Jeffrey,
I always say, “Everything is possible in programming!” But, as Richei says, it can be very complicated.
Working on many sites that have a “front-end” for clients and a “back-end” for the administrators or the
owners, what you are talking about is standard these days.
But, again as Richei says, you should start out simple. Get the front-end going for the clients first.
Once all of your system is working and your data is storing and protected inside your database, then
work on a back-end page for your dentist or assistant to access. This would be really and admin panel
which would give access to all the data.
CMS systems prebuilt for this type of system are available for free. One common one that is used by
millions is the WordPress system. You might want to search around for a free WordPress system which
gives you control with a front-end/back-end type of layout. Something to think about.
As a beginning, a full fledged system for a dental office is a big job. A pre-built system might be easier for
you to start with. Good luck!