FI68217C - STARKT ISOTROPT SINTRAT TVAOFASIGT KERAMISKT MATERIAL - Google Patents

Description

πΓΤ * 5Ξ71 KU UULUTUSJULZ AISU / οο ΛΠ 'Mi [Β] (11) UTLÄGGNINGSSKRIFT 68217 c Patent extended 12 08 1985' 'Patent ceddeiat (51) Kv.lk.> tCi. 6l K 6/06, 6/08 FINLAND —FINLAND (21) Patent application - Patentansökning 792181 (22) Filing date - Ansöknlngsdag 11 .07.79 (23) Starting date - Giltighetsdag 31.07.75 (41) Becomes Public - Blivit offentlig ^ 07 79

Patent and Registration Office ..... ... .......

1/441 Date of launch and hearing. -

Patent- and Register-Registration in 1 Ansökan utlagd och utl.skriften publicerad 30.04.85 (32) (33) (31) Privilege requested - Begärd priority 07-07-75 Avenue, New York, New York, USA (US) (72) Michael Jarcho, Nassau, New York, USA (74) Oy Koister Ab (54) Strong, isotropic sintered two-phase ceramic material -Starkt, isotropic sinter tvSfasigt keramiskt This invention relates to a strong, hard, dense, isotropic and polycrystalline sintered biphasic ceramic material. (62) Separated from application 752194 (patent 64131) -Avdelad frän trap 752194 (patent 64131) The new material is especially suitable for use in dentistry and orthopedics.

Current dental research is largely focused on the manufacture of material that can be used as a tooth and bone substitute, as a dental repair material for fillings, shells and crowns, and as a prosthetic filling material for bone. Dental research has also focused on preventing the formation of tooth rust in teeth, which is considered to be the cause of both dental caries and periodontal disease.

Fillers currently used in dental restorative compositions, such as quartz, alumina, silicates, glass beads, etc., resemble little tooth enamel chemically and physically. The actual weakness of these materials is the difference in the coefficients of linear thermal expansion of the filling material and the tooth, which can potentially cause cracks at the joints and new caries formation. Thus, in the treatment of teeth, a filler composition has long been desired, the physical properties of which closely correspond to those of natural teeth.

In addition, in the field of surgical prosthetic materials, which is currently dominated by strong, non-corrosive alloys, there has been a need for a material that better resembles biological, hard tissues, as difficulties in tissue acceptance and attachment have not yet been completely eliminated (Hulbert, et al., Material Science). Research 5, 417 (1971)).

In research to find effective anti-rust chemotherapeutic agents, there has been a need for a standard test material with a surface resembling a tooth in terms of both tooth rust formation and chemical action. Although natural tooth has been used for this purpose, it has the disadvantage of high variability, relatively difficult availability in large quantities, and the complex cleaning required before use. Therefore, other materials that form dental rust, such as powdered hydroxylapatite, acrylic teeth, glass, and metal wire, have been used. Although they may be suitable for studying the formation of dental fever per se, these materials bear little resemblance to the surface of a natural tooth and are thus not entirely suitable for finding an effective anti-rust agent. For example, it is known that chemicals that prevent rust from forming on teeth may not be effective on glass and metal wire (Turesky et al., J. Periodontology 43, 263 (1972)). Therefore, there is a need for an inexpensive, readily available material that is chemically similar to tooth enamel, is hard, dense, and highly polishable.

Hydroxyl apatite, Ca 2 g (PO 2) g (OH) 2 / also known as basic calcium orthophosphate, a tooth and bone mineral base, has been proposed for use in the various purposes set forth above, and in fact U.S. Patent 2,508,816 discloses a method for recovering hydroxyl apatite from tooth enamel and for use as a prosthetic dental composition mixed with a synthetic resin. This method is long and laborious and is limited to the preparation of finely divided hydroxylapatite. In addition, the method naturally depends on the availability of natural teeth.

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Kutty (Indian J.Chem. 11, 695 (1973)) discloses mixtures of hydroxylapatite and whitlocyte formed by decomposing powdered hydroxylapatite at different temperatures.

Bett, et al. (J.Amer.Chem.Soc. 89, 5535 (1967)) disclose the preparation of finely divided hydroxylapatite with a stoichiometric Ca / P ratio ranging from 1.67 to 1.57. The materials thus prepared contain large internal pores of the crystals. It has also been mentioned that when heated to 1000 ° C, the calcium-deficient hydroxylapatites are partially converted to the whitlocyte phase.

U.S. Patent 3,787,90Q discloses a prosthetic bone and dental material containing a high melting material and a calcium phosphate compound, e.g., whitlocyte.

Several attempts have been made to obtain the macro form of hard, strong hydroxylapatite. However, no previously known form of hydroxylapatite has been completely satisfactory. Thus, Roy and Linnehan (Nature 247, 220 (1974)) have proposed a complex hydrothermal exchange process in which the calcium carbonate backbone of sea coral was converted to hydroxylapatite. The material thus produced inevitably retains the very porous properties of the coral structure and, in addition, its tensile strength is relatively low, about 19-33 kp / cm, which is a serious drawback in the prosthetic material.

Monroe, et al. (Journal of Dental Research 50, 860 (1971)) have reported the preparation of a ceramic material by sintering compressed hydroxylapatite tablets. The material thus formed is in fact a mixture of hydroxylapatite with about 30% of t-vitloclite, Ca 3 (PO 2) 2 or tricalcium phosphate, as an ordered mosaic pattern of polyhedral crystals and proved to be too porous to be used as a dental material.

Rao and Boehm (Journal of Dental Research 53, 1351 (1974)) have disclosed a polycrystalline form of hydroxylapatite prepared by compressing isostatic powdered hydroxylapatite into a mold and sintering the formed body isothermally.

The ceramic body formed was porous and had a maximum compressive strength of about 1200 kp / cm.

Bhaskar et al., (Oral Surgery 32, 336 (1971)) disclose the use of a biodegradable calcium phosphate ceramic material to fill tooth cavities. The material is highly porous, resorbed at its planting point and does not have the strength of a metal or non-dispersed ceramic spot.

Master application 752194 of this application discloses a process for obtaining a polycrystalline sintered ceramic material in which calcium ion and phosphate ion are reacted in an aqueous medium at pH 10-12 to form a gel-like calcium phosphate precipitate having a molar ratio of calcium to phosphorus of 1.44 72 (which is the molar ratio between the approximate molar ratios of calcium and phosphorus in hydroxylapatite and whitlocyte) the precipitate is separated from the solution, heated to at least 1000 ° C but below the temperature at which considerable decomposition of hydroxylapatite occurs and kept at this temperature for a sufficient time. for sintering the product, in which case it is generally advantageous to produce the ceramic material in macroform by sintering the entire mass formed by the precipitate, if desired in the form of a mold, in order to achieve substantially maximum compaction.

The invention relates to a novel biphasic ceramic material containing hydroxylapatite and whitlocyte. As discussed in more detail below, this biphasic material is a hard, dense, non-porous biocompatible, easily prepared in any desired form, and due to the known resorbing nature of whitlocyte, it is useful as a strong, partially resorbable surgical implant material.

The use of a new biphasic ceramic form of hydroxylapatite in dental restorative compositions provides a dense filling material with a coefficient of thermal expansion substantially equal to that of natural tooth enamel.

The dental and surgical implant material provided by the present invention is hard, strong and fully biocompatible and can be made into any desired shape without high pressures or other complicated procedures. In addition, as will be detailed later, any desired degree of porosity can be imparted to this material, allowing tissues to adhere.

As will be seen below, the features of the new article of manufacture disclosed herein, which is also subject to the claims, make it ideally suited for the manufacture of wafers, sheets or tanks for testing anti-rust agents.

Although a certain degree of porosity in surgical implant materials may be advantageous to allow circulation of body fluids and tissue adhesion, this same porosity necessarily reduces the mechanical strength of the implant. The biphasic ceramic material of the invention, although dense, mechanically strong and substantially non-porous, nevertheless allows the circulation of body fluids and tissue adhesion because the whitlocyte phase it contains is slowly resorbed from the implanted object and replaced by natural, biological, hard tissue.

The term dense, as used herein, refers to a very dense order of particles, with almost completely no gaps and distances between the particles.

In addition to the above-mentioned properties of the novel biphasic ceramic material of the present invention, it is also fully biologically compatible and thus excellently suitable as a dental and surgical prosthetic material. Thus, the ceramic material of the present invention can be cast or processed into dental crowns, artificial teeth, bone and bridge prostheses, cannulas for attachment to artificial body members that can be attached to bone and extends through the skin, nasal strain, and test surfaces. and to study other diseases that can affect the tooth and bone. Appropriately ground, the novel ceramic material of this invention can be used as a synthetic bone filler in bone defect repair, as an abrasive, and as a dental replacement composition combined with conventional resins, as described below.

As a test surface for testing anti-rust agents, the ceramic material of this invention can be machined into a body of any suitable shape and size, a preferred size and shape that can be easily placed in a normal test tube. This is conveniently done by cutting or machining a large plate-like piece of dried filter cake to fit and then sintering. The sintered products can be polished to a high gloss using standard patching procedures, and the formed bodies are then used as substrates in the study of anti-rust agents according to the procedure of Turesky, et al., Supra. After use, the ceramic bodies are simply polished again to form a new moisture surface.

Conventionally made, the ceramic materials of this invention are not only dense but also non-porous, and although non-porous material is essential in dental applications, a certain degree of porosity in the implant material may be advantageous in allowing body fluids to circulate and tissue to grow. Various degrees of porosity can be formed in this ceramic material in the manner proposed by Monroe, et. ai, supra. In this case, an organic material such as starch, cellulose powder, cotton or collagen can be mixed in amounts of 5 to 25% by weight of the gelatinous precipitate of hydroxylapatite. In the next sintering process, the organic materials are removed by combustion, thus causing cavities and channels in the otherwise non-porous product. Alternatively, the porosity can be achieved mechanically by drilling or machining holes or openings in the non-porous ceramic.

In this way, an artificial tooth consisting of a ceramic according to this aspect of the invention can be made porous at its implantation point and the bare tooth surface remains non-porous. Implantation can be performed as described by Hodosh, et al., Journal of the American Dental Association 70, 362 (1965). Alternatively, a polymerizable or polymerized bonding material may be added to the ceramics of the invention, as described below, and the resulting composition may be used as a coating for metallic implants, as disclosed in U.S. Patent 3,609,867.

The present invention relates to a strong, hard, dense, isotropic, polycrystalline sintered biphasic ceramic material, characterized in that it has about 14 to 98% by weight of hydroxylapatite as the second phase and about 2 to 86% by weight of white matter as the second phase, which ceramic material is substantially non-porous and splits along uniform curved surfaces.

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Whitlocyte, also known as tricalcium phosphate, is a mineral with the chemical formula Ca 2 iPO 2 and which can exist in either - or β-crystal form. The term whitlocyte as used herein means either the or fb form or a mixture of the two forms.

The biphasic ceramic material of the present invention remains a non-porous polycrystalline material regardless of the relative concentrations of hydroxylapatite and whitlocyte contained therein. It should be noted, however, that the physical properties, such as density and optical properties, of hydroxylapatite and whitloclite depend on the relative amounts of hydroxylapatite and whitloclite it contains. For example, the theoretical density of whitloclite is lower than that of a sample of hydroxylapatite and thus a biphasic ceramic material containing about 40% hydroxylapatite 3 and 60% whitloclite at an observed density of 2.98 g / cm and a density of hydroxylapatite ceramics of 3.10.

The biphasic ceramic material described above is also biologically compatible and thus suitable as a surgical prosthetic material. This material can thus be cast or machined into bone and joint prostheses or into any shape suitable for filling bone cracks or lesions. The whitlocyte contained in this prosthesis article made of biphasic ceramic material is finally resorbed and replaced as natural biological hard tissue grows into the prosthesis. Naturally, the amount of tissue growth in the prosthesis depends on the amount of whitlocyte contained in the ceramic material.

Normally made, the biphasic ceramic material of this invention is non-porous. However, if desired, varying degrees of porosity can be formed in the ceramic, as described above, to obtain a new ceramic form of hydroxylapatite.

The biphasic ceramic material can also be made acid resistant by fluorination, as will be discussed later.

The above composition, in which the second phase is hydroxylapatite and the second whitloclite, can be prepared by precipitating from an aqueous medium having a pH of about 10-12 hydroxylapatite having a molar ratio of calcium to phosphorus of 8 6821 7 in the range of approximately 1.44-1, 60, preferably 1.46-1.57, by separating the precipitate from the solution and heating it for a sufficient time at a sufficiently high temperature to effect sintering and maximum condensation without substantially decomposing.

Thus, hydroxylapatite is precipitated from an aqueous medium by reacting calcium ions with phosphate ions at a pH of about 10-12. Any calcium- or phosphate-containing compound which forms calcium and phosphate ions in an aqueous medium is suitable provided that the corresponding counterions of said compounds can be readily separated from the hydroxylapatite product, are not themselves associated with the hydroxylapatite structure or otherwise adversely affect substantially pure hydrogenation. put asunder. Compounds that donate calcium ions include, for example, calcium nitrate, calcium hydroxide, calcium carbonate, and the like. Phosphate ions are obtained from diammonium hydrogen phosphate, ammonium phosphate, phosphoric acid and the like. In the present method, calcium nitrate and diammonium hydrogen phosphate are the preferred sources of calcium and phosphate ions, respectively.

The preparation of the new form of hydroxylapatite is suitably carried out as follows: First, a molar ratio of calcium nitrate to diammonium hydrogen phosphate of 1.50 to 1.60: 1 is allowed to act in an aqueous solution at a pH of about 10-12 to form a gelatin precipitate of hydroxylapatite. The procedure presented by Hayek, et al., Inorganic Syntheses 7, 63 (1963) is suitable for this purpose. The gel-like suspension of hydroxylapatite thus obtained is then allowed to contact the initial solution for a time sufficient to allow the ratio of calcium and phosphorus in the suspended hydroxylapatite to reach a value of about 1.50-1.60. This is conveniently done either by stirring the suspension for 10-90 minutes and combining the boiling with subsequent standing at room temperature. Preferably, the suspension is boiled for 10 minutes and then allowed to stand at room temperature for 15-20 hours. The precipitate is then separated from the solution in a suitable manner, for example by centrifugation and vacuum filtration. The gel-like product thus obtained contains a large amount of water, which can be largely removed by compression. If desired, the wet clay-like material formed can be cut or shaped to suit

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6821 7 mold or alternatively cast in a suitable mold. It should be noted that a shrinkage of about 25% usually occurs when the wet hydroxylapatite is dried and a further shrinkage of about 25% occurs during sintering as described below. This must, of course, be taken into account when shaping or casting the material. The wet product can be slowly heated to a sintering temperature of 1000-1250 ° C, removing any remaining water. Maintaining the temperature at 1000-1250 ° C for 20 minutes to 3 hours will cause sintering and maximum compaction of the product. It is usually recommended to isolate the dried product before sintering. In this case, the wet product can be dried at a temperature of about 90-900 ° C for 3-24 hours until the amount of water it contains has decreased to 0 to about 2%. It is generally preferred to carry out the drying at 90-95 ° C for about 15 hours, or until the water content has dropped to 1-2%. The product obtained in this way is brittle and porous, but its mechanical strength is relatively good. Slight separation or cracking may occur in the clay-like material during drying, especially if a thick filter cake is used. However, pieces as large as 100 cm 2 in area and 3 mm thick are easily obtained. Separation or cracking during drying can be reduced or completely prevented by adding 0.4 to 0.6% by weight of an organic binder, such as collagen, powdered cellulose to the freshly precipitated precipitate, usually a suspension of about 0.5% collagen, is preferred. The organic binder evaporates during sintering and the physical properties of the ceramic product appear to be substantially unchanged compared to a product made without such a binder. Naturally, relatively large amounts of organic binder cause a porous ceramic product, as discussed above. Other organic and inorganic binders known in the ceramics field may be used.

It is generally appropriate at this stage to cut or shape the dried precipitate approximately from the final product to the desired shape, taking into account the aforementioned shrinkage in sintering.

Macro-shaped pieces of precipitate must be smooth and flawless before sintering. The presence of cracks and fissures causes the pieces to crack during sintering.

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The products are then sintered at a temperature of 1000-1250 ° C for 20 minutes to 3 hours, the temperature and time being inversely proportional to each other. The sintering is preferably carried out at a temperature of 1100-1200 ° C for 0.5-1 hours. The resulting hard, dense ceramic body can be polished or machined using conventional procedures.

In the above process, it is critical that an aqueous solution yields a gel-like precipitate, because only in this cohesive gel-like state can the precipitate be shaped or cast and then dried and sintered to obtain a ceramic body in macro form. Dry, finely divided, or granular biphasic material cannot be restored to this cohesive, gel-like form. For example, if the ground biphasic material is suspended in water and filtered, a non-cohesive, finely divided filter cake is obtained which simply dries and crumbles and cannot be shaped, cast or turned into a ceramic body. In addition, although powdered hydroxylapatite can be mechanically compressed into a shaped body, such as a tablet, the product obtained by sintering is highly porous and does not crack along flat surfaces, but merely crumbles into pieces.

In fabrication, sintering time and temperature are critical. An unsintered precipitate having the desired ratio of calcium to phosphorus is converted from 1.44 to 1.60 into the ceramic material of this invention by heating at a temperature of at least 1000 ° C. At 1000 ° C, sintering and maximum condensation may take 2-3 hours, while at 1200 ° C the process is complete in 20-30 minutes. It is recommended to perform sintering at a temperature of about 1100 ° C for about an hour. Temperatures well below 1000 ° C cause incomplete sintering despite the length of the heating cycle, while heating above 1250 ° C for more than an hour causes partial decomposition of hydroxylapatite to whitlocyte.

The biphasic ceramic material may also be prepared by reacting calcium nitrate and diammonium hydrogen phosphate in a molar ratio of 1.67: 1, as described above, provided that the initially obtained gel precipitate is not heated and allowed to remain in contact with the original solution for not more than 4 hours or alternatively. that the molar ratio of calcium n 6821 in the phosphorus precipitate is not allowed to exceed a value of about 1.60.

The amount of whitlokite contained in the ceramic material formed depends on the time at which the precipitate is separated from the original solution and is in the range of 2-83%. If the product is isolated 5 minutes after precipitation, the ratio of calcium to phosphorus is 1.55 and the final ceramic material contains 83% whitlocyte. If the product insulation! 2 hours after precipitation, the ratio of calcium to phosphorus is 1.57 and the ceramic material formed contains about 61% whitlocyte. Isolation of the product 4.5 hours after precipitation finally gives an amount of ceramic material containing about 2% whitlocyte, which is hardly detectable by X-ray diffraction with a minimum sensitivity of 2-3%. Of course, if the product is allowed to contact the initial solution for more than about 7 hours, the ceramic material finally obtained is essentially single phase hydroxylapatite.

When the biphasic ceramic material of the invention is prepared by reacting calcium ions, phosphate ions in a molar ratio of 1.50 to 1.60: 1, the molar ratio of calcium to phosphorus cannot exceed about 1.60 regardless of the time during which said precipitate remains in contact with the original solution. In this process, a ceramic material containing about 30-50% hydroxylapatite and about 50-70% whitloclite is obtained.

The whitlok tite phase can be further enriched in the ceramic material by combining the main features of the two above-mentioned methods, i. by reacting the calcium ion and the phosphate ion with an approximate molar ratio of 1.50 to 1.60: 1 and isolating the precipitated calcium phosphate compound shortly after precipitation, preferably from 5 minutes to 4 hours. The ceramic material thus formed contains about 10-30% hydroxylapatite and 70-90% whitloclite.

Hydroxyl apatite is known to decompose, forming whitlocyte at a temperature of about 1250 ° C, and thus it should be noted that prolonged heating of the single phase ceramic hydroxylapatite of this invention at about 125 ° C or higher 7 12 for producing a biphasic ceramic material as claimed in this claim.

The invention also relates to a dental replacement composition comprising a mixture of the hydroxylapatite of this invention and a polymerizable or polymerized binder suitable for oral conditions. The dental packaging composition of this invention contains 10-90% by weight of a finely divided biphasic ceramic material, the remainder of said composition, 10-90% by weight, being a dentally acceptable polymerizable or polymerized binder together with known suitable polymerization catalysts such as aliphatic ketone peroxide ketone peroxide diluents such as di-, tri-, and tetraethylene glycol dimethacrylate, hardeners such as N-3-oxo-hydrocarbon-substituted acrylamide, as disclosed in U.S. Patent 3,277,056, promoters or accelerators, such as tertiary amines of metal acetylacetonates, e.g. with bis- (2-hydroxyethyl) -p-toludine, etc. or crosslinking agents such as zinc oxide, etc. in amounts of about 0.01 to 45% of the total weight of the composition. Although not essential, a surfactant comonomer or blocking agent such as the reaction product of N-phenylglycine and glycidyl methacrylate disclosed in U.S. Patent 3,200,142 may be added to methacryloxypropyltrimethoxysilane, 3,4-epoxycyclohexyltrimethoxysilane or vinyltrichloros. 0.05-10% of the total weight of the composition. The bonding or locking agent promotes the adhesion of the ceramic material to the resin and the adhesion of the tooth replacement composition to the natural tooth. In this case, the ceramic hydroxylapatite of the present invention is reduced to a suitable particle size, e.g. sold by Allied Chemicals Co. 23 LS8275 and Pitssburgh Plate Glass under the name Selectron 580001, styrene-modified unsaturated polyesters such as Glidien Glidpol 1008, G-136 and 4CS50, epoxy resins such as Ciba Araldite 6020, Union Carbide ERL2774 il 6821 7 and glycidyl methacrylate and glycidyl methacrylate; with a monomer disclosed in U.S. Patent 3,066,112. The resin may comprise a single monomer or a mixture of two or more comonomers. If desired, additives such as colorants, inorganic pigments and fluorinating agents may be added to the above composition according to principles known in the art of handling these materials. It is preferred to mix the resin, ceramic hydroxylapatite and any additives such as silane blocking agents, dyes, inorganic pigments or fluorescent agents before adding the catalyst, hardener, crosslinking agent, promoter or accelerator. However, the order of mixing of the ingredients is not critical and said ingredients may be mixed simultaneously. Using conventional procedures, the composition thus prepared can be used as a dental filling material, dental care cement, dental lining, dental cortex shell material, or the composition can be molded into a suitable mold to make an artificial tooth or group of teeth.

It is, of course, highly preferred that the material used in the oral cavity be caries resistant. This is easily achieved by using the present invention by adding 0.01-1% fluoride ions such as ammonium or tin fluoride to a suspension of freshly precipitated hydroxylapatite. The ceramic material obtained by sintering the formed product is very resistant to the action of lactic, acetic or citric acid, which is a normal in vitro method for determining caries resistance. Alternatively, resistance to caries can be obtained in the final ceramic material by maintaining it in a 0.5-5% aqueous solution of sodium fluoride for 12 hours to 5 days. Preferably, the ceramic body is allowed to remain in about 5% aqueous sodium fluoride for about 4 days.

It will, of course, be of interest to those skilled in the art of ceramics that in addition to organic and inorganic binders and fluoride ions, the ceramic material of the present invention may contain small amounts of other elements which, while not altering the essential nature of ceramic products, may provide useful properties.

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It is known, for example, that barium and strontium can be associated with the crystal structure of apatite and that these elements transmit significantly less X-rays than calcium. Therefore, the addition of a small amount of barium or strontium ions to the calcium ions prior to reacting the latter with phosphate finally gives a ceramic of barium or strontium inoculated hydroxylapatite / which, when used in dental replacement compositions as described above, has sufficient X-ray absorption for patched teeth. Magnesium is also associated with the crystal structure of apatite and is known to retard the crystallization of hydroxyl apatite while promoting the crystallization of whitlocyte (Eanes et al., Calc. Tiss. Res. 2, 32 (1968)). Thus, the addition of a small amount of magnesium ions to the calcium ions prior to the reaction of the latter with phosphate promotes the formation of whitlocyte, eventually forming a biphasic ceramic enriched with whitlocyte.

The properties of the ceramic materials obtained as described above were determined by one or more of the following studies: Elemental analysis, density, X-ray diffraction, translucent electron microscopy, microscopy using polarized light, and mechanical properties.

The invention is illustrated by the following examples.

Example 1

The pH of a solution containing 0.24 moles of diammonium hydrogen phosphate in 600 ml of distilled water was adjusted to 11.4 by adding 340 ml of concentrated ammonia and distilled water was added until the final volume was 1280 ml. This solution was added dropwise over 30 minutes to a vigorously stirred solution of 0.4 moles of calcium nitrate in 360 ml of distilled water, the pH of which had been previously adjusted to 11 with concentrated ammonia and diluted to a volume of 72 ml with distilled water. The resulting suspension was stirred uncooked and periodically removed with 250 ml aliquots from which the products were separated, washed and dried as described in Example 2 of strain application 752194. All samples were then heated for one hour at 1100 ° C and the compositions of the formed ceramic products were determined by X-ray diffraction. The results are shown in the following table.

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Table Sample Mixing time Standing Elemental analysis No time in X-ray diffraction before the observed phases% Ca% P Ca / P 7ΓΖ; ΓΓ77Τ1

Hydroxy-Whitloocapatite tite _% _% _ 1 5 min - 36.6 18.2 1.55 17 83 2 45 min - - 21 79 3 2 h - 36.6 18.0 1.57 39 61 4 4 , 5 h - - 98 2a 5 7 h - 37.0 17.0 1.68 98 2a 6 7 h 17 h 37.2 17.0 1.69 100 0 7 24 h - 37.4 17.1 1, 69 100 0 8 48 h - 37.4 16.8 1.72 100 0 a. These values are limited by the resolution of the X-ray diffractometer with respect to the minimum concentration (2-3%) and the accuracy is thus questionable.

Example 2 A. The procedure of Example 2 of strain application 752194 was followed except that 0.3 moles of calcium nitrate and 0.2 moles of diammonium hydrogen phosphate were used to give a hard, brittle, porous product having the following elemental analysis: Ca = 38.85 %; P = 19.77%; Ca / P = 1.52. This material was heated at 1200 ° C for 1 hour to give a strong, hard, non-porous, white, partially opaque ceramic material containing approximately 40% hydroxylapatite and 60% whitlocyte as detected by X-ray diffraction.

B. Carrying out the above reaction by adding the starting materials in reverse order, a product was obtained which contained about 40% hydroxylapatite and 60% whitlocyte and had a Ca / P ratio of 1.52 and a density of 2.982.

Example 3

A solution of 0.0625 moles of diammonium hydrogen phosphate in 150 ml of distilled water was treated with 95 ml of concentrated ammonia and distilled water was added until the final volume was 320 ml. This solution was added dropwise over 30 minutes to a vigorously stirred solution of 0.1 mol of calcium nitrate and 2.5 ml of concentrated ammonia in 180 ml of distilled water. The resulting suspension was stirred for 5 minutes, cooled on ice for 45 minutes and the suspended solids were separated, washed and dried as in Example 2 to give a hard, brittle, porous, white solid having the following Elemental analysis: Ca = 35.4 P = 18.59 %} Ca / P = 1.46. This material was heated at 1350 ° C for 1 hour to give a strong, hard, non-porous, slightly opaque ceramic product containing about 14% hydroxylapatite and 86% whitlocyte as detected by X-ray diffraction.

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