Cements and Bioceramics

Considerable development has occurred on sintered ceramics as bone substitutes. Sintered ceramics, such as alumina-based ones, are uru eactive materials as compared to CBPCs. CBPCs, because they are chemically synthesized, should perform much better as biomaterials. Sintered ceramics are fabricated by heat treatment, which makes it difficult to manipulate their microstructure, size, and shape as compared to CBPCs. Sintered ceramics may be implanted in place but cannot be used as an adhesive that will set in situ and form a joint, or as a material to fill cavities of complicated shapes. CBPCs, on the other hand, are formed out of a paste by chemical reaction and thus have distinct advantages, such as easy delivery of the CBPC paste that fills cavities. Because CBPCs expand during hardening, albeit slightly, they take the shape of those cavities. Furthermore, some CBPCs may be resorbed by the body, due to their high solubility in the biological environment, which can be useful in some applications. CBPCs are more easily manufactured and have a relatively low cost compared to sintered ceramics such as alumina and zirconia. Of the dental cements reviewed in Chapter 2 and Ref. [1], plaster of paris and zinc phosphate 

The biocompatible CBPC development has occurred only in the last few years, and the recent trend has been to evaluate them as biocompatible ceramics. After all, biological systems form bone and dentine at room temperature, and it is natural to expect that biocompatible ceramics should also be formed at ambient temperature, preferably in a biological environment when placed in a body as a paste. CBPCs allow such placement. We have discussed such calcium phosphate-based cements in Chapter 13. Calcium-based CBPCs, especially those constituting hydroxyapatite (HAP), are a natural choice. HAP is a primary mineral in bone [3], and hence calcium phosphate cements can mimic natural bone. Some of these ceramics with tailored composition and microstructure are already in use, yet there is ample room for improvement. This Chapter focuses on the most recent biocompatible CBPCs and their testing in a biological environment. To understand biocompatible material and its biological environment, it is first necessary to understand the structure of bone and how it is formed. 

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A US patent was granted to Bindan Corp. on a Ceramicrete-based composition [5]. This patent emphasizes the importance of recent Mg-based CBPC formulations for dental cements and bioceramics. 

CBPCs may have an important role even in the production of artificial implants. Typically, one may exploit rapid-prototyping to produce exact shapes of the implants. From a practical standpoint, formation of a ceramic out of a paste would appear to be most suitable for rapid-prototyping processes [11]. Thus, coupling CBPC with rapidprototyping should lead to artificial body parts that not only match the namral bones in their composition, but in structure as well. The science of CBPCs paves the way for their use not only as dental cements and bioceramics for the 21st century, but as discussed in earlier chapters, many other applications as well. 

There have been significant advances in CBPC-based biomaterials in the last few years, particularly Ceramicrete-based dental cement and dahllite-based bioceramics. 

Aluminate compositions include calcium aluminate cements, which have high chemical resistance, especially to sulfate, and is also used in refractory applications where ordinary Portland cements would be unsuitable. These same cements are used in bioceramic applications. The bioceramic applications reflect both the high mechanical strength of the calcium aluminate cements and also the biocompatibility of Ca-bearing phases, which bond well with, for example, bone. 

Ishikawa, K. 2008. Calcium phosphate cement. In Bioceramics and their Clinical Applications, ed. T. Kokubo. Boca Raton CRC Press, pp. 438-63. 

Fluorine is an essential element involved in several enzymatic reactions in various organs, it is present as a trace element in bone mineral, dentine and tooth enamel and is considered as one of the most efficient elements for the prophylaxis and treatment of dental caries. In addition to their direct effect on cell biology, fluoride ions can also modify the physico-chemical properties of materials (solubility, structure and microstructure, surface properties), resulting in indirect biological effects. The biological and physico-chemical roles of fluoride ions are the main reasons for their incorporation in biomaterials, with a pre-eminence for the biological role and often both in conjunction. This chapter focuses on fluoridated bioceramics and related materials, including cements. The specific role of fluorinated polymers and molecules will not be reviewed here. 

Bioceramics - [ALUMDIUMCOMPOUNDS - ALUMINIUM OXIDE (ALUMNA) - CALCINED, TABULAR, AND ALUMINATE CEMENTS] (Vol 2)... 

Naturally occurring phosphate cements are also known. Krajewski [3] cites calcium-based phosphate cements in the Albeian condensed Glauconitic Limestone of the Tatra Mountains in Western Carpathians. In recent years methods have been developed to fabricate calcium phosphate ceramics by direct reaction of calcium compounds and either phosphoric acid or an acid phosphate. The mineralogy of the products has also been well studied. Most of these efforts are directed towards development of calcium-based bioceramics containing calcium phosphate compounds, such as hydroxyapatite. These developments are discussed below. 

The last five chapters of the book are devoted to major applications of CBPCs. Chapter 14 covers CBPC matrix composites that are finding commercial applications in the United States. Discussed in Chapter 15 are drilling cements developed mainly by the U.S. Department of Energy laboratories with industrial collaborations. Applications of CBPCs in the stabilization of hazardous and radioactive waste streams are discussed in Chapters 16 and 17. Finally, recent advances in CBPC bioceramics are covered in Chapter 18. Appendixes A, B, and C compile relevant thermodynamic and mineralogy data that were useful in writing the book. They serve as a ready reference to researchers who venture into further development of CBPCs. 

Abstract Aluminates form in binary systems with alkali, alkaline earth or rare-earth oxides and share the high melting point and resistance to chemical attack of the pure A1203 end-member. This means that these ceramics have a variety of applications as cements, castable ceramics, bioceramics, and electroceramics. Calcium aluminate cements are used for example in specialist applications as diverse as lining sewers and as dental restoratives. 

Sedel L., Meunier A., Nizard R.S., and Witvoet J. 1991. Ten year survivorship of cemented ceramic xramic total hip replacement. In Bioceramics Volume 4. Proceedings of the 4th International Symposium on Ceramics in Medicine. W. Bonfield, G.W. Hastings, and K.E. Tanner (Eds.), pp.27-37. Butterworth-... 

Bioceramic coatings are often used on metallic substrates in which the fracture toughness of the metal is combined with the ability of the coating to present a bioactive surface to the surrounding tissue. The use of a bioceramic coating on a metal implant can lead to earlier stabilization of the implant in the surrounding bone and extend the functional life of the prosthesis. Under the proper conditions a cementless prosthesis should remain functional longer than a cemented device in which stability is threatened by fracture of the bone cement. 

Dental Ceramics, dental porcelain (q.v.) has been supplemented by other BIOCERAMICS, in particular apatites and alumina, for general maxillofacial restorative work, using crowns and implants. Metallising, metal-ceramic bonding and colour matching are important in dental ceramic work. BS 3365 specifies dental silicate and silico-phosphate cements BS 6039 glass-ionomer cements. 

Bioceramic materials have developed into a very powerful driver of advanced ceramics research and development. For many years bioceramics, both bioinert materials such as alumina, zirconia and, to a limited extent titania (Lindgren et al., 2009), and bioconductive materials such as hydroxyapatite, tricalcium phosphate and calcium phosphate cements, have been used successfully in dinical practice. In addition, applications continue to emerge that use biomaterials for medical devices. An excellent account of the wide range of bioceramics available today has recently been produced by Kokubo (2008), in which issues of the significance of the structure, mechanical properties and biological interaction of biomaterials are discussed, and their clinical applications in joint replacement, bone grafts, tissue engineering, and dentistry are reviewed. The type and consequences of cellular responses to a variety of today s biomaterials have been detailed in recent books (Di Silvio, 2008 Basu et al., 2009 Planell et al., 2009). 

M. Otsuka, H. Nakagawa, K. Otsuka, A. Ito, and W. I. Higuchi, Drug release from a three-dimensionally perforated porous apatite/collagen composite cement. Bioceramics Development and Applications, 2, D110189,2012. 

Dense and inert bioceramics They are materials without porosity. The bond to the bone is morphologic by growth of the tissue in the superficial irregularities of the implants or bond through acrylic cement or by fit the implant in a defect by pressure. Typical example of this group is monocrystalline as much as polycrystalline alumina. 

Technical ceramics are composed of raw materials generally as powder and of natirral or synthetic chemical additives, favoring either compaction (hot, cold or isostatic), or setting (hydraulic or chemical) or accelerating sintering processes. According to the formulation of the bioceramic and the shaping process used, we can obtain ceramics, dense or with variable porosity, cements, ceramic depositions or ceramic composites. 

KHO 92] KHORASANI S.N., DEB S., BEHIRI J.C., BRADEN M. and BONFIELD W., Modified hydroxyapatite reinforced PMMA bone cement . Proceedings of the 5 International Symposium on Ceramics in Medicine, Bioceramics, vol. 5, p. 225-232, 1992. 

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