Table 3. Pre- and postoperative Air–bone gap.

ABG	Preoperation	Postoperation	Z	P
Average(500-4000 HZ)	28(20~35)	15(10~20)	−6.288	<0.001
250 HZ	35(30~45)	20(15~25)	−6.216	<0.001
500 HZ	35(30~45)	20(10~20)	−6.146	<0.001
1000 HZ	35(25~40)	15(10~20)	−6.281	<0.001
2000 HZ	20(10~25)	10(5~15)	−4.553	<0.001
4000 HZ	25(15~35)	15(10~25)	−4.054	<0.001