Biomedical Engineering Reference
In-Depth Information
AFM has been utilized as a tool to evaluate the surface roughness of stainless steel, beta-tita-
nium, and nickel
Ti) wires
[10]
. In this study, AFM measurement of surface rough-
ness reiterated the fact that the roughness influences the effectiveness of sliding mechanics,
corrosion behavior, and esthetics of orthodontic archwires. The effects of decontamination and clin-
ical exposure on elastic modulus, hardness, and surface roughness of stainless steel and Ni
titanium (Ni
Ti
archwires were evaluated using AFM coupled with a nanoindenter
[11]
. The results of AFM evalu-
ation showed that the decontamination regimen and clinical exposure had no statistically significant
effect on Ni
Ti wires but did have a statistically significant effect on stainless steel wires. The
study concluded that it is difficult to predict the clinical significance of these statistically significant
changes in archwire properties on orthodontic tooth movement.
Surface roughness of various orthodontic bracket slots before and after the sliding movement of
an archwire in vitro and in vivo was observed quantitatively using AFM in a recent study
[12]
.
Conventional stainless steel, ceramic, self-ligating stainless steel, and ceramic brackets were evalu-
ated. In vitro sliding test results with beta-titanium wire in the conventional stainless steel and
ceramic brackets showed that there was significant increase in surface roughness only in stainless
steel brackets. The results of surface roughness with AFM measurements on the brackets after a
2-year orthodontic treatment regime showed that self-ligating ceramic brackets had undergone less
significant changes in roughness parameters than self-ligating stainless steel brackets. The study
concluded that the self-ligating ceramic bracket has great possibility to exhibit low friction and bet-
ter biocompatibility than the other tested brackets including the conventional brackets. Such studies
using AFM have shown that it can be utilized as an effective imaging tool to visualize and analyze
the surface properties and understand the changes taking place at the nanoscale dimension of ortho-
dontic wires or brackets during treatment.
11.3
Friction reducing nanocoatings on orthodontic archwires
Orthodontic archwires are used to generate mechanical forces that are transmitted through brackets
to move teeth and correct malocclusion, spacing, and/or crowding. They are also used for retentive
purposes, i.e., to maintain teeth in their current position. Currently orthodontic archwires are fabri-
cated from base metal alloys. The types of wires most commonly used are stainless steel, Ni
Ti,
and beta-titanium alloy wires (composed of titanium, molybdenum, zirconium, and tin). When
employing sliding mechanics, friction between the wire and the bracket is one of the primary fac-
tors influencing tooth movement. When one moving object contacts another, friction is introduced
at the interface, which results in resistance to tooth movement. This frictional force is proportional
to the force with which the contacting surfaces are pressed together and is governed by the surface
characteristics at the interface (smooth/rough, chemically reactive/passive, or modified by lubri-
cants). Minimizing the frictional forces between the orthodontic wire and brackets has the potential
to increase the velocity of desired tooth movement and therefore result in less treatment time.
In recent years, nanoparticles have been used as a component of dry lubricants. Dry lubricants
are solid phase materials that are able to reduce friction between two surfaces sliding against each
other without the need for a liquid media. Biocompatible nanoparticles have been coated on ortho-
dontic stainless steel wires to reduce friction. Inorganic fullerene-like nanoparticles of tungsten
