Cells and Materials

Volume 2 Number 2 Article 2

1992

Microstructure of Mica -Ceramics and Interface Reactions between Mica Glass-Ceramics and

W. Holand Ivoclar AG, Liechtenstein

W. Gotz Friedrich-Schiller-Universitat Jena

G. Carl Friedrich-Schiller-Universitat Jena

W. Vogel Friedrich-Schiller-Universitat Jena

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Recommended Citation Holand, W.; Gotz, W.; Carl, G.; and Vogel, W. (1992) "Microstructure of Mica Glass-Ceramics and Interface Reactions between Mica Glass-Ceramics and Bone," Cells and Materials: Vol. 2 : No. 2 , Article 2. Available at: https://digitalcommons.usu.edu/cellsandmaterials/vol2/iss2/2

This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Cells and Materials by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. CEU.S AND MATERIALS, Vol. 2, No. 2, 1992 (Pages 105-112) 1051-6794/92$3. ()() + .()() Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA

MICROSTRUCTURE OF MICA GLASS-CERAMICS AND INTERFACE REACTIONS BETWEEN MICA GLASS-CERAMICS AND BONE

W. Holand1*, W. Gotz2, G. Carl2, and W. Vogel2

1Ivoclar AG, Bendererstrasse 2, FL-9494 Schaan, Liechtenstein 2Friedrich-Schiller-Universitat Jena, Otto-Schott-lnstitut, 0-6900 Jena, Germany

Abstract Introduction

This review paper characterizes glass-ceramics con­ The first machinable glass-ceramic, which contains taining mica as main crystal phase. The phase formation mica as main crystal phase is ® which was de­ reactions in dependence of the chemical composition and veloped by Beall et al. (1971). The composition of the the microstructure are shown. Microstructure of mica base glass is 47.2 Si02, 8.5 B20 3, 16.7 Al20 3, 14.5 glass-ceramics has been studied by ele..ctron replica and MgO, 9.5 K2 and 6.3 F. scanning electron microscopic (SEM) techniques. A special method of controlled nucleation via phase Mica glass-ceramics have previously been developed separation and crystallization of has been in Si02-B20rA120rMgO-F--base glasses. The material used by Beall et al. (1971) to precipitate fluoro­ is machinable because of the precipitation of micas of phlogopite, namely KMg3(AlSi30 10)F2 as main crystal fluorophlogopite-type. Also, a machinable glass-ceramic phase. The result was a glass ceramic which could be for dental applications was developed based on machined with standard metal working tools. Because KMg2_5(Si40 10)Frmicas. We developed mica glass-cer­ of the combination of favorable properties, such as amics in the Si02-Al20rMgO-NaiO-K20-F glass sys­ machinability and electrical isolation, very interesting tem. Phase formation within these glasses was observed technological applications can be considered. In order by SEM. A double controlled nucleation and crystalliza­ to ensure good machinability the precipitated mica crys­ tion of mica and apatite crystals was possible in glasses tals in the glass matrix need an optimal size and contact of the SiOrMgO-NaiO-K20-F-CaO-P20s-(Al20 3) sys­ with each other. The material is machinable because of tem. The main crystal phases of phlogopite-type were the preferred cleavage of the micas. Beall (1979) called characterized by SEM and energy dispersive x-ray spec­ the microstructure of the glass ceramic a "house of cards troscopy (EDS) and apatite crystals Ca5(P04)J(OH,F) structure", which describes the orientation of the micas were analyzed by X-ray diffraction measurements. The in the glassy phase. glass-ceramics are useful for bone substitu­ Based on this development of Beall et al. (1971) tion. EDS analysis shows the ion exchange between further mica glass-ceramics (e.g. , Beall, 1991) have glass-ceramics and body fluids. The interface reaction been developed also for medical applications. The is characterized by formation of a small phosphate layer, authors of the present paper review these developments and particularly by alkali ion exchange. (see chapters "glass-ceramic of DICOR®-type", "precipitation of micas rich in ea2+ -ions"). Key Words: Glass-ceramics, mica, apatite, bone substi­ Further mica type glass-ceramics for technical pur­ tution, scanning electron microscopy, machinability, poses have been developed by Vogel et al. (1973) in the interface reactions, microstructure, phase formation, magnesium-aluminosilicate base glass system. Based on bioreactivity, ion diffusion. these investigations, the authors of this paper developed a phlogopite-type glass ceramic for medical application. This glass ceramic is biocompatible but not bioactive •Address for correspondence: (see chapter "glass-ceramic of BIOVERIT® II-type"). w. Roland The development of bioactive biomaterials has lvoclar AG, Bendererstrasse 2 strongly been influenced by Hench et al. (1972) who FL-9494 Schaan developed the BIOGLASS® from the SiOi­ Principality of Liechtenstein NaiO-CaO-P20rF system. The new biomaterials show Phone No.: (0041/75) 5 35 35 bioactive properties and the materials are bonded to Fax: (0041/75) 81 279 living bone. BIOGLASS® forms apatite on the surface

105 W. Roland, W. Gotz, G. Carl and W. Vogel

Figure 1. Microstructure of DICOR* glass ceramic observed during replica investigation of fracture surface in a transmission electron microscope (fEM). Specimen was etched for 5 seconds in 1 % HF. Figure 2. SEM of cross-section through globular aggregates of curved phlogopite showing initial stage of crystal­ lization. Polished sample and etched 2.5 seconds in 2 % HF. Figure 3. Advanced stage of the precipitation of curved phlogopite crystals. SEM. Polished sample and etched 2.5 seconds in 2 % HF. Figure 4. Curved phlogopite crystals in glass ceramics (BIOVERIT* II-type) having high translucency. SEM. Polished sample and etched 2.5 seconds in 2 % HF. in contact and reaction with the body fluid and the living ing strength. Hence, the material is used in dental bone. On the basis of the knowledge of this apatite for­ medicine as crowns. mation in BIOGLASS*, further bioactive glass-ceramics, containing apatite crystals, have been developed Glass-Ceramics of BIOVERIT* II-Type (Blencke et al., 1977; Strunz et al., 1978). (Mica Glass-Ceramic) Kokubo et al. (1982) showed a preferred bonding of bone and apatite-wollastonite glass ceramic, and an addi­ The crystallization behavior of magnesium-alumino­ tional apatite formation in reaction with simulated body silicate base glasses was investigated by Vogel et al. fluid could be shown on the surface of the biomaterial (1973). N820, K20 and F were added to Si~-Al20r (Kokubo et al., 1990). MgO-glasses and the mica precipitation has been stud­ The authors of this present paper developed a ied. Based on these results, Roland et al. (1981) machinable bioactive glass-ceramic consisting of two analyzed the phase formation processes in glasses of the crystal phases, namely mica and apatite, and a glassy composition: 43-50 Si~, 26-30 Al20 3, 11-15 MgO, 7- phase. The microstructure and the properties, especially 10 R20, 3.3-4.8 F, 0.01-0.6 Cl, 0.1-3 CaO, 0.1-5 the interphase reactions between mica and bone are pre­ P20 5, wherein R20 is the sum of 3-5.5 wt. % N820 and sented (see chapter "BIOVERIT* I-type glass-ceram­ 4-6 wt. % K20. A new type of phlogopite in a curved ics"). Other glass-ceramics containing micas and phos­ shape was precipitated in a glass ceramic. The forma­ phates are reviewed (see "glass-ceramics containing tion of this new phlogopite was investigated in a glass micas and CaO-, P20s-additives"). with the chemical composition (wt. %): 44.5 Si~, 29.9 Al203, 11.8 MgO, 4.2 F, 4.4 Na2, 4.9 K10, 0.1 Cao, Glass-Ceramic of DICOR*-Type 0.1 P20 5, 0.1 Cl by TEM and SEM (HOland et al., (Mica Glass-Ceramic) 1991a). The chemical composition of this new curved mica, (N a0 .18K0 .82)(Mg2_24AI0 .61 )(Si2. 78Al1.22) Grossman (1972, 1983) crystallized glasses consist­ 010.1of1.90could be analyzed by energy dispersive spec­ ing essentially of 45-70 % Si~, 8-20 % MgO, 8-15 % troscopy (EDS) (Roland et al., 1991a). MgF2, 5-35 % R20 and RO; where R20 consists of In comparison to glasses which form flat mica crys­ K20, R~O and C520 and RO consists of SrO or BaO tals, the control of the reduced phase separation process and other alkaline earth oxides. Additions, such as allowed the formation of the new curved mica crystals Zr02, A120 3 and colourants were used. These (HOland et al., 1981). Because of a low concentration investigations have been the basis for the development of of nucleating centers, curved micas and cordierite a glass of the composition (in weight percent): 60.9 crystals (as secondary crystal phase) grow in the range Si02, 0.6 A120 3, 17.1 MgO, 13.8 K20, 4.9 F, 4.7 700-1050 °C. The phase formation and the structure of Zr02, 0.05 Ce02 (Adair, 1984). Ce02 can give the curved mica crystals, that are typical for glass-ceramics glass-ceramic fluorescence. This glass was heat treated ofBIOVERIT* II-type, have been studied in comparison and the microstructure was investigated by scanning to flat crystals (Vogel and ROiand, 1982; Roland et al., electron microscopy (SEM) (Grossman, 1989; Adair, 1983b; Elsen et al. 1989). Crystal structure investiga­ 1984). tion by X-ray diffractometry of phlogopite micas showed Grossman (1989) showed that the base glass is that the curved mica has a still higher content of alumi­ phase separated and mica crystals of KMg2_5Si40u12- num ions in the octahedral coordination. type grow during heat treating the glass from 625 to Small glassy phase separated droplets are the nu­ 1075 °C. A typical microstructure is shown in Figure cleating centers of the curved phlogopite. Curved phlo­ 1 (the preparation technique is indicated in the caption of gopites grow as isolated ball shaped aggregates (Figure the Figure). The glass ceramic shows excellent proper­ 2). The crystallization up to 980 °C can be controlled ties, such as machinability, translucency and good bend- so that the curved crystals come into contact with each

106 Mica glass-ceramics, structure and reactions

•107 W. ROiand, W. Gotz, G. Carl and W. Vogel

108 Mica glass-ceramics, structure and reactions

The experiences of the surgeon (Beleites et al., 1988) showed that middle ear implants have to have a very good machinability, that means a high content of curved micas (Beleites et al., 1988) and dental products should show a special translucency.

Precipitation of Micas Rich in Ca2+ -Ions

Silicate glasses rich in CaO were developed by Ehrt and Heidenreich (1978), and Kasuga and Kasuga (1991). A characteristic composition which has been investigated by Ehrt and Heidenreich was 50 % SiOi, 18 % A120 3 , 7 % MgO, 10 % CaO, 3.5 % N310, 4.5 K20, 7 Ma. % F. Kasuga and Kasuga (1991) could get glass-ceramics

of the composition 43 .5 Si02, 12. 7 Al20 3 , 25.5 MgO, 6.5 CaO, 1.7 K20 and 10.1 F. The main crystal phase is a mica rich in Ca2+ -ions and secondary phases, such as diopside, anorthite, richterite and others were pre­ cipitated in the glass-ceramic (Kasuga and Kasuga, 1991). Developments of Ehrt and Heidenreich (1978) and Kasuga and Kasuga ( 1991) to increase the Cao-content in mica type glass-ceramics had given the possibility to develop machinable glass ceramics with high mechanical strength (bending strength 210-300 MPa). The micro­ Figure 9. Interface between bone (guinea pig) and structure of the glass ceramic formed by Kasuga and mica-apatite glass ceramic (BIOVERIT® I) one year Kasuga contains mica and diopside crystals and a glass after implantation. matrix phase. An application for dental crowns was proposed by Kasuga and Kasuga (1991). Figure 5. Mica-cordierite glass-ceramic (BIOVERIT® II-type). The precipitation of cordierite takes place BIOVERIT® I-Type Glass-Ceramics between the curved mica plates. SEM. Polished sample (Mica-Apatite Glass-Ceramics) and etched 2. 5 seconds in 2 % HF. A combination of different properties within a glass Figure 6. Base glass of mica-apatite glass-ceramic. ceramic material, especially the combination of machina­ The glass consists of three glassy phases. TEM/replica. bility and bioactivity was possible in multi-component Fractured surface etched 5 seconds in H Cl. glasses of the SiOi-(A120 3)-MgO-NaiO-K20-P--Ca0- Figure 7. Precipitation of Ca (P0 )J(OH,F) apatite 5 4 P205 system. Typical compositions are 35.9 Si02, 18.1 within the CaO-P 0 -F rich droplet phase. TEM/rep­ 2 5 A120 3, 6.5 MgO, 5.1 Na20, 4.0 K20, 16.7 CaO, 11.2 lica. Fractured surface etched 5 seconds in HCI. P20 5 and 2.5 wt. % F_ or 38.7 Si02, 1.4 Al20 3 , 27.7 Figure 8. Mica.apatite glass-ceramic after one week in MgO, 6.8 K20, 10.4 CaO, 8.2 P20 5 and 1.9 wt. % Ringer's solution. TEM/replica. Ti02 (Roland et al., 1983a, Roland et al., 199la). Mica-apatite glass-ceramics show a characteristic other (Figure 3). The content of crystals within the microstructure and phase formation reactions (Vogel and glass-ceramic can be varied, e.g., lowered in compari­ Roland, 1987). The base glass shows three glassy son to Figure 3 and the translucency becomes higher phases, a Si02-ricb glass matrix, a CaO-P20rF--rich (Figure 4). big droplet phase, and a Na20-K20-Al20rMgO-P--rich Varying the chemical composition, to add more b~g droplet phase (Figure 6). Heat treating the glass at temperatures between 610 and 1050 °C allowed a double MgO and Al20 3 to the melt, it is possible to increase the content of the second crystal phase, cordierite (Figure controlled in situ crystallization of mica and apatite. 5). Therefore, the properties of the glass-ceramic, such Apatite grows inside the CaO-P20rF-rich big droplet as translucency, mechanical properties and thermal ex­ phase (Figure 7) and phlogopite formation is a result of pansion coefficient can be controlled depending on the a solid state reaction of the glass matrix phase and the particular application in medicine (Roland et al., 199 la). small droplet phase (Figure 8). The apatite crystals of

109 W. Holand, W. Gotz, G. Carl and W. Vogel

Ca5(P04)J(OH,F)-type could be determined by X-ray Conclusiom diffraction measurements and the flat phlogopitecrystals, (Nao.21Ko.s1)(Mgo.52Alo.44)(Si2.8oA11 .20)010.18F 1.s2 The results of the authors of papers cited in the bib­ could be analyz.ed by EDS (Holand et al., 1983 a, liography and the authors of this paper showed that mica 1985). glass-ceramics are biocompatible materials which can be The authors of the present paper assume that similar used for bone substitution in medicine. reactions take place in glasses containing low concentra­ DICOR~-type glass ceramic is used for dental tions of Al20 3 (or Al20rfree glasses). The difference restoration. Mica glass-ceramics of BIOVERIT* IT-type between the phase formation in glasses shown in Figures and mica-apatite glass ceramics of BIOVERIT* I-type 6-8 is that the phases formed are very small and the have been successfully applied in head and neck surgery mica consists of KMg2.s(S4010)F2-type. and orthopaedic surgery in more than 600 patients Electron microprobe investigations carried out by (Schubert et al., 1988; Holand et al., 1990). Holand et al. (1991b) show a very good contact of mica­ apatite glass-ceramic and bone. One year after opera­ tion, the reaction interface between bone (tibia of guinea References pig) and mica-apatite glass-ceramic is less than 15 µm (Figures 9 and 10). Apatite is present within the bio­ Adair PJ (1984). Glass ceramic dental products. US material but an additional small calcium phosphate layer Patent 4,431,420. will be formed on the surface of the glass-ceramic. Sec­ Beall GH, Montierth MR, Smith P (1971). Work­ ondary ion mass spectroscopy (SIMS) investigations able glass ceramics. Glas-Email-Keramo-Technik, 22, show the tendency that phosphate groups become en­ 409-415. riched at the surface of BIOVERIT* I glass-ceramics Beall GH (1979). Microstructure of glass-ceramics under simulated conditions (Holand et al., 1991b). and photosensitive glasses. Wiss. Zeitschrift Universitit Figure 11 shows that the peak positions 31, 47 and 63 Jena, mat.-nat.wiss. Reihe, 28, 415-423. are responsible for the enrichment of phosphate groups. Beall GH (1991). Chain silicate glass-ceramics. J. Additionally an NaCl-rich layer from the simulated body Non-Cryst. Solids, 129, 163-173. fluid seems to be deposited onto the sample (position 35, Beleites E, Gudziol H, Holand W (1988). 37). Maschinell bearbeitbare Glaskeramik fur die Kopf-Hals­ The process of bioactivity seems to be of a complex Chirurgie (Machinable glass ceramics for head and neck nature. It includes solid state reactions (apatite-apatite surgery). HNO-Prax. 13, 121-125. reaction), ion diffusion processes (e.g. Na+-, ea2+ -dif­ Blencke B, Bromer H, Deutscher K, Pfiel E (1977). fusion), Ca-phosphate formation and a possible positive Glaskeramiken fur Osteoplastik und Osteosynthese influence of (Hench, 1991) on the bone regener­ (Glass ceramics for osteoplastics and osteosynthesis). ation reaction. This corresponds with results of bio­ Bundesministerium fur Forschung und Tecbnologie FRG active behavior of glasses and glass-ceramics reported by Forscbungsbericbt T 77-91. Hench (1991), Kokubo et al. (1990), and Wilson (1991). Ehrt R, Heidenreich E (1978). Maschinell bearbeitbare glimmerhaltige Glaskeramiken und Gl~-Ceramics Containing Micas Verfahren zu ihrer Herstellung (Machinable mica­ and Cao, P20 5-Additives containing glass ceramics and procedures for their production). German Patent DD 132 332. Shibuya et al. (1990) also formed glasses by adding Elsen J, King GSD, Holand W, Vogel W, Carl G CaO and P20 5 to Si02-(AI20 3)-MgO-K20-F- glasses, (1989). Crystal structure of a fluorophlogopite synthe­ e.g.: 57.1 SiOi, 11.7 MgO, 13 K20, 5.9 F, 4.8 Zr02, siz.ed mica glass ceramic. J. Chem. Research (M) 1253- 3.1 CaO, 2.6 P20 5 and 1.84 Ce02. The formation of 1263. different crystal phases was investigated by X-ray Grossman DG (1972). Machinable glass ceramics diffraction measurements (Shibuya et al., 1990). based on tetrasilicic mica. J. Am. Ceram. Soc. SS, 446- Shibuya et al. (1990) developed a KMg2.s 449. (Si40 10)Frmica glass-ceramic containing also calcium Grossman DG (1983). Stain-resistant mica composi­ phosphate groups. Apatite crystals have been analyz.ed tions and articles thereof in particular dental constructs. by X-ray diffraction measurement after beat treating the European Patent EP 0 083 828. glass up to 1050-1075 °C. Shibuya et al. (1990) report­ Grossman DG (1989). Der Werkstoff Guss/Glas­ ed also, that they have carried out scanning electron mi­ keramikmaterial (Castable glass-ceramic). In: Perspek­ croscopic measurements which show that the. crystals are tiven der Dentalkeramik, Preston ID (ed.). Quintessenz­ in close contact with each other, they are cross-linked. Verlag-GmbH, Berlin, 117-133.

110 Mica glass-ceramics, structure and reactions

SIMS

® glass ceramic ® bone Cl

B

~ c ::J >. ., ~ I A 15 ../ ·' ro \... ,,.... 30.0 35.0 40.0 45.0 50.0 55.0 60 .0 65.0 I \ /I I m/e \ I / I \ I '1 KKoc '-I Figure 11 (above). Negative secondary ion mass spectra (SIMS) of BIOVERIT® I glass-ceramic ._ . ...-...... before (A) and after soaking (B) in simulated body Ca Koc fluid (SBF) at 95 °C for 64 hours. PKoc Figure 10 (at left). Electron microprobe investiga­

10 20 30 40 50 60 70 80 µm tion of the interface between mica-apatite glass ceramic and bone (16 weeks after implantation).

Roland W, Vogel W, Naumann K, Gummel J (1985). Interface reactions between machineable bio­ active glass-ceramics and bone. J. Biomed. Mater. Hench LL, Splinter RJ, Allen WC, Greenlee Jr. Res. 19, 305-312. TK (1972) . Bonding mechanisms at the interface of Roland W, Vogel W, Beleites E, Schubert T, ceramic prosthetic material. J. Biomed. Mater. Res . Naumann K, Vogel J, Wange P (1990). Reactions Symp. 2, 117-141. between BIOVERIT® glass-ceramics and hard tissue. Hench LL (1991). The compositional dependence In: Clinical materials, Heimke G, Soltesz U, ofbioactive glasses and glass-ceramics. In: Ceramics Lee AJC (eds.), Advances in Biomaterials 9, 265- in substitutive and reconstructive surgery, 270. Vincencini P. (ed.). monograph Roland W, Wange P, Naumann K, Vogel J, Carl 69, Elsevier, 259-274. G, Jana C, Gotz W ( 1991 a). Control of phase Ho land W, Naumann K, Seiferth HG, Vogel W formation processes in glass-ceramics for medicine (1981). Neuartige Erscheinungsform von Phlogopit­ and technology. J. Non-Cryst. Sol. 129, 152-162. kristallen in maschinell bearbeitbaren Glaskeramiken Roland W, Vol ks ch G, Naumann K, Carl G, (New appearance of phlogopite crystals in machina­ Gotz W ( 1991 b). Characterization of bone-glass­ ble glass ceramics). Zeitschrift fur Chemie, 21, 108- ceramic interface. In: Bioceramics, Bonfield W, 109. Hastings GW Tanner KE (eds.), vol. 4, 171-178. Roland W, Naumann K, Vogel W, Gummel J Kasuga T, Kasuga T (1991). Glaskeramiken, ( 1983a). Maschinell bearbeitbare bioaktive Glas­ ihre Herstellung und ihre Verwendung als keramiken (Machinable bioactive glass ceramics). Zahnkronen (Glass ceramics, their production and Wiss. Zeitschrift U niversitat Jena, mat.-nat. wiss. use as dental crowns). German Patent PE 4028 187. Reihe 32, 571-580. Kokubo T, Shigematsu M, Nagashima Y, Ho land W, Vogel W, Mortier W, Duvigneaud Tashiro M, Nakamura T, Yamamuro T, Higashi S PH, Naessens G, Plumat E (1983b). A new type of (1982). Apatite and wollas.tonite-containing glass phlogopite crystal in machineable glass ceramics. ceramics for prosthetic application. Bull. Inst. Glass Technology 24, 318-322. Chem. Res. Kyoto Univ. 60, 260-268.

111 W. Roland, W. Gotz, G. Carl and W. Vogel

Kokubo T, Oktsuki C, Kotani S, Kitsugi T, Discussion with Reviewers Yamamuro T (1990). Surface structure of bioactive glass-ceramic A-W implanted into sheep and human Reviewer III: The paper reviews some material as­ vertebra. In: Bioceramics, Vol. 2 (Proceedings of pects of glass-ceramics that are considered by the in­ 2nd International Symposium of Ceramics in ventors to be biocompatible. The biological behav­ Medicine), G. Heimke (ed.), German Ceramic ior of this type of material is neither investigated, Society, Cologne, 113-120. nor documented, nor published carefully enough! Schubert T, Purath W, Liebscher P, Schulze KJ Authors: The biomaterials which have been devel­ (1988). Klinische Indikationen fur die Anwendung oped at Otto-Schott-Institute of Jena University are der Jenaer bioaktiven maschinell bearbeitbaren glass-ceramic of BIOVERIT® type. The biocompati­ Glaskeramik in Orthopadie und Traumatologie bility of BIOVERIT® I-type has been investigated by (Clinical indications for the use of Jena bioactive J. Gummel, T. Schubert, K.J. Schulze and W. machinable glass ceramics in orthopedics and Purath and are documented in qualification thesis of traumatology). Beitrage Orthop. Traumatol. 35, 7- orthopaedic clinic, Dresden, Germany and partly in 16. the text reference Schubert et al., 1988. The bio­ Shibuya T, Matsui A, Morita Y, Okunaga K, compatibility of BIOVERIT® II-type is shown by E. Ninomiya M (1990). Biokompatible Glaskeramik Beleites, University Jena, clinic for otorhino­ (Biocompatible glass ceramics). German Patent DE laryngology and the results are documented in his 39 39 8310. qualification theses and partly in text reference Strunz V, Bunte M, Gross UM, Manner K, Beleites et al. (1988), and in Vogel and Roland Bromer H, Deutscher K (1978). Beschichtung von (1987). Metallimplantaten mit bioaktiver Glaskeramik The well established cell culture test method was Ceravital (Coating of metal implants with the utilized for the determination of toxicity for both bioactive glass ceramic Ceravital). Dtsch. Zahnarztl. ceramic types. Neither the "bioactive" ceramics nor z. 33, 862-865. the "bioinert" reference materials demonstrated a Vogel W, Heidenreich E, Ehrt R (1973) . significant influence on the cellular activity Maschinell bearbeitbare Glaskeramik (Machinable (proliferation). glass ceramics). German Patent DD 113 8 85. Additional testing protocols are documented in Vogel W, Roland W (1982). Nucleation and the references listed previously. We have also per­ crystallization kinetics of a Mg0-Al20 3-Si02 base formed further studies with labora­ glass with various dopants. In: Nucleation and tory animals: Sixteen weeks after subcutaneous im­ crystallization of plantation of Bioverit I, with its higher solubility, a glasses. Simmons JH, Uhlmann DR, Beall GH stabilization of the cellular reaction was observed. (eds.). Advances in Ceramics 4, Am . Ceram. Soc. The investigators concluded that this result can be 125-145. interpreted as a sign of controlled surface solubility Vogel W, Roland W (1987). The development of factors and excellent biocompatibility. bioglass-ceramics for medical applications. Angew. Chem. Int. Ed. Engl. 26, 527-544. Wilson J (1991). Bonding of bioactive ceramics in soft tissue. In: Ceramics in substitutive and recon­ structive surgery, Vincencini P (ed.), Materials Science Monograph 69, Elsevier, 523-530.

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