O

occlusion
the alignment and spacing of the upper and lower teeth when biting down

onlay
laboratory-produced restoration covering the cusps of a tooth

oral hygiene
the process of cleaning the teeth or mouth by removing food, germs, and plaque

oral (maxillofacial) surgery
operations on the jaws and mouth (e.g., extractions or removal of cysts)

orthodontics
dental specialty that deals with crooked and poorly aligned teeth

overdenture
denture that fits over the roots of a tooth or dental implants