I encourage anyone that disagrees with the idea of oral health practitioners (or dental therapists) to look into the Dental Health Aid Therapists in Alaska. I was fortunate enough to do an Indian Health Service externship at the Alaska Native Medical Center's dental clinic last summer in Anchorage, so I was able to see firsthand the impact that the lack of dentists in an area has on the oral health of that population; and the Dental Health Aid Therapists are able provide basic dental care to these people.
Many dentists, after busting their tails through undergrad and then dental school, choose to work in private practice in non underserved areas. While there is nothing wrong with that, it does not help the underserved populations. So while it may seem that these practitioners may pose a threat to dentistry, they will only be in areas that need them and will only perform the most minor of procedures. As long as they're trained well, they will help meet some of the dental needs of underserved Americans... and I see nothing wrong with that. Like BillytheEchidna said, if more dentists were willing to practice in these areas, this would not even be an issue.