Available mean time from implant placement to exchange for a permanent prosthesis in the CO2 group was shorter [ 106.3 ( 42.9 ) days ; median , 99 ; range , 42-237 ; number of expanders , 53 ] than for the women in the control group [ 151.7 ( 62.6 ) days ; median , 140 ; range , 69-433 ; number of expanders , 33 ] .