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ORIGINAL ARTICLE
Year : 2015  |  Volume : 4  |  Issue : 2  |  Page : 91-96

A comparative study of the physical and elastic properties of new generation elastomeric ligatures with conventional elastomeric ligatures


Department of Orthodontics and Dentofacial Orthopedics, Panineeya Dental College, Hyderabad, Telangana, India

Date of Web Publication12-Jun-2015

Correspondence Address:
Shubhaker Rao Juvvadi
Department of Orthodontics and Dentofacial Orthopedics, Panineeya Dental College, Road No 5, Kamala Nagar, Dilsukh Nagar, Hyderabad - 500 060, Telangana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2277-8632.158581

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  Abstract 

Context: One of the most common methods of securing arch wires to orthodontic brackets is the application of elastomeric ligatures. New generation elastomeric ligatures were introduced to overcome the disadvantages of force decay and staining in conventional ligatures.
Aims: The aim was to compare the physical and elastic properties of new generation elastomeric ligatures with the conventional elastomeric ligatures.
Materials and Methods: Four groups of clear elastomeric modules (conventional polyurethane based modules, latex free elastomeric modules, alastik easy to tie modules, silver and silicone impregnated super ligatures) were tested for tensile properties, frictional resistance, and color stability in as received condition and following 1-week, 2 weeks, and 1-month of intra-oral exposure. A universal testing machine was used for testing tensile properties. The color stability was tested by measuring the color change using scanned images of the modules at different time periods.
Statistical Analysis: Two-way ANOVA, post-hoc multiple comparisons Bonferroni-Dunn test and the paired t-test were used.
Results: The alastik group showed the highest mean tensile strength and super ligatures showed the lowest tensile strength values. There was a statistically significant decrease in the mean tensile strength in all groups following intra-oral exposure (P < 0.05). The super ligatures showed the lowest mean frictional resistance and latex free group showed the highest mean frictional resistance values. The color change following intra-oral exposure was significant in all the groups (P < 0.05) with the change being the highest in super ligatures group and the least in alastik group.
Conclusions: There are significant differences in physical and elastic properties of different brands of ligatures, which should be considered during the selection of these products.

Keywords: Colour stability, elastomeric modules, frictional resistance, tensile properties


How to cite this article:
Gandikota CS, Neeharika C, Juvvadi SR, Poornima KY, Manne R, Apuri LP. A comparative study of the physical and elastic properties of new generation elastomeric ligatures with conventional elastomeric ligatures. J NTR Univ Health Sci 2015;4:91-6

How to cite this URL:
Gandikota CS, Neeharika C, Juvvadi SR, Poornima KY, Manne R, Apuri LP. A comparative study of the physical and elastic properties of new generation elastomeric ligatures with conventional elastomeric ligatures. J NTR Univ Health Sci [serial online] 2015 [cited 2019 Nov 18];4:91-6. Available from: http://www.jdrntruhs.org/text.asp?2015/4/2/91/158581


  Introduction Top


One of the most common methods of securing arch wires to orthodontic brackets is the application of elastomeric ligatures (modules) which are synthetic elastics made of polyurethane materials; however, the exact composition is proprietary information. Although these ligatures show some disadvantages such as microbial colonization and sliding resistance, their advantages such as quickness of application, patient comfort, and a variety of colors have resulted in greater popularity than stainless steel ties. Newer elastomeric products are being introduced by many companies to overcome the drawbacks of the conventional elastomeric ligatures and to increase their clinical efficiency. This aim of this study was to compare the physical and elastic properties of conventional elastomeric ligatures with the new generation elastomeric ligatures.


  Materials and Methods Top


Four groups of clear elastomeric modules (inside diameter 1.3 mm, outside diameter 3.1 mm, thickness 0.9 mm) were evaluated and compared in this study [Figure 1]. The first group (CO) comprised of the conventional polyurethane-based elastomeric modules obtained from Millenium Orthodontics, New Delhi, India. The second group (LF) constituted the latex free elastomeric modules obtained from Desires Orthodontics, Davangere, India. The third group (AL) comprised of Alastik™ Easy-to-tie modules (with 45° bend) obtained from 3M Unitek, Monrovia, CA, USA. The fourth group (SL) constituted the super ligatures which were silver and silicone impregnated obtained from D-tech, Pune, India.
Figure 1: Four groups of clear elastomeric modules

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A split-mouth design was employed [Figure 2], and these were placed in the patient by the same operator for standardization. 10 elastomeric modules of each type were tested at four different time periods: T0-as received state, T1-after 1-week of intra-oral exposure, T2-after 2 weeks of intra-oral exposure, and T3-after 1-month of intra-oral exposure. The ultimate tensile strength and modulus of elasticity were measured on the universal testing machine (Autograph, Shimadzu AG 15, Japan). Using U-shaped hooks which were formed from 0.8-mm stainless steel wire secured in the jigs made of self-cure acrylic, elastomeric ligatures were stretched on the testing machine until they were broken [Figure 3]. This was carried out with a crosshead speed of 5 mm/min according to the recommendation of Kovatch et al. [1] Load extension curve of each module was recorded graphically and the ultimate tensile strength and modulus of elasticity of the ligatures were determined.
Figure 2: Split-mouth design

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Figure 3: Ultimate tensile strength and modulus of elasticity measured on the universal testing machine

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For the measurement of color, the elastomeric modules were scanned using a scanner (HP Deskjet 1050 J410 series, USA) and digital images were obtained. Digital image files were opened in commercial software (Image J 1.44d, National Institutes of Health, USA) and the RGB values were obtained. The mean gray component was measured and analyzed at T0, T1, T2, and T3 time periods.

The frictional resistance was evaluated in vitro. An experimental model consists of maxillary right incisor bracket (0.022" slot, MBT prescription, 3M Unitek, USA) was mounted on an acrylic resin block using cyanoacrylate adhesive (Fewikwick SP , Pidilite Industries Ltd., Mumbai, India). The bracket was oriented with the long axis of the slot vertical and in line with the direction of measurement of the load cell [Figure 4]. The acrylic block was then secured to the load cell using the clamps provided by the manufacturer. A straight 60-mm of test wire (0.019 × 0.025-inch stainless steel wire, 3M Unitek, USA) was embedded in acrylic block to secure it in the clamps. The wire was secured in the brackets using elastomeric ligatures. Static friction was recorded while 5-mm of wire was drawn through the bracket at a speed of 20 mm/min, and it was defined as the force needed to start the wire moving through the bracket. Kinetic friction, the force that resists motion, was also recorded at 5-mm, 7-mm and 9-mm. After each test, the testing machine was stopped, the wire-bracket-ligature unit was removed, and a new assembly was placed. For each type of elastomeric ligature, a series of 5 friction recordings were taken. The friction tests were started immediately after ligation with new elastomeric ligatures placed in a conventional manner (figure-O pattern). All the measurements were made in a dry state at room temperature (30°C ± 2°C).
Figure 4: Frictional resistance measured on the universal testing machine

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The mean and standard deviation values for each group at T0, T1, T2, T3 time periods were obtained for tensile strength, modulus of elasticity and color stability. The mean and standard deviation values for frictional resistance for each group were obtained at the start of wire movement, at 5-mm, 7-mm and 9-mm distance.

Statistical analysis

Statistical analysis was performed using the two-way ANOVA, post-hoc multiple comparisons Bonferroni-Dunn test and the paired t-test. All the statistical procedures were carried out using SPSS for Windows XP (version 15, IBM corp, NY, USA).


  Results Top


The ultimate tensile strength decreased significantly in all the groups after 1-week, 2 weeks, and 1-month of intra-oral exposure (P < 0.01) except in SL group in which the decrease was not statistically significant (P > 0.05). Within the groups, the AL group showed the highest mean tensile strength followed by LF, CO, and SL groups at all time periods [Table 1] and [Figure 5].
Figure 5: Mean tensile strength among groups

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Table 1: Mean and Standard Deviation Values

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The modulus of elasticity decreased in all the groups after 1-week, 2 weeks, and 1-month of intra-oral exposure; but, the decrease was not statistically significant (P > 0.05). Within the groups, the AL group showed the highest values of modulus of elasticity followed by SL, CO, and LF groups [Table 1] and [Figure 6].
Figure 6: Modulus of elasticity among groups

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The LF group showed the highest mean frictional force values at all time periods followed by CO and AL groups. The SL group showed the lowest mean frictional force values at all time periods [Table 1] and [Figure 7]. The results of ANOVA and paired t-test indicated that the frictional force decreased significantly in all the groups after movement at 5-mm, 7-mm, and 9-mm distance (P < 0.001).
Figure 7: Mean frictional force values among groups

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The color change was statistically significant in all the groups after 1-week, 2 weeks, and 1-month of intra-oral exposure (P < 0.001), and it was the greatest for SL group. The AL group showed the least color change [Table 1] and [Figure 8].
Figure 8: Color change among groups

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  Discussion Top


The newer generation elastomeric modules were introduced to overcome the drawbacks of conventional elastomeric ligatures. This study was devised to compare the physical and elastic properties of the conventional elastomeric ligatures with the newer generation elastomeric ligatures after intra-oral exposure. Latex has widespread uses within dentistry as in many other fields of medicine. Since the early 90 s, nonlatex elastics have been made available for orthodontic use but the guidelines for the clinical use of latex-containing elastics are not necessarily applicable to nonlatex elastics. For this reason, the properties of these materials need to be evaluated experimentally. This study was, therefore, devised to compare the latex free elastomeric modules with the conventional and other new generation modules.

The silicone and silver impregnated ligature rings were claimed to possess extended elastic memory and improved stain resistance compared to the other elastomeric ligatures. The findings of the previous studies [2],[3],[4],[5],[6],[7],[8] indicated that incorporation of lubricating agent into the elastomeric ligatures had decreased the frictional forces compared to the conventional elastomeric modules, but the effect of the additives on the tensile properties and color stability were not evaluated. The earlier studies [9],[10] compared the properties of colored and clear modules from different manufacturers, the properties of colored modules from different manufacturers [11] and the properties of open and closed elastomeric modules. This study compares the physical and elastic properties of clear modules obtained from different manufacturers.

Ultimate tensile strength and modulus of elasticity

Ultimate tensile strength is defined as the maximum stress required fracturing a material. If elastomeric modules lack adequate tensile properties, clinical application will be difficult and time-consuming. In addition, the force of ligation contributes to friction and consequently counteracts free sliding. There has been extensive research on the effects of time, [12] temperature, fluoride treatment, water sorption, prestretching [13] and environmental conditions [14] on force delivery, force degradation, permanent deformation and strength of elastomeric chains and orthodontic elastics. The results obtained in this study indicated that the ultimate tensile strength decreased significantly in all the groups after 1-week, 2 weeks, and 1-month of intra-oral exposure [Table 1]. These findings are similar to the results obtained from previous studies on force decay of elastomeric ligatures after immersing in different disinfectant solutions for different time periods, tested in vitro. [15],[16],[17]

Frictional resistance

Orthodontic sliding mechanics using preadjusted brackets is a common method of translating a tooth or a group of teeth. The major disadvantage with the use of sliding mechanics is the friction that is generated between the bracket and the archwire during orthodontic movement. The dissipation of the orthodontic force as resistance to sliding may vary between 12% and 60%, or it may restrict tooth movement. The friction encountered during tooth movement can be divided into static friction and kinetic friction. [18] Frictional resistance must be kept to a minimum during sliding mechanics so that orthodontic tooth movement can be generated through light optimal forces. A number of studies have identified the principal factors that may influence orthodontic frictional resistance: Archwire size, [19] archwire section, [19] torque at the bracket-wire interface, [20] surface conditions of the archwires and bracket slot, [21] bracketand archwire materials, [22],[19] bracket type, [23],[24],[25] type and force of archwire ligation. [23] The results of this study are similar to the results obtained from above mentioned studies on the effect of different types of elastomeric ligatures on frictional resistance. The LF group showed the highest mean frictional force value (224-332 g) at all time periods followed by CO (161-216 g) and AL groups (83.9-154 g). The SL group showed the lowest mean frictional force values at all time periods (80.9-96.8 g) [Table 1].

Color stability

Ceramic brackets have become popular as aesthetic appliances and have been available for clinical use for approximately 20 years in spite of several negative clinical properties. The use of clear elastomeric modules to ligate ceramic brackets has enhanced the aesthetic value of these appliances. However, the modules can discolor if patients consume certain foods or beverages, such as coffee and tea, between appointments. A spectrophotometer is an instrument widely used for measuring surface color due to its reliability and accuracy. However, it is difficult to measure the color of orthodontic elastomeric modules using a spectrophotometer due to limitations such as the need for a relatively large measurement area and geometric problems caused by the curvature of the elastomeric modules. [26] Recent advances in photography and computer science have resulted in the widespread use of digital cameras for color imaging. Therefore, when combined with appropriate calibration protocols, digital cameras, especially commercial single lens reflex (SLR) digital cameras show potential to be used in color measurement for clinical dentistry. This study is different from the previous studies in that changes in color of the clear elastomeric modules were evaluated following intra-oral exposure for 1-week, 2 weeks, and 1-month time period. The digital images were obtained by scanning the elastomeric modules using scanner (Hewlett-Packard Deskjet 1050 J410 series, California, USA). This is a more cost-effective and simpler process than the use of traditional color measurement devices such as a spectrophotometer or a colorimeter and even the commercial SLR digital cameras. The results indicated that color change was statistically significant in all the groups after 1-week, 2 weeks, and 1-month of intra-oral exposure, and it was the greatest for SL group (39.9 units) [Table 1].

The color change between 1-week and 2 weeks of intra-oral exposure was significant in all the experimental groups with the difference being the greatest for SL group (12.9 units) and least for AL group (2.3 units). The CO and LF groups showed similar color change (6.8-7.5 units). In between 1-week and 1-month of intra-oral exposure, all the groups showed significant color change and the difference was the greatest for SL group (30.8 units) and least for AL group (10.14 units). The CO and LF groups showed similar color change (14.7-16.5 units). The color change from 2 weeks to 1-month of intra-oral exposure was significant for all the experimental groups with the difference being the greatest for SL group (17.8 units) and least for CO (7.2 units) and AL groups (7.7 units).


  Conclusion Top


The decrease in tensile properties of elastomeric ligatures shows that they may have to be replaced at each appointment to reduce the risk of rupture. There are significant differences in tensile properties of different brands of ligatures, which should be considered during the selection of these products. Considering the number of variables evaluated in this study, it is difficult to conclude about the best elastomeric ligature from the point of physical and elastic properties. It is also suggested that manufacturers offer the relevant data to their customers in order to facilitate the selection of appropriate elastomeric ligatures as per their clinical demands.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
 
 
    Tables

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