Dentist ortodontist periodontist endodontics what's the difference?

Different specialist. Orthodontist specializes in braces endodontist specializes in root canal treatment periodontist specializes in gum diseases. A general dentist treats a wide range of oral and dental problems and is not limited to any one area.
Training/experience. All dental specialists are dentists first. 4yrs college + 4 yrs (8000 hrs) dental school. About 10% of all dentists then take an additional 2-5 yrs (4000-10000 hrs) training in one of the 7 specialty areas of dentistry and limit their practices to just that discipline. Orthodontist corrects malocclusion (bad bite), periodontist treats diseased gums, endodontist treats infected root canals.