The best use of Twitter that I’ve heard so far for dental practices is to use it to post an opening in the schedule. If you have a day when the schedule suddenly falls apart, even if it’s today, but that’s less than three days out, if you tweet it, and perhaps put a special offer with it like discount whitening, or a gift certificate, then what happens is your followers will retweet the offer. Specify if you want it to be a first-come, first-served offer.
Be sure to tell them in the tweet that it is OK to retweet the offer, and more people will do it. This captures the viral aspect of Twitter.