stoggiemanI'm 99% sure dentists must be board certified by an exam called the NBDE, national board dental exam, and I know for certain that pharmacists do, considering my sister just sat for a two day national board certification exam so your argument is invalid and makes no sense. I hope you were trolling.
No, it is not mandatory that dentists be board certified to practice in the United States. They do need to be certified in their state of practice, however.
https://www.abgd.org/boardcertified.php Currently less that 1% of general dentists are certified by the National Board of General Dentists.
It also doesn't seem that pharmacists have to be board certified.
As for MDs, not all have to be board certified. But almost every MD practicing in a hospital is required by the hospital to have a board certification. All board certifications, whether for an MD, pharmacist, or dentist are optional, but MDs are the only ones who are required to hold certification if they want to practice in a hospital, their primary place of practice.