in vitro investigation of the cleaning efficacy, shaping ability, preparation time and file deformation of continuous rotary, reciprocating rotary and manual instrumentations in primary molars

background. efficient canal preparation is the key to successful root canal treatment. this study aimed to assess the cleaning and shaping ability, preparation time and file deformation of rotary, reciprocating and manual instrumentation in canal preparation of primary molars. methods. the mesiobuccal canals of 64 extracted primary mandibular second molars were injected with india ink. the samples were randomly divided into one control and three experimental groups. experimental groups were instrumented with k-file, mtwo in continuous rotation and reciproc in reciprocating motion, respectively. the control group received no treatment. the files were discarded after four applications. shaping ability was evaluated using cbct. after clearing, ink removal was scored. preparation time and file fracture or deformation was also recorded. data were analyzed with spss 19 using chi-squared, fisher’s exact test, kruskal-wallis and post hoc tests at a significance level of 0.05. results. considering cleanliness, at coronal third reciproc was better than k-file (p < 0.001), but not more effective than mtwo (p = 0.080). furthermore, mtwo leaved the canal cleaner than k-file (p = 0.001). in the middle third, only reciproc exhibited better cleaning efficacy than k-file (p = 0.005). in the apical third, no difference was detected between the groups (p = 0.794). regarding shaping ability, no differences were found between reciproc and mtwo (p = 1.00). meanwhile, both displayed better shaping efficacy than k-file (p < 0.05). between each two groups, there were differences in preparation time (p < 0.05), with reciproc being the fastest. no file failure occurred. conclusion. fast and sufficient cleaning and shaping could be achieved with mtwo and especially with reciproc.