Indirect Restoration Technology

Abstract

Dental restorations such as crowns, are made from lithium silicate glass ceramic that is heated and pressed onto a metal substrate, the latter being shaped to an impression or scan of the area of the mouth to receive the restoration. The metal substrate is made from an alloy selected to exhibit a coefficient of thermal expansion which is slightly greater than the CTE of the lithium silicate. In a preferred embodiment, the CTE of the lithium silicate glass ceramic is in the range of 11.5 to 12.5 and the alloy is selected to have a CTE of 12 to 13.5. A palladium tin alloy provides that CTE in the preferred embodiment.

Claims

1. A method for fabricating a dental restoration, the method comprising: preparing a metal alloy substrate to a shape to conform to a base impression or scan of a portion of a mouth of a patient; heating a blank comprising a lithium silicate glass ceramic material; and pressing the heated blank onto the metal alloy substrate to form a shape replicating an external tooth structure; wherein the lithium silicate glass ceramic material has a coefficient of thermal expansion in the range of 11.5 to 12.510.sup.6/K and a flexural strength of between 300 to 380 MPa.

2. The method for fabricating a dental restoration of claim 1, wherein the coefficient of thermal expansion of the metal alloy substrate is in the range of 12 to 13.510.sup.6/K.

3. The method for fabricating a dental restoration of claim 1, wherein the metal alloy comprises palladium and tin.

4. The method for fabricating a dental restoration of claim 1, wherein the coefficient of thermal expansion of the metal alloy substrate is in the range of 12 to 13.510.sup.6/K and the metal alloy comprises palladium and tin.

5. The method for fabricating a dental restoration of claim 1, wherein the coefficient of thermal expansion of the metal alloy substrate is greater than the coefficient of thermal expansion of the lithium silicate glass ceramic material.

6. The method for fabricating a dental restoration of claim 1, wherein the metal alloy substrate and the lithium silicate glass ceramic material both expand during the heating and pressing steps, and wherein the metal alloy substrate expands slightly more than the lithium silicate glass ceramic material during the heating and pressing steps.

7. The method for fabricating a dental restoration of claim 1, wherein the dental restoration comprises a dental crown.

8. The method for fabricating a dental restoration of claim 1, wherein the dental restoration comprises a bridge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The aforementioned objects and advantages of the present invention, as well as additional objects and advantages thereof, will be more fully understood herein after as a result of a detailed description of a preferred embodiment when taken in conjunction with the following drawings in which:

[0024] FIGS. 1A and 1B are cross-sectional views of respective dental crowns comprising the combination of materials of the invention hereof;

[0025] FIG. 2 is a cross-sectional view of a more complex dental restoration consisting of a bridge formed by the materials of the invention; and

[0026] FIG. 3 is a graph showing the percentage linear change vs. temperature for the lithium silicate glass ceramic and the PdSn alloy of a preferred embodiment.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0027] The present invention may be best understood by referring to the accompanying drawings which show a preferred embodiment of the restorations made with lithium silicate on a metal alloy substrate. The lithium silicate, when pressed onto a metal alloy substrate, may be deemed to be a substitute material for porcelain fused to metal. One significant advantage derived from the use of lithium silicate instead of porcelain is the strength of the material. Lithium silicate has a strength in MPa which is approximately three times that of dental porcelain. The flexural strength of porcelain is in the range of 70 to 125 MPa. The flexural strength of lithium silicate glass ceramic is in the range of 300 to 380 MPa.

[0028] In one preferred embodiment, the lithium silicate is heated and pressed onto a metal alloy substrate made primarily of palladium and tin. This alloy has a coefficient of thermal expansion in the desired range of 12 to 13.5. This CTE is slightly higher than the CTE of the lithium silicate which is about 11.5 to 12.5. Having the CTE of the metal alloy substrate slightly higher than the CTE of the lithium silicate, permits the restoration to undergo increases in temperature with relatively little risk of separation because of over expansion of the lithium silicate glass relative to the metal substrate. There may be other suitable metal alloy formulations which would be compatible with the lithium silicate CTE of 11.5 to 12.5, and which would thus have a CTE preferably in the range of 12 to 13.5. FIG. 3 shows graphically the relative percentage linear change versus temperature for the selected palladium tin alloy and the lithium silicate glass ceramic in the preferred embodiment.

[0029] The preferred fabrication process comprises the steps of forming a block of the lithium silicate glass of selected color and texture and preparing the metal alloy substrate for geometric compatibility with an impression or digital scan of the tooth or teeth to be replaced or covered. Then the glass is inserted, heated and pressed over the alloy substrate to form the restoration such as depicted by way of example in FIGS. 1A, 1B and 2. The resulting restoration will have a more accurate tooth color and superior strength as compared to typical PFM restorations. Moreover, it will be more stable at elevated temperatures and easier to press onto the substrate, thus reducing the complexity of fabrication.

[0030] Thus it will be understood that the present invention comprises an indirect dental restoration formed of lithium silicate translucent glass ceramic heated and pressed onto a metal alloy substrate. In the preferred embodiment, the metal alloy has a slightly higher coefficient of thermal expansion than the lithium silicate glass ceramic. In one such preferred embodiment, the metal alloy substrate is formed from a palladium tin alloy wherein the relative constituents are selected to provide a CTE of 12 to 13.5 as compared to the lithium silicate CTE of 11.5 to 12.5.