Out of all the places to be incarcerated, county jails in the USA have a pretty poor record on healthcare. They are run by the counties, not the states, and therefore it is open season on how they provide the services. Most [1] just contract to the lowest bidder private provider. These providers' jobs are to dispense the lowest amount of healthcare to the lowest amount of patients in order to maximize profits. Mostly providing only emergency care to those who are in immediate risk of death. Many also require the prisoners to use the funds provided by their family (for phone calls, letters, clothing, food etc) to pay to even put a medical request into the system in the first place.

In terms of dental, most county jails will only do tooth pulls, not any other type of dental work. They will not try to save teeth at all.

[1] some larger areas like Cook County have their own healthcare systems and can be somewhat more sophisticated and less constrained by monetary concerns

State prisons are usually only a smidge better than county. They’re a slight improvement in that they’ll give shitty prison dentures instead of just pulling all the teeth.

The other side of it is that prison is the first time many people get any dental work done at all so they cone in with large problems all ready.