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AN IN-VITRO EVALUATION OF FRICTIONAL RESISTANCE OF PREADJUSTED
EDGEWISE ESTHETIC BRACKETS WITH DIFFERENT ARCHWIRES
Dr.Tejesh Kumar.S.P post graduate student*, Dr. Padmini.M.N.MDS*,
Dr.ShashikalaKumari.V MDS*, Dr.Kumarswamy.K.M MDS*.
*Department of orthodontics and dentofacial orthopedics, Govt. Dental College and Research
Institute, Bangalore 560002 INDIA
For correspondence: Dr Tejesh Kumar.S.P, post graduate student, Dept. of orthodontics and
dentofacial orthopedics. GDC & RI, Fort, Bangalore- 560002 INDIA
Email: tejeshsp@gmail.com
Word count: Abstract-284, Manuscript-3145
Tables-8
Graph-4
Short running title: FRICTIONAL RESISTANCE OF ESTHETIC BRACKETS WITH
DIFFERENT ARCHWIRES
Summary: Self ligating ceramic brackets have the least static and kinetic friction with
0.019"x 0.025" stainless steel archwires for sliding mechanics in orthodontics treatment
mechanics.

Abstract
Background: Friction is a clinical challenge particularly with sliding mechanics and must be
dealt efficiently to provide orthodontic results. Hence considering esthetic demands by the
patient and frictional resistance in bracket-archwire, a study was done to know which bracket
archwire combination fulfill the esthetic requirement and least friction for sliding mechanics in
tooth movement.
Material and methods: An in-vitro study was carried out to compare the frictional force
generated between the archwires and bracket slots with simulated retraction of tooth during
sliding mechanics. Three types of brackets of preadjusted edgewise appliance MBT Versatile+
with 0.022 ×0.028 inch slot size namely stainless steel brackets, ceramic with metal slot and
ceramic self ligating brackets and fifty millimeter straight lengths of 0.016" Nitinol,
0.019"x0.025" stainless steel, TMA and epoxy archwires were used. The archwires were ligated
to the conventional bracket with elastomeric module. Each bracket-archwire was bonded on the
jig and mounted on an instron machine. Frictional resistances of all bracket-archwire
combination were tested in dry state and at room temperature.
Results: Factorial ANOVA revealed that mean and kinetic friction of brackets and archwires
were statistically significant with P

INTRODUCTION
The earliest recorded experiments on friction were carried out by the versatile genius
Leonardo da Vinci approximately 450 years ago. According to Palmer, the reason Leonardo’s
works were never published was related to his methods of writing. He states that Coulomb and
Morin were credited with the classic works in laws of friction. 1
Friction is the resistance to motion when one object moves tangentially against
another. A distinction is made between static frictional force—the smallest force needed to start
the motion—and kinetic frictional force—the force needed to resist the sliding motion of one
solid object over another at a constant speed. For one object to slide against the other the force
application must overcome the frictional force; higher frictional resistance requires greater
orthodontic forces. 2
When friction prevents the movement of the tooth to which the bracket is attached, friction
can reduce the available force by almost 40%, resulting in an anchorage loss. Some authors
suggest developing ceramic brackets with smoother slot surfaces to decrease any possible effects
of static fatigue. Recently, a new ceramic bracket was designed with a metal-lined archwire slot. 3
Also gold liners have been placed in polycrystalline alumina bracket slots.
Schumacher et al stated that friction was determined mostly by the nature of ligation. Selfligating
brackets were introduced in the mid 1930s in the form of the Russell attachment, which
was intended to reduce ligation times and improve operator efficiency. Self-ligating brackets are
ligatureless bracket systems that have a mechanical device built into the bracket to close off the
edgewise slot. From the patient’s perspective, self ligating brackets are generally smoother, more
comfortable, and easier to clean because of the absence of wire ligature. Reduced chair time is
another significant advantage. 2
Two types of self-ligating brackets have been developed.
1) Active SL brackets have a spring clip that presses against the archwire, such as the In-
Ovation, SPEED, and Time brackets.
2) Passive SL brackets have a self-ligating slide that does not press against the wire, such as the
Activa, the TwinLock, Damon SL 3, SmartClip and more recently Clarity SL brackets.

Considering the esthetic requirements and also least friction essential for sliding
mechanics during tooth movement an in-vitro study was done to compare the frictional
resistances among preadjusted edgewise brackets namely stainless steel, esthetic ceramic
brackets with metal slot and ceramic self ligating brackets having 0.022× 0.028 inch slot using
0.016 inch nickel titanium archwire, 0.019× 0.025 inch stainless steel, TMA and esthetic epoxy
coated stainless steel archwires.
MATERIAL AND METHODS
An in-vitro study was carried out to compare the frictional resistance produced between the
archwires and the bracket slots similar to simulated retraction of tooth during sliding mechanics.
Since metallic archwires do not fulfill the esthetic demands completely, epoxy coated esthetic
archwires were also used in this study.
Brackets: Three types of brackets were used. Each type consisted of twenty upper right
premolar MBT brackets having 0.022 ×0.028 inch slot size.
Brackets Tip Torque Company
Type 1 MBT stainless steel, Twin bracket Zero -7 Gemini 3M
Type 2 MBT Ceramic-metal slot (Slot is Zero -7 Ormco Sawbros Int. Ltd
electroplated with gold)
Type 3 MBT Ceramic-self ligating. Passive Zero -7 Clarity SL 3M
The Clarity SL bracket is a ceramic version of SmartClip. It is a ceramic bracket with passive
self ligating mechanism having two NiTi clip but does not have a moving door/slide. When
engaging the archwire into the slot the NiTi clips open and close through elastic deformation.
Hence partial engagement of the archwire to either mesial or distal NiTi clips is possible in
severely malposed teeth. Since these brackets have tie wings conventional ligation is possible
with a feature known as “Active on demand”. This provides the clinician to augment rotation
correction and anchorage control.

Archwires: Fifty millimeter straight lengths of the following archwires were used.
Archwires
Length Company
1 0.016" nitinol 50 mm Optima
2 0.019"x 0.025" stainless steel 50 mm Optima
3 0.019"x 0.025" Titanium Molybdenum Alloy 50 mm Optima
4 0.019"x 0.025" epoxy coated stainless steel 50 mm Ortho organizer
For stainless steel bracket and ceramic with metal slot bracket, ligation was done with
standardized and conventional elastomeric modules just before starting the test so that the
degradation force of the elastomeric ligation was avoided. The test assembly in this study was
similar to the one used by Kapur Wadhwa R, Kwon HK, Close JM. 4 This test assembly mimics
the works carried out by various authors.
The frictional resistance between the bracket and archwire was tested at room temperature
and in dry state without using artificial saliva. Each bracket was tested only once, and each wire
specimen of 50 mm long was drawn through one bracket only, so as to eliminate the influence of
wear. 4 The total sample size of the experiment was sixty.
A custom made jig of plastic was used to hold the wires parallel to the vertical framework
of the Instron universal testing machine. The jig measured 10 cm in length, 4cm in width and had
a thickness of 3 mm.
Each bracket was secured on the jig using cyanoacrylate adhesive. The straight lengths of
different archwires were ligated to the bracket using conventional elastomeric modules. The jig
with the different bracket-archwire combination was vertically mounted on the Instron universal
testing machine. The archwire protruding from the bracket was carefully clamped to the lower
jaws of the moveable crosshead, so that the wire was parallel to the line scribed on the steel bar and
also to the long axis of the Instron machine. Each test run lasted for two minute and the rate of
movement of the wire through the bracket was 0.02 inch / minute fitted with 10 pound tension
load cell. The static and kinetic frictional resistances were recorded in grams.
RESULTS: In this experiment two factors influence friction namely bracket and archwire.
Null Hypotheses:

H 0(a) : There was no significant difference between the different types of brackets.
H 0(b) : There was no significant difference between the different wires.
H 0(c) : The interaction (joint effect) of brackets and wires were not significant.
Alternate Hypotheses:
H 1(a) : There is a significant difference between the different types of brackets.
H 1(b) : There is a significant difference between the different wires.
H 1(c) : The interaction (joint effect) of brackets and wires were significant.
Level of significance: α=0.05.
Decision Criterion: We compare the p-values with the level of significance. If P0.05, we accept the null hypothesis.
If there is a significant difference, we carry out multiple comparisons (post hoc-test) using
Bonferroni method to find out among which pair of groups there exist a significant difference.
Statistical technique used: Factorial ANOVA
Since significant difference was found among the different brackets and significant
difference was found among the archwires Alternate hypothesis was accepted. Null hypothesis
was accepted for the interaction of brackets and archwires since it was not significant.(Table 4
and 8)
Comparison of Static Friction: (Table 3)
Ceramic-self ligating bracket and 0.016" round nitinol archwire showed the least static friction
of 0.007 grams with standard deviation of 0.008.
Ceramic-self ligating bracket and 0.019"x0.025” SS archwire showed the least static friction of
0.019 grams with standard deviation of 0.006 among rectangular wires.
Metal bracket and 0.019"x0.025" TMA archwire showed the highest static friction of 0.365
grams with standard deviation of 0.060 among rectangular wires.
Comparison of kinetic Friction: (Table 7)
Ceramic-self ligating bracket and 0.016" round nitinol archwire showed the least kinetic friction
of 0.005 grams with standard deviation of 0.004
Ceramic-self ligating bracket and 0.019" X 0.025" SS archwire showed the least kinetic friction
of 0.020 grams with standard deviation of 0.007 among rectangular wires
Metal bracket and 0.019" X 0.025" epoxy archwire showed the highest kinetic friction of 0.343
grams with standard deviation of 0.070 among rectangular wires.

DISCUSSION
The classical laws of friction state that a frictional force is (1) proportional to the force
normally acting on the contact, (2) independent of the area of contact, and (3) independent of the
sliding velocity. 5 As two surfaces in contact slide against each other, two components of total
force arise: the frictional force component (F) and the normal force component (N) perpendicular
to the contacting surfaces and to the frictional force component. Frictional force is directly
proportional to the normal force, such that F =µN, where µ is coefficient of friction. 6
The Resistance to Sliding (RS) of an archwire-bracket couple is the combined effect of
up to 3 components: classical friction (FR), elastic binding (BI), and/or physical notching (NO). 7
RS = FR + BI + NO
This study was carried out to test the friction during two fundamental therapeutical phases:
(1) leveling and aligning phase with a superelastic round nickel titanium archwire , and
(2) sliding mechanics on aligned brackets with rectangular archwires of different alloys i.e.
TMA, stainless steel and epoxy.
Among the different wires, NiTi recorded the lowest mean static friction of 0.044 grams.
Highest mean static friction of 0.244 grams was recorded in epoxy wire followed by TMA with
0.226 grams and stainless steel wire with 0.135 grams. (Table 1 and Graph 1) The differences
in mean static friction recorded in the different wires were found to be statistically significant.
NiTi also recorded the lowest mean kinetic friction of 0.049 grams. Highest mean kinetic
friction of 0.237 grams was recorded in epoxy wire, followed by 0.199 grams and 0.109 grams of
kinetic friction in TMA and stainless steel archwires respectively. (Table 5 and Graph 3) The
differences in mean kinetic friction recorded in the different wires were found to be statistically
significant. The TMA archwires had revealed relatively rough surface due to the cold welding of
titanium to the rollers during manufacturing and also localized sites of cold welding to the
brackets slot during sliding mechanics. These two factors contribute to the high friction. Because
stainless steel wires do not cold weld or bind to the rollers during manufacturing have relatively
smooth surface and hence less coefficient of friction. Frictional properties of composite wires are
high because the reinforcement fibers were abrasively worn from the wire surfaces when tests
were conducted at high normal forces or angulations.

Bracket/wire interaction
Lowest mean static friction of 0.05 grams was recorded in SLC bracket compared to the
others. (Table 3 and Graph 2) Highest mean static friction of 0.238 grams was recorded in metal
bracket followed by ceramic-metal slot bracket with 0.199grams. The differences in mean static
friction recorded in the three brackets were found to be statistically significant. Lowest mean
kinetic friction of 0.049 grams was recorded in SLC bracket compared to the others (Table 7 and
Graph 4). Highest mean kinetic friction of 0.227 grams and 0.170 grams was recorded in metal
bracket followed by ceramic-metal slot bracket respectively. The differences in mean kinetic
friction recorded in the three brackets were found to be statistically significant. The passive
ceramic self ligating bracket showed least resistance to all the wires since there was no ligation
force on the bracket-archwire combination. Finally, the static frictional force was greater than the
kinetic force in all bracket-archwire combinations and supports the study done by Downing and
McCabe. 8
CONCLUSION
This is an in-vitro study that was carried out to compare the static and kinetic
frictional resistance of ceramic self ligating bracket, ceramic bracket with metal slot, metal
bracket with 0.016" nitinol and 0.019"x0.025" stainless steel, TMA and epoxy coated archwires.
Friction produced by the metal bracket with conventional ligation was the control group in the
study. The results of the study were as follows
• The kinetic and static friction of ceramic self ligating bracket were least with all archwire
combinations in comparison to the ceramic bracket with metal slot and metal bracket.
• The kinetic and static friction of epoxy coated archwire was the highest with all the
bracket combinations compared to other archwires.
• Metal bracket with 0.019"x0.025"TMA and epoxy archwire showed the highest friction.
• The static and kinetic friction of ceramic self ligating bracket was least with
0.019"x0.025" stainless steel archwire.
• 0.016" Nitinol archwire showed least static and kinetic frictional resistance with ceramic
self ligating bracket.

• 0.016" Nitinol archwire showed highest static frictional resistance with ceramic–metal
slot bracket and highest kinetic frictional resistance with metal bracket.
• Round wire had lesser frictional resistance than rectangular wire. Hence the cross section
of the archwire affects the frictional resistance with bracket.
• Static frictional force was comparatively more than the kinetic frictional force with all the
bracket-archwire combinations.
Self-ligating ceramic brackets not only make archwire placement more convenient and
secure, from patient point of view it is comfortable and esthetically acceptable and also have
lower kinetic frictional forces than conventional brackets. These features can be substantial
advantages for orthodontists who use sliding mechanics. The advantages of self-ligating brackets
and different archwires with less friction should be borne in mind when considering their use.
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TABLE 1: Mean static friction (grams) recorded in the brackets
Bracket Mean SD Minimum Median Maximum
Metal 0.238 0.146 0.030 0.237 0.452
Ceramic-metal 0.199 0.163 0.029 0.145 0.650
SLC 0.050 0.058 0.001 0.028 0.220
SLC-self ligating ceramic, SD-standard deviation
TABLE 2: Mean static friction (grams) recorded in the wires
Wire Mean SD Min Median Max
NiTi 0.016” 0.044 0.031 0.001 0.050 0.082
SS 0.019”x0.025” 0.135 0.163 0.014 0.111 0.650
TMA .019”x0.025” 0.226 0.166 0.028 0.183 0.518
Epoxy 0.019”x0.025” 0.244 0.124 0.056 0.244 0.452
NiTi-nitinol, SS-stainless steel, TMA-titanium molybdenum alloy,
TABLE 3: Mean static friction (grams) of bracket-archwire combination
Bracket Wire Mean SD Min Median Max
NiTi 0.054 0.020 0.030 0.056 0.080
Metal SS 0.175 0.050 0.129 0.157 0.258
TMA 0.365 0.060 0.299 0.344 0.435
Epoxy 0.357 0.098 0.215 0.369 0.452
Ceramic- NiTi 0.070 0.013 0.050 0.069 0.082
SS 0.210 0.254 0.029 0.111 0.650
metal slot TMA 0.266 0.163 0.130 0.183 0.518
Epoxy 0.248 0.079 0.121 0.256 0.333
NiTi 0.007 0.008 0.001 0.004 0.020
SLC SS 0.019 0.006 0.014 0.020 0.028
TMA 0.047 0.029 0.028 0.037 0.099
Epoxy 0.126 0.067 0.056 0.123 0.220
┼ denotes significance
TABLE 4: ANOVA -Comparison of Static Friction
Source df Sum of Squares Mean F P-Value
Bracket 2 0.392 0.196 19.840

TABLE 5: Mean kinetic friction (grams) recorded in different brackets
Bracket Mean SD Min Median Max
Metal 0.227 0.125 0.051 0.229 0.412
Ceramic-metal 0.170 0.118 0.038 0.131 0.488
SLC 0.049 0.057 0.001 0.026 0.205
TABLE 6: Mean kinetic friction (grams) recorded in the wires:
Wire Mean SD Min Median Max
NiTi 0.016" 0.049 0.038 0.001 0.058 0.136
SS 0.019"x0.025" 0.109 0.079 0.013 0.115 0.242
TMA 0.019"x0.025" 0.199 0.156 0.014 0.149 0.488
Epoxy 0.019"x0.025" 0.237 0.113 0.060 0.243 0.412
TABLE 7: Mean kinetic friction (grams) of different bracket-archwire combinations
Bracket Wire Mean SD Min Median Max
NiTi 0.079 0.033 0.051 0.069 0.136
Metal SS 0.173 0.048 0.109 0.172 0.242
TMA 0.314 0.091 0.226 0.292 0.411
Epoxy 0.343 0.070 0.245 0.359 0.412
Ceramic NiTi 0.064 0.008 0.057 0.063 0.076
SS 0.133 0.063 0.038 0.130 0.195
-metal slot TMA 0.242 0.161 0.117 0.149 0.488
Epoxy 0.241 0.089 0.104 0.243 0.348
NiTi 0.005 0.004 0.001 0.003 0.010
SLC SS 0.020 0.007 0.013 0.018 0.028
TMA 0.042 0.031 0.014 0.031 0.092
Epoxy 0.128 0.055 0.060 0.140 0.205
TABLE 8: ANOVA- Comparison of Kinetic Friction
Source df Sum of Squares Mean ss F P-Value
Bracket 2 0.332 0.166 34.016

Main Effects Plot (fitted means) for Static Friction
Interaction Plot (fitted means) for Static Friction
0.25
Bracket
Wire
0.4
Bracket
Ceramic
Metal
SLC
Mean of Static Friction
0.20
0.15
0.10
Mean
0.3
0.2
0.1
0.05
Ceramic
Metal
SLC
Epoxy
NiTi
SS
TMA
0.0
Epoxy
NiTi
Wire
SS
TMA
GRAPH 1 GRAPH 2
Main Effects Plot (fitted means) for Kinetic Friction
Interaction Plot (fitted means) for Kinetic Friction
0.25
Bracket
Wire
0.35
0.30
Bracket
Ceramic
Metal
SLC
Mean of Kinetic Friction
0.20
0.15
0.10
Mean
0.25
0.20
0.15
0.10
0.05
0.05
Ceramic
Metal
SLC
Epoxy
NiTi
SS
TMA
0.00
Epoxy
NiTi
Wire
SS
TMA
GRAPH 3 GRAPH 4