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Table of Contents   
ORIGINAL RESEARCH  
Year : 2014  |  Volume : 25  |  Issue : 2  |  Page : 208-213
An in-vitro study to compare the force degradation of pigmented and non-pigmented elastomeric chains


Department of Orthodontics, Mar Baselios Dental College, Ernakulam, Kerala, India

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Date of Submission02-Dec-2013
Date of Decision25-Dec-2013
Date of Acceptance19-Feb-2014
Date of Web Publication4-Jul-2014
 

   Abstract 

Aim: The purpose of the study was to compare the force delivery and force decay property of pigmented and non-pigmented elastomeric chains, widely used in orthodontic practice.
Materials and Methods: Force delivered by the samples consisting of pigmented and non-pigmented elastomeric chains obtained from 3 manufacturers were tested at 3 time intervals (as received, after 24 hours and 21 days of stretching) to measure the force delivered by the test samples, as well as the force decay over time.
Results: The force delivered by the non-pigmented samples was significantly greater than the pigmented ones at all 3 time intervals irrespective of the brand. Force decay was more significant in case of pigmented samples. Force decay was greater noticed in first 24 hours of testing and a gradual decrease in force was observed from 24 hours to 21 days in all test samples irrespective of the brand or color.
Conclusion: Non-pigmented elastomeric chains exhibited better force delivery and less force decay percentage when compared to pigmented chains. Though colored elastomeric chains are widely used in present day orthodontic practice to satisfy the younger age group patients, the study ascertains the prudential use of pigmented and non-pigmented chains for efficient and faster orthodontic treatment.

Keywords: Elastomeric chains, force decay, force degradation, polyurethanes

How to cite this article:
Antony PJ, Paulose J. An in-vitro study to compare the force degradation of pigmented and non-pigmented elastomeric chains. Indian J Dent Res 2014;25:208-13

How to cite this URL:
Antony PJ, Paulose J. An in-vitro study to compare the force degradation of pigmented and non-pigmented elastomeric chains. Indian J Dent Res [serial online] 2014 [cited 2020 Jan 19];25:208-13. Available from: http://www.ijdr.in/text.asp?2014/25/2/208/135924
Elastomeric chains (e-chains) are force generating units used to deliver force to move the teeth in a predetermined manner. They were widely used in orthodontic practice since 1960s for effective tooth movement with minimal adverse effects. [1],[2],[3] Elastomeric chains are polyurethanes, possessing low molecular weight polymer (usually polyester or polyether) to produce a complex structure of urethane linkage. [2],[4] Polyurethane polymers possess rubber like elasticity and have long- chain, lightly cross-linked structures with a weak molecular attraction consisting of primary and secondary bonds. [5] Prior to stretching, elastomeric chain consists of folded linear molecular chains. On extension, these molecular chains unfold in an ordered linear fashion at the expense of the secondary bonds. [6],[7],[8] Cross links of primary bonds are maintained at a few locations along the molecular chains. The release of the extension will allow return to a passive configuration unless the distraction of the chains does not cause rupture of the primary bonds. If the force applied exceeds the elastic limit of the chains, permanent deformation occurs due to the breakage of primary bonds.

Elastomers are relatively easy to use, inexpensive, easily applied, require little or no patient cooperation and are relatively hygienic but they are not without any disadvantages. In the oral environment they absorb water and saliva, permanently stain and undergo permanent deformation. [7] They also experience a rapid loss of force due to stress relaxation resulting in gradual loss of effectiveness. The force decay makes it difficult for orthodontists to determine the actual force transmitted by elastomeric chains to the dentition from time to time. A force decay of 50 to 75 percentage was noticed after 24 hours of stretching. The force reduced by 10 percentage more by 3 weeks and retained only 30 to 40 percentage of the original force after 4 weeks. [1],[4],[6],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20]

Initially clear elastomeric chains were manufactured. The increasing demand for esthetics led to the production of colored chains. Recently, a number of manufacturers have added colored elastomeric chains to their inventories. Filler particles were incorporated to provide color to e-chains. The information regarding the pigmentation process is not available since the composition of the orthodontic chains is proprietary information. Various in vitro and in vivo studies have been conducted to assess the force delivery and force degradation of elastomeric chains. Williams and von Fraunhofer [21] observed that the force delivery properties of tooth-colored elastomeric chains were significantly affected by the filler material used in tinting the chains. David L. Baty [5] also demonstrated that the force delivery behavior of elastomeric chains is color specific but varies with the manufacturer of the chain. Kochenborger et al. [22] evaluated the force delivered by commercially available orthodontic elastomeric chains that were immersed in artificial saliva at 37 0 C based on stretching time. Dittmer et al. [23] has evaluated the influence aging on the mechanical properties of orthodontic elastomeric chains. A perusal of literature reveals that no study has been undertaken so far to compare the force delivery and force decay property of pigmented and non-pigmented elastomeric chains. Hence an in vitro study was done to understand the effect of addition of pigments on the mechanical property of elastomeric chains.


   Materials and Methods Top


The sample consisting of 8 groups included both pigmented and non-pigmented elastomeric chains obtained from 3 manufacturers [Table 1]. Thirty test specimens from each group consisting of 4 links with connector were used for the study (30 × 8 = 240 specimens). Two hundred and forty such specimens were tested to evaluate the force delivery in the as received condition, 24 hours and 21 days' time interval, thus making a sum total of 720 samples. Samples were cut from the same spool to eliminate all possible errors that may occur due to batch influence.
Table 1: Samples used for the study


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A specially designed apparatus with jig was fabricated [Figure 1]: The apparatus consisted of stainless steel screws with jig fixed on an acrylic sheet at a predetermined distance. The distance between the jig varied since the length of four links of each brand of elastomeric chain ranged between 11.15 and 12.16 mm, when measured with a vernier caliper. The distance between the jigs was customized such that, the test samples were stretched uniformly by 10 millimeters more than their initial length.
Figure 1: Specially designed apparatus with jigs

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Artificial saliva was prepared using 20 mmol/L or 1.68 gm/L of NaHCO3, 3 mmol/L or 0.47 gm/L of NaH2PO4 and 1 mmol/L or 0.11099 gm/L of CaCl2. [24] The ingredients were measured using a weighing balance and was dissolved completely in 1 litre of distilled water. The apparatus with stretched elastomeric chains were kept immersed in artificial saliva [Figure 2] for a period of 24 hours and 21 days prior to testing.
Figure 2: Glass tank to keep the apparatus immersed in artificial saliva

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The elastomeric chains were tested in Instron machine (Instron India Private Limited, Model 1321). Custom made jig was used to hold the elastomeric chains between the load cell and crosshead of the testing machine [Figure 3]. The samples were stretched by 10 mm at the rate of 1mm per minute and were left undisturbed for a minute to record the force delivered by the sample. Force delivered by the samples in the as received condition, after 24 hours and 21 days of stretching time were recorded. The force values obtained in this study were tabulated and force degradation of pigmented and non-pigmented samples was ascertained.
Figure 3: Universal instron testing machine

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   Statistical Evaluation Top


The statistical analysis was done using SPSS software (version 16). The mean and standard deviation (SD) of force delivered by the pigmented and non-pigmented elastomeric chains of each brand were calculated. The independent sample test and ANOVA was done to compare the pigmented and non-pigmented elastomeric chains with respect to brand, color and time intervals. Post Hoc test of Scheffe was performed to compare the force values of as received samples to 24 hours and 21 days respectively.


   Results Top


As-received sample: The force delivered by each pigmented and non-pigmented elastomeric chains of each brand in the as-received condition is summarized in [Table 2]. It was observed that the force delivery was lower for pigmented chains, but their statistical significance varied with brand. The force delivered by 3M Unitek clear chain had higher force value than Glenroe and Forestadent [Graph 1]. A statistically significant difference was observed in force delivered by 3M Unitekand Forestadent clear chains [Table 3]. The statistical significance on comparing the force delivery between pigmented and non-pigmented products within the same brand is explained in [Table 4]. Red and clear chains of glenroe and forestadent brands showed significant difference in initial force.



Test Results after 24 Hours: A decrease in force delivery was observed on testing the specimens after 24 hours of stretching compared to the as received condition [Table 2]. A statistically significant difference in force value was observed on comparing the clear chains of 3M Unitek, Glenroe and Forestadent [Table 3] and Graph 1].The P values on comparing the force delivered by pigmented and non-pigmented products within each brand are given in [Table 4]. Forestadent Green chains showed a maximum decrease in force among all the 8 specimens used in the study after 24 hour testing.
Table 2: Mean and standard deviations of force value of pigmented and non- pigmented chains


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Table 3: P values for in vitro comparisons of non-pigmented products which reveals the statistical significance P<0.05


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Table 4: P values for comparisons of pigmented and non-pigmented products within the same brands P<0.05


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Test Results after 21 Days: The force delivered by each pigmented and non-pigmented elastomeric chains of each brand in the 21 day is summarized in [Table 2]. Force delivered by3M Unitek clear chains was higher than Glenroe and Forestadent similar to as received and 24 hour results [Table 3] and Graph 1]. A statistically significant variation in force delivered by pigmented and non-pigmented elastomeric chains within same brand was observed after 21 days [Table 4]. A minimal decrease in force delivery was noted in case of 3M Unitek and maximum in Forestadent chains.

The mean force delivered by non-pigmented elastomeric chain samples were always higher compared to the pigmented, irrespective of brand at all intervals of time [Graph 2-4]. Comparing the mean force delivered by both pigmented and non-pigmented chains (pooled sample) at as received and 24 hrs time intervals, a significant decrease in force by 220.3 gms is clearly evident [Table 5].The maximum decrease in force delivery was recorded in the first 24 hours (220.3 gms) in contrast to the minimum change from 24 hours to 21 days (22.23gms). On the 21 st day of testing, elastomeric chains retained only 40% of their initial force. A negative Pearson correlation coefficient indicated a decrease in force delivery over time [Table 6]. This could be better appreciated when force decay percentage was calculated for clear and pigmented chains of each brand separately for as received, 24 hours and 21 days' time interval [Table 7].
Table 5: The comparison of average force value at 2 time intervals using Post Hoc test (Scheffe) P<0.05


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Table 6: Pearson Correlation between the force decay and time interval (0, 1 day and 21 days testing). A negative correlation exists indicating a decrease in force as the testing time increases


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Table 7: The difference in percentage of force decay of elastomeric chains over the 3 time intervals


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   Discussion Top


Elastomeric chains have been used in orthodontic practice to perform various types of tooth movement. [1],[2],[3] Elastomeric chains are manufactured in 2 ways - die-cut stamping and injection molding technique. [9] The method of manufacture may influence the mechanical properties of the material. Hershey and Reynolds found that die-cut stamped elastomeric chains maintained a higher level of remaining force than the injection molded ones. [25] Though elastomeric chains on initial placement deliver sufficient force to move the teeth, they exhibit force decay. Moisture and temperature plays an important role in influencing the rate of force decay. [26] The rate and duration of loading also influences the force decay. Two different mechanisms account for force degradation of the elastomeric chains namely elastic stretch and chain slippage. [5],[10],[27] Elastic stretch is a reversible process that occurs when an applied load causes individual polymer molecules to uncoil, straighten and extend. But when the load is sustained, the polymer molecules slide past one another resulting in chain slippage which irreversibly reduces the force delivered to the teeth resulting in elastic deformation. [5],[10] Rate at which the elastomeric chains are stretched over a distance would alter the force decay percentage of elastomeric chains over time. [5],[10] The addition of pigment alters the molecular configuration resulting in steric interference [28] exhibiting greater force loss.

In the present study 4 links of elastomeric chains was chosen as a representative of what is being normally used during canine retraction. Since the length of 4 links of each brand of elastomeric chain varied with brand, the distance between the jigs was customized such that the test samples were stretched uniformly by 10 millimeters more than their initial length. The length of 4 links of e-chains combined with 10 mm stretch of elastomeric chains approximated the distance from the hook of canine bracket to the buccal tube in pre-adjusted edgewise appliance treatment and simulated canine retraction in to the pre-molar extraction site. Literature reveals that the force delivered by the elastomeric chain is not uniform throughout. Studies on force delivery have been done at 1 hour, 24 hour, 7 days and 21 days of stretching in vitro or in vivo. [5],[21],[22] Hence in the present study force delivery property was evaluated in vitro in the as-received condition, 24 hrs and 21 days time interval.

Methodologically comparative studies of in vitro and in vivo investigations of elastic chains have revealed strong differences between dry and in vivo testing. Though studies were reported using a test setup according to DIN EN ISO 21606:2007, a different testing technique was implemented here. The specially designed apparatus was immersed in artificial saliva in a glass tank to simulate an intra oral environment. Various researchers reported that saliva and moisture contributes to the force decay percentage of the elastomeric chains. [8],[29] Significant effects on force decay behaviour were found with thermal cycling in artificial saliva (De Genova [10] ) when chains were exposed to simulated oral conditions, and also in vivo conditions (Andreasen and Bishara [20] ), as well as different pH media (Ferriter [13] ). Long-term storage of elastomeric chains in water was found to substantially increase the force decay rates. [2] Stuart et al. and many other researchers has reported that elastomeric chains absorb water and saliva when exposed to oral environment and suffer breakdown of internal bonds leading to permanent deformation. [1],[6],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18] In the earlier studies the force delivery of polyurethane products were evaluated using spring gauges, electronic force gauges, dial type dynamo meter, corex gauge and universal instron testing machine. [30],[31] In the present study universal instron testing machine was used as it was more accurate for measuring the force value on stretching elastomeric chains between the load cell and cross head of the instron to a pre-determined distance, thus avoiding the parallax error and inter- polation errors associated with other methods.

A decrease in the force value was observed after 24 hours and 21 days of stretching. Force decay was significantly greater over 24 hours (47.64%) and a minimal change in force delivery was noticed from 24 hours to 21 days (22.43%).The present study goes hand in hand with the observations ofmany researchers on the force degradation of elastomeric chains. [6],[29],[30],[32],[33] A greater variation in force value was noticed for pigmented rather than the non-pigmented elastomeric chains. Though the pigmented e-chains delivered lesser force compare to non-pigmented ones, there was a significant variation in the force delivery property among the pigmented elastomeric chains of each brand depending on the color. This could be attributed to the filler material used in tinting the chains. Williams and von Fraunhofer [21] in their study had also reported that the force delivery properties of tooth-colored elastomeric chains were significantly affected by the filler material used in tinting the chains. The present study is in agreement with the findings of William and Von Fraunhofer. [21] Pigmented elastomeric chains delivered lesser force at all 3 time intervals. Force decay over 21 days was pronounced during the first 24 hours, with a gradual loss of force levels in the remaining time period. Colored elastomeric chains demonstrated greater force decay at 24 hours and 21 days. Pigmented elastomeric chains delivered lesser force at all 3 time intervals. Loss of force over 21 days was pronounced during the first 24 hours, with a gradual loss of force levels in the remaining time period. Coloured elastomeric chains demonstrated greater force degradation at 24 hours and 21 days time interval compared to non-pigmented ones. Since environmental factors (artificial saliva and room temperature) were kept constant, the distinct difference in the force degradation property between pigmented and non-pigmented elastomeric chains over 3 time intervals may be attributed to the addition of pigment and variation in the manufacturing process.

Though an in vivo evaluation would be ideal, in the present study an in vitro test was planned to limit the variables to pigments and brands, with the samples immersed in artificial saliva to simulate intra oral environment at room temperature. Further the color of pigmented chains was not uniform for all three brands due to non-availability.


   Conclusion Top


Clinician should have adequate knowledge on the force decay property of pigmented and non-pigmented elastomeric chains of different brands. Though pigmented chains are used widely in clinical practice to satisfy the patients in the lower age group, they yield less initial force and exhibit greater force decay that varies with color and the manufacturer. Therefore prudential selection of elastomeric chain will result in optimal force application for efficient tooth movement.

 
   References Top

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Correspondence Address:
Joby Paulose
Department of Orthodontics, Mar Baselios Dental College, Ernakulam, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.135924

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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]

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