Table 1.

The minimal width in three surface in male and female respectively

Sex	Upper (mm)	Middle (mm)	Lower (mm)	Channel length
Male	12.12 ± 2.89	16.22 ± 2.95	18.07 ± 2.76	130.85 ± 8.02
Female	11. 20 ± 2.71	14.97 ± 2.81	15.65 ± 2.49	124.30 ± 7.71
Z	−1.388	− 1.660	− 3.487	−2.912
P	0.165	0.097	< 0.001*	0.004*

*means that there was significant differences