sábado, 26 de junio de 2010

Hybrid materials for dental applications

Inorganic–organic hybrid materials can be used as filling composites in dental applications. As schematized in Fig. 13(a), these composites feature tooth-like properties (appropriate hardness, elasticity and thermal expansion behaviour) and are easy to use by the dentist as they easily penetrate into the cavity and harden quickly under the effect of blue light.

Moreover, these materials feature minimum shrinkage, are non-toxic and sufficiently non-transparent to X-rays. However, the composition of the hybrid material and the chemistry behind it depends strongly on its later application: as filler/particles, as matrix materials, as composites, as glass ionomer cements or as bonding.

Traditional plastic filling composites had long-term adhesion problems and a high degree of polymerisation shrinkage resulting in marginal fissures. The dual character of the ORMOCER1s as inorganic–organic copolymers is the key for improving the properties of filling composites. The organic, reactive monomers are bound in the sol–gel process by the formation of an inorganic network. Thus, in the subsequent curing process, polymerisation takes place with less shrinkage.

Furthermore, abrasion resistance, in particular, is significantly enhanced by the existing inorganic Si–O–Si network. For example, in dental fillers organic functionalities including ring-opening reactions, such as functionalized spyrosilanes, are commonly included in the hybrid network. Other systems are based on multiacrylate silanes, offering a high organic density. In addition, mechanical properties of the composite can be tuned through variation of the spacer between the silicon atom and the reactive functionality. All these possibilities are already taken into account, and most of these hybrids include various fillers in their composition. As examples of available commercial filling composites based on dental ORMOCER1s from Fraunhofer ISC one can appoint ''Definite1'' and ''Admira1'' (Fig. 13(b)). In the case of the Admira1 product, a specifically designed dentineenamel bonding, an adhesive ORMOCER1 developed in cooperation with VOCO GmbH, is used to make this product especially advantageous. In glass ionomer cement based dental composites blue light polymerisable carboxyl functionalised ORMOCER1s have been developed. In this case, the cement forming reaction compensates the shrinkage resulting from organic crosslinking reaction of e.g. methacryl functionality.
Asignatura: CRF
Fuente: www.rsc.org/materials Journal of Materials Chemistry

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