Electronic apex locators (seen in Part 5) may be used as an alternative to a workinglength radiograph, assuming that a pre-operative film has been examined to obtain an estimated figure. These machines are capable of accurate measurement, and will give the location of the apical foramen. Apex locators are essential when a patient elects to have a minimum number of further radiographs taken. Many practitioners now use them routinely, particularly when the outline of the canal on the pre-operative film is indistinct or the canal curves towards or away from the radiograph beam. Modern apex locators work using different frequencies, determining the ratio between the different electric potentials proportional to each impedance. There is no longer any need to
dry the canal before use as they work in the presence of electrolytes. There is a distinct learning curve with their use, but it is usually apparent whether or not the measurement is in accordance with the original radiographic estimated working length. Errors may occur if there is a large coronal restoration or metallic crown causing a short circuit; if there is an open apex with a large periradicular lesion, or if there is a perforation. These are usually apparent and further measures should be taken. In use, a file is inserted into the root canal and an electrical contact is made with the shank of the instrument. The device has a second electrode, which is placed in contact with the patient s oral mucosa. A digital display or audible signal shows when the tip of the instrument reaches the apical foramen. There is no
doubt that modern apex locators can be even more accurate in length determination than a radiograph.
dry the canal before use as they work in the presence of electrolytes. There is a distinct learning curve with their use, but it is usually apparent whether or not the measurement is in accordance with the original radiographic estimated working length. Errors may occur if there is a large coronal restoration or metallic crown causing a short circuit; if there is an open apex with a large periradicular lesion, or if there is a perforation. These are usually apparent and further measures should be taken. In use, a file is inserted into the root canal and an electrical contact is made with the shank of the instrument. The device has a second electrode, which is placed in contact with the patient s oral mucosa. A digital display or audible signal shows when the tip of the instrument reaches the apical foramen. There is no
doubt that modern apex locators can be even more accurate in length determination than a radiograph.