<b>OBJECTIVEb>To investigate the failure mode of various types of glass ionomer cements by Hertzian indentation test.

<b>METHODSb>Discs of 10 mm diameter and 2 mm thickness were prepared for six glass ionomer cement products (A-D: conventional type setting through an acid-base chemical reaction, A and B without reinforcement, C with silver reinforcement, D with ceramic reinforcement; E and F: resin-modified type), ten for each. These were tested on top of glass-reinforced polyamide-nylon 6, 6 substrates by a universal testing machine, loading centrally with a 20 mm diameter ball. Load at the first crack was recorded. Failure mode was observed under scanning electron microscope.

<b>RESULTSb>The former four products presented typical brittle fracture, while the latter two usually fractured incompletely. The failure loads at the first crack of the six glass ionomer cements were (258.86 +/- 10.49), (230.88 +/- 21.66), (281.90 +/- 25.39), (282.11 +/- 9.60), (756.67 +/- 83.50) and (1 148.00 +/- 147.78) N, respectively. Significant difference was found between the former four and the latter two products.

<b>CONCLUSIONSb>The type (setting mode) of glass ionomer cement controls its failure mode. Inclusion of metallic or ceramic filler has little effect on increasing the load bearing capacity of glass ionomer cement.

Compressive Strength ; Dental Porcelain ; chemistry ; Glass Ionomer Cements ; chemistry ; Materials Testing ; methods ; Resins, Synthetic ; chemistry ; Silver ; chemistry