Lithium silicate glass ceramic and glass with ZrO2 content

0001The invention relates to the use of lithium silicate glass ceramic and glass, the ZrO₂ and are particularly suitable for coating zirconium oxide ceramics.

0002Zirconium oxide ceramics are characterized by excellent biocompatibility and excellent mechanical properties, which is why they have been increasingly used in recent years as a material for implants and prostheses, but also as framework materials for dental restorations. Ceramics based on partially stabilized zirconium oxide are mainly used.

0003In many cases it is desirable to modify the surface of the zirconium oxide ceramic by coating it with a different material. Such a coating is regularly used in the manufacture of dental restorations based on zirconium oxide ceramics in order to give the restoration the desired optical properties.

0004Glass ceramics have already been used in the past for coating or veneering oxide ceramics, such as zirconium oxide ceramics. These include feldspar-based ceramics or fluoroapatite glass ceramics.

0005Lithium disilicate glass-ceramics are also known which, due to their high translucency and very good mechanical properties, are used especially in the dental field and primarily for the production of dental crowns and small bridges.

0006The <patcit id="pcit0001" dnum="EP1505041A"><text>EP 1 505 041</text></patcit> describes lithium silicate glass-ceramics that additionally contain 0 to 2% by weight of ZrO₂ may contain. These are processed into the desired dental restorations in the form of lithium metasilicate glass ceramics using CAD / CAM processes, with subsequent heat treatment converting the metasilicate phase into the high-strength disilicate phase. The glass ceramics can also be used to press over ceramic restorations.

0007The <patcit id="pcit0002" dnum="EP1688398A"><text>EP 1 688 398</text></patcit> describes similar lithium silicate glass ceramics which are essentially free of ZnO and, in addition to other components, 0 to 4% by weight of ZrO₂ may contain. To achieve high strength, however, small amounts of 0 to 2% by weight of ZrO are required₂ prefers. These glass ceramics are also used in particular for the production of dental restorations after mechanical processing by means of CAD / CAM.

0008These lithium silicate glass ceramics known from the prior art, however, have the disadvantage that they are not suitable for coating zirconium oxide ceramics, in particular by means of a pressing process in the viscous state. This is because after the viscous flow process has been pressed on, cracks and fissures appear in the glass ceramic. Thus, such a composite does not have the mechanical properties that are essential for use as a dental restoration material.

0009Next are from the <patcit id="pcit0003" dnum="WO2008106958A"><text>WO 2008/106958</text></patcit> Glass ceramics with lithium disilicate as the main crystal phase are known, which are said to be suitable for veneering dental restorations made of yttrium-stabilized zirconium dioxide. However, these glass ceramics only contain amounts of up to 6.0% by weight of ZrO₂ and substantial amounts of Na₂O. The existing ZrO₂ serves only as a classic nucleating agent together with optionally available other nucleating agents such as TiO₂to bring about the formation of the desired lithium disilicate crystal phase.

0010Based on the disadvantages of the already known glass ceramics described above, the invention is based on the object of providing a glass ceramic which can be coated onto a zirconium oxide ceramic in particular by pressing on in the viscous state and thereby forms a coating essentially free of cracks and cracks. In addition, the glass ceramic should be able to form a solid bond with the zirconium oxide ceramic to be coated, and it should have optical and mechanical properties in order to be able to be used in particular as a coating material for dental restorations but also as a material for dental restorations.

0011This object is achieved through the use of a lithium silicate glass ceramic or a lithium silicate glass with nuclei according to one of Claims 1 to 13. The invention also relates to the method for coating a dental restoration and in particular a zirconium oxide ceramic according to claims 14 and 15 and the coated dental restoration according to claim 16.

0012The lithium silicate glass ceramic used according to the invention is characterized in that it contains 8.0 to 16.0% by weight of ZrO₂ and has lithium metasilicate or lithium disilicate as the main crystal phase.

0013In a further preferred embodiment, the glass ceramic contains in particular 10.0 to 16.0% by weight ZrO₂.

0014A glass ceramic is also preferred which contains 55.0 to 71.0, preferably 60.0 to 71.0 and in particular 60 to 69% by weight SiO₂ contains.

0015In addition, a glass ceramic is preferred that contains 9.0 to 17.0 and in particular 11 to 15% by weight Li₂O contains.

0016It has also proven to be particularly preferred if the glass ceramic contains 0.5 to 12.0 and in particular 2.5 to 7.0% by weight of nucleating agents. Preferred nucleating agents are selected from P₂O₅, TiO₂, Nb₂O₅, Metals such as Pt, Pd, Au and Ag, or mixtures thereof. The glass ceramic particularly preferably contains P₂O₅ as a nucleating agent. Surprisingly, P in particular₂O₅ as a nucleating agent, the formation of the desired lithium disilicate crystals and, on the other hand, largely avoids the formation of ZrO₂-containing crystal phases that could significantly worsen the translucency. Its use also evidently largely avoids the formation of other undesirable secondary crystal phases.

0017The glass ceramic used according to the invention preferably contains further alkali metal oxide in an amount of 1.0 to 7.0, preferably 2.0 to 7.0 and particularly preferably 2.0 to 5.0% by weight. The term "further alkali metal oxide" denotes alkali metal oxide with the exception of Li₂O. The further alkali metal oxide is in particular K₂O, Cs₂O and / or Rb₂O and is particularly preferably K₂O. It is believed that the use of K₂O compared to the Na used in conventional glass ceramics₂O contributes to the strengthening of the glass network. It is preferred that the glass ceramic has less than 2.0, in particular less than 1.0, preferably less than 0.5 and particularly preferably essentially no Na₂O contains.

0018It is further preferred that the glass ceramic contains up to 5.0% by weight of alkaline earth metal oxide, the alkaline earth metal oxide being in particular CaO, BaO, MgO, SrO or a mixture thereof.

0019A glass ceramic is also preferred which contains 0.2 to 10.0, in particular 2.5 to 7.0 and preferably 2.5 to 3.5% by weight of oxide of trivalent elements, this oxide being selected in particular from Al₂O₃, Y₂O₃, La₂O₃, Bi₂O₃ and mixtures thereof, and preferably Al₂O₃ is.

0020A glass ceramic that contains at least one and preferably all of the following components is particularly preferred:<tables id="tabl0001" num="0001"><table frame="none"><tgroup cols="2" colsep="0"><colspec colnum="1" colname="col1" colwidth="24mm" /><colspec colnum="2" colname="col2" colwidth="56mm" /><thead><row><entry valign="top">component</entry><entry valign="top">Wt%</entry></row></thead><tbody><row rowsep="0"><entry>SiO₂</entry><entry>55.0 to 71.0</entry></row><row rowsep="0"><entry>Li₂O</entry><entry>9.0 to 17.0</entry></row><row rowsep="0"><entry>K₂O</entry><entry>1.0 to 7.0, especially 2.0 to 5.0</entry></row><row rowsep="0"><entry>Al₂O₃</entry><entry>0.5 to 5.0, especially 2.5 to 3.5</entry></row><row rowsep="0"><entry>P₂O₅</entry><entry>0.5 to 12.0, especially 2.5 to 7.0</entry></row><row rowsep="0"><entry>ZrO₂</entry><entry>8.0 to 16.0.</entry></row></tbody></tgroup></table></tables>

0021The glass ceramic used according to the invention can also contain additional components which are selected in particular from further oxides of tetravalent elements, further oxides of pentavalent elements, oxides of hexavalent elements, melting accelerators, colorants and fluorescent agents.

0022The term "further oxides of tetravalent elements" denotes oxides of tetravalent elements with the exception of SiO₂ and ZrO₂. Examples of further oxides of tetravalent elements are SnO₂ and GeO₂.

0023The term "further oxides of pentavalent elements" denotes oxides of pentavalent elements with the exception of P.₂O₅. An example of another oxide of pentavalent elements is Bi₂O₅.

0024Examples of oxides of hexavalent elements are WO₃ and MoO₃.

0025A glass ceramic which contains at least one further oxide of tetravalent elements, one further oxide of pentavalent elements or an oxide of hexavalent elements is preferred.

0026Examples of melt accelerators are fluorides.

0027Examples of colorants and fluorescent agents are oxides of d and f elements, such as the oxides of Ti, Sc, Mn, Fe, Ag, Ta, W, Ce, Pr, Nd, Tb, Er and Yb.

0028The term “main crystal phase” used in the following refers to the crystal phase which has the highest volume fraction compared to other crystal phases.

0029The glass ceramic used according to the invention preferably has lithium metasilicate as the main crystal phase. In particular, the glass ceramic contains more than 10% by volume, preferably more than 20% by volume and particularly preferably more than 30% by volume of lithium metasilicate crystals, based on the total glass ceramic.

0030In a further preferred embodiment, the glass ceramic has lithium disilicate as the main crystal phase. In particular, the glass ceramic contains more than 10% by volume, preferably more than 20% by volume and particularly preferably more than 30% by volume of lithium disilicate crystals, based on the total glass ceramic.

0031The lithium disilicate glass ceramic used according to the invention is distinguished by particularly good mechanical properties and it can be produced by heat treatment of the lithium metasilicate glass ceramic used according to the invention.

0032It has surprisingly been shown that the lithium disilicate glass ceramic used according to the invention, despite its high content of ZrO₂ has advantageous mechanical parameters, such as high fracture toughness values ​​and can be applied to zirconium oxide ceramic by sintering or, in particular, pressing in the viscous state, without tension in the

0033Glass ceramic comes, which is noticeable through cracks or cracks. It is particularly surprising that these very good mechanical properties are achieved even though the structure of the glass ceramic has lithium disilicate crystals that are generally not crosslinked with one another. Such crosslinking, on the other hand, occurs with the known lithium disilicate glass ceramics and is regarded as an essential reason for their high strengths. It is currently believed that the ZrO₂ in the glass ceramic used according to the invention, unlike in known products, does not serve as a nucleating agent for other crystal phases, but rather reinforces the glass network via built-in Zr-O polyhedra. These polyhedra can [ZrO_6/2]^2-- or [ZrO_8/2] ^4-Be structural units that act as network builders or network converters.

0034It is also surprising that the lithium disilicate glass ceramic used according to the invention, despite its high ZrO content₂ has a high translucency and no amorphous-amorphous phase separation occurs with it and it can thus be used for the aesthetically pleasing coating of dental restorations in particular based on zirconium oxide ceramics.

0035The lithium disilicate crystals present in the lithium disilicate glass ceramic used according to the invention are in particular in the form of platelets. It is assumed that this special morphology enables a crack-free material bond with zirconium oxide ceramics. The critical build-up of stress in the composite material during the thermal cooling phase seems to be less pronounced in the platelet-shaped crystal form than in lithium disilicate glass-ceramics with elongated or needle-shaped crystals. In addition, the platelet-shaped crystal morphology has good fracture toughness, expressed by the K_ICValue, reached.

0036The lithium disilicate glass ceramic used according to the invention has, in particular, a fracture toughness, measured as K._IC Value of at least 1.5 MPa • m^0.5 and especially more than 1.8 MPa • m^0.5. It also has a high biaxial breaking strength of preferably 200 to 500 MPa. In addition, it shows a high chemical resistance, which was determined by the loss of mass after storage in acetic acid. The chemical resistance is in particular less than 60 µg / cm². Finally, it has a coefficient of linear thermal expansion of in particular less than 10.3 × 10^-6 K^-1 m / m, measured in the range from 100 to 500 ° C, which is therefore regularly lower than that of the zirconium oxide ceramic to be coated.

0037The invention also relates to the use of a lithium silicate glass with nuclei which are suitable for the formation of lithium metasilicate and / or lithium disilicate crystals as the main crystal phase, the glass containing the components of the above-described glass ceramics used according to the invention. This glass thus contains 8.0 to 16.0% by weight of ZrO₂. With regard to preferred embodiments of this glass, reference is made to the above-described preferred embodiments of the glass ceramics used according to the invention.

0038The glass with nuclei used according to the invention can be produced by heat treatment of a correspondingly composed starting glass. The lithium metasilicate glass ceramic used according to the invention can then be formed by a further heat treatment, which in turn can be converted into the lithium disilicate glass ceramic used according to the invention by further heat treatment. The starting glass, the glass with nuclei and the lithium metasilicate glass-ceramic can therefore be viewed as precursors for producing the high-strength lithium disilicate glass-ceramic.

0039The glass ceramic used according to the invention and the glass used according to the invention are in particular in the form of powders or blanks, since they can easily be further processed in these forms. However, they can also be in the form of dental restorations such as inlays, onlays, crowns, veneers, shells or abutments.

0040The glass ceramic used according to the invention and the glass with nuclei used according to the invention can be produced by a process in which a starting glass with the components of the glass ceramic or the glass is subjected to at least one heat treatment in the range from 450 to 950 ° C.

0041The starting glass therefore contains 8.0 to 16.0% by weight of ZrO₂. In addition, it preferably also contains suitable amounts of SiO₂ and Li₂O, to enable the formation of a lithium silicate glass ceramic. Furthermore, the starting glass can also contain other components, as indicated above for the lithium silicate glass ceramic used according to the invention. In this case, those embodiments are preferred which are also specified as preferred for the glass ceramic.

0042To produce the starting glass, the procedure is in particular that a mixture of suitable starting materials, such as carbonates, oxides, phosphates and fluorides, is melted at temperatures of in particular 1300 to 1600 ° C. for 2 to 10 hours. To achieve a particularly high degree of homogeneity, the glass melt obtained is poured into water in order to form glass granules, and the granules obtained are then melted again.

0043The melt can then be poured into molds in order to produce blanks of the starting glass, so-called solid glass blanks or monolithic blanks.

0044It is also possible to put the melt back into water to produce granules. This granulate can then be pressed into a blank, a so-called powder compact, after grinding and, if necessary, addition of further components such as coloring and fluorescent agents.

0045Finally, after granulation, the starting glass can also be processed into a powder.

0046The starting glass, for example in the form of a solid glass blank, a powder compact or in the form of a powder, is then subjected to at least one heat treatment in the range from 450 to 950.degree. It is preferred that a first heat treatment is carried out initially at a temperature in the range from 500 to 600 ° C. in order to produce a glass with nuclei which are suitable for the formation of lithium metasilicate and / or lithium disilicate crystals. This glass can then preferably be subjected to at least one further heat treatment at a higher temperature and in particular more than 570 ° C. in order to bring about crystallization of lithium metasilicate or of lithium disilicate.

0047The at least one heat treatment carried out in the described method can also take place in the course of pressing or sintering the glass or the glass ceramic used according to the invention onto the selected zirconium oxide ceramic.

0048The glass ceramic used according to the invention and the glass used according to the invention are, however, particularly suitable for coating zirconium oxide ceramics. The invention is therefore also directed to the use of the glass or the glass ceramic for coating zirconium oxide ceramics.

0049The invention also relates to a method for coating zirconium oxide ceramic, in which the glass ceramic used according to the invention or the glass used according to the invention is applied to the zirconium oxide ceramic and exposed to elevated temperature.

0050This can be done in particular by sintering on and preferably by pressing on. During sintering, the glass ceramic or the glass is applied to the ceramic to be coated in the usual way, for example as a powder, and then sintered at an elevated temperature. In the preferred pressing, the glass ceramic used according to the invention or the glass used according to the invention, for example in the form of powder compacts or monolithic blanks, at an elevated temperature, for example 700 up to 1200 ° C, and under application of pressure, for example 2 to 10 bar, pressed on. For this purpose, in particular, the<patcit id="pcit0004" dnum="EP231773A"><text>EP 231 773</text></patcit> described method and the press furnace disclosed there are used. A suitable furnace is, for example, the Programat EP 5000 from Ivoclar Vivadent AG, Liechtenstein.

0051It is preferred that the glass ceramic with lithium disilicate as the main crystal phase is present after the coating process has been completed, since it has particularly good properties. It is surprisingly found that the glass ceramic has practically no cracks and cracks after it has been layered on the zirconium oxide ceramic, and a firm bond between the glass ceramic and the ceramic is achieved.

0052It is preferred that the zirconium oxide ceramic contains at least one oxide of Ce, Y, Sr, Ca or Mg to stabilize the tetragonal phase. The zirconium oxide ceramic can also be in the form of a composite with other inorganic components.

0053The zirconium oxide ceramic coated with the glass ceramic used according to the invention or the glass used according to the invention represents a further subject matter of the invention.

0054Because of the properties described above of the glass ceramic used according to the invention and the glass used according to the invention as its precursor, these are also particularly suitable for use in dentistry. The invention therefore also relates to the use of the glass ceramic or the glass as a coating material for dental restorations, such as crowns and bridges.

0055It is surprising that no cracks occur in the glass ceramic in the bond between the lithium disilicate glass ceramic used according to the invention and zirconium oxide ceramic. It is assumed that the special platelet-shaped morphology of the lithium disilicate crystals is of particular importance for this. The critical build-up of stress in the composite material during the thermal cooling phase seems to be less pronounced in the platelet-shaped crystal form than in lithium disilicate glass-ceramics with elongated or needle-shaped crystals. In addition, the platelet-like crystal morphology in particular has a good fracture toughness of up to 2.1 MPa · m^0,5 achieved, although in the structure essentially no direct crosslinking of the lithium disilicate crystals can be seen. The coated zirconium oxide ceramic according to the invention is thus a strong composite of high-strength and highly tough zirconium oxide ceramic on the one hand and tough glass ceramic on the other, which is why this composite is capable of high loads in the chewing cycle. The glass ceramic used according to the invention can therefore also be used advantageously when coating long-span bridges with more than three links based on zirconium oxide ceramic.

0056The glasses and glass ceramics used according to the invention can finally also be mixed together with other glasses and glass ceramics in order to produce dental materials with the desired properties. The glass used according to the invention or the glass ceramic used according to the invention can therefore be used in particular as the main component of an inorganic-inorganic composite or in combination with a large number of other glasses and / or glass ceramics, the composites or combinations being able to be used in particular as dental materials. The combinations or composites can particularly preferably be in the form of sintered blanks. Examples of other glasses and glass-ceramics for making inorganic-inorganic composites and combinations are disclosed in U.S. Pat <patcit id="pcit0005" dnum="DE4314817"><text>DE 43 14 817</text></patcit>, <patcit id="pcit0006" dnum="DE4423793"><text>DE 44 23 793</text></patcit>, <patcit id="pcit0007" dnum="DE4423794"><text>DE 44 23 794</text></patcit>, <patcit id="pcit0008" dnum="DE4428839"><text>DE 44 28 839</text></patcit>, <patcit id="pcit0009" dnum="DE19647739"><text>DE 196 47 739</text></patcit>, <patcit id="pcit0010" dnum="DE19725552"><text>DE 197 25 552</text></patcit> and <patcit id="pcit0011" dnum="DE10031431"><text>DE 100 31 431</text></patcit> disclosed. These glasses and glass ceramics belong to the silicate, borate, phosphate or aluminosilicate group. Preferred glasses and glass ceramics are from SiO₂-Al₂O₃-K₂O-type (with cubic or tetragonal leucite crystals), SiO₂-B₂O₃-N / A₂O-type, alkali-silicate-type, alkali-zinc-silicate-type, silico-phosphate-type and / or SiO₂-ZrO₂-Type. By mixing such glasses or glass ceramics with the glasses and / or glass ceramics used according to the invention, the coefficient of thermal expansion can, for example, be in a wide range from 6 to 20 · 10^-6 K^-1 can be set in the desired manner.

0057The invention is explained in more detail below using examples.

Examples

Examples 1 to 23 - Composition and Crystal Phases

0058A total of 23 glasses and glass ceramics with the composition given in Tables I to IV were produced by melting corresponding starting glasses and subsequent heat treatment for controlled nucleation and crystallization.

0059For this purpose, the starting glasses on a 100 to 200 g scale were first melted from conventional raw materials at 1400 to 1500 ° C and converted into glass frits by pouring them into water. These glass frits were then melted a second time at 1450 to 1550 ° C. for 1 to 3 h for homogenization. The resulting glass melts were poured into preheated molds to produce glass monoliths. These glass monoliths were transformed into glasses and glass ceramics through thermal treatment.

0060The thermal treatment used for controlled nucleation and controlled crystallization is given in Table V for selected examples. The first heat treatment in the range of 500 to 560 ° C usually led to the formation of lithium silicate glasses with nuclei for lithium metasilicate or lithium disilicate crystals, the second heat treatment at 650 to 710 ° C to the formation of lithium metasilicate glass ceramics and the third heat treatment in the Range from 800 to 920 ° C for the formation of lithium disilicate glass ceramics.

0061In some examples, after a first heat treatment, a second non-isothermal heat treatment with simultaneous analysis of the crystal phases formed was carried out at the specified temperature by high-temperature X-ray diffraction (HT-XRD).

0062The crystal phases obtained after the completion of all heat treatments are also listed in Table V. Surprisingly, glass ceramics with lithium disilicate as the main crystal phase were always obtained. Examples 4 and 5 were additionally repeated by only carrying out the first and second heat treatments. In this way, glass ceramics with lithium metasilicate as the main crystal phase were produced.

Example 24 - Glass and Glass Ceramic Blanks

0063A glass with the composition according to Example 4 was produced by mixing appropriate raw materials in the form of oxides and carbonates for 30 minutes in a Turbola mixer and then melting them at 1450 ° C. for 120 minutes in a platinum crucible. The melt was poured into water in order to obtain finely divided glass granules. These glass granules were melted again at 1530 ° C. for 150 minutes in order to obtain a glass melt with particularly high homogeneity. The temperature was lowered to 1500 ° C. for 30 min and then cylindrical glass blanks with a diameter of 12.5 mm were poured into preheated, divisible steel molds or graphite molds. The resulting glass cylinders were then relaxed at 550.degree. A glass with nuclei for lithium metasilicate or lithium disilicate crystals was obtained.

0064The <figref idref="f0001">Figure 1</figref> shows the result of differential thermal analysis (DSC) of a crushed glass cylinder.

0065The <figref idref="f0002">Figure 2</figref> shows the dependence of the formation of lithium metasilicate (Li2Si03) and lithium disilicate (Li2Si205) on the temperature using high-temperature X-ray diffraction (HT-XRD) of a glass cylinder.

0066The glass cylinders were then subjected to a first crystallization at 680 to 700 ° C. for 20 minutes. The heating rate was 15 ° C. per minute. The glass cylinders were then subjected to a second crystallization at 850 to 880 ° C. for 30 minutes. After this treatment, the crystal phase analysis showed a glass ceramic with lithium disilicate as the main crystal phase and small proportions of lithium metasilicate and lithium phosphate as secondary phases.

0067The <figref idref="f0003">Figure 3</figref> shows a scanning electron microscope (SEM) image of a crystallized cylinder that has been polished and etched with HF vapor for 30 s.

0068The crystallized cylinders were further processed to test specimens by hot pressing at a pressing temperature of 910 ° C. using an EP600 press furnace, Ivoclar Vivadent AG. The properties of these test pieces were as follows:<tables id="tabl0002" num="0002"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="59mm" /><colspec colnum="2" colname="col2" colwidth="107mm" /><tbody><row><entry>Colour:</entry><entry>white translucent without fluorescence</entry></row><row><entry>Solubility:</entry><entry>24 µg / cm² (according to ISO 6872 of September 1, 2008)</entry></row><row><entry>Biaxial strength:</entry><entry>420 MPa (according to ISO 6872 from September 1, 2008)</entry></row><row><entry>Fracture toughness:</entry><entry>2.0 MPam^0,5 (determined as K_IC-Value according to the SEVNB method according to ISO 6872 of September 1, 2008)</entry></row><row><entry>Thermal expansion coefficient:</entry><entry>9.9*10^-6* 1 / K (in the range 100 to 500 ° C)</entry></row></tbody></tgroup></table></tables>

Example 25 - Hot pressing on zirconium oxide ceramic

0069The lithium disilicate glass ceramic according to Example 4 was hot-pressed at 920 ° C. in a combined Press and Firing furnace Programat EP 5000 from Ivoclar Vivadent AG, Liechtenstein, onto zirconium oxide ceramic of type 3 Y-TZP, available from Tosoh. After the coating process was completed, the joint was free of defects.

0070<figref idref="f0004">Figure 4</figref> shows a scanning electron micrograph (SEM) of this composite after etching with 40% HF vapor.

Example 26 - Hot pressing on tooth caps and bridge frameworks

0071Single tooth copings and four-unit bridge frameworks made of densely sintered zirconium oxide (e.max ZirCAD, Ivoclar Vivadent AG) were supplemented with a burn-out plastic (PMMA) to form anatomically shaped restorations. Both the bridge frameworks and the plastic parts were manufactured using CAD / CAM processes, which made it possible to achieve a reproducible geometry and layer thickness. The restorations were embedded in dental investment (IPS PressVest Speed, Ivoclar Vivadent AG), the plastic was burned out and the crystallized cylinders according to Example 24 were pressed directly onto the framework at a temperature of 910 ° C. No intermediate layer (liner) was applied to the zirconium oxide.

0072After they had completely cooled down, the objects were devested with a sandblasting device, whereby no special care was required due to the high strength of the glass ceramic layer. The objects were separated from the sprues, reworked dry with a diamond grinder, and then treated for 20 minutes with IPS INVEX Liquid (Ivoclar Vivadent AG) under ultrasound in order to loosen any remaining investment material, which was then treated with Al₂O₃-S and the grain size 100 µm were blasted at 1-2 bar pressure.

0073The surface was cleaned with superheated steam and glazed twice with IPS e.max Ceram Glaze (Ivoclar Vivadent AG) at 770 ° C, creating a beautiful gloss. No special cooling (relaxation cooling) was used for the glaze firing. The restorations produced in this way, ie crowns and bridges, were aesthetically pleasing and free of defects. They showed no cracks, bubbles, or lifts. After sawing it open, an excellent bond between the layered lithium disilicate glass ceramic and the zirconium oxide could be seen by means of SEM.

0074Eight crowns and eight bridges were loaded in a chewing machine (Willitec) with 300,000 cycles in water storage with thermocycling from 5 to 55 ° C. The test force was 30, 60 and 90 N for each 100,000 cycles. The load was applied at a frequency of 0.8 Hz. No chippings were found in the veneer structure.

Example 27 - Glass and Glass Ceramic Blanks

0075Example 24 was repeated with the difference that a glass with the composition according to Example 18 was used. The crystallized cylinders obtained were processed further by hot pressing at a temperature of 905 ° C. to give test specimens. The properties of these test pieces were as follows:<tables id="tabl0003" num="0003"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="58mm" /><colspec colnum="2" colname="col2" colwidth="84mm" /><tbody><row><entry>Colour:</entry><entry>Tooth-colored translucent with tooth-like fluorescence</entry></row><row><entry>Solubility:</entry><entry>30th µg / cm² (according to ISO 6872 of September 1, 2008)</entry></row><row><entry>Biaxial strength:</entry><entry>405 MPa (according to ISO 6872 from September 1, 2008)</entry></row><row><entry>Thermal expansion coefficient:</entry><entry>9.9*10^-6* 1 / K (in the range 100 to 500 ° C)</entry></row></tbody></tgroup></table></tables>

Example 28 - Hot pressing on tooth caps and bridge frameworks

0076Example 26 was repeated with the difference that the crystallized cylinders according to Example 27 were used. After up to four final glaze firings, crowns and bridges were obtained, which again showed no cracks, bubbles or lifts.

Example 29 - Glass ceramic blank (powder compact)

0077Analogously to Examples 1 to 23, a starting glass with the composition according to Example 19 was melted twice. However, the glass was then not poured into steel molds, but rather quenched in water in order to obtain fine-grained glass granules. The glass granulate was thermally treated at 550 ° C. for 20 min and then at 680 ° C. for 20 min in order to bring about the nucleation and the first crystallization. The granules pretreated in this way were dry-ground to a mean grain size of 20 μm and mixed with 0.1% by weight of a ceramic color pigment. The mixture was moistened with a little water and pressed into a powder compact at a pressing pressure of 20 MPa. The powder compact was sintered at 850 ° C. for 30 minutes. The crystal phase analysis of the sintered blank showed lithium disilicate as the main crystal phase and small proportions of lithium metasilicate and lithium phosphate as secondary phases.

0078The sintered blanks were processed further to test specimens by hot pressing at 905 ° C. using the EP600 press furnace (Ivoclar Vivadent AG). The properties of the test pieces were as follows:<tables id="tabl0004" num="0004"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="29mm" /><colspec colnum="2" colname="col2" colwidth="81mm" /><tbody><row><entry>Colour:</entry><entry>Tooth-colored translucent and tooth-like fluorescence</entry></row><row><entry>Biaxial strength:</entry><entry>302 MPa (according to ISO 6872 from September 1, 2008)</entry></row></tbody></tgroup></table></tables>

Example 30 - Hot pressing on tooth caps

0079Example 26 was repeated, with the difference that the sintered blanks according to Example 29 were used for pressing over tooth caps. After two final glaze firings, crowns were obtained, which again showed no cracks, bubbles or lift-offs.

Example 31 - Sintering onto dental caps

0080Glass ceramic powder of the composition according to Example 19 colored with 0.1% by weight of pigment was produced analogously to Example 29. However, this time no powder blanks were pressed. The powder was mixed with a modeling liquid (e.max Ceram Build Up Liquid, Ivoclar Vivadent AG)) and the mixture was applied to a prefabricated single tooth coping made of zirconium oxide in order to model an occlusal morphology. The layered mixture was then sintered in a dental furnace (P500, Ivoclar Vivadent AG) at a holding temperature of 850 ° C. and a holding time of 2 minutes.

0081After sintering, the crowns were finished with diamond grinders and coated a second time. This was followed by two more glaze firings at a temperature of 770 ° C. As a result, aesthetically high-quality tooth-colored crowns with natural-looking fluorescence and opalescence were obtained. These also showed no cracks, bubbles or lift-offs.<tables id="tabl0005" num="0005"><table frame="all"><title><u>Table I.</u></title><tgroup cols="7"><colspec colnum="1" colname="col1" colwidth="14mm" /><colspec colnum="2" colname="col2" colwidth="14mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><colspec colnum="4" colname="col4" colwidth="14mm" /><colspec colnum="5" colname="col5" colwidth="14mm" /><colspec colnum="6" colname="col6" colwidth="14mm" /><colspec colnum="7" colname="col7" colwidth="14mm" /><thead><row><entry colsep="0" align="center" valign="top" /><entry colsep="0" align="center" valign="top">1</entry><entry colsep="0" align="center" valign="top">2</entry><entry colsep="0" align="center" valign="top">3</entry><entry colsep="0" align="center" valign="top">4</entry><entry colsep="0" align="center" valign="top">5</entry><entry align="center" valign="top">6</entry></row></thead><tbody><row><entry align="center"><b>SiO₂</b></entry><entry align="center">63.8</entry><entry align="center">67.9</entry><entry align="center">66.4</entry><entry align="center">65.0</entry><entry align="center">63.5</entry><entry align="center">62.0</entry></row><row><entry align="center"><b>K₂O</b></entry><entry align="center">3.0</entry><entry align="center">3.7</entry><entry align="center">3.6</entry><entry align="center">3.5</entry><entry align="center">3.4</entry><entry align="center">3.4</entry></row><row><entry align="center"><b>Li₂O</b></entry><entry align="center">13.6</entry><entry align="center">14.1</entry><entry align="center">13.8</entry><entry align="center">13.5</entry><entry align="center">13.2</entry><entry align="center">12.9</entry></row><row><entry align="center"><b>Al₂O₃</b></entry><entry align="center">3.0</entry><entry align="center">3.2</entry><entry align="center">3.2</entry><entry align="center">3.1</entry><entry align="center">3.0</entry><entry align="center">2.9</entry></row><row><entry align="center"><b>P₂O₅</b></entry><entry align="center">3.0</entry><entry align="center">3.1</entry><entry align="center">3.0</entry><entry align="center">2.9</entry><entry align="center">2.9</entry><entry align="center">2.8</entry></row><row><entry align="center"><b>ZrO₂</b></entry><entry align="center">9.6</entry><entry align="center">8.0</entry><entry align="center">10.0</entry><entry align="center">12.0</entry><entry align="center">14.0</entry><entry align="center">16.0</entry></row><row><entry align="center"><b>MoO₃</b></entry><entry align="center">4.0</entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center" /><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry></row></tbody></tgroup></table></tables><tables id="tabl0006" num="0006"><table frame="all"><title><u>Table II</u></title><tgroup cols="10"><colspec colnum="1" colname="col1" colwidth="15mm" /><colspec colnum="2" colname="col2" colwidth="14mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><colspec colnum="4" colname="col4" colwidth="14mm" /><colspec colnum="5" colname="col5" colwidth="14mm" /><colspec colnum="6" colname="col6" colwidth="14mm" /><colspec colnum="7" colname="col7" colwidth="14mm" /><colspec colnum="8" colname="col8" colwidth="14mm" /><colspec colnum="9" colname="col9" colwidth="14mm" /><colspec colnum="10" colname="col10" colwidth="14mm" /><thead><row><entry colsep="0" align="center" valign="top" /><entry colsep="0" align="center" valign="top">7</entry><entry colsep="0" align="center" valign="top">8</entry><entry colsep="0" align="center" valign="top">9</entry><entry colsep="0" align="center" valign="top">10</entry><entry colsep="0" align="center" valign="top">11</entry><entry colsep="0" align="center" valign="top">12</entry><entry colsep="0" align="center" valign="top">13</entry><entry colsep="0" align="center" valign="top">14</entry><entry align="center" valign="top">15</entry></row></thead><tbody><row><entry align="center"><b>SiO₂</b></entry><entry align="center">69.8</entry><entry align="center">64.1</entry><entry align="center">65.2</entry><entry align="center">60.5</entry><entry align="center">66.4</entry><entry align="center">55.0</entry><entry align="center">70.1</entry><entry align="center">64.3</entry><entry align="center">64.2</entry></row><row><entry align="center"><b>K₂O</b></entry><entry align="center">2.0</entry><entry align="center">5.0</entry><entry align="center">3.5</entry><entry align="center">3.3</entry><entry align="center" /><entry align="center">4.0</entry><entry align="center">3.6</entry><entry align="center">3.0</entry><entry align="center">1.0</entry></row><row><entry align="center"><b>Li₂O</b></entry><entry align="center">16.0</entry><entry align="center">13.3</entry><entry align="center">12.0</entry><entry align="center">15.0</entry><entry align="center">13.6</entry><entry align="center">15.0</entry><entry align="center">9.0</entry><entry align="center">13.2</entry><entry align="center">13.2</entry></row><row><entry align="center"><b>N / A₂O</b></entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center">0.1</entry><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>CaO</b></entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center">2.0</entry><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>MgO</b></entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center">0.1</entry><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>SrO</b></entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center">0.1</entry><entry align="center" /><entry align="center">1.0</entry></row><row><entry align="center"><b>Al₂O₃</b></entry><entry align="center">0.2</entry><entry align="center">5.0</entry><entry align="center">3.1</entry><entry align="center">2.9</entry><entry align="center">3.0</entry><entry align="center">4.0</entry><entry align="center">3.5</entry><entry align="center">2.9</entry><entry align="center">0.5</entry></row><row><entry align="center"><b>La₂O₃</b></entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>Y₂O₃</b></entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center">6.5</entry></row><row><entry align="center"><b>P₂O₅</b></entry><entry align="center">3.3</entry><entry align="center">2.9</entry><entry align="center">4.1</entry><entry align="center">5.0</entry><entry align="center">3.0</entry><entry align="center">12.0</entry><entry align="center">3.5</entry><entry align="center">2.9</entry><entry align="center">3.5</entry></row><row><entry align="center"><b>ZrO₂</b></entry><entry align="center">8.6</entry><entry align="center">9.7</entry><entry align="center">12.1</entry><entry align="center">13.3</entry><entry align="center">10.0</entry><entry align="center">8.0</entry><entry align="center">10.0</entry><entry align="center">9.7</entry><entry align="center">10.1</entry></row><row><entry align="center"><b>Cs₂O</b></entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center">4.0</entry><entry align="center" /><entry align="center" /><entry align="center">4.0</entry><entry align="center" /></row><row><entry align="center"><b>VO₂</b></entry><entry align="center">0.1</entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center" /><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry></row></tbody></tgroup></table></tables><tables id="tabl0007" num="0007"><table frame="all"><title><b><u>Table III</u></b></title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="15mm" /><colspec colnum="2" colname="col2" colwidth="14mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><colspec colnum="4" colname="col4" colwidth="14mm" /><colspec colnum="5" colname="col5" colwidth="14mm" /><thead><row><entry colsep="0" align="center" valign="top" /><entry colsep="0" align="center" valign="top">16</entry><entry colsep="0" align="center" valign="top">17</entry><entry colsep="0" align="center" valign="top">18</entry><entry align="center" valign="top">19</entry></row></thead><tbody><row><entry align="center"><b>SiO₂</b></entry><entry align="center">61.3</entry><entry align="center">62.6</entry><entry align="center">64.9</entry><entry align="center">64.9</entry></row><row><entry align="center"><b>K₂O</b></entry><entry align="center">3.3</entry><entry align="center">5.0</entry><entry align="center">3.5</entry><entry align="center">3.5</entry></row><row><entry align="center"><b>Li₂O</b></entry><entry align="center">12.7</entry><entry align="center">12.7</entry><entry align="center">13.5</entry><entry align="center">13.5</entry></row><row><entry align="center"><b>CaO</b></entry><entry align="center">3.0</entry><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>Al₂O₃</b></entry><entry align="center">2.9</entry><entry align="center">2.9</entry><entry align="center">3.1</entry><entry align="center">3.1</entry></row><row><entry align="center"><b>P₂O₅</b></entry><entry align="center">7.0</entry><entry align="center">3.5</entry><entry align="center">3.0</entry><entry align="center">3.0</entry></row><row><entry align="center"><b>ZrO₂</b></entry><entry align="center">9.0</entry><entry align="center">11.3</entry><entry align="center">10.4</entry><entry align="center">10.9</entry></row><row><entry align="center"><b>F.</b></entry><entry align="center">0.5</entry><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>MnO₂</b></entry><entry align="center">0.2</entry><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>Fe₂O₃</b></entry><entry align="center">0.1</entry><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>V₂O₅</b></entry><entry align="center" /><entry align="center" /><entry align="center">0.1</entry><entry align="center" /></row><row><entry align="center"><b>Tb₄O₇</b></entry><entry align="center" /><entry align="center">0.4</entry><entry align="center">0.5</entry><entry align="center">0.5</entry></row><row><entry align="center"><b>CeO₂</b></entry><entry align="center" /><entry align="center">1.3</entry><entry align="center">1.0</entry><entry align="center">0.6</entry></row><row><entry align="center"><b>He₂O₃</b></entry><entry align="center" /><entry align="center">0.3</entry><entry align="center" /><entry align="center" /></row><row><entry align="center" /><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry></row></tbody></tgroup></table></tables><tables id="tabl0008" num="0008"><table frame="all"><title><u>Table IV</u></title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="14mm" /><colspec colnum="2" colname="col2" colwidth="14mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><colspec colnum="4" colname="col4" colwidth="14mm" /><colspec colnum="5" colname="col5" colwidth="14mm" /><thead><row><entry colsep="0" align="center" valign="top" /><entry colsep="0" align="center" valign="top">20</entry><entry colsep="0" align="center" valign="top">21</entry><entry colsep="0" align="center" valign="top">22</entry><entry align="center" valign="top">23</entry></row></thead><tbody><row><entry align="center"><b>SiO₂</b></entry><entry align="center">66.4</entry><entry align="center">63.8</entry><entry align="center">64.5</entry><entry align="center">63.8</entry></row><row><entry align="center"><b>K₂O</b></entry><entry align="center" /><entry align="center">3.0</entry><entry align="center">3.2</entry><entry align="center">3.0</entry></row><row><entry align="center"><b>Li₂O</b></entry><entry align="center">13.6</entry><entry align="center">13.6</entry><entry align="center">13.8</entry><entry align="center">13.6</entry></row><row><entry align="center"><b>Rb₂O</b></entry><entry align="center">4.0</entry><entry align="center" /><entry align="center" /><entry align="center" /></row><row><entry align="center"><b>BaO</b></entry><entry align="center" /><entry align="center" /><entry align="center">2.0</entry><entry align="center" /></row><row><entry align="center"><b>Al₂O₃</b></entry><entry align="center">3.0</entry><entry align="center">3.0</entry><entry align="center">3.0</entry><entry align="center">3.0</entry></row><row><entry align="center"><b>Bi₂O₃</b></entry><entry align="center" /><entry align="center" /><entry align="center" /><entry align="center">4.0</entry></row><row><entry align="center"><b>P₂O₅</b></entry><entry align="center">3.0</entry><entry align="center">3.0</entry><entry align="center">3.5</entry><entry align="center">3.0</entry></row><row><entry align="center"><b>ZrO₂</b></entry><entry align="center">10.0</entry><entry align="center">9.6</entry><entry align="center">10.0</entry><entry align="center">9.6</entry></row><row><entry align="center"><b>WHERE₃</b></entry><entry align="center" /><entry align="center">4.0</entry><entry align="center" /><entry align="center" /></row><row><entry align="center" /><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry><entry align="center">100.0</entry></row></tbody></tgroup></table></tables><tables id="tabl0009" num="0009"><table frame="all"><title><u>Table V</u></title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="32mm" /><colspec colnum="2" colname="col2" colwidth="64mm" /><colspec colnum="3" colname="col3" colwidth="71mm" /><thead><row><entry valign="top"><b>Glass ceramic, no.</b></entry><entry valign="top"><b>Thermal treatment (° C / min) or HT-XRD</b></entry><entry valign="top"><b>Crystal phases HP = main phase NP = secondary phase (s)</b></entry></row></thead><tbody><row rowsep="0"><entry>2</entry><entry>500/10, 650/20, 840/7</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₃PO₄, Li₂SiO₃</entry></row><row rowsep="0"><entry>3</entry><entry>500/10, 650/20, 840/7</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₃PO₄, Li₂SiO₃; Li₄SiO₄</entry></row><row rowsep="0"><entry>4</entry><entry>540/10, 690/20</entry><entry>HP: Li₂SiO₃</entry></row><row><entry /><entry /><entry>NP: none</entry></row><row rowsep="0"><entry>4</entry><entry>540/10, 650/20, 840/7</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₂SiO₃; Li₄SiO₄</entry></row><row rowsep="0"><entry>5</entry><entry>540/10, 710/20</entry><entry>HP: Li₂SiO₃</entry></row><row><entry /><entry /><entry>NP: none</entry></row><row rowsep="0"><entry>5</entry><entry>540/10, 650/20, 840/7</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₄SiO₄</entry></row><row rowsep="0"><entry>6</entry><entry>560/10 and HT-XRD with cutout at 860</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₃PO₄, Li₂SiO₃</entry></row><row rowsep="0"><entry>11</entry><entry>520/10, 650/20, 800/10</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₃PO₄</entry></row><row rowsep="0"><entry>12</entry><entry>HT-XRD with cutout at 840</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₃PO₄</entry></row><row rowsep="0"><entry>20</entry><entry>520/10, 650/20, 800/10</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₃PO₄</entry></row><row rowsep="0"><entry>21</entry><entry>520/10, 650/20, 850/10</entry><entry>HP: Li₂Si₂O₅</entry></row><row><entry /><entry /><entry>NP: Li₃PO₄, Li₂SiO₃</entry></row><row><entry namest="col1" nameend="col3" align="left">A heating rate of approx. 2 K / min was used for the HT-XRD analysis.</entry></row></tbody></tgroup></table></tables>