trepan

Trepan refers to a drill or cutting tool designed to remove a circular piece of material by cutting around its edge. In medical terminology, it is most closely associated with trepanation, a procedure in which a circular section of skull bone is removed to access the brain or relieve pressure. In woodworking and metalworking, a trepan (also called a hole saw or crown bit in some contexts) is used to create circular holes by removing a ring of material.

Historically, trepans have been used since ancient times. Evidence from ancient Greece and Rome and later medieval Europe shows surgeons using circular blades to open the skull, a practice that carried substantial risks. The development of anesthesia, antisepsis, and refined surgical techniques reduced the mortality associated with skull surgery; by the 19th and 20th centuries, craniotomy techniques had largely replaced crude trepanation outside experimental contexts. The word trepan originated from French trepan, with roots in Latin and possibly Greek terminology.

Today, skull trepanation as a standalone procedure is rare, with modern craniotomy techniques employing high-speed burrs and cutting tools to create a bone flap under surgical control. In non-medical settings, trepans remain in use as hole-cutting tools for wood and soft metals, with hollow, circular bits that remove a plug of material.

Variants include manual, crank-powered, and electric trepans; sizes and tooth configurations vary with material and precision needs. As with any invasive procedure, trepanation carries risks such as bleeding, infection, and neurological injury, and is performed only in appropriate clinical contexts.