Abstract: Objective: To evaluate the role of standardized manipulation in endodontics by comparing the quality of root canal filling before and after standardized manipulation training, according to the digital radiography. Methods: Using stratified random sampling method a total of 598 endodontically treated teeth with 1208 roots, which were completed by four dentists, were retrospectively studied. The quality of root canal filling was analysed radiographically according to the length, density, and taper of root fillings, meanwhile the presence of overfilling and ledge formation was recorded for each root canal. Results: The overall percentages of adequate teeth filling and root canals filling after taking standardized manipulation training were 64.9% and 72.6% respectively, which were significantly higher than those before taking standardized manipulation. Meanwhile, regardless of anterior teeth, premolars or molars, the percentages of adequate teeth filling and root canals filling after taking standardized manipulation were significantly higher. The overall rate of ledge formation before taking standardized manipulation were 20.7%, which was declined to 14.2% after taking standardized manipulation. The difference between the two groups was statistically significant. Conclusion: The quality of root canal filling was improved greatly after taking standardized manipulation.

Key words: Root canal obturation, Ledge formation , Standardized manipulation