ABSTRACT
This chapter gives an overview of the most critical test methods used for determining important properties for nanostructural chemically bonded bioceramics (CBBCs). The test methods dealt with in the chapter comprise nanostructural evaluation, including contact zone determination and mechanical strength and dimensional stability evaluation. Test methods related to chemical stability, microleakage, biocompatibility, bioactivity, anti-bacterial properties, and others will be treated in relation to examples of nanostructures and properties in Chapters 7 and 8. 5.1 Introduction When evaluating new biomaterials it is very important to know and understand the relationship between the new material, the specific test methods used, and what application the material is intended for. Often according to standards the methods are established and decided related to specific early commercially introduced biomaterials. A new material may be a good choice for a given application but can exhibit problems related to the test method. As an example, for a chemically bonded ceramic material based on Ca-aluminate, testing at body temperature or at least above 30°C
is critical, since this material develops different hydrated phases, depending on the test temperature [1, 2]. Often standards relate to room temperature. Another example is how mechanical strength is measured and how the test rig is designed. Size, shape, and time aspects may influence the result. In this chapter are presented a few critical test methods used in the evaluation of new CBBCs. 5.2 Test Methods and Nanostructures
5.2.1 Micro-/Nanostructural EvaluationMethods used in the evaluation of microstructures, and phase and elemental analyses are traditional scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM) with energy-dispersive X-ray (EDX) [3]. To analyse interfaces and calcified tissue at the highest level, TEM in combination with focused ion beam (FIB) microscopy for intact site-specific preparation of the TEM samples at very high site-specific accuracy is recommended. This procedure is treated in detail in Ref. [4]. Cross-sectional TEM samples from the interface between, for example, enamel and a dental filling material, are produced by FIB. The system scans over a beam of positively charged gallium ions over the samples, similar to an electron beam in SEM. The ions generate sputtered neutral atoms, secondary electrons, and secondary ions. Here it is possible to increase the beam current of the primary ion beam and use FIB as a fine-scale micromachining tool to cut TEM samples with high accuracy. See Fig. 5.1. To produce the TEM samples the so-called ‘lift-out’ technique can be used [4]. The thickness of the samples used is approximately 150 nm. 5.2.2 Mechanical PropertiesImportant properties for mechanical evaluation deal with compressive strength, flexure strength, Weibull modulus, Young’s modulus, fracture toughness, and, for dental applications, also wear resistance [5-8].
