krmower is Army and this thread is 4 years old.
You do not receive additional pay until your educational service obligations are complete and you become eligible for the DOMRB. Currently the Comprehensive Dentistry DOMRB is 50K/yr for a 4 year contract, less for a 2 or 3 year contract. As I noted in the other thread you started, the special pays for specialists will be changing shortly and by the time you finish school all new specialists will be taking the new plan, which is slightly more for a brand new officer just coming on active duty.
Residencies performed at a Navy or other federal institution are paid back concurrently with any preexisting educational service obligation. If selected for outservice residency (only available as the needs of the Navy warrant), the payback is cumulative with any remaining educational obligation.
In your scenario, if you were to be accepted to Comp to begin immediately upon entering active duty you would finish your residency and pay back 4 years. If you were to be accepted to OMFS for an outservice residency, you would owe 4 years for OMFS plus 4 years for the original HPSP/HSCP obligation, for a total of 12 years (including the OMFS residency itself). Endo and Orthodontics both incur 1.5 years per year of training for a total of 3 years of payback.