Dental Materials · MU Sofia

43. Glass-ionomer cements

Covers the setting reaction of glass-ionomer cements, in which calcium binds the acid chains first and aluminium forms stronger links over weeks, followed by the water balance needed in the first 24 hours and the two routes of adhesion to tooth tissue. It then explains fluoride release and reports strength, elasticity and wear values in a summary table, with notes on toxicity, solubility and clinical uses. Two diagrams illustrate the setting stages and fluoride action.

Inside: 6 sections · 2 labelled pictures · 1 table · 15 flashcards · 3 min

Topic 43 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 6 sections, about 376 words (3 min of reading), with 15 flashcards.

In this note

  1. Introduction
  2. Setting reaction
  3. Water balance
  4. Adhesion
  5. Fluoride
  6. Properties

Introduction

Glass-ionomer cements, or polyalkenoate cements, contain glass powder and set by ion-exchange reactions. They bond chemically to the tooth and release fluoride, which makes them the most biologically active dental materials.

Setting reaction

Mixing starts an acid-base reaction. The acids dissolve the surface of the glass and free calcium, aluminum and fluoride ions.

  1. Calcium reacts first, linking the acid chains into calcium polyacrylate. This gives the initial set, but it is soluble in water.
  2. Aluminum then forms aluminum polyacrylate chains, which are stronger and insoluble.
  3. Maturation: cross-linking goes on for weeks, and silica gel forms around the glass particles, which protects them from acid.

Fluoride ions take no part in the setting, so they stay free in the matrix.

Water balance

The reaction needs water, which makes up about 20% of the cement. In the first 24 hours the cement is very sensitive. Moisture washes out reacting ions and soluble calcium chains, while drying stops the ion exchange. Both leave it porous, weak and unattractive, so the cement is sealed with a varnish, either a volatile resin solution or a light-cured one.

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