I agree with Andy.
If you want to choose Dr. XXX YYYY - there is no obligation to share your field or specialty with anyone. This is good - it shows that you are a professional as well as any other doctor. The anonymity itself is why the title Dr. was created for doctors to be viewed as experts.
However, XXX YYY, DDS - allows you to distinguish yourself from other Doctors when it comes to certain things like: Your name in publications, your name in the yellow pages, your name on your private practice etc.