Occlusal wear - loss of enamel on the biting surface of the teeth due to the abrasive action of chewing natural unprocessed food.

    Odontoblast process - the extension of the cy lasm of an odontoblast which remains surrounded by dentine during tooth formation. The process is still an active part of the cell and contributes to the production of intratubular dentine in response to ageing, tooth wear or arrested caries.

    Odontoblasts- cells lining the dental pulp, derived from the dental papilla wich form the dentine of the tooth crown and root. New odontoblasts may become differentiated from less specialised pericytes in the pulp.

    Occlusal interference - contact between opposing teeth during chewing, which prevents the other teeth touching. In extreme lateral and protrusive positions of the jaw, this would happen in most dentitions and be of no concern. When occlusal interference occurs close to the area of maximum tooth contact, it may be troublesome.

    Oncogenes - genes which have the capacity if expressed to cause tumour formation.

    Organelle - a structures within a cell which has a specific structure or function, such as thenucleus, endoplasmic reticulum, golgi apparatus, lysosomes and mitochondria.. Cell organelles are a feature of eucaryotic cells.

    Osmotic pressure - Water tends to move towards dense concentrations of ions. Sugar solutions on the surface of exposed dentine cause water to be drawn out of the dentinal tubules causing which distorts the odontoblast causing pain.

    Osseous integration - a term used to describe the desired adhesion between an implant and the bone which holds it in place.