Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C13/00—Dental prostheses; Making same
  • A61C13/08—Artificial teeth; Making same
  • A61C13/083—Porcelain or ceramic teeth
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C13/00—Dental prostheses; Making same
  • A61C13/0003—Making bridge-work, inlays, implants or the like
  • A61C13/0006—Production methods
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C13/00—Dental prostheses; Making same
  • A61C13/0003—Making bridge-work, inlays, implants or the like
  • A61C13/0022—Blanks or green, unfinished dental restoration parts
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C5/00—Filling or capping teeth
  • A61C5/70—Tooth crowns; Making thereof
  • A61C5/77—Methods or devices for making crowns
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C8/00—Means to be fixed to the jaw-bone for consolidating natural teeth or for fixing dental prostheses thereon; Dental implants; Implanting tools
  • A61C8/0012—Means to be fixed to the jaw-bone for consolidating natural teeth or for fixing dental prostheses thereon; Dental implants; Implanting tools characterised by the material or composition, e.g. ceramics, surface layer, metal alloy
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C8/00—Means to be fixed to the jaw-bone for consolidating natural teeth or for fixing dental prostheses thereon; Dental implants; Implanting tools
  • A61C8/0048—Connecting the upper structure to the implant, e.g. bridging bars
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B32/00—Thermal after-treatment of glass products not provided for in groups C03B19/00, C03B25/00 - C03B31/00 or C03B37/00, e.g. crystallisation, eliminating gas inclusions or other impurities; Hot-pressing vitrified, non-porous, shaped glass products
  • C03B32/02—Thermal crystallisation, e.g. for crystallising glass bodies into glass-ceramic articles
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
  • C03C10/0009—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing silica as main constituent
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
  • C03C10/0036—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing SiO2, Al2O3 and a divalent metal oxide as main constituents
  • C03C10/0045—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing SiO2, Al2O3 and a divalent metal oxide as main constituents containing SiO2, Al2O3 and MgO as main constituents
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/062—Glass compositions containing silica with less than 40% silica by weight
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/062—Glass compositions containing silica with less than 40% silica by weight
  • C03C3/064—Glass compositions containing silica with less than 40% silica by weight containing boron
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/062—Glass compositions containing silica with less than 40% silica by weight
  • C03C3/064—Glass compositions containing silica with less than 40% silica by weight containing boron
  • C03C3/066—Glass compositions containing silica with less than 40% silica by weight containing boron containing zinc
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/062—Glass compositions containing silica with less than 40% silica by weight
  • C03C3/064—Glass compositions containing silica with less than 40% silica by weight containing boron
  • C03C3/068—Glass compositions containing silica with less than 40% silica by weight containing boron containing rare earths
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
  • C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
  • C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
  • C03C3/087—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal containing calcium oxide, e.g. common sheet or container glass
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
  • C03C3/093—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium containing zinc or zirconium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C4/00—Compositions for glass with special properties
  • C03C4/0007—Compositions for glass with special properties for biologically-compatible glass
  • C03C4/0021—Compositions for glass with special properties for biologically-compatible glass for dental use
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2204/00—Glasses, glazes or enamels with special properties

Definitions

• the invention relates to glass ceramic having a quartz solid solution phase, which is suitable in particular for use in dentistry and preferably for preparing dental restorations, as well as to precursors for the preparation of the glass ceramic.
• JP 2000/063144 discloses magnesium aluminosilicate glasses for preparing substrates for recording media, which have low amounts of from 0 to 10 mol.-% of ZrO 2 and large amounts of B 2 O 3 .
• GB 2 172 282 A describes magnesium aluminosilicate glass ceramics, which can contain a maximum of 13.0 wt.-% ZrO 2 in view of the solubility limit.
• the glass ceramics are provided for microelectronic applications and in particular as coating for substrates such as e.g. aluminium and, in addition to high strength, they have a suitable dielectric constant in the range of from 7 to 10 as well as a high electrical resistance.
• the object of the invention is therefore to provide a glass ceramic which shows a combination of high strength and good translucence.
• the glass ceramic should further be easy to be processed into dental restorations and thus be excellently suitable as restorative dental material.
• This glass ceramic also called “quartz solid solution glass ceramic” in the following, surprisingly shows an advantageous combination of mechanical and optical properties which are desirable for a restorative dental material. It is additionally surprising that the indicated high amounts of ZrO 2 can be incorporated into it.
• quartz solid solution phase is meant a crystal phase of SiO 2 , in which in the SiO 2 lattice foreign ions or foreign atoms are incorporated either into interstitial lattice sites or into lattice sites.
• These foreign ions or foreign atoms can in particular be Al as well as Mg, Li and/or Zn.
• Al can be present in the solid solution in the same molar concentration as Zn and Mg together.
• the quartz solid solution glass ceramic according to the invention comprises in particular 38.0 to 49.0 wt.-% and preferably 38.5 to 48.0 wt.-% SiO 2 .
• the glass ceramic comprises 26.0 to 38.0 and in particular 27.0 to 37.0 wt.-% Al 2 O 3 .
• a glass ceramic that comprises 6.0 to 14.0 and in particular 7.0 to 13.5 wt.-% MgO is also preferred.
• a glass ceramic is preferred that comprises 14.0 to 18.0 wt.-% ZrO 2 .
• the glass ceramic according to the invention comprises at least one and preferably all of the following components in the indicated amounts:
• the glass ceramic comprises the divalent oxides CaO, SrO, MgO and ZnO, as well as mixtures thereof, in an amount of from 5.0 to 20.0 wt.-%.
• the glass ceramic according to the invention can also comprise further additional components which in particular are selected from colorants and fluorescent agents.
• colorants are oxides of d- and f-elements, such as e.g. CeO 2 .
• the glass ceramic according to the invention comprises the quartz solid solution phase as main crystal phase.
• main crystal phase denotes the crystal phase which has the highest percentage by weight of all the crystal phases present in the glass ceramic.
• the amounts of the crystal phases are in particular determined using the Rietveld method.
• a suitable method for the quantitative analysis of the crystal phases using the Rietveld method is described e.g. in M. Dittmer's doctoral thesis “Glaser and Glaskeramiken im System MgO—Al 2 O 3 —SiO 2 mit ZrO 2 als Keimsentner” [Glasses and glass ceramics in the MgO—Al 2 O 3 —SiO 2 system with ZrO 2 as nucleating agent], University of Jena 2011.
• the glass ceramic according to the invention preferably also comprises zirconium oxide, in particular tetragonal zirconium oxide, and/or MgAl 2 O 4 as crystal phase.
• the quartz solid solution phase present in the glass ceramic according to the invention is usually formed by a high-quartz solid solution phase, a low-quartz solid solution phase or a mixture of these crystal phases.
• the glass ceramic according to the invention comprises high-quartz solid solution phase, low-quartz solid solution phase or a mixture of these.
• the glass ceramic comprises high-quartz solid solution phase in a higher amount than low-quartz solid solution phase and in particular the glass ceramic comprises high-quartz solid solution phase as main crystal phase.
• the glass ceramic of this embodiment is in the following also referred to as “high-quartz solid solution glass ceramic”.
• the glass ceramic comprises low-quartz solid solution phase in a higher amount than high-quartz solid solution phase and in particular the glass ceramic comprises low-quartz solid solution phase as main crystal phase.
• the glass ceramic of this embodiment is in the following also referred to as “low-quartz solid solution glass ceramic”.
• the low-quartz solid solution glass ceramic according to the invention is characterized by particularly good mechanical properties and optical properties and it can be formed by heat treatment of a corresponding starting glass, a corresponding starting glass with nuclei or a corresponding high-quartz solid solution glass ceramic. These materials can therefore serve as precursors for the low-quartz solid solution glass ceramic according to the invention.
• the low-quartz solid solution glass ceramic according to the invention has a fracture toughness, measured as K IC value, of in particular at least about 1.5, preferably at least about 1.7 and particularly preferred at least about 1.9 MPa ⁇ m 0.5 . This value was determined using the Vickers method and calculated using the Evans-Charles equation.
• the low-quartz solid solution glass ceramic according to the invention has a high biaxial breaking strength of in particular at least 350 MPa and preferably at least 500 MPa and up to in particular 800 and preferably up to 1000 MPa.
• the biaxial breaking strength was determined according to ISO 6872 (2008).
• the high-quartz solid solution glass ceramic according to the invention is characterized in particular by mechanical properties which allow particularly easy and quick machining to give the glass ceramic the shape of e.g. a dental restoration.
• the invention also relates to precursors with the corresponding composition, from which the quartz solid solution glass ceramic according to the invention, in particular the high-quartz solid solution glass ceramic according to the invention or the low-quartz solid solution glass ceramic according to the invention can be prepared by heat treatment.
• These precursors are a starting glass with corresponding composition and a starting glass with nuclei with corresponding composition.
• corresponding composition means that these precursors comprise the same components in the same amounts as the glass ceramic, with the components, apart from fluorine, being calculated as oxides as is customary for glasses and glass ceramics.
• the invention therefore, also relates to a starting glass which comprises the components of the quartz solid solution glass ceramic according to the invention.
• the starting glass according to the invention therefore comprises as components
• the starting glass can also comprises still further components, such as are indicated above for the quartz solid solution glass ceramic according to the invention. All those embodiments which are indicated as being preferred for the components of the quartz solid solution glass ceramic according to the invention are also preferred for the components of the starting glass.
• the invention also relates to such a starting glass which comprises nuclei for the crystallization of quartz solid solution phase.
• the starting glass with nuclei By heat treatment of the starting glass, first of all the starting glass with nuclei can be produced, which can then be converted into the quartz solid solution glass ceramic by further heat treatment.
• the high-quartz solid solution glass ceramic can be produced first of all by the heat treatment of the starting glass or of the starting glass comprising nuclei and the high-quartz solid solution glass ceramic can be converted into the low-quartz solid solution glass ceramic by further heat treatment. It is also possible to form the low-quartz solid solution glass ceramic directly by heat treatment of the starting glass or of the starting glass comprising nuclei.
• the preparation of the starting glass is carried out in particular in such a way that a mixture of suitable starting materials, such as carbonates and oxides, is melted at temperatures of in particular about 1500 to 1700° C. for 0.5 to 4 h.
• suitable starting materials such as carbonates and oxides
• the glass melt obtained can be poured into water in order to form a glass frit, and the frit obtained is then melted again.
• the melt can then be poured into moulds, e.g. steel or graphite moulds, in order to produce blanks of the starting glass, so-called solid glass blanks or monolithic blanks.
• monolithic blanks are usually stress-relieved first of all, e.g. by keeping them at 750 to 850° C. for 5 to 30 min and then slowly cooling them to room temperature.
• the starting glass can also be processed to form a powder.
• the starting glass with nuclei can then be produced from the starting glass by heat treatment. This is also called nucleation process.
• the invention is therefore also directed to a process for preparing the starting glass comprising nuclei for the crystallization of quartz solid solution phase, wherein
• the quartz solid solution glass ceramic according to the invention can then be formed from the starting glass with nuclei by heat treatment.
• the invention is therefore also directed to a process for preparing the quartz solid solution glass ceramic, in which the starting glass, in particular the starting glass comprising nuclei for the crystallization of quartz solid solution phase, is subjected to at least one heat treatment at a temperature of from 850 to 1200° C.
• the starting glass or the starting glass comprising nuclei can be subjected to the at least one heat treatment e.g. in the form of a solid glass blank, a powder green compact or in the form of a powder.
• the at least one heat treatment carried out in the process according to the invention can also take place during a sintering-on.
• the high-quartz solid solution glass ceramic according to the invention and the low-quartz solid solution glass ceramic according to the invention are preferably prepared by means of specific heat treatments as are indicated in the following.
• the invention is therefore directed to a process in which
• the invention is therefore directed to a process in which
• the high-quartz solid solution glass ceramic according to the invention or the low-quartz solid solution glass ceramic according to the invention can be formed, depending on the composition of the starting glass and on the heat treatment chosen for the controlled crystallization.
• the quartz solid solution phase of the glass ceramic according to the invention is produced by incorporating foreign ions in the SiO 2 lattice and possibly replacing two Si ions with two Al ions and one Mg ion. It is further assumed that, by crystallizing the starting glasses at lower temperatures, in particular 850 to 1000° C., the high-temperature modification of the quartz is preferably formed and that this modification is stable also at room temperature due to the incorporation of the foreign ions and does not convert to the low-temperature modification, as would be the case with pure quartz.
• the glass ceramics according to the invention and the glasses according to the invention are present in particular as powder or blanks in any shape and size, e.g. monolithic blanks, such as platelets, cuboids or cylinders, or powder green compacts. They can easily be further processed in these forms, e.g. to form dental restorations. They can, however, also be present in the form of dental restorations, such as inlays, onlays, crowns, veneers, facets or abutments.
• Dental restorations such as bridges, inlays, onlays, crowns, veneers, facets or abutments, can be prepared from the glass ceramics according to the invention and the glasses according to the invention.
• the invention therefore also relates to their use as dental material and in particular to their use for preparing dental restorations. It is preferred that the glass ceramic or the glass is given, by machining, the shape of the desired dental restoration.
• the machining usually takes place by material removal processes and in particular by milling and/or grinding. It is particularly preferred that the machining is carried out as part of a CAD/CAM process.
• the starting glass according to the invention, the starting glass comprising nuclei according to the invention as well as the quartz solid solution glass ceramic according to the invention can be used for the machining.
• the glasses and glass ceramics according to the invention are in particular used in the form of blanks, preferably solid blanks.
• the high-quartz solid solution glass ceramic according to the invention is preferably used for the machining.
• the quartz solid solution glass ceramic according to the invention can also be used in a not yet fully crystallized form which was produced by heat treatment at a lower temperature. This has the advantage that an easier machining and thus the use of simpler equipment for the machining is possible. After the machining of such a partly-crystallized material, it is usually subjected to a further heat treatment in order to effect a further crystallization of quartz solid solution phase.
• the dental restoration shaped as desired e.g. by machining
• it can in particular be heat-treated again in order to convert precursors used, such as starting glass, starting glass comprising nuclei or high-quartz solid solution glass ceramic, into low-quartz solid solution glass ceramic or to increase the crystallization of low-quartz solid solution phase.
• the glass ceramics according to the invention and the glasses according to the invention are also suitable as coating material of e.g. ceramics and glass ceramics.
• the invention is, therefore, also directed to the use of the glasses according to the invention or the glass ceramics according to the invention for coating in particular ceramics and glass ceramics.
• the invention also relates to a process for coating ceramics and glass ceramics, in which glass ceramics according to the invention or glasses according to the invention are applied to the ceramic or glass ceramic and are exposed to a temperature of at least 950° C.
• the glass ceramic or the glass is applied to the material to be coated, such as ceramic or glass ceramic, in the usual way, e.g. as powder, and then sintered.
• the low-quartz solid solution glass ceramic according to the invention is present after the coating process has finished, as such a glass ceramic has particularly good mechanical and optical properties.
• a subject-matter of the invention is therefore also the use of the glass ceramics according to the invention or the glasses according to the invention as dental material and in particular for preparing dental restorations or as coating material for dental restorations, such as crowns, bridges and abutments.
• a total of 14 glasses and glass ceramics according to the invention with the composition indicated in Table I were prepared by melting corresponding starting glasses followed by heat treatment for controlled nucleation and crystallization.
• T N and t N Temperature and time used for nucleation T C and t C Temperature and time used for crystallization of high-quartz solid solution glass ceramic T FC and t FC Temperature and time used for crystallization of low-quartz solid solution glass ceramic
• the starting glasses were melted in a batch size of 100 to 200 g from customary raw materials at 1500 to 1700° C., wherein the melting was very easily possible without formation of bubbles or streaks.
• glass frits were produced which were then melted a second time at 1500 to 1700° C. for 0.5 to 4 h for homogenization.
• the melts of the starting glasses were poured into graphite or steel moulds to produce glass monoliths. These glass monoliths were stress-relieved and slowly cooled to room temperature.
• these nuclei-containing starting glasses crystallized to form low-quartz solid solution glass ceramics according to the invention which comprised low-quartz solid solution phase as main crystal phase, as was established by X-ray diffraction experiments at room temperature.
• the glasses, glasses comprising nuclei and high-quartz solid solution glass ceramics produced as precursors were able to be very satisfactorily machined into the form of various dental restorations in a CAD/CAM process, which restorations were also provided with a veneer if required.
• the glass with the composition according to example 1 was melted from corresponding raw materials at a temperature of 1650° C. for 2 h and then converted into a glass frit by pouring into water. After drying in a drying furnace, the glass frit was melted again at 1650° C. for 2 h and then poured into graphite moulds to produce glass monoliths. Immediately after removing the hot glass monoliths from the mould they were stress-relieved for 10 min at 810° C. and then slowly cooled to room temperature.
• Corresponding holders were adhesively bonded to the glass blocks obtained to enable CAM processing by Sirona inLab grinders.
• the grinding was carried out using diamond-coated grinding tools. Platelets with a diameter of about 12 mm and a thickness of about 2 mm were ground out of the blocks.
• the ground platelets were converted into the low-quartz solid solution glass ceramic using a thermal treatment.
• the platelets were heated to a temperature of 1100° C. in a muffle kiln from the company Nabertherm and, after a holding time of 180 min, slowly cooled to room temperature.
• Some of the platelets were ground with diamond grinding discs to a thickness of about 1.2 mm and polished to 0.5 ⁇ m before crystallization of the low-quartz solid solution phase, i.e. in the glass state or high-quartz solid solution state, and others after crystallization of the low-quartz solid solution phase.
• the biaxial strength of the samples produced and prepared in this way was then determined according to ISO 6872 (2008). Average strengths of 257 MPa were obtained for samples processed afterwards and average strengths of 849 MPa were obtained for samples processed before the crystallization.
• the CR value was determined according to British Standard BS 5612 using a CM-3700d spectrometer (Konica-Minolta) and resulted in a value of 82.5. Additionally, the CR value of the glass ceramic C was determined in the same way, which glass ceramic is described in the article by M. Dittmer and C. Russel in J. Biomed. Mater. Res. Part B:100B:463-470 (2012). The CR value of this glass ceramic was 97.7%.
• the Vickers hardness and the fracture toughness K Ic were determined on platelets with approximate dimensions of 13 mm ⁇ 12 mm. After the crystallization, the samples were ground to a thickness of about 2 mm and polished to 0.5 ⁇ m. 6 indentations were then carried out on each sample with a load period of 30 s, a load of 2.5 kg and a force F of 24.54 N, respectively. The crack lengths after the indentation were then determined from the corner of the indentation to the tip of the crack. The following values were determined:
• the glass with the composition according to example 4 was melted from corresponding raw materials at a temperature of 1600° C. for 30 min and 1610° C. for 30 min and then converted into a glass frit by pouring into water. After drying in a drying furnace, the glass frit was melted again at 1630° C. for h and then poured into graphite moulds to produce glass monoliths. Immediately after removing the hot glass monoliths from the mould these were stress-relieved for 10 min at 820° C. and then slowly cooled to room temperature.
• Corresponding holders were adhesively bonded to the glass blocks obtained to enable CAM processing by Sirona inLab grinders.
• the grinding was carried out using diamond-coated grinding tools. Platelets with a diameter of about 12 mm and a thickness of about 2 mm were ground out of the blocks.
• the ground platelets were converted into the low-quartz solid solution glass ceramic via a thermal treatment.
• the platelets were heated to a temperature of 1100° C. in a muffle kiln from the company Nabertherm and, after a holding time of 180 min, slowly cooled to room temperature.
• Some of the platelets were ground with diamond grinding discs to a thickness of about 1.2 mm and polished to 0.5 ⁇ m before crystallization of the low-quartz solid solution phase, i.e. in the glass state or high-quartz solid solution state, and others after crystallization of the low-quartz solid solution phase.
• the biaxial strength of the samples produced and prepared in this way was then determined according to ISO 6872 (2008). Average strengths of 393 MPa were obtained for samples processed afterwards and average strengths of 825 MPa were obtained for samples processed before the crystallization.
• the CR value was determined according to British Standard BS 5612 using a CM-3700d spectrometer (Konica-Minolta) and gave a value of 63.0.
• the Vickers hardness and the fracture toughness K Ic were determined on platelets with approximate dimensions of 13 mm ⁇ 12 mm. After the crystallization, the samples were ground to a thickness of about 2 mm and polished to 0.5 ⁇ m. 6 indentations were then carried out on each sample with a load period of 30 s, a load of 2.5 kg and a force F of 24.54 N, respectively. The crack lengths after the indentation were then determined from the corner of the indentation to the tip of the crack. The following values could be achieved:
• the glass with the composition according to example 8 was melted from corresponding raw materials at a temperature of 1650° C. for 1 h and then converted into a glass frit by pouring into water. After drying in a drying furnace, the glass frit was melted again at 1650° C. for 1 h and then poured into graphite moulds to produce glass monoliths. Immediately after removing the hot glass monoliths from the mould, these were stress-relieved for 10 min at 800° C. and then slowly cooled to room temperature.
• Corresponding holders were adhesively bonded to the glass ceramic blocks obtained to enable CAM processing by Sirona inLab grinders.
• the grinding was carried out using diamond-coated grinding tools. Platelets with a diameter of about 12 mm and a thickness of about 2 mm were ground out of the blocks.
• the ground platelets were converted into the low-quartz solid solution glass ceramic via a thermal treatment.
• the platelets were heated to a temperature of 1100° C. in a Programat-type furnace (Ivoclar Vivadent AG) and, after a holding time of 60 min, slowly cooled to room temperature.
• Programat-type furnace Ivoclar Vivadent AG
• the platelets were then ground to a thickness of about 1.2 mm with diamond grinding discs and polished to 0.5
• the biaxial strength of the samples produced and prepared in this way was then determined according to ISO 6872 (2008). Average strengths of 227 MPa were established.
• the CR value was determined according to British Standard BS 5612 using a CM-3700d spectrometer (Konica-Minolta) and resulted in a value of 85.3.

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