a white tongue is different than a tongue covered in a white film... which is full of bacteria and yeast which often times work symbiotically. Eventually if it gets bad enough, the yeast and bacteria doing thier thing in a person mouth will start to cause pain and other infections in the mouth.
a white tongue to my knowledge is a symptom of a weak liver... MH said that during fasting a white tongue is due to the detox of aluminum, i cant say for sure.