If i receive nitrous oxide for a dental procedure will i be wearing the mask all the time and will i hear conversations of the dentist and hygienist?

Nitrous: The answer is yes and yes. First, nitrous must be given continuously via nasal mask as it is quickly expelled if not (remember the dentist works in your mouth). Second, nitrous oxide at the levels that can legally be given do not result in loss of consciousness, thus you will hear conversations and noise. Sadly, many patients believe that "laughing gas" will "put them to sleep". It won't.

Yes and Yes: You will not be asleep. Time and other sense perception may be somewhat distorted.