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Elastomeric and coil springs


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Elastomeric and coil springs

  1. 1. Elastomeric and coil springs By : Dr. Khaled Wafaie
  2. 2. Introduction • Through years a lot of ways have been developed to deliver optimal force to move teeth with light and continuous forces, but it is not known exactly how much force is required to move teeth. Indeed, clinicians apply a wide range of forces for space closure and there is no evidence of an optimal force level in the orthodontic literature. • Quinn and Yoshikawa (1985) suggested that 100–200 g is optimal for canine retraction and the residual force provided by nickel titanium coil springs during the plateau period of force delivery after 6 weeks fell into this range. Elastomeric chain provided residual forces lower than this, mostly between 50 and 150 g, yet space closure continued successfully!!
  3. 3. • Dixon et al. (2002), RCT found mean monthly (4 weeks) rates of space closure to be 0.58 mm for elastomeric chain and 0.81 mm for nickel titanium coil
  4. 4. Elastomeric: • Elastomeric chains were introduced to the dental profession in the 1960’s • The elastic are made either of latex or synthetic rubber, it absorbs saliva and loses elasticity of about 50-70% at first day and 10% at 3 weeks. • They are used to generate light continuous forces for : canine retraction, diastema closure, rotational correction, arch constriction.
  5. 5. • Advantages: Inexpensive Relatively hygienic Easily applied Require little or no patient cooperation. • Disadvantages: When extended and exposed to oral environment • Absorb water and saliva • Permanently stain • suffer a breakdown of internal bonds that leads to permanent deformation. They experience a rapid loss of force due to • Stress relaxation resulting in a gradual loss of effectiveness. This loss of force makes it difficult to determine the actual force transmitted to the dentition.
  6. 6. • Storei et al have showed that fluoride releasing elastomerics were not able to deliver the required force for three weeks as conventional types. • Color coded chains  The initial force delivery and effects of fluid immersion of colored chains were studied (Baty and von Fraunhofer). They compared three colors of elastomeric chains with the standard gray chain from three different manufacturers, and the data indicated that the coloring of the chains had little effect on the initial force delivery levels of the chains.
  7. 7. Closed spring coil: • Nickel titanium closed coil springs typically are used in 9 mm and 12 mm lengths. • It should be noted that only a portion of a 9 mm or 12 mm nickel titanium coil spring can be activated or stretched. • It is found in ‘‘Ultra Light, Light, Medium, Heavy, and Extra Heavy’’.
  8. 8. • According to Maganzini et al., 2010 and Nightingale and Jones 2003 Nickel titanium closed coil springs vary greatly in the peak load forces generated during activation. Most nickel titanium closed coils tested had inconsistent unload forces generated throughout deactivation, but according to Samuels et al.,1993 the use of super-elastic nickel- titanium coil springs resulted in a significantly greater and more consistent rate of space closure than elastic modules. • Tripolt et al., 1999 concluded that spring can produce a relatively constant force during deactivation, provided that the correct technique is used with the standardized springs: A)15-mm activation, B)followed by a 7.5-mm deactivation to the desired activation of 7.5 mm, C)delivers a relatively constant force if the spring is used for 5 mm of tooth movement.
  9. 9. • Superelastic coil springs are extremely temperature sensitive and thus produce a large force variation at different mouth temperatures. However, in a narrow temperature range, this variation is small.
  10. 10. A clinical investigation of force delivery systems for orthodontic space closure By: (C. Nightingale & S. P. Jones, 2003) • Twenty-two orthodontic patients: a)15 put both quadrants b)7 put elastomeric only ( the extraction space was too great for a nickel titanium coil spring to be stretched directly between the two hooks) • The range of initial forces applied was 70–450 g, with a mean force of 209 g, whilst the range of final forces was 50–230 g, with a mean force of 109 g • The nickel titanium coil springs gave variable forces, even when stretched the same distance, and so do not appear to provide a predictable force • One patient achieved no space closure at all over a period of 10 weeks, despite a range of forces (135–270 g) being applied.
  11. 11. Results: • 59% of the elastomeric sample maintained at least 50 % of the initial force over a time period of 1–15 weeks. No sample lost all its force, • mean loss was 47 % • mean rate of space closure weekly for elastomeric chain was 0.21 mm • Nickel titanium coil springs lost force rapidly over 6 weeks, following that force levels plateaued. 46% maintained at least 50 % of their initial force over a time period of 1–22 weeks, • mean force loss was 48 % • mean rate of space closure weekly for nickel titanium coil springs 0.26 mm
  12. 12. Conclusion: • In clinical use, the force retention of elastomeric chain was better than previously concluded. High initial forces resulted in high force decay. • Nickel titanium coil springs and elastomeric chain closed spaces at a similar rate.
  13. 13. Effects of pre-stretching on force degradation of synthetic elastomeric chain By: (Kim et al., 2005) • A lot of ways were used to decrease force degradation, Andersen and Bishara 1970 suggested over stretching of elastic but that will deliever high forces (undermining resorption) and discomfort. Kovatch et al., suggested to put elastic slowly to reduce decay, and Ferriter et al., suggested that PH below 7.26 will decrease force decay. • Then Brooks and Hershey heated the elastomeric and noted the force is only 30% at first hour but when they pre-stretch they loss only 50%.
  14. 14. • So this study will evaluate pre-stretching of 5 and 6 by 100% module elastomeric for:1)1hour 2)1day 3)2week 4)4weeks in distilled water. and then their forces are evaluated at 1)0hour 2)1hour 3)24hour 4)1 to 4 weeks.
  15. 15. Results • pre stretched 5 and 6 module show initial lower forces to control, and both groups show decay in force however after 1 hour 5 unit module and control group become equal and small difference to the 6 group.
  16. 16. Conclusion: • The effect of pre-stretching is seen only at the first hour; its clinical value is still questionable.
  17. 17. Final conclusion: • High initial forces resulted in high force decay.(Samuels et al., 1993). • There is significant difference between different types of companies when comparing 28- day mean forces (Josell et al., 1997). • In general, the most force decay occurs at the first hour.(Samuels et al., 1993)(Lu et al., 1993). • Nickel titanium coil springs and elastomeric chain closed spaces at a similar rate. (Dixon et al. 2002)(Samuels et al., 1993). • In a study by Norman et al. (2016) shows that stainless steel springs are clinically effective and produce as much space closure as their more expensive rivals, the NiTi springs.