I think all new dentists need more training, but don't necessarily agree that formally mandated GPRs are the way to go about it. As the mandated residency becomes the norm, the states are going to start viewing the GPRs merely as medicaid "dumping grounds". The associated hospitals are going to start viewing them as a source of income. There is a serious danger that the quality of education will take a back seat to those goals.
The last thing a new dentist needs is to be stuck plugging amalgams and shucking teeth all day in a state-run medicaid mill because the state won't grant him licensure until they've had their way with him. Not to mention that mandatory GPRs are likely going to suck patients, faculty, and resources away from dental schools - most of which are already seriously lacking in one or more of those areas. The system of associating for a few years after dental school has been working well for many decades; I see no reason to mess with things now. I vote for keeping the optional GPR/AEGD.