The aim of this report is to analyze the microstructures of glass-ceramics of the IPS Empress 2 and IPS Empress systems by scanning electron microscopy. The main properties of the glass-ceramics were determined and compared to each other. The flexural strength of the pressed glass-ceramic (core material) was improved by a factor of more than three for IPS Empress 2 (lithium disilicate glass-ceramic) in comparison with IPS Empress (leucite glass-ceramic). For the fracture toughness, the K(IC) value was measured as 3.3 +/- 0.3 MPa. m(0.5) for IPS Empress 2 and 1.3 +/- 0.1 MPa. m(0.5) for IPS Empress. Abrasion behavior, chemical durability, and optical properties such as translucency of all glass-ceramics fulfill the dental standards. The authors concluded that IPS Empress 2 can be used to fabricate 3-unit bridges up to the second premolar.

Glass ceramics are advanced materials composed of one or more glass and crystal phases. By developing base glasses with appropriate compositions and by controlling crystal nucleation and growth in these glasses, glass ceramics with tailor-made properties can be fabricated. The key to developing this type of material is control of the nucleation processes. Both volume and surface nucleation can be exploited. Heterogeneous volume nucleation has been used to develop glass ceramics showing minimal thermal expansion and high strength. Two nucleation mechanisms can be combined and the precipitation of two crystal phases can be controlled. That the nucleation processes can be controlled by nano-and microscale immiscibility is a special feature, allowing selective nanophase formation or the development of needle-like apatite phases demonstrating a natural morphology. This represents a biomimetic process. The control of nucleation has enabled the development of biomaterials for dental applications.

Sintered ceramics and glass-ceramics are widely used as biomaterials for dental restoration, especially as dental inlays, onlays, veneers, crowns or bridges. Biomaterials were developed either to veneer metal frameworks or to produce metal-free dental restorations. Different types of glass-ceramics and ceramics are available and necessary today to fulfill customers' needs (patients, dentists and dental technicians) regarding the properties of the biomaterials and the processing of the products. All of these different types of biomaterials already cover the entire range of indications of dental restorations. Today, patients are increasingly interested in metal-free restoration. Glass-ceramics are particularly suitable for fabricating inlays, crowns and small bridges, as these materials achieve very strong, esthetic results. High-strength ceramics are preferred in situations where the material is exposed to high masticatory forces.

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