Application of 21 mm nickel-titanium rotary files in root canal therapy for posterior molars

Objective To clinically evaluate the root canal preparation of posterior molars by 21 mm-length ProTaper nickel-titanium rotary instruments.Methods A total of 198 patients(198 posterior molars) requiring root canal therapy were randomly divided into tw o groups: 21 mm-length ProTaper nickel-titanium rotary files and crow n-dow n technique were used in PT group,and stainless steel K-files and step-back technique were used in K-files group.All the root canals were obturated with lateral condensation method.The quality of obturation was determined by radiographs.The pain reaction after root canal preparation and the root canal filling were recorded.Results The pain reaction after preparation therapy was less in PT group(3.03%) than in K-files group(18.18%).The reasonable filling ratio was significantly higher in PT group(92.53%) than in K-files group(85.16%).Conclusion Twenty-one mm-length ProTaper nickel-titanium rotary files can alleviate the pain caused by root canal preparation in the root canal therapy of posterior molars,and the satisfactory results of root canal filling can be achieved as well.