730 ° C he follows.

4 provides a phase analysis by XRD of Example 13 after nucleation at 500 ° C for 7 min. and first crystallization at 650 ° C and 20 min. represents.

The corresponding data are summarized in Table I: TABLE I 1 2 3 d-spacing in 0.1 nm of the scan d-spacing in 0.1 nm of the pattern index 4,628 4,690 LS 020 3,296 3,301 LS 111 2,708 LS 130 2,685 2,700 LS 200 2,355 2,342 LS 131 2,333 2.331 LS 002

5 Figure 8 shows an SEM photomicrograph, backscattered electrons, of the same sample with the same thermal history, with the surface exposed to 1% HF for 8 sec. was etched. There are clearly recognizable holes that show the earlier lithium metasilicate crystals.

The resulting blocks were now ready for step (e), ie, forming the lithium metasilicate glass-ceramic to the desired shape, either by cutting by sawing or by milling in a CAD-CAM milling machine (ie, CEREC ^3® ). The obtained lithium metasilicate glass-ceramic blanks were analyzed for machinability and edge strength. 10 slices were made from a bar with 12 mm diameter cut to measure the biaxial strength. The results of these analyzes are given in Table IV. Another 10 slices were prepared and subjected to a third heat treatment (f).

In the case of blanks containing coloring and fluorescent oxides, the blanks appeared to have a reddish or bluish color in the state of the metasilicate. However, this effect disappeared once the disilicate phase had formed, and the blanks took on the color that was desired.

Finally, the lithium metasilicate glass-ceramic blanks of a second crystallization, step (f), were heated at 850 ° C for 10 min. with the exception of Example 3, which crystallized at 830 ° C, d. H. the third heat treatment, which is generally conducted at temperatures of 700 to 950 ° C, preferably 820 to 880 ° C and for a period of 5 to 30 minutes, preferably 5 to 20 minutes, to convert the lithium metasilicate to lithium disilicate.

The resulting products were analyzed for their crystal phases. To further illustrate the process, the phase analysis for Example 13 is after nucleation at 500 ° C for 7 min, first crystallization at 650 ° C for 20 min. and second crystallization at 850 ° C for 10 min. in 6 shown. The corresponding data are summarized in Table II: TABLE II 1 2 3 d-spacing in 0.1 nm of the scan d-spacing in 0.1 nm of the pattern index 5,369 5,420 LS2101 3,986 3,978 LP 120 3,855 3,834 LP 101 3,714 3,737 LS2 130 3.629 3,655 LS2 040 3,562 3,581 LS2 111 2,929 2,930 LS2 131 2,901 2,908 LS2 200 2,379 2,388 LS2 002 2,346 2.35 LS2 221 2,283 2.29 LS2 151 2,050 2,054 LS2 241

7 Figure 3 shows a SEM photomicrograph, backscattered electrons, of the same sample with the same thermal history, with the surface exposed to 3% HF for 30 sec. was etched, causing the glass phase to be etched away leaving the lithium disilicate crystals.

In addition to the analysis on crystal phases, the samples were also analyzed for their biaxial strength and chemical resistance. Furthermore, their translucency was determined. The results are also given in Table IV.

• LS - Lithiummetasilicat
• LS2 - Lithiumdisilicat
• LP - Lithiumphosphat

wobei die Hauptphase durch Fettdruck markiert ist.In Table IV, the observed crystal phases are designated as follows:

• LS - lithium metasilicate
• LS2 - lithium disilicate
• LP - lithium phosphate

the main phase being marked in bold.

To obtain information about the machinability tests were performed on a Cerec ^®, and new tools were used for each test. A "Lego ^{® building} block" served as a model, which was milled from all compositions that were subjected to this test and from a leucite reinforced glass ceramic of the name ProCAD from Ivoclar Vivadent AG ^®. The sequence of treatment was as follows: First a blank of ProCAD ^® was milled, then a blank of the ceramic to be tested was milled, and then again a ProCAD ^® blank is was milled. The machinability was found to be "very good" in the event that the time required for the milling of the blank to be tested ceramic was less than 95% of the time required for milling the ProCAD ^® Döhring adds. Times in the range of 95 to 105% of this time led to the grade "good" for machinability, times in the range of 105 to 115% to "acceptable" and times above 115% to "poor". The average time required for the milling process was 14.0 min.

To compare the machinability of the test specimens with another glass-ceramic, a blank of the composition as described in U.S. Pat DE 197 50 794 and subjected to the test described above. After 15 min. the test was stopped because only 10% of the milled volume was already milled and the tools used for milling were already worn, which did not happen to any of the test samples.

The edge strength was determined as follows:

With the help of a milling unit (CEREC 3 ^® ) blanks were milled to give Lego building blocks. Blind holes were milled with a 1.6 mm cylindrical diamond cutter. The quality of these blind holes was determined by the area of the corners broken was compared with those of a reference sample (ProCAD ^®). The ratio of the area of the broken corners to the area of the blind holes is a measure of the edge strength.

Edge strength is considered to be "very good" if the said ranges are smaller than that of the reference, it is considered "good" if the ratios are approximately equal, and it is considered "acceptable" if the area is greater than 110% of the reference sample.

The chemical resistance was determined according to ISO 6872, ie as a loss of mass after 16 h in 4% acetic acid at 80 ° C. "Good" means that the solubility according to this method is below 100 μg / cm ² .

The strength was determined as biaxial strength according to ISO 6872 or as 3-point bending strength according to WN 843-1:

Bars of 12 mm diameter were poured and crystallized once. From these bars, 20 slices with a thickness of 1.2 mm were sawn out. Ten of these slices were then smoothed and the surfaces of the slices were polished using 1000 grit SiC paper. The biaxial strength was measured as disclosed in ISO 6872. The other 10 disks were crystallized a second time at 800 to 900 ° C to give the lithium disilicate phase. These solidified samples were smoothed on both sides and the surfaces were polished using 1000 grit SiC paper. The biaxial strength was then determined according to ISO 6872.

On the other hand, the flexural strength was determined for rods of dimensions 25 x 3.5 x 3.0 mm, which were sawn out from a block of lithium metasilicate glass-ceramic. These rods were smoothed to give 25 x 2.5 x 2.0 mm rods, which were then polished using 1000 grit SiC paper. The edges were also chamfered with 1000 grit SiC paper. The span was 20 mm. The results are comparable to the biaxial strength results.

In addition, the fracture toughness was determined by applying a Vickers embossment to a polished surface and determining the size of the corner defects (embossing force method ... IF). This method is useful as a comparative method but does not provide absolute values. For comparative purposes measurements were carried out on notched bending samples (SENB, SEVNB). For the lithium disilicate glass ceramics, fracture toughness values> 2 MPa ^{0.5 were} obtained.

Table II gives the values for biaxial strength and fracture toughness of the samples having the disilicate phase, i. H. such samples that were crystallized twice. In addition, quotients representing the ratio of the biaxial strength of the disilicate system to the biaxial strength of the metasilicate system (biaxial consolidation factor) or the fracture toughness ratio of the disilicate system to the fracture toughness of the metasilicate system (strengthening factor K1C) are reported.

• außerordentlich: CR < 0,4
• sehr gut: 0,4 < CR < 0,5
• gut: 0,5 < CR < 0,6
• akzeptabel: 0,6 < CR < 0,8
• opak: 0,8 < CR.

The translucency was determined after the second crystallization: a test piece 16 mm in diameter and 2 mm thick was prepared and polished on both sides. The contrast value CR was determined according to BS 5612 (British Standard) using a spectral colorimeter (Minolta CM-3700d). The determination of the contrast value consisted of two individual measurements. The test piece to be analyzed was minimally arranged in front of a black ceramic body with a reflection of 4% and then in front of a white ceramic body with a reflection of 86% and was then analyzed colorimetrically. When using highly transparent test pieces, reflection / absorption is mainly caused by the ceramic background, while the reflection is caused by the test piece when an opaque material is used. The ratio of reflected light in a black background to reflected light in a white background is the measure of the contrast value, with complete translucency leading to a contrast value of 0 and full opacity to a contrast value of 1. The samples were rated as follows:

• extraordinary: CR <0.4
• very good: 0.4 <CR <0.5
• good: 0.5 <CR <0.6
• acceptable: 0.6 <CR <0.8
• opaque: 0.8 <CR.

The data in Table II show that the lithium metasilicate glass-ceramic combines very good machinability and high edge strength with the ease of converting it to lithium disilicate glass ceramics by a simple heat treatment, which has a very high flexural strength as well as having excellent chemical resistance and translucency, all characteristics that make them very attractive as a material useful for the preparation of dental restorations.

Here are some examples that are described in more detail:

Example 1:

The glass was melted at a temperature of 1500 ° C for 3 hours and then poured into steel molds heated to 300 ° C. After 1 min. The glass rods were transferred to a cooling oven and at 500 ° C for 10 min. annealed and then cooled to room temperature.

The glass was homogeneous and transparent.

Subsequently, the glass rod of a first crystallization at 650 ° C for a period of 20 min. subjected.

Slices of a round bar were cut out from such a ceramized bar and the biaxial strength was determined. The phase content was analyzed by XRD (X-ray diffraction). Lithium metasilicate was the only phase that was detected. The biaxial strength was 119 +/- 25 MPa.

Also, the milling time for test specimens was determined. The milling time of the test piece was 1 min. less than that of ProCAD ^®, which was used as reference.

The edge strength was good.

In addition, 10 slices of a second crystallization at 850 ° C for a period of 10 min. and determines the biaxial strength and fracture toughness.

The biaxial strength was 395 +/- 117 MPa, which corresponds to a consolidation factor of 3.0.

The fracture toughness (IF) was 1.6 MPam ^0.5 .

The translucency was very good.

The chemical stability according to ISO 6872 (4% acetic acid, 80 ° C, 16 h) was 37 μg / cm ² .

Example 6:

Glass rods were prepared according to Example 1. The glass was again homogeneous and transparent.

The first crystallization was at 650 ° C for a period of 20 min. carried out.

Lithium metasilicate was determined to be the major phase, with traces of lithium disilicate also present. The biaxial strength was 135 +/- 24 MPa.

Again, the milling time was determined for a test specimen. The milling time of the test piece was 1 min. shorter than ProCAD ^® , which was used as a reference again.

The edge strength was very good.

After a second crystallization was carried out according to Example 1, the biaxial strength was 472 +/- 85 MPa, which corresponds to a consolidation factor of 3.5.

The fracture toughness (IF) was 2.3 MPam ^0.5 .

The translucency was extraordinary.

Example 9

Glass rods were prepared according to Example 1. The glass was again homogeneous and transparent.

The first crystallization was at 650 ° C for a period of 20 min. carried out.

Lithium metasilicate was detected as the only phase. The biaxial strength was 112 +/- 13 MPa.

Again, the milling time was determined for a test specimen. The milling time of the test piece was 1 min. shorter than that for ProCAD ^® , which was used again as reference.

The edge strength was good.

After carrying out a second crystallization according to Example 1, the biaxial strength was 356 +/- 96 MPa, which corresponds to a solidification factor of 3.16.

The fracture toughness (IF) was 1.9 MPam ^0.5 .

The translucency was acceptable.

Example 20 (comparison):

Glass rods were prepared according to Example 1. The glass was again homogeneous and transparent.

The first crystallization was at 650 ° C for a period of 20 min. carried out.

Lithium disilicate was identified as the major phase and lithium metasilicate was present only in trace amounts. The biaxial strength was 194 +/- 35 MPa.

Again, the milling time was determined for a test specimen. The milling time of the test body was longer than that for ProCAD ^®, which was again used as a reference 4 min.

The edge strength was poor.

After a second crystallization, which was carried out according to Example 1, the biaxial strength was 405 +/- 80 MPa, which corresponds to a hardening factor of 2.09.

The fracture toughness (IF) was 1.88 MPam ^0.5 .

The translucency was very good.

Claims (26)

Use of a lithium silicate latent material containing lithium metasilicate as a main crystal phase for making a dental restoration, the blank having a holder for mounting in a machine and being machined to a desired geometry to produce a shaped one Lithium silicate product, and the shaped lithium silicate product of a heat treatment at a temperature of about 820 to 950 ° C for a period of about 5 to 20 minutes. wherein the shrinkage occurring during the heat treatment is less than 0.5% by volume. Use after Claim 1 in which the lithium metasilicate phase forms 20 to 50% by volume of the lithium silicate blank. Use after Claim 1 in which the lithium metasilicate forms 30 to 40% by volume of the lithium silicate blank. Use according to one of Claims 1 to 3 in which the lithium metasilicate crystals are lamellar or platelet-shaped. Use according to one of Claims 1 to 4 in which the lithium silicate blank has a biaxial strength of at least 90 MPa and a fracture toughness of at least 0.8 MPa ^0.5 . Use according to one of Claims 1 to 5 in which the holder is attached to the blank and connected thereto. Use according to one of Claims 1 to 6 in which the holder is made of a different material than the blank. Use after Claim 7 in which the holder is made of an alloy, a metal, a glass ceramic or a ceramic. Use according to one of Claims 1 to 6 in which the holder is made of the same material as the blank and integral with the blank. Use according to one of Claims 1 to 9 in which the blank is provided with information. Use after Claim 10 in which the information on the blank includes the material, size and type of mold to be machined from the blank. Use according to one of Claims 1 to 11 in which the lithium silicate blank contains the following components: component Wt .-% SiO ₂ 64.0 - 73.0 Li ₂ O 13.0 - 17.0 K ₂ O 2.0 - 5.0 Al ₂ O ₃ 0.5 - 5.0 Nucleating agents 2.0 - 5.0. Use after Claim 12 in which the lithium silicate blank also contains the following additional components independently of one another component Wt .-% ZnO 2.0 - 6.0 Na ₂ O 0 - 2.0 Me ^II O 0 - 5.0 ZrO ₂ 0 - 2.0 coloring and fluorescent metal oxides 0 - 7.5, wherein Me ^II O is one or more members selected from the group consisting of CaO, BaO, SrO and MgO. Use after Claim 12 or 13 in which the lithium silicate blank contains the following components independently in the following amounts: component Wt .-% SiO ₂ 65.0 - 70.0 Li ₂ O 14.0 - 16.0 K ₂ O 2.0 - 5.0 Al ₂ O ₃ 1.0 - 5.0 Nucleating agents 2.0 - 5.0 ZnO 2.0 - 6.0 Na ₂ O 0.1 - 2.0 Me ^II O 0.1 - 5.0 ZrO ₂ 0.1 - 2.0 coloring and fluorescent metal oxides 0,5 - 3,5, wherein Me ^II O is one or more members selected from the group consisting of CaO, BaO, SrO and MgO, and wherein the metal of the one or more coloring and fluorescent metal oxides is selected from the group consisting of Ta, Tb, Y, La, Er , Pr, Ce, Ti, V, Fe and Mn are selected. Use according to one of Claims 12 to 14 in which the lithium silicate blank contains 67.0 to 70.0% by weight of SiO ₂ . Use according to one of Claims 12 to 15 in which the nucleating agent is P ₂ O ₅ . Use according to one of Claims 1 to 16 in which the dental restoration has a biaxial strength of at least 250 MPa and a fracture toughness of at least 1.5 MPa ^0.5 . Use according to one of Claims 1 to 17 in which the shaped lithium silicate product has the shape of the dental restoration. Use according to one of Claims 1 to 18 in which the dental restoration is an inlay, onlay, bridge, post, veneer, shell, facet, crown, partial crown, scaffold or cap. Use according to one of Claims 1 to 19 in which the mechanical processing is performed by grinding or milling. Use according to one of Claims 1 to 20 in which machine processing is controlled by a computer. Use according to one of Claims 1 to 21 in which the lithium silicate product subjected to the heat treatment has lithium metasilicate as the main crystal phase, and wherein the heat treatment converts the lithium metasilicate crystals to lithium disilicate crystals as the main crystal phase of the dental restoration. Use according to one of Claims 1 to 22 in which the heat treatment involves increasing the strength and fracture toughness of the lithium silicate product. Use according to one of Claims 1 to 23 which also includes the final treatment of the dental restoration to obtain a natural appearance. Use after Claim 24 wherein the finishing step includes applying a coating to the dental restoration by coating powdered materials or by hot pressing a coating material onto the unfinished dental restoration. Use after Claim 25 in which the heat treatment is carried out during firing of the coated materials or hot pressing of the coating material onto the unfinished dental restoration.

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