Patent ID: 7452208

Claim:
A handpiece for measuring root canal length, comprising: an outer sleeve that is substantially non-insulating and has no insulating coating, a connecting device for coupling the handpiece to a control and evaluation unit, to a measuring circuit with a current source for measurement of root canal length and to a drive unit, an instrument carrier configured to receive a dental instrument, at least one transmission element within the outer sleeve that transmits force to move the instrument carrier so that the dental instrument received in the instrument carrier executes a rotating, reciprocating and/or vibrating working movement, a length measuring circuit portion disposed inside the handpiece and operable to transmit measuring signals for measuring length, a contact portion operable to establish a conductive path between the dental instrument serving as an electrode and the length measuring circuit portion, and an insulating portion that insulates the length measurement circuit portion and a contact device, through which a voltage is applied during measurement, from the outer sleeve, wherein the length measuring circuit portion comprises the conducting wire and the insulating portion comprises a wire sheath of non-conductive material, and wherein the contact portion comprises the contact device for use with a dental instrument having a conductive shaft, further comprising a sliding contact operable to establish a connection between the conducting wire and a head spindle of the instrument carrier.