In group 1 , teeth were prepared and irrigated with 3 % sodium hypochlorite and calcium hydroxide inter-appointment dressing was applied ; in group 2 teeth were prepared with saline solution and irradiated with Er , Cr : YSGG laser using RFT2 ( 140 s , 37.5 mJ , 20 Hz ) and RFT3 ( 140 s , 62.5 mJ , 20 Hz ) at the first and second appointments , respectively , four times each , moving at 2 mm/sec ( -1 ) from apical to coronal .