How long can treated, but undetected lice eggs remain attached on hair?

I work in a classroom with children who frequently have head lice. Something that the staff does is put tea tree oil in our shampoo at home, not too much, just enough so that when you shake it up to mix it, you can faintly smell the tea tree oil. Lice hate the stuff and will stay away from it. We've also found that rather from using an expensive lice shampoo like Nix, just use cheap dog/cat shampoo for treating lice and fleas. It works much better and isn't as harsh on your hair. You should continue to try and remove all of the lice eggs by using the tiny combs while your hair has conditioner in it. Have your wife use the tiny comb while shes in the shower each day for about 10 minutes until you don't find the eggs anymore. I would do one more clean sweep of all household linens and furniture, you can buy lice killing sprays for couches and chairs and what not. Even after getting rid of all the eggs I would continue to wash my hair with the lice shampoo at least once or twice a month, ...  more