Jeana, you know i'm not really sure, maybe it does, but then i only ever go to the dentist when i'm fairly well anyway.
And as far as using gas for a clean goes, if the customer is paying, they should do whatever is asked of them. If you are a nervous patient, just tell them that and explain you won't let them anywhere near your mouth with pointy, sharp things until you're gassed to within an inch of your life!! <img src="i/expressions/face-icon-small-happy.gif" border="0">
I never go to the dentist for just cleans though so i personally have never dealt with this particular issue. Good luck, finding the gas at the dentist is the best thing that ever happened to my teeth!! I'd never go otherwise.