Advanced Ceramics For Dentistry

The growth of implant and fixed prosthodontics practices in dentistry has created a rapidly increasing demand for advanced ceramics and ceramic processes. Innovations in ceramics and ceramic processes are vital to ensure reliable and affordable dental-restoration solutions with aesthetically pleasing outcomes. The work aims to engage the bioceramics and engineering communities to meet the challenges of modern dental restoration using advanced ceramics. Incorporating fundamental science, advanced engineering concepts, and clinical outcomes, the work is suitable for bioceramicists, ceramics manufacturers, dental clinicians and biologists. State-of-the-art-coverage encompasses bioresorbable ceramics for bone regeneration and bioactivating surfaces of inert, high-strength ceramics for implantation, keeping research knowledge appropriately updated Discusses transition from the baseline stable and physically stiff ceramics research into engineering of highly coherent laminate composites for prosthetic crowns and bridges Showcases current feasible techniques for producing, in cost-effective and materials-saving ways, long-lasting individualized ceramic components with biocompatibility, complexity and high precision

Ceramic materials are currently applied to two categories of restorative dentistry, as all-ceramic fixed-partial dentures and as implantable components. While the former demands mainly integrated and balanced properties of mechanical and aesthetic origins, the latter also relies strongly on the material’s bio-oriented properties. This chapter discusses the material demands for solving the problems encountered in current practice that indicate the direction for future developments. This is done by bearing in mind both process restrictions and compatibilities. Focus is placed on developing materials that have the potential for improving aesthetics, for preserving a healthy situation to secure a prolonged treatment survival, and for improving the durability and reliability of the restorations while also simplifying the procedures of materials manufacture and clinical operation. Biomimetic materials and processes related to them are topics of general importance from a long perspective.

This chapter reviews the structure, mechanical properties, and biocompatibility of load-bearing ceramics used in dentistry. The development of this class of ceramic biomaterials is traced from the late sixties when alumina was introduced in dentistry. The literature on both polycrystalline and single crystal alumina dental implants is reviewed. The use of alumina declined when zirconia-toughened ceramics were introduced in orthopedics in the eighties. The use of yttria partially-stabilized tetragonal zirconia (Y-TZP) in dentistry allowed the production not only of dental implants and abutments, but also a broad range of load-bearing fixed partial dentures, such as multi-unit bridges and crowns, thanks to the development of CAD/CAM technology. Today, the trend is to use alumina and zirconia ceramics for making more aesthetic parts by improving their optical translucency.

Ceramic materials are frequently and increasingly used in dentistry. However, they are very brittle, the tensile strength has a large scatter, and their total fracture strain is very low. The strength depends on the loaded volume and on time under load. These properties cause special needs with respect to design, manufacturing tolerances, and handling, in production as well as in application. In ceramics, strength is limited by small flaws that are either caused by the processing of the material or by the machining of surfaces of specimens and components. This chapter introduces the principles of linear elastic fracture mechanics as the basis for understanding brittle fracture, and then presents fracture statistics. These topics are followed by an example for designing with ceramics. In subsequent sections, several other damage mechanisms and their relevance in dental applications will be discussed. The chapter closes with sections that deal with mechanical testing of ceramics and fractography.

Feldspathic porcelains, leucite, and lithium disilicate glass-ceramics are important materials used in restorative dentistry for their biocompatibility, excellent aesthetic properties, good mechanical strength, and relative ease of use. As a general rule in clinical practice, the choice of material should be dictated by the specific clinical situation. It depends on the space available to build the aesthetic and functional restoration, but also on the nature of the underlying tooth or restorative structure. The best aesthetic results are obtained with feldspathic porcelain restorations directly resin-bonded to the tooth, whereas the best function is obtained with the stronger and tougher fully anatomical or veneered glass-ceramic crowns and bridges. The main limitation with these ceramics is their insufficient strength for use as posterior crowns and bridges. Possible means to obtain aesthetically pleasing and long-term performing posterior restorations are the development of stronger glass-ceramics, the use of translucent colored zirconia, or the use of the new class of more elastic hybrid polymer-ceramic materials.

Microstructure characterization of advanced ceramics involves qualitative and quantitative analysis of surface topography, porosity, crystal defects, and interfaces. The structure of the surface controls interaction of ceramics with its surroundings, such as adhesion, gas adsorption, and electron exchange, which play an important role in determining overall properties of a material. Pores in ceramic materials originate from incomplete densification during the sintering process. Their presence interferes with functional properties such as mechanical strength, optical transparency, electrical conductivity, and dielectric response. Crystal defects mostly form either as a result of imperfections during the crystal growth process or as a consequence of structural phase transitions. They generally affect most functional properties of materials. So-called extended defects are interfaces that are boundaries between two solids. The most widespread tools for characterization of ceramic microstructures are microscopic techniques involving optical microscopy, different types of electron microscopy, and various scanning-probe methods. This chapter gives a brief introduction of the features of ceramic microstructure and the corresponding techniques for characterizing them.

Fractographic analysis is a useful tool for finding fracture origins that is necessary for improving the reliability of ceramic restorations. The general analysis begins with the determination of fracture patterns and origins. The crack propagation markings found by examination of fracture surfaces allow one to follow crack paths and to trace back to an origin, including fracture mirror, hackle, Wallner line, arrest line, and compression curl. This method is introduced and applied to define the origins of common clinical failures of ceramic dental prostheses. They are classified as several major types, namely, cracking initiated at the margin or at occlusal contacts, and porcelain chipping or delamination. The fracture origin is always found near the spot where the highest tensile stress concentration accumulates, and/or microscopic defects or flaws are located nearby. The fracture of ceramic dental restorations may initiate at micro-defects in the porcelain or ceramic body that are introduced during the materials fabrication process or after clinical adjustment.