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| Year : 2011 | Volume
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| Issue : 1 | Page : 95-99 |
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| Frictional characteristics of the newer orthodontic elastomeric ligatures |
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AV Arun, Anna Cecilia Vaz
Department of Orthodontics and Dentofacial Orthopedics, PMNM Dental College and Hospital, Bagalkot, Karnataka, India
Click here for correspondence address and email
| Date of Submission | 19-Sep-2009 |
| Date of Decision | 13-Jul-2010 |
| Date of Acceptance | 19-Aug-2010 |
| Date of Web Publication | 25-Apr-2011 |
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 Abstract | | |
Introduction: Elastomeric ligatures reduce chairside time but increase friction. Polymeric coatings and 45° angulations have been introduced to the ligature modules to combat its disadvantages and reduce friction. This in vitro study compared the frictional characteristics of six different types of the most commonly used elastomeric modules.
Materials and Methods: Thecoefficient of friction for six ligation methods: the non-coated Mini Stix† and coated Super Slick Mini Stix™ (TP Orthodontics), 45° angulated but non-coated Alastik Easy-To-Tie™ (3M Unitek) elastomerics and non-angulated non-coated Alastik QuiK-StiK * , 0.110'- and 0.120'-diameter elastomerics™ (Reliance Orthodontics) were measured in dry conditions utilizing a jig according to the protocol of Tidy.
Results: A significant difference was observed between the various types of elastomeric ligatures (P<.01). Among the six types of elastomeric ligatures, the 45° angulated elastomeric ligatures produced the least friction, followed by the coated Super Slick† elastomers. No difference in the friction was noted when the diameter of the elastomeric ligatures was varied.
Conclusions: Polymeric surface coatings and introduction of angulations into elastomeric ligatures reduce the friction during sliding; however, the diameter of the ligature made no difference to sliding friction. Keywords: Friction, elastomeric ligatures, Super Slick™, preangulated elastomers
How to cite this article:
Arun A V, Vaz AC. Frictional characteristics of the newer orthodontic elastomeric ligatures. Indian J Dent Res 2011;22:95-9 |
How to cite this URL:
Arun A V, Vaz AC. Frictional characteristics of the newer orthodontic elastomeric ligatures. Indian J Dent Res [serial online] 2011 [cited 2023 Mar 23];22:95-9. Available from: https://www.ijdr.in/text.asp?2011/22/1/95/80005 |
Although various techniques are available to effectuate tooth movement, the most common consists of an edgewise bracket that slides along a continuous archwire. The sliding, arch-guided system, generally referred to as sliding mechanics, can be influenced by counteracting frictional forces at the interface of the bracket, archwire, and ligature. [1]
Friction is defined as 'the force tangential to the common boundary of two bodies in contact that resists the motion of one relative to the other. The amount of friction generated is proportional to the force with which the two surfaces are pressed together and upon the nature of the surfaces in contact.' [2]
A number of studies have identified the principal factors that may influence orthodontic frictional forces. The type and force of archwire ligation is one of these factors. [2] Elastomeric ligatures were introduced into orthodontics to reduce the chairside time. The advantages of using elastomeric ligatures are that they can be applied quickly, are comfortable to the patient, and are relatively hygienic and inexpensive. [3]
The methods of archwire ligation have been investigated in a few studies. The majority of authors agree that loosely tied stainless steel ligatures produce less friction than the standard elastomeric ligatures. [4],[5],[6],[7] There are a few studies [8],[9] that have shown that the frictional forces produced by elastomeric ligatures and stainless steel ligatures are similar, whereas other studies [10],[11] have found that friction caused by elastomeric ligatures was less than that generated by steel ligatures. In the recent years, different types of elastomeric ligatures have been introduced and these have been claimed to reduce friction. These include modules coated with covalently bonded Metafasix (Super Slick TM† ) and 45° angulated modules (Alastik Easy-To-Tie TM* ). The present literature review revealed scarce information concerning the recently modified elastomeric ligatures, and the findings with regard to resistance in sliding between the various modes of ligation with the elastomeric ligatures were inconsistent.
Therefore, our aim in this study was to evaluate and compare the frictional forces generated by different forms of modified elastomeric ligatures: namely, coated and non-coated elastomeric ligatures, small- and large-diameter elastomeric ligatures, and the 45° angulated and non-angulated elastomeric ligatures.
| Materials and Methods | |  |
The measurement of friction between the different types of elastomeric ligature ties and bracket-archwire combinations were obtained using the Instron universal testing machine (Unitek p450 (pc), FIE-Bluestar, India; sensitivity: 0.0001 kN). An experimental model simulating the fixed appliance was prepared similar to the model used by Tidy [12] for measuring friction between the archwire and bracket combinations.
Four Roth prescription stainless steel premolar edgewise brackets of 0.022' slot dimensions from Ortho Organizers were selected. These brackets were bonded onto a rigid base of Perspex sheet, with an inter-bracket distance of 8 mm. At the center of the sheet a 16-mm space was provided for a movable bracket. A cuspid bracket was used as a movable bracket. This movable bracket was fitted with a 10-mm power arm onto which a weight of 100 gm was added. This setup represents the single equivalent force acting at the center of the tooth root. The length of the power arm was chosen to represent the distance from the slot to the center of resistance of a typical canine bracket. The weight suspended from the power arm provided a load of 100 gm. A stainless steel rectangular wire (0.019' × 0.025') was used as a base arch. The movable bracket was suspended from the load cell, while the other end of the baseplate was held in the crosshead of the testing machine. The crosshead was moved at a speed of 5 mm/min to a distance of not less than 2.5 mm. The load cell reading represented the clinical force of retraction that would be applied to the tooth, part of which would be lost in friction while the remainder would be transmitted to the tooth root. Thus, the difference between the load cell reading and the load on the power arm represented friction [Figure 1].
Six different elastomeric ligature ties from different companies were compared [Figure 2] [Table 1]. The diameter of these ligature ties (according to the manufacturer's description) were noted and its salient features recorded prior to performing the test. | Table 1: Frictional resistance values obtained for elastomeric ligatures and their significance assessed by the one-way ANOVA test
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These ligatures were placed on the brackets using the Straight-Shooter® ligature gun. This allowed the elastomerics to be stretched by a standard amount prior to placement. Care was taken not to distort the ligature ties when placing them on the brackets; the elastomerics were changed, keeping the bracket, archwire unaltered.
All tests were conducted in dry conditions. Five test readings were taken for each group of ligature ties immediately after placement. Each elastomeric was tested only once to eliminate the possibility of surface-wear effects; that is, five test readings were taken using five different elastomerics in each group. The readings were recorded from the monitor of the testing machine. The difference between the load cell reading and the load on the power arm represented friction (P). The coefficient of friction was calculated using the formula P=2Fhμ/w, where P is the frictional resistance, w the bracket width, μ the coefficient of friction between bracket and arch wire, and F the equivalent force (100 gm) that acts at a distance h (10 mm) from the arch wire. [12]
The results obtained were analyzed by using one-way ANOVA test [Table 1]. Pair-wise comparison of eight groups was done by Scheffe's multiple comparison test [Table 2]. Student's t-test was employed for the pair-wise comparison between similar groups [Table 3].  | Table 2: Pair-wise comparison of the six types of elastomers obtained by Scheffe's multiple comparison test
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 | Table 3: Intragroup comparison of frictional resistance by Student's unpaired t-test
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| Results | | |
The ligation methods produced statistically significant differences between groups at P=.0002 (<.01) and an F-value of 18.765 [Table 1]. Pair-wise comparison of eight groups was done by Scheffe's multiple comparison tests procedure [Table 2], which revealed that the coated elastomerics Super Slick† and the preangulated Alastik Easy-To-Tie * showed statistically significant differences from the the other brands. The pre-angulated Alastik Easy-To-Tie * ligatures lowered the frictional resistance to an even greater extent than the Super Slick† elastomers; however, this difference was not statistically significant.
The coated Super Slick† elastomers showed significantly reduced friction compared to non-coated elastomerics from the same manufacturer (P=.0087, [Table 3]). When the smaller- and larger-diameter ligatures were compared using ligatures from the same manufacturer, (0.110'- and 0.120'-diameter elastomeric ligatures # ), there was no statistically significant difference in the friction generated by these modules (P=.7207; [Table 3]). The 45° angulated Alastik Easy-To-Tie * ligatures showed a reduction in the frictional resistance to a greater extent than the conventional elastomers: Alastik QuiK-StiK * (P=.0014; [Table 3]).
| Discussion | | |
Friction is an important consideration in the sliding mechanics. During space closure, 60% of the applied force is spent overcoming friction. [13] The factors responsible for frictional resistance are multiple. Several variables exist that can directly or indirectly contribute to the frictional force levels between the bracket and the wire. [14] The mode of ligation has been shown to affect the frictionproduced. [15] The ligating material and the ligating force were seen to influence the frictional resistance between the bracket and the archwire. Loosely tied steel ligatures were seen to offer lower resistance to friction than the elastomerics. [2] However, the resistance offered by steel ligatures to friction was dependent upon the force used to ligate the bracket to the archwire. [2] Elastomerics, on the other hand, offered greater resistance initially to tooth movement but, owing to the fact that these materials undergo stress relaxation and slow hydrolytic decomposition, their ligating forces alter with time. [16],[17]
Our results showed that the 45° angulated Alastik Easy-To-Tie * ligature produced the lowest coefficient of friction and the larger size (0.120'-diameter) elastomeric ligature # showed the highest coefficient of friction. Pair-wise comparison revealed that the coated Super Slick† and the preangulated elastomerics showed statistically significant differences from the other brands. Preangulated elastomers showed lower coefficient of friction when compared with Super Slick† . However, the difference was statistically not significant, implying that both the elastomeric ligatures were equally efficient in reducing frictional resistance when compared with the noncoated, nonangulated elastomers.
The variations in the experimental methods used in different studies in the literature makes it difficult to compare our results with that of other studies of this type. However, some similarities in the findings were observed. This study was in agreement with the studies of Hain, Dhopatkar, and Rock [6],[18] and disagreed with the results of Khamby, Millett, and Mchugh [19] and Griffiths, Sherriff, and Ireland. [20] Hain, Dhopatkar, and Rock [6],[18] in their studies showed that the coated elastomer Super Slick† was superior to the non-coated elastomers. Our findings are concordant with theirs.
This study was carried under dry conditions. Devanathan [21] in his study found that these elastics are superior under wet conditions. It is postulated that if these coated elastomerics are better than the non-coated ones in dry conditions, the difference would be more marked under wet conditions. However, investigating this was beyond the scope of our study and will have to be confirmed through another one. The variation in the friction can be attributed to the surface characteristics of these modules. [7] It has been postulated that the covalently bonded Metafasix polymeric coating was the reason for the reduced amount of friction in the coated Super Slick† ligatures. [18] Khambay, Millet, and Huge [22] observed that there were differences in frictional resistance between the Super Slick† elastomers and the Alastik Easy-To-Tie * elastomers. According to the authors both the elastomers showed lowered frictional resistance, with the Alastik Easy-To-Tie * elastomers showing lower frictional resistance than the Super Slick† elastomers. However, these differences were not statistically significant. This study also found differences between Super Slick† elastomers and the Alastik Easy-To-Tie * elastomers. The preangulated Alastik Easy-To-Tie * ligatures lowered the frictional resistance to a greater extent than the Super Slick† elastomers; however, the difference was not statistically significant. Thus, the preangulated elastomers performed as well as the Super Slick† elastomers. The change in the angulation was perhaps responsible for the lowered frictional resistance in the preangulated elastomers, as it reduces the binding force of the arch wire on the bracket base
When the smaller- and larger-diameter ligatures were compared using ligatures from the same manufacturer (0.110'- and 0.120'-diameter elastomeric ligatures # ), there was no statistically significant difference in the friction generated by these modules. Chimenti et al.[2] demonstrated a 13%-17% reduction in static friction with the smaller- and medium-diameter elastomers than that with the larger-diameter ones. In their study, there was no statistically significant difference observed in the friction produced when small elastomers were compared with medium elastomers. They concluded that the increased friction seen with large elastomers was due to the greater thickness of large elastomers compared to small or medium elastomeric ligatures and that the diameter of the ligature did not influence friction. The findings of this study are in agreement with those of Chimenti et al., [2] who too found that difference in the diameter did not produce statistically significant differences in the frictional resistance seen between the two groups. This probably shows the greater importance of the surface characteristics rather than the inner diameter of these elastomers in generating friction.
When the 45° angulated elastomeric ligatures were compared with conventional elastomeric ligatures from the same manufacturer we found a greater reduction in the frictional resistance with the 45° angulated elastomeric ligatures. Although there are no similar studies in the literature with which we could compare our results, it can be inferred that the introduction of angulations in these elastomeric ligatures alter the surface characteristics and binding forces, thus influencing the friction generated at the archwire-bracket-ligature interface.
| Conclusions | | |
- Among the different types of elastomeric ligatures compared in this study, in dry conditions, 45° angulated elastomeric ligatures produced the least friction, followed by coated Super Slick† elastomers.
- Conventional 0.120'-diameter elastomeric ligatures showed the maximum friction.
- Angulation introduced into the elastomeric ligatures reduces the friction in comparison to conventional elastomeric ligatures.
- Polymeric surface coating of the elastomeric ligatures reduces the friction in comparison to conventional elastomeric ligatures.
- There was no difference in the friction produced by smaller- and larger-diameter elastomeric ligatures.
- The findings in this study therefore suggest that in these times, when friction is an important factor in sliding mechanics and the conservation of anchorage is critical, the preangulated elastomers, Alastik Easy-To-TieTM* and the Super SlickTM† elastomers, provide viable options. This study, however, was carried out in vitro and under dry conditions. The results obtained may differ in vivo, and testing under wet conditions also would be advisable.
| Endnotes | | |
† - ™ TP Orthodontics, * - ™ 3M Unitek, # - ™ Reliance Orthodontics.
| References | | |
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Correspondence Address:
Anna Cecilia Vaz
Department of Orthodontics and Dentofacial Orthopedics, PMNM Dental College and Hospital, Bagalkot, Karnataka
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0970-9290.80005
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3] |
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