Just to add some balance to the picture, as Taxhelper says, HMRC has focused on various sectors over many years, with a view to getting workers onto PAYE if they really are employees.
However, you're unlikely to be in any trouble when you are doing what thousands of other dentists do. HMRC are likely to change things by giving new orders to the companies that "employ" you.
Keep good records of all that you receive and spend and find a recommended advisor to help you with recors/accounts and tax return.