Biomedical Engineering Reference
In-Depth Information
4.1
INTRODUCTION
Since the pioneering research in the 1950s, numerous innovations have been applied in operative den-
tistry. Composite resin technology has continuously evolved since its inception by Bowen as a rein-
forced Bis-GMA (bisphenol A-glycidyl methacrylate) system
[1]
. This color-based filling material is
basically composed by a triad: organic phase (dimethacrylates), inorganic phase (silanated fillers),
and initiator/activator system. One of the most important breakthroughs in composite resin technol-
ogy was the development of photocurable resin material. This was followed by the development of
reduced filler particle size and increased filler loading which significantly improved the universal
applicability of light-cured composite resins.
Resin composites are widely used in dentistry and have become one of the most common aes-
thetic restorative materials due to their mechanical strength, excellent aesthetics properties, moderate
cost (when compared to ceramics), ability to bond with the tooth, improved formulation, simplified
clinical procedures, and the decline in amalgam usage due to mercury toxicity. During the last few
decades, the increasing demands in aesthetic dentistry have led to the development of resin compos-
ites for direct restorations with improved physical and mechanical properties, aesthetics, and clinical
longevity. The latest innovation in the field has been the introduction of nanofilled materials, by com-
bining nanometer scale particles and nanoclusters in a conventional resin matrix.
4.2
HISTORICAL REVIEW: NANOTECHNOLOGY APPLICATIONS
IN OPERATIVE DENTISTRY
The term “nanotechnology” was coined by the researcher named Norio Taniguchi in 1974.
Nanotechnology aims at the creation and utilization of materials and devices at the level of atoms, mol-
ecules, and supramolecular structures, and in the exploitation of unique properties of particles with size
ranging from 0.1 to 100 nm (1 nm
10
9
m). Nanofilled composite resin materials are believed to offer
excellent wear resistance, strength, and ultimate aesthetics due to their exceptional polishability and lus-
ter retention
[2]
. In operative dentistry, nanofillers constitute spherical silicon dioxide (SiO
2
) particles
with an average size of 5-40 nm (0.005-0.04 μm). However, this 0.04-μm scale filler is not new in den-
tistry. In the 1970s, the minifilled composites (0.04 μm, i.e., 40 nm) were launched in the marketplace.
The nanometer scale filler particles have been already applied in composite resins. So, the following
question can be asked: What is the difference between this resin and the actual nanofilled resins? The
answer lies in the manufacturing procedure. While the colloidal silica from the 1970s obtained by pyro-
genic method allows a maximum load of 55 wt%, the ordered growth of nanofillers allows up to 87 wt%
of inorganic phase (for details of filler weight content, refer to
Figure 4.4
).
It was only in 2003 that the primary results of a nanofilled composite were published in the
Journal of American Dental Association by Mitra et al.
[3]
. The authors reported improvements in
optical properties, similar mechanical behavior when compared to microhybrid material, and same
polishability of minifilled resins.
4.3
BIOMIMETICS
The early stages of dental materials as a science were characterized by answering how the natural and
artificial material behaves. The development and discovery of new materials were based on fortuitous
