Biomedical Engineering Reference
In-Depth Information
and the nanoscopic (1
10 nm in size) tooth structure
[12]
. Nanoscale particles have more similari-
ties to natural tooth as far as crystal size is concerned. Additionally, the high surface area of the
nanoscopic particles would offer a good mechanical interlocking with the polymer matrix
[13]
.
This is true for purpose-designed nanostructures, which can be used to produce low shrinkage, high
wear resistance, and biocompatibility of the dental materials. The fundamental application is the
resistance of nanoparticles-filled materials to the loss of substance during the propagation of micro-
fracture through cyclic fatigue loading
[14]
. Inorganic nanoparticles are hard and dense and these
characteristics make them interesting for improving a material's mechanical properties. Due to
large surface area, the particles show thixotropic thickening effect and low viscosity and improve
the handling properties. Nanofillers also show smooth surface effects and volume effects as well as
high optical properties. In addition, they have higher contact surface with the organic phase when
compared to minifilled composites, consequently improving the material hardness
[15]
.
The hybrid system of nanoparticles dispersed in polymer matrix has received extensive atten-
tion recently
[16]
. The major difference between nanometric (
,
100 nm) and micrometric
(
100 nm) particles is that nanoparticle facilitates the transfer of load from polymer matrix to
nanoparticles
[17]
. Therefore, nanoparticle-reinforced hybrid system exhibits higher stiffness and
better resistance to wear
[18]
. In contrast, large specific surface area can easily lead to particle
agglomeration, which makes nanoparticles more difficult to be evenly dispersed into polymer
matrix, thus resulting in a strength reduction. In restorative dentistry, there has also been a grow-
ing interest in using nanoparticles to improve the properties of dental restoratives
[11]
. However,
little work has been reported so far regarding use of any nanoparticles to improve dental glass
ionomer cement (GIC)
[19]
.
.
5.4
Glass ionomer cement
GIC was invented by Wilson and Kent in 1969 at the English Laboratory of the Government
Chemist
[20]
. GIC commonly known as polyalkenoate cement is water-based cement and formed
by the reaction of an acidic polymer and a basic glass in the presence of water
[21,22]
. The generic
name of glass ionomers is based on the original components fluorosilicate glass and polyacrylic
acid. The resulting cement is an inorganic and organic network with a highly cross-linked structure
that adheres to tooth structure and is translucent
[23,24]
. The first GIC introduced had the acronym
“ASPA,” and comprised alumina-silicate glass as the powder and polyacrylic acid as the liquid.
This product was first sold in Europe (De Trey Company and Amalgamated Dental Company) and
later in the United States
[25]
. For glass ionomers the mixing process and working time combined
should last about 2
3 min and the setting reaction should be complete several minutes after place-
ment. GIC have exceptional properties that make them useful as restorative and adhesive materials,
which include chemical bonding to tooth structure, adhesion to base metals, anticariogenic proper-
ties due to fluoride release, thermal compatibility with tooth structure, biocompatibility, and low
cytotoxicity. This material has tendency to be used as luting cements, filling materials, and lining
cements
[26]
; hereas, limitations of GIC include brittleness, poor fracture toughness material, and
sensitivity to moisture in the early stages of the placement. Although stronger and more esthetic
glass ionomers with improved handling characteristics are now available, low fracture toughness
