Biomedical Engineering Reference
In-Depth Information
grows. When the plate-like (also called lath-like) crystals are heated, they
grow into an interlocking microstructure. This process reinforces the
material, so that its resistance to bending (flexural strength) is very high
at 400-700MPa. The large concentration of crystals (50 to 60 vol%)
contained in the microstructure of the glass-ceramic is responsible for
making the material much stronger than other glass-ceramics. However,
as the material also contains some glass, it softens if it is heated to
920
◦
C. Therefore, it can be molded into different shapes. In a nutshell,
the material combines the advantages of ceramics (high strength) with
those of glass (moldability).
Both high strength and moldability are important features of the bio-
compatible materials used to repair teeth. Very strong lithium disilicate
glass-ceramics, for example, are popular for making dental crowns and
bridges that do not need to be strengthened with metal. A very strong
glass-ceramic is used to make a base. Another glass-ceramic material con-
taining apatite crystals is applied on this base and shaped to resemble the
original tooth. Figure 7.3 shows a bridge that has been made to replace
Figure 7.3
A dental bridge (on a mirror) made of biocompatible materials. A
very strong glass-ceramic has been used to create the base. This framework has
been coated with a glass-ceramic that looks like natural enamel. (Reprinted with
permission from [2]. Copyright (2006) W. Holand.) For a better understanding of
the figure, please refer to the colour section (Figure 10).
