|Year : 2015 | Volume
| Issue : 4 | Page : 246-252
Comparison of frictional resistance between various bracket types and archwire materials ligated with low-friction and conventional elastic ligatures
Vasu Murthy Sesham1, Anupriya Jaitly1, Lalitha Chigurupati1, Praveen Kumar Neela1, Pavan Kumar Mamillapalli1, Revathi Peddu2
1 Department of Orthodontics and Dentofacial Orthopaedics, Kamineni Institute of Dental Sciences, Narketpally, Telangana, India
2 Department of Orthodontics and Dentofacial Orthopaedics, Sibar Institute of Dental Sciences, Guntur, Andhra Pradesh, India
|Date of Web Publication||14-Dec-2015|
Vasu Murthy Sesham
Department of Orthodontics and Dentofacial Orthopaedics, Kamineni Institute of Dental Sciences, Narketpally, Nalgonda - 508 254, Telangana
Source of Support: None, Conflict of Interest: None
Background: Friction plays a very crucial role in our daily life and orthodontics is no exception. Various materials possess friction of varying intensity, which ultimately affects tooth movement.
Aim: The aim was to compare the frictional resistance (FR) between various bracket types and archwire materials when ligated with low-friction and conventional elastic ligatures so as to obtain best bracket-archwire combination possessing least FR for clinicians in achieving optimal mechanotherapy.
Materials and Methods: Study consisted of three types of preadjusted edgewise brackets including ceramic, stainless steel (SS) and self-ligating brackets (0.022" slot, MBT prescription), two types of archwire materials, 0.019 × 0.025" SS and 0.019 × 0.025" Teflon coated (TC) and two types of ligatures including low-friction and conventional elastic ligature. A total of 10 combinations were formed with the above mentioned material. Each combination was tested 10 times on universal testing machine for FR. The data was statistically analyzed using one-way ANOVA and unpaired t-tests.
Results: Self-ligating brackets exhibited least FR (2.35 ± 0.15N) followed by metal brackets. Ceramic brackets showed the highest FR (7.32 ± 0.10N). In general, the mean value for TC wire was less than that of SS wire indicating low FR possessed by TC wires. Results also showed that low-friction ligatures produce lower-friction when compared with conventional elastic module (P > 0.05).
Conclusion: The study demonstrated that self-ligating brackets with TC wire showed the least FR and ceramic brackets with SS wire when ligated with conventional elastic ligature showed the highest FR.
Keywords: Ceramic brackets, frictional resistance, Teflon coated wires
|How to cite this article:|
Sesham VM, Jaitly A, Chigurupati L, Neela PK, Mamillapalli PK, Peddu R. Comparison of frictional resistance between various bracket types and archwire materials ligated with low-friction and conventional elastic ligatures. J NTR Univ Health Sci 2015;4:246-52
|How to cite this URL:|
Sesham VM, Jaitly A, Chigurupati L, Neela PK, Mamillapalli PK, Peddu R. Comparison of frictional resistance between various bracket types and archwire materials ligated with low-friction and conventional elastic ligatures. J NTR Univ Health Sci [serial online] 2015 [cited 2020 Jan 28];4:246-52. Available from: http://www.jdrntruhs.org/text.asp?2015/4/4/246/171741
| Introduction|| |
In contemporary orthodontics, many practitioners utilize sliding mechanics for both closing extraction spaces and aligning irregular teeth. As this procedure requires the teeth to be displaced relative to the archwire, a portion of any force that is applied to move the tooth will be consumed to overcome the inherent friction of the system.  In sliding mechanics, mesiodistal tooth movement is accomplished by guiding or "walking" a tooth along a continuous arch wire with the use of an orthodontic bracket. The friction that is generated between the bracket and archwire is the limiting factor as it tends to resist the movement of the tooth in the desired direction.  For the clinicians practicing sliding mechanics, it becomes necessary to understand the friction produced in the appliance in order to better plan the treatment. It is important to understand that by merely increasing the force in an orthodontic appliance will not remedy high friction archwire/bracket combination as doubling the drawing force will merely double the frictional force. In addition, excessive amount of archwire/bracket friction may ultimately result in loss of anchorage or in binding accompanied by little or no tooth movement.  Apart from sliding mechanics, factors such as archwire size, cross-sectional shape of wire, torque present in the archwire, and surface roughness affects the frictional forces in the appliance. Taylor and Ison demonstrated that bracket design can also influence frictional forces.  Berger reported reduced friction with the self-ligating SPEED bracket (Strite Industries Ltd., Cambridge, Ontario, Canada) when compared with preadjusted edgewise brackets that had stainless steel (SS) ligature or elastomeric ligature.  Ceramic brackets have come into widespread use because of their outstanding esthetic characteristics, however it comes with its own share of shortcomings. 
Ligatures commonly used in orthodontics are either heat-treated SS or elastomeric ligatures. The friction arising from a ligature depends upon its coefficient of friction and the forces it exerts on the bracket and archwire. Reilly et al.  showed that steel ligatures produce greater friction than elastomers. Budd et al. studied the frictional characteristics of four commercially available self-ligating bracket systems and SS archwires of different cross-sections. They concluded that passively ligated brackets produce less frictional resistance (FR). However, this may result in decreased control of tooth movement. 
The present study is an attempt to compare the FR between various bracket types and archwire materials, when ligated with low-friction and conventional elastic ligatures and to obtain the best bracket-archwire combination possessing least FR for clinicians in achieving optimal mechanotherapy.
| Materials and Methods|| |
Sixty preadjusted edge-wise upper left central incisor brackets with 0.022″ slot, which includes 24 ceramic, 24 SS and 12 passive self-ligating metal brackets were taken for the study. 0.019 × 0.025″ SS and esthetic archwires were also selected. Low-friction and conventional elastic ligature were used to ligatate the archwire to the bracket. The details of the brackets, wires and ligatures used are given in [Table 1].
All the brackets were bonded using cyanoacrylate adhesive on a metal bar. [Figure 1] depicts the testing model.
Three brackets of the same kind were arranged in a row as shown in [Figure 2]. Alignment of the brackets was obtained through the preliminary insertion of a 0.021 × 0.028″ SS archwire into the slots of the brackets, without ligation, before bonding on the metal bar. After definitive bonding of the brackets was completed on the metal bar, the 0.021 × 0.028″ SS archwire was accurately removed. 0.019 × 0.025″ SS straight length wire was placed in the brackets bonded onto the assembly, which were ligated with conventional elastomeric ligatures and FR between the bracket and SS wire was tested.
A mechanical universal testing machine (auto graph AG 15) [Figure 3] with a 10-lb tension load cell that was set on a range of 1-lb and calibrated from 0 to 1000 g was employed to test this FR [Figure 4]. Each archwire was gripped by crimping brass fittings on the distal ends. The load cell registered the force levels required to move the wire along the three aligned brackets; these levels then were transmitted to a computer hard disk. The archwires moved at a crosshead speed of 0.5 mm/min. Load values of FR were calculated in Newton (N).
After each test, the testing machine was stopped, the bracket/archwire assembly was removed, and a new 0.019 × 0.025″ SS wire was placed and tied with a new conventional ligature and the FR was tested. Like this FR was tested 5 times. Afterwards, a new Bracket assembly was prepared, and FR was tested similarly like described above for 5 more times using the new 0.019 × 0.025″ SS archwire and new conventional ligatures. The bracket arrangement was replaced by new bracket assembly after every five tests. For each test, a new archwire and ligature were employed.
A total of ten combinations were made [Table 2] and the same procedure was repeated for the rest of the combinations similarly like described above to find the FR in each of the combinations. No modules/ligation was used for self-ligating brackets. Each combination was tested 10 times. A total of 100 tests were performed, and all tests were conducted in the dry state at an ambient temperature of 34°C at the Central Institute of Plastics Engineering and Technology, Hyderabad.
| Results|| |
Descriptive statistics, including the mean, standard deviation, minimum and maximum values were calculated for each bracket-archwire combination. ANOVA was applied to statistically compare the means of FR of all the combinations using F distribution [Table 3].
|Table 3: Comparison of Means of Frictional Resistance Between Various Variables by One-Way ANOVA Test|
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The measurements showed statistically significant difference between the means of the variables.
The mean was larger with SS (2.83 ± 0.06) wire than Teflon coated (TC) (2.35 ± 0.15) wire; therefore indicating greater FR with SS wire, as shown in [Table 4].
|Table 4: Comparison of Means, Using Self-Ligating Brackets With Respect to Archwire Material By Unpaired T-Test|
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[Table 5] shows the FR of metal brackets with SS and TC archwires with conventional elastic ligature. The mean is greater with SS wire (5.74 ± 0.05) when compared with TC wire (5.10 ± 0.08), indicating that SS wire shows more FR.
|Table 5: Comparison of Means, Using Metal Brackets With Conventional Elastic Ligature With Respect to Archwire Material by Unpaired T-Test|
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As shown in [Table 6], the mean values of FR are compared among SS and TC wires with metal bracket using low-friction ligature. Results indicate that SS wire shows more FR (4.51 ± 0.01) than TC wire (3.45 ± 0.03).
|Table 6: Comparison of Means, Using Metal Brackets With Low-Friction Ligature With Respect to Archwire Material by Unpaired T-Test|
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The results in [Table 7] presents the mean values of FR obtained using ceramic bracket with SS and TC wire ligated with conventional elastic ligature. SS wire shows the highest FR (7.32 ± 0.10) in the study.
|Table 7: Comparison of Means, Using Ceramic Brackets With Conventional Elastic Ligature With Respect to Archwire Material By Unpaired T-Test|
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Frictional resistance of SS wire (4.70 ± 0.10) is higher than TC wire (4.71 ± 0.10) when low-friction ligature is used with ceramic bracket and archwire combination, as shown in [Table 8].
|Table 8: Comparison of Means, Using Ceramic Brackets With Low-Friction Ligature With Respect to Archwire Material by Unpaired T-Test|
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Ceramic bracket with SS wire when ligated with conventional elastic ligature showed the highest mean of 7.32 with SD of 0.10. Self-ligating brackets with TC wire show the least FR of 2.35 ± 0.15N. In general, TC wire shows less FR when compared to SS wire. Low-friction ligatures have also shown lesser FR when compared to conventional elastic ligature.
| Discussion|| |
Orthodontic brackets transmit forces from the archwire and auxiliaries to the teeth. When sliding mechanics is employed for space closure in orthodontics for the retraction of individual tooth or a segment of teeth, a distally directed force retracts the anterior teeth by sliding an archwire through the brackets and tubes in the buccal segments. Significant resistance to movement may arise due to the frictional force that is generated.  This force slows or resists the movement of the archwire through the bracket slots as anterior teeth are retracted and may additionally transmit excessive forces to the posterior anchor teeth which results in a loss of anchorage.  Thus when orthodontic tooth movement is being planned, the frictional forces should be accounted for and an effort should be made to minimize it.
Frictional force has two components; the initial friction between the archwire and the bracket when a force is applied is termed as static friction and must be overcome to initiate tooth movement. As the tooth is moving, the second component to friction termed dynamic friction occurs with the archwire moving in the direction of the applied force as it is guided through the molar and premolar bracket slots.  Frictional force increases or varies with factors such as increased archwire size,  torque present in the archwire,  2 nd order displacement,  ligation method,  force of ligation,  bracket material  and surface roughness.  Bracket design can also additionally influence frictional forces and many studies have shown reduced frictional forces with self-ligating brackets when compared to conventional brackets.  Furthermore, the types of ligature used in securing the archwire in bracket slot also plays an important role in the resultant friction values. To minimize friction produced by ligation an innovative ligature manufactured with a special polyurethane mix by injection molding was introduced. The "nonconventional" elastomeric ligature is used on conventional brackets to produce low levels of FR in treatment mechanics with the preadjusted appliance. Once the ligature is applied on the bracket, the interaction between the ligature and the slot forms a "tube like" structure, which allows the archwire to slide freely and to produce its effects more readily on the dentoalveolar component.
The present study was aimed at comparing the FR between various bracket types including passive self-ligating brackets (SmartClip™), SS brackets (Victory Series) and ceramic brackets (clarity advanced). The archwires used were SS (3M Unitek) and TC (Rabbit Force), both of 0.019 × 0.025″ cross-section. The types of ligation used were conventional elastic module (3M Unitek) and low-friction module (SLIDE, Leone).
Statistical results indicate that the least FR was seen with self-ligating bracket and TC wire (2.35 ± 0.15). Lower values of FR with self-ligating brackets can be explained by the fact that application of ligature is not required with such brackets, therefore reducing the friction to sliding. Ceramic bracket when combined with SS wire and conventional elastic ligature showed the highest mean value of FR (7.32 ± 0.10). In keeping with Loftus et al.,  we found that slots of ceramic material generate more friction than SS slots. The likely reason is that ceramic material possesses higher coefficient of friction than SS because of increased roughness and porosity of the material surface. Manufacturing procedure, finishing, and polishing are difficult to do; this might explain the granular and pitted surface of the ceramic brackets thereby increasing the surface roughness. This finding matches with the findings of Nishio et al. who also concluded that ceramic bracket shows the highest FR. 
In general, TC wire has shown lower values of FR when compared to SS wire. Most likely, the lower-friction values were a result of Teflon material possessing a lower coefficient of friction.
Low-friction ligature has shown lower mean values than conventional elastic ligature. This may be due to the build-in elastic device in low-friction ligatures that transforms the bracket slot into the tube and closed the archwire into the slot. This elastic device is more rigid and is rather stiff when compared with the soft and elastic surfaces of the conventional ligatures.
| Conclusion|| |
The following conclusions were drawn from the study:
- Passive self-ligating brackets showed significantly lower values of friction than metal and ceramic brackets.
- In general, TC wires produced lower resistance to sliding when compared with SS wire.
- The findings of this study shows that Leone slide ligature possess less friction in comparison with conventional elastic ligatures.
- Ceramic bracket has shown the highest value of FR when compared to other brackets used in this study.
In vitro studies do not correspond to what really happens during dental movement, and therefore, clinicians must be careful when evaluating the results. The friction magnitude recorded in this study is substantially different from the applied forces in clinical orthodontic movement. There are some valuable findings regarding low-friction ligature and TC wires showing low FR which can be applied clinically for better treatment outcomes.
Clinical implications of the present study
Our findings seem to indicate that TC wires possess low FR when compared to SS wire. In addition, TC wires are esthetically pleasing to patients.
On the basis of the results of this study, as the innovative elastomeric ligatures produce significantly lower levels of frictional force than conventional elastomeric ligature, so the new ligature may represent a valid alternative to passive self-ligating bracket when minimal amount of friction is desired. One of the most favorable features of the new ligature is the possibility of turning any type of existing conventional bracket system into a "low-friction" bracket system. Furthermore, the innovative ligature can be applied on specific groups of teeth where lower levels of friction at the bracket/archwire/ligature unit are desired.
Another clinical significance of this study may be manifested where steel brackets are used on posterior teeth and ceramic brackets being esthetic are used on the anterior teeth. Typically, the posterior teeth are used as anchorage to retract anterior teeth. If sliding mechanics was used, the differences in friction between steel and ceramic brackets could result in the posterior teeth moving more readily than anterior teeth, the consequences of which would be more anchorage loss than would otherwise be expected. This would be especially true when light archwires are used. Additional measures like placement of palatal bar, Nance button or extra oral devices can be used to reinforce the anchorage, if required.
Short comings of the study
The variety of experimental methods used in literature makes it difficult to compare the results of different studies. Differences in the results among such studies may therefore reflect differences in methods. Some error may be encountered due to inaccurate mounting of the models in testing machine. Moreover intra oral variables such as saliva, plaque, corrosion, chewing, bone density, tooth numbers, anatomic configurations, root surface area and occlusion were not evaluated in this study.
Scope for future studies
Additional in vivo testing of the protocols established in this study need to be undertaken to evaluate the clinical applicability with increase in sample size. Newer archwire materials with various brackets may be used to form new combinations. For patients with high esthetic demands, esthetic self-ligating brackets may be included in future research with more advanced testing machines.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]