Biomedical Engineering Reference
In-Depth Information
11.2
Nanoindentation and atomic force microscopy studies on
orthodontic brackets and archwires
Orthodontic brackets bonded to teeth provide the means to transfer force from the activated archwire to
the teeth to facilitate tooth movement. Orthodontic brackets can be metallic (stainless steel, titanium, or
gold) or tooth colored (plastic or ceramic). The surface characteristics (roughness and surface free
energy (SFE)) of the brackets play a significant role in reducing friction and plaque (biofilm) forma-
tion. Micro- and nanoscale roughness of these brackets can facilitate early bacterial adhesion. Even
though the surfaces of newly placed brackets are smoother, there can be changes in the surface rough-
ness and SFE during the course of orthodontic treatment. A nanoindenter coupled with atomic force
microscope (AFM) has been traditionally used to evaluate nanoscale surface characteristics of bio-
materials. They have also been used to evaluate mechanical properties like hardness, elastic modulus,
yield strength, fracture toughness, scratch hardness, and wear properties by nanoindentation studies.
AFM, also called the scanning force microscopy, was developed in 1986, subsequently to the
invention of the scanning tunneling microscope (STM)
[8]
. Similar in operation to the STM, the
AFM involves scanning a sharp cantilever tip across a sample surface while monitoring the tip-
sample interaction to allow the reconstruction of the three-dimensional surface topography. A typi-
cal AFM can provide resolutions of the order of 1 nm laterally and 0.07 nm (sub-angstrom) verti-
cally. AFM has been utilized to look at the nanoscale dimension of the orthodontic armamentarium
and the changes taking place during the course of treatment. Orthodontic brackets and archwires
can undergo changes in surface characteristics during treatment due to the effects of food and oral
hygiene habits and/or calcification (
Figure 11.1
)
[9]
.
FIGURE 11.1
AFM image of retrieved Ni
Ti archwire exposed in oral cavity for 1 month, depicting rough surface produced
by calcification on wire surface
[9]
.
