If the effective date for Denticon Patient Communication has not been set, when viewing the mailing lists and selecting get count you'll receive the following error:
In order for Denticon Patient Communication to begin sending out appointment campaigns, an effective date must be in place by going to Setup>Offices>Office Setup>Advanced>Denticon Patient Communication.
Once this has been set, you'll be able to get a count of patients on the list, and your campaigns should start going out.