I have no idea what the effects of CoQ10 are, but the only way to "cure" gingivitis is very good oral hygine. If the bacteria can't stick to your teeth and under your gums you can't get gingivitis. Some substances may help with the healing process and the like but you need the physical removal of bacteria and the like no matter what else you are taking.
I did some quick research and found that there are claims that CoQ10 cures ageing, heart disease, obesity, gum disease, huntingtons disease and high blood pressure. In an earlier time this would have been called snake oil . Every website that mentioned this also had a link to sell it. I couldn't find any that citied any scientific proof, but I would look around more before you spend your money.