Journal Article

Permissible limit for mandibular expansion

Mitsuru Motoyoshi, Sawa Shirai, Shinya Yano, Kotoe Nakanishi and Noriyoshi Shimizu

in The European Journal of Orthodontics

Published on behalf of European Orthodontics Society

Volume 27, issue 2, pages 115-120
Published in print April 2005 | ISSN: 0141-5387
Published online April 2005 | e-ISSN: 1460-2210 | DOI: http://dx.doi.org/10.1093/ejo/cjh092
Permissible limit for mandibular expansion

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In recent years, mandibular expansion has been increasingly performed in conjunction with orthodontic treatment. Lateral tipping of the molars associated with mandibular expansion should, however, be considered, because excessive expansion may result in excessive buccal tooth inclination, which may disturb the occlusal relationship. This study was conducted to quantitatively clarify molar movement during mandibular expansion using the Schwarz appliance to determine the permissible limit of mandibular expansion as a clinical index for inclination movement. Inclinations in the masticatory surface of the first molar and intermolar width were measured before expansion (T1), after expansion (T2), and before edgewise treatment (T3). Lower plaster models from 29 subjects treated with expansion plates were used and compared with models from 11 control subjects with normal occlusion.

The average treatment change (T1–T2) in intermolar width was 5.42 mm (standard deviation 1.98), and the average angle of buccal tooth inclination was 10.16 degrees (standard deviation 3.83). No significant correlation was found between age prior to treatment and the treatment period when they were compared with the intermolar width increments and inclination angles. There was a significant positive correlation between retention duration and the amount of expansion. The regression coefficient of the angle of buccal tooth inclination during expansion to the increment of the intermolar width was approximately 0.2. This means that 1 mm of expansion is accompanied by 5 degrees of molar lateral tipping. This coefficient is clinically useful for estimating the permissible limit for mandibular expansion.

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Subjects: Restorative Dentistry and Orthodontics

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