Objective To improve the digestion method of sewage samples for determing mercury with cold atomic absorption spectrometry.Methods 1+1 aqua fortis was used in microwave digestion of sewage samples instead of KMnO4-K2S2O8,then mercury was determined by cold atomic absorption spectrometry.Results The linear range was 0-10.0 ?g/L,the detection limit was 0.25 ?g/L,the relative standard deviation was less than 2.7% and the recovery rate was 95.0%-102.0%.It proved that the results by 1∶1 aqua fortis by microwave had high.Conclusion Compared with the KMnO4-K2S2O8 digestion method,microwave digestion method is simple,sensitive and suitable for determination of heavy metals in the environmental samples.

[Objective]To study effect of pain and stress response of NiTi rotary instrument for children with root canal therapy , and analyzed possible mechanisms.[Methods]60 cases(60 teeth)children with Dental pulp disease or root tip disease by root canal therapy from March 2015 to March 2017 were divided into observation group and control group. The control group used Hand NiTi en-larging file,observation group used NiTi rotary instruments,then root canal preparation,stress response,pain,filling effect and long-term efficacy were compared between two groups.[Result]The observation group root canal preparation time were significantly shorter than control group(P < 0.01),root canal deviation etc morphological changes(6.67%)was significantly lower than control group(26.67%,P < 0.05);gingival crevicular fluid TNF-α,IL-6,IL-1β were significantly lower than control group(P < 0.05, P < 0.01). In root canal preparation,after root canal preparation,pain rate were significantly lower than control group(10.00% vs 33.33%,3.33% vs 23.33%,P < 0.05);1 week after surgery,just fill rate(93.33%)was significantly higher than control group (70.00%,P<0.05). Followed up 6 months,root canal success rate(90.00%)was significantly higher than control group(66.67%, P<0.05).[Conclusion]NiTi rotary instruments help to reduce the pain in children with root canal,improve clinical efficacy,May be related to inhibition of surgical stress response.