No, majority of U.S. dental schools do not have their own Post-bac. programs, but those that do, it is 100% guaranteed admssion to a U.S. dental school if you do well in them.
For example, at Nova Dental, we have a Post-bac. program called Master of Biomedical Sciences (MBS) program. It's a master's program (2 years) on paper, but it's essentially a side-door to get into the our dental and medical programs here at Nova. In this MBS program, you're taking the same basic science courses with the dental and medical students. Courses include Biochem, Histo, Gross Anatomy, Microbiology, Neuroanatomy, and Physiology during the first year.
You must earn a 80/100 in every course after the first year during the MBS program for you to be guaranteed to be admitted into the next incoming dental class and you do not have to do the second year of the MBS program. If you earn 90/100 in any course during your MBS first year, then those courses will be waived in your first year of dental school. For example, you earned a 96/100 as a final grade in Biochem in the MBS program, then you do not have to take Biochem during your first year of dental school at Nova.
Each year Nova Dental set aside 5 seats out of 100 for the MBS students in each incoming class. With that said, the MBS program here at Nova is just as competitive as regular dental admission. Official DAT scores, a bachelors degree and 3 letters of recommendations are required to apply. This is kind of odd because the MBS program is a remedial route where they should be a bit more lenient on numbers, but they don't?
Each year there are roughly 80 applicants apply to those 5 seats and around ~15 interview invitations are granted to those seem qualified. Tuition for this MBS program is not cheap either, I believe it's around $23.5K for the year.
This MBS program was initially tailored to the medical school since there are always so much more applicants than available seats per class, but now it has branched out to the dental side and made available to dental applicants that weren't successful applying through AADSAS.
There are 20 MBS seats for medical and only 5 MBS seat for the dental here at Nova. For more info, visit the Nova MBS official site at:
http://medsciences.nova.edu/aboutbs.html
Bottom line, an official dental Post-bac. program is not only effective if you do well, but it's also competitive to get in one and expensive to attend!