Endosteum - a layer of bone forming cells, osteoblasts which covers the entire surface of the internal aspect of cortical and spongy bone, separating it from the surrounding connective tissue. see also bone membrane.

Endothelial cells - the epithelial cells of the endothelium which lines blood vessels. The cells are flattened18 into a pavement stone shape and are usually two or three layers thick.

Endotoxins - the contents and cell wallsof dead bacteria which may be toxic to the host.

Enkephalins - similar in structure and action to endorphins.

Environment - describes the surroundings in which organisms live. Some physical features of an environment are fairly stable, like trees, rivers, mountains, houses, soil, teeth. Some physical features are changeable, like wind, water, light, pH, food supply. Others features are less predictable, such as the balance in the community of collaborators, competitors and parasites20. All forms of life including bacteria in the mouth, have an environment, which has an important influence on their survival. Successful organisms manage to exploit their environment to the best advantage or to adapt to it, perhaps only after several generations, if it becomes a serious challenge to the species.

Enzyme21 - a protein that controls and helps a chemical reaction to take place, but is not used up in the process. Usually each enzyme is specific for a particular step in a reaction. Enzymes are sensitive to their environment, especially to excessive temperature or pH.

Epidermal1 growth factor - a cytokine that stimulates epithelial cell proliferation.

Epinephrine - a neurotransmitter substance found at all adrenergic synapses (nor epinephrine or epinephrine). It is the most common neurotransmitter in the nervous system, in particular at ganglion cells of the sympathetic nervous system.

Epitaxy - the initiation of crystalformation in a saturated solution by providing a template against which crystal can form. There are specific sites on collagen molecules6 which appear to function as templates against which hydroxyapatite crystals form.

Epithelial attachment- the cuff of junctional epithelium which joins the gingival sulcus epithelium to the enamel of the tooth. Apical migration of the epithelium down onto the cementum may occur due to ageing or periodontal disease. Loss of attachment produces a periodontal pocket and a new habitat for anaerobic oral bacteria.

Epithelium - a layer of cells which forms alining for a tube or the covering for an organ or the whole body.

Eucaryote - a cell in which the genetic material is confined to the nucleus, in distinction to a procaryote in which the genetic material is dispersed throughout the cell. Other distinctions of eucarytoic cells are the presence of organelles such as the golgi apparatus, endoplasmic reticulum, lysosomes and mitochondria

Exocrine glands - the secretion passes intoa duct like sweat, saliva and mucous.

Extinct - a plant or animal species may entirely cease to exist. Recent examples are the dodo, a large flightless bird which used to live as recently as two hundred years ago, on the island of Mauritius. There are today many species of birds, flowers, fish, insects, large mammals, including certain types of whale, which are threatened with extinction, most as a result of human activity. Happily, the smallpox virus is about to become extinct

Extra cellular matrix - the supporting surrounding material of a cell including ground substance and fibres.

Extrinsic fibres - refers to those fibres of cementum which are continuous with periodontal ligament fibres. Extrinsic fibres have been trapped in cementum during its formation in order to anchor them. see also intrinsic fibres, and sharpey's fibres.

Exudate - the fluid plasma which leaks out of blood vessels due to an increase in capillary permeability. The increased permeability, is caused by histamine, and bradykinin, which are released in response to tissue damage. The formation of an exudate is the first step in the process of inflammation.