DOH124 Lecture Notes - Lecture 2: Copolymer, Optical Rotation, Ionomer
COMPOSITION
The composition and chemistry of all glass ionomers has remained essentially the same
and therefore the following discussion can be regarded as universal. They are supplied
in one of three forms --- as a powder and a liquid, as a powder that is mixed with water
(anhydrous form), or in an encapsulated form. When the polyalkenoic acid is
dehydrated and incorporated in the powder, the liquid is usually water or tartaric acid
diluted with water. For both practical and patent reasons, there is a considerable
difference between the powders and liquids produced by different manufacturers.
Therefore, components of various products must not be interchanged.
Glass powder
The approximate, typical, composition of the calcium fluoroaluminosilicate glass that
forms the basis of the powder component in glass ionomer cements, is in weight % :
SCO2 (quartz) 29.0; Al2O3 (alumina) 16.6; CaF2 (fluorite) 34.2; Na3AlF6 (cryolite) 5.0;
AlF3 5.3; AlPO4 9.9. The mixture is fused, quenched, ground and sieved to obtain a
particle size of 4-50 µm, depending upon the proposed clinical application for each
material. Generally, finer particles are used for luting cements and for some lining
cements; coarser particles are used for restorative materials because these are likely to
provide better translucency. The range and particle size distribution will have a bearing
on the working properties and final physical properties of each material. The glass
powder can be modified in many ways and research will continue with the aim of
improving physical properties and therapeutic potential. Onemanufacturer has
incorporated lanthanum to improve radiopacity and another has entirely replaced the
calcium with strontium for the same reason. As calcium and strontium are closely
related on the periodic table they behave in a similar fashion and it is even possible to
develop a strontium apatite in tooth structure.
Reactivity
The reactivity of the glass is controlled by the fusion temperature and the heat history.
Materials formed with higher temperature glasses, set more quickly and reactivity can
be varied by modifying the annealing process.
Radiopacity
Radiopacity can be achieved by the incorporation of barium, strontium or lanthanum.
Fluoride content
Fluoride is an essential component because of its effect on the temperature of glass
fusion, working characteristics and ultimate physical properties. Its presence promotes
remineralisation in surrounding tooth structure. The fluoride content of the glass can be
Document Summary
The composition and chemistry of all glass ionomers has remained essentially the same and therefore the following discussion can be regarded as universal. They are supplied in one of three forms --- as a powder and a liquid, as a powder that is mixed with water in an encapsulated form. When the polyalkenoic acid is (anhydrous form), or dehydrated and incorporated in the powder, the liquid is usually water or tartaric acid diluted with water. For both practical and patent reasons, there is a considerable difference between the powders and liquids produced by different manufacturers. Therefore, components of various products must not be interchanged. The approximate, typical, composition of the calcium fluoroaluminosilicate glass that forms the basis of the powder component in glass ionomer cements, is in weight % : Sco2 (quartz) 29. 0; al2o3 (alumina) 16. 6; caf2 (fluorite) 34. 2; na3alf6 (cryolite) 5. 0;
