according to the GPs i've shadowed they are licensed to do almost anything the specialists can, with the exception of a few oral surgery procedures and others (GPs can't apply general anesthesia). but most GPs dont have the right staff or equipment to, let's say, gives braces to someone. And if they did, they would still be held to the same standards as the specialists. Cost and time is also a huge factor. An endodontist may be able perform a root canal on someone in 20 min whereas a GP may take 1 hour or long, simply bc he/she is out of practice and/or does not have all of the best equipment (the specialists usually charge a bit more too). So from a business standpoint, most GPs stick to doing crowns, fillings, cleanings etc.