Patent ID: 12207982

DETAILED DESCRIPTION

The process described in the present text is advantageous in a number of aspects:

It was found that highly aesthetic dental restorations based lithium disilicate material can be obtained, when during a certain temperature range the sintering is conducted under reduced atmospheric pressure conditions.

Applying the reduced atmospheric pressure conditions during a temperature range which is too low, the desired translucency of the resulting dental restoration cannot be obtained.

Further, if desired, the porous 3-dim article can easily be individualized in an early stage, e.g. by applying a coloring solution to its absorbing surface. As the 3-dim article is in a porous stage, it can also be machined easily, e.g. by using a dry milling process. In addition, the final dental restoration can be obtained in a one-step sintering process. There is no need to isolate a product having lithium metasilicate as main crystalline phase.

In contrast to the process described in EP 2 450 000 (3M IPC), there is also no need to support the inner surface of the dental restoration during sintering. It has been found that the porous dental restoration described in the present text is self-supporting during sintering. Thus, the porous 3-dim article can be sintered to its final stage without distortion of its geometry during sintering.

It was found, that in particular those dental restorations were suitable to be sintered without support during the sintering step, which were obtained from porous 3-dim articles having been manufactured by using a build-up technology.

Previously, the veneering of e.g. a zirconia dental support structure with a facing out of lithium disilicate material was either done by applying a hot-pressing technique or by grinding the veneer out of a solid dental milling block containing lithium metasilicate as main crystalline phase and conducting a crystallizing step. The process described in the present text simplifies this procedure to a great extend.

The dental restoration (e.g. veneer) can now be machined (e.g. milled) out of a pre-sintered and thus porous milling block in an efficient way and sintered to its final shape without supporting the dental restoration during sintering.

Further, according to the process described in the present text it is now possible to provide the porous 3-dim article in different shapes. The shape is not restricted by the available pressing equipment. Any shape which can be obtained by applying a build-up technology is now possible.

It was also found that conducting the sintering under reduced atmospheric pressure can be beneficial for obtaining a self-supporting 3-dim porous article, in particular a 3-dim porous article having the shape of a dental crown, dental bridge, veneer, inlay, onlay or part thereof and is advantageous for the translucency and the color.

The invention relates to a process for producing a sintered lithium disilicate glass ceramic dental restoration.

The process comprises the step of sintering a porous 3-dim article having the shape of a dental restoration with an outer and inner surface without using a support structure during the sintering process, i.e. support less. The sintering is done under reduced atmospheric pressure, in particular during a temperature range from 600 to 800° C. After sintering a sintered lithium disilicate ceramic dental restoration is obtained.

According to a further embodiment, the process comprises the steps ofproviding a porous 3-dim article, the 3-dim dental article having either the shape of a dental milling block or of a dental restoration with an outer and inner surface,for porous 3-dim articles having the shape of a milling block, machining the porous 3-dim article to obtain a machined porous 3-dim article having the shape of a dental restoration with an outer and inner surface,sintering the porous 3-dim article having the shape of a dental restoration with an outer and inner surface to obtain a sintered lithium disilicate glass ceramic dental restoration.

Thus, according to one embodiment, the porous 3-dim article has the shape of a dental milling block. According to another embodiment, the porous 3-dim article has the shape of a dental restoration with an outer and inner surface. In any case, the sintering step is applied to a porous 3-dim article having the shape of a dental restoration with an outer and inner surface, but not the 3-dim article in the shape of a dental milling block.

The porous 3-dim article can be characterized by one or more or all of the following parameters:Pore volume: from 20 to 70%Density: from 0.5 to 2 g/cm3,Flexural strength: from 20 to 75 MPa or from 30 to 60 MPa according to ISO 6872.
If desired, the parameters can be measured as described in the Example section below.
The porous 3-dim article comprises the same oxides as the sintered lithium disilicate ceramic article.

The porous 3-dim article can be provided by using different technologies. According to one embodiment, the porous 3-dim article is provided by using an additive manufacturing technology. Suitable additive manufacturing technologies are given in the definition section above. Using an additive manufacturing technology allows the manufacturing of basically any desired shape of the porous 3-dim article. Using an additive manufacturing technology also allows the manufacturing of fully or only partially colored porous 3-dim articles.

In particular, using an additive manufacturing technology allows the manufacturing of a porous 3-dim article having the shape of a dental restoration and containing coloring components (e.g. ions or pigments), which after sintering result in a tooth-colored dental restoration.

The coloring components can be applied in liquid or solid form during the additive manufacturing process. Suitable coloring components include those as described for the coloring solutions in the text further down below.

If desired, a heating or pre-sintering step can be applied to strengthen the structure of the porous 3-dim article. According to one embodiment, the build-up technology makes use of a glass powder. The particles in the glass powder typically have a particle size below about 70 μm or below about 60 μm or below about 25 μm. If desired, the particle size can be measured with laser diffraction. The adjustment of the particle size can be done using a sieve having the desired maximum mesh size.

If larger particles are used for producing the article (e.g. particles having a particle diameter above about 70 μm or above about 80 μm), the surface resolution of the final product might be reduced.

The nature and structure of the glass powder is not particularly limited unless it is detrimental to the desired performance of the composition.

The glass powder is preferably selected to be compatible for use in human bodies. Furthermore, the glass powder is preferably selected to provide good aesthetic appearance for the dental restoration, in particular when combined with a dental framework.

Glass powder which can be used can typically be characterized by at least one of the following features:comprising:Si oxide calculated as SiO2: from 55 to 80 wt.-%, or from 59 to 72 wt.-%;Li oxide calculated as Li2O: from 7 to 20 wt.-%, or from 10 to 16 wt.-%;Al oxide calculated as Al2O3: from 1 to 5 wt.-%;P oxide calculated as P2O5: from 1 to 5 wt.-%;coefficient of thermal expansion: about 8*10−6K−1to about 15.8*10−6K−1or 8*10−6K−1to about 9*10−6K−1or about 12*10−6K−1to about 13.6*10−6K−1or from about 15*10−6K−1to 15.8*10−6K−1;melting temperature (range): around or less than about 1000° C.;density: about 2.0 to about 3.0 or about 2.2 to about 2.6 g/cm3and/orglass transition temperature: 500 to 600° C. or 520 to 580° C., preferably about 550° C.

According to another embodiment, the porous 3-dim article is provided by using a technology comprising a pressing step and heating step or pre-sintering step.

According to this embodiment, a glass powder is provided first and pressed to a 3-dim article (sometimes also referred to as “green body”).

In a further step, the 3-dim article is heated or pre-sintered to obtain a porous 3-dim article (sometimes also referred to as “white body”).

The temperature is adjusted to a range so that the porous 3-dim article does not contain lithium metasilicate or lithium disilicate as main crystalline phase. Instead, the 3-dim article is mainly still in an amorphous state.

Suitable pressure ranges for the pressing step include: from 0.1 to 20 MPa or from 0.5 to 15 MPa or from 1 to 10 MPa.

Suitable temperature ranges for the heating or pre-sintering step include: from 400 to 700° C. or from 450 to 650° C. or from 500 to 600° C.

The sintering of the porous 3-dim article having the shape of a dental restoration is typically conducted within a temperature range from 800 to 1000° C. or from 850 to 975° C. or from 900 to 950° C.

It was found that conducting the sintering under reduced atmospheric pressure is beneficial, in particular, if a self-supporting porous 3-dim article and a high translucent and tooth colored restoration is desired.

Without wishing to be bound to a certain theory, it is assumed that reducing the atmospheric pressure during sintering may help to reducing the number of voids which may be present in the sintered article

“Reduced atmospheric pressure” means that the pressure is at least 80% or at least 90% or at least 95% below the ambient conditions.

Suitable conditions include the following ranges: from 200 to 5 hPa or from 100 to 10 hPa or from 50 to 25 hPa.

Applying reduced pressure only during certain time and/or temperature regimes during sintering may also help to reduce or avoid the formation of higher porosities, improves the translucency, may help to reach the desired coloration, and may help to reduce the overall sintering time.

It can be preferred, if the reduced atmospheric pressure conditions are applied not from the beginning of the sintering process, but later, e.g. after having conducted a first heat treatment.

It can also be preferred, if the reduced atmospheric pressure conditions are applied not until end of the cooling down period, but stopped at the temperature obtained by conducting the first heat treatment.

According to one embodiment, the sintering process is conducted as follows:Conducting a first heat treatment to obtain a first temperature T1 at an atmospheric pressure P1, T1 being preferably in the range of 600 to 800° C. or 700 to 800° C., P1 being in the range of 900 to 1100 hPa,Holding temperature T1 and applying reduced atmospheric pressure conditions P2, P2 being preferably in the range of 20 to 50 hPa,Conducting a second heat treatment to obtain a second temperature T2, T2 being preferably in the range of 850 to 1,000° C.,Holding at that temperature T2 for a defined time t, t being preferably in the range of 180 to 1,800 s,Conducting a first cooling treatment until T1 is reached,Increasing the atmospheric pressure until P1 is reached,Conducting a second cooling treatment until room temperature (e.g. 23° C.) is reached.

At the end of the sintering step a sintered litihium disilicate glass ceramic dental article in the shape of a dental restoration is obtained. That is, the obtained dental restoration comprises lithium disilicate as main crystal phase (i.e. more than 50 vol.-%).

The sintering of the porous 3-dim article having the shape of a dental restoration is typically done without supporting the inner surface of the dental restoration during sintering.

This is a great benefit compared to other processes described in the art, which typically require that at least the inner surface of the porous dental restoration is supported during sintering to avoid distortion, e.g. as described in US 2013 224688 (3M IPC).

In that document, the outer surface of the corresponding support structure is used to support the inner surface of the porous dental restoration.

Likewise, WO 2013/167723 A1 suggests conducting the sintering step by supporting the article to be sintered.

During sintering, the material of the porous 3-dim article having the shape of a dental restoration undergoes a sintering and a crystallization process with the result that at the end the material contains lithium disilicate as main crystalline phase (i.e. above 50 vol.-%).

The obtained sintered lithium silicate glass ceramic material may fulfill at least one or more or all of the following parameters:Translucency: from 0.03 to 0.60 or from 0.1 to 0.4 (Mac Beth TD 932 sample thickness 1.50+/−0.05 mm polished with 9 μm sandpaper); a translucency of 0.0 means that the sample is fully transparent.Radiopacity: of more than 200%, or more than 300% (according to ISO 6872);Coefficient of thermal expansion: from 8.0 to 12*10−6/K or from 8.0 to 11*10−6/K or from 9.0 to 10.4*10−6/K (according to ISO 6872);Vickers hardness: at least 500 or at least 520 or at least 550 (HV; 0.2 kg);Flexural strength: of at least 250 MPa or at least 350 or at least 400 (according to ISO 6872);Refractive index: in the range of 1.545 to 1.525 or in the range of 1.530 to 1.540 (measured with an Abee Refractometer).

If desired, the respective parameters can be determined as outlined in the example section below.

The sintered lithium disilicate glass ceramic material is characterized by comprising the following components:Si oxide calculated as SiO2: from 55 to 80 wt.-%, or from 59 to 72 wt.-%;Li oxide calculated as Li2O: from 7 to 20 wt.-%, or from 10 to 16 wt.-%;Al oxide calculated as Al2O3: from 1 to 5 wt.-%;P oxide calculated as P2O5: from 1 to 5 wt.-%.

The sintered lithium disilicate glass ceramic may further comprise:K oxide calculated as K2O from 0 to 0.1 wt.-% or from 0.001 to 0.002 wt.-%;Zr oxide calculated as ZrO2 from 0.0 to 4.0 wt.-% or from 0.01 to 0.05 wt.-%;Zn oxide calculated as ZnO from 0 to 0.2 wt.-% or from 0.002 to 0.01 wt.-%;Ce oxide calculated as CeO2 from 0.0 to 3.0 wt.-% or from 0.1 to 2.0 wt.-%;Cs oxide calculated as Cs2O from 6 to 30 wt.-% or from 10 to 15 wt.-%;Coloring components calculated as the respective oxides: from 0 to 10 wt.-% or from 0.25 to 8 wt.-% or from 0.5 to 6 wt.-%.

Suitable coloring oxides comprise the oxides of V, Mn, Fe, Er, Tb, Y, Ce, Sm, Dy and mixtures thereof.

The lithium disilicate glass ceramic material does typically not comprise Zr oxide calculated as ZrO2: more than 20 wt.-%, more than 15 wt.-% or more than 12 wt.-%.

According to another embodiment, the sintered lithium disilicate glass ceramic material may have the following composition, wherein the content of the various ions is calculated based on the respective oxide:Si oxide calculated as SiO2 from 55 to 80 wt.-% or from 60 to 65 wt.-%,Al oxide calculated as Al2O3 from 1 to 5 wt.-% or from 1 to 2 wt.-%,B oxide calculated as B2O3 from 0 to 5 wt.-% or from 0 to 2 wt.-%,Li oxide calculated as Li2O from 7 to 16 wt.-% or from 8 to 13 wt.-%,Na oxide calculated as Na2O from 0 to 1 wt.-% or from 0.05 to 0.2 wt.-%,Cs oxide calculated as Cs2O from 6 to 30 wt.-% or from 10 to 15 wt.-%,P oxide calculated as P2O5 from 1 to 5 wt.-% or from 1.5 to 3.0 wt.-%.

According to a further embodiment, the following components might be present either alone or in combination with others.Sr oxide calculated as SrO from 0.0 to 5 wt.-% or from 0.1 to 3.0 wt.-%;Ba oxide calculated as BaO from 0.0 to 7 wt.-% or from 0.1 to 3.0 wt.-%;Ti oxide calculated as TiO2 from 0.0 to 2 wt.-% or from 0.1 to 3.0 wt.-%;Zr oxide calculated as ZrO2 from 0.0 to 4.0 wt.-% or from 0.01 to 0.05 wt.-%;Hf oxide calculated as HfO2 from 0.0 to 5.0 wt.-% or from 2.0 to 4.0 wt.-%;Fe oxide calculated as Fe2O3 from 0.0 to 0.5 wt.-% or from 0.1 to 0.3 wt.-%;V oxide calculated as VO2 from 0.0 to 0.5 wt.-% or from 0.01 to 0.3 wt.-%;Y oxide calculated as Y2O3 from 0.0 to 1.5 wt.-% or from 0.1 to 1.0 wt.-%;Ce oxide calculated as CeO2 from 0.0 to 3.0 wt.-% or from 0.1 to 2.0 wt.-%;Sm oxide calculated as Sm2O3 from 0.0 to 2.0 wt.-% or from 0.0 to 1.0 wt.-%;Er oxide calculated as Er2O3 from 0.0 to 2.0 wt.-% or from 0.01 to 0.4 wt.-%;Dy oxide calculated as Dy2O3 from 0 to 1.0 wt.-% or from 0.1 to 0.2 wt.-%;K oxide calculated as K2O from 0 to 0.1 wt.-% or from 0.001 to 0.002 wt.-%;Mg oxide calculated as MgO from 0 to 0.2 wt.-% or from 0.002 to 0.01 wt.-%;Zn oxide calculated as ZnO from 0 to 0.2 wt.-% or from 0.002 to 0.01 wt.-%;La oxide calculated as La2O3 from 0 to 0.1 wt.-% or from about 0.0001 to 0.01 wt.-%;wt.-% with respect to the weight of the lithium silicate glass ceramic.

Certain of these oxides may fulfill specific functions during the production process:SiO2 may function as a network former and lithium silicate precursor.Al2O3 may increase the chemical stability of the glass matrix.Li2O may act as lithium silicate precursor.Cs2O may function as fluxing agent and may help to control the phase separation and increase the radiopacity.P2O5 may function as nucleating agent.CeO2 may act as oxidative coloring stabilizer.Er2O3 may act as a color adjusting agent (e.g. to reduce the greenish color fault).BaO, SrO, Y2O3, ZrO2 and HfO2 can be used to adjust the refractive index of the glass matrix.The inventive lithium silicate glass ceramic does typically not comprise K2O, MgO, ZnO, La2O3 or a mixture of those in an amount above 0.5 wt.-% or above 0.4 wt.-% or above 0.3 wt.-% or above 0.2 wt. % or above 0.1 wt.-% with respect to the weight of the ceramic.According to a particular embodiment, the lithium silicate glass ceramic does not comprise K2O in an amount 0.4 wt.-% or above 0.3 wt.-% or above 0.2 wt.-% or above 0.1 wt.-% with respect to the weight of the ceramic.The Li2O content is typically below 17 wt.-% or below 16 wt.-% with respect to the weight of the glass ceramic.Reducing the amount of either of oxides K2O, MgO, ZnO, La2O3 may facilitate the production of a translucent ceramic material having the desired CTE value.

The lithium disilicate glass ceramic material described in the present text does typically not comprise either of the following crystal phases in an amount above 50 or above 40 or above 30 or above 20 or above 10 or above 5% (at room ambient conditions; e.g. 23° C.): apatite, tetragonal or cubic leucit,

If desired, the porous 3-dim article in the shape of a dental restoration can be colored using a suitable coloring solution.

According to one embodiment, the coloring solution is used for being selectively applied to parts of the surface of the porous 3-dim article. That is, the solution is only applied to parts of the surface of the 3-dim article but not to the whole surface.

According to another embodiment the solution is used for being applied to the whole surface of the porous 3-dim article. This can be achieved, e.g. by dipping the article completely into the coloring solution.

The porous 3-dim article is usually treated with the solution for about 0.5 to about 5 minutes, preferably from about 1 to about 3 minutes at room temperature (about 23° C.). Preferably no pressure is used. A penetration depth of the solution into the article of about 5 mm is considered to be sufficient.

If a coloring solution is used, the process of producing the dental restoration comprises the following steps:providing a porous 3-dim article, the 3-dim article having either the shape of a dental milling block or of a dental restoration with an outer and inner surface,for porous 3-dim articles having the shape of a milling block, machining the porous 3-dim article to obtain a machined porous 3-dim article having the shape of a dental restoration with an outer and inner surfaceapplying a coloring solution as described in the present text to the surface of the porous 3-dim article,optionally drying the porous 3-dim article to which the coloring solution has been applied,sintering the porous 3-dim article having the shape of a dental restoration with an outer and inner surface to obtain an at least partially colored and sintered lithium disilicate ceramic dental restoration.

Coloring solutions which can be used typically comprise a solvent and coloring ions.

Suitable solvents include water, alcohols (especially low-boiling alcohols, e.g. with a boiling point below about 100° C.) and ketons.

The solvent should be able to dissolve the coloring ions used.

Specific examples of solvents which can be used for dissolving the cations contained in the solution include water, methanol, ethanol, iso-propanol, n-propanol, butanol, acetone, ethylene glycol, glycerol and mixtures thereof.

The solvent is typically present in an amount sufficient to dissolve the components contained or added to the solvent.

Suitable coloring ions include the ions of V, Mn, Fe, Er, Tb, Y, Ce, Sm, Dy or combinations thereof. Besides those cations the solution may contain in addition coloring agent(s) selected from those listed in the Periodic Table of Elements (in the 18 columns form) and are classified as rare earth elements (including Ce, Nd, Sm, Eu, Gd, Dy, Ho, Tm, Yb and Lu) and/or of the subgroups of the rare earth elements and/or salts of transition metals of the groups 3, 4, 5, 6, 7, 9, 10, 11.

Anions which can be used include OAc−, NO3−, NO2−, CO32−, HCO3−, ONC−, SCN−, SO4−, SO32−, gluturate, lactate, gluconate, propionate, butyrate, glucuronate, benzoate, phenolate, halogen anions (fluoride, chloride, bromide) and mixtures thereof.

The solution may also contain organic components. By adding organic molecules, the properties (e.g. viscosity, vapor pressure, surface tension, stability, etc) can be modified.

Organic components which can be added include PVA, PEG, ethylenglycol, surfactants or mixtures thereof.

The solution may also contain one or more complexing agent(s). Adding a complexing agent can be beneficial to improve the storage stability of the solution, accelerate the dissolving process of salts added to the solution and/or increase the amount of salts which can be dissolved in the solution.

The solution may also contain marker substance(s). Adding a marker substance(s) can be beneficial in order to enhance the visibility of the solution during use, especially, if the solution is transparent and color-less.

Examples of marker substance(s) which can be used include food colorants like Riboflavin (E101), Ponceau 4R (E124), Green S (E142).

Suitable coloring solutions are also described in WO 2004/110959 (3M), WO 00/46168 A1 (3M), WO 2008/098157 (3M), WO 2009/014903 (3M) and WO 2013/022612 (3M).

The coloring solution is typically applied to the surface of the porous 3-dim article with a suitable application device comprising a reservoir and an opening, the reservoir containing the coloring solution as described in the present text.

According to a particular embodiment, the device may have the shape of a pen, the pen comprising a housing, a brush tip, a removable cap and a reservoir for storing the solution described in the present text.

The brush tip is typically attached or fixed to the front end of the housing. The reservoir is typically fixed or attached to the rear end of the housing. The removable cap is typically used for protecting the brush tip during storage.

Using a pen may facilitate the application of the coloring solution and will help the practitioner to save time.

According to one embodiment, the process can be described as follows:

A process for producing a sintered lithium disilicate glass ceramic dental restoration out of a porous 3-dim article, the process comprising the step ofa) providing a porous 3-dim article, the 3-dim article having the shape of a dental milling block, the porous 3-dim article having a density from 0.5 to 2 g/cm3,b) machining the porous 3-dim article to obtain a machined porous 3-dim article having the shape of a dental restoration with an outer and inner surface,c) optionally coloring the porous 3-dim article having the shape of a dental restoration,d) sintering the porous 3-dim article having the shape of a dental restoration with an outer and inner surface without supporting the inner surface of the porous 3-dim article having the shape of a dental restoration during sintering to obtain a sintered lithium disilicate ceramic dental restoration, the sintering preferably being done under reduced atmospheric pressure conditions,the sintered lithium disilicate glass ceramic dental restoration having a density from 2 to 3 g/cm3 and comprisingSi oxide calculated as SiO2 from 55 to 80 wt.-%,Li oxide calculated as Li2O from 7 to 16 wt.-%,Al oxide calculated as Al2O3 from 1 to 5 wt.-%, andP oxide calculated as P2O5 from 1 to 5 wt.-%,wt.-% with respect to the weight of the dental restoration.

According to another embodiment, the process can be described as follows:

A process for producing a sintered lithium disilicate glass ceramic dental restoration out of a porous 3-dim article, the process comprising the step ofproducing a porous 3-dim article having the shape of a dental restoration with an outer and inner surface using a build-up technology, the porous 3-dim article having a density from 0.5 to 2 g/cm3,optionally coloring the porous 3-dim article having the shape of a dental restoration,sintering the porous 3-dim article having the shape of a dental restoration with an outer and inner surface without supporting the inner surface of the porous 3-dim article having the shape of a dental restoration during sintering to obtain a sintered lithium disilicate ceramic dental restoration,the sintering being done under reduced atmospheric pressure conditions, the reduced atmospheric pressure conditions being applied at a temperature above 600 or 700° C.,optionally sintering the porous dental restoration without using a support structure during sintering,the sintered lithium disilicate glass ceramic dental restoration having a density from 2 or 2.1 to 3 g/cm3 and comprisingSi oxide calculated as SiO2 from 55 to 80 wt.-%,Li oxide calculated as Li2O from 7 to 16 wt.-%,Al oxide calculated as Al2O3 from 1 to 5 wt.-%, andP oxide calculated as P2O5 from 1 to 5 wt.-%,wt.-% with respect to the weight of the dental restoration.

According to a further embodiment the present invention is directed to a process for producing a sintered lithium disilicate glass ceramic dental restoration out of a porous 3-dim article, the process comprising the step ofsintering the porous 3-dim article having the shape of a dental restoration with an outer and inner surface to obtain a sintered lithium disilicate ceramic dental restoration, the sintered lithium disilicate glass ceramic dental restoration comprisingSi oxide calculated as SiO2 from 55 to 80 wt.-%,Li oxide calculated as Li2O from 7 to 16 wt.-%,Al oxide calculated as Al2O3 from 1 to 5 wt.-%, andP oxide calculated as P2O5 from 1 to 5 wt.-%,wt.-% with respect to the weight of the dental restoration,
the sintering of the porous 3-dim article having the shape of a dental restoration being conducted without supporting the inner surface of the dental restoration during sintering, wherein the description of the process conditions and formulations and shapes of the article are as described in the present text.

The invention is also directed to a kit of parts comprisinga porous 3-dim article having the shape of a dental milling block,an instruction of use comprising the following process steps:machining a porous dental restoration out of the 3-dim porous article having the shape of a dental milling block,optionally coloring the porous dental restoration with a coloring solution,sintering the porous dental restoration, the sintering being done under reduced atmospheric pressure conditions, the reduced atmospheric pressure conditions being applied at least above a temperature of 600 or 700° C.,
the porous 3-dim article having a pore volume from 20 to 70 vol.-% and comprising the following oxides:Si oxide calculated as SiO2 from 55 to 80 wt.-%,Li oxide calculated as Li2O from 7 to 16 wt.-%,Al oxide calculated as Al2O3 from 1 to 5 wt.-%, andP oxide calculated as P2O5 from 1 to 5 wt.-%,
wt.-% with respect to the weight of the porous 3-dim article.

The porous 3-dim article, the dental milling block, the dental restoration, the coloring solution, the machining step, the coloring step, the sintering step and the other process conditions are as described in the present text above.

All components used for producing the dental restoration described in the present text should be sufficiently biocompatible either from the beginning or in its final state (e.g. due to incorporation in a matrix); that is, the composition should not produce a toxic, injurious, or immunological response in living tissue.

The dental restoration described in the present text does not contain components or additives which jeopardize the intended purpose to be achieved with the invention. Thus, components or additives added in an amount which finally results in a non-tooth-colored dental article after sintering are usually not contained. Typically, a dental article is characterized as not being tooth colored, if it cannot be allocated a color from the Vita™ color code system, known to the person skilled in the art. Additionally, components which will reduce the mechanical strength of the dental restoration to a degree, where mechanical failure will occur, are usually also not included in the dental article.

The process described in the present text does typically not comprise either or all of the following process steps:machining a sintered lithium disilicate 3-dim article;machining an article containing lithium metasilicate as main crystalline phase;machining an article containing lithium disilicate as main crystalline phase.

The complete disclosures of the patents, patent documents, and publications cited herein are incorporated by reference in their entirety as if each were individually incorporated. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. The above specification, examples and data provide a description of the manufacture and use of the compositions and methods of the invention. The invention is not limited to the embodiments disclosed herein. One skilled in the art will appreciate that many alternative embodiments of the invention can be made without departing from the spirit and scope of thereof.

The following examples are given to illustrate, but not limit, the scope of this invention. Unless otherwise indicated, all parts and percentages are by weight.

Examples

Unless otherwise indicated, all parts and percentages are on a weight basis, all water is de-ionized water, and all molecular weights are weight average molecular weight. Moreover, unless otherwise indicated all experiments were conducted at ambient conditions (23° C.; 1013 mbar).

Measurements

Quantitative Rietveld Phase Analysis/Crystalline Content

If desired, a quantitative Rietveld phase analysis can be done with a Bruker (Germany) AXS Type: D8Discover spectrometer. Such an analysis allows e.g. the determination of the content of crystalline phases.

Flexural Strength

If desired, the flexural strength can be measured with a Zwick (Germany) type Z010 machine according to ISO 6872.

X-ray Opacity

If desired, x-ray opacity can be measured with an X-ray machine (60 kV; sample thickness: 2 mm) according to ISO 6872.

Coefficient of Thermal Extension (CTE)

If desired, CTE can be determined with a Netzsch (Germany) Type DIL 402 C dilatometer according to ISO 6872 (sample size: 4.5*4.5*26 mm; heating rate: 5.00 K/min).

If desired, the CTE value(s) can also be calculated similar to refractive indices by using additive factors as described in the literature known to the skilled person (e.g. Appen, A. A., Ber. Akad. Wiss. UDSSR 69 (1949), 841-844).

Chemical Stability

If desired, chemical stability can be tested according to ISO 6872. Test specimens having a surface of 30-40 cm2; (50*30 mm; 1-4 mm thickness) are typically cut and stored for 18 h in 4% acetic acid (80° C.).

Translucency/Contrast Ratio (CR)

If desired, the translucency can be determined with a Macbath TD 932 System. Samples are cut into slices (thickness: 1.50+/−0.05 mm), polished (surface roughness: 9 μm) and the translucency is measured.

Milling Properties

If desired, milling experiments can be done on a Sirona, Cerec™ Inlab machine. Blocks from sample GK 79 (14×12×18 mm) were pressed and an anterior crown was milled out of a porous presintered block (650° C./20 min). The porous presintered block could easily be milled.

Particle Size

If desired, the mean particle size can be determined using a commercially available granulometer (Laser Diffraction Particle Size Analysis Instrument, MASERSIZER 2000; Malvern Comp.) according to the instruction of use provided by the manufacturer.

Porosity

If desired, the porosity or open porosity can be measured using a mercury porosimeter in accordance with DIN 66133 as available under the designation “Poremaster 60-GT” from Quantachrome Inc., USA.

Density

If desired, the density can be determined by determining the weight and the dimension of the sample and calculating the density

Example 1 (Non-Colored Lithium Disilicate Ceramic Disc)

The following amounts of powder were mixed in a bottle: 72.1 wt.-% SiO2, 15.1 wt.-% Li2CO3, 3.4 wt.-% Li3PO4, 3.5 wt.-% Al(OH)3, 3.2 wt.-% K2CO3 and 2.7 wt.-% ZrO2.

In a next step the powder mixture was melted in a platinum crucible at 1500° C. and fritted in water. This was repeated three times. Afterwards the frit was milled. The resulting glass powder had the following particle size distribution: d50: 13.5 μm (d10: 2.5 μm, d90: 49.6 μm).

The powder was mixed with 10 wt.-% water and pressed to discs (dimensions: 20 mm×1.5 mm) or blocks (dimensions: 12 mm×14 mm×18 mm) by applying a pressure of 7.5 MPa).

Glass ceramic bodies with 98-100% theoretical density were achieved with the following one step crystallization and sintering program:Heating with 5 K/min to 730° C.;Holding at 730° C. till Vacuum on;Heating with 10 K/min to 930° C.;Holding time 10 min;Cooling with 10 K/min to 730° C.;Holding at 730° C. Vacuum off,Cooling within furnace.

Conducting these processing steps resulted in dense glass ceramic discs with the following properties:Density: 2.43 g/cm3Crystallinity: 54%Bending strength: 250 MPaOpacity: 55%.

The obtained sample is shown inFIG.1.

Example 2 (Colored Lithium Disilicate Ceramic Disc)

A disc as described in Example 1 was prepared. The disc was pre-sintered at 550 to 650° C. to obtain a porous body.

The porous body was colored by immersing it in commercially available coloring liquids or by applying commercially available coloring liquids with a brush to its surface (Lava™ Plus Coloring Liquids and/or Lava™ Plus Effect Shades; 3M ESPE).

After sintering, a colored lithium disilicate glass ceramic was obtained, which has been colored in the amorphous and porous state (i.e. before sintering). The sample obtained is shown inFIG.2on the right side. For comparison, the left disc is non-colored.

Example 3 (Dental Restorations)

A crown was machined out of a pre-sintered dental milling block obtained as described in Example 1 using a Lava™ CNC 500 milling machine (3M ESPE). A picture of the crown machined from a dental milling block made of a pre-sintered lithium silicate material is shown inFIG.3.

Similarly, an inlay was machined out of a pre-sintered block obtained as described in Example 1 using a Sirona CEREC™ inLab.

InFIG.4a sintered lithium disilicate crown is shown. The crown was produced by machining it out of a pre-sintered block, coloring the obtained crown in a pre-sintered stage as described in Example 2 and sintering the crown in one step applying the conditions described in Example 1.

The crown was sintered without using a sintering support. The obtained sintered dental restoration did not show any relevant distortion.

FIG.5shows an inlay produced in the same manner as the crown above.

Example 4 (Comparison)

An artificial tooth stump was provided, the surface of the tooth stump was scanned and a dental crown designed for that tooth stump using Lava™ Design 7 software 3M ESPE). One dental crown was machined out of a pre-sintered lithium disilicate block—Crown A. One dental crown was machined out of a pre-sintered Lava™ DVS block (3M ESPE)—Crown B. Crown A was sintered according to the process described in Example 1 without supporting the inner surface of the dental crown during sintering.

Crown B was sintered as described in the instruction of use provided by the manufacturer, but without supporting the inner surface of the dental crown during sintering.

The sintered crowns were placed on the artificial tooth stump and inspected visually for fit. The results are shown inFIGS.6and7. Crown A fitted nearly perfectly on the artificial tooth stump (FIG.6), whereas Crown B did not fit (FIG.7).

Example 5 (Reduced Atmospheric Pressure Conditions)

Discs as described in Example 1 were prepared. Different conditions of heating rate and duration of vacuum were applied. The sintering temperature was 925° C. and the dwell time at this temperature was 600 s. The respective conditions are shown in Table 1.

TABLE 1Temperature range T1during which reducedatmospheric pressureHeatingAppearance (determined byNrconditions were installedrateinspecting with human eyes)1730° C.-730° C.5K/minClear white,translucent (see FIG. 1)2500° C.-500° C.5K/mingrayish3450° C.-300° C.5K/mingrayish423° C.-23° C.5K/mingrayish523° C.-23° C.25K/minmore grayish

It was found that a sufficiently translucent article can only be obtained when the reduced atmospheric pressure conditions are applied above a certain temperature range. Applying the reduced atmospheric pressure conditions already below a certain temperature resulted in articles having a grayish appearance.

Further the heating rate should be not too fast. It was found that a moderate heating rate (e.g. 2 to 10 K/min) may be further beneficial for achieving an aesthetic article.

FIG.8visualizes the reduced pressure and temperature conditions applied in the Examples 1-4 described above. The level of vacuum corresponds to the levels which can be adjusted according to the instruction of use provided by the manufacturer. Level 0 means no vacuum (i.e. ambient conditions); level 10 means maximum vacuum possible.

Example 6 (Additive Manufacturing)

If desired, a porous 3-dim article having the shape of a dental restoration can also be produced by applying an additive manufacturing technology, e.g. using a 3d-printing technique. A suitable process can be described as follows: An STL computer file describing the 3-dim. shape of the dental restoration to be produced (e.g. dental veneer) is loaded into the software of the printer (ZCorp 310 plus printer; ZCorporation, Burlington, USA).

The printing is done as described in the instruction for use provided by the manufacturer of the printer, wherein parameters like shrinkage and layer thickness are additionally taken into account.

A water based binder (obtainable from ZCorporation, Burlington, USA) is jetted onto specific sections of the uppermost layer of the powder as calculated by the software of the printer. The binder component on the surface of the powder is partly dissolved. The respective particles will stick together. This step is repeated until the shape of the desired article is obtained. After drying, the printed article is removed from the powder-bed and excessive powder is removed (e.g. using pressurized air).