（单词翻译:单击）
Rest Position - a position the jaw1 adopts when at rest with the lips lightly together.
Reticular fibres - are fine type III collagen fibres forming a net-like supporting framework or reticulum. They are found around small blood vessels2, nerve cells, muscle fibres and in particular beneath epithelial membranes3 as part of thebasal lamina.
Reticular formation - in the central core of the medulla, it consists of several structures, including the periaquaductal grey. The reticular formation integrates information from many sources and influences sensory4 motor and autonomic activity. It is involved in aversive drive (behaviour which is an instinctive5 turning away from the unpleasant).
Retinoic acid - a product of retinol(Vitamin A) which binds6 onto cell membranes and controls cell division and differentiation7 through gene8 expression.
Ribosomes - - structures in the cy lasm of cells which attach onto messenger RNA. At the ribosome, the code of nucleotides on the mRNA is translated into a series of aminoacids.
RNA - Ribosenucleic acid - seenucleic acids.
Root resorption - resorption of cementum and underlying9 root dentine by osteoclasts. Temporary zones of root resorption may occur during orthodontic tooth repositioning. More extensive and irreversible root resorption may occur if the root becomes ankylosed.
Rugae - raised ridges10 of epithelium, each with its core of lamina propria, found on the anterior11 wall of the hard palate.
