Biomedical Engineering Reference
In-Depth Information
12.2
Nanoscale in orthodontics
One of the known challenges in orthodontics is bond failure of orthodontic attachments includ-
ing orthodontic brackets and tubes. In order to minimize bond failure, many attempts have been
introduced to enhance the strength of orthodontic bonding composites. One of these attempts
was to introduce nanocomposite and nanoionomer
[3]
. The introduction of nanofiller compo-
nents originally was introduced to enhance some physical properties of the hardened restorative
composites. Because of the decreased dimension of the particles in the nanofillers, a wide size
distribution and increased filler load is achieved, which decreases polymerization shrinkage
[4]
,
and increases mechanical strength and resistance to fracture. In addition, it has been reported
that nanocomposites had a good marginal seal to enamel and dentin compared with total-etch
adhesives
[5]
. Since these nanofiller-containing resin-modified glass ionomer cements (Ketac
N100) were reported to have improved physical properties, as well as increased fluoride release
than other restorative materials, it has been suggested to be used as a bonding material for ortho-
dontic attachments. The increased fluoride release by nanofiller-bonding materials compared to
other restorative materials make them more attractive in orthodontics since demineralization of
the labial surfaces of teeth during orthodontic therapy is one of the major challenges facing
orthodontists and orthodontic patients, especially in patients with compromised oral hygiene.
However, although the results of using such nanocomposite and nanoionomer bonding system
may be suitable for bonding since they fulfill suggested ranges for clinical acceptability, they
are inferior to a conventional orthodontic composite
[3]
. There may be ongoing attempts to
enhance bonding strength of these nanocomposite and nanoionomer bonding systems to utilize
their high fluoride release property in order to make them at least comparable in bond strength
to conventional orthodontic bonding systems.
Because of the increased awareness of enamel demineralization around orthodontic attach-
ments, different materials have been used to minimize enamel demineralization. The effective-
ness of these materials has been evaluated using atomic force microscopy (AFM) measurements
that quantitatively evaluate nanoscale enamel surface roughness after using these materials
[6]
(
Figure 12.1
).
Orthodontic treatment may involve removal of some teeth to alleviate dental crowding or to
treat some types of malocclusions. Closing extraction spaces usually requires moving bracketed
teeth along arch wires made from different types of materials using sliding (also known as arch-
guided) tooth movement. The friction between orthodontic brackets and wires, especially with a
combination of metals, sometimes affects the efficiency of tooth movement. Also, friction in ortho-
dontics has contributed to loss of anchorage due to application of increased forces to overcome fric-
tion between the brackets and wires. Increased friction between orthodontic wires and bracket
surfaces has been attributed to micro/nanoasperities or mechanical interlocking at the micro- or
nanolevels
[7]
(
Figure 12.2
).
For this purpose, nanotechnology has been introduced to study different orthodontic wires and
bracket slots to evaluate nanomechanical properties and topographic pattern of these materials in
order to understand factors affecting friction between orthodontic wires and brackets. However, the
exact measurements of these micro/nanoasperities have only been evaluated using AFM. AFM
allows for quantitative evaluation of the nanoscale surface roughness of various orthodontic bracket
slots before and after sliding movement of archwire in vitro and in vivo
[8]
.
