Abstract: PURPOSE: To study the correlation between apical foramen area and accuracy of PropexII electronic apex locator under destroyed apical constriction. METHODS: Forty extracted teeth with single straight root canal were ground down 1 mm in the root tip and placed in 2% liquid agar gel injected into Castro model. The length of root canal was measured by PropexII electronic apex locator. The difference (ΔL) between the electronic length (LP) and actual length (L) was calculated. Imaging of apical foramen was recorded under microscope and apical foramen area (S) was measured by image processing software Photoshop CS. SPSS 22.0 software package was used to analyze the linear correlation and regression. RESULTS: With ±0.5 mm as the allowable range, all value of ΔL was positive. The precise rate of PropexⅡ was 52.5% when apical constriction was destroyed. There was a linear relationship between S and ΔL (S=0.04+0.11×ΔL,R=0.903）. CONCLUSIONS: The accuracy decreases when apical constriction is destroyed. The accuracy is worse when the apical foramen area is larger.

Key words: Electronic apex locator, Apical constriction, Apical foramen area