To investigate the difference in the nose-lip-chin relationship of adult males and females with bimaxillary protrusion before and after orthodontic treatment as well as the difference between genders.

Sixty adult patients with bimaxillary protrusion, including 25 males and 35 females, were treated with straight wire technique, and cephalometrics were taken subquently. The difference in the nose-lip-chin relationship before and after treatment, and that between males and females were compared using paried and independent sample t test.

The NLA (female vs male: 86.23° vs 91.86°, P= 0.033) , Pog′B′-FH (61.03° vs 68.19°, P= 0.014) , UL-U1 (8.99 mm vs 10.87 mm, P= 0.000) , LL-L1 (11.84 mm vs 13.59 mm, P= 0.000) and Pos′-Pos (8.14 mm vs 9.37 mm, P= 0.014) in females were statistically less than males. while LL-E (7.90 mm vs 6.40 mm, P= 0.023) was larger than males before treatment. After treatment, there was no difference in FCA, NLA, Pog′B′-FH and Pog′-Pog between males and females. The length and thickness of upper and lower lips were substantially less in females than that in males, while LL-E (3.90 mm vs 2.50 mm, P= 0.013) of females was larger than males. Both males and females had the same changes in FCA, NLA, H angle, Pog′B′-FH, UL-U1, Pog′-Pog, UL-E and LL-E after treatment, without significant difference between genders.

There was sexual difference in the nose-lip-chin relationship before and after treatment. Substantial treatment changes were observed both in males and females, and orthodontic treatment can improve the facial profile and the harmony of nose-lip-chin relationship.