 Abstract | | |
Objective: To evaluate and compare the effect of variation in storage temperatures and duration on a tensile load at failure of elastomeric modules. Methods: In total, 140 modules were used in the study, 20 of which were tested on day 0 as received from a company using a Universal testing machine for baseline estimation of tensile load at failure. The rest 120 modules were divided into 6 groups. Groups I, II, and III modules were stored at low (T1 = 1–5°C), moderate (T2 = 20–25°C) and high (T3 = 35–40°C) temperatures, respectively, for 6 months. Groups IV, V and VI modules were stored at temperatures T1, T2 and T3 for 1 year, respectively, and were tested for tensile load at failure. Results: The tensile load at failure for the control group was 21.588 ± 1.082 N and for 6-month interval at temperatures T1, T2 and T3 was 18.818 N ± 1.121 N, 17.841 N ± 1.334 N and 17.149 N ± 1.074 N, respectively, and for 1 year, it was 17.205 N ± 1.043 N, 16.836 N ± 0.487 N and 14.788 N ± 0.781 N, respectively. The tensile load at failure decreased significantly from 6 months to 1 year among each temperature group. Conclusions: Maximum force degradation was seen in modules at high temperature followed by medium temperature and low temperature at both 6 months and 1 year intervals, and tensile load at failure decreased significantly from 6 months to 1 year storage duration. These results conclude that the temperature and duration at which the samples were exposed during storage produce a significant change in the forces exerted by the modules.
Keywords: Elastomeric modules, low temperature and high temperature, orthodontic modules, tensile strength
How to cite this article:
Sharma S, Singh AK, Batra P, Arora N, Kannan S. Effects of different storage temperatures on the properties of nonlatex orthodontic modules. Indian J Dent Res 2022;33:350-5 |
How to cite this URL:
Sharma S, Singh AK, Batra P, Arora N, Kannan S. Effects of different storage temperatures on the properties of nonlatex orthodontic modules. Indian J Dent Res [serial online] 2022 [cited 2023 Jun 9];33:350-5. Available from: https://www.ijdr.in/text.asp?2022/33/4/350/372908 |
| Introduction | |  |
The most commonly used method of treatment in orthodontics is fixed mechanotherapy that involves the use of brackets and archwires. The bracket system itself can now be divided into conventional and self-ligating systems. The conventional bracket system uses different modes of ligation to hold the archwire to the bracket system; among them elastomeric modules and stainless steel ligatures are commonly used.[1]
During the initial levelling and aligning phase of orthodontic treatment, elastomeric modules are preferred over stainless steel ligature as they are more convenient and less time-consuming, despite having more friction with elastomeric modules than stainless steel ligature.[2]
Over time, elastomeric elastics display permanent deformation and subsequent force decay.[3],[4],[5] Force degradation depends upon several factors like the manufacture of elastomeric modules,[6] transition temperature,[7] refreshments,[8] pH,[9] patient diet,[10] salivary enzymes,[11] drinks,[12] fluoride flushes[13] and tooth brushing.[14]
In routine orthodontic practice, practitioners usually purchase modules in bulk quantity. The storage temperature and duration of storage may influence the properties of elastomeric modules, especially in a country like India, which is predominantly tropical and accounts for a wide array of temperature changes because of polarizing weather conditions in various parts of the country and during the cyclical seasons wherein the temperature falls from a high of 49–50°C to as low as 1–2°C. The temperature differences between these storage durations can also affect the mechanical properties of elastomeric modules. When the intraoral environment was simulated of having hot beverages by immersing elastics in a hot water bath, it was concluded that high-temperature liquids can cause an increase in force decay of elastics over time.[7] There are few studies on the effects of temperature and storage duration on elastics.[7],[15],[16],[17] However, no concrete information on the effect of temperature and duration of storage on orthodontic modules is available; therefore, this study was designed to investigate the effects of different temperature variations on nonlatex orthodontic modules over a variable period of time.
| Materials and Method | | |
Institutional Ethical Board clearance was taken before commencing the study (MRDC/IEC/2019/02). Sample size calculation was done by using G*Power software (version 3.1). The sample size was determined keeping the effect size as 1.15 (based upon the mean and standard deviation of the pilot study (Control group (CG) – 21.60 N ± 0.60 N, Experimental group 24.62 N ± 3.64 N)), power of the study at 90% and the significance level of 5% (alpha = 0.05); the required sample size was calculated having 20 modules in each group.
The investigation was carried out on 140 nonlatex orthodontic modules made by 3M Unitek with a thickness of 0.125 inches and a diameter of 3.2 mm that are used to MBT 0.22 brackets in accordance with the manufacturer's recommendations. Modules were divided into 7 groups with 20 modules in each group [Figure 1]. | Figure 1: Nonlatex elastomeric module (3M Unitek) and sample size distribution
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A custom-made jig was fabricated by modifying a number 23 explorer (Shepherd hook), which was placed in an acrylic block to test the tensile load at failure. The samples were subjected to undergo testing by a universal testing machine. A 50-N load cell was used to measure the test's needed force, and the machine's operating speed was set at 100 mm/min. Twenty unexposed orthodontic modules as provided by manufacturer were tested at the commencement of the study, and initial force values were obtained. Elastic modules were purchased from the manufacturer within 1 month of the manufacturing date to avoid any unfavourable effects on the module. This group served as the CG.
The remaining 120 modules were divided into 6 groups having 20 modules in each group. Group I and Group IV modules were stored at T1 (1–5°C) temperature in the refrigerator for 6 and 12 months, respectively, and transported in an icebox at the time of testing. Group II and Group V modules were stored at T2 (20–25°C) temperature in a dark room with no access to sunlight for 6 and 12 months, respectively.
Group III and Group VI modules were stored at T3 (35–40°C) temperature in an incubator for 6 and 12 months, respectively, and transported using a hot water bag to maintain the temperature at the time of testing. Group I, II and III modules were tested for tensile load at failure after storing them for 6 months at the respective temperature, and Group IV, V and VI modules were tested for tensile load at failure after 1 year of the duration of storage. The results were obtained and compared for the tensile load at failure. Values for tensile load at failure for all orthodontic modules were tabulated and subjected to statistical analysis.
Statistical analysis
The Excel 2016 (Microsoft, Redmond, Washington, USA) and SPSS (SPSS Inc, Chicago, Version 21.0) software packages were used for data entry and analysis. The descriptive statistics consisted of the average and standard deviation for the forces required to access the tensile load a failure of modules in each group. The one-way analysis of variance (ANOVA) was used for multiple comparisons of means for each group. Test of homogeneity was performed to analyse any possible deviations within the group. Post hoc pairwise intragroup comparison was done using the Bonferroni test. Intergroup comparison was done using paired t-test.
| Results | | |
The samples were subjected to tensile load at failure done on a universal testing machine. The tensile load at failure for CG was measured initially at day zero (in as is received state from manufacture), and the following exposure to different storage temperatures for 6 months and 1 year are tabulated [Table 1]. Intergroup comparison of a tensile load at failure of modules kept at different temperatures at 6-month and 1-year intervals was done using repeated measures of ANOVA, which showed that there was an overall statistically significant difference between them. Modules in the CG underwent tensile load at failure at 21.588 N ± 1.082 N force. Modules which were stored for 6 months at T1, T2 and T3 temperatures underwent tensile load at failure at 18.818 N ± 1.121 N, 17.841 N ± 1.334 N and 17.149 N ± 1.074 N, respectively, during testing and when compared with the CG, the difference was statistically significant (p < 0.001). Modules which were stored for 1 year at T1, T2 and T3 temperatures underwent tensile load at failure at 17.205 N ± 1.043 N, 16.836 N ± 0.487 N and 14.788 N ± 0.781 N, respectively, during testing, and when compared with the CG, the difference was statistically significant (p < 0.001). | Table 1: Average force exerted by the nonlatex orthodontic modules during the tensile load at failure test among all four groups at 6-month and 1-year intervals
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Test of homogeneity was applied to the samples of each group using Levene statistics to access and analyse any possible deviations within the group. Statistically, nonsignificant difference was obtained for the samples in both 6-month and 1-year interval groups (p > 0.05) [Table 2].
When intragroup comparison was done at 6 months, the result after 6 months shows that CG presented with significantly high tensile load at failure compared to the modules kept at T1 temperature, T2 temperature and T3 temperature (p < 0.005) [Table 3]. When the T1 temperature group was compared with CG, T2 temperature and T3 temperature group, statistically significant difference was found between the control and T3 group (p < 0.005), but the same was not found to hold true with the T2 group (p > 0.05). When the T2 temperature group was compared with the CG, T1 temperature and T3 temperature group, statistically significant difference was found only with CG (p < 0.005). When the T3 temperature group was compared with the CG, T1 temperature and T2 temperature group, a statistically significant difference was found only with the control and T1 group (p < 0.005). | Table 3: Intragroup comparison of tensile load at the failure of modules kept at different temperatures at 6-month and 1-year intervals
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After a period of 1 year, results showed that the CG had significantly high tensile load at failure compared to the modules kept at T1 temperature, T2 temperature and T3 temperature (p < 0.005) [Table 3]. When the T1 temperature group was compared with the CG, T2 temperature and T3 temperature group, a statistically significant difference was found between the control and T3 temperature group (p < 0.005), but the same was not found with the T2 temperature group (p > 0.05). When the T2 temperature group was compared with the CG, T1 temperature and T3 temperature group, a statistically significant difference was found only with the CG and T3 (p < 0.005). When the T3 temperature group was compared with the CG, T1 temperature and T2 temperature group, a statistically significant difference was found with all three groups (p < 0.005).
Intergroup comparison of tensile load at failure of modules after 6 months and 1 year kept at different temperatures was done using paired t-test. It was found that the tensile load at failure decreased significantly from 6 months to 1 year among each temperature group (p < 0.05) [Table 4]. When tensile load at failure was assessed at 6-month to 1-year interval at T1 temperature, T2 temperature and T3 temperature, the difference were 1.613, 1.005 and 2.361 N, respectively. | Table 4: Intergroup comparison of tensile load at failure after 6-month and 1-year intervals kept at different temperatures
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| Discussion | | |
Elastomeric modules commonly used in contemporary orthodontics are composed of polyurethane and consist of blocks of copolymers that have sequences of soft and hard segments. These materials act like cross-linked elastomers at room temperature and at high temperature get softened and show thermoplastic properties. Orthodontic modules may undergo changes in their mechanical properties depending on the environment in which they are stored and can be influenced by temperature, heat, humidity, exposure to light and shelf life.[5],[15],[18] In a country like India, which is predominantly tropical, it is stored in extreme temperature variations in different parts of the country ranging from a high of 50°C to as low as up to − 1°C. The recommended storage temperature by some manufacturers is 16–25°C. This temperature, however, is not mentioned on the product itself and sometimes clinicians utilizing the product buy it in bulk, unaware of the ideal storage temperature. Our research aims to verify the manufacturer's claim about the storage temperature of elastomeric modules.
In the present study, a direct relationship was found between the mechanical properties of orthodontic modules, storage temperature and duration of storage. Any variation in the storage temperature (16°C to 25°C) and storage duration led to a change in the mechanical properties of modules. Billmeyer[19] stated that the mechanical properties of elastomers can be modified by a change in temperature as they are viscoelastic in nature. This change was seen as a decrease in the tensile load at failure of modules. Clinically, this reduction in the tensile load of failure will cause breakage of the elastomeric module, leading to a decrease in the rotational control of the archwire during the initial levelling and alignment phase.
The effect of storage temperature and storage duration on elastics has previously been studied by Gonzaga et al.,[15] and Piradhiba et al.,[17] However, there has been no available literature that determines the effect of storage temperature and storage duration upon the physical properties of elastomeric modules. In one study, Jamilian A et al.,[20] investigated the impact of mouthwashes on the tensile strength of elastomeric modules and came to the conclusion that elastomeric ligatures' tensile strength was reduced when exposed to disinfection solution.
The results of the present study are not in accordance with the study done by Gonzaga et al.,[15] who observed the characteristics of the force degradation in different temperature conditions for 1 year and found that different storage conditions of temperature and duration did not interfere with the mechanical properties. The reason for not being in accordance may be due to differences and variations in the temperature range (refrigerated and room temperature) in their study.
The results of the present study are also not in accordance with the study of Piradhiba et al.,[17] in which they assessed the influence of different storage temperatures on latex orthodontic elastics over a period of 1 month. They had considered storage temperatures groups as 4–8, 26–28 and 37°C, the difference between their result and the result of the present study maybe due to different storage durations, and in their study, samples only consisted of latex orthodontic elastics in comparison to the present study in which only nonlatex orthodontic modules were used.
Limitations
In the present study, clinically, the effects of absorption of various liquids by modules, diet, pH, temperature change and salivary enzymes in the oral cavity were not assessed, which may also have an effect on tensile at the failure of modules. Furthermore, how the absorption affects the chemical/biomechanical nature of elastomeric modules and its effect on the tensile load at failure needs to be studied.
| Conclusion | | |
The following conclusions were drawn after this study:
- The duration and temperature at which the modules are stored have a significant effect on the force degradation of modules.
- Orthodontic modules should be stored at no more than 25°C and used within 1 year after manufacturing to maintain optimal ligation to the archwire.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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Correspondence Address:
Dr. Ashish K Singh
Department of Orthodontics and Dentofacial Orthopedics, Manav Rachna Dental College, Faridabad, Haryana
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/ijdr.ijdr_453_22
[Figure 1]
[Table 1], [Table 2], [Table 3], [Table 4] |
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