The present invention relates to a glass ceramic for veneering a dental frame structure, wherein said glass ceramic is characterized by a high content of B.sub.2O.sub.3, to a process for the preparation thereof, and to the use thereof in the production of dental restorations.

Embodiments of glass ceramic articles and precursor glasses are disclosed. In one or more embodiments, the glass-ceramic articles are transparent and include a nepheline phase and a phosphate phase. The glass-ceramic articles are colorless and exhibit a transmittance of about 70% or greater across the visible spectrum. The glass-ceramic articles may optionally include a lithium aluminosilicate phase. The crystals of the glass-ceramic articles may have a major cross-section of about 100 nm or less.

Embodiments of glass ceramic articles and precursor glasses are disclosed. In one or more embodiments, the glass-ceramic articles are transparent and include a nepheline phase and a phosphate phase. The glass-ceramic articles are colorless and exhibit a transmittance of about 70% or greater across the visible spectrum. The glass-ceramic articles may optionally include a lithium aluminosilicate phase. The crystals of the glass-ceramic articles may have a major cross-section of about 100 nm or less.

Disclosed herein are opaque glass-ceramics comprising at least one nepheline crystal phase and comprising from about 30 mol % to about 65 mol % SiO.sub.2, from about 15 mol % to about 40 mol % Al.sub.2O.sub.3, from about 10 mol % to about 20 mol % (Na.sub.2O+K.sub.2O), and from about 1 mol % to about 10 mol % (ZnO+MgO). Also disclosed herein are opaque-glass ceramics comprising at least one nepheline crystal phase and at least one spinel-structure phase doped with at least one colorant chosen from transition metals and rare earth elements. Further disclosed herein are methods for making these opaque glass-ceramics.

A glass-ceramic comprising, in weight percent on an oxide basis, of 50 to 70% SiO.sub.2, 0 to 20% Al.sub.2O.sub.3, 12 to 23% MgO, 0 to 4% Li.sub.2O, 0 to 10% Na.sub.2O, 0 to 10% K.sub.2O, 0 to 5% ZrO.sub.2, and 2 to 12% F, wherein the predominant crystalline phase of said glass-ceramic is a trisilicic mica, a tetrasilicic mica, or a mica solid solution between trisilicic and tetrasilicic, and wherein the total of Na.sub.2O+Li.sub.2O is at least 2 wt. %; wherein the glass-ceramic can be ion-exchanged.

The application relates to bond materials for a grinding wheel, in particular a glass ceramic and a preparation method thereof, and a bond for the composite grinding wheel. The glass ceramic is prepared from raw materials comprising kaolin, silica, diboron trioxide, lithium superoxide, albite, potassium feldspar, talc, dolomite, phosphorus pentoxide, and yttrium oxide. A glass ceramic composed entirely of microcrystalline phases is obtained from the glass prepared by the above raw materials at 900-1020 C., achieving a complete conversion of the glass phase at a low temperature. The application also provides a bond for a composite grinding wheel, comprising glass ceramic and glass with mass ratio of (20-50):(50-80), the glass phase having a low flow temperature and, together with the glass ceramic phase, forming encapsulation of the abrasive particles, realizing low-temperature sintering of the grinding wheel. Microcrystalline phase in the bond results in high mechanical strength for the obtained grinding wheel.

A glass-ceramic comprising, in weight percent on an oxide basis, of 50 to 70% SiO.sub.2, 0 to 20% Al.sub.2O.sub.3, 12 to 23% MgO, 0 to 4% Li.sub.2O, 0 to 10% Na.sub.2O, 0 to 10% K.sub.2O, 0 to 5% ZrO.sub.2, and 2 to 12% F, wherein the predominant crystalline phase of said glass-ceramic is a trisilicic mica, a tetrasilicic mica, or a mica solid solution between trisilicic and tetrasilicic, and wherein the total of Na.sub.2O+Li.sub.2O is at least 2 wt. %; wherein the glass-ceramic can be ion-exchanged.

Disclosed herein are opaque glass-ceramics comprising at least one nepheline crystal phase and comprising from about 30 mol % to about 65 mol % SiO.sub.2, from about 15 mol % to about 40 mol % Al.sub.2O.sub.3, from about 10 mol % to about 20 mol % (Na.sub.2+K.sub.2O), and from about 1 mol % to about 10 mol % (ZnO+MgO). Also disclosed herein are opaque-glass ceramics comprising at least one nepheline crystal phase and at least one spinel-structure phase doped with at least one colorant chosen from transition metals and rare earth elements. Further disclosed herein are methods for making these opaque glass-ceramics.

A leucite glass-ceramic is prepared from a glass comprising: about 66.8 to about 71.9 mol % of SiO.sub.2, about 8.5 to about 10.6 mol % of Al.sub.2O.sub.3, about 9.5 to about 12.8 mol % of K.sub.2O, about 0.5 to about 4.0 mol % of CaO, about 0 to about 3.0 mol % of TiO.sub.2, about 1.8 to about 4.0 mol % of Na.sub.2O, about 0.1 to about 6.0 mol % of Li.sub.2O, about 0 to about 1.0 mol % of MgO, about 0 to about 3.0 mol % of Nb.sub.2O.sub.5, and about 0 to about 3.0 mol % of B.sub.2O.sub.3. The leucite glass-ceramic is prepared by subjecting the glass components to a nucleation heat treatment, followed by a growth heat treatment. The leucite glass-ceramic may be used in the fabrication of a Dental restoration using various processes, and may be used in the construction of Dental restorations such as ceramic Dental inlays, crowns, veneers, bridges, veneering materials for zirconium oxide restoration substrates, alumina oxide restoration substrates, or metal restoration substrates.

Disclosed herein are glasses that are capable of forming nepheline crystal phases when exposed to light, photoformable glass-ceramics comprising at least one nepheline crystal phase, products containing such glasses and glass ceramics, and methods for making the same.