occlusion – lineup of upper and lower teeth surfaces when mouth is closed, also known as “bite”

onlay – prosthetic restoration that covers the occlusal (biting/chewing) surface of a tooth, but not the whole tooth
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operculectomy – surgical removal of the operculum

operculum – tissue flap covering partially or fully unerupted tooth

oral – referring to the mouth

oral and maxillofacial surgeon – specialist with at least 4 additional years of specialized training beyond the dental degree, diagnoses and treats oral diseases, injuries, deformities, defects, or other issues, including surgical treatments of the oral and maxillofacial areas

oral and maxillofacial surgery – surgical treatment of the mouth, jaw, and related areas, may include extraction, repair of defects or fractures, removal of tumors or cysts, and others

oral cavity – the inside of the mouth

oral hygiene – establishment and maintenance of habits designed to keep mouth, gums, and teeth healthy

oral pathologist – dental specialist who focuses on study, diagnosis, and management of diseases affecting the oral cavity, jaws, and other connected areas

oral pathology – the study, diagnosis, and management of diseases affecting the oral cavity, jaws, and other connected areas

orthodontics – dental specialty concerned with the diagnosis, prevention, and treatment of malocclusion and other neuromuscular or skeletal abnormalities of the orofacial structure

orthodontist – dental specialist who focuses on the diagnosis, prevention, and treatment of malocclusion and other neuromuscular or skeletal abnormalities of the orofacial structure

orthognathic – refers to the functional relationship between the mandible and maxilla (upper and lower jaws)

osseous – refers to bone tissue

osteoplasty – surgical procedure that modifies bone structure

osteotomy – surgical procedure involving the cutting of bone structure

overbite – orthodontic issue, when upper front teeth significantly overlap the lower