The purpose is to treat the mild crowding cases with Invisalign expansion protocol and to evaluate its clinical results.

Eleven adults with classⅠdental malocclusion, classⅠskeletal pattern and straight profile were enrolled into the study. The arches were mild crowding in maxilla and mild or moderate in mandible. All patients were treated with Invisalign non-extraction protocol. In the treatment planning, the central incisors were maintained in sagittal positions and the crowding was corrected by arch expansion. The cephalometry were measured and analyzed. Meanwhile, the upper canines width, first premolars width, second premolars widths, and first molars width were measured in the digital model to evaluate the expansion efficiency by paired-t tests.

The crowding was corrected and the inclination of central incisor was maintained in eleven patients. The width (mm) of canines, first premolar, second premolar and first molar were increased by (2.01 ± 1.31; t= 4.85, P= 0.001) , (4.12 ± 2.58; t= 5.04, P<0.001) , (4.68 ± 2.22; t= 6.66, P<0.001) , (3.13 ± 2.96; t= 3.34, P= 0.007) , respectively, in which the significant differences were found. However, the expansion efficacy did not meet the treatment plans though with significant difference between post-treatment and pre-treatment (-2.01±1.12; t= 5.67, P<0.001) .

Mild crowding can be solved by expansion performed with Invisalign, maintaining the inclination of central incisor. The efficiency of upper canine expansion may not meet the treatment planning requirement.