The scores of visual analogue scale ( VAS ) and present pain intensity ( PPI ) after treatment were all improved significantly as compared with those before treatment in the 4 groups ( all P < 0.01 ) , and the result in the 45 min group was superior to the other 3 groups ( VAS : 2.90 + / -0.87 vs 5.52 + / -1.01 , 4.45 + / -0.81 , 5.95 + / -1.07 ; PPI : 1.40 + / -0.21 vs 2.26 + / -0.54 , 2.21 + / -0.43 , 2.28 + / -0.74 , all P < 0.01 ) .