occlusion:
    how the upper and lower teeth come together
onlay:
    laboratory-produced restoration covering the cusps of a tooth
oral and maxillofacial surgeon:
    a specialist who deals with the diagnosis & surgical treatment of diseases, injuries, and deformities of the mouth and supporting structures. Generally requires four additional years of training after dental school
oral cavity:
    the mouth

oral hygiene:

    the process of maintaining the cleanliness of the mouth
oral surgery:
    operations on the mouth; for example, extractions, removal of cysts or tumors, and repair of broken jaw bone

orthodontics:

    dental specialty that treats misalignment of teeth

overdenture:

    denture that fits over tooth roots or dental implants