The objective of this study was to determine the flexural strength (FS), compressive
strength (CS), diametral tensile strength (DTS), Knoop hardness (KHN) and wear resistance
of ten commercial glass-ionomer cements (GICs). The fracture surfaces of these cements
were examined using scanning electron microscopic (SEM) techniques to ascertain relationships
between the mechanical properties and microstructures of these cements.
Specimens were fabricated according to the instructions from each manufacturer. The
FS, CS, DTS, KHN and wear rate were measured after conditioning the specimens for
7 d in distilled water at 37 degrees C. One-way analysis of variance with the post
hoc Tukey-Kramer multiple range test was used to determine which specimen groups were
significantly different for each test. The fracture surface of one representative
specimen of each GIC from the FS tests was examined using a scanning electron microscope.
The resin-modified GICs (RM GICs) exhibited much higher FS and DTS, not generally
higher CS, often lower Knoop hardness and generally lower wear resistance, compared
to the conventional GICs (C GICs). Vitremer (3M) had the highest values of FS and
DTS; Fuji II LC (GC International) and Ketac-Molar (ESPE) had the highest CS; Ketac-Fil
(ESPE) had the highest KHN. Ketac-Bond (ESPE) had the lowest FS; alpha-Silver (DMG-Hamburg)
had the lowest CS. Four GICs (alpha-Fil (DMG-Hamburg), alpha-Silver, Ketac-Bond and
Fuji II) had the lowest values of DTS, which were not significantly different from
each other; alpha-Silver and Ketac-Silver had the lowest values of KHN. The highest
wear resistance was exhibited by alpha-Silver and Ketac-Fil; F2LC had the lowest wear
resistance. The C GICs exhibited brittle behavior, whereas the RM GICs underwent substantial
plastic deformation in compression. The more integrated the microstructure, the higher
were the FS and DTS. Higher CS was correlated with smaller glass particles, and higher
KHN was found where there was a combination of smaller glass particles and lower porosity.
Larger glass particle sizes and a more integrated microstructure contributed to a
higher wear resistance.
The mechanical properties of GICs were closely related to their microstructures. Factors
such as the integrity of the interface between the glass particles and the polymer
matrix, the particle size, and the number and size of voids have important roles in
determining the mechanical properties.