Biomedical Engineering Reference
In-Depth Information
and nanofilled composites, comprise filler particles ranging from approximately 20 to 600 nm. In
composite resin technology, particle size and the amount of particles represent crucial informa-
tion in determining how best to use the composite materials. Alteration of the filler component
remains the most significant development in the evolution of composite resins
[60]
because filler
particle size, distribution, and the quantity incorporated dramatically affect the mechanical
properties and the clinical success of composite resins. In general, mechanical and physical prop-
erties of composites improve in relationship to the amount of filler added
[61]
.Manyofthe
mechanical properties depend upon this filler phase, including compression strength and/or
hardness, flexural strength, the elastic modulus, coefficient of thermal expansion, water absorp-
tion, and wear resistance.
Nanotechnology or molecular manufacturing may provide resin with filler particle size that is
dramatically smaller in size, can be dissolved in higher concentrations and polymerized into the
resin system with molecules that can be designed to be compatible when coupled with a polymer,
and provide unique characteristics (physical, mechanical, and optical)
[62]
. In addition, optimizing
the adhesion of restorative biomaterials to the mineralized hard tissues of the tooth is a decisive
factor in enhancing the mechanical strength and marginal adaptation and seal, while improving the
reliability and longevity of the adhesive restoration. Currently, the particle sizes of conventional
composites are dissimilar to the structural sizes of the HAP crystal, dental tubule, and enamel rod,
and there is a potential for compromises in adhesion between the macroscopic (40 nm to 0.7
m)
restorative material and the nanoscopic (1 to 10 nm in size) tooth structure. However, nanotechnol-
ogy has the potential to improve this continuity between the tooth structure and the nanosized filler
particle and provide a more stable and natural interface between the mineralized hard tissues of the
tooth and these advanced restorative biomaterials
[63]
.
The surface quality of the composite is influenced not only by the polishing instruments and
polishing pastes but also by the composition and filler characteristics of the composite. The newer
formulations of nanocomposites with smaller particle size, shape and orientation, and increased
filler concentration provide improved physical, mechanical, and optical characteristics. Although
clinical evidence of polishability with these new nanoparticle hybrids appears promising, the long-
term durability of the polish will need to be evaluated in future clinical trials
[64]
. Research in
modern dentistry has discovered the uses for nanoparticles for fillings and sealant, and could lead
to the creation of artificial bone and teeth. The mechano-physical properties and resultant clinical
longevity of dental composites are insufficient. To improve these properties, the ongoing develop-
ment of RBCs has sought to modify the filler size and morphology and to improve the loading and
distribution of constituent filler particles. This has resulted in the introduction of the so-called nano-
fills which possess a combination of nano- and microsized filler to produce a hybrid material.
A variation to this approach was the introduction of “nanocluster” particles, which are essentially
an agglomeration of nanosized silica and zirconia particles. Although these materials have demon-
strated a degree of clinical and experimental success, debate remains as to their specific benefit
compared with existing conventionally filled systems. The “nanoclusters” provided a distinct
reinforcing mechanism compared with the microhybrid, microfill, or nanohybrid RBC systems
resulting in significant improvements to the strength and reliability, irrespective of the environmen-
tal storage and testing conditions. Silane infiltration within interstices of the nanoclusters may mod-
ify the response to preloading induced stress, thereby enhancing damage tolerance and providing
the potential for improved clinical performance
[16]
.
µ
