GLASS CERAMICS COMPOSITION

Abstract: A glass ceramics composition suitable for use as materials for live bodies such as dental materials, surgical materials or industrial articles, which consists, on the weight basis, of 15 - 40 % CaO, 15 - 35 % TiO2 + Ti2O3 and 35 - 65 % P2O5, the degree of crystallization thereof being not less than 20 %. The composition can further contain, based on 100 parts by weight of the above-mentioned three components, not more than 20 parts by weight of silicon oxide and/or boron oxide and not more than 20 parts by weight in total of one or more members selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, zinc oxide, aluminum oxide and transition metal oxides except for titanium oxides, each member not exceeding 5 parts by weight, the degree of crystallization thereof being not less than 20 %. The oxygen atoms of the above-mentioned oxides may be partially replaced with fluorine atom, chlorine atom and/or hydroxyl group.

Description: SPECIFICATION GLASS CERAMICS COMPOSITION The present invention relates to a glass ceramics composition suitable for use as materials for live bodies, particularly dental materials such as artificial dentition, crown of a tooth, root of a tooth, inlary and bridge, surgical materials such as an artificial bone or artificial joint, or industrial articles such as an electrically insulative plate, capacitor, various substrates and thread guide. The application range of ceramics has recently been remarkably developed. Ceramics has been much in demand not only as industrial materials, but also in the medical field. Particularly a calcium phosphate-containing glass ceramics has been noted as having a bioaffinity. In this field, such glass ceramics there has heretofore been predominantly used a silicate glass (containing, for example, 40 to 80 wt % or often more SiO,) , but recently CaO-P-O, glass ceramics almost or entirely free of SiO has been developed (for example, see Japanese Patent Publication No. 11625/80) . This ceramics has a composi- tion near that of an inorganic salt of bone and, therefore, it has a good bioaffinity and has been developed to be utilized as bioceramics such as artificial root of a tooth or artificial crown of a tooth. The "glass ceramics" is a polycrystal obtained by reheating a shaped glass article to crystallize the glass. When this crystallization process is a surface crystallization (the crystallization starts at the surface of a shaped glass article) , the resultant glass ceramics is generally poor in mechanical strength, a long period of time is required for the crystallization, and cracks are easily produced in the glass ceramics when manufactured. Therefore, the bulk crystallization (crystallization uniformly proceeds in the whole of a shaped glass article) is desired. A glass having such a composition as disclosed in the above-mentioned Patent Publication No. 11652/80 has a tendency of surface crystallization and, therefore, it can be used when it is a thin shaped article but otherwise questionable. Since calcium phosphate is an inorganic com¬ ponent of bones or enamels of live bodies, a ceramic material containing a great amount of the calcium phosphate is expected as a material having a good bioaffinity. Processes for preparing such a ceramic material are roughly classified in (a) a process in which a powder is compacted and then fired at a high tempera¬ ture and (b) a process in which a glass is provided and then reheated to be crystallized in a polycrystalline ceramics. The former requires the pressing step and is difficult to produce a complicated shape of an article with good precision. The latter can easily achieve the formation of an article with good. recision. An example of the latter is disclosed in the above-mentioned Patent Publication No. 11625/80. However, the calcium phosphate-containing glass has a tendency to so-called surface crystallization by which the crystallization starts at the surface of glass. Therefore, the resultant glass ceramics has vacancies produced therein, and glass ceramics having an adequate mechanical strength is relatively difficult to produce with ease and stability. Furthermore, the color tone of the resultant glass ceramics is not ivory but undesirably white, particularly not preferred for the artificial dentition or crown of a tooth. Generally, so-called bulk crystallization by which the crystallization starts uniformly inside a glass article is very important to produce a high strength glass ceramics. The object of the present invention is to eliminate the above-mentioned problems and to provide a composition capable of facilitating the bulk crystal¬ lization to form a high strength glass ceramics having a color near ivory color and not reduced but rather improved chemical durability. The present inventors have found that a great amount of titanium oxides are introduced into a CaO-P-Cv-containing composition. In accordance with the present invention, the basic composition consists, on the weight basis, of CaO 15 - 40%, Ti0 2 + Ti2θ3 - 15 - 35% and P 2 0 5 35 - 65%. If the CaO content is less than 15%, good bioaffinity is not expected. If the CaO content exceeds 40%, then the titanium oxide content is not increased to bring about the bulk crystallization and to achieve the desired strength. If the TiO, and T 2 °3 total content is less than 15%, the bulk crystallization does not occur. If the total content exceeds 35%, then the glassification is difficult. Furthermore, if the P 2 °5 content is less than 35%, the glassification does not occur and if the content exceeds 65%, then good bio¬ affinity cannot be expected. A Ca/P atomic ratio is not specifically limited, but preferably the ratio is in the range of 0.5 to 1.7. Furthermore, not more than 20 parts by weight of the following other oxides based on 100 parts by weight of the basic or main components may be added singly or in combination to the composition. That is, as glass-forming components, not more than 20 parts by weight of silicon oxide and/or not more than 20 boron oxide may be added. Furthermore, conventional glass modifiers such as alkali metal (lithium, sodium, potassium or the like) oxides, alkaline earth metal (magnesium, barium, strontium or the like) oxides, zinc oxide, aluminum oxide and transition metal oxides may be added singly or in combination. However, these glass modifiers do not exceed 5 parts by weight for each and 20 parts by weight in total based on 100 parts by_weight of the main components. The above-mentioned oxides fall within the scope of oxides conventionally used in CaO-P 2 O ς -containing glasses. If the content of these oxides exceeds the indicated upper limit, then the characteristics of the main components are reduced. That is, if the amount of these oxides is too high, then the CaO and P 2 0 5 contents are relatively smaller, then good bioaffinity cannot be expected. The transition metal oxides are used for adjusting the color tone and at the same time promotes the formation of crystal seeds. In addition, fluorine atom, chlorine atom and/or hydroxyl group may be partially substituted for the oxygen atoms of the main oxides and the other oxides, preferably in an amount not exceeding about 5% based on the total amount of all the oxygen. This substitution makes the glassification at a low temperature possible, promotes the crystallization and changes properties of the glass ceramics such as hardness to some extent. The glass ceramics according to the present invention requires a degree of crystallization of at least 20%. If the degree of crystallization is lower than 20%, then the glass ceramics contains an excess of a glassy material to be brittle. The glass ceramics according to the present invention can be produced by, for example, the following procedure. That is, starting raw materials having a composition adjusted as mentioned above are heated to, for example, a temperature of 1,000 to 1,400°C. The resultant melt is shaped in a desired article such as an artificial dentition, crown of a tooth or artificial bone, and reheated to, for example, a temperature range of 500 to 1,000°C to be crystallized in a glass ceramic body. However, the melting and crystallizing tempera- tures vary depending upon the difference in composition and thus not specified. Raw materials for supplying the composition may not only be in an oxide form but also in a salt form such as CaCO-, Ca(OH) _, Ca(COO) 2 , Ti0 2 , Ti 2 0 3 , H 3 P0 4 , CaHP0 4 , Ca(H_P0 4 ) and etc. EXAMPLES Raw materials having compositions adjusted as shown in TABLE 1 and mixed in the usual way were molten at 1,200 to 1,350°C, poured into a mold having a predetermined shape to obtain shaped glass articles. Then the following heat treatment for crystallization was carried out. This heat treatment of all the shaped glass articles was firstly carried out at 740°C for 2 hours for crystal seed formation, and then at 790°C for 24 hours for crystallization. Properties of the glass ceramics obtained in each example are reported in TABLE 2. The color of the glass ceramic articles all was ivory. The change of shape of the shaped glass articles was at most 1%, normally 0.3% when crystallized. TABLE 1 EXAMPLE No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Component Wt.% wt.% wt..% wt.% wt.% wt.% CaO 26.8 29.0 25.0 28.0 23.0 20 Ti0 2 22.0 26.8 25 +Ti 2°3 22.0 24.0 27.0 49.0 45.0 48.0 47.2 30.0 32 P 2°5 Na 2 0 1.0 _ — 0.5 κ 2 o 0.5 MgO 0.1 0.2 1.0 SiO„ 1.0 0.5 0.4 15.0 5 0.5 0.6 2.0 15 B 2°3 A1 2 0 3 0.1 1.0 1 NiO 1.0 0.2 1 TABLE 2 EXAMPLE No. 1 No. 2 N No. No. 4 No. No. Coeff. Of Expansion _ (deg-ljxlO * - 110 110 100 95 Bending Str. (MPa) 150 200 180 210 130 120 Hardness (GPa) 4.9 5.0 4.9 5.1 5.5 5.5 Conventional tendency to the surface crystal¬ lization is eliminated and the bulk crystallization is made possible by adopting the composition containing a great amount of titanium oxides according to the present invention. Thus, the present invention provides the excellent glass ceramic articles having a conspicuously improved bending strength and no cracks nor vacancies such as interstices or bubbles generated therein. Furthermore, an ivory color required particularly by a crown of a tooth, good chemical durability, cast shaping of articles with ease and precision and little change of shape during the crystallization to obtain an exactly desired shape of the article with ease were achieved by the present invention.

Claims: CLAIMS 1. A glass ceramics composition which consists, on the weight basis, of CaO 15 - 40%, Ti0 2 + Ti 2 0 3 15 - 35% and P 2 0 5 35 - 65%, the degree of crystallization thereof being not less than 20%. 2. A glass ceramics composition which comprises, on the weight basis, CaO 15 - 40%, Ti0 2 + Ti 2 0 3 15 - 35% and P 2 0 5 35 - 65% as main components, and further contains, based on 100 parts by weight of said main components, not more than 20 parts by weight of silicon oxide and/or boron oxide and not more than 20 parts by weight in total of one or more members selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, zinc oxide, aluminum oxide and transition metal oxides except for titanium oxides, each member not exceeding 5 parts by weight, the degree of crystallization there¬ of being not less than 20%. 3. A glass ceramics composition which comprises, on the weight basis, CaO 15 - 40% , Ti0 2 + i 2 0 3 15 - 35% and as main components, and further contains, based on 100 parts by weight of said components, not more than 20 parts by weight of silicon oxide and/or boron oxide and not more than 20 parts by weight in total of one or more members selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, zinc oxide, aluminum oxide and transition metal oxides except for titanium oxides, each member not exceeding 5 parts by weight, the oxygen atoms of all the oxides being partially replaced with fluorine atom, chlorine atom and/or hydroxyl group, and the degree of crystallization thereof being not less than 20%.

Inventors: ABE YOSHIHIRO, HOSONO HIDEO, ABE, YOSHIHIRO, HOSONO, HIDEO
Applicants: ABE YOSHIHIRO, ABE, YOSHIHIRO
Application year: 1987
Main classification: C03C10
IPC codes: C03C3, C03C10