Patent ID: 7758342

Claim:
An apparatus to determine the proximity of a dental instrument to a tooth's apical foramen while the instrument is in the tooth's canal, the apparatus comprising: a handpiece that includes: a dental instrument operable to remove tissue from a tooth of the patient, a handpiece driver operable to drive the dental instrument via a mechanical coupling between the handpiece driver and the dental instrument, and an electrically conductive path that includes at least a portion of the mechanical coupling between the dental instrument and the handpiece driver; a signal generator coupleable to body tissue of a patient and to the handpiece, wherein, while the signal generator is coupled to the body tissue and the handpiece, the signal generator generates a divider signal that is used to determine the proximity of the dental instrument to the tooth's apical foramen, and that travels the electrically conductive path; and a microprocessor coupleable to the handpiece and that, while coupled to the handpiece and while the instrument removes tissue from the patient's tooth, senses a stimulation signal that includes the divider signal modified by the impedance of the patient's body, demodulates the stimulation signal to isolate the stimulation signal from electrical noise received via the electrically conductive path between the dental instrument and the handpiece driver, and compares the stimulation signal to the divider signal generated by the signal generator.