Abstract: Abstract: Objective To observe the accuracy of estimating work length by direct digital panoramic. Methods 191 Root-Canal-Therapy-finished canals without symptoms in 3 months after treatment and with preoperative direct digital panoramic view were selected. Easy Dent 4 was used to measure the lengths and estimate the work lengths. The measurements were included into Group A, and the results measured by electronic apex locator Raypex4 (as standards) were included into Group B. The correlation and consistency between Group A and B were observed by SPSS18.0. Results The data of Group A was highly correlated with that of Group B: 95% confidence interval of error within 1mm between Group A and B was (-0.635,0.362). Conclusion Estimating the work length by direct digital panoramic is reliable, which can be used for preliminary estimate before root canal therapy.

Key words: work length estimate direct digital panoramic(DDP)