Darwinian medicine - an approach to the treatment of infective diseases which takes account of the co-evolution between the host and its parasite.

    Deciduous - from the Latin falling it applies both to trees which lose their leaves in winter and teeth which are lost to make way for the permanent set.

    Demineralisation - reduction in amount of mineral in tissue. This reduction occurs when the crystals of apatite are dissolved, usually in an acid environment.

    Dental abscess- an abscess around the apex of a tooth due to spread of infection from the pulp .

    Dental papilla - the condensation of dental mesenchyme which provides the stem cells from which ondontoblasts, cementoblasts and osteoblasts will form the pulp-dentine, cementum and alveolar bone of the tooth socket.

    Dentary - one of several bone which together made up the lower jaw in early reptiles. During evolution the other bones, the articular and quadrate bones, became part of the inner ear, and the dentary became the single the mandible of mammals.

    Dentine - a hard material like bone which forms the root and inner core of the crown of teeth. Unlike bone, dentine has fine tubules which contain the elongated process of odontoblasts, the dentine forming cells.

    Dentine-pulp - a term used to describe the unity between dentine and pulp, and to view it as one integrated tissue.

    Depolarisation - all cells have a slight difference in electrical potential between the inside and outside of the cell membrane. This difference is called a membrane potential and is due to a greater number of sodium ions (positively charged) outside the cell than inside. This imbalance is maintained by a membrane pump which pushes sodium ions out of the cell. Another pump also pushes potassium ions into the cell so there should be no difference in the balance of positive ions. But the potassium ions leak back out again, so there is always a potential difference across the membrane. Nerve cells have the ability to depolarise or reverse the membrane potential so that the inside is positive and outside negative. This reversal is short lived and is soon corrected, but it is long enough to influence the adjacent parts of the membrane and to be carried, like a wave, all the way along a nerve axon to the next nerve where it reaches a synapse The reversal is caused by a sudden opening of cell membrane gates which allow a flood of sodium ions into the cell. This flood causes the inside to become positive, but the gates are soon shut and potassium gates opened, which allows potassium ions to flood out and restore the membrane potential. This can all happen several times in one second, but after a while there is no flood, and the sodium pump has to get to work to build up enough pressure for the depolarisation to work again.