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nasion A cephalometric landmark on the bony profile at the junction of the frontal and nasal bones.

natural head position A standardized orientation of the head, assumed when the subject focuses on a point in the distance at eye level. It is used for clinical examination of the face by anthropologists, orthodontists and maxillofacial surgeons.

neutroclusion Normal mesiodistal occlusal relationships of the buccal teeth.

nightguard A removable plastic appliance worn at night to prevent deleterious effects of nocturnal parafunctional activity (i.e., clenching, bruxism).  See mouthguard.