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 dominant.

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 attachment 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 molecule adenosine triphospate (ATP) via the electron transport system . See also Anaerobic 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 enzyme 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 indicator 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 differentiate 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 assessment 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 aerobic 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

Angiogenesis - the development of blood vessels - a key event in embryology and healing.

Ankylosis - bony fusion of the two surfaces of a joint to each other, which prevents movement. Ankylosis of the tooth root to its bony socket may causes root resorption.

Antibacterial - inhibiting the growth of bacteria.

Antibodies -are proteins called immunoglobulins which circulate in the blood and body fluids. They bind specifically to antigens that have induced them. Antibodies are able to inactivate bacterial toxins, viruses and help phagocytes to engulf whole bacteria. They have a vital role to play in the bodies immune response to foreign proteins.

Antigens - proteins, usually foreign, which cause the bodies defense system to produce an antibody. Antigens may be food proteins, bacteria ,viruses or protozoa or cells from another individual(transplant).

Antrum - a hollow cave or SINUS, inside the maxillary bone which is lined by respiratory epithelium.

Apatites- a family of calcium phosphate salts which are found in hard tissues like bone, teeth and shells.

Apoptosis - death of a cell which is programmed by a set of specific genes. Apoptosis of chondrocytes allows osteoblasts to attach to their calcified matrix, and the epithelial cells forming webs between the fingers to die.

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

Artificial mouth - a laboratory device for keeping bacteria growing in a controlled environment It allows for observing bacteria and their growth under different experimental conditions.

Ascorbic acid - or Vitamin C is a dietary requirement for the proper formation of collagen. Deficiency causes scurvy.

ATP - adenosine triphosphate - ATP is a convenient packet of energy used by both animals and plant cells. The energy in ATP is stored in its three negatively charged phosphate groups which are held close together, in spite of their repulsion for each other. This energy, multiplied many hundreds of thousand of times, for each cell is able to move our muscles, transport molecules across membranes and power all the cells other energy requirements. Once the energy has been used the ATP molecule now only has two phosphate groups. It needs energy now from either aerobic or anaerobic respiration to charge it up again, a process known as phosphorylation. Large stores of ATP are not kept as it is highly reactive. The long term storage of energy in animals is in carbon rich molecules, such as glycogen or fatty acids. In plants energy is stored as starch.

Attachment, see epithelial-attachment

Autocrine; cell messengers which are produced by the cell itself and regulate the expression of genes .

Autonomic nervous system - controls routine body functions such as gut activity, respiration, blood pressure and heart rate. There are two main divisions the sympathetic nervous system and the parasympathetic system.

Axon - the extension of a nerve cell, as a thin tube which may be as long a metre or a few short microns in length. The axon, like the cell body is able to depolarise and carry impulses along its length. The impulses from one axon to another nerve cell are transmitted at a synapse. Axons may be myelinated or unmeyelinated, and they may vary in diameter. Thicker, myelinated axons transmit impulses faster than thins unmeyelinated axons.