A silicate dental ceramic-based blasting medium for the improvement of the adhesive bond between fire-on ceramic and alloy. In contrast to the traditionally used Al.sub.2 O.sub.3 blasting medium, the complete sealing of the alloy-ceramic contact layer is guaranteed. In this way, the penetration of moisture (from the milieu of the mouth) in the contact layer is prevented. The phenomenon of bubble formation known from practice in dental work worn on a trial basis can thus be stopped after correction firing.
In order to guarantee a good bond between alloy and ceramic, a so-called adhesive firing is also recommended by dental ceramic manufacturers. As in the normal process, a thin opaque layer is first applied to the alloy and then fired at higher temperatures, specifically about 30-50.degree. C. above the normal firing temperature. In this way, the opaque is converted into a low viscosity state, whereby all cavities and uneven places are wetted. After cool-down, a glassy, smooth ceramic coating forms on the metal substructure. Depending on the manufacturer, the adhesive firing can also be executed with a compound offered for this which is characterized as "adhesive bond"--a special bonding agent.
An overfiring of the opaque is unproblematic as far as heat resistance, substructure deformation and fitting are concerned, since, in spite of increased firing temperatures (e.g. 980.degree. C.), the interval to the solidus point of the alloy amounts to more than 200.degree. C. However, it appears differently in the so-called bio-alloys which have been present on the market for several years. This alloy type has a gold portion of over 75% by weight and is correspondingly gold colored. As a result, alloy technology requires the solidus point to be lowered 250 to 350.degree. C. in relation to the classic dental alloys to an absolute value between 900 and 1000.degree. C. The bio-alloys are faced with specially developed, low-melting-point ceramics in order to guarantee the substructure stability and compatibility of the thermal expansion coefficient.
An adhesive firing analogous to the technique of overfiring typical for the classic dental alloys increases the probability of deformation in the dental substructure and for this reason is executed at a correspondingly low temperature for the bio-alloys.
However, in combination with the practice, which was introduced for these new alloy types, of "wearing the prosthetic tooth on a trial basis", an increased bubble formation, compared to the classic metal-ceramic system, is observed in the finish firing. In this process, the prosthetic tooth is temporarily installed in the patient's mouth for a certain period of time (from a few days to a few months) by the dentist for the purpose of reviewing the bio-compatibility and occlusion. After this trial time, the dental work (crowns or bridges) goes back to the dental technology laboratory and is corrected according to dental technology processes and lastly is subjected to a finish or glaze firing.
In the blasting of the metal substructure, residues of the blasting medium remain on or in the surface of the alloy and can be detected by scanning electron microscopic examination and x-ray fluorescence analysis. It is assumed that the additional steps of surface conditioning for the formation of residual pore channels between alloy and first ceramic layer (opaque or adhesive bond) are required with the use of Al.sub.2 O.sub.3 blasting medium, but also with other inert hard materials such as silicon carbide (SiC) or boron carbide (B.sub.4 C) fundamentally suited for this. Moisture is sucked into the channels by capillary forces and the bubbles observed many times in practice after wearing the prosthesis on a trial basis are generated in the subsequent correction firing.
Surprisingly, it was discovered that, after the replacement of the customarily used blasting medium with a silicate dental ceramic-based blasting medium, the bubble formation after wearing of the prosthetic teeth on a trial basis and after subsequent correction firing can be completely suppressed. The disadvantage of the metal-ceramic bio-alloys, compared to the traditional high-melting-point alloy--facing ceramic systems, is thus eliminated.
SUMMARY OF THE INVENTION
A feature of the invention is a glass ceramic silicate blasting medium which improves the wetting properties between alloy and ceramic (opaque) in comparison to the conventionally used Al.sub.2 O.sub.3 blasting medium. In contrast to the latter, the contact surface between the two components is completely "sealed".
Another feature of the invention is a blasting medium for use in dental technology, which is characterized by the fact that it consists of fine particle silicate dental ceramic.
Still a further feature of the invention is the use of such a blasting medium for surface conditioning of metal substructures to be faced with dental ceramic, in particular in low-melting-point alloy--fire-on-ceramic systems.
Any silicate dental ceramic is suitable as a blasting medium in the sense of the invention as long as it is available in the essentially homogenous composition of the ceramic components in a particular form typical for blasting media. This assumes that the dental ceramic is present in fine-particle form after sintering or from the melt, or can be milled to the corresponding particle size, which as a rule is the case.
The blasting medium according to the invention has a suitable particle size of 50 to 200 .mu.m, preferably 100 to 150 .mu.m.
The blasting medium particles are irregular in their outer form and are mostly in the form of splinters.
Preferably, the blasting medium consists of
40-98% by weight SiO.sub.2
2-25% by weight Me(III).sub.2 O.sub.3
0-30% by weight Me(I).sub.2 O
0-20% by weight Me(II)O
0-30% by weight Me(IV)O.sub.2
0-8% by weight B.sub.2 O.sub.3
0-15% by weight P.sub.2 O.sub.5
0-3% by weight F
in which
Me(III).sub.2 O.sub.3 stands for Al.sub.2 O.sub.3, La.sub.2 O.sub.3 and Sb.sub.2 O.sub.3 ;
Me(I).sub.2 O stands for K.sub.2 O, Na.sub.2 O and Li.sub.2 O;
Me(II)O stands for CaO, BaO, MgO, ZnO and SrO; and
Me(IV)O.sub.2 stands for TiO.sub.2, ZrO.sub.2, CeO.sub.2 and SnO.sub.2.
In an especially preferred version, the blasting medium has the following composition:
56-63% by weight SiO.sub.2
8-24% by weight Al.sub.2 O.sub.3
7-14% by weight K.sub.2 O
4-14% by weight Na.sub.2 O
0-2% by weight Li.sub.2 O
0-8% by weight B.sub.2 O.sub.3
0-1.5% by weight CaO
0-1.5% by weight TiO.sub.2
0-0.5% by weight CeO.sub.2
0-0.6% by weight Sb.sub.2 O.sub.3
0-3% by weight F
DETAILED DESCRIPTION OF INVENTION
It is assumed that, in the blasting of dental metal substructures with the blasting media according to the invention, residual blasting media remaining on or in the metal surface leads to an intensive bond of the fire-on ceramic to the metal substructure. This is shown in, among other things, a clear increase of the adhesion values compared to substructures blasted with Al.sub.2 O.sub.3. In particular, no residual pore channels form in this process, in contrast to Al.sub.2 O.sub.3 blasting media, in which moisture is later drawn in, which in a subsequent finish firing can lead to bubble formation. The dental ceramic blasting medium according to the invention instead guarantees that the contact layer between metal substructure and ceramic (opaque) is free of pores and completely "sealed".
The blasting medium according to the invention can accordingly be used very advantageously in the surface conditioning of metal substructures to be faced with dental ceramic. This advantage is especially noticeable with low-melting-point alloy--fire-on-ceramic systems.
By completely sealing opaque-alloy contact layer, the penetration of moisture into it is prevented; the bubble formation after wearing the prosthetic teeth on a trial basis and subsequent correction, or finish firing is stopped.
The blasting process with the blasting medium according to the invention occurs under standard conditions with standard equipment.
EXAMPLE 1
Table 1 below shows the compositions of blasting media according to the invention based on fine-particle (100-150 .mu.m) silicate dental ceramic.
They are obtained by quenching melts of correspondingly composed ceramic compounds in water, then milling, e.g. in a ball mill, and by classification of the desired particle size range.
TABLE 1
Blasting
medium
particle size
100-150 .mu.m No. 1 No. 2 No. 3
SiO.sub.2 58.1 62.4 57.8
Al.sub.2 O.sub.3 14.1 8.8 22.2
K.sub.2 O 13.0 11.6 8.9
Na.sub.2 O 5.7 10.6 11.0
Li.sub.2 O 0.9 1.0 --
B.sub.2 O.sub.3 6.9 1.0 --
CaO 0.4 1.0 0.1
TiO.sub.2 0.1 1.1 --
CeO.sub.2 0.3 0.2 --
Sb.sub.2 O.sub.3 0.4 0.3 --
F -- 2 --
EXAMPLE 2
In order to simulate in the laboratory the bubble formation after wearing the prosthetic teeth on a trial basis, the following experiment was executed:
Production and facing of crowns occurred according to typical operating instructions or manufacturer specifications from a commercially available low-melting-point, high-gold-content dental alloy (DEGUNORM.RTM., Degussa) and a commercially available paste opaque based on low-melting-point dental ceramic (DUCERAGOLD.RTM., Ducera). 10 crowns each were blasted with the blasting media according to the invention as per Example 1 and comparable to Al.sub.2 O.sub.3 (110 .mu.m) as well as to SiC (110 .mu.m) and B.sub.4 C (110 .mu.m). The work was done with a commercial blasting device of the Bego company (Ministar; pressure: 2 bar; 1.2 mm blasting nozzle).
The crowns were then stored under pressure (6 bar) at 80.degree. C. in artificial saliva for 20 hours. After this treatment, the crowns were dried briefly and then fired again (correction firing). The results are summarized in Table 2 according to the particular blasting medium.
TABLE 2
Blasting medium Number of defective crowns
Blasting medium no. 1 0
Blasting medium no. 2 0
Blasting medium no. 3 0
Al.sub.2 O.sub.3 10
SiC 10
B.sub.4 C 10
Further variations and modifications of the foregoing will be apparent to those skilled in the art and are intended to be encompassed by the claims appended hereto.
German priority application 198 34 106.7 filed Jul. 29, 1998 is relied on and incorporated herein by reference.
