I believe that most dentists are only open 32 hours a week so that they don't have to provide benefits for their employees. It's an efficient, if uncompassionate, way of running a small business.
Medium/long term: Benefits really need to be a function of the government that taxes cover for all workers.
Health Care should be handled by a single payer.
My dentist is open 43hrs/wk.
Legally, 30hrs is full time for benefits, so it's hard to see any truth at all to anything you wrote.
Plenty of other businesses do hire lots of part time people and manage their hours in order to avoid obligations. If you don't think that is true, well, I don't even know where to start.