Abductors - muscle taking a limb or the jaw away from the body.

Acetyl choline - Aneurotransmitter substance found at all cholinergic synapses including those of motoneurones at the neuromuscular junction.

Acini - the secreting units of a gland. Each acinus is a sack-like structure, lined by secreting cells. The sack opens out into a tubule.

Acute necrotising ulcerative gingivitis -abbreviated to ANUG- a painful and destructive infection of the gingiva caused by a shift in the normal balance of bacteria in the gingival sulcus, in which fusobacteria and spirochaetes become dominant6.

Adapt- to modify in response to change. When used in regard to evolution, it means that some structure or behaviour of an organism may over time, appear to change in response toa new threat or opportunity in the environment. The bacterium which causes tuberculosis has developed certain strains which have adapted to the antibiotics used to treat the disease which is now becoming more difficult to treat.

Adductors - muscle bringing a limb or the jaw towards the body.

Adhesion - to form a chemical bond of attachment10 between two surfaces (see Ligand and lectin).

Adrenalin - see epinephrine.

Aerobic respiration -a type of respiration which requires oxygen and in which glucose is broken down to release energy in a series of steps. The end products are carbon dioxide and water. Step 1;glucose is broken down to pyruvic acid in the cell cylasm with the release of 4 hydrogen atoms. Step 2; pyruvic acid is oxidised to acetylcoenzyme A (acetyl CoA), with the release of 4 further hydrogen atoms. Step 3; In the KREB cycle, 16 atoms of hydrogen are released. At all stages the hydrogen atoms are used to form the high energy molecule15 adenosine triphospate (ATP) via the electron transport system . See also Anaerobic16 respiration.

Affected dentine - dentine which has been demineralised by acids in advance of invading caries bacteria. A distinction is made between affected dentine and infected dentine, because affected dentine is able to remineralise and should not be removed during cavity preparation.

Aggregate - clumps or collections of small particles or bacteria .

Alkaline phosphatase - an enzyme14 which removes phosphate groups from organic compounds at an alkaline pH. It is found in high concentrations in matrix vesicles which are about to form new bone mineral. Alkaline phosphatase activity is a good indicator20 of bone formation.

Alveolar bone - bone which develops around the roots of the teeth to hold them firmly in place. See gomphosis. If the teeth are extracted, the alveolar bone resorbs away. Alveolar bone consists of both trabecula and cortical types of bone.

Ameloblasts- cells which differentiate1 from ectoderm and secrete enamel during tooth development.

Amino acids - building blocks of proteins containing a carboxyl group (COOH) and an amino group(NH2) both attached to the same carbon atom . The difference between the 20 common amino acids lies in the nature of a side chain the "R" group. Each amino acid, has a code of three adjacent nucleotides on the DNA molecule. Amino acids are joined together by peptide bonds to form polypeptides and proteins.

Amorphous calcium phosphate - a non crystalline form of apatite which may form as much as30% of bone mineral.

Amygdala- part of the limbic system, which seems to provide the emotional assessment8 of a new sensation with the memory of a similar sensation.

Anaerobic respiration - the first step in the production of ATP is to break down glucose. This process of glycolysis is a 10 step series of reactions leading finally to the smaller molecule pyruvate. The energy derived from this process is a hydrogen ion and an electron, which are both placed onto the carrier molecule as nicotinamide adenine dinucleotide (NADH+). As the pyruvate and NAD H+ are produced they could move into the mitochondria, for the nextstage of aerobic10 respiration, provided oxygen is available. If there is no oxygen, NAD H H+ is used in a process of substrate phosphorylation to form ATP. But the pyruvate builds up. It is then converted to lactic acid and removed to the liver. If lactic acid is not removed fast enough it causes muscle weakness and pain. Anaerobic glycolysis does not produce a high yield of energy. There are still high energy bonds remaining in the pyruvate and there is no benefit from the large yield of ATP made possible by the electron transport system in the mitochondria