FECHER STEFAN (DE)
DEGUDENT GMBH (DE)
| WO2012175450A1 | 2012-12-27 | |||
| WO2012175615A1 | 2012-12-27 | |||
| WO2013053865A2 | 2013-04-18 |
| FR2454796A1 | 1980-11-21 | |||
| US4784606A | 1988-11-15 | |||
| BE618738A | ||||
| US20130295523A1 | 2013-11-07 | |||
| US20070042889A1 | 2007-02-22 | |||
| DE19750794A1 | 1999-06-17 | |||
| DE10336913B4 | 2014-01-09 | |||
| DE102009060274A1 | 2011-06-30 | |||
| EP2662342A1 | 2013-11-13 | |||
| DE3015529A1 | 1980-11-06 | |||
| US4784606A | 1988-11-15 | |||
| DE2401275A1 | 1974-07-18 |
R.R. SEGHI: "Effects of Ion Exchange on Hardness and Fracture Toughness of Dental Ceramics", THE INTERNATIONAL JOURNAL OF PROSTHODONTICS, vol. 5, no. 4, 1992, pages 309 - 314
DIN EN ISO 6872, January 2009 (2009-01-01)
| Patent claims Method to increase the strength of a form body of lithium silicate glass ceramic 1. Method to increase the strength of a form body of lithium silicate glass ceramic in the form of a dental object (20), in particular a bridge or a part of a dental object, wherein the form body once it has a desired final geometry and application of a material that influences the surface (22) of the form body, such as a smoothing and/or color-imparting material, such as a glaze material, veneering material and/or stain material, is subject to heat treatment to form a coating characterized in that the material is applied to the surface except for at least one region (32, 33, 34) of the surface (22) of the form body, and the heat treatment is carried out and thereafter to generate a surface compressive stress through the replacement of lithium ions by alkali ions of greater diameter at least that region not covered by the coating is covered by a melt or paste of a salt, or a melt or paste containing a salt, of an alkali metal or a number of alkali metals with ions of greater diameter, that the form body is in contact with the melt or paste for a time t at a temperature T and the melt or paste is then removed from the form body. 2. Method according to claim 1, characterized in that the form body (20) during the ion exchange is completely covered by the melt / paste. 3. Method according to claim 1 or 2, characterized in that a portioned quantity of salt is used for the melt. 4. Method according to at least one of the foregoing claims, characterized in that the paste is applied at least to the region (32, 33, 34) of the form body (20) not covered by the material. 5. Method according to at least one of the foregoing claims, characterized in that the region or those regions (32, 33, 34) of the form body (20) that are subject to a tensile stress remain uncovered by the material. 6. Method according to at least one of the foregoing claims, characterized in that the form body (20) at least in several regions (32, 33, 34) which are subject to a tensile stress, in particular in its basal region, does not have a coating that is formed by application of the material and subsequent heat treatment. 7. Method according to at least one of the foregoing claims, characterized in that a salt body is prepared from the salt as the portioned quantity from the alkali metal / alkali metals through pressing or compression and that the salt body is laid on the form body or the form body is laid directly or indirectly on the salt body and then the salt body is melted. 8. Method according to at least one of the foregoing claims, characterized in that the form body (20) is laid in a receptacle having perforations, such as a wire basket, and that thereafter - the receptacle with the form body is dipped in the melt or - the receptacle with the form body is introduced into the salt and the salt is then melted or the receptacle with the form body is placed on the salt or the salt body and the salt is melted concurrently with immersion of the form body in the melt which is forming. 9. Method according to at least one of the foregoing claims, characterized in that the form body (20) is enveloped by a heat-resistant foil that contains the portioned quantity of salt and that the salt is then melted. 10. Method according to at least one of the foregoing claims, characterized in that the portioned salt is made available in a receptacle such as a capsule, with a closure that can be removed, for example by tearing off. 11. Method according to at least one of the foregoing claims, characterized in that to the alkali metal salt, which enables ion exchange, a phosphate salt, such as K2HPC4, is added for the binding of lithium ions. 12, Method according to at least one of the foregoing claims, characterized in that Na, K, Cs and/or Rb ions are used as alkali metal ions to generate the surface compressive stress. 13. Method according to at least one of the foregoing claims, characterized in that the form body (20) is annealed in a melt containing potassium ions, in particular in a melt containing KN03, KC1 or K2CO3, or a melt containing sodium ions, in particular in a melt containing NaN03, sodium acetate or sodium salts of organic acids, or in a melt containing a mixture of potassium ions and sodium ions, in particular in a ratio of 50:50 molar percentage, preferably in a melt containing NaN03 and KN<¾. 14. Method according to at least one of the foregoing claims, characterized in that the form body (20) is annealed at a temperature T where T > 300 °C, in particular 350 °C < T < 600 °C, preferably 430 °C < T < 530 °C, for a time t, in particular where t > 5 minutes, preferably 0.5 hours < t < 10 hours, especially preferred 3 hours < t < 8 hours. 15. Method according to at least one of the foregoing claims, characterized in that the form body (20) is prepared from a glass melt which contains at least the following as starting components: Si02, A1203, Li20, K20, at least one nucleating agent such as P2O5 and at least one stabilizer such as Zr02. 16. Method according to at least claim 15, characterized in that the form body (20), or a blank from which the form body is manufactured, is prepared from a glass melt that contains the following components in percentage by weight: - Tb407 0 - 8, preferably 0.5 - 6, especially preferred 1.0 - 2.0 optionally an oxide or a number of oxides of an earth alkali metal or a number of earth alkali metals from the group magnesium, calcium, strontium, barium 0 - 20, preferably 0-10, especially preferred 0-5, optionally one or more additives from the group B203, Mn02, Fe203, V205, TiO2, Sb203, ZnO, Sn02 and fluorides 0-6, preferably 0-4, - optionally one or more oxides of the rare earth metals with the atomic numbers 57, 59 - 64, 66 - 71, in particular lanthanum, yttrium, praseodymium, erbium, europium, 0-5, preferably 0-3. 17. Method according to at least claim 15, characterized in that the glass melt contains the following as starting components in percentage by weight Method according to at least claim 15, characterized in that the blank is fonned from the glass melt in the course of cooling or following cooling to room temperature, said blank then being subject to at least one first Corresponding salts can also be used for the paste. The invention is preferably characterized in that the form body is annealed in a melt containing potassium ions, in particular a melt containing KNO3, KC1 or K2CO3, or a melt 5 containing sodium ions, in particular a melt containing NaN<¾, sodium acetate or sodium salts of organic acids, or in a melt containing a mixture of potassium ions and sodium ions, in particular in a ratio of 50:50 mol.%, preferably in a melt containing NaN03 and KNO3. Independently thereof, the form body may be covered with a viscous solution or dispersion 0 of the salt as the paste. To ensure that there is a constant ion exchange potential during ion exchange, this invention further proposes that lithium ions entering the salt are bound. In particular it is proposed to bind lithium ions by adding a salt such as an alkali metal phosphate salt, like5 K2HPC>4- to the alkali metal salt enabling ion exchange. The salt containing lithium, such as phosphate, is precipitated in the melt. Independently thereof, the required ion exchange in the surface region is found to be especially good if the form body is annealed in the melt, or is in contact with a0 corresponding paste, at a temperature T > 300 °C, in particular 350 °C < T < 600 °C, preferred 430 °C < T < 530 °C, for a period of time t > 5 minutes, in particular 0.5 hours < t < 10 hours, especially preferred 3 hours < t < 8 hours. Shorter annealing/contact times in the region of up to 30 minutes are in principle sufficient5 to create the desired surface compressive stress in the surface region. Insofar as an increase in strength of the form body down to a depth of 20 μηι or more is desired, then longer contact / annealing times of, for example, 6 or 10 hours will be necessary, depending on the annealing temperature. 0 The paste covering the form body, to enable ion exchange, preferably has the same composition in terms of potassium metal ions as the melt referred to above. To enable the salt to be melted in an energy-conserving and controlled manner to the required temperature and to anneal the form body for the desired length of time the 23. Method according to claim 22, characterized in that the paste is applied to the form body (20) or at least to that region (32, 33, 34) not covered by the coating through spraying on to the form body. 24. Method according to at least one of the foregoing claims, characterized in that to prepare the paste the salt is mixed with at least one substance from the following group: non-flammable substance, monohydric or polyhydric alcohols, halogenated hydrocarbon compound, water, in particular from the group 1,4- butanediol, hexanetriol, acetone, water, or a mixture of one or more substances. 25. Method according to at least one of the foregoing claims, characterized in that the paste is preferably applied to all the surfaces of the form body (20), in particular at a thickness D of at least 0.5 mm, in particular at 1 mm < D < 3 mm. 26. Form body (20) in the form of a dental object, in particular a bridge or a part of a dental object of lithium silicate glass ceramic, wherein the surface (22) of the form body has a fired coating at least over regions through a material applied to the form body such as a glaze material, veneering material and/or stain material and subsequent heat treatment, characterized in that the coating is confined exclusively to regions of the surface (22) of the form body (20) and that at least in the region (32, 33, 34) of the form body not covered by the coating a surface compressive stress is generated through the replacement of lithium ions by alkali metal ions of greater diameter. 27. Form body according to claim 26, characterized in that there is no coating at least in the basal region (24) of the form body (20), in particular in the basal region of connectors of a bridge. Form body according to claim 26, characterized in that there is no coating in the region of the region (32, 33, 34) subject to a tensile stress of the form body (20). Form body according to claim 26, characterized in that the alkali metal ions are Na, K, Cs and/or Rb ions, in particular Na ions or K ions, or Na and K ions. Form body according to claim 26, characterized in that the glass phase of the form body (20) or a blank from which the form body is prepared, contains at least one stabilizer, in particular in the form of Zr02, that increases the strength of the form body, the concentration of which in the starting composition of the form body is preferably 8 - 12% by weight. Form body according to at least claim 26, characterized in that the form body (20) is prepared from a glass melt that contains the following components in percentage by weight - Tb407 0-8, preferably 0,5 - 6, especially preferred 1.0 - 2.0 - optionally an oxide or a number of oxides of an earth alkali metal or a number of earth alkali metals from the group magnesium, calcium, strontium, barium 0 - 20, preferably 0-10, especially preferred 0-5, - optionally one or more additives from the group B20?, Mn02, Fe203, V205, Ti02, Sb203, ZnO, Sn02 and fluorides 0-6, preferably 0-4, - optionally one or more oxides of the rare earth metals with the atomic numbers 57, 59 - 64, 66 - 71, in particular oxide/oxides of lanthanium, yttrium, praseodymium, erbium, europium, 0-5, preferably 0-3. Form body according to at least claim 26, characterized in that the form body (20) is prepared from a glass melt that contains the following components in percentage by weight: Form body according to at least claim 26, characterized in that the form body has a glass phase in the range 20 - 65% by volume Form body according to at least claim 26, characterized in that the fonn body contains lithium silicate crystals between 35% and 80% by volume of the body (20). Form body according to at least one of claims 26 to 34, characterized in that the percentage of alkali ions replacing the lithium ions, commencing from the surface of the region (32, 33, 34) not covered by coating down to a depth of 10 μιη is in the range 5 - 20% by weight, and/or at a depth between 8 and 12 μηι from the surface the percentage of alkali ions is in the range 5 - 10% by weight, and/or at a layer depth of between 12 and 14 μηι from the surface the percentage of alkali ions is in the range 4 - 8% by weight, and/or at a depth from the surface between 14 and 18 μιη the percentage of alkali ions is in the range 1 - 3% by weight, wherein the percentage by weight of the alkali ions diminishes from layer to layer. |
Method to increase the strength of a form body of lithium silicate glass ceramic
Method to increase the strength of a form body of lithium silicate glass ceramic in the form of a dental object (20), in particular a bridge or a part of a dental object, wherein the form body once it has a desired final geometry and application of a material that influences the surface (22) of the form body, such as a smoothing and/or color-imparting material, such as a glaze material, veneering material and/or stain material, is subject to heat treatment to form a coating
characterized in that
the material is applied to the surface except for at least one region (32, 33, 34) of the surface (22) of the form body, and the heat treatment is carried out and thereafter to generate a surface compressive stress through the replacement of lithium ions by alkali ions of greater diameter at least that region not covered by the coating is covered by a melt or paste of a salt, or a melt or paste containing a salt, of an alkali metal or a number of alkali metals with ions of greater diameter, that the form body is in contact with the melt or paste for a time t at a temperature T and the melt or paste is then removed from the form body.
2. Method according to claim 1,
characterized in that
the form body (20) during the ion exchange is completely covered by the melt / paste. Method according to claim 1 or 2,
characterized in that
a portioned quantity of salt is used for the melt.
Method according to at least one of the foregoing claims,
characterized in that
the paste is applied at least to the region (32, 33, 34) of the form body (20) not covered by the material.
Method according to at least one of the foregoing claims,
characterized in that
the region or those regions (32, 33, 34) of the form body (20) that are subject to a tensile stress remain uncovered by the material.
Method according to at least one of the foregoing claims,
characterized in that
the form body (20) at least in several regions (32, 33, 34) which are subject to a tensile stress, in particular in its basal region, does not have a coating that is formed by application of the material and subsequent heat treatment.
Method according to at least one of the foregoing claims,
characterized in that
a salt body is prepared from the salt as the portioned quantity from the alkali metal / alkali metals through pressing or compression and that the salt body is laid on the form body or the form body is laid directly or indirectly on the salt body and then the salt body is melted.
Method according to at least one of the foregoing claims,
characterized in that
the form body (20) is laid in a receptacle having perforations, such as a wire basket, and that thereafter
- the receptacle with the form body is dipped in the melt or - the receptacle with the form body is introduced into the salt and the salt is then melted or
- the receptacle with the form body is placed on the salt or the salt body and the salt is melted concurrently with immersion of the form body in the melt which is forming.
9. Method according to at least one of the foregoing claims,
characterized in that
the form body (20) is enveloped by a heat-resistant foil that contains the portioned quantity of salt and that the salt is then melted.
10. Method according to at least one of the foregoing claims,
characterized in that
the portioned salt is made available in a receptacle such as a capsule, with a closure that can be removed, for example by tearing off.
11. Method according to at least one of the foregoing claims,
characterized in that
to the alkali metal salt * which enables ion exchange, a phosphate salt, such as K2HP04, is added for the binding of lithium ions.
12. Method according to at least one of the foregoing claims,
characterized in that
Na, K, Cs and/or Rb ions are used as alkali metal ions to generate the surface compressive stress.
Method according to at least one of the foregoing claims,
characterized in that
the form body (20) is annealed in a melt containing potassium ions, in particular in a melt containing KNOj, KC1 or or a melt containing sodium ions, in particular in a melt containing NaNC^, sodium acetate or sodium salts of organic acids, or in a melt containing a mixture of potassium ions and sodium ions, in particular in a ratio of 50:50 molar percentage, preferably in a melt containing NaN0 3 and KNO 3 .
Method according to at least one of the foregoing claims,
characterized in that
the form body (20) is annealed at a temperature T where T > 300 °C, in particular 350 °C < T < 600 °C, preferably 430 °C < T < 530 °C, for a time t, in particular where t > 5 minutes, preferably 0.5 hours < t < 10 hours, especially preferred 3 hours < t < 8 hours.
Method according to at least one of the foregoing claims,
characterized in that
the form body (20) is prepared from a glass melt which contains at least the following as starting components: SiC>2, AI2O3, LijO, K.2O, at least one nucleating agent such as P 2 O 5 and at least one stabilizer such as Zr0 2 .
Method according to at least claim 15,
characterized in that
the form body (20), or a blank from which the form body is manufactured, is prepared from a glass melt that contains the following components in percentage by weight:
- Tb 4 0 7 0-8, preferably 0.5— 6, especially preferred 1.0 - 2.0
- optionally an oxide or a number of oxides of an earth alkali metal or a number of earth alkali metals from the group magnesium, calcium, strontium, barium
0 - 20, preferably 0-10, especially preferred 0-5,
- optionally one or more additives from the group B
T1O2, Sb 2 0 3 , ZnO, Sn0 2 and fluorides
0-6, preferably 0-4,
- optionally one or more oxides of the rare earth metals with the atomic numbers 57, 59 - 64, 66 - 71, in particular lanthanum, yttrium, praseodymium, erbium, europium,
0-5, preferably 0-3.
Method according to at least claim 15,
characterized in that
the glass melt contains the following as starting components in percentage by weight
Method according to at least claim 15,
characterized in that
the blank is formed from the glass melt in the course of cooling or following cooling to room temperature, said blank then being subject to at least one first heat treatment Wl at a temperature T W1 for a time twi, wherein 620 °C < Twi≤ 800 °C, in particular 650 °C < T W t < 750 °C, and/or 1 minute < t W i < 200 minutes, preferably 10 minutes < twi < 60 minutes.
Method according to at least claim 18,
characterized in that
the first heat treatment Wl is carried out in two steps, wherein in particular in the first step a temperature Tsn is set where 630 °C < Tsn < 690 °C and/or in the second step a temperature T ST2 where 720 °C < Tse≤ 780 °C and/or the heating rate ASH up to the temperature Tsu is 1.5 K/minute < Asu < 2.5 K/minute and/or the heating rate Ase up to the temperature Τ ¾ ι is 8 K/minute < T St2 < 12 K/minute.
Method according to at least claim 18,
characterized in that
the lithium silicate glass ceramic blank is subjected, after the first heat treatment Wl, to a second heat treatment W2 at a temperature Tw 2 for a time tw 23 wherein 800 °C < T W2 < 1040 °C, preferably 800 °C < T W 2 < 870 °C, and/or 2 minutes ≤ tw2≤ 200 minutes, preferably 3 minutes < tw2≤ 30 minutes.
Method according to at least claim 18,
characterized in that
after the first or second heat treatment step, in particular after the first heat treatment step, the form body (20) is prepared from the blank through grinding and/or milling or pressing, wherein the heat treatment step or steps is/are carried out during or after pressing.
Method according to at least claim 1 ,
characterized in that
the form body (20), or at least that region (32, 33, 34) not covered by the coating, is coated with a viscous solution or dispersion of the salt as the paste. Method according to claim 22,
characterized in that
the paste is applied to the form body (20) or at least to that region (32, 33, 34) not covered by the coating through spraying on to the form body.
Method according to at least one of the foregoing claims,
characterized in that
to prepare the paste the salt is mixed with at least one substance from the following group: non-flammable substance, monohydric or polyhydric alcohols, halogenated hydrocarbon compound, water, in particular from the group 1,4- butanediol, hexanetriol, acetone, water, or a mixture of one or more substances.
Method according to at least one of the foregoing claims,
characterized in that
the paste is preferably applied to all the surfaces of the form body (20), in particular at a thickness D of at least 0.5 mm, in particular at 1 mm < D < 3 mm.
Form body (20) in the form of a dental object, in particular a bridge or a part of a dental object of lithium silicate glass ceramic, wherein the surface (22) of the form body has a fired coating at least over regions through a material applied to the form body such as a glaze material, veneering material and/or stain material and subsequent heat treatment,
characterized in that
the coating is confined exclusively to regions of the surface (22) of the form body (20) and that at least in the region (32, 33, 34) of the form body not covered by the coating a surface compressive stress is generated through the replacement of li thium ions by alkali metal ions of greater diameter.
Form body according to claim 26,
characterized in that
there is no coating at least in the basal region (24) of the form body (20), in particular in the basal region of connectors of a bridge. Form body according to claim 26,
characterized in that
there is no coating in the region of the region (32, 33, 34) subject to a tensile stress of the form body (20).
Form body according to claim 26,
characterized in that
the alkali metal ions are Na, K, Cs and/or Rb ions, in particular Na ions or K ions, or Na and K ions.
Form body according to claim 26,
characterized in that
the glass phase of the form body (20) or a blank from which the form body is prepared, contains at least one stabilizer, in particular in the form of Zr0 2 , that increases the strength of the form body, the concentration of which in the starting composition of the form body is preferably 8— 12% by weight.
Form body according to at least claim 26,
characterized in that
the form body (20) is prepared from a glass melt that contains the following components in percentage by weight
- Tb 4 0 7 0-8, preferably 0,5 - 6, especially preferred 1.0 - 2.0
- optionally an oxide or a number of oxides of an earth alkali metal or a number of earth alkali metals from the group magnesium, calcium, strontium, barium
0 - 20, preferably 0-10, especially preferred 0-5,
- optionally one or more additives from the group B
Ti0 2 , SbsOs, ZnO, Sn0 2 and fluorides
0— 6, preferably 0-4,
- optionally one or more oxides of the rare earth metals with the atomic numbers 57, 59 - 64, 66— 71 , in particular oxide/oxides of lanthanium, yttrium, praseodymium, erbium, europium,
0— 5, preferably 0— 3.
Form body according to at least claim 26,
characterized in that
the form body (20) is prepared from a glass melt that contains the following components in percentage by weight:
Form body according to at least claim 26,
characterized in that
the form body has a glass phase in the range 20— 65% by volume Form body according to at least claim 26,
characterized in that
the form body contains lithium silicate crystals between 35% and 80% by volume of the body (20).
Form body according to at least one of claims 26 to 34,
characterized in that
the percentage of alkali ions replacing the lithium ions, commencing from the surface of the region (32, 33, 34) not covered by coating down to a depth of 10 μηι is in the range 5 - 20% by weight, and/or at a depth between 8 and 12 μηι from the surface the percentage of alkali ions is in the range 5 - 10% by weight, and/or at a layer depth of between 12 and 14 μηι from the surface the percentage of alkali ions is in the range 4 - 8% by weight, and/or at a depth from the surface between 14 and 18 μηι the percentage of alkali ions is in the range 1 - 3% by weight, wherein the percentage by weight of the alkali ions diminishes from layer to layer.
In particular it is provided for the salt comprising one or more alkali metal salts to be pressed/compressed into a salt body and for it to be laid on the form body or for the form body to be laid on it and the salt body then melted, so that the salt melt completely envelops the fonn body and the desired ion exchange can take place. The form body may be accommodated in this process in a receptacle with perforations.
To enable ion exchange to be carried out using a melted salt that as mentioned may be a single alkali salt or a number of alkali salts, or which may contain them, the salt may be made available in aliquots in a receptacle - referred to below as the second receptacle - such as a capsule with a closure that can be removed by tearing or twisting. The second receptacle may at the same time be used as a receptacle for the form body, so that the salt is melted with the form body lying on the salt. There is naturally also the possibility of first melting the salt and then immersing the fonn body in the melt. The description above also embraces the possibility of first surrounding the form body with salt and then melting it. There is also the possibility of immersing the form body in the melt in a receptacle with perforations such as a wire basket.
To enable a simple handling of the fonn body, i.e., to facilitate its immersion in the melt or remo val from the melt without difficulty in a further development of the invention the form body is introduced with the first receptacle into a receptacle containing the salt, referred to below as the third receptacle.
The invention is also characterized in that the form body is coated with a viscous alkali metal salt solution or dispersion as the paste. To this end it is in particular provided for one or a number of alkali metal salts to be mixed with at least one substance from the following group: a non-flammable substance, monohydric or polyhydric alcohols, a halogenated hydrocarbon compound, water, in particular one of the group 1 ,4-butanediol, hexanetriol, acetone, water, or a mixture of one or more substances. For the paste alkali ions, in particular Na or K ions, are used to generate the surface compressive stress. independently thereof, the paste may be applied to the fonn body to the extent that all ss D of not less than 0.5 mm, preferably 1 mm < D < 3 ram, should be maintained. Naturally the paste may also be applied only to those regions in which there is no coating and ion exchange is to take place.
According to the invention it is in particular also provided for the glass phase to be 20 - 65% by volume, in particular 40 - 60% by volume.
The invention is consequently characterized by a form body in which the lithium silicate crystals are present in the range 35 - 80% by volume and in particular 40 - 60% by volume. Lithium silicate crystals here mean the sum of lithium disilicate crystals, lithium metasilicate crystals and lithium phosphate crystals if P9O5 is contained.
The form body is in particular characterized in that the concentration of alkali metal ions that replaces the lithium ions, in particular if potassium ions are used, from the surface of the region not covered by the coating down to a depth of 10 μπι is in the range 5 to 20% by weight. At a depth between 8 and 12 μηι from the surface the alkali ions should be present in the range 5 to 10% by weight. At a depth between 12 and 14 μηι from the surface the alkali ions should be present in the range 4 to 8% by weight. At a depth of between 14 and 18 μπι from the surface the corresponding range for the alkali ions is between 1 and 3% by weight. The percentage by weight of the alkali ions diminishes from layer to layer.
As mentioned, the percentage by weight values do not take into account the alkali ions already present in the form body. The numerical values hold in particular for potassium ions. Further details, advantages and characteristics of the invention derive not just from the claims, the characteristics to be derived from them - alone and/or in combination - but also from the examples given below.
Figures
Fig. 1 A schematic representation of a bridge as a form body, and
Fig. 2 A schematic representation of the test apparatus set-up for three-point ement. It should firstly be exemplified that as a result of the replacement of lithium ions present in the glass component of a form body of a lithium silicate glass ceramic with alkali metal ions of greater diameter the surface compressive stress is increased, leading to an increase in strength,
In the tests described below at least raw materials, such as lithium carbonate, quartz, aluminum oxide, zirconium oxide, were mixed in a drum mixer until a visually uniform mixture resulted. The compositions according to the data of the manufacturers used for the tests are given below.
The following holds in principle for the tests given below:
The mixture in question was melted at a temperature of 1500 °C for a period of 5 hours in a high-temperature resistant, platinum alloy crucible. The melt was subsequently poured into molds to derive rectangular bodies (blocks). The blocks were subsequently subjected to a two-step heat treatment, designated the first heat treatment step, to create lithium metasilicate crystals as the main crystal phase (1st treatment step). The blocks were thereby heated in the first heat treatment step Wl at a heating rate of 2 K/minute to 660 °C and held at that temperature for 40 minutes. They were then heated further to 750 °C at a heating rate of 10 K/minute. The specimens were held at that temperature for 20 minutes. This heat treatment influences nucleation and lithium metasilicate crystals are formed.
The blocks were then subjected to a second heat treatment step W2 (2nd treatment step) to form lithium disilicate crystals as the main crystal phase. In this heat treatment step the blocks were maintained at a temperature T 2 for a period of time t 2 . The corresponding values are given below. They were then cooled to room temperature.
The cooled blocks were then machined to yield bending rods (specimens) of rectangular shape (3rd treatment step), through grinding of the blocks. The bending rods had the following dimensions: length 15 mm, width 4.1 mm and height 1.2 mm. The specimens were then polished (treatment step 4). A simulated glaze firing was then carried out (5th treatment step), i.e., a temperature treatment without any material being applied to the bending rods (specimens). For some specimens a glaze material was applied after d a firing carried out (6th treatment step) to create an coating layer. The temperature treatment (firing) was carried out at a temperature between 650 °C and 800 °C.
In this procedure, as can be seen schematically in Fig. 2, the glaze may be applied exclusively to that side of the specimens (6th treatment step) on which a loading piston and thus a force F acts so that a three-point measurement of fiexural strength is earned out as specified in DIN EN ISO 6872:2009-01. As Fig. 2 further makes clear, no material is applied to the opposite side 50 so that no coating can result upon firing. The glaze or glaze layer is indicated by the number 16 in Fig. 2. The rectangular specimen itself is indicated by the number 10. The Figure also shows that the side surfaces of the specimen 10 and the front faces are not coated.
The three-point flexural strength measurements were earned out as specified in DIN EN ISO 6872:2009-01. For this purpose the specimens (small rods) 10 were mounted on two supports 12, 14 at a distance of 10 mm apart as shown in Fig. 2. A loading piston acted on the specimens between the rods 10, with the tip in contact with the specimen having a radius of 0.8 mm.
For the fabrication of the blocks the following initial composition was adopted (in percentage by weight) according to the data of the manufacturers, to derive lithium silicate glass and therefrom lithium silicate glass ceramic material.
The glass phase was in the range 40 - 60% by volume.
The final crystallization (second heat treatment step) to form the lithium disilicate crystals was carried out at a temperature T 2 = 830 °C for a period of time t 2 - 5 minutes. A total of 70 rods were prepared and treatment steps 1 to 5 carried out for them. The following tests were performed with them.
Test series #1
Ten of these rods, for which treatment steps 3 - 5 were performed, without material application, were then tested to determine their strength. The mean value obtained in the three-point flexural strength test referred to above was 358 MPa. Test series #2
Ten further rods were then annealed in a salt bath of technically pure KN0 3 at a temperature of 480 °C for 10 hours. The rods were then removed from the melt and the melt residues removed using warm water. Three-point flexural strength measurements were then carried out as described above. The mean three-point flexural strength value was 870 MPa.
Test series #3 Ten of the 70 rods were annealed in a technically pure KNO 3 salt bath at a temperature of 480 °C for 10 hours. A glaze material was then partially applied to the rods - as shown in Fig. 2 - to one side upon which the force F acts and the specimens were fired at a temperature T 3 = 660 °C, maintained for a period t 3 = 60 seconds. A mean three-point flexural strength value of 407 MPa was obtained.
Test series #4
Ten rods as in test series #3 were first annealed in a technically pure KNO 3 salt bath at a temperature of 480 °C for 10 hours. A glaze material was then partially applied to the rods to the side upon which the force F acts and the specimens were fired at a temperature T 3 = 680 °C maintained for a period t 3 = 60 seconds. A mean three-point flexural strength value of 381 MPa was obtained. Test series #5
Ten further rods - as in test series #3 and #4 - were first annealed in a technically pure KNO3 salt bath at a temperature of 480 °C for 10 hours. As before, a glaze material was then partially applied to the side upon which the force F acts and the specimens were fired at a temperature T 3 = 750 °C, maintained for a period t 3 = 90 seconds. A three-point flexural strength value of 326 MPa was obtained.
Test series #6
A further 10 rods were partially coated with a glaze material on that side on which the stamp acts in the three-point flexural strength measurement test, i.e., the force F, as indicated in Fig. 2. The region 50 which is subject to tensile stresses therefore remained uncovered. The same held for the sides. Firing was carried out at a temperature T 3 = 750 °C for a period t 3 = 90 seconds. The specimens were then annealed as described for test series #2 in a technically pure KNO3 salt bath at a temperature of 480 °C for 10 hours. The specimens were removed from the melt and melt residues removed and three-point flexural strength measurements carried out, and as described above the force was applied to that side of the rod which bore the coating layer 16 (glaze). A mean three-point flexural strength value of 874 MPa was obtained.
Test series #7
The remaining 10 rods were coated in their entirety with a glaze material. A glaze firing was then carried out at a temperature T 3 = 750 °C for a period t 3 = 90 seconds. The specimens were then annealed as described for test series #2 in a technically pure KNO 3 salt bath at a temperature of 480 °C for 10 hours. The specimens were removed from the melt and melt residues removed and three-point flexural strength measurements carried out as described above. The three-point flexural strength value was 353 MPa.
It was found in these tests that when ion exchange was carried out to increase the hardness of the surfaces prior to further heat treatment - in this case the glaze firing - the surface compressive stress previously attained through the ion exchange was reduced again. The likely reason for this was that during the further heat treatment the potassium ions diffuse further into the specimens to a degree that the surface compressive stress is lost.
If a coating (glaze) is applied to all parts of the specimen bodies then the glaze forms a diffusion block so that an increase in the hardness of the surfaces is not possible in principle.
A partial application of a material required for a coating by contrast does not influence the desired creation of a surface compressive stress through the replacement of lithium ions by alkali metal ions of greater diameter, insofar as at least the zone subject to tensile stress remains uncovered, i.e., has no coating applied to it.
Fig. 1 shows a dental form body in the form of a three-element bridge 20 that is fabricated from a lithium disilicate ceramic material, with its outer surface 22 provided with a glaze in the labial, buccal and occlusal regions and at the very maximum partially in basal region 24. The basal region 24, and in regions 32, 33 of the connectors 30, 31 and the basal region 34 of the intermediate member 36 are free of glaze. To arrive at this the bridge 20 was only partially covered with a glaze material or other material forming a coating through firing such as a stain material or composite ceramic material.
The basal region 24 not covered by the glaze ends in the embodiment example at a distance to the bridge anchor edge 35, 37. This allows a layer which elicits an aesthetically pleasing effect to be applied between the corresponding bridge anchor edge 35, 37 and in regions of the basal regions 32, 33, 34. This region to which the layer has been applied extends in Fig. 1 between the respective bridge anchor edge 35 / 37 and the near point 40 / 42. In the sectional representation the basal regions 32, 33 and the basal region 34 of the tooth bridge 20 extend partially between the points 40, 42 and remain uncovered, i.e., do not have a layer applied to them which elicits an aesthetically pleasing effect to facilitate ion exchange in these regions. The internal surface of the bridge 20, i.e., the inner region of the bridge anchor 28, is also uncovered so that - as with the state of the art - imprecise fit through a glaze can be avoided.
The strength of corresponding bridges 20 of a lithium silicate ceramic material with in the main crystal phase is significantly higher than those for which the procedure according to the invention was not carried out. It is possible to obtain values that are more than 100% higher than those for bridges fabricated according to the state of the art. The prerequisite is that lithium ions are replaced by alkali metal ions of greater diameter according to the teaching of the invention in regions in which an elevated tensile stress is seen, i.e., in particular in the basal regions, i.e., for bridges in particular at the undersides of intermediate elements 36 and connectors 30, 31 that are regions of the outer surface.