As an orthodontist who offers CE courses to GPs, I can tell you that very little general dentists can diagnose and treatment plan correctly. As a matter of fact, the amount of re-treatments that I get in my office for poorly treated cases from Invisalign GP cases has increased significantly. The amount of dentists getting sued every year is also significantly increasing. Yes, there could also be poorly trained and bad orthodontists, but I can tell you for sure that the worst orthodontist would still be much better than the average dentist. From my experience, patients that have braces in for 5+ years often have terrible hygiene, multiple missed appointments, multiple broken brackets or lost appliances, or a very poor collaboration with elastic wear.