Orthodontic Waves ISSN: 1344-0241 (Print) 1878-1837 (Online) Journal homepage: https://www.tandfonline.com/loi/todw20 The effect of static and dynamic testing on orthodontic latex and non-latex elastics Ali S. Aljhani & Abdullah M. Aldrees To cite this article: Ali S. Aljhani & Abdullah M. Aldrees (2010) The effect of static and dynamic testing on orthodontic latex and non-latex elastics, Orthodontic Waves, 69:3, 117-122, DOI: 10.1016/j.odw.2010.04.003 To link to this article: https://doi.org/10.1016/j.odw.2010.04.003 Published online: 28 Nov 2019. Submit your article to this journal View related articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=todw20 orthodontic waves 69 (2010) 117–122 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/odw Research paper The effect of static and dynamic testing on orthodontic latex and non-latex elastics Ali S. Aljhani a, Abdullah M. Aldrees b,* a b King Abdullah International Medical Research Centre, King Saud University for Health Sciences, Riyadh, Saudi Arabia Department of Pediatric Dentistry and Orthodontics, College of Dentistry, King Saud University, P.O. Box 60169, Riyadh 11545, Saudi Arabia article info abstract Article history: The purpose of this study was to test the force decay properties of different kinds of Received 1 September 2009 orthodontic elastics after subjecting them to static and cyclic testing. Latex and non-latex Received in revised form elastics obtained from GAC, American Orthodontics and Ortho-Organizers were used in a 12 April 2010 sample size of 10 elastics per group. Static testing involved stretching the elastics three Accepted 24 April 2010 times the internal diameter, while in cyclic testing, the elastics were stretched up to 50 mm Published on line 26 May 2010 to simulate maximum mouth opening. Elastic forces generated were measured using the Instron testing machine and recorded in grams. Elastics on average lose 10% and 12% as a Keywords: result of static test and 30% and 35% as result of cyclic test for latex and non-latex brands Elastics respectively, and most of the force loss occurs during the first half hour and after the first 10 Latex cycles. This difference in force loss between latex and non-latex elastics could be due to the Non-Latex different structure and composition of the polymer involved. There are no significant differences between different groups of latex elastics in terms of force loss or even between the different groups of the non-latex elastics under static testing, however, under cycling testing differences between the groups were detected. Forces generated by the elastics are different from the manufacturers’ labeled forces. # 2010 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved. 1. Introduction Elastics have been used in orthodontics to move teeth for more than a century [1,2]. Orthodontic elastic are inexpensive, relatively hygienic and are easily applied. Elastics in the oral cavity absorb water and saliva, permanently stain and undergo both fatigue and creep . They lose forces rapidly due to stress relaxation which leads to gradual loss of their effectiveness. The loss of force delivery and degradation of orthodontic elastics are major defects that affect clinical choice. Andreason and Bishara found that in a period of 24 h, latex elastics lost 42% of initial force, and the greatest percent of force decay occurred during the first hour [4,5]. Kovatch and Keller found that rapid stretching produced greater initial forces compared to slow stretching , while Ash and Nikolai concluded that more force loss may occur due to the effect of mastication, oral hygiene, salivary enzymes and temperature variation within the mouth (in vivo) . A similar pattern of force degradation in the wet environment was observed by Wang et al. in vivo . Bertl et al. found a significant force loss generated by elastics within the first half an hour, which continued to decrease up to 8 h reading . To achieve the * Corresponding author. Tel.: +966 1 4676057; fax: +966 1 4679017. E-mail address: [email protected] (A.M. Aldrees). 1344-0241/$ – see front matter # 2010 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved. doi:10.1016/j.odw.2010.04.003 118 orthodontic waves 69 (2010) 117–122 reported force of the latex elastics, an extension of 2.7 and five times the original length was found to be required by Gioka et al. . Orthodontic elastics are not subjected to static stresses only when they are in the patient’s mouth. They also undergo repeated stretching as the patient talks, eats, and yawns. Effects from these movements had not been investigated until 1993 when Liu et al. studied this elastic property. The authors found that cyclic stress will significantly lead to force loss. However, most of the effect occurs in the first 200 cycles . Due to the recent increase in awareness of the health risks of latex products , several companies have started marketing synthetic non-latex elastics and are offered as an alternative to latex elastics. Russell et al. compared the mechanical properties of latex and non-latex orthodontic elastics . They reported that after 24 h, the relationship between the different groups was significantly different . In their study, Kersey et al. reported that the latex elastics lost 25% of their force after 24 h while the non-latex elastics lost nearly 50% of their force over 24 h, and they concluded that latex elastics are superior to non-latex elastics . Kersey et al. also compared the effect of cyclic fatigue on force decay properties of four different brands of non-latex elastics . The authors concluded that all elastics in the study are comparable in terms of their mechanical properties. The rapid loss of force of the orthodontic elastics due to static and cyclic stress relaxation, resulting in a gradual loss of effectiveness was a major drawback. Bertoncini et al. compared latex to non-latex elastics produced by a single manufacturer and they confirmed previous studies that reported that latex elastics undergo less loss of force than the non-latex elastics . The same researchers has also investigated these two groups under cyclic testing, and concluded that the latex-free elastics must be replaced more frequently than conventional latex elastics . The extensive body of literature regarding this property has been difficult to evaluate because of the different investigation methods and the different types of elastics available. The mechanical properties of the elastics varied considerably with the type of material and the manufacturer. Clinicians using orthodontic elastics need to know the forces applied to teeth at certain extensions and how these forces decline over time. The literature lacks a comparison between different types of latex and non-latex elastics supplied from different manufacturers with respect to static and cyclic stress. This study aimed to compare the force decay pattern of different latex and non-latex elastics from different manufacturers subjected to static and cyclic stresses. Also, another objective was to determine the differences from a single supplier and between different suppliers. Furthermore, to determine the accuracy of initial forces generated by different latex and non-latex elastics as stated on by the suppliers and determine the variation in force produced in each group (package). 2. Materials and methods Orthodontic latex and non-latex elastics from three manufacturers were tested: GAC International (Islanda, NY) 6 mm (1/4 in.) 4 oz (113 g), American Orthodontics (Sheboygan, Wis.) 6 mm (1/4 in.) 4 1/2 oz (127 g), and Ortho-Organizers (San Marcos, Calif.) 6.4 mm (1/4 in.) 4 1/2 oz (127 g). All elastics were similar in terms of structure. Samples obtained were within their expiration dates and stored as recommended in sealed bags in a dark environment at room temperature. 2.1. Testing apparatus An Instron testing machine (Model 4202, Instron Corporation, Canton, Mass.) with load cell capacity of 100 Newton was used. Elastics were stretched on the testing machine using two hooks made of 1.3 mm diameter stainless steel (Fig. 1a). The loads were recorded in Newton and then converted to grams. The load cell was calibrated before each data collection to confirm the validity of reading. Fig. 1 – (a) Elastic stretched three times the internal diameter with the hooks attached to the Instron testing machine. (b) Elastic stretched in an environmental chamber. 119 orthodontic waves 69 (2010) 117–122 Table 1 – Comparison of initial forces and force loss over time for latex and non-latex elastics between manufacturers (static test). Data are presented as means W standard deviation (range) in grams. Time (h) GAC International American Orthodontics Ortho-Organizers Initial Latex Non-latex 104.2* 3.6 (100–110) 139** 6.9 (112–129) 117.5* 5.1 (110–126) 120.5 5.6 (124–148) 109.4 8.5 (101–126) 137.6*** 8.9 (100–149) 0.5 Latex Non-latex 95.9 3.3 (90–101) 124.9 7.3 (115–135) 109.6 5.2 (103–120) 110.53 5.9 (104–120) 102.6 7.4 (95–115) 125.6 9.7 (112–137) 1.0 Latex Non-latex 94.8 3.0 (90–99) 122.8 7.0 (113–132) 97.9 5.0 (110–117) 107.2 5.8 (101–116) 100.5 7.6 (93–113) 123.2 9.2 (110–134) 1.5 Latex Non-latex 93.9 2.9 (88–97) 121.7 7.1 (112–131) 106.6 5.0 (101–115) 104.9 5.6 (101–11) 99.15 7.7 (91–111) 120.6 9.0 (110–134) 2.0 Latex Non-latex 93.4 2.9 (87–97) 121.1 6.7 (112–131) 107.0 5.0 (101–116) 103.6 5.3 (96–112) 98.14 7.6 (90–110) 119.5 7.7 (107–130) * Significantly different from manufacturer’s published value at p < 0.05. GAC non-latex elastics are significantly different from GAC latex elastics at p < 0.05. *** Ortho Organizer non-latex elastics is significantly different from Ortho Organizer latex elastics at p < 0.05. ** 2.2. Study design A sample size of 10 elastics per group was used. The static test contained six groups from three different manufacturers (3 latex and 3 non-latex groups). Elastics were stretched by the use of two hooks from a resting position to three times the internal diameter. The lower hook was attached to a fixture, which was secured to the base of the Instron machine. The upper hook is the movable part and it was attached to the load cell which moved at crosshead speed of one cycle per minute. The cross head speed was 36 mm per minute (1 cycle/min). Forces generated were recorded immediately at the end of the following hold time: 0.5, 1, 1.5, and 2 h. Another six groups were used for the cyclic tests. In the cyclic tests the elastics were stretched from three times the internal diameter to 50 mm and returned back to the previous length which is considered as one cycle. The speed was 2 cycles per minute, a good representation of the average cycle speed in the oral cavity. Forces generated were recorded at zero cycles and after 10, 25, 50, 75, and 100 cycles. At the end of each experiment, elastics were stretched until they broke and the breaking force was recorded. Elastics were also weighed before the beginning of each experiment using an electronic scale (Mettler Toledo, Switzerland). All the above tests were made in a dry environment at room temperature. These tests have been repeated at 37 8C in dry condition in an environmental chamber (incubator) (Fig. 1b). The same tests have been performed after the elastics were soaked in water for 24 h to test the effect of water sorption. No differences have been noticed between the different environmental conditions on either absolute force values or the force decay pattern. 2.3. for type-I error, the Scheffe method was used. Calculations were performed using the computer program Statistical Package for the Social Sciences (SPSS Inc., Chicago, IL). 3. Results The initial force levels for the different types of elastics are mentioned in Table 1. GAC and American Orthodontics latex elastics showed significantly less force compared to the manufacturer’s value ( p < 0.05). GAC and Ortho-Organizers latex and non-latex elastics were also significantly different. Furthermore, the range of forces produced by these elastics was large (Table 1). The weight of these elastics also varied, however, in smaller range than the force produces. There was a significant difference in the weight between GAC latex (21.3 1.7 g) and non-latex elastics (42.5 3.8 g). Latex and non-latex elastics lose force over time (Table 1). No statistical differences were noticed within the groups from the same materials ( p > 0.05) (intra group; latex brands or non- Statistical analysis The difference between groups was first analyzed by ANOVA. If a statistically significant difference was observed, the difference between the two groups was analyzed by post hoc multiple comparisons to determine significant differences between the elastics and different testing methods. To control Fig. 2 – Force decay pattern of static test: mean percent remaining of initial force loss over time for the latex elastics. 120 orthodontic waves 69 (2010) 117–122 Fig. 3 – Force decay pattern of static test: mean percent remaining of initial force loss over time for the non-latex elastics. latex brands). However, the non-latex groups lose force significantly higher than the latex groups. The percentage of force loss over time is almost the same for the different latex elastics. The decay pattern starts by losing the big amount of force at the first half hour. The elastics continue to lose forces until 2 h and then a stable curve is created (Fig. 2). The nonlatex elastics mimic the same behavior, however, the amount of force loss during the first half hour is significantly more (Fig. 3). The loss of force over number of cycles for both latex elastics and non-latex elastics is displayed in Table 2. Elastics lose more force under the cyclic test. Most of this force loss occurs in the first 10 cycles (Fig. 4). The different brands of the latex elastics act the same. The non-latex elastics have the same pattern with more force loss occurring in the first 10 cycles (Fig. 5). The latex elastics are significantly superior in retaining forces than the non-latex ones. In the latex elastics groups, Ortho-Organizers is significantly different than the other latex groups ( p < 0.05). In the non-latex groups, GAC elastics are statistically different from the others ( p < 0.05). Similar to the results of the static part of the study, statistical analysis showed that there were significant differences Fig. 4 – Force decay pattern of cyclic test: mean percent remaining of initial force loss over number of cycles for the latex elastics. between any latex elastic group and non-latex elastic group regardless of the manufacturer at p < 0.05. Fig. 6 shows the breaking forces of the different types of orthodontic elastics. GAC latex elastics’ breaking forces are considered statistically higher than the other groups. 4. Discussion The environments in which the elastics have been tested in the literature vary considerably. Latex and non-latex orthodontic elastics have been tested in a dry environment [4,5,17], wet environment at 37 8C [18,19], in artificial saliva [16,19,20], in saline [9,17], and in vivo [7,8]. Most authors reported no difference in the behavior of elastics in different environments. However, few mentioned that greater force relaxation is associated with a wet environment but this is after a minimum of 6 h up to three weeks of testing [7–10,19,21–23]. This study examined the effect of one day of exposure to oral environment. The testing conditions in this study were selected after reviewing the results obtained from three different environments which showed that there was no statistical difference among them. For this reason, the Table 2 – Initial force loss over number of cycles for latex and non-latex elastics (cyclic test). Data are presented as means W standard deviation (range) in grams. Cycles GAC International American Orthodontics Ortho-Organizers 10 Latex Non-latex 86.7 4.6 (81–94) 112.2 3.7 (104–116) 97.3 6.1 (87–105) 96.1 6.8 (85–109) 87.5 7.4 (79–102) 109.8 6.1 (98–117) 25 Latex Non-latex 81.4 2.9 (77–85) 105.0 2.3 (100–107) 91.5 5.9 (83–102) 87.3 6.6 (74–99) 80.9 6.7 (75–94) 102.4 5.1 (98–117) 50 Latex Non-latex 78.5 3.2 (73–82) 102.5 2.5 (97–106) 88.3 5.5 (80–79) 81.3 5.8 (69–91) 76.3 5.9 (70–87) 93.8 5.1 (86–104) 75 Latex Non-latex 77.1 2.9 (73–82) 101.2 3.4 (93–105) 86.7 5.6 (79–96) 77.1 4.8 (67–85) 75.7 6.0 (70–87) 91.1 3.9 (84–97) 100 Latex Non-latex 76.0 2.7 (72–81) 100.3 3.1 (93–104) 85.1 5.6 (78–94) 75.0 4.3 (67–82) 75.4 6.0 (70–86) 90.8 3.9 (84–96) orthodontic waves 69 (2010) 117–122 Fig. 5 – Force decay pattern of cyclic test: mean percent remaining of initial force loss over number of cycles for the non-latex elastics. Fig. 6 – The mean breaking force of the orthodontic elastics tested. selected testing condition is considered representative of the clinical use of the orthodontic elastics and the test results of this study are expected to provide guidelines for choosing orthodontic elastics for clinical use. In the literature, there is a wide range of extensions ranging from 20 to 40 mm [4– 6,18,21,24–26]. In this study, the extension of the elastics in the static experiment was three times the internal diameter in order to simulate the clinical use of elastics. This also corresponds well to Gioka et al. study which found that in 6 out of 7 types of elastics tested, an extension of 2.6–3 times the original diameter is enough to achieve the reported force . In the cyclic experiment, the extension of the elastics from three times the internal diameter to 50 mm was chosen to mimic normal maximum mouth opening . Although no statistical differences were noticed, the decision was made to select a speed of 2 cycles/minute to reflect a balance between chewing (higher frequency) and other times such as sleeping (lower frequency). One of the advantages of this testing protocol is that the elastics are tested and the results are recorded immediately without the need of transferring the elastics to another machine for reading which will affect the actual result [7,9]. The elastics tested produced a wide range of forces. The trend observed in this study was that GAC and OrthoOrganizers latex elastics initial forces were lower and the non-latex ones were higher than the manufacturer marketed 121 values. This result was not reported by Kersey et al., however, American Orthodontics non-latex elastics produced initial forces that were close to those reported by Kersey et al. [14,15]. One explanation for that is the relationship with the weight of the elastics, i.e., the heavier the elastics the higher the force. This was true for all non-latex elastics. They are heavier and stiffer compared with the latex elastics, and they produce higher forces than their latex counterpart. The arguments about how the forces produced in this study differ from those labeled by the manufacturers are not similar until the testing protocol used by those companies is known. One interesting observation is the wide range of forces produced by different elastics from the same bag. This study is in general agreement with other studies that reported variability between samples in the same batch [6,19,21,24]. However, the variation did not coincide with the type but rather with the manufacturer. GAC were found to be more consistent with respect to labeled force whether it is latex or non-latex followed by American Orthodontic elastics and then Ortho Organizer elastics. Clinically, there is no important significance to this observation since the variation is still within acceptable limits and force production is clinically acceptable for the desired tooth movement because it falls within the reported range of optimal force for retraction (100– 250 g) suggested by Storey and Smith  and by Reitan . The percentage of the initial force loss of elasticity was compared rather than the actual values due to the wide variability of force production by the elastics. Force degradation for the different brands of elastics in this study exhibits an almost identical pattern. In the static part, the three latex groups lost most of their force in the first half hour and maintained an almost steady curve afterwards. This steady curve will continue for up to 12 h. The main difference between the latex and non-latex elastics at this point is that the non-latex material continues to lose strength slowly after the first half hour while the force from the latex material remains steady after the initial drop. The pattern of force decay observed is very much in agreement with the pattern observed in previous studies [6,18,24]. Even as a percent of force loss it is similar to Russell et al., Kersey et al., Gioka et al., and Wang et al. [8,10,13–15]. Bertoncini et al. were able to detect significant difference between latex and non-latex elastics only after 24 h of stretching, and this may be due to the interruptions in their force measurement protocol . The force decay pattern observed in the cyclic test is the same as that in the static part but with respect to number of cycles instead of elapsed time. The first 50 cycles are the most significant ones, with the largest amount of force loss. After that, the curve starts flattening indicating little force loss. The difference between the elastics was in the first 50 cycles where the non-latex elastics lost more force than the latex ones ending their hundred cycles with lower remaining force. This was in contrast to the findings of Kersey et al. and Gandini et al. and who reported that the loss of force noted for the nonlatex elastics was significant only after a high number of opening/closing cycles [14,17]. The current study reported significant differences between the tested brands in the cyclic test and this was not indicated by Kersey et al. who reported that GAC, American Orthodontics and Ortho-Organizers nonlatex elastics behaved similarly under cyclic testing . 122 orthodontic waves 69 (2010) 117–122 Differences in testing conditions may explain the discrepancy in the behavior of non-latex elastics in these studies. Bertran reported that intermaxillary elastics are used mainly over a distance of 20–40 mm, producing forces of 60– 300 g . In their study, Bales et al. stretched 3/16 in. heavy elastics a distance of 30–40 mm and the forces produced did not exceed 318 g . The lowest breaking force recorded in this study was above 2700 g, and this indicates that the tested elastics’ breaking forces exceed in magnitude any force expected from mouth activity Between all the six groups, the three latex groups are statistically superior to the non-latex ones which means they retain more forces. There was also some recovery of forces generated by the elastics after the cycling testing. This recovery ranges from 4% to 6% in ten minutes period after stopping the cyclic stress. Kersey et al. was not able to observe this phenomenon [14,15]. The difference in force loss between latex and non-latex elastics could be due to the different structure and composition of the polymer involved. The nonlatex elastics, synthetic polymer, may rely more on molecular entanglement for structural integrity rather than the covalent cross-linking that is present in the natural rubber used in the latex elastics. These structural differences may lead to the long term poorer behavior of the non-latex elastics . 5. Conclusions 1. Elastics’ decay pattern starts by losing a big amount of force at the first half hour, and more force is lost in the first 10 cycles in the cyclic test. 2. Latex elastics are significantly superior in retaining forces than the non-latex ones, and this may indicate that nonlatex elastics need to be changed more frequently. 3. In the static test, there are no significant differences between the tested different groups of latex elastics or even between the different groups of the non-latex elastics, however, under cycling testing, significant difference were detected. 4. 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