Dental investment material

Abstract

To provide an irreversible expansion agent-containing dental investment material applicable for metal casting, where the dental investment material incorporates a component that exhibits irreversible expansion upon heating, making it possible to compensate for metal casting shrinkage even at low mold temperatures.SOLUTION: A dental investment material powder comprises silicone powder.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a dental embedding material containing an irreversible expansion agent used in the dental field.

Background Art

[0002] When indirectly producing a metal prosthetic device in dental defect restoration, a method called the lost wax method is generally used. The explanation of this method is as follows.

[0003] In dental defect restoration, an impression material, a profile material, is used to take the defect form, and a model material such as plaster is poured into it to produce a model that reproduces the patient's defect form outside the oral cavity. Next, wax is used on this model to reproduce the form to be restored to obtain a prototype. This prototype is called a wax pattern. To replace the obtained wax pattern with metal, a mold is produced. The mold is made by pouring a slurry kneaded with a powder material called an embedding material and a liquid material such as water or / and a colloidal silica aqueous solution into a profile material to embed the wax pattern. After the embedding material hardens, it is heated to burn out the wax pattern in the mold, and molten metal is poured into the space of the formed mold. Further, after cooling, the mold is broken to take out the casting, and the target metal prosthetic device can be obtained. This lost wax method is generally used to produce these prosthetic devices.

[0004] These investment materials generally include gypsum-based investment materials used for alloys with relatively low melting points (low-melting alloys) such as gold alloys, silver alloys, and gold-silver-palladium alloys; phosphate-based investment materials used for alloys with relatively high melting points (high-melting alloys) such as gold alloys for porcelain firing, semi-precious alloys for porcelain firing, and Ni-Cr alloys and Co-Cr alloys; and non-phosphate-based investment materials, including alumina cement and magnesia cement, used for metals with even higher melting points and higher reactivity, such as titanium and titanium alloys. These investment materials consist of a powder and a liquid. The powder contains a binder to maintain the shape of the mold and a refractory material to impart heat resistance to the mold. The liquid is an aqueous solution containing water and / or colloidal silica. The powder and liquid are mixed in appropriate amounts, and the mold is produced by the reaction and hardening of these materials.

[0005] In general, in dental casting, casting shrinkage occurs when molten alloy is poured into the mold cavity. Therefore, to ensure a proper fit, an expanded mold is required to compensate for this casting shrinkage. Here, casting shrinkage of metal refers to both the solidification shrinkage that occurs when the molten alloy solidifies and the thermal shrinkage that occurs when the solidified material cools to room temperature. Obtaining a mold that compensates for casting shrinkage is achieved through both the hardening expansion that occurs when the investment material hardens and the thermal expansion that occurs when the hardened mold is heated.

[0006] For example, the composition of a phosphate-based investment material is as follows: the powder contains magnesium oxide and monoammonium phosphate as binders, silica, alumina, and zirconium silicate as refractory materials, and the liquid material consists of an aqueous solution containing water and / or colloidal silica. A mold can be made by mixing and hardening these materials. By adjusting the concentration of the aqueous solution containing colloidal silica in the liquid material, a total expansion (sum of hardening expansion and heating expansion) that matches the casting shrinkage of various metals can be obtained.

[0007] Hardening expansion can be varied depending on the particle size and concentration of colloidal silica. Furthermore, when the hardened mold is heated to 700-1000°C during the burning of the wax pattern, thermal expansion also occurs. The sum of this hardening expansion and thermal expansion compensates for the casting shrinkage of the metal and adjusts the fit of the prosthetic device.

[0008] If the mold temperature becomes excessively high when burning the wax pattern, the molten metal and mold material may react and stick together, forming a reaction layer, or the surface of the casting may become rough all over or partially, resulting in surface roughness. This can lead to poor fit due to surface removal of the casting. For example, in titanium casting, if the mold temperature is high, a thick reaction layer is formed between the titanium and the mold. Casting in a mold with a temperature of 700°C to 1000°C will cause a significant reaction and should be avoided. Preferably, casting in a mold at 400°C or lower, more preferably at room temperature, can suppress the reaction between titanium and the mold.

[0009] However, when casting at mold temperatures below 400°C, for example, silica used in refractory materials tends to shrink due to thermal expansion, which may not compensate for the casting shrinkage of the metal. Therefore, by adding components that undergo irreversible thermal expansion to the investment material, it is possible to compensate for the casting shrinkage of the metal even at low mold temperatures.

[0010] Patent Document 1 discloses a technique for compensating for casting shrinkage of metal by adding metallic zirconium powder. Specifically, this technique involves oxidizing metallic zirconium powder by heating it at a high temperature and utilizing the resulting volume expansion to compensate for casting shrinkage. However, with this technique, metallic zirconium powder readily reacts with oxygen, hydrogen, nitrogen, etc. in the atmosphere through oxidation, making it difficult to stably store the investment material over a long period of time.

[0011] Patent Document 2 discloses a technique for compensating for casting shrinkage of metals by adding alumina and magnesia. Specifically, this technique involves heating alumina and magnesia at high temperatures to cause a reaction that generates spinel, which irreversibly expands in volume and compensates for casting shrinkage. However, in this technique, the spinel reaction occurs rapidly at firing temperatures below 1200°C, so the amount of expansion that occurs will differ depending on the set temperature of the furnace used to fire the mold. Therefore, in furnaces with poor temperature distribution, the amount of expansion may differ in parts of the mold even within the same furnace, potentially leading to differences in mold fit.

[0012] Patent Document 3 discloses a technique for compensating for metal casting shrinkage by adding aluminum fine powder. Specifically, this technique involves mixing aluminum fine powder into the investment material and expanding the mold using the pressure of the hydrogen gas generated. However, this technique has problems such as the generation of bubbles due to the reaction between the metal and water, the generation of cracks during heating, and roughness of the casting surface after casting. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Application Publication No. 61-9940 [Patent Document 2] Japanese Patent Application Publication No. 1-31549 [Patent Document 3] Japanese Patent Application Publication No. 59-218237 [Overview of the project] [Problems that the invention aims to solve]

[0014] The present invention aims to provide a dental investment material that can be used for metal casting, which contains an irreversible expanding agent that expands irreversibly when heated, thereby compensating for metal casting shrinkage even at low mold temperatures. [Means for solving the problem]

[0015] As a result of diligent research into these issues, the inventors of this invention were able to arrive at the present invention. In other words, the present invention is a dental investment material powder characterized by containing silicone powder. [Effects of the Invention]

[0016] The effect of the present invention is that even at low mold temperatures, the expansion of the mold is maintained in a way that can stably compensate for the casting shrinkage of the metal. [Modes for carrying out the invention]

[0017] The dental investment material according to the present invention will be described in detail below. However, the present invention is not particularly limited to those exemplified below. The dental investment material of the present invention is composed of a powder and a liquid.

[0018] The silicone powders used in this invention include silicone rubber powder, silicone resin powder, and silicone composite powder having a silicone rubber portion and a silicone resin portion.

[0019] The silicone rubber powder in the present invention is a crosslinked polysiloxane powder having a structure in which a linear silicone main chain is crosslinked, and its functional group contains at least one of the following: alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group, undecyl group, dodecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, and eicosyl group; alkenyl groups such as vinyl group, allyl group, propenyl group, butenyl group, pentenyl group, hexenyl group, heptenyl group, octenyl group, decenyl group, undecenyl group, and dodecenyl group; allyl groups such as phenyl group, tolyl group, and naphthyl group; and aralkyl groups such as benzyl group and phenethyl group. Specific examples of silicone resin powders include cross-linked powders of polydimethylpolysiloxane and polydiethylpolysiloxane. The silicone resin powder in the present invention is a polyorganosylsesquioxane powder having a structure in which the silicone main chain is crosslinked in a three-dimensional network, and its functional group contains at least one of the following: alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group, undecyl group, dodecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, and eicosyl group; alkenyl groups such as vinyl group, allyl group, propenyl group, butenyl group, pentenyl group, hexenyl group, heptenyl group, octenyl group, decenyl group, undecenyl group, and dodecenyl group; allyl groups such as phenyl group, tolyl group, and naphthyl group; and aralkyl groups such as benzyl group and phenethyl group. Specific examples of silicone resin powders include polymethylsilsesquioxane and polyphenylsilsesquioxane powders. The silicone composite powder in the present invention is a powder having a structure in which the silicone rubber powder particles are coated with the resin of the silicone resin powder. The functional groups applied to the silicone rubber powder and silicone resin powder are the same as described above. Among the above-mentioned silicone powders, silicone resin powder is most preferable because it contains a relatively small amount of carbon in its structure and results in the greatest expansion of the mold.

[0020] When burning the wax pattern, the mold is heated in the temperature range of 700 to 1000°C. Therefore, in order to achieve the effects of the present invention, it is preferable that the oxidation start temperature of the silicone powder be 700°C or lower. In the present invention, the silicone powder undergoes volume expansion by oxidation at around 400°C, pushing out the particles of other refractory materials, causing the mold to expand. Even after cooling to room temperature, the oxidized and decomposed silicone powder does not shrink, maintaining the irreversible expansion of the mold. In gypsum-based investment materials, the binder, gypsum, decomposes at temperatures above 750°C and exhibits significant shrinkage. Therefore, it is desirable to fire gypsum-based investment materials at temperatures below 750°C. Consequently, if the oxidation start temperature of the added silicone powder is higher than 700°C, sufficient effects may not be obtained.

[0021] The compounding amount of the silicone powder added to the powder material of the present invention is preferably 0.1 to 10.0 wt%, more preferably 0.5 to 3.0 wt%. By adding an appropriate amount of the silicone powder in the present invention, the expansion due to the crystal growth of the binder during the hardening of the embedding material can be efficiently propagated, thereby increasing the hardening expansion. The embedding material added with the silicone powder in the present invention has an increased expansion amount of the mold during hardening, and when the mold expands irreversibly during heating, the expansion of the mold is maintained even when the mold is cooled, and the casting shrinkage of the metal can be compensated. When the compounding amount of the silicone powder is less than 0.1 wt%, there may be no expansion to compensate for the casting shrinkage, and when it exceeds 10.0 wt%, cracks may occur in the embedding material during incineration.

[0022] The average particle size of the silicone powder in the present invention is preferably 0.1 to 30 μm, particularly preferably 0.5 to 5 μm. If it is 30 μm or more, cracks may occur in the embedding material during incineration, and if it is less than 0.1 μm, there is a problem that expansion to compensate for the casting shrinkage cannot be obtained. Here, in the present invention, the "average particle size" means the particle size at 50% of the integrated value in the particle size distribution obtained by a precision particle size measuring device using the Coulter principle.

[0023] In the dental embedding material of the present invention, in order to exhibit the effects of the present invention, there is no particular limitation on the type of the binder. The same effects can be obtained in the phosphate-based embedding material using ammonium phosphate and magnesium oxide as the binder, the gypsum-based embedding material using dihydrate gypsum and hemihydrate gypsum as the binder, and the non-phosphate-based embedding material using alumina cement or magnesia cement as the binder.

[0024] Hereinafter, the phosphate-based embedding material will be described as an example. The phosphate-based embedding material contains magnesium oxide and monoammonium phosphate in the powder material, and undergoes a curing reaction by reacting with the liquid material to form a mold.

[0025] There are no particular restrictions on the type of magnesium oxide contained in the powder material constituting the dental investment material of the present invention, but higher purity is preferable, and finer particle size is also preferable. Hereinafter, "average particle size" in the present invention refers to the particle size at 50% of the cumulative value in the particle size distribution determined by laser diffraction-scattering method. The average particle size of magnesium oxide is not particularly limited, but it is preferably 15 to 40 μm, and more preferably 20 to 30 μm. Furthermore, it is preferable that the particle size distribution of magnesium oxide contains no more than 1.0 wt% of particles 100 μm or larger, and more preferably that it contains no particles 100 μm or larger. Multiple average particle sizes may also be combined. When multiple average particle sizes are combined, the average particle size after combination is preferably 15 to 40 μm. In order to achieve the effects of the present invention in the dental investment material of the present invention, the amount of magnesium oxide added is preferably in the range of 1 to 30 wt% relative to the investment material powder. If it is less than 1 wt%, sufficient mold strength may not be obtained, and it may become insufficient as a mold material. If it exceeds 30 wt%, the permeability of the mold decreases, and cracks or fissures may occur during incineration.

[0026] The ammonium monophosphate contained in the powder material constituting the dental investment material of the present invention is not particularly limited as long as it is soluble, and can be used without any problems regardless of average particle size or shape. However, since ammonium monophosphate acts as a binder in the investment material, it is preferable that the maximum particle size be small. In order to maintain the smoothness of the surface of the cast metal, it is preferable that there are no particles with a particle size of 60 μm or larger, and more preferably that 10 to 45 wt% of the particles with a particle size of 25 μm or smaller out of the particles with a particle size of 60 μm or less are present, and even more preferably that 20 to 35 wt% are present. In order for the effects of the present invention to be exhibited in the dental investment material of the present invention, the amount of ammonium monophosphate blended must be in the range of 1 to 30 wt% relative to the investment material powder. If the blending amount is less than 1 wt%, sufficient mold strength cannot be obtained, and it becomes insufficient as a mold material, and if it exceeds 30 wt%, the permeability of the mold decreases, and cracks or fissures may occur during incineration.

[0027] Next, regarding the mixing ratio of magnesium oxide and monoammonium phosphate contained in the powder material constituting the dental investment material of the present invention, it is preferable that the weight ratio of magnesium oxide / monoammonium phosphate is 0.3 to 1.0, and more preferably, magnesium oxide / monoammonium phosphate is 0.4 to 0.6.

[0028] Taking gypsum-based investment materials as an example, the type and manufacturing method of hemihydrate gypsum contained in the powder material constituting the dental investment material of the present invention are not particularly limited. For example, conventionally known α-type hemihydrate gypsum or β-type hemihydrate gypsum can be used alone or in combination. In order to exhibit the effects of the present invention in the dental investment material of the present invention, the amount of hemihydrate gypsum added is preferably in the range of 10 to 80 wt%, and more preferably 20 to 50 wt%, relative to the investment material powder. If the amount added is less than 10 wt%, sufficient mold strength cannot be obtained, and the material becomes insufficient as a mold material. If it exceeds 80 wt%, problems may arise such as a rough surface texture of the casting or insufficient thermal expansion.

[0029] Taking non-phosphate investment materials as an example, the alumina cement contained in the powder material constituting the dental investment material of the present invention is not particularly limited in type or manufacturing method, and commercially available grade products can be used, for example. In order to exhibit the effects of the present invention in the dental investment material of the present invention, the amount of alumina cement added is preferably in the range of 2 to 50 wt%, and more preferably 10 to 35 wt%, relative to the investment material powder. If the amount added is less than 2 wt%, sufficient mold strength cannot be obtained, and the material becomes insufficient as a mold material. If it exceeds 50 wt%, the problem of not being able to obtain sufficient thermal expansion may occur.

[0030] Next, the powder material constituting the dental investment material of the present invention contains a refractory material, but any refractory material used in dental investment materials can be used without any limitations. Specific examples include quartz, cristobalite, zirconium silicate, zirconia, spinel, alumina, amorphous silica, calcia, mullite, and yttria. To adjust the fluidity of the investment material, refractory materials with an average particle size of 5 to 300 μm can be used in combination.

[0031] While there are no particular restrictions on the amount of these refractory materials used in the dental investment material of the present invention to achieve the effects of the present invention, the total amount of refractory materials with low coefficients of thermal expansion, such as zirconium silicate, zirconia, spinel, alumina, and amorphous silica, is preferably 10 to 90 wt%. If the amount is less than 5 wt% or more than 90 wt%, cracks may occur in the investment material.

[0032] The liquid material used in combination with the dental investment material powder of the present invention is not limited, but colloidal silica aqueous solution, alumina sol aqueous solution, zirconia sol aqueous solution, water, etc., can be used, and colloidal silica aqueous solution is particularly preferred. [Examples]

[0033] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. For the particle size measurement of the silicone resin powder, a precision particle size analyzer using the Coulter principle was used. For the particle size measurement of magnesium oxide, a laser diffraction / scattering particle size distribution analyzer was used.

[0034] (Silicone resin powder used) As an irreversible expanding agent, a silicone resin powder with an average particle size of 2 μm was used. (Preparation of magnesium oxide) Magnesium oxide raw material was crushed and classified to prepare a product with an average particle size of 25 μm and a proportion of particles larger than 100 μm of 1 wt% or less. (Preparation of monoammonium phosphate) After grinding monoammonium phosphate, it was passed through a 250-mesh (60 μm) sieve and then sieved through a 500-mesh (25 μm) sieve until the particles below the sieve amounted to 30 wt%. (Preparation of hemihydrate gypsum) Hemihydrate gypsum was crushed and classified to prepare a material with an average particle size of 25 μm and a proportion of particles larger than 100 μm of 1 wt% or less. (Preparation of alumina cement) Alumina cement raw materials were crushed and classified to prepare a material with an average particle size of 3 μm and a proportion of particles larger than 50 μm of 1 wt% or less. (Preparation of fire-resistant materials) As refractory materials, alumina (77 μm, all-through), zirconium silicate (200 mesh (77 μm), all-through), cristobalite (200 mesh (77 μm), all-through), quartz (200 mesh (77 μm), all-through), and zirconia (200 mesh (77 μm), all-through) were used.

[0035] (Mixing of powdered materials) The powders listed in the example composition tables (Tables 1-5) were mixed, a small amount of air was added to a plastic bag, and the powder was stirred for 1 minute. The mixture was then sieved through a 1000 μm sieve to obtain the powder.

[0036] (Preparation of the liquid material (colloidal silica aqueous solution)) SN-ZL (manufactured by Nissan Chemical Corporation) was used as the aqueous solution containing colloidal silica. (Preparation of liquid material (water)) Tap water was used during the mixing process.

[0037] (Measurement of linear thermal expansion coefficient) Examples 1-14 and 16-19 below involved mixing the powder and liquid materials listed in the composition table, allowing them to harden. After heating to 900°C and cooling to 25°C according to the JIS T 6612:2020 standard (investment material for high-temperature dental casting, investment material for press ceramics, and refractory model material for ceramics), the linear thermal expansion coefficient at room temperature was measured. In Example 15, the maximum heating temperature was set to 700°C, and the linear thermal expansion coefficient at room temperature was measured using the same method. (Measurement of curing expansion rate) Examples 1 to 19 below used the powder and liquid materials listed in the composition table. A stainless steel ring with a diameter of 40 mm x height of 40 mm was lined with a ring liner, and the mixed slurry was filled inside. The curing expansion rate was measured by placing a dial gauge on the top surface of the mold. (Evaluation of overall expansion rate) The total expansion coefficient in the following examples was calculated as the sum of the linear thermal expansion coefficient at room temperature and the curing expansion coefficient obtained using the powder and liquid materials listed in the composition table.

[0038] Total expansion coefficient (comparative sample) For comparison, a reference sample was prepared that contained only the silicone powder, compared to the composition of the example, and the overall expansion rate was evaluated.

[0039] [Table 1]

[0040] [Table 2]

[0041] [Table 3]

[0042] [Table 4]

[0043] Examples 1-19 all showed a total expansion rate of 0.1% or more compared to the total expansion rate (comparative sample), indicating that it is possible to compensate for metal casting shrinkage even at low mold temperatures. Examples 13 and 14 confirmed that it can be used regardless of the type of binder. (effect) Based on the above results, the present invention has made it possible to obtain a dental investment material that can compensate for metal casting shrinkage even at low mold temperatures by using silicone powder.

Claims

1. A dental investment material powder characterized by containing silicone powder, wherein the silicone powder is one or more selected from silicone rubber powder, silicone resin powder, and silicone composite powder having a silicone rubber portion and a silicone resin portion. The aforementioned dental investment material is a dental investment material powder which is one of the following: a phosphate-based investment material with ammonium phosphate and magnesium oxide as binders; a gypsum-based investment material with dihydrate and hemihydrate as binders; or a non-phosphate-based investment material with alumina cement or magnesia cement as a binder.

2. The dental investment material powder according to claim 1, characterized in that it contains 0.1 to 10.0 wt% of the aforementioned silicone powder.

3. The dental investment material according to claim 1, characterized by containing 1 to 30 wt% magnesium oxide and 1 to 30 wt% monoammonium phosphate.

4. The dental investment material according to claim 1, characterized in that it contains 10 to 80 wt% hemihydrate gypsum as a binder.

5. The dental investment material according to claim 1, characterized in that it contains 2 to 50 wt% of alumina cement as a binder.

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