When finely dispersed components are added to the glass in the mass, it is possible to grow crystalline structures. This phenomenon is often referred to as devitrification. This crystallisation can be obtained by adding metal oxides (TiO2, B2O5, SnO2, ZrO2, fluoride, etc.) -the germination cycles require specific thermal cycles and the partial crystallisation thereby obtained may be modified afterwards using appropriate heat treatments. This crystalline phase can therefore be developed or stabilised according to the heat treatments used. The thermal expansion coefficient of a glass-ceramic can be negative, zero or positive. This makes it possible to produce either very robust welds from materials with exceptional dimensional stability or products that are highly resistant to shocks.
Glass-ceramics have attractive properties in terms of electrical (insulation, electrical constant, resistivity and electrical strength), thermal (low thermal expansion coefficient and thermal conductivity) but also tribiological (low friction coefficient).
Lastly, they are distinguished by their biocompatibility and the ease with which they can be coloured to obtain a range of shades corresponding to natural teeth.
Thanks to these properties, they are used as insulators or substrates for printed circuits. A less known but very widespread application is as a covering material for dental prostheses.