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GLOSSARY OF TECHNICAL TERMS AND PHRASES. 299
of cavity walls, of angles of cavities and their terms of cavity description, together
with the rules of their use.
Non-cohesive gold. Gold in the form of foil or crystals in which the welding
property is obscured, usually by the condensation of some gaseous substance upon
it, or a film of a salt from the union of two or more gases.
Non-conductor. A substance which offers much resistance to the passage of any
form of energy, as heat or electricity. The term applied to a non-conductive substance
placed in a thin layer over the wall of a cavity nearest the pulp, to protect the pulp
against thermal shock.
Oblique ridge. A ridge running obliquely across the occlusal surface of the
upper molars. It is formed by the union of the triangular ridge of the disto-buccal
cusp with the distal portion of the ridge forming the mesio-lingual cusp.
Occlude. To shut; to close.
Occlusal, a. The surfaces of the teeth which come together when the jaws are
closed, are called occlusal surfaces.
Occlusal cavities. Cavities formed by decay beginning in the occlusal sur-
faces in the bicuspids and molars. They are all pit or fissure cavities.
Occlusal surface, n. That surface of a bicuspid or molar tooth that makes
contact with a tooth of the opposite jaw when the mouth is closed.
Occlusion. The act of closing or shutting. The closing of the teeth. "Correct
occlusion," the normal contact of the teeth of each jaw when the mouth is closed.
Odontoblasts. A layer of oblong cells that line the pulp chambers of the teeth.
They are the dentin forming cells. Processes from the odontoblasts pass through
the dentinal canals to the dento-enamel junction, and to the junction of the dentin
and cementum. See Fibrils of Tomes.
Odontoclasts. The giant cells which are the active agents in the absorption of
the roots of the deciduous teeth.
"One-two-three." "1-2-3." A local antiseptic composed of oil of cassia, 1
part, carbolic acid (melted crystals) 2 parts, oil of wintergreen, 3 parts. The oils
should be mixed and the melted crystals of carbolic acid added.
Operative dentistry. Those operations upon the natural teeth and the soft
parts connected with them that are usually performed by the dentist for their con-
servation, or cure of disease. It includes the employment of such drugs or remedial
agents as may be necessary.
Oral. Pertaining to the mouth, as Oral Surgery.
Order names, of instruments. A name given to any group of instruments which
designates their use, as excavators, pluggers, etc.
Ordinaries, as applied to cutting instruments. The usual hatchets and hoes
used by dentists in excavating cavities.
Orthodontia. The moving of malposed teeth to correct positions. The art of
regulating the position of malposed teeth.
Osmosis. The act of the passage of soluble salts through animal membranes.
Osteoblasts. The cells which form bone.
Osteoclasts. The giant cells which effect the absorption and removal of bone.
Outline eorm. In cavity preparation; the form of the area of tooth surface
included in the prepared cavity.
Outward inclination. Said of cavity walls when they diverge from each other
fn approaching the surface of the tooth.
Packer. See Plugger.