Biomedical Engineering Reference
In-Depth Information
properties such as degree of conversion, hardness, modulus, and shrinkage of a series of polyhedral
silsesquioxane methacrylate monomers developed for dental applications have been found to be lower
than those of conventional materials of proven clinical performance
[29]
.
2.3.3
Calcium Phosphate and Calcium Fluoride Nanoparticles-Based Composites
Materials that release calcium, fluoride, or phosphate ions have been shown to provide remineraliza-
tion to the tooth structure
[30]
. Accordingly, the use of nanoparticles based on calcium phosphates
and calcium fluoride in nanocomposites have been investigated. Xu and coworkers
[31]
have reported
the synthesis of anhydrous dicalcium phosphate nanoparticles incorporated in composites. However,
it was necessary to incorporate nanosilica-fused whiskers into the composites for the mechanical
strength to be adequate. Similar results have been seen for composites into which nanocalcium fluo-
ride particles were incorporated
[32]
. In an interesting approach, nanohydroxyapatites (HAP) having
a particle size of 20 nm were synthesized to mimic the natural building blocks of human enamel and
were found to provide anticaries repair effect
[33]
. It is hypothesized in the report that nanoHAP with
a size of 20 nm shares the same characteristics of natural building block of enamel and can thus serve
as repair material. Conventional HAP was not found to perform similarly in control experiments.
2.3.4
Nanoparticles in Glass Ionomer Systems
Conventional and resin-modified glass ionomers (RMGIs) are important classes of dental mate-
rials due to their ability to release fluoride in the oral environment and remineralize tooth structure.
Additionally, RMGIs provide excellent moisture compatibility and ability to control postoperative
sensitivity
[34]
. However, their optical properties are not ideal for situations where highly aesthetic
restorations are desirable. In order to preserve the beneficial properties of these materials and at the
same time improve the aesthetic properties, a novel RMGI material has been developed in which nano-
clusters of silica and zirconia as well as unagglomerated zirconia nanomers were added to a two paste
RMGI (3M™ ESPE™ Ketac™ Nano)
2
[35,36]
. An SEM of a section of the cured nanomer is dis-
played in
Figure 2.4
in which the nanoparticles are clearly visible. The visual opacity of the resultant
nanoionomer is very low compared to conventional materials yet the mechanical properties, fluoride
release, remineralization ability, adhesion strength, and mechanical properties have not been compro-
mised
[37,38]
. Further detail is shown in Section 2.4. Titania nanoparticles have also been dispersed
into conventional glass ionomer systems to improve their optical translucency without compromising
the mechanical properties
[39]
. In another approach, nano HAP and nanofluorapatite were synthe-
sized using an ethanol-based sol-gel method, mixed with commercial fluoroaluminosilicate powders
and incorporated in conventional glass ionomer systems to improve their mechanical properties
[40]
.
Nanoparticles of ytterbium fluoride and barium sulfate have been added to glass ionomers with an aim
to improving their radiopacity
[41]
. While improvement in this property was observed, other proper-
ties such as compressive strength and setting time suffered indicating that using nanoparticles is not a
guarantee of a superior product and careful design and optimization of materials are needed.
2
Ketac™ Nano Light Curing Glass Ionomer Restorative, 3M ESPE Dental Products, 3M Co, St. Paul, MN 55144-1000.
