Objective    To observe the effect of different energy levels of pulsed Nd:YAG laser irradiation on the changes of NO and NOS levels in ulcer tissue of oral ulcer model.     Methods    Forty-eight Sprague-Dawley rats were inflicted with oral ulcer

and then randomly and equally assigned to 6 groups

that is

oral ulcer group

1% iodine glycerin group and the rest 4 groups receiving pulsed Nd:YAG laser irradiation at 1.5 W 40 mJ

1.5 W 60 mJ

1.5 W 80 mJ or 1.5 W 100 mJ (once per day

for 3 consecutive days). The other

8 rats served as normal control. In 24 h after last treatment

4 rats from each group were sacrificed and their cheek pouches were taken out for NO and NOS levels in the mucosal tissue by spectrophotomentry. Ulcer healing were observed 24 h after the last treatment for 8 consecutive days. The efficiency of Nd:YAG laser irradiation at different powers were evaluated.     Results    Irradiation groups had significantly shorter healing time compared with iodine glycerin group. Level of NO and NOS activity in 1.5 W 60 mJ and 1.5 W 80 mJ groups was evidently lower than the ulcer group (

P

<

0.05); but the changes of NO and NOS activity had no significant difference (

P

<

0. 05) between the 2 groups and normal control.     Conclusion    Proper energy of pulsed Nd:YAG laser irradiation has therapeutic effect on oral ulcer and decreases the NO activity and NOS content

and it is an effective approach to oral cavity mucosa ulcer.