Lithium silicate glass ceramic

Abstract

The invention relates to a lithium silicate glass ceramic, which contains at least lithium disilicate as a crystal phase, and lithium aluminum silicate as further crystal phase. The lithium silicate glass ceramic in its initial composition contains Al.sub.2O.sub.3 at 1.5 to 3.5 percent by weight, and K.sub.2O at 0.6 to 1.8 percent by weight.

Claims

1. A lithium silicate glass ceramic intended for a dental molded body, comprising at least lithium disilicate crystals/crystallites and lithium aluminum silicate crystals/crystallites as crystal phases, wherein the dental molded, body is formed from a composition that includes Al.sub.2O.sub.3 at 1.5 to 3.5 percent by weight, and K.sub.2O at 0.6 to 1.8 percent by weight.

2. The lithium silicate glass ceramic according to claim 1, wherein the lithium silicate glass ceramic includes lithium disilicate crystals/crystallites as a main crystal phase.

3. The lithium silicate glass ceramic according to claim 1, wherein besides lithium aluminum silicate crystals/crystallites, the lithium silicate glass ceramic includes exclusively lithium disilicate crystals/crystallites and lithium phosphate crystals/crystallites as crystal phases.

4. The lithium silicate glass ceramic according to claim 1, wherein the lithium silicate glass ceramic includes: spodumene crystals/crystallites at a percentage of more than 0 vol % to 10 vol % of the lithium silicate glass ceramic, and virgilite crystals/crystallites at a percentage of greater than 0 vol % to 5 vol % of the lithium silicate glass ceramic.

5. The lithium silicate glass ceramic according to claim 1, wherein the lithium silicate glass ceramic includes sogdianite crystals/crystallites at a percentage of greater than 0 vol % to 20 vol % of the lithium silicate glass ceramic.

6. The lithium silicate glass ceramic according to claim 1, wherein the lithium silicate glass ceramic includes spodumene crystals/crystallites and sogdianite crystals/crystallites as crystal phases.

7. The lithium silicate glass ceramic according to claim 3, wherein the percentage by volume of the lithium phosphate crystals/crystallites and lithium disilicate crystals/crystallite in the range 40 vol % to 60 vol % of the lithium silicate glass ceramic.

8. The lithium silicate glass ceramic according to claim 1, wherein the lithium aluminum silicate crystals/crystallites assemble/form on the lithium disilicate crystals/crystallites within the lithium silicate glass ceramic.

9. The lithium silicate glass ceramic according to claim 4, wherein the length LS of the spodumene crystals/crystallites is 1 nm≤LS≤500 nm.

10. The lithium silicate glass ceramic according to claim 4, wherein the length LV of the virgilite crystals/crystallites is 0.2 μm≤LV≤20 μm.

11. The lithium silicate glass ceramic according to claim 1, wherein the starting composition includes the following in percentage by weight TABLE-US-00006 SiO.sub.2 54.0 to 62.0 P.sub.2O.sub.5 5.0 to 6.0 Al.sub.2O.sub.3 1.5 to 3.5 Li.sub.2O 13.0 to 16.0 K.sub.2O 0.6 to 1.8 ZrO.sub.2  8.0 to 11.5 B.sub.2O.sub.3   0 to 6.0 Na.sub.2O   0 to 1.9 color pigments   0 to 8.0 and/or one or more additives being selected from the groug consisting of MnO, Fe.sub.2O.sub.3, Tb.sub.2O.sub.3, Er.sub.2O.sub.3, Pr.sub.2O.sub.3, CeO.sub.2 Y.sub.2O.sub.3, and V.sub.2O.sub.3.

12. The lithium silicate glass ceramic according to claim 1, wherein the starting composition includes the following in percentage by weight TABLE-US-00007 SiO.sub.2 57.0 to 60.0 P.sub.2O.sub.5 5.2 to 5.6 Al.sub.2O.sub.3 2.6 to 3.2 Li.sub.2O 13.5 to 15.0 K.sub.2O 0.8 to 1.4 ZrO.sub.2  9.0 to 11.0 B.sub.2O.sub.3   0 to 5.0 Na.sub.2O   0 to 1.5 color pigments and/or one or more 2.0 to 7.0 additives being selected from the group consisting of MnO, Fe.sub.2O.sub.3, Tb.sub.2O.sub.3, Er.sub.2O.sub.3, Pr.sub.2O.sub.3, CeO.sub.2, Y.sub.2O.sub.3, and V.sub.2O.sub.3.

13. The lithium silicate glass ceramic according to claim 1, wherein the starting composition includes the following in percentage by weight TABLE-US-00008 SiO.sub.2 58 P.sub.2O.sub.5 5 Al.sub.2O.sub.3 3 Li.sub.2O 15 K.sub.2O 1 ZrO.sub.2 10 color pigments 4 that include at least one of MnO, Fe.sub.2O.sub.3, Tb.sub.2O.sub.3 Er.sub.2O.sub.3, Pr.sub.2O.sub.3, CeO.sub.2, Y.sub.2O.sub.3, and V.sub.2O.sub.3 one or more additives being selected from the group consisting of B.sub.2O.sub.3, CeO.sub.2, and Na.sub.2O.

14. A use of a lithium silicate glass ceramic, which comprises as the crystal phase lithium aluminum silicate crystals/crystallites, at least in the form of spodumene crystals/crystallites, at a percentage of more than 0 vol % to 10 vol % of the lithium silicate glass ceramic, for the production of a dental molded, body.

15. The use according to claim 14, wherein the lithium silicate glass ceramic includes virgilite crystals/crystallites.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a electron microscope photograph of a disilicate crystal with grown spodumene crystallite,

(2) FIG. 2 shows a x-ray diffraction photograph of the spodumene crystallite of FIG. 1,

(3) FIG. 3 shows a electron microscope photograph of disilicate crystals,

(4) FIG. 4 shows a electron microscope photograph of disilicate crystals with spodumene crystals, and

(5) FIG. 5 shows a further electrone microscope photograph of disilicate crystals with spodumene crystals.

DETAILED DESCRIPTION OF THE INVENTION

(6) In a first test molded parts in the form of pellets were fabricated and then pressed in a so-called muffle system (DentsplySirona Press muffel and ProFire Press furnace) to obtain a dental restoration in the form of a bridge.

(7) To produce the pellets the raw materials were first melted for a period of 2.25 hours at a temperature of 1540° C. The raw materials had the following composition in percentage by weight:

(8) TABLE-US-00004 SiO.sub.2 58 P.sub.2O.sub.5 5 Al.sub.2O.sub.3 3 Li.sub.2O 15 K.sub.2O 1 ZrO.sub.2 10 color pigments 4 degassing agents, network builder 4.

(9) The melt was then filled into containers, with the filling temperature of the melt 1360° C. The temperature in the containers was approximately in the range 800° C. to 1250° C. The melt was then cooled in the containers to a temperature between 300° C. and 500° C. The temperature was then allowed to drop slowly to room temperature over a period of 2 hours.

(10) This was followed by a 3-stage heat treatment as a first heat treatment to form crystal phases. In a first crystallization step the pellets were maintained at a temperature of 530° C. for 30 minutes. In a second step they were heated at 670° C. for almost 120 minutes. In a third step they were maintained at 800° C. for 30 minutes. They were then cooled to room temperature. The pellets were found to contain exclusively lithium disilicate and lithium phosphate as crystal phases.

(11) The pellets (press pellets) were held in a muffle system (Dentsply Sirona Pressmuffel and ProFire Press) at a temperature TP of 860° C. for a period tP of 30 minutes and then pressed. After cooling of the molded body formed in the cavity of the embedding mass, which was a bending rod according to ISO 6872, the strength was measured. Measurements were performed in accordance with ISO 6872 and yielded a mean strength of 398 MPa.

(12) A further (second) heat treatment was then carried out according to the teaching of the invention. For this purpose the mold bodies were heated to 760° C. at a heating rate of 55° C./minute and were then held at 760° C. for 2 minutes. During this second treatment lithium aluminum silicate crystals are formed. The mold bodies were then cooled under standard conditions in a Multimat dental furnace (manufacturer: Dentsply Sirona).

(13) Three-point measurements in accordance with ISO 6872 yielded a strength of 591 MPa.

(14) In further tests the second heat treatment was carried out in such a way that the holding temperature was 770° C. and the holding time was 1.5 minutes. The same increase in strength was achieved.

(15) In a second test run moldings were produced with lithium disilicate and lithium phosphate as the crystal phases as described above, with the composition of the starting materials in percentage by weight as follows:

(16) TABLE-US-00005 SiO.sub.2 58 P.sub.2O.sub.5 5 Al.sub.2O.sub.3 3 Li.sub.2O 15 K.sub.2O 1 ZrO.sub.2 10.0 color pigments 4 degassing agents, network builders 4

(17) Rods with the dimensions length 15 mm, width 4.1 mm and height 1.2 mm were derived from the moldings after crystallization through grinding. Three-point bending strength measurements in accordance with ISO 6872 yielded a strength value of 270 MPa.

(18) Corresponding rods were then subjected to the further or second heat treatment according to the invention, and were heated to 760° C. at a heating rate of 55° C./minute. The rods were held at this temperature for 2 minutes. They were then cooled under standard conditions in a Multitmat MT dental furnace (manufacturer: Dentsply Sirona). The strength upon measurement in accordance with ISO 6872 was 598 MPa.

(19) X-ray diffraction examination with a transmission electron microscope (TEM) revealed that spodumene crystals had grown on the ends of the lithium disilicate crystals. Virgilite crystals were also seen in some samples.

(20) FIG. 1 is an electron microscope photograph of a lithium disilicate crystal with a spodumene crystallite which is marked by a surrounding circle.

(21) FIG. 2 is a x-ray diffraction photograph of the spodumene crystallite of FIG. 1. This makes spodumene identifiable.

(22) FIG. 3 is an electron microscope photograph of lithium silicate glass ceramic. The rod-like or plate-like disilicate crystals are visible.

(23) FIGS. 4 and 5 are electron microscope photographs of silicate glass ceramic which was subjected to heat treatment according to the invention. In FIG. 4, the further or second heat treatment was carried out at a temperature of 760° C. at a holding time of 2 min., and in FIG. 5 at 760° C. at a holding time of 60 min. The spodumene crystallites grown are visible at the faces of the disilicate crystals.