Process for providing fluorescence to a dental ceramic body

Abstract

A process for providing fluoresence to a dental ceramic body by treating at least a portion of the outer surface of the dental ceramic body or a precursor thereof with a bismuth containing substance, characterized by the steps of placing the dental ceramic body or the precursor thereof into a closeable container, in particular a crucible; generating a bismuth containing atmosphere in the container and exposing at least a portion of the outer surface of the dental ceramic body or of the precursor to the bismuth containing atmosphere at a temperature above 1000° C.

Claims

1. A dental ceramic body based on zirconia and/or alumina comprising: a core region being at least essentially free of bismuth, and a surface region surrounding the core region and containing bismuth, wherein the surface region in which bismuth is contained reaches down from the surface to a depth of 500 μm at most.

2. The dental ceramic body according to claim 1, wherein the molar amount of bismuth contained in the surface region is less than 0.5 mol-%.

3. The dental ceramic body according to claim 1, wherein the dental ceramic body consists essentially of the core region and the surface region.

4. A process for providing a fluorescent dental ceramic body based on zirconia and/or alumina, the process comprising: A) providing a ceramic precursor powder containing apart from zirconia and/or alumina, respectively, bismuth oxide in an amount that is lower than 0.7 mol-% and higher than 0.06 mol-%, and a binder, B) pressing the ceramic precursor powder to form a green body, C) debinding the green body obtained in B) to form a porous brown body, and D) sintering the porous brown body obtained in C) to obtain the fluorescent dental ceramic body.

5. The process according to claim 4, wherein the sintering of D) is carried out in the presence of a bismuth containing atmosphere.

6. The process according to claim 4, further comprising step E) milling the dental ceramic body to a dental article.

Description

(1) The present invention is exemplified and illustrated by way of the following examples in combination with attached

(2) FIG. 1 showing the emission spectra (for an excitation wavelength of 365 nm) of various samples prepared according to the process of the present invention invention; and

(3) FIG. 2 showing the excitation spectrum (for an emission wavelength of 460 nm) of a sample prepared according to the process of the present invention invention.

EXAMPLES

Example 1

Relating to the First Aspect of the Present Invention

(4) 1.1 g of partially stabilized zirconia powder containing 3.0 mol % ytrria (Tosoh TZ-3YSB-E) was pressed with 65 kN (resulting in a pressure of 171 MPa) to a disc-shaped green body having a diameter of 22 mm.

(5) The resulting green body was then subjected to a heat treatment for debinding (at about 300° to 350° C.) and burning the carbon residues (at about 700° C.), followed by pre-sintering at 1050° C.

(6) The pre-sintered body was then placed in a crucible together with predefined amounts of a bismuth compound, namely of 1% bismuth nitrate in nitric acid (obtained by adding 100 mg of bismuth nitrate pentahydrate to 10 ml of 1% nitric acid) or of bismuth (III) oxide.

(7) Specifically, an alumina vessel having the shape of a hollow cylinder with an outer diameter of 20.5 mm and a height of 18 mm was put into a crucible with inner dimensions of 42×92×25.8 mm. The vessel was placed in a region of the crucible other than the region where the pre-sintered body was placed.

(8) For each of the samples, different amounts of bismuth nitrate or bismuth (III) oxide were given into the alumina vessel and, in case of the bismuth nitrate being in solution, were dried in a drying chamber. The respective amounts are given in Table 1:

(9) TABLE-US-00001 TABLE 1 Mass of Volume of Atomic Sample Bismuth bismuth solution mass of Bi No. compound compound (μl) (μg) 1 Bismuth 0.1 10 43.08 nitrate 2 Bismuth 0.5 50 215.41 nitrate 3 Bismuth 1.0 100 430.82 nitrate 4 Bismuth 2 861.65 nitrate 5 Bismuth 5 2154.12 nitrate 6 Bismuth 7 3015.76 nitrate 7 Bismuth 8 3446.59 nitrate 8 Bismuth 10 8969.90 oxide 9 Bismuth 100 89699.3 oxide

(10) Sintering of the pre-sintered body was then performed in the presence of a bismuth containing atmosphere generated from evaporation of the bismuth compound. Specifically, dwelling was performed at a sinter temperature of 1450° C. for 2 hours.

(11) As shown in FIG. 2, sample 3 prepared according to the process of the present invention produced an excitation maximum at 315 nm. As further shown in FIG. 1, the emission maximum produced was at 455 or 460 nm, whereby the highest fluorescence intensity was achieved for the sample using 8.97 mg atomic mass of bismuth (sample 8).

(12) Thus, both the use of bismuth nitrate as well as of bismuth oxide led to the generation of a bismuth-containing atmosphere during the sintering process and consequently to the incorporation of bismuth, specifically in the form of bismuth oxide, in an amount sufficient to impart fluorescent properties closely resembling the one of a natural tooth. Specifically, a bismuth oxide containing atmosphere was generated due to the evaporation of bismuth oxide in one case and to due to the evaporation and oxidation of bismuth nitrate in the other case.

(13) Further experiments have shown that using a zirconia sample infiltrated with a bismuth nitrate solution of higher concentration (100 mg/ml) as bismuth source likewise led to the generation of a bismuth containing atmosphere during sintering.

(14) The visual inspection of the samples under UV-light showed that the upper side of the sample, i.e. the side that was directly exposed to the bismuth-containing atmosphere, was homogeneously doped with bismuth. Thus, a uniform incorporation of bismuth was achieved on this side.

(15) The results shown in FIG. 1 further suggest that the fluorescence intensity is tunable by the amount of bismuth compound put into the crucible and, hence, the concentration of bismuth compound in the bismuth containing atmosphere.

(16) A fluorescence intensity under 365 nm similar to the one of a natural tooth was obtained for an atomic bismuth mass of 3.45 mg in the crucible. Given the volume of about 100 ml of the crucible's inner space, the optimum mass concentration of bismuth was therefore about 0.035 g/l.

Example 2

Relating to the Second Aspect of the Present Invention

(17) Preparation of Bismuth-Doped Yttria

(18) A powder of bismuth doped yttria (Y.sub.2O.sub.3:Bi) was prepared by dissolving 19.96 g of yttrium (III) nitrate hexahydrate (Y(NO.sub.3).sub.3.6 H.sub.2O) and urea (CH.sub.4N.sub.2O) in nitric acid (10%) and adding 2.15 ml of a solution of bismuth (III) nitrate.pentahydrate (Bi(NO.sub.3).sub.3.5 H.sub.2O) in nitric acid (10 mg/1 ml).

(19) The mixture was then dried at 95° C. in a rotational evaporator at 200 mbar vacuum.

(20) The powder was then fired at 1000° C. for 1 hour in air in an alumina crucible.

(21) The cake received from firing were broken up and crushed to a coarse powder. This powder was washed with deionized water to remove remaining flux and dried in a rotational evaporator. The powder was then sieved with 250 μm mesh.

(22) Preparation of Ceramic Precursor Powder

(23) Zirconia powder TZ-3YSB-E was blended with Y.sub.2O.sub.3:Bi. Specifically, two mixtures of 10 g were prepared with either 1 wt.-% or 5 wt.-% of Y.sub.2O.sub.3:Bi powder according to Table 2.

(24) TABLE-US-00002 TABLE 2 Percentage Mass of Mass of Y.sub.2O.sub.3:Bi Y.sub.2O.sub.3:Bi zirconia Sample powder powder powder No. (wt-%) (g) (g) 10 1.0 0.1 9.9 11 5.0 0.5 9.5

(25) The mixtures were given in mixer beakers and mixed in the speedmixer for 1 minute at 800 rpm.

(26) Samples were then pressed and sintered as described for Example 1 above.

(27) Fluorescence measurments revealed for an excitation wavelength of 365 nm an emission maximum at about 415 nm. The excitation maximum lies at about 328 nm with another maximum at 304 nm.