Patent Application
20080081103
A glass according to the invention for dental applications can comprise the following components:
wherein
The glass may essentially consist of the above-identified components.
Further, the glass may comprise at least one of the components in the following amount(s):
It has also been proven advantageous that the glass comprises less than 2.0 wt.-% ZnO.
Further, a glass which comprise 0.5 to 2.5 wt.-% ZrO2 is encompassed by the present invention.
In a further embodiment, the glass comprises 15.5 to 19.0, in particular 17.5 to 19.0 wt.-% K2O.
According to a further embodiment of the present invention, the glass may comprise at least one of the components in the following amount(s):
The glass according to the invention surprisingly proves dimensionally stable at the high temperatures which are used for a simultaneous crystal formation of a suitable dental restoration. Thus the final ceramization of a suitable framework material can take place simultaneously with the desired application of a glaze in one step. This represents an enormous advantage to the user.
The use of the glass according to the invention is particularly advantageous on restoration parts which have been ground or milled in an only partial strengthened state and are then subjected to a further thermal treatment in order to improve the mechanical properties. In particular, the use of the glass is suitable as glaze on restoration parts from a lithium metasilicate glass-ceramic which forms lithium disilicate crystals as a result of the thermal treatment.
Further, the glass according to the invention preferably has a firing temperature of 900 to 950° C., in particular of 910 to 930° C. The firing temperature is determined in the manner given in the examples.
In addition, the glass according to the invention does not react with the framework material and, after the thermal treatment, provides it with an aesthetic high gloss. It also possesses a very good chemical stability. This is an important property for materials which constantly come into contact with various fluids in the oral cavity.
When used as glaze material for a restoration based on a glass or a glass-ceramic, the coefficient of thermal expansion of the glass according to the invention can be suitably adapted by varying the type and amount of the components present in the glass. A glass is preferred which has a linear coefficient of thermal expansion of 8.0 to 9.5×10−6 K−1 and in particular of 8.4 to 9.1×10−6 K−1 in the temperature range of 100 to 500° C.
The glass according to the invention can be prepared according to the processes known from the state of the art by forming a glass melt at temperatures of about 1200° C. to about 1600° C. from suitable starting materials such as oxides, hydroxides and carbonates.
The glass melt is then usually poured into water and the glass granules formed are reduced to a particle size of at most 100 μm, preferably at most 50 μm.
The glass according to the invention can be used in particular as glazing material of a dental restoration and the invention is also directed to this method of use.
The dental restoration can be a bridge, a crown, an inlay, an onlay, a veneer or a cap, or a part thereof.
The dental restoration can be based on a glass, a ceramic, a metal or a glass-ceramic and in particular based on a glass-ceramic.
Lithium silicate glass-ceramic, a mica glass-ceramic or a chondrodite glass-ceramic can be used as glass-ceramic. These can be prepared from suitable precursors which after the application of the glass according to the invention as glaze show a strong increase in strength and lead to the formation of the desired glass-ceramic as a result of the thermal treatment and the crystal formation triggered thereby.
The lithium silicate glass-ceramic can comprise a lithium metasilicate or a lithium disilicate glass-ceramic.
When using a lithium metasilicate glass-ceramic as precursor the thermal treatment leads to the transformation of the metasilicate crystals into disilicate crystals, whereby the structure is greatly strengthened.
The invention also relates to a process for applying a glaze to a dental restoration in which:
(a) the glass comprising a composition of the present invention is applied onto the dental restoration; and
(b) the dental restoration provided with the glass is subjected to a thermal treatment in order to transform the glass into a glaze which adheres firmly to the restoration.
The thermal treatment preferably takes place at a temperature of at least 860° C., in particular at 860 to 960° C.
As already mentioned, a dental restoration based on a glass, a ceramic, a metal or a glass-ceramic is used in particular.
The thermal treatment may also lead to the formation of crystals in the glass or the glass-ceramic. By formation of crystals is also meant the transformation of crystals, e.g., transformation of metasilicate into disilicate crystals.
The glass according to the invention not only offers great advantages when used in processes for applying a glaze to lithium silicate glass-ceramics but can also be used in an advantageous manner in other glass-ceramic materials which precipitate different crystal phases depending on the thermal treatment used. Examples of such other glass-ceramic materials are given in K. Chyung, G. H. Beall, D. G. Grossman; Fluorophlogopite Mica Glass-Ceramics; 10th Int. Cong. on Glass, Kyoto, The Ceramic Soc. Japan 14 (1974) 33-40.
In a process performed according to the invention glasses or glass-ceramics can be used which can form lithium disilicate crystals or mica crystals during the thermal treatment. Therefore in step (a) a restoration based on lithium metasilicate glass-ceramic or chondrodite glass-ceramic may be used.
Further, a process of the present invention that leads to the formation of crystals brings about an increase in the strength, in particular the bending strength, of the dental restoration.
The invention is described in further detail below with reference to illustrative, non-limiting examples:
A total of 4 different glasses according to the invention were prepared having the chemical compositions given in the following table:
For their preparation, in each case, a mixture of suitable oxides, hydroxides and carbonates was melted in a platinum/rhodium crucible at a temperature of 1500° C. to 1550° C. over a homogenization time of 1 to 1.5 hours. The glass melt was quenched in water and ground to an average particle size of less than 100 μm, relative to the number of particles.
Selected properties measured using suitable testpieces made from the respective glass are given in Table 2 for the glasses from Table 1. The examples illustrate that glasses with the desired properties can be prepared by varying the components and their amounts in the given ranges.
These properties were measured in the manner described below using the cited standards:
The firing temperature was measured using platelets with a diameter of 12 mm and a height of 2 mm which were prepared according to DIN ISO 6872. These platelets were fired at different temperatures and then the degree of firing was assessed using the criteria of number of bubbles, surface gloss and edge rounding.
To measure the linear coefficient of thermal expansion a according to ISO 6872, a rod-shaped green body which was sintered in a vacuum furnace at a heating-up rate of 60° C./min and with a holding time of 1 min at the firing temperature given in Table 2 to prepare the testpiece was prepared from the powder of the respective glass. The linear coefficient of thermal expansion was then measured in the range of 100° C. to 500° C. using the thus-obtained testpieces.
The acid resistance is a measure of the chemical resistance of the very glasses used in dentistry, as these are permanently exposed to the action of acid substances in the oral cavity.
Acid resistance was measured according to ISO 6872 (1995). To this end, firstly test platelets with a diameter of 12 mm and a thickness of 1 mm were prepared by sintering together the glass powder with an average particle size of less than 50 μm. The powder was kept for 1 minute at the respective firing temperature to prepare the testpieces. The test platelets were then treated for 16 hours with 4 vol.-% aqueous acetic acid at 80° C. The loss of mass which occurred was then measured in relation to the surface of the testpiece platelets as a measure of the acid resistance.
Hardness is a measure of the mechanical resistance of materials. As the glasses used are exposed to wear by chewing forces it is advisable to quantify this property.
To measure Vickers hardness, testpieces with a diameter of 20 mm and a thickness of 3 mm were prepared by sintering together the glass powder with an average particle size of less than 50 μm. The powder was kept for 1 minute at the respective firing temperature to prepare the testpieces. The Vickers hardness was measured according to ISO 14705 (2000) by using the average value from 6 measurements taken on polished surfaces.
This example describes the use of the glass according to the invention as glaze material for restoration parts which have been ground or milled in an only partially strengthened state and which subsequently are subjected to a further thermal treatment in order to improve the mechanical properties. A restoration of a lithium metasilicate glass-ceramic was used. Surprisingly the one step thermal treatment led not only to a clear increase in strength, but simultaneously also to the glazing of the restoration. The glass according to the invention can thus be described as instant glazing material.
Glass powder according to example 2 with an average particle size of at most 50 μm was mixed with a universal glaze and staining dye from Ivoclar Vivadent AG and applied in an average layer thickness of about 150 μm to a lithium metasilicate glass-ceramic model crown prepared by means of CAD/CAM technology (Cerec® 3 from Sirona, Bensheim, Germany). The thermal treatment then took place at a temperature of 860° C. at a heating-up rate of 60° C./min and with a holding time of 10 min. The lithium metasilicate glass-ceramic was transformed into a lithium disilicate glass-ceramic and the glaze firing with the glass according to the invention took place at the same time.
Studies of the strength of the glass-ceramic used and obtained after the thermal treatment (biaxial bending strength) produced the following results (average value from 4 measurements taken by using unglazed testpieces):
Furthermore the glossiness of an unglazed testpiece and one lithium disilicate glass-ceramic testpiece glazed with the glass according to the invention was measured (average value of 2 testpieces and 4 measurements each):
The gloss was measured with the novo-curve from Rhopoint, Great Britain, which allows a measurement of the glossiness of even small samples. Measurement took place according to the standard ISO 2813. The measurement principle is that a light beam is directed onto the surface of the testpiece at an angle of 60° and the intensity of the reflected light is measured in the equipment and compared with a reference value.
This example describes the use of the glass according to the invention as glazing material for a mica glass-ceramic.
For this, a glass block made of a glass which is capable of precipitating mica crystals was annealed at a temperature of 750° C. for 1 hour. Chondrodite crystals were precipitated in the glass by volume crystallization with this treatment. The glass-ceramic was still workable with diamond tools in this state. A model crown was prepared from this by means of CAD/CAM technology (Cerec® 3 from Sirona, Bensheim, Germany).
Glass powder according to example 1 with an average particle size of at most 50 μm was mixed with a universal glaze and staining dye from Ivoclar Vivadent AG and applied to the model crown in an average layer thickness of about 150 μm. Thermal treatment followed at a temperature of 950° C. with a heating-up rate of 60° C./min and a holding time of 20 min. The chondrodite glass-ceramic was thereby transformed into a mica glass-ceramic and the glaze firing took place at the same time with the glass according to the invention.
Studies of the strength (biaxial bending strength) produced the following results (average value from 4 measurements taken on unglazed testpieces):
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06020553.1 | Sep 2006 | EP | regional |
