You can find DDS/PhD program at schools like ucsf, ucla, etc (schools with strong research). The program at ucsf is fully funded.
This year, at ucsf, after 80 students are accepted to the DDS program, admissions reccomended 10 students for applying to DDS/PhD. Of those ten, they will have to do another round of application, take the GRE, and only 2 will get accepted.
Last year, nobody at ucsf even got accepted. The whole school now probably has 4 of those diamond students altogether. It's a TOUGH, VERY TOUGH program. You are guided each step through out 8 years to successfully complete two degrees. And you have to start your PhD track after your third year.