Study On The Working Length Variations Of Root Canals During Mechanical Preparation

Objective:To evaluate the variations in root canal working length occurring during mechanical preparation stages and compare the relevant ability of three different frequently-used Ni-Ti rotary instruments.Methods: Sixty root canals selected from forty-three extracted human molars were randomly divided into three groups(n=20)and prepared using M3(groupM3)? Reciproc(group RP)and ProTaper(group PT)respectively.Their working length(WL)measurements were taken before,after coronal preflaring,and at the end of operation respectively.Using statistical method to analysis the changing regularity during different chemical-mechanical preparation stages and compare the relevant ability of the three different preparing instruments.Results: Statistically significant differences were found among each analyzed stage,which is observed in all groups(P<0.05),demonstrating that the reduction after coronal preflaring is more obvious than that after apical area preparation,and the greatest reduction was found when considering the the overall variation.When come to the comparation of different groups,we can find that groupPT shows significant difference considering the reduction after preflared and the overall recuction(P<0.05),while there is no obvious difference between groupM3 and groupRP(P(29)0.05).In the Preflared–concluded stage,there's only difference between groupRP and groupPT.Conclusions: The working length of the cannals presented significant reduction in extent during chemical-mechanical preparation,making it necessary to perform measurement in different stages of the instrumentation procedure,which can help clinicians control the apical limit during instrumentation and obturation.Considering the relevant ability of three different instruments,M3 and Reciproc can better maintain the initial root cannal working length compared with ProTaper in mechanical preparation process.