Ecological balance  - astable balance in the numbers of each species in an  ecosystem. In the ecosystem of the mouth this balance is brought about by competition and cooperation between the different organism and the hosts defences which tend to control population size.

Ecosystem - a stable environment in which live a large number of different forms of life, each affecting the other. Example are a forest, desert, tidal area, soil, oral cavity, gut.

Ectoderm - the outer of the three cell layers which form, as the clump of early embryonic cells begins to differentiate. The ectoderm will form the epidermis7 of the skin and the nervous system. The other two layers are the mesoderm and the endoderm.

Ectomesenchyme - a name given to dental MESENCHYME which reflects its partly ectodermal origin.

Eicosanoids - are a class of hormones which are all made from phospholipids. They include prostaglandins, thromboxanes, and leucotriens.

Elastic fibres -are long, thin, ribbons-like fibres, sometimes even sheet-like. They are composed of a central core of elastin, a rubbery protein, surrounded by glycoprotein microfilaments. Elastin is found all over the body but particularly in the walls of blood vessels and in our vocal chords.

Electron - the negatively charged elements of an atom which circle the nucleus. If an electron is lost the atom becomes a relatively positively charged ion. It has been ionised.

Electron Transport System- Hydrogen ions produced during the 3 preparatory steps of aerobic respiration are carried by nicotinamide adenine dinucleotide (NAD). The hydrogen ion plus one electron form NADH, which is taken to the electron transport system. This transport system is run by a series of 5 molecules. The first, removes the two electrons from NADH,( one comes from the hydrogen atom, leaving behind a hydrogen ion). These two electrons, bounce from the first molecule in the transport system to the second, third, forth19 and then last one, cytochrome oxidase, which finally places the electrons onto oxygen gas O2. The electron rich oxygen atoms are attractive to the hydrogen ions and they combine to form water. (Oxygen in the process of aerobic respiration acts therefore as an electron acceptor). In the process of bouncing "downhill" the electrons have released sufficient energy to power up a small battery. This battery has been made by pumping hydrogen ions out of the inner membrane of the mitochondria. The collection of hydrogen ions outside, piles up and their electrical pressure mounts. They want to get back across the membrane, and are allowed, one at a time to pass back through the enzyme ATP synthase. This enzyme sits like a water wheel in the cell membrane, turned by the passage of hydrogen ions. Its turning wheel builds an ATP molecule in every turn. The wheel may be going at about 200 revolutions per second, powering the synthesis of an ATP molecule with each turn. ATP formed in this way takes a while but can be sustained to fuel the body during aerobic exercise. When the demand for power exceeds this rate, the cells have to rely on anaerobic respiration.

Electrostatic - a force generated by differences in electric charge of two particles.

Enamel prisms - rod-like bundles of hydroxyapatie crystals which are orientated at right angles to the tooth surface. Each prism can be traced from the outside of the enamel all the way to the dentine junction.

Enamel - the outer layer hard layer which covers the dentine around the crown of a tooth. Enamel consists of closely packed crystals of hydroxyapatite with very little organic material. A recognisable unit of structure in enamel is the enamel prism.

Enameloid - a type of enamel found in fish and reptiles in which the enamel prisms are haphazardly arranged; in contrast enamel prism are parallel to each other and orientated at right angle to the tooth surface.

Endocrine glands - the secretion passes into the blood stream, like insulin, epinephrine.

Endoderm - the inner of the three cell layers which form, as the clump of early embryonic cells begins to differentiate. The endoderm will form the gut system and its associated organs. The other two layers are the mesoderm and the ectoderm.

Endoplasmic reticulum - a system of inner cell membranes which is continuous with the nuclear membrane. It transports products of cell synthesis to the golgi apparatus. Described as rough endoplasmic reticulum when there are many ribosomes attached.

Endorphins - a neuropeptide which has specific binding sites on nerve cells called opiate receptors. When the receptor is activated16 by endorphins or morphine it reduces the excitability of the post synaptic cell. Peptide receptors are also found on lymphocytes which suggest an association between neuropeptides and the regulation of the immune response.