Inconclusive evidence to determine the efficiency of sliding mechanics to close extraction space Critical Summary Prepared by: Alfonso Navarrete DDS; Greg Huang DMD, MSD, MPH 


  • Systematic Review Conclusion:

    The existing literature suggests that NiTi coils and elastomeric power chain produce similar rates of space closure; however, more research is needed on space closure efficiency in orthodontics.

  • Critical Summary Assessment:

    This thorough review found limited evidence that nickel-titanium springs and elastomeric chain produce similar rates of space closure.

  • Evidence Quality Rating:


A Critical Summary of:

Factors influencing efficiency of sliding mechanics to close extraction space: a systematic review

Barlow M, Kula K. Orthod Craniofac Res. 2008;11(2):65-73

  • Clinical Questions:

    What factors influence sliding mechanics for space closure in orthodontic patients?

  • Review Methods:

    The authors searched two electronic data bases for articles in English published from 1966 to 2006. They also hand searched selected journals. Articles were screened by two independent investigators. The inclusion criteria were prospective clinical human trials that focused only on closing extraction space using sliding mechanics and comparing efficiency under different variables. Two investigators selected the studies included in the review.

  • Main Results:

    Ten prospective clinical trials were selected for inclusion; seven trials compared material variables to apply force (elastomeric variations and NiTi coils); two trials compared archwire variables (size and material); and one trial examined bracket variables (Tip-Edge and traditional twin brackets). A meta-analysis could not be performed due to the heterogeneity of the data collected. The studies found that active ligatures (a long ligature and elastomeric unit) are less efficient than NiTi coils, NiTi coils and elastic chain are not statistically different, NiTi coils are more efficient than Class I elastics alone, archwire size and material do not statistically impact efficiency, and there is no space closure efficiency difference between Tip-Edge and A-Company Roth brackets.

  • Conclusion:

    The evidence does not support a significant difference in the efficiency of NiTi coils over elastic chain. However, more research with larger samples is needed on space closure efficiency.

  • Source of funding:

    Indiana University School of Dentistry (personal e-mail communication with Dr. Kula).


  • Importance and Context:

    Treatment efficiency and appliance costs are practical concerns in orthodontics. There are many hypotheses about the clinical efficiency of various sliding mechanics to close extraction spaces. 1,2 Also, the cost difference are significant between NiTi coils and elastomeric products. This review attempted to summarize the present literature regarding the different factors affecting space closure using sliding mechanics.

  • Strengths and Weaknesses of the Systematic Review:

    This systematic review was thorough. The authors searched for English-only publications in 4 databases and performed a hand search of many journals. The inclusion criteria were stated. However, the authors did not provide a list of qualifying but excluded literature. Two independent reviewers selected the trials to be included and performed data abstraction analyses.

  • Strengths and Weaknesses of the Evidence:

    The available literature does not provide a high level of evidence regarding most factors affecting sliding mechanics. All of the sample sizes in the included studies were small (15 to 33 patients), and the methods of measurement and data collection varied. The data collected were too dissimilar for the reviewers to perform a meta-analysis.

  • Implications for Dental Practice:

    Although it is theoretically possible that the constant force delivered by NiTi coils results in more efficient space closure than elastic chain, current evidence does not confirm this theory. Also, the available evidence is inconclusive regarding efficiency for various archwire sizes and materials. REFERNCES [1] Kim SH, Park YG, Chung K. Severe Class II anterior deep bite malocclusion treated with a C-lingual retractor. Angle Orthodontist. 2004 Apr;74(2):280-5. [2] Galicia-Ramos GA, Killiany DM, Kesling PC. A comparison of standard edgewise, preadjusted edgewise, and tip-edge in Class II extraction treatment. Journal of Clinical Orthodontics. 2001 Mar;35(3):145-53.

  • Critical Summary Publication Date: 10/30/2009

These summaries are not intended to, and do not, express, imply, or summarize standards of care, but rather provide a concise reference for dentists to aid in understanding and applying evidence from the referenced systematic review in making clinically sound decisions as guided by their clinical judgment and by patient needs. American Dental Association ©

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