|Year : 2014 | Volume
| Issue : 4 | Page : 146-149
Force relaxation of 3/16 inch heavy orthodontic latex elastics used in maxillofacial trauma in simulated jaw fracture situation
Amin Rahpeyma1, Saeedeh Khajehahmadi2
1 Department of Oral and Maxillofacial Surgery, Oral and Maxillofacial Diseases Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
2 Department of Oral and Maxillofacial Pathology, Dental Research Center, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran
|Date of Web Publication||12-Sep-2014|
Dr. Saeedeh Khajehahmadi
Dental Research Center of Mashhad University of Medical Sciences, Vakilabad Blvd, Mashhad
Source of Support: None, Conflict of Interest: None
Introduction: Orthodontic elastic has been investigated for tooth movement. Study about their use in treatment of jaw fractures is limited. This study is designed to measure force relaxation of 3/16 inch heavy latex orthodontic elastics in jaw fracture treatment simulated conditions. Materials and Methods: This study is designed to study the force relaxation of 45 heavy 3/16 inch orthodontic elastic (American Orthodontist, AO) (4/8 mm internal diameter) were measured using Zwick testing machine (Zwick GmbH & Ulm Germany) in 0, 1, and 14 days of immersion in simulated oral environment. In each of these three occasions, 15 specimens were placed in jigs with metallic pins that inserted 15 mm and 20 mm apart that is equivalent to the normal inter-arch space in a closed mouth position. The jigs were incubated in 37°C and each 24 hours they received 10 thermal cycles of 55°C and 5°C for 30 seconds in a thermocycle. The distribution of the data was evaluated by Klomogrov-Simirnov test and after confirmation of a normal distribution; data was analyzed using analysis of variance (ANOVA). Results: Mean force decay at 15 mm stretch was significantly differ between 0-1 days and 0-14 days (P < 0.05) but was not significantly differ between 1-14 days. The same relations exist for 20 mm stretch. Conclusions: This study creates scientific basis for use of orthodontic elastics in treatment of fractured jaws.
Keywords: Force decay, jaw fracture, orthodontic elastics
|How to cite this article:|
Rahpeyma A, Khajehahmadi S. Force relaxation of 3/16 inch heavy orthodontic latex elastics used in maxillofacial trauma in simulated jaw fracture situation. Dent Hypotheses 2014;5:146-9
|How to cite this URL:|
Rahpeyma A, Khajehahmadi S. Force relaxation of 3/16 inch heavy orthodontic latex elastics used in maxillofacial trauma in simulated jaw fracture situation. Dent Hypotheses [serial online] 2014 [cited 2019 Oct 15];5:146-9. Available from: http://www.dentalhypotheses.com/text.asp?2014/5/4/146/140592
| Introduction|| |
Dental occlusion is a major factor in treatment of jaw fractures. Restoration of pre-injury occlusion and anatomic reduction of fractured segments are two main goals.  Arch bar and inter-maxillary fixation (IMF) are tools to reach this object. Upper and lower teeth fixed together with wires for special time (Rigid IMF).  Elastic bands occasionally used in trauma patients to achieve proper occlusion and preserve it (Elastic IMF). 
Indications for elastic therapy in jaw fracture treatments are:
- Old fractures with mobile segments and bony callus formation. 
- Vertical step in occlusion. 
- Condylar fractures (unilateral or bilateral). ,
- Minor occlusual adjustment after open reduction and internal fixation of jaw fracture. 
One of the benefits of elastics for maxillomandibular fixation is that elastic IMF can readily released by scissors in emergent situation like vomiting.
Oral and maxillofacial surgeons use 3/16 inch heavy orthodontic elastics in box form or class II, and class III vector between upper and lower arch bar hooks. Orthodontic elastic has been investigated for orthodontic purposes. Study about their use in treatment of jaw fractures is limited.  There are published articles about elastic properties of 3/16 inch heavy latex elastics by manufactures and researchers in wet, dry, and simulated oral conditions, ,,,, Application of orthodontic elastics in maxillofacial trauma patients needs information about elastic properties of these materials in this special clinical situation. Whole time wearing, two weeks elastic interval change and traction length are three major differences with orthodontic application of this elastics.  This study tries to create scientific basis for orthodontic elastics that are used in treatment of jaw fractured patients.
| Materials and Methods|| |
This study designed to evaluate elastomeric properties of 3/16 inch heavy latex elastics in conditions similar to real jaw fractures situation. Maximal interincisal opening (MIO) is reduced hence previous investigation on 3/16 inch heavy latex elastics that are measured in MIO dimensions (30-50 mm) are not usable. We designed study to evaluate their force and force decay in conditions in which they are used in jaw fracture patient. Distance between upper and lower arch bar hooks in fractured jaw with limited mouth opening, is between 15-20 mm that is distance between the upper and lower arch bar hooks in closed mouth plus 5-10 mm of interincisor clearance to allow chewing a soft diet [Figure 1]. 9 for the same reason we used static testing. In this experimental laboratory-based study, we select forty-five 3/16 inch heavy latex elastics American Orthodontics (AO) (Sheboygan, Wi, USA), the elastic characteristics of 45 specimens of silicone coated natural latex were assessed in T0 (as received condition), after being under tension for 1 days (T1), and 2 weeks (T2) incubation in a simulated oral environment.
|Figure 1: Inter arch elastic at closed mouth position in gypsum cast with arch bar|
Click here to view
In each of these three occasions, 15 specimens were placed in jigs with metallic pins that inserted 15 mm and 20 mm apart that is equivalent to the normal inter-arch space in a closed mouth position. The jigs were incubated in 37°C and each 24 hours they received 10 thermal cycles of 55°C and 5°C for 30 seconds in a thermocycle according to the Iso 10,477 standards. 
Elastic properties were measured on the Zwick testing machine (Zwick GmbH x Co, Ulm, Germany) with 5 mm/min cross head speed from the zero to the rupture point [Figure 2]. The strength-strain curve was determined for all the specimens to identify the force extension at 15-20 mm. The distribution of the data was evaluated by Klomogrov-Simirnov test and after confirmation of a normal distribution; data was analyzed using analysis of various (ANOVA). The statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) version 11.5 program.
| Results|| |
The data were extracted from strength-strain curve [Figure 3]. The mean force generated at T0 (as received specimens) for 15 mm extension was 1.6 ± 0.13 Newton (N) and for 20 mm stretching was 1.97 ± 0.18 N.
|Figure 3: Graph of the strength-strain curve in a sample of surgical elastic at T0 in 15 mm and 20 mm stretching|
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The mean force generated for elastics after 1 day incubation in simulated oral condition (thermal cycles, temperature, and artificial saliva embedding) while being under tension between protruding pins with 15 mm distance was 1.1 ± 0/08 and for 20 mm extension was 1.28 ± 0/08. The mean force generated for elastics with above-mentioned conditions after fourteen days was o/98 ± 0/20 N for 15 mm extension was o/98 ± 0/20 and for 20 mm extension was 1.14 ± 0/23 N. Mean force decay at 15 mm stretch was significantly differ between 0-1 days and 0-14 days (P < 0.05) but was not significantly differ between 1-14 days. The same relation exist for 20 mm stretch [Table 1].
|Table 1: Comparison of mean (SD) tensile properties of elastics in the as received condition, after 1 days of immersion and after 2 weeks of immersion in the simulated oral environment|
Click here to view
| Discussion|| |
In search of English language articles published in Pubmed, there was any article that focused on force generation and force decay of elastics in simulated jaw fracture conditions.
Elastics that are used for correction of minor malocclusion after lefort and mandibular fractures are 3/16 inch heavy latex orthodontic elastic but differs in goals, duration of weaning and generated force while the same elastics are used for tooth movement in routine orthodontic patients. The differences between these two situations are:
- Brackets are in middle third of clinical crown but arch bears are in cervical third.
- Muscle spasm and pain from fracture restricts interincisal opening, (0-5 mm) in jaw trauma patients.
- Elastic wearing in maxillofacial trauma patients is limited (4-6 weeks). But orthodontic patients wear these equipments for long time.
- Goal in jaw trauma surgery is bone movement and muscle adaptation but in orthodontics, tooth movement is the target. ,
- Trauma patients wear elastics 24 hours in a day but in orthodontic patients they can be removed during eating.
- In jaw fractured patients elastics are changed with 2 weeks interval but in orthodontics they are changed every day. ,
And, 3/16 inch heavy latex elastics (AO) had 31% force decay after 24 hour stretching and 39% force decay after 2 weeks stretching in 15 mm (simulated oral conditions). Slightly larger percentages exist for 20 mm stretching. Results showed that force decay between 0 and 1 days was significant (P-value < 0.05). Force decay between (1-14 days) was not significant. This is consistent with clinical behavior of maxillofacial surgeons that use these elastics whole time for 14 days. So longer time elastic IMF application in trauma patients has scientific basis and recommended to continue elastic wearing after the first day as the force decay is not much significant. 
Orthodontic elastics are changing every day by patient but surgical elastics changes every 2 weeks by surgeon. This wearing time is similar to orthodontic elastomeric chains.  Orthodontic elastics are made from latex and non-latex materials and in orthodontics are used for closure of extraction spaces and teeth extrusion.
Elastics are part of maxillomandibular fixation hence they should be wear all times without interruption or change. Elastic traction was placed between the hooks to partially immobilize the jaws as well as to approximate the jaws in good occlusion. It is possible to direct the elastic forces to bring the occlusion into a relationship normal for that patient. Force reduction between 1-14 days is not significant but force reduction between 0-1 days is significant even in low tractions (15-20 mm). These results are compatible with other studies that showed force decay in elastics has an initial high slope component and a latent part of decrease force.
This topic is open to investigate the force generated and force decay in different lengths of elastics in box form, class II and class III elastic direction and when IMF screws or IVY loop is used for closed treatment of mandibular fracture. Light elastic traction for minor adjustment of the occlusion that needs to dynamic tests for evaluation of the forces and time interval that a surgeon choose for elastic change is the other fields in this topic.
| Conclusion|| |
Surgeons that apply orthodontic elastics for jaw fracture treatment should know force generation and force decay of these elastics in simulated jaw fracture situation to decide about elastic selection and interval change of them that is different from orthodontic patients. This study showed that the force decay of 3/16 inch heavy latex elastics (AO) is not statistically differ between 1-14 days immersion in simulated jaw fracture condition. However, this property was significantly decreased between 0-1 day.
| Acknowledgment|| |
This study (number: 900300) was supported by a grant from the Vice Chancellor of Research of Mashhad University of Medical Sciences.
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[Figure 1], [Figure 2], [Figure 3]