Biomedical Engineering Reference
In-Depth Information
emphasising advanced techniques used to elucidate the presence of complex
species within the glass network.
12.3 IONOMER GLASS COMPOSITIONS
Four main types of ionomer glasses have been used for cement forming:
1. Alumino silicate glasses, that have been mainly studied by Wilson and
co-workers [4, 5, 12] in the early 1970's and are based on the systems SiO 2 -
Al 2 O 3 - CaO or SiO 2 - Al 2 O 3 - CaF 2 ;
2. Aluminoborate glasses studied by Combe et al. [13 - 15] based mainly on
the system Al 2 O 3 - B 2 O 3 - ZnO - ZnF 2 ;
3. Zinc silicate glasses based on the systems CaO - ZnO - SiO 2 or Al 2 O 3 - ZnO -
SiO 2 and
4. Alumino - phospho - silicate glasses based on the system SiO 2 - Al 2 O 3 - P 2 O 5 -
CaO - CaF 2 .
Among the glasses with interesting properties were the aluminoborate glasses
formulated by Combe et al. [14]. These glasses can undergo hydrolysis in the
presence of aqueous environment, which can be controlled by appropriate heat
treatments resulting in controlled reactivity of the glass ionomer cements and
enhancing compressive strength [13, 15]. However, the reported compressive
strengths were not comparable to aluminosilicate glass based ionomer cements
and therefore the aluminoborate glasses were abandoned for cement formation
[8]. Zinc silicate glasses were investigated by Hill and co-workers [16, 17] and the
resulting glass ionomer cements exhibited high strength. The main characteristic
of the glass compositions was that in contrast to the aluminosilicate glasses, the
ratio of Al/Si was not an important factor to determine the reactivity of the
glasses. Depending on the role of zinc in the glass network whether it was a
network modifi er or an intermediate oxide, the network connectivity of the glass
determined its reactivity and cement forming ability. According to Nicholson [8]
these cements were very weak for clinical dental applications and as they could
degrade by hydrolysis, the glasses did not prove to be successful substitutes for
alumino-silicate glasses. However, Boyd et al. [17] recently reported that there is
a great potential for the glasses to be used for bone cement formation. Especially
when aluminium is considered a potent neuro-toxin promoting cellular oxidation,
zinc-silicate glasses may have a positive effect in vivo , increasing the DNA of
osteoblasts, which would result in increased bone mass. Furthermore, zinc is
important for the function of the immune system and has been recognised as an
antibacterial agent. All these factors make zinc-silicate glasses interesting materi-
als that could be used for aluminium-free-cement formation.
In order to serve the purpose of this chapter, the authors will concentrate
on the design and characterisation of the fl uorine containing alumino - phospho -
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