Textur- und Mikrostrukturanalysen an Materialien für den direkten und indirekten Zahnersatz

Abstract

Physical properties like hardness, e-modulus and thermal expansion of dental materials are supposed to be nondirectional (isotropic), although these materials can possess directional (anisotropic) properties due to their mineralogical composition. Indeed, the ideal dental restorative should possess similar anisotropic physical properties like the restored tooth, which is – in the case of dental enamel – highly anisotropic. Therefore, already existing materials are examined via x-ray analysis for their mineralogical composition and their anisotropic physical properties first and then compared with natural tooth. Dental composites, denture resins and glass ionomer cements are composed of amorphous components, namely glass filler particles and resin, and show an isotropic physical behaviour: Vickers hardness and e-modulus are in the same range as for dentin, whereas their thermal expansion (35-75∙10-6/K) is considerably higher than that of dentin and enamel (11∙10-6/K and 17∙10-6/K). γ2-free amalgam consists of the crystalline phases Ag2Hg3, Ag3Sn and Cu6Sn5. It shows no preferred orientation and no anisotropic behaviour. Its Vickers hardness and e-modulus (191 HV 0.03/20 and 68 GPa, respectively) are between the values for dentin (70 HV 0.01/30 and 2-29 GPa) and enamel (370 HV 0.01/30 and 10-169 GPa). Its thermal expansion (25.5∙10-6/K) is slightly higher than that of natural tooth. Most dental ceramics are glass ceramics and show a complex mineral texture: the crystallites of the ceramics Cercon base and Vita In-Ceram Alumina are randomly oriented, whereas the ceramics Vita In-Ceram Zirkonia and Vitablocs Esthetic Line show a slightly preferred orientation (4mrd and 3mrd in ODF). Only the crystalline Li2Si2O5-phase of the glass ceramic IPS e.max Press shows a highly preferred orientation (11mrd in ODF). These crystal orientations result in slight anisotropies of the physical properties. With ≥650 HV 0.01/20 their Vickers hardness is markedly higher than that of natural tooth. With the exception of the high-perfomance ceramics, their e-moduli are between 60 GPa and 98 GPa and range between that of dentin and enamel. Their thermal expansion (7.2-10.5∙10-6/K) is below that of dentin and enamel. Gold alloys and non-precious alloys are coarse and contain precipitation phases which harden the alloys. Alloys for crowns have Vicker hardness numbers and e-modulus in the range of dental enamel, whereas the Co-Cr-Mo-alloy used for dental models is considerably harder and more elastic (582 HV 0.03/20; E=211 GPa). Their thermal expansion is between that of dentin and enamel. Titanium endodontic post and the dental implant OsseoSpeed show a highly preferred orientation (21mrd and 19mrd in ODF) and slightly anisotropic physical behaviour. Values for e-modulus and thermal expansion range between 159-167 GPa and 7.62-9.29∙10-6/K, respectively. All in all the differences in the macroscopic physical properties of the examined dental materials in comparison to natural teeth are higher than the variations due to their crystalline composition and texture. Hence, new dental materials should be adapted more to human tooth in general and only in the next step their physical properties can be adapted to the anisotropic behaviour of dental enamel.