IMPRESSION COMPOSITION

Abstract: The present invention provides an impression composition of the alginate type which comprises (a) an alginate, (b) calcium sulfate and/or lead silicate, and (c) a filler as its main components and which is characterized in that the alginate component comprises in combination an alginate having a distribution of molecular weights in the lower range and an alginate having a distribution of melecular weights in the higher range.

Description: The present invention relates to an impression composition of the alginate type. Dental impression materials are used for preparing, for example, an impression of a decayed tooth to remedy tie tooth. Impression materials include those of the alginate type, silicon type and polysulfide type. In view of economy and ease of handling, alginate impression materials are generally, used; see e.g. GB-A- 2090272 which discloses a two-component system comprising an alkali metal alginate. Many characteristics are required for impression materials. For example, they must have a dust-free property, be compatible with water and easy to knead, possess high rubber elasticity and high strength, exhibit a smooth texture on gelation, afford smooth-surfaced plaster models and be readily usable in combination with ager. However, none of the conventional impression materials fulfill all of these requirements. The main object of the present invention is to provide an impression composition which fulfills all the characteristics required of impression materials, such as dust-free property, ease of kneading, rubber elasticity, strength, surface smoothness or gloss and amenability to combination use. The present invention provides an impression composition of the alginate type which comprises (a) an alginate, (b) calcium sulfate and/or lead silicate, and (c) a filler as its main components and which is characterized in that the alginate component comprises in combination an alginate having a distribution of molecular weights in the lower range and an alginate having a distribution of melecular weights in the higher range as defined in claim 1. Examples of alginates (a), calcium sulfates (b) and fillers (c) useful for the invention are those already known for use in conventional alginate impression materials. More specifically, suitable examples are sodium alginate, potassium alginate and alginic acid triethanolamine and like alginates, and calcium sulfate dihydrate, calcium sulfate hemihydrate, anhydrous calcium sulfate and like calcium sulfates. Lead silicate is usable singly or in combination with such a calcium sulfate. Examples of suitable fillers are kieselguhr, talc, silica, aluminum hydroxide and the like. The amount of components to be used in the invention are not limited specifically but can be determined from the ranges already known. It is especially suitable to use, for example, 5 to 25wt. % of the component (a), 5 to 30wt. % of the component (b) and the balance the filler, based on the combined amount of the three components. The impression composition of the present invention is characterized in that the component (a) comprises in combination an alginate having a distribution of molecular weights in the lower range (hereinafter referred to as "low-molecular-weight alginate") and an alginate having a distribution of molecular weights in the higher range (hereinafter referred to as "high-molecular-weight alginate"). The low-molecular-weight alginate is selected from among those having a viscosity of about 50 to about 900mPa.s as measured at 25°C using a B -type rotation viscometer when in the form of a 1% aqueous solution. The high-molecular-weight alginate is selected from among those having a viscosity of about 150 to about 1000mPa.s as measured under the same conditions as above. Such two alginates which differ from each other by at least about 100mPa.s preferably at least about 200mPa.s, in viscosity are used in combination. In the invention, the proportion of the low-molecular-weight alginate and the high-molecular-weight alginate is preferably in the range of 10 : 90 to 90 : 10 in weight ratio. We have further conducted research on useful alginates and found that when the alginic acid molecules present in the composition are up to 1 in the ratio of D-mannuronic acid (hereinafter abbreviated as "M") to L-guluronic acid (hereinafter abbreviated as "G"), i. e. in M/G ratio, the composition exhibits improved properties in respect of strain in compression, permanent deformation, compressive strength, etc. The M/G ratio was measured according to the method described in Acta Chemica Scandinavica 16, (1962) No. 8, p1908-1918. With the present invention, the M/G ratio is more preferably in the range of 0.3 to 1, most preferably in the range of 0.5 to 1. According to the present invention, materials other than the foregoing components, such as magnesium oxide and zinc oxide, can be added to the impression composition in an amount of 0.1 to 20wt. % to reduce the premanent deformation of the composition as kneaded. It is also possible to incorporate hexafluorotitanates, hexafluorozirconates and the like into the impression composition in order to assure the kneaded composition of reduced permanent deformation while minimizing the reduction in the strain thereof in compression and to give improved surface smoothness and gloss to plaster model prepared from the impression. To suitably adjust the gelation time, for example, to about 1 to about 5 minutes and thereby render the composition easy to handle, it is also desirable to add to the composition phosphates such as tertiary phosphates, pyrophosphates, tripolyphosphates and hexametaphosphate, oxalates, carbonates, etc. Such phosphates, oxalates and carbonates are used preferably in an amount of 0.05 to 5.0wt. % based on the composition . The components of the present composition can be mixed together by a known method of mixing powders or mixing powder and liquid. For example, the components are mixed together in a mixer or mixed together while being pulverized in a crusher-mixer. The impression composition of the invention is usable for preparing various impression. For example, for dental treatments and remedies, the composition is usable for preparing impressions of teeth. Further in making molds for metal casting, the composition is usable for preparing patterns of the configuration to be cast. In molding plastics, the impression is usable for preparing patterns of the shape to be molded. The impression composition of the present invention fulfills all the characteristics required of impression materials, such as dust-free property, ease of kneading, rubber elasticity, strength, surface smoothness and gloss, and amenability to combination use. Thus, the present composition is compatible with water to give a uniform paste rapidly, kneadable free from dust, affords smooth-surfaced plaster models and is readily usable in combination with agar. The composition has high rubber elasticity and strength and therefore assures very high dimensional stability. For example, the composition has outstanding characteristics of at least 10% in strain in compression, up to 3% in permanent deformation and at least 5000g in compressive strength as measured according to J I S T 6505. The invention will be described with reference to the following examples and comparative examples, in which percentages, other than those listed in Table 1, are all by weight. Example 1 An impression composition was prepared from 10% of sodium alginate (M/G ratio 1.3) having a viscosity of 100mPa.s (viscosity of 1% aqueous solution thereof as measured at 25°C by a B - type rotation viscometer, the same as hereinafter), 3% of sodium alginate (M/G ratio 1.3) having a viscosity of 600mPa.s, 12% of anhydrous calcium sulfate, 1 % of anhydrous Na₃P O₄, 74 % of kieselguhr and small quantities of propylene glycol, perfume and pigment. Example 2 An impression composition was prepared in the same manner as in Example 1 with the exception of using 6% sodium alginate (M/G ratio 1.3) having a viscosity of 100mPa.s, 6% of sodium alginate (M/G ratio 1.3) having a viscosity of 300mPa.s and 75% of kieselguhr. Example 3 An impression composition was prepared in the same manner as in Example 1 with the exception of using 10% sodium alginate (M/G ratio 1.3) having a viscosity of 100mPa.s, 5% of sodium alginate (M/G ratio 1.3) having a viscosity of 700mPa.s and 72% of kieselguhr. Example 4 An impression composition was prepared in the same manner as in Example 1 with the exception of using 10% sodium alginate (M/G ratio 1.3) having a viscosity of 100mPa.s and 3% of sodium alginate (M/G ratio 1.3) having a viscosity of 400mPa.s. Example 5 An impression composition was prepared in the same manner as in Example 1 with the exception of using 10% sodium alginate (M/G ratio 0.5) having a viscosity of 120mPa.s and 3% of sodium alginate (M/G ratio 1.3) having a viscosity of 690mPa.s. Example 6 An impression composition was prepared in the same manner as in Example 1 with the exception of using 10% sodium alginate (M/G ratio 0.75) having a viscosity of 120mPa.s and 3% of sodium alginate (M/G ratio 1.3) having a viscosity of 690mPa.s. Example 7 An impression composition was prepared in the same manner as in Example 1 with the exception of using 10% sodium alginate (M/G ratio 1.0) having a viscosity of 120mPa.s and 3% of sodium alginate (M/G ratio 1.3) having a viscosity of 690mPa.s. Comparative Example 1 An impression composition was prepared in the same manner as in Example 1 with the exception of using 12% of sodium alginate (M/G ratio 1.3) having a viscosity of 100mPa.s and 75% of kieselghur. Comparative Example 2 An impression composition was prepared in the same manner as in Example 1 with the exception of using 12% of sodium alginate (M/G ratio 1.3) having a viscosity of 300mPa. and 75% of kieselguhr Table 1 shows the M/G ratios of alginic acid properties of the compositions of the above Examples and Comparative Examples. The ease of kneading was determined by kneading 6.7g of the impression composition with addition of 15.7ml of water for about 30 seconds to prepare a paste. The composition was evaluated as good in ease of kneading when it was compatible with water and kneadable easily free from dust. When the ease of kneading thus determined is ordinary, the result is evaluated as being usual. In case the ease of kneading is low, the result is shown as poor. The strain in compression, permanent deformation and compressive strength were determined according to J I S T 6505 with use of the paste obtained in the above kneading test.

Claims: An impression composition comprising (a) an alginate, (b) calcium sulfate and/or lead silicate, and (c) a filler as its main components, characterized in that the alginate component comprises in combination (1) an alginate with a distribution of molecuar weights in the lower range and having a viscosity of about 50 to 900 mPa.s as measured at 25°C using a B-type rotation viscometer when in the form of a 1% aqueous solution and (2) an alginate with a distribution of molecular weights in the higher range and having a viscosity of about 150 to 1000 mPa.s as measured under the same conditions, the viscosities of the two alginates differing by at least about 100 mPa.s. An impression composition as defined in claim 1 wherein the viscosities of the two alginates differ by at least about 200 mPa.s. An impression composition as defined in claim 1 or 2 wherein the weight ratio of the alginate (1) having a distribution of molecular weights in the lower range and the alginate (2) having a distribution of molecular weights in the higher range is in the range of 10:90 to 90:10. An impression composition as defined in one or more of the claims 1-3 wherein the alginic acid molecules which constitute the alginate have a ratio of D-mannuronic acid to L-guluronic acid in the range of 0.3 to 1. An impression composition as defined in claim 4 wherein the alginic acid molecules which consititute the alginate have a ratio of D-mannuronic acid to L-guluronic acid in the range of 0.5 to 1.

Inventors: HIGASHIHATA, YOSHIHIDE, INOMATA, MINAKO, NAGANO, TORAHIKO, NISHIOKA, TAKASHI, SAITO, JOUJI, SAKUMA, HIROMICHI, TANAKA, YOSHITO, YAGI, TOSHIHARU, YUHARA, SUMIKO
Applicants: DAIKIN INDUSTRIES, LIMITED
Application year: 1987
Main classification: A61K6
IPC codes: C08L5, A61K6