Dentists and doctors are not all of one mind about treatment effectiveness or necessity, so the tails of the bell curve matter. There may very well be some small percentage of dentists who believe that procedure X is beneficial in almost all cases. They might be quacks, but most quacks I've met believe what they are selling (even if they are wrong.)
If there also is a government program that reimburses for X in almost all cases, then you could see the emergence of clinics that "exploit" the rule even if everyone involved believes they are behaving ethically.
There are feedback loops that then exacerbate the problem- for example a successful clinic might bring on additional dentists, who despite misgivings will be influenced by existing practice at the clinic and begin self justifying the procedures to conform to the senior partner. After all, they clearly know what they are doing, right?
While I have no idea if that's what happened here, it is well with in the realm of possibility. The government does bear some responsibility to ensure that thier programs and rules provide sufficient oversight and feedback to keep fringey participants within the bounds of what the government considers acceptable.