Can I do upper jaw surgery a second time to lengthen my upper jaw gum after having double jaw surgery 8 months ago?

There is as far as I know, no reliable statistical data to allow a definitive answer to this question. By this, I mean there are no well conducted, randomised blinded controlled trials comparing different procedures with respect to residual refractive error. As I mentioned in another answer, a Cochrane Database meta-analysis showed similarly good outcomes between LASIK and PRK at one year, but this is in no way a 'statistical' validation of their equality.

Mercury is a toxic heavy metal which is widely dispersed in nature. Most human exposure results from fish consumption or dental amalgam. Human exposure to the vapour of metallic mercury dates back to antiquity but continues today in occupational settings and from dental amalgam. Health risks from methylmercury in edible tissues of fish have been the subject of several large epidemiological investigations and continue to be the subject of intense debate. Mercury is most notable for its neurological effects. Too much mercury can cause numbness, memory issues, anxiety, low mood, and tremors.