Through the government there is a loan forgiveness act (click on link). You have to sign up for it (it is not retroactive), you have to work continuously for the government for 10 yrs, and you have to be paying back your loan continuously (income based loan repayment) - no deferments or forbearance. If you work for the government for 10 yrs they will wipe out your remaining debt. May not be as applicable for HPSP applicants unless they had large undergrad loans, but for a direct accession it may be beneficial.
So, you could do either of these three things as well to get those loans forgiven:
Join the reserves (Army, Navy or Air Force) and, depending on the programs available at the time of joining, you could get anywhere from $10 - $40k/year forgiven
Work as a civilian on a military base - you're paid a "salary" that is allegedly commensurate with a civilian dentist salary and you are technically working at a qualifying "public facility" and thus any year (and remember, you only need 6 more to get the rest of the loans forgiven) you work is also counted towards PSLF
Join the National Guard in a reserve capacity and take advantage of their loan forgiveness programs