CA1266685A

CA1266685A - Controlled pore size ceramics particularly for orthopaedic and dental applications

Info

Publication number: CA1266685A
Application number: CA000552590A
Authority: CA
Inventors: George Arthur Graves Jr.; Dale E. Mccullum; Steven M. Goodrich
Original assignee: University of Dayton
Current assignee: University of Dayton
Priority date: 1986-11-25
Filing date: 1987-11-24
Publication date: 1990-03-13
Anticipated expiration: 2007-03-13
Also published as: EP0271236A1; US4737411A

Abstract

Abstract The present invention provides a ceramic composite having an open porous network and a controlled pore size comprising a plurality of ceramic particles having a fused glass coating and a method for producing the same. The ceramic particles are enveloped by and bonded to adjacent ceramic particles at their interfaces by the glass coating.

Description

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CONTROLLED PORE SIZE CERAMICS PARTIC~LARLY
FOR ORTHOPAEDIC AND DENTAL APPLICATIONS
Background of the Invention The present invention relates to a ceramic having a controlled pore size and, more particularly, to a con-trolled pore structure, liquid phase sintered ceramics for orthopaedic and dental applications.
Ceramic materials which are useful as bone sub-stitutes are used in nu~erous orthopaedic and dental ap-plications including as implants. Examples of such bone substitutes are described in U~S. Patent Nos. 4,097,935 to Jarcho; 4,113,500 to Ebihara et al; 4,149,893 to Aoki et al and 4,330,514 to Nagai et al.
Two bone substitute materials, hydroxyapatite and tricalcium phosphate, have been approved for general dental implant use, and in some selected instances, orthopaedi-c- ~' clinical trials. Howev'e~r,''~'hës'ë''ma'~'erla~s''arë''only avair-able in particulate or solid bulk closed cell forms.
~'~ Thus, the use of such materials in orthopaedic and dental applications has been limited.
Bone substitutes such as hydroxyapatite have been combined with other agents in various medical applications.
~` 20 Surgical cements including hydroxyapatite as the bone substitute are used in numerous orthopaedic and dental applications including repairing bone fractures, in at-~; taching bone plates and other prostheses, in bridging comminuted ractures, and in filling or aligning dental ~ ~ 25 cavities. Examples of such compositions are described in ;' U.S. Patent Nos. 4,518,430 to Brown et al; and 4r542,167 :-:"
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to Aoki et al. U.S. Patent No. 4,451,235 to Okuda et al discloses a dental root ma~erial comprising hydroxyapatite and an organic matrix such as polyethylene.
U.S. Patent No. 4,135,935 to Pfeil et al discloses a composite material useful as an implant. A first start-ing material which is preferably an apatite and a secondstarting material which is pre~erably a glass are ground, preferably jointly, to a particle size preferably between ~ about 200-500 microns. The resultant mixture is finely i 10 comminuted to a particle size preferably between about 20-50 microns. The mixture is compressed to form shaped bodies and sintered. This material does not have the open pore structure which characterizes the ceramic material of the present invention.

Summary of the Invention The present invention provides a ceramic composite having an open porous network of controlled pore size comprising a plurality of ceramic particles having a glass coating which bonds the ceramic particles at their inter-faces. While the present invention is particularly dir-ected to providing ceramics which are useful in orthopaedic and surgical applications, those skilled in the art will ;~ appreciate that the teachings herein are relevant to cera-mics generally where a controlled pore size is desired.
By varying the size of the ceramic particles and the thickness of the glass coating, the pore size of the composite ceramic can be varied.
Accordingly, one object of the present invention is to provide a ceramic material having a controlled pore s l z e .

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A further object of the present invention is to provide a ceramic composite having a controlled pore size comprising a plurality of particles of a bone ingrowth promoting material useful in dental and orthopaedic appli-¦ 5 cations.
An additional object of the present invention is ! to provide a ceramic composite having a controlled pore si7~e useful in dental and orthopaedic applications wherein the degree of resorbability can be varied.
Another object of the present invention is to provide ceramic particles having a finely divided or fused glass coating useful in providing a ceramic composite having a controlled pore size.
Still another object of the present invention is to provide a process for preparing a ceramic composite in accordance wi~h the present invention.
Other objects and advantages-o~ the--present in-vention will become apparent from the followin-g-description and the appended claims.

2~ Brief Description of the Drawings Figure l illustrates an agglomerator useful in coating the ceramic particles of the present invention with a ground glass.
Figure ~ illustrates a spray dryer useful in ; 25 coating the ceramic particles of the present invention with a ground glass.
Figure 3 illustrates the ceramic particles of the present invention with a glass powder coating prior to sintering.
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3, UVD 0~2 P2 4-Figure 4 illustrates a plurality of the ceramic particles of the present invention with a glass coating after liquid phase sintering.
Figure 5 is a scanning electron microscope photo-- 5 graph (magnification 50X) of a ceramic in accordance with the present invention showing the glass coated ceramic particles and the glass necking between them.
Yigure 6 illustrates a prosthesis carrying ceramic particles in accordance with the present invention.

Detalled Description of the Invention As stated earlier, the principal object of the present invention is to provide a ceramic composite having a controlled pore siæe. In order to achieve this object, the size of the ceramic particles must be controlled.
Knowing the size of the ceramic particle and the thickness of the glass coating, the por~ size of the ceramic-~materi-al -- ~
can be calculated by using the equation for closely packed particles. The ceramic particles used in the present invention typically have a particle size of less than about 2000 microns. If the particle size is larger than 2000 microns, the present invention can be used, but us-ually there are more expedient means available to achieve ; the desired pore size. The amount of glass necking is ;~ also less and the porous ceramic is not as strong. Pre-ferably, the ceramic particles of the present invention have a size of about lO0 to lO00 microns and, more prefer-ably 500 to lO00 microns.

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The ceramic composite of the present invention has broad application because the ceramic particles can be any of a variety of ceramic materials. It is useful in providing bone implants, surgical cements or grouts, and drug delivery devices. Outside of the biomedical field its open cell pore structure is useful in providing microporous filters.
Typical examples of useful ceramics are Al2o3, MgO, ZrO2, SiC, etc. However, the ceramic composite of the present invention is particularly useful in dental and orthopaedic applications. Ceramic particles which are useful for such dental and orthopaedic applications are a bone ingrowth promoting material. The term ~bone ingrowth promoting material" means a material, which upon im-planting into the human body, will promote or aid the growth of new bone around the ceramic material. This material may function as à scaffold for bone-growth-and-/or-~
provide nutrients which promote-bo-ne growth. - ---~ In some applications, it is anticipated that a - 20 ceramic particle of a nonresorbable bone ingrowth pro-moting material would be useful. Examples of nonresorbable bone ingrowth promoting materials are hydroxyapatite, aluminum oxide, pyrolytic carbon, etc. A preferred non-resorbable bone ingrowth promoting material is hydroxy-apatite. Examples of commer-cially available hydroxyapatite include Calcitite 20~0, a nonresorbable synthetic hydroxy-apatite available ~rom Calcitek, Inc. of San Diego, Cali-fornia and Biogel, a hydroxyapatite produced by Bio Rads Lab of Richmond, California~

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In other applications, the ceramic particles are A~ a resorbable bone ingrowth promoting material. Examples of useful resorbable bone ingrowth promoting materials include various calcium aluminates, calcium phosphates, 5 calcium aluminophosphates and calcium sulfatesO A pre-ferred resorbable bone ingrowth promoting material is ~' tricalcium phosphate. Specific examples of resorbable bone ingrowth promoting materials are the ALCAP (calcium aluminophOsphate) ceramic described in V.S. Patent No.

4,218,255 to Bajpai in ground or powdered form; calcium phosphates described in U.S. Patent No. 4,192,021; and the ALCAP ceramics described by Graves, G. A., et al, ~Resorb-able Ceramic Implants, n J Biomed. Mater. Res. Symp. 2 (Part I): 91, 1972.
Calcium aluminophosphate ceramics useful in the present invention can be obtained by mixing calcium oxide ¦ (CaO), aluminum oxide (A12o3), and phosphorus pentoxide (P2O5) in weight ratios o~--about 35-to 40%~CaO, about- ---- -- - -----45 to 55% A12o3, and about 10 to 20% P2O5; com-pressing the mixture; and calcining. A typical ceramic is ~- prepared from a 38 50 12 mixture of calcium oxide, aluminum ; oxide, and phosphorus pentoxide which is calcined at 1300C
; for 12 hours and ground.
~esorbable and nonresorbable bone ingrowth pro-;~ 25 moting materials may be combined to provide a partially resorbable ceramic. For example, in order to stimulate bone growth, it may be desirable to formulate the composi-tion such that a major or a minor portion of the ceramic is resorbed.

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~VD 082 P2 -7-The ceramic particles of the present invention are enveloped by a fusible glass and are bonded to adjacent ceramic particles at their interfaces by the fusible glass.
Any glass is useful in the ceramic material of the present invention, but preferably, a biocompatible glass having a melting point in the range of about 500 to 1000C is used.
In many biological applications~ the fusible glass is resorbable. A particularly useful resorbable glass comprises calcium oxide ~CaO) and phosphorus pent-oxide (P2O5). Other ingredients such as calciumfluoride (CaF2), water (H2O), and other metal oxides containing cations such as magnesium, zinc, strontium, sodium, potassium, lithium, silicon, boron and aluminum oxides may also be incorporated in small amounts. In terms of the binary mixture, the preferred Ca:P mole ratio ranges from about 0.25 to 0.33. Preferably, the glass ; ~ comprises by weight 5-50~ CaO, 50-95~ P2O5, 0-5%
CaF2, 0-5~ H2O and 0 10% of a metal oxide selected from the group consisting of magnesium, zinc, strontium, Sodium, potassium, lithium, and aluminum oxides. In a preferred embodiment, the calcium oxide (CaO) is present by weight in the amount of 15-25%; the phosphorus pentoxide (P2O5) is present by weight in the amount of 65-90~
while either calcium fluoride (CaF2) or water (H2O) is present by weight in the amount of 0.1-4%.
Comparable to the ceramic particles, the degree of resorbability of the glass coating can be controlled.
For example, as the amount of CaO increases, the degree of resorbability decreases. Also, as the amount of Na2o :
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In Table 1 below, glass compositions are provided in order of increasing resorbability:

10 Example CaO P2o5 Na20 K2o ~1203 MgO ZnO SiO2 . _ . ~ . _ _ . . .. _ . ... _ ..... .. .. _ . _ _ _ B -- 58 -- 37 5 -~
C -- 56 21 20 -- -- 3.0 --D __ 63 - 30 _ _ 7 In making the ceramic material of the present invention, the glass is ground to a particle size of about 10 to 50 microns and coa~ed on the surface of the larger ceramic particles. The particle size should be as uniform as possible.
Typically the glass is adhered to the ceramic particles as a slurry in a solution of a binder such as polyvinyl alcohol (PVA). When the ceramic is subsequently sintered, the binder burns off. The coating is typically ~- about the thickness of the glass particle, although thicker coatings may also be useful. The weight ratio of the ceramic par~icles to the glass coating is about 8:1 to :`

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14:1 and preferably about 10:1 to 12:1. In a preferred embodiment~ ~he ratio which provides a desirable thin coating with good porosity and good necking between the ceramic particles is about 11:1. Of coursel this will vary with the particle size of the ceramic.
Methods for obtaining hydroxyapatite and trical-cium phosphate particles are known in the art. Two rel~
atively new techniques can also be used. One is sol-gel processing, a method of preparing solid materials that result when certain combinations of chemicals are mixed and precipitated from solution. The sol-gel, if dried slowly, can yield very fine grained ceramics which sinter to high density. The second is a process that provides particles of well controlled size and shape by using spray drying and agglomeration techniques which, until now, were used primarily in the food and drug industry. A slurry of the ceramic and a binder such as PVA is fed to a spray dryer (e.g., a Bowen Ceramic Spray Dryer, Bowen Engineering, Inc. Somerville, N.J.) where it is atomized into fine droplets which are rapidly dried to yield :
; relatively uniform spheres of the ceramic which are sintered for example in a tunnel kiln. Both techniques after sintering provide dense, spherical shaped ceramic particles such as hydroxyapatite or tricalcium phosphate in controlled sizes which may be used to form the porous ceramic of the invention. These materials are also avail-j~ able commercially.
Figure 1 illustrates an agglomerator 10 useful incoating the ceramic particles of the present invention with glass. Ceramic particles 12 are fed by air through , ~' : .
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tube 14 into the agglomerator 10. A slurry of a glass powder 1~ in a binder is fed to a rotary disc 18 through tube 17. As the disc 18 rotates, the glass powder 16 collides with and coats ceramic particles 12. The glass coated particles roll off the plate 18 and are dried in a hot air stream and collected. The resulting glass coated ceramic particles 20 appear as schematically illustrated in Figure 3.
Figure 2 illustrates a spray dryer 22 useful in coating the ceramic particles 12 with the glass powder slurry 160 Glass powder 16 is fed through a tube 24 into spray dryer 22. The ceramic particles 12 are dropped through tube 26 into the spray dryer 22. The ceramic ; particles 12 and the glass powder 16 collide and the glass powder 16 coats the ceramic particles 12 to produce the glass coated ceramic particles 20 of Figure 3~
The glass coated ceramic ~articles 20 of Figure 3 are lightly compacted into a desired shape and then sin-tered. The particles may be compacted in a mold under pressures of about 5 to 1000 psi. Virtually any simple shape can be produced. Upon sintering, surface tension causes the glass powder 16 to melt and flow on the surface ~ of the ceramic particles 12 to form the ceramic material ;~ 28 of Figure 4. Typically, the glass coated ceramic particles 20 are sintered at temperatures of about 600 to 1200C (other temperatures can also be used) for about 5 to 30 minutes. The glass powder 16 envelops the ceramic particles 12 and bonds the adjacent ceramic particles 12 at their interfaces by necking between the ceramic particles 12. Pores 30 form in the ceramic material 28~

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ll V D 1) f3 2 P 2 In ~t(l(lit l.on to coatLng lar~Jer ceralllic particles w:ltll a lm~ .3r ~u~L~).Le c3.las;i~ pow(ler, other meEIns are also a ~3nvi~3Lorltlcl eor provicJLn~J ~Jlcl.3r3 co ited ceramLc particles ~ olul ln eorlllLrl(J tl~ porc~uC3 CeralniC3 o~ tn~3 present in-rj vcrltLotl. In uart Lcular, ceralnic particlt s ~uch a~ E~A and I.CP, w~lt~n eormI~d t~y r~pray clryin-J or acJc31OIneration~ are ~3:LIltt.~rt3cl pr:Lor t:o coat:Lnc~ with cJIa3~3 rll.is sintering i~3 ~I~;u7~].ly pt3reormti~d by ~he manu~ac~urer o commerci.~lly ~lval.laL).le mal:t3i-ial.q. ~lowevt~r, a contLnuous proce~;s ic3 I 10 t3nvl~Lc)ned in whictl ~ht3 ~:lntt.~ced partLcl~ ai-e elUidiZt3d ancl c onr~act.ecl w~l th t.lle cJ.lac3~ powdcr while they are at an 1ev.ltt~cl kt)mperaturc~ ~luctl tl~at t~le gla.r3s r~ilm~3 out directly on cc-~ntac~t wllh tt~e ~urfrlce ol tlle~ particle.
I rrc~ ~romot~ bone inlJrow~h, ~he ceramtc material of h~ pr~sen~ lnvantioll stlould h~lve, or acquire through r~ orp~:Lorl, a ps)re~ ~tze oE at least abo~lt 100 microns.
.Inc 1uclLng oth~r app.lications~ the ceralnic mat~rial has a pore ~I~.e Oe c~i~out 20 to 15n micron~, anc3 pre~erablY, ~rom t~bout. 100 t.o I!iQ m L~rons.
In ~ld.Lt Lon tc~ the ~la~5 compositlon and the c~ami~ p~r~ eolnpo; ltion, t~ ;la~s. thlokne~3s is a t l~a~kor in e~orl~rol:ltn~ rca~e o~ resor~abi:lity oE the c~ralni~ c0~ In ~ eréll~ Eor a s;lowly resorbable ~;~ c~r~ compo~lt~, k~le gl~s~ coatin~ i~ thi~ker than for a E~k~r ~*~;or~c~ eralnic compo~.ike.
A~ an ~ mple oE a colnp.letely nonresorbable cer ~m:l~ comp~lt~ yclroxyclpatL~e pc3rt1~1es can be cod~ed Wiktl an in~c~.lu~ ss ~ucil as ~xampl~ A in Table 1 (a typ.i~3.l ~30da llm~ t~ XE on~ theQ w~n~ed to increase .lll ~ r~sorb~bili~.y of ~h~ ~omplQt~ly nonr~sorbable cQralnic .

) UVD ~)~2 l~2 -L2-colllpoilt~, re~or~ ble cerar(lic pclrtLclec3 can be mi~ec3 with.hle tly(3rOXydp(lt' i.~,e or a re:~ort~able ylaf3s can be u~ed. An xamp:le Oe a comple~ly rescrbahLe cerarllic composite i~3 a tr:Lccllcillln pho~;~)hllte cecaw~ic ~drtic le c.~oat~d w:lth a glas~
cor~lprinln~3 Ct10 an(l P2~5 Ln a weiyhk % rat:Lo of about 20:~0. ~rlu~, th~ cer~lmic COmpQ~ite~C3 o~ the present in-c311tLOrl tlaV~ broad appllccltLon t~ecause t)le degree and rate o~ resorpt:Lc)n can ~? wiclel.y varie~ by caee~ully clloo~ing the proper colllbinal:i.on o~ ceralnic l~article composition, 1(~ glclss compositlon and it~3 ~.hickne~;f~.
When ~elect:incl a ceralnic ~article ancl glass foe n.~e :I.n ttl~3 c~ralllic corllpo~c3Lte~ tne mechanicdl s~ren~h of tl~e implant ~Ind tl~e rate o~ bone ingrowt.h sho~lld be con-c~:Ld~3red, 'l'he c~t3ra~ c pore f3ize grea~ly in~1uences both.
Gen~ra.lly~ tl cerallliC havlll~ a ~slnall pore ~:ize exhibLt~ a hi-Jh ~l~r~C3119~h t~Ut a lower rd~e o~ ingrow~.t~ compared to a c~3ramic havinl3 ~ lar~er ~ore c3iæe. I~ the ceramic and/o~
l~s iL~ re~orbable, ~he pore siæe will lncreac3e a~ the a ln 1 c a ~
I ~Q In partlclllar, i~ nkicipat~d thak a ceeamic : wi:ll bc d~ic3ncd ka tlave lligh strength initially ~In~il a :~ call~ls ~a~ forlned nround khe lmplc~nc and becolne ~ully m:ln~r~liæQ(l. ~y cde~ully desic~lllny th~ resoepkion rate a~: ~h~ cJk~s~ clndt~r khe cer~mic partic:le, the implant will onLy ~ ~t~c~b~l a~^~.er ~t~Q new bon~ ha~ enouc3h strenyth~
~h~ th~ rp~ion ra~ o~ kt~ cer~m:ic typically wi.ll be le~ han ~h~ l`A~e ak which n~w ban~ eO~n~
'rh~ c~ramlc compc)~ik~s oE t.he present inventian h~ nulil~rou.~ u~ in or~ho~aed~c nl~d d~rlk~l app.Lications.
3~ rrh~ cerc~lnlc campc)~ mc~y ~ suppli~d in a ~olid ~orm and ~ :
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cut to the desired size by the practitioner. In another application, ceramic particles coated with glass powder or the fused glass powder are sold to the surgeon who would have his own furnace and mold. The mold is filled with the ceramic particles and the ceramic material in the desired shape is sinteredO
In another application, it is anticipated that the glass coated ceramic particles could be adhered to the surface of a prosthetic device to enhance bone attachment to the device. This is accomplished by first applying a thin glass coating to the prosthesis, adhering glass coated particles to the prosthesis and then sintering. Figure 6 is an example o~ a prosthesis 40 used in hip replacements.
The shank 42 of the prosthesis is driven into the bone.
By applyiny glass-coated ceramic particles 44 to the shank, bone growth around the prosthesis and attachment of bone to the prosthesis is promoted.
The present invention is illustrated in more detail by the following non-limiting examples:

Example_l Approximately 2 g of a spherical particulate ; hydroxyapatite (HA 500, a product of Orthomatrix, Inc.) screened to 40 x 60 mesh was placed in a glass dish, 4 to

5 drops of a saturated solution of polyvinyl alcohol was added to the HA. T~le HA was coated with the PVA solution by spreading it throuyh the solution with a spatula until it is well coated (approximately 3 to 5 minutes). The PVA
coated HA was dried at 90C and separated with a spatula.
Glass composition E (Table 1) was ground to 10-40 microns :

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' UVD 082 P2 -14-and sprinkled over the PVA coated HA. The mixture was then vibrated to uniformly coat the H~ particles (approxi-mately 1-2 minutes ). The glass composition uniformly adhered to the HA particle surfaces. The glass coated HA
particles were placed in a ~/32 inch die on a Clifton Hydraulic Press. Enough HA was placed in the die to dis-place the plunger of the die approximately 3/8 inch. 100 microliters of the PVA solution was then added to the die and the plunger was replaced and ~he die vibrated until the PVA solution stopped running out of the die (30-60 seconds). The press was activated and the HA particles were compacted (approximately 500 psi). The compacted cylinder was removed from the die and dried at 90C for ; appoximately 4 hours. The dried cylinder was sintered at ~ 15 1000C for 5 minutes~
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Hydroxyapatite was bonded to a prosthesis using the following procedure;
~` The procedure was evenly coated with a thick slurry of a glass having composition E in Table 1 using a paint brush. The slurry on the surface of the prosthesis ¦ ~ was dried at 90C and glazed by heating at 1000C for 5 minutes. Glass coated hydroxyapatite particles were pre-pared ~s in Example 1 above and spread on the prosthesis and dried. ~he prosthesis was then fired at 1000C for 5 minutes and allowed to cool slowly.
Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
l. A ceramic composite having an open porous network of a controlled pore size comprising a plurality of ceramic particles having a coating of a fused glass on their sur-faces, said ceramic particles being bonded to adjacent ceramic particles at their interfaces by said fused glass coating to provide an open porous network between said ceramic particles.
2. The ceramic composite of claim 1 wherein said ceramic particles are a material selected from the group consisting of Al2O3, MgO, ZrO2, and SiC.
3. The ceramic composite of claim 1 wherein said ceramic composite is useful for dental and orthopaedic implants and said ceramic particles are a bone ingrowth promoting material.
4. The ceramic composite of claim 3 wherein said ceramic particles are a nonresorbable bone ingrowth pro-moting material.
5. The ceramic composite of claim 4 wherein said nonresorbable bone ingrowth promoting material is selected from the group consisting of hydroxyapatite, aluminum oxide, and pyrolytic carbon.
6. The ceramic composite of claim 3 wherein said ceramic particles are a resorbable bone ingrowth promoting material.
7. The ceramic composite of claim 6 wherein said resorbable bone ingrowth promoting material is selected from the group consisting of calcium aluminate, calcium phosphates, calcium aluminophosphates and calcium sulfates.
8. The ceramic composite of claim 7 wherein said ceramic composite has a pore size of about 20 to 150 mi-crons.
9. The ceramic composite of claim 8 wherein said ceramic composite has a pore size of at least about 100 microns.
10. The ceramic composite of claim 9 wherein said glass is resorbable.
11. The ceramic composite of claim 10 wherein said resorbable glass comprises calcium oxide (CaO) and phos-phorus pentoxide (P2O5).
12. The ceramic composite of claim 11 wherein said resorbable glass comprises by weight:

CaO 5-50%
P2O5 50-95%
CaF2 0-5%
H2O 0-5%
XO 0-1 0%

wherein XO is a metal oxide selected from the group con-sisting of magnesium, zinc, strontium, sodium, potassium, lithium and aluminum oxides.
13. The ceramic composite of claim 12 wherein said ceramic particles have a particle size of less than about 2000 microns.
14. The ceramic composite of claim 13 wherein said ceramic particles have a particle size of about 500 to 1000 microns.
15. The ceramic composite of claim 14 wherein the ratio of said ceramic particles to said glass coating based on the weight of said ceramic material is about 8:1 to 14:1.
16. The ceramic composite of claim 15 wherein said ceramic material is formed by coating said ceramic part-icles with fusible glass particles, molding said fusible glass coated ceramic particles into a desired shape and sintering.
17. The ceramic composite of claim 16 wherein said ceramic particles are coated with said fusible glass part-icles in an agglomerator or a spray dryer.
18. Ceramic particles having a coating of a fused glass on the surface thereof.
19. The ceramic particles of claim 18 wherein said glass comprises calcium oxide (CaO) and phosphorus pento-xide (P2O5).
20, The ceramic particles of claim 19 wherein said particles are a bone ingrowth promoting material.
21. A process for preparing a ceramic composite having a controlled pore size comprising the steps of:
coating ceramic particles with a glass, molding said glass coated ceramic particles into a desired shape, and sintering.
22. The process of claim 21 wherein said glass is a fusible glass powder.
23. The process of claim 22 wherein said ceramic particles are coated with said fusible glass particles in an agglomerator or a spray dryer.
24. The ceramic composite of claim 9 wherein said glass is non-resorbable.