Camporesi M, Baccetti T, Franchi L Forces released by esthetic preadjusted appliances with low-friction and onventional elastomeric ligatures. Am J Orthod Dentofacial Orthop. 2007; 131:772-775
Mayberry D, Allen R, Close J, Kinney DA Effects of disinfection procedures on elastomeric ligatures. J Clin Orthod. 1996; 3:49-51
Jeffries CL, von Fraunhofer JA The effects of 2% alkaline glutaraldehyde solution on the elastic properties of elastomeric chain. Angle Orthod. 1991; 61:25-30
Stevenson JS, Kusy RP Force application and decay characteristics of untreated and treated polyurethane elastomeric chains. Angle Orthod. 1994; 64:455-467
De Genova DC, McInnes-Ledoux P, Weinberg R, Shaye R Force degradation of orthodontic elastomeric chains - a product comparison study. Am J Orthod. 1985; 87:377-384
Baty DL, Storie DJ, von Fraunhofer JA Synthetic elastomeric chains: a literature review. Am J Orthod Dentofacial Orthop. 1994; 105:536-542
Mayberry D, Allen R, Close J, Kinney DA Effects of disinfection procedures on elastomeric ligatures. J Clin Orthod. 1996; 3:49-51
Jeffries CL, von Fraunhofer JA The effects of 2% alkaline glutaraldehyde solution on the elastic properties of elastomeric chain. Angle Orthod. 1991; 61:25-30
Evangelista MB, Berzins DW, Monaghan P Effect of disinfecting solutions on the mechanical properties of orthodontic elastomeric ligatures. Angle Orthod. 2007; 77:681-687
Eliades T, Eliades G, Watts DC, Brantley WA Elastomeric ligatures and chains. In: Brantley WA, Eliades T Stuttgart: Thieme; 2001
Nattrass C, Ireland AJ, Sherriff M The effect of environmental factors on elastomeric chain and nickel titanium coil springs. Eur J Orthod. 1998; 20:169-176
Huget EF, Patrick KS, Nunez LJ Observations on the elastic behavior of a synthetic orthodontic elastomer. J Dent Res. 1990; 69:496-501
Evangelista MB, Berzins DW, Monaghan P Effect of disinfecting solutions on the mechanical properties of orthodontic elastomeric ligatures. Angle Orthod. 2007; 77:681-687
Wong AK Orthodontic elastic materials. Angle Orthod. 1976; 46:196-205
Ash J, Nikolai R Relaxation of orthodontic elastic chains and modules in vitro and in vivo. J Dent Res. 1978; 57:685-690
Andreasen GF, Bishara S Comparison of alastik chains andelastics involved with intra-arch molar-to-molar forces. Angle Orthod. 1970; 40:151-158
One hundred elastomeric ligatures from one manufacturer were chosen for this study: 10 ligatures were tested at room temperature; the other 90 ligatures were divided into three equal groups and were stretched over stainless steel dowels. Group 1 samples were kept in artificial saliva. Group 2 samples were rinsed twice a day with 15 ml of Orthokin®, each time for 1 minute, and the Group 3 samples were rinsed twice a day with 15 ml of Oral B®, each time for 30 seconds, both samples being immersed in another artificial saliva prior to being put back in the test tubes. Each time, 10 of the samples were tested for their tensile strength at different intervals of 1, 7 and 28 days until they ruptured. One-way and two-way ANOVA and Tukey test were used for evaluation.
Clinical Relevance: The aim of this study was to evaluate the in vitro effects of Orthokin®, Oral-B®, and artificial saliva on tensile bond strength of elastomeric ligatures.
Article
Wire and elastomeric ligatures are the most common types of bracket ligation used in orthodontics.1 The advantages of elastomeric ligatures are that they can be applied quickly, are comfortable to the patient, and are available in a variety of colours. Numerous studies have evaluated the strength characteristics of elastomeric ligatures in various environments and different conditions.2,3,4,5,6 It has been a common finding that rubber elastics will lose some part of their initial force after they are applied in the mouth for the purpose of oral activities. Several factors have been found to be effective on the force degradation of elastomers:
Oral temperature;
Tooth movement;
pH variations;
Salivary enzymes;
Masticatory forces; and
Foods and drinks with different acidity and alkalinity.7
Nowadays, the application of a mouthrinse for oral hygiene purposes is increasing, especially for orthodontic patients. A few studies have been conducted on the effects of disinfecting and antibacterial solutions on the properties of lastomeric ligatures.8,9,10 However, the effects of different types of mouthrinse on force degradation of elastomeric ligatures have not been reported in the literature. The aim of this study was to evaluate the in vitro effects of Orthokin®, Oral-B®, and artificial saliva on the tensile bond strength of elastomeric ligatures.
Material and methods
One hundred transparent moulded elastomeric ligatures (Dentaurum, Germany. Batch: 774-5513-00) were selected. The samples were divided into three test groups. Each group had 30 ligatures. The remaining 10 ligatures were tested at room temperature (25 °C). The ligatures of the test groups were stretched over stainless steel dowels (0.155″ in diameter) to simulate the stretch necessary to apply an elastomeric ligature over a maxillary first premolar twin bracket (standard edgewise 0.018″ slot). A bracket-jig was fabricated by brazing a Dentaurum bracket (0.018″ slot) to one end of each dowel. Ten ligatures were stretched on each stainless steel dowel, therefore, each test group consisted of three dowels. All the dowels were tested in a simulated oral environment and were put in artificial saliva test tubes with the temperature at 37 °C.
Group 1 samples were kept in artificial saliva. However, group 2 samples were rinsed twice a day with 15 ml of Orthokin®, each time for 1 minute and the group 3 samples were rinsed twice a day with 15 ml of Oral B®, each time for 30 seconds. The rinsing times were chosen according to mouthrinse manufacturer instructions. Groups 2 and 3 samples were immersed in another artificial saliva prior to being put back in the test tubes. This action was taken in order to prevent mouthwash entering the test tubes. The samples were removed for force testing at the following intervals: 1 day, 7 days and 28 days.
Tensile testing of ligatures was performed on an Instron universal testing machine (Instron Corp®, Canton, MA, USA) at 1, 7 and 28 days. Each sample was placed in a test jig compromising two metal pins attached to the fixed and movable crossheads of the tensometer and loaded in tension at a crosshead speed of 5 mm/min until they ruptured.
A Kolmogorov-Smirnov test was used to control the normality distribution of samples. The data were evaluated by one-way and two-way ANOVA. A Tukey test was also used for intra-group analyses in all intervals. Statistical software of SPSS, Version 16 (SPSS Inc, Chicago, Ill) was used to examine the data. Statistical significance was set at P<0.05.
Results
The highest tensile strength of ligatures could be seen in the control group, which was 26.59 ± 1.9 Newton (N). The Tukey test showed that there were significant differences between this amount and each of the groups in all intervals (P<0.001).
The tensile strength was 20.98 ± 1.9 N in artificial saliva after 1 day of intervention. This strength was slightly lower than its respective amount after 7 and 28 days of intervention. A oneway ANOVA showed that there was no statistically significant difference between these intervals (P<0.7).
The tensile strengths of Orthokin® were 22.7 ± 1.3 N, 23 ± 1.9 N and 20.7 ± 2 N after 1, 7 and 28 days of intervention, respectively. A Tukey test showed that the difference between 7- and 28-day interventions was statistically significant (P<0.02). This difference also applied for 1- and 28-day interventions (P<0.04).
A one-way ANOVA showed that there were statistically significant differences between the three intervals in the Oral B® group. A Tukey test showed that the difference between 1- and 7-day interventions was statistically significant (P<0.01). This difference also applies for 1- and 28-day interventions (P<0.008) and 7- day and 28-day interventions (P<0.001)
A two-way ANOVA showed that these three solutions did not have any statistically significant differences between each other (P<0.1) (Table I, Figure 1).
Groups
24 Hours Mean ± SD
7 Days Mean ± SD
28 Days Mean ± SD
P Value
Artificial Saliva
20.84±1.9a
21.97±1.2a
21.94±1.4a
0.7
Orthokin®
22.76±1.3a
23±1.9a
20.75±2b
0.02
Oral B®
22.22±1.7a
24.2±1.5b
20.15±1.1c
0.001
a, b and c indicate statistically significant differences at significance level of p<0.05.
Figure 1. Tensile strength in three different solutions in three different intervals.
Discussion
This study showed that the tensile strengths of all ligatures immersed in artificial saliva, Orthokin® and Oral B® were lower than the control group. Surprisingly, their tensile strengths increased after 7 days, however, they showed a decrease after 28 days.
Tensile strength is an important property of elastic ligatures because maintenance of force delivery is needed to sustain full engagement of archwires in the bracket slot for tooth movement.11 The effects of food on elastomeric ligatures have previously been studied by different researchers. Nattrass et al found that Coke® and turmeric solution had a greater effect on force loss of elastomeric ligatures than water alone, suggesting that some factor within the former two solutions might be modifying the properties.12 Huget et al found that moisture and heat decrease the force levels of elastomeric materials.13 Lam et al stated that the tensile strength of clear and coloured elastomeric ligatures was found to be significantly different; moreover, some significant differences were seen between different brands of elastomeric ligatures.14 It was also found by Evangelista et al that tensile load to failure of elastomeric ligatures decreased when exposed to disinfectant solution for one hour or more.15 Wong16 and Ash and Nikolai17 stated that greater force decay was observed in wet conditions than dry conditions with the same temperature. On the contrary, Andreasen and Bishara carried out experiments in dry and simulated oral environments of 100% humidity conditions and reported no significant differences for the different conditions.18
In this study, time of exposure was also a significant factor. The strength values of the elastomeric ligatures, regardless of the solutions, fluctuated at different intervals. More research is needed to clarify the increase of tensile strength after 7 days of intervention.
The in vitro conditions of the present study apparently fail to simulate the complex intra-oral environment, and thus no conclusive comments on the in vivo degradation mechanism of orthodontic elastomeric modules can be made.
Conclusions
Compared to control samples, tensile load to failure of elastomeric ligatures decreased when exposed to disinfectant solution. However, no distinguishable differences could be seen between the three different solutions.
