Periodontist is a dentist that deals with the supporting structures of the teeth. They may perform simple cleanings to complicated bone surgeries. They perform bone grafting where indicated and do soft tissue grafts to treat gum recession. Most also place implants in the jaw for future restoration. They have usually 3 or more years of continuing education after graduating dental school, and most limit their practice to only periodontics.
Prosthodontist is a dentist that deals with simple to complicated full mouth restorations.
They may be crowns, fixed bridges, dentures, implant cases, or mixed implant and fixed bridge cases. They sometimes encompass the majority of the patients remaining teeth. They also perform needed restorative procedures, such as obturators, after removal of cancerous portions of the mouth. They have usually 3 or more years of continuing education after graduating dental school, and most limit their practice to only prosthodontics. These are the only official specialties in the field of dentistry.