You don't have to be an "orthodontist" to do "ortho."
There are a lot of terrific ortho courses for GPs that will allow you to have the best of both worlds by doing general dentistry and ortho as well.
If you would like to go back to school to get the ortho degree you can.
One of the programs that I've taken as a GP in private practice is one given by Dr. Brock Rondeau
www.RondeauSeminars.com. Brock is a GP from Toronto, ON Canada that has been doing ortho for close to 30 years and has been teaching it for almost as long!
There are other great courses available from other ortho teachers as well.
I don't have any financial interest in Brock's course or receive anything by recommending it to you. I've enjoyed taking the course and have also enjoyed implementing ortho into my practice as a GP. It's a terrific service for my patients.
We also have been involved with Invisalign and that has also worked well for my practice.
The best advice I can give is to have an open mind and constantly learn and don't be afraid to try things. Just because you don't have the additional 2-year degree doesn't mean you can't treat patients the way you want. There are programs out there that will allow you to create the type of dental practice that you like.