FR2655264A1 - Machinable glass-ceramics for dental prostheses - Google Patents

Abstract

The invention relates to vitreous materials which can be converted by thermal treatment into glass-ceramics in which the essential crystalline phase possesses the crystallographic structure of tainiolite. The vitreous material is obtained by fusion of the mixture having the following composition, expressed in percentages by weight: SiO2: 45-70; MgF2: 12-20; MgO: 8-15; Li2O: 3-10; CaO: 0-10; M2O + M'O: 5-20; Al2O3 + ZrO2: 2-9; TiO2: 0-7; conventional dyes for glasses: 0-10; M2O representing one or more oxides chosen from K2O, Cs2O and Rb2O; M'O representing BaO and/or SrO; the quantity of M'O, expressed as the number of moles, being less than or equal to 50 % of the quantity of M2O; the weight percentage of Al2O3 being less than or equal to 3 and the weight percentage of ZrO2 being less than or equal to 6. The glass-ceramics obtained are especially useful for the production of dental prostheses.

Description

 The present invention relates to materials useful for producing dental prostheses, and more particularly to machinable glass-ceramics comprising a crystalline phase of the tetrasilicic mica type.

 Much work has been done in the dental field to develop materials suitable for use in the manufacture of dental prostheses. Among the materials used, vitroceramics have proved particularly interesting. Vitroceramics are semi-crystalline materials obtained in situ by controlled crystallization of glasses during a heat treatment.

In these materials, the crystalline phase generally represents more than 50% by volume of the entire material, and in some cases even more than 90% by volume. The properties of the glass-ceramic are therefore more closely related to the properties of the crystalline phase than to the glass from which they are derived.

Vitroceramics for which the crystalline phase is a mica, as described for example in the patent
No. 3,689,293, are particularly suitable for use as a material for dental prostheses. Indeed, these materials have, due to the tight interweaving of the mica crystals, a micro-structure called "in a house of cards". The fracture lines follow either the mica cleavage planes or the mica-glass interfaces. The propagation of cracks or fractures in a direction normal to the basic planes of the mica crystals is very difficult.

These glass-ceramics are said machinable, because they can be cut and shaped by the tools and processes usually used for metals. They contain, as major crystalline phase, fluorophlogopite crystals (KMg3AlSi3O10F2) and / or borofluorophlogopite crystals (KMg3BSi301oF2).

It has subsequently been found that vitroceramics containing a fluorinated tetrasilicic mica as a major crystalline phase have advantages over glass-ceramics containing a crystalline phase of fluorophlogopite. Such fluorinated tetrasilicic mica vitroceramics are described, for example, in European Patent Application No. 22,655. An exemplary crystalline phase is fluorinated tetrasilicic mica having the formula KMg25Si4010F2.

A13 + and B3 + ions have been replaced by Si4 +. This modification of the crystalline phase has made it possible to improve the chemical stability and the mechanical strength of glass-ceramics. Further improvement has been made in these vitroceramics containing fluorinated tetrasilicic mica by the addition of small amounts of alumina or zirconia to the compositions. This addition has had the effect of improving the resistance to coloring, which is an important point when glass-ceramics are used for the production of dental prostheses.

 A technique for manufacturing a dental prosthesis consists, from an impression of the dental arch, to prepare a mold for the prosthesis, for example by the lost wax method, and to project by centrifugation, a molten glass in the mold. The glass ingot is obtained industrially by melting its constituents and refining.

After cooling the glass piece obtained, it undergoes a ceramization treatment after coating in a ceramization coating, intended to limit dimensional variations. After ceramization, the prosthesis is translucent and must undergo makeup to integrate properly into the oral environment. The makeup is made by applying an opaque ceramic and a coloring ceramic which undergo a heat treatment.

 The present inventors have now discovered that, surprisingly, it is possible to prepare, by high temperature melting, vitreous lithium materials, which can be converted into glass-ceramics by a heat treatment, the lithium, which is a volatile element, being preserved. both in vitreous materials and in the crystalline phase of glass-ceramics. In addition, the crystalline phase can be obtained at temperatures lower than those required to ceramise vitreous materials of the same type containing no lithium, and by shorter heat treatments.

 The present invention relates to vitreous materials convertible by a heat treatment glass-ceramic.

 The subject of the invention is also glass-ceramics made from said vitreous materials, as well as dental prostheses constituted by these glass-ceramics.

The vitreous materials according to the invention are characterized
in that they are obtained by melting an initial mixture having the following composition, expressed as a percentage by weight
SiO2 45-70
MgF2 12-20
MgO 8-15
Li2O 3-10
CaO 0-10
M2O + M'O 5-20
A1203 + ZrO2 2-9
TiO2 0-7
Conventional dyes
for 0-10 glasses
- M20 representing one or more oxides
selected from K2O, Cs20 and Rb20,
- M'O representing BaO and / or SrO
the quantity of M'O, in number of moles, being less than or equal to 50% of the quantity of M2O.

the weight percentage in Au 2 O 3 being less than or equal to 3 and the weight percentage in ZrO 2 being less than or equal to 6,
and in that they can be converted by heat treatment into machinable glass-ceramics whose crystalline phase has the crystalline structure of tainiolite.

A preferred vitreous material according to the invention is obtained by melting an initial mixture having the following composition, expressed as a percentage by weight
SiO2 45-70
MgF2 12-20
MgO 8-15
Li2O 3-10
CaO 0-10
K2O 5-20
Au203 + ZrO2 2-9
Conventional dyes 0-10 the weight percentage in A1203 being less than or equal to 3 and the percentage in ZrO2 being less than or equal to 6.

The composition of the glass obtained, expressed in atomic percentages, is as follows
If 15-25
Ca 0- 5 Al 0- 3
Zr 0- 2

Al + Zr: 0.5-5
F 5-15
K 2-10
Mg 4-15
Li 1-10
0 45-65
This preferred family of vitreous materials makes it possible to obtain vitroceramics containing the actual tainiolite, KLiMg2Si4010F2, as a crystalline phase.

 Differential thermal analysis of vitreous materials according to the invention is essentially characterized by three exothermic peaks at 570 ° C., 885 ° C. and 985 ° C., respectively.

 The first exothermic peak at 570 ° C. corresponds to the formation of tainiolite in the form of spherical particles.

Indeed, the X-ray diffraction pattern obtained for a vitreous material according to the invention having undergone a prolonged annealing at 580 ° C. exhibits the characteristic lines of the tainiolite corresponding to ASTM sheet No. 15-237. The width of the lines formed indicates that the crystallites are small, of the order of 100 nm. This fact is confirmed by the scanning micrographs performed on the annealed vitreous material at 580 ° C, which further show the spherical shape of the crystallites.

 The second exothermic peak at 885 ° C. corresponds to the growth of platy tioliolite crystallites well separated by a few microns in length At about 800 ° C., the spherical crystallites begin to grow to become platelets. At 885 ° C almost all of the crystallites are in the form of platelets.On the X-ray diffraction pattern corresponding to a material treated at a temperature greater than 885 ° C, for example at 950 ° C, the characteristic lines tainiolite are always present, but they are finer, which confirms the growth of crystals.

 The third exothermic peak around 985 ° C corresponds to the formation of enstatite, MgSiO3.

The crystalline structure of the tainiolite is a monoclinic structure consisting of leaflets parallel to the (a, b) plane, and separated from each other by large cations (K +,
Cs +, Rb +, and optionally Ba2 + or Sr2 +). Each sheet has four anionic layers between which small cations are intercalated, for example Mg + and Li + ions, which are located at the center of the sheet in coordination 6, the silicon ions in coordination 4, are placed on either side of the octahedra.

 It therefore appears that the vitreous materials according to the invention can be converted into vitroceramics containing tainiolite as the essential crystalline phase, by a heat treatment at a temperature of between 800 ° C. (corresponding to the beginning of the second thermal anomaly) and 985 ° C. C.

 The process for transforming the vitreous material according to the invention into a glass-ceramic whose crystalline phase is of the tainiolite type consists in bringing said vitreous material to a temperature of between 800 ° C. and 985 ° C., to maintain it at this temperature for a period of time. between 10 minutes and 1 hour, then cool slowly to room temperature.

 It is particularly desirable to use a ceramization temperature of 950 ° C. and to bring the material to this temperature at a rate of 8 to 10 C./min, a cooling of 10 to 15 C / min, and more particularly of 12 C / min. mn, is particularly suitable.

 The glass-ceramics obtained from the vitreous materials according to the invention are characterized in that they comprise at least 30% of a crystalline phase having the crystallographic structure of tainiolite. Vitroceramics containing at least 50% by volume tainiolite phase are particularly suitable for the preparation of dental prostheses.

 To obtain a dental prosthesis from the vitreous materials according to the invention, the vitreous material is sprayed, in the molten state, directly into the mold corresponding to the prosthesis, and ceramized in this mold.

 The present invention is illustrated in more detail with the aid of the examples below given by way of illustration, but without limitation.

EXAMPLE 1
Preparation of a lithiated glass
In a high frequency induction furnace, the following mixture was melted at 1400 ° C. for 90 minutes to obtain a glass
Silo2 12.244 g
MgF2 3,411
MgO 2.51
LiF 1,517
K2O 2,755
AlF3 0.21
Z2 2 0.874
CaO 0.673
The chemical composition of the glass obtained V1 was determined by analysis with the electronic micro-probe, and by flame spectrometry for the determination of lithium.

The following results, expressed as atomic percentages, were obtained
If 19.62
Ca 0.11
Al 0.456
Zr 0.58
F 11,998
K 3,765
Mg 10.186
Li 2,691
O 50.594
EXAMPLE 2
Preparation of a vitroceramic to spread glass
The glass V1 obtained in Example 1, which has excellent flowability, was sprayed by melt centrifugation into a preheated mold. After cooling to room temperature, the resulting part was coated with a plaster binder ceramizing coating, and then the whole was heated to 950 ° C at a rate of 8 ° C / min, which took about 2 hours .

The assembly was held at 950 ° C for 20 minutes and then cooled to 200 ° C at 12 C / min.

The totality of the treatment therefore required approximately 2h30.

The radiocrystallographic analysis of the glass ceramic C1 obtained indicates the presence of tainiolite in strong favor.

Microscopic examination of this glass ceramic reveals
in scanning: a microstructure consisting of closely interlocking platelets, a few microns long.

 in transmission: characteristic facies of the tainiolite with fringes spaced about 1 nm apart, corresponding to the parameter c of the structure.

 The proportion of crystalline phase tainiolite is evaluated at 55% by volume.

 FIG. 1 represents the X-ray diffraction pattern (KS radiation of cobalt) of the glass-ceramic obtained. In this diagram, the diffraction angle e in degrees is plotted in abscissa. The specific lines of tainiolite are identified by the letter T.

EXAMPLE 3
From several samples of the glass V1 obtained in Example 1, glass ceramics C2 to C6 were prepared according to the procedure of Example 2, by modifying the ceramization temperature and maintaining it for 1 hour. The temperature of the treatment, the nature and the proportion of the phases (expressed as a percentage by volume) constituting the glass-ceramics obtained are collated in the following Table 1
TABLE 1

<tb> Vitroceramic <SEP> Temperature <SEP> Tainiolite <SEP> MgSiO3 <SEP> Phase <SEP> amorphous
<tb><SEP> n "<SEP>
<tb><SEP> C2 <SEP> 800 <SEP> 40 <SEP> 10 <SEP> 50
<tb><SEP> C3 <SEP> 900 <SEP> 60 <SEP> 10 <SEP> 30
<tb><SEP> C4 <SEP> 950 <SEP> 70 <SEP> 15 <SEP> 15
<tb><SEP> C5 <SEP> 1000 <SEP> 60 <SEP> 1 <SEP> 20 <SEP> 20
<tb><SEP> C6 <SEP> 1050 <SEP> 60 <SEP> 20 <SEP> 20
<Tb>
From these results, it appears that, at 800 ° C, a large proportion of tainiolite is formed, the optimum temperature being around 950 ° C. At higher temperatures, it is formed at the expense of tainiolite.

EXAMPLE 4
The various glass samples V1 to V4, whose compositions are summarized in Table 2 below, were subjected to a ceramization treatment similar to that of Example 2, but maintaining the temperature at 900 ° C for 1 hour.

TABLE 2

Glass <SEP> Composition <SEP> Chemical <SEP> 0 <SEP> Ceramic
<tb><SEP> obtained
<tb><SEP> If <SEP> F <SEP> C <SEP> Al <SEP> Mg <SEP> K <SEP> Zr <SEP> Li + O
<tb> V1 <SEP> 19.62 <SEP> 11.99 <SEP> 0.11 <SEP> 0.45 <SEP> 10.18 <SEP> 3.76 <SEP> 0.58 <SEP> 53 , 31 <SEP> C7
<tb> V2 <SEP> 19.76 <SEP> 9.42 <SEP> 0.11 <SEP> 0.11 <SEP> 11.66 <SEP> 3.63 <SEP> 0.67 <SEP> 54 , 64 <SEP> C8
<tb> V3 <SEP> 20.02 <SEP> 7.61 <SEP> 0.098 <SEP> 0.18 <SEP> 11.57 <SEP> 4.38 <SE> 0.69 <SE> 54.57 <SEP> C9
<tb> V4 <SEP> 21.42 <SEP> 7.35 <SEP> 0.094 <SEP> 0.12 <SEP>;<SEP> 9.70 <SEP> 4.46 <SEP> 0.58 <SEP > 55.43 <SEP> ClO <SEP>
<Tb>
The nature and the proportion, expressed as a percentage by volume, of the phases constituting each glass-ceramic obtained are given in Table 3 below.
TABLE 3
Vitroceramic Tainiolite MgSiO3 amorphous phase
C7 60 10 30
C8 60 20 20
C9 30 20 50
C10 30 20 50
COMPARATIVE EXAMPLE
A glass is marketed under the trademark DICOR by
Corning Glass Works and recommended for the preparation of dental prostheses. The proposed ceramization treatment consists in bringing the glass to 1070 ° C in 90 minutes, maintaining this temperature for 6 hours, or better still, for 9 hours, and then cooling for 1 hour.The minimum duration of the entire treatment The glass-ceramic obtained contains KMg2.5si4010F2 as the crystalline phase.

 Dicor glass has now been applied a heat treatment similar to that used to obtain the glass-ceramics according to the invention, namely: heating the glass to bring it to 950 ° C. at a rate of 8 ° C./min, maintaining the temperature at 950 ° C for 20 minutes, then cooling at 12 ° C / min.

 The X-ray diffraction pattern (Kx radiation of cobalt) shown in FIG. 2 shows that there is obtained a crystalline phase corresponding to mica KMg2.5Si4O10F2, whose lines are indexed M.

 If one compares this diagram with that obtained, under the same conditions, from the glass-ceramic according to the invention of Example 2 (FIG 1), it is found, by evaluating the heights of respective peaks, that the proportion The crystalline phase in the material according to the invention is at least three times that of the crystalline phase of the glass-ceramic obtained from DICOR glass.

 The vitreous materials according to the invention are therefore particularly well suited for the preparation of dental prostheses. They can be converted into a glass-ceramic, and therefore, in dental prostheses, at temperatures of the order of 950 ° C, in a relatively short time, of the order of 2:30 to 3:30, which is a saving of time and of significant energy compared to vitreous materials of the prior art.

Claims (9)

 1. Glassy materials, characterized in that  they are obtained by melting an initial mixture having the following composition, expressed as a percentage by weight  SiO2 45-70  MgF2 12-20  MgO 8-15  Li2O 3-10  CaO 0-10  M2O + M'O 5-20  A1203 + Zr 2 2-9  TiO2 0-7  Conventional dyes  for 0-10 glasses  - M2O representing one or more oxides  chosen from K2O, Cs2O and Rb2O,  - M'O representing BaO and / or SrO  the quantity of M'O, in number of moles, being less than or equal to 50% of the quantity of M2O.  the weight percentage of Al 2 O 3 being less than or equal to 3 and the weight percentage of Z 2 being less than or equal to 6.  and in that they can be converted by heat treatment into machinable glass-ceramics whose crystalline phase has the crystalline structure of tainiolite.  2. vitreous material according to claim 1, characterized in that the initial mixture has the following composition  SiO2 45-70  MgF2 12-20  MgO 8-15  Li2O 3-10  CaO 0-10  K2O 5-20  Au203 + ZrO2 2-9  Ti 2 O- 7  Conventional dyes 0-10  the weight percentage in Al 2 O 3 being less than or equal to 3 and the weight percentage in ZrO 2 being less than or equal to 6.  3. vitreous materials according to one of claims 1 or 2, characterized in that they have the following composition, expressed in atomic percentages  If 15-25  Ca 0- 5  Al 0- 3  Zr 0- 2  F 5-15  K 2-10  Mg 4-15  Li 1-10  O 45-65  the total Al + Zr being from 0.5 to 5  4. Application of a vitreous material according to any one of claims 1 to 3, to the preparation of vitroceramics comprising, as essential crystalline phase, a crystalline phase of tainiolite type.  5. Application according to claim 4, characterized in that it consists in bringing the vitreous material to a temperature between 800 "C and 985" C, maintain it at this temperature for a period of between 10 minutes and 1 hour, then to cool.  6. Application according to claim 5, characterized in that the vitreous material is heated to a temperature of 950 ° C at 8 to 10 C / min, it is maintained at this temperature for 20 minutes, then cooled with 12 "C / min.  7. Glass ceramic comprising as essential crystalline phase a crystalline phase tainiolite type, obtained from a glass material according to any one of claims 1 to 3.  8. Vitroceramic ceramic according to claim 7, characterized in that the crystalline phase consists essentially of KLiMg2Si4O10F2.  9. Vitroceramic ceramic according to one of claims 7 and 8, characterized in that it is obtained in the form of a dental prosthesis.