A simple model to demonstrate the electronic apex locator

To describe and evaluate a newly developed model for demonstrating and teaching the use of electronic apex locators. A phantom model, master jaw model and extracted human teeth were used to construct the demonstration model with alginate impression material as the periapical conductive medium. The model was validated in a series of length determinations with apical foramina enlarged to 0.20, 0.30 and 0.45 mm diameter, and the stability of the model was evaluated up to 45 h after construction. All evaluations were conducted with the Root ZX apex locator with 2.65 and 5.25% NaOCl in the canals. Most length measurements were within 1 mm of actual root length (range: -2.2 to +0.21 mm) and did not change significantly over 45 h for teeth with foramina of 0.3 mm or less. Measurements for teeth with wide (0.45 mm) apices were stable up to 28 h. NaOCl concentration did not significantly affect the readings. A simple, inexpensive model can be manufactured from plastic dental jaws, natural teeth and alginate impression material to demonstrate electronic working length measurement. The model is stable for many hours and provides consistent results with different concentrations of NaOCl in the canal and various apical diameters. The model is a useful teaching aid but needs further evaluation and refinement before use in research applications.