MX2009013702A - Ceramic nanocomposite for dental restoration and method for obtaining the same. - Google Patents

Abstract

The purpose of the present invention is to obtain a ceramic compound that mainly comprises powders of zirconium-alumina reinforced by alumina nanofibres. The mixture is subjected to a pressing process and sintered under specific conditions for obtaining solid preformed ceramics useful in a dental restorative system, which are made in cylindrical shapes of different sizes. Said material will modulate the hardness upon modifying the ratio of the components in order to obtain better mechanical properties which are suitable to be used in dental prosthesis.

Description

Ceramic nanocomposite for dental restorations and its method of obtaining OBJECT OF THE INVENTION The objective of the present invention is to obtain a ceramic compound comprising mainly aluminum oxide (alumina) - zirconia (zirconia) oxide doped with yttrium oxide (Itria), reinforced by alumina nanofibers (also called Whiskers by its name in English). The mixture is subjected to pressing and sintering under specific conditions to obtain solid ceramics preformed for a dental restorative system, made in cylindrical forms of different dimensions.

BACKGROUND There are patents and scientific articles that treat various types of ceramic materials and indirect restorative systems used as restorative materials for dental pieces, determining some parameters different from the present invention, such as the following: U.S. Patent 5,849,068 discloses a high strength ceramic prosthesis made by pressing a vitreous particle composition into a mold and 50% to 99% by weight of inorganic oxide particles sintered at temperatures of 1000 ° C up to 1200 ° for its application in crowns, bridges and intracoronal dental restorations. The glass ceramic composition preferably contains alumina powders, and / or zirconia powders, combined with glass powders; The compound of the invention is a glass-ceramic with content: Boron-alumino-boron-aluminate, zirconia and glass composition, Investigative material prepared by the mixture of 1.0 parts by weight of magnesium oxide, 1.0 parts of monoammonium phosphate in the following chemical composition: Zr02 with HFO2, 93.5%, 6.0% MgO, S1O2 < 0.4%, CaO < 0.2%, AI 2O3 < 0.2%, Fe2Ü3 < 0.1%, T1O2 < 0.2%. Preparation of the prosthesis; Zirconia (3Y-TZP) is liquefied with 3g of lanthanum boro alumino silicate glass and the mixture is sintered (baked) for one hour at 1100 ° C. After cooling the material is sifted to powder with a particle size smaller than 10 μ ??, then the primary powder incorporates 20g of glass of the following composition: S1O2 66.7%, AI2O3 10.5%, K2O 8.3%, Na20 7.4%, L21O 1.8%, CaO 3.2%, BaO 0.9%, Ce02 0.5%, F 0.7%. A dental prosthesis is obtained by molding a ceramic of zirconia and alumina content; The preparation is pressed at 25 MPa and sintered.

In U.S. Patent 5,916,498, a non-metallic prosthetic manufacturing process is described which includes a frame and a coating ceramic. The method describes the preparation of the framework by pressing in a mold a vitreous particle composition and from 99% to 50% by weight of inorganic oxide particles, under a pressure and a temperature from 800 ° C to 1300 ° C; covering the framework by the compound of the invention, which is a vitreous glass ceramic of lanthane-oborosilicate (S1O2, B2O3, AI2O3, La2O3, CaO, Zr02, Y203) to make a dental prosthesis whose application includes crowns and bridges.

In the United States Patent 6,126,732, a patent similar to the previous ones is described for the ceramic compounds, but with modifications in the method of preparation and filling to the mold.

In the United States Patent 6,120,591 of Fine Granule Leucite content, a porcelain composition for dental use containing a vitreous matrix embedded with leucite crystals processed in a temperature range from 600 ° C to 885 ° C is described; This feldspathic fine-grained leucite porcelain is useful for its application in dental restorations made of metal-porcelain, pure porcelain, intracoronal restorations, partial-coverage crowns and full crowns.

In the United States patent 6,133,174 of leucite content - porcelain compounds, a method for the production of machinable feldspathic porcelain based on leucite produced in block is described. The composition of the porcelain-leucite contains a vitreous matrix; the amorphous glass is melted to temperatures from 1400 ° C, up to 1700 ° C to produce a homogeneous vitreous compound, to be machined using diamond tooling techniques, especially under the CAD / CAM computer-aided design and manufacturing technology system, and includes a schematic diagram of the system CAD / CAM mentioned in some other patents such as United States patents 5,549,476; 5,527,182 and 5,775,912.

In the United States patent 6,155,830, a dental restoration for porcelain containing a matrix of leucite and ceramic oxide crystals, prepared at low melting 800 ° C, is described to be applied in combination to metallic or ceramic base structures. temperatures lower than 1, 200 ° C; unlike the present invention, it does not include zirconia which in the present invention is the main compound.

In U.S. Patent 6,375,729, a micaceous Vitro-ceramic is described that includes in its formula zirconia and alumina used in the manufacture of multi-unit dental restorations, using the CAD / CAM system; the components are mixed and melted at a temperature of 1400 ° C; for 4 hours, the vitreous mixture is processed with water and commercial pigments are added, as well as fluorescent agents, the powder is pressed in block and sintered at temperatures from 1400 ° C to 1600 ° C.

In the United States Patent 6,420,288, a process is described that describes the preparation and the formation of a translucent glass-ceramic lithium disilicate in rectangular blocks of 18x14x20mm to be machined under the CAD / CAM system and used in dental restorations, the components of the compound include: zirconia and alumina oxides, besides carbons and phosphates.

In United States Patent 6,495,073, a method for the manufacture and forming of parts for technical-dental purposes is described, under the following procedure: the ceramic powders are compressed in a compacted ceramic cube, are contoured in and out, and they are coupled for machining in a work receiving part, subsequently it is machined in presynthesized, with the help of diamond tools of the CAD / CAM system and finally the sintering.

The ceramic pieces can be made of aluminum oxide or zirconia, the preparation of the restoration requires a dental impression from which a positive model of plaster is obtained, which is measured with a three-dimensional recording equipment and under a program of specific software, machining is carried out by programmed erosion and milling of the material, subsequently it is sintered and receives chromatic characterization.

In US Pat. No. 6,517,623, the formula for lithium disilicate oxide (Li2 Si2 Os) based on compressed silica, lithium oxide, alumina, potassium oxide, phosphors and pigments used in the manufacture of dental restorations is described. The composition is melted between 1200 ° C to 1600 ° C in temperature cycles in ranges of 400 ° C, subsequently the glass ceramic is pulverized, pressed in the desired shape, or injected into a mold for dental restoration applications.

In United States Patent 6,797,048, the method of preparing a glass-ceramic based on leucite crystals under a compound of 53-65% by weight content of SiO 2 (silica oxide) 13-23% Al 203 (alumina ), 17-23% K20, the compound receives a heat treatment during mixing (750-950 ° C for 1-5 hours), with the addition of Zr02 (zirconia), CeO (ceria), MgO (magnesia), Y2Ü3 (Itria) ).

In the United States Patent 7,091, 142, the process for the production of a glass ceramic based on tetragonal leucite structured by the following compound is described: 58-75% by weight content of SiO 2 (silica oxide) 8-15 % Al203 (alumina), 7-15% K20, 1% CeO (ceria), 2% MgO (magnesia), the thermal treatment of the powders is carried out at 1000 ° C, the mixture is then subjected to a sintering of 1100 ° C for 1.5 hrs.

In the article Written by Se Fei Yang, Li Qiang Yang, Zhi Hao Jin, Tian Wen Guo, Wang Lei, Hong Chen Liu. Titled: New Size Composites Nanometric AI203-BN, Coated with 3Y-TZP to Produce Restorations CAD / CAM All Ceramics ,. Part I Powder Manufacturing (New nano-sized AI2O3-BN coating 3Y-TZP ceramic composites for CAD / CAM-produced all-ceramic dental restorations, Part I. Fabrication of powders), published in the journal Nanomedicine: Nanotechnology, Biology and Medicine , Volume 5, Issue 2, June 2009, Pages 232-239, describes the preparation of a ceramic compound (Y-TZP / alumina / h-BN) zirconia stabilized by Itria, alumina, making the mixture of powders in nitrate solution aluminum and 99% pure water, the powder is dried and the nitrate is removed by filtering, mixed in precipitated acetone, to calcinate the powders at 450 ° C for 2 hours, then at 1200 ° C for 1 hour.

In the article written by Duza. J. Entitled Microfractography of Advanced Ceramics. Key Engineering Materials Vol. 223 (2002): 107-118, the characteristics of a ceramic enriched with SiC whiskers are described, mentioning superior hardness results, the difference with the present material is that the whiskers or nanofibers are made of alumina and that being less hard BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a graph that represents the hardness values of the ceramic with respect to its content by weight of alumina nanofibers, with higher microhardness values observed for the compound containing 2% of nanofibers. Figure 2 is a graph that represents the values of fracture toughness of the ceramic with respect to its content by weight of alumina nanofibers, observing higher values to the fracture toughness to the content compound 2% of nanofibers.

Figure 3 is an image obtained by scanning electron microscopy of the fracture surface of the sintered ceramic composite.

Figure 4 is a photograph of the sintered ceramic composite.

Figure 5 is a photograph of the stainless steel molds in which the compaction of the ceramic powders is carried out.

DETAILED DESCRIPTION OF THE INVENTION The present invention presents a ceramic compound to be used in a system of direct dental restoration, presented in the form of cylindrical cartridges as shown in Figure 5, of different dimensions characterized by being constituted of alumina-zirconia compounds, reinforced by nanofibers of alumina, the solid ceramic cartridges are product of the following composition: Alumina AI2O3 particles 18% by weight percent Alumina nanofibers 2.0% by weight percentage Zirconia stabilized with Itria 80% of weight percentage Alumina powders (Al203 Baikalox SM8, Baikowski, USA) with a purity level of 99.99%), magnesium oxide (MgO, UBE Chemical Industries, Japan) > 99.999% degree of purity and zirconia (ZrC "2 + 3 mol.% Y2O3 abbreviated as TZ-3Y Tosoh, Japan)> 99.99% degree of purity, are used for the preparation of the ceramic compound.

The characteristics of particle size, surface area and theoretical density of the compounds mentioned above are indicated in Table 1: With the method proposed in the present invention, it is possible to modulate the hardness by modifying the proportion of the components and thus have better mechanical properties, suitable for use in dental prostheses.

As an example, the incorporation of nanowhiskers allows the modulation of the hardness of the ceramic, obtaining a more suitable material for dental applications since it does not wear the opposing teeth in the denture where the inserts are applied, as it happens with ceramics currently in use, representing this a substantial improvement to what exists within the state of the art.

Likewise, the tenacity values are better than those of the current ceramics.

PREPARATION OF THE COMPOUND The homogenous mixture of zirconia stabilized by Itria at 3% mole of a content by weight of 80% of the alumina compound, AI2O3 nanoparticles 18% by weight + nanofibers AI2O3 2.0% by weight, is prepared by dispersing the nanoparticles and the nanofibers of AI2O3 in 500 mL of acetone, undergoing a process of agitation to the ultrasound for 30 minutes to destroy agglomeration states. The nanopowders thus obtained are mixed in a magnetic stirrer with the Zirconia powder stabilized with Itria in a time range of 30 to 45 minutes to achieve an adequate dispersion of the alumina nanofibers until the acetone evaporates. Subsequently the mixture is dried at 100 ° C for 12 hrs. The AI2O3 powders used in the compound have been previously doped with 25 ppm of MgO in order to inhibit the growth of the grains during sintering.

That is to say that the steps for the preparation of the compound are the following: a) The nanoparticles and the nanofibers of AI2O3 are dispersed in 500 mL of acetone. b) The powders of a) are dosed with 25 ppm of MgO. c) The mixture of a) and b) is subjected to an ultrasound stirring process for 30 minutes. d) The nanopowders thus obtained are mixed in a magnetic stirrer with Zirconia powder stabilized with Itria in a time range of 30 to 45 minutes to achieve an adequate dispersion of the alumina nanofibers until the acetone evaporates. e) The mixture is dried at 100 ° C for 2 hrs.

The quantities of powders required for the manufacture of restorative cartridges of 2.5mm in diameter by 4.0mm in length, is equivalent to 0.5gr: 0. 4gr of zirconia powders doped with 3% Itria mole equivalent to 80% of the weight of the total compound. 0. 998gr of alumina doped by 0.025% magnesia equivalent to 18% of the weight of the total compound. 0. 002gr of alumina nanofibers equivalent to 2% of the weight of the total compound.

CERAMIC PRODUCTION PROCESS For the compacting of the ceramic powders, molds of specific measures of cylindrical shape shown in Figure 6 are used. Taking into account that there is a decrease of the diameter corresponding to 26.57%, therefore the diameter required in green to obtain ceramics of 2.5 mm, corresponds to 3.1 mm in diameter, the height of the compound when sintering it contracts a 24.43% in its millimeter length, according to contraction calculations, then the length of the sample in green should be 5.0mm, to obtain ceramics synthesized from 4.0mm in length Compaction and sintering To produce ceramic cartridges of the compound in specific dimensions of 2.5mm in diameter and 4.0mm in length, 0.5gr quantities of the powdered compound are required to be poured into the mold, subsequently the powders are subjected to uniaxial pressing in hydraulic press programmed at 50 Mpa, and at a constant compression rate of 30 kgf ls- The green ceramics are then placed in ceramic crucibles prepared with sintered powder beds of alumina and zirconia, the sintering of the ceramic compound is performed at a temperature of 1500 ° C for 2 hrs. In air at a heating rate of 10 ° C / m-. A photomicrograph of the already sintered compound can be seen in Figure 4.

STRUCTURAL CHARACTERISTICS AND MECHANICAL PROPERTIES OF SINTERED CERAMIC COMPOUND Relative density: 94.41% of the theoretical density of 5.636 gr./cm3 Average grain size: 0.37 + 0.15 μ ?? Mechanical properties.

Hardness of 12.54 Gpa Figure 1 Tenacity to fracture between 4.66 MPa m ½. Figure 2 Resistance to compression 1, 199.28 MPa. Table 2 Table 2 shows the values of superior compressive strength of the compound: 18.0% A1203 + 2.0% W + 80% Zr02 compared to other prepared compounds, observing a difference in favor of the compound with 2% alumina Whiskers compared to the rest compounds TABLE 2 Ceramic compounds Compressive strength (Mpa) A1203 Pure 618.85 + 436.03 80. 0% A1203 + 20% Zr02 481.22 ± 308.63 79. 5% A1203 + 0.5% W + 20% Zr02 604.55 + 402.88 79. 0% A1203 + 1.0% W + 20% Zr02 453.16 + 279.6 78. 5% A1203 + 1.5% W + 20%? 1? 2 419.67 + 168.84 78. 0% A1203 + 2.0% W + 20% Zr02 450.08 + 151.9 20. 0% A1203 + 80% Zr02-3Y 879.57 + 343.62 19. 5% A1203 + 0.5% W + 80% Zr02 749.18 + 358.06 19. 0% AI2O3 + 1.0% W + 80% Zr02 863.37 + 435.67 18. 5% A1203 + 1.5% W + 80% Zr02 905.23 + 237.32 18. 0% A1203 + 2.0% W + 80% Zr02 1, 199.28 ± 349.6 Zr02 Pure 525.2 + 183.4

Claims (8)

1. A ceramic compound to be used in a direct dental restoration system characterized because it comprises: a) 99.99% purity alumina powders doped by 0.025% magnesia comprising 18% of the total weight of the compound. b) Alumina nanofibers comprising 2% of the total weight of the compound. c) Zirconia powders doped with 3% Itria mole that constitute 80% of the total weight of the compound.

2. A ceramic compound to be used in a direct dental restoration system according to claim 1, characterized in that its composition is expressed as follows: 18% by weight of Al203 nanoparticles + 2.% by weight of Al203 nanofibers + 25 ppm MgO + 80% by weight of Zirconia stabilized with Itria.

3. A ceramic compound to be used in a direct dental restoration system according to claim 1, characterized in that its relative density is 94.41% of the theoretical density of 5,636 gr./cm3.

4. A ceramic compound to be used in a direct dental restoration system according to claim 1, characterized in that its average grain size is 0.37 μ ??. + 0.15μ ??

5. A ceramic compound to be used in a direct dental restoration system according to claim 1, characterized in that its average hardness of 12.77 GPa. + 1.1 GPa.

6. A ceramic compound to be used in a direct dental restoration system according to claim 1, characterized by manifesting a fracture toughness of 4.66 MPa m ½ + 0.75 MPa m ½

7. A ceramic compound to be used in a direct dental restoration system according to claim 1, characterized in that its high resistance to compression is 1, 199.28 MPa. + 349.6 MPa.

8. A method for the preparation of a ceramic compound to be used in a direct dental restoration system according to claims 1 and 2, characterized in that it comprises the following steps: a) The nanoparticles and the nanofibers of AI2O3 are dispersed in 500 mL of acetone. b) The powders of a) are dosed with 25 ppm of MgO. c) The mixture of a) and b) is subjected to an ultrasound stirring process for 30 minutes. d) The nanopowders thus obtained are mixed in a magnetic stirrer with Zirconia powder stabilized with Itria in a time range of 30 to 45 minutes to achieve adequate dispersion of the alumina nanofibers until the acetone evaporates. e) The mixture is dried at 100 ° C for 12 hrs.