Method of making a dental restoration

Abstract

A method of making a monolithic dental restoration. The method includes the steps of providing a monolithic precursor of a dental restoration and firing the monolithic dental restoration precursor to provide the monolithic dental restoration. The zirconia material of both the dental restoration precursor as well as the dental restoration has a relative density of greater than 98% of the theoretic density of the zirconia material. The invention helps providing a color of a non-glazed dental restoration which resembles the color of a glazed dental restoration.

Claims

1. A method of making a monolithic dental restoration, comprising: providing a green body monolithic precursor of a dental restoration; sintering the green body to provide a monolithic precursor of a dental restoration being made of zirconia material having a relative density of greater than 98% of the theoretic density of the zirconia material; polishing the monolithic dental restoration precursor; and firing the monolithic dental restoration precursor at a temperature of at least 800° C. for a duration of at least 10 seconds to provide the monolithic dental restoration, wherein the monolithic dental restoration precursor does not have a glazing; wherein the firing step comprises a heating phase, a steady state phase, and a cooling phase, and wherein the steady state phase is performed for a duration of less than 10 minutes, wherein the duration of the firing refers to the duration of the steady state phase.

2. The method of claim 1, wherein zirconia material comprising between 85% by weight and 95% by weight ZrO.sub.2.

3. The method of claim 1 wherein the green body is made of zirconia material having a relative density which is between about 40% and about 70% of the theoretic density of the zirconia material.

4. The method of claim 3, further comprising providing the green body by milling or grinding from a blank of zirconia material.

5. The method of claim 3, further comprising soaking the green body with a coloring liquid.

6. The method of claim 5, further comprising drying the green body soaked with the coloring liquid.

7. The method of claim 3, further comprising smoothing the green body.

8. The method of claim 1, comprising providing the monolithic dental restoration precursor in a pre-colored form.

9. The method of claim 1, wherein the step of sintering causes the relative density to be increased to the relative density of greater than 98%.

10. The method claim 1, wherein the step of polishing the monolithic dental restoration precursor comprises applying a polishing paste on the monolithic dental restoration precursor and polishing the monolithic dental restoration precursor by use of the polishing paste and a polishing tool.

11. The method of claim 8, wherein the pre-colored dental restoration precursor is made of a zirconia material comprising between about 5% by weight to 10% by weight yttrium oxide, Er.sub.2O.sub.3, Tb.sub.4O.sub.7, Bi.sub.2O.sub.3, MnO, and Fe.sub.2O.sub.3; and wherein Er.sub.2O.sub.3 is present in an amount up to about 1% by weight, Tb.sub.4O.sub.7 is present in an amount up to about 1% by weight, Bi.sub.2O.sub.3 is present in an amount up to about 0.3% by weight, MnO is present in an amount up to about 0.05%, and Fe.sub.2O.sub.3 is present in an amount up to about 0.5% by weight.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a diagram illustrating the results of color measurements of Examples including an Example obtained by a method according to an embodiment of the invention.

EXAMPLES

(2) Six zirconia anterior crowns were milled from Lava™ Plus high translucency zirconia blocks (available from 3M Deutschland GmbH, #679670, multi XL block size). The crowns were removed from the holding device with a turbine handpiece and the area of the holding pins were smoothened with a P2500 grits grain sandpaper. The crowns were assorted into three groups of two crown each:

(3) Group A: crowns for finishing by a glazing

(4) Group B: crowns for finishing by only polishing

(5) Group C: crowns for finishing by polishing and subsequently firing

(6) The outer surfaces of the crowns of groups B and C were smoothened with the sandpaper (P2500 grits) for facilitating the polishing after sintering.

(7) Coloring

(8) All six crowns were soaked for two minutes with Lava™ Plus high translucency dyeing liquid A3 (available from 3M Deutschland GmbH, #515601), air-dried at room temperature 23° C. and fired at 1450° C. for 2 hours in a Lava™ Furnace 200 oven available from 3M Deutschland GmbH.

(9) Firing/Finishing

Comparative Example 1

(10) The crowns of group A were glazed with a dental glaze material (VITA AKZENT Plus; #A0764 from the company Vita Zahnfabrik H. Rauter GmbH & Co. KG) and fired twice at 970° C. for 1 minute in a dental furnace (DEKEMA Austromat 3001 from the company DEKEMA Dental-Keramiköfen GmbH). In each of the firing steps the dental furnace was pre-heated to 500° C. The crowns were placed on a firing support at room temperature (23° C.) and moved into the furnace. The furnace was then heated at a heating rate of 80° C. per minute to a temperature of 970° C. The temperature was maintained at 970° C. while the crowns were fired at that temperature for 1 minute before the crowns were moved outside the dental furnace for cooling toward room temperature.

Comparative Example 2

(11) The crowns of group B were polished with dental polishing paste (Fino carat plus II).

Example 3 According to the Invention

(12) The crowns of group C were polished with dental polishing paste (Fino carat plus II) and fired twice after polishing. The additional firing steps were performed at 970° C. for 1 minute.

(13) The firing steps performed for crowns of groups A and C therefore were the same, although the crowns of group C were not provided with any glazing.

(14) Color Measurement

(15) All crowns were measured with a photospectrometer that is available under the designation Vita Easyshade® Advance, from Vita Zahnfabrik, Germany. The Vita Easyshade® Advance can be used to measure color differences, for example between different objects. The difference is measured in the form of a so-called Delta E value. A higher Delta E value represents a greater color difference than a lower Delta E. The crowns of group A were used as reference.

(16) FIG. 1 is a diagram which represents a color deviation on the vertical axis based on the Delta E metrics. The zero value represents the color value of the reference samples (crowns of group A). The diagram further illustrates the color deviation of the crowns of groups B in relation to the reference color (group A) and the color deviation of the crowns of group C in relation to the reference color (group A).

(17) The visual appearance of the crowns of group B (finished by polishing only) is significantly different than the visual appearance of the crowns of group A. The measuring results of the color measurement of the crowns of group A and the crowns of group B confirm, that the colors of group A and B significantly deviate. In particular, the crowns of group B appear more dark or gray, compared to the crowns of group A (finished by glazing). This color deviation had to be accepted in case zirconia material was used to make dental restorations without glazing. Therefore there has been a general tradeoff between, on the one hand, applying the additional step of glazing in the manufacturing of dental restorations and, on the other hand, the achievement of color precision. Although this tradeoff can be mitigated by selecting differently colored zirconia materials there is a general desire to use one zirconia material for different manufacturing techniques (glazing optional).

(18) The invention allows minimizing the color deviation between dental restorations that are finished by a glazing and dental restorations that do not have a glazing but are just polished. This is illustrated in the diagram for the crowns of group C. As apparent from the diagram the color difference between the crowns of group A and group C is significantly smaller than the color difference between the crowns of group A and group B. The only difference between the crowns of group C and B is the additional firing step applied to the crowns of group C.