Quadrate - one of the bones which together with the articular bones and the dentary, made/make up a reptile's jaw. In mammals the quadrate bone is incorporated into the middle ear as the incus.

Ramus - the vertical part of the mandible which supports the coronoid and the condylar processes.

Recombinant DNA - is DNA from a plasmid into which has been inserted a foreign gene. The plasmid is then introduced into a host cell, often the bacterium E.coli. The host cell may then express the foreign gene and secrete the desired protein. This process, commonly known as genetic7 engineering, has been used to great effect in synthesising proteins such as insulin and interferon.

Reduced enamel epithelium - (REE) the epithelium produced by the combination of the external and internal enamel epithelium. The REE remains covering the enamel crown until the tooth erupts when it fuses with the oral epithelium. The REE remaining on the enamel surface becomes the junctional epithelium.

Refined carbohydrates - natural carbohydrates from which other bulk such as fibres have been removed. Granulated sugar is a refined form of sugar cane.

Remineralisation - the replacement of mineral salts lost by de-mineralisation of a solid salt.

Remodelling - of bone refers to the constant removal by osteoclasts and rebuilding by osteoblasts The mass of bone can be controlled constantly by altering the balance between removal and rebuilding. The shape of a bone can also be altered by removing in one place and building somewhere else, without necessarily changing the total mass of a bone mass.