The first teeth which are shed and replaced by permanent teeth. The first primary tooth comes in at about 6 months of age and the 20th and last primary tooth erupts at around 2 1/2 years of age. The primary teeth are replaced beginning usually at about age 6. Also called baby teeth, milk teeth, temporary teeth or deciduous teeth. (In Latin, decidere means to fall off or be shed, like leaves from a tree).
- Primary tumor
A tumor that is at the original site where it first arose. For example, a primary brain tumor is one that arose in the brain as opposed to one that arose elsewhere and metastasized (spread) to the brain. The original tumor is sometimes called “the primary.”
- Primitive neuroectodermal tumor
Ewing tumor of bone; extraosseus Ewing tumor (tumor growing outside of the bone); primitive neuroectodermal tumor (PNET), also known as peripheral neuroepithelioma; and Askin tumor (PNET of the chest wall).
In embryology, organ or tissue in its earliest recognizable stage of development. Take, for example, the thyroid primordium. The plural is primordia. Borrowed directly from the Latin primordium (to begin), derived from the Latin words primus (first) + ordiri (to begin). Known also as the anlage or rudiment.
- Primum non nocere
The Latin words for medical slogan “First do no harm,” a fundamental medical precept of Hippocrates (ca. 460-ca.377 B.C.).
- Principal investigator
In biomedical research, the person who directs a research project or program. The principal investigator (the PI) usually writes and submits the grant application, oversees the scientific and technical aspects of the grant, and has responsibility for the management of the research.