Physical property investigation of contemporary glass ionomer and resin-modified glass ionomer restorative materials

Objectives

The objective of this study was to investigate selected physical properties of nine contemporary and recently marketed glass ionomer cement (GIC) and four resin-modified glass ionomer cement (RMGI) dental restorative materials.

Materials and methods

Specimens (n = 12) were fabricated for fracture toughness and flexure strength using standardized, stainless steel molds. Testing was completed on a universal testing machine until failure. Knoop hardness was obtained using failed fracture toughness specimens on a microhardness tester, while both flexural modulus and flexural toughness was obtained by analysis of the flexure strength results data. Testing was completed at 1 h, 24 h, 1 week, and then at 1, 3, 6, and 12 months. Mean data was analyzed with Kruskal-Wallis and Mann-Whitney (p = 0.05).

Results

Physical properties results were material dependent. Physical properties of the GIC and RMGI products were inferior at 1 h compared to that at 24 h. Some improvement in selected physical properties were noted over time, but development processes were basically concluded by 24 h. A few materials demonstrated improved physical properties over the course of the evaluation.

Conclusions

Under the conditions of this study:

1. 1.

   GIC and RMGI physical property performance over time was material dependent;

2. 2.

   Polyalkenoate maturation processes are essentially complete by 24 h;

3. 3.

   Although differences in GIC physical properties were noted, the small magnitude of the divergences may render such to be unlikely of clinical significance;

4. 4.

   Modest increases in some GIC physical properties were noted especially flexural modulus and hardness, which lends support to reports of a maturing hydrogel matrix;

5. 5.

   Overall, GIC product physical properties were more stable than RMGI;

6. 6.

   A similar modulus reduction at 6 months for both RMGI and GIC produced may suggest a polyalkenoate matrix change; and

7. 7.

   Globally, RMGI products demonstrated higher values of flexure strength, flexural toughness, and fracture toughness than GIC materials.

Clinical relevance

As compared to RMGI materials, conventional glass ionomer restorative materials demonstrate more stability in physical properties.