Introduction
Glass-ionomer cement is made by mixing an acid-soluble glass powder with polymeric acids. Careful dosing and mixing matter here more than in most cements, because they decide its final quality.
Composition
Powder
The powder is a calcium-aluminosilicate glass, made by melting and sintering its ingredients above 1100 °C. The cooled glass is crushed and sieved.
Some cements also contain strontium oxide, which helps protect against caries.
Liquid
The liquid is about a 40% aqueous solution of polyalkenoate acids: acrylic, itaconic, maleic, tricarballylic and tartaric acids, with reactive carboxyl groups. It comes in a plastic dropper bottle.
Water-mixed cements have cold-dried acids in the powder and are mixed with distilled water. Both powder and liquid are sensitive to moisture, so close the containers tightly.
Preparation
- Condition the tooth: apply 10% polyacrylic acid for 10 seconds and rinse. This removes the smear layer without opening the tubules, and it improves wetting.
- Fluff the powder: shake or tap the jar before dosing.
- Dose the powder: fill the measuring spoon and level it with a spatula.
- Dose the liquid: hold the bottle vertically, so that the drops are equal.
- Mix with a plastic spatula: divide the powder in two. Mix one half with all the liquid for 10 seconds, then add the rest and mix for 15 seconds, on an area about the size of a small coin.
- Place it while it is shiny: working time is only 2 to 3 minutes and ends when the surface loses its shine.
- Protect it: cover the cement with a moisture-proof varnish straight after initial hardening.
Use a plastic spatula, and never change the dose to gain time. Cooling the materials in a refrigerator extends working time, but it thins the mix and can weaken adhesion.