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Related Experiment Videos

Permissible limit for mandibular expansion.

Mitsuru Motoyoshi1, Sawa Shirai, Shinya Yano

  • 1Department of Orthodontics, Nihon University School of Dentistry, Tokyo, Japan. motoyosi@cc.rim.or.jp

European Journal of Orthodontics
|April 9, 2005
PubMed
Summary

Mandibular expansion using the Schwarz appliance can lead to molar tipping. This study found that 1 mm of expansion results in approximately 5 degrees of buccal tooth inclination, providing a clinical index for safe expansion limits.

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Area of Science:

  • Orthodontics
  • Dental Biomechanics

Background:

  • Mandibular expansion is common in orthodontic treatment.
  • Excessive expansion can cause buccal tooth inclination, potentially disrupting occlusion.

Purpose of the Study:

  • To quantitatively assess molar movement during Schwarz appliance-assisted mandibular expansion.
  • To establish a clinical index for permissible mandibular expansion limits based on molar inclination.

Main Methods:

  • Measurements of first molar inclination and intermolar width were taken before (T1), after expansion (T2), and before edgewise treatment (T3).
  • Data from 29 subjects using expansion plates were compared to 11 controls.
  • Statistical analysis included correlation between age, treatment duration, retention, and expansion outcomes.

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Main Results:

  • Average intermolar width increase was 5.42 mm; average buccal inclination was 10.16 degrees.
  • No significant correlation between age/treatment period and expansion/inclination.
  • Significant positive correlation between retention duration and expansion amount.
  • A regression coefficient of ~0.2 indicated 1 mm expansion corresponds to 5 degrees of molar tipping.

Conclusions:

  • Mandibular expansion with the Schwarz appliance causes predictable molar buccal tipping.
  • A 1 mm expansion is associated with approximately 5 degrees of molar lateral tipping.
  • This relationship provides a clinically useful index for determining safe mandibular expansion limits.