The influence of interfacial forces and duration of filing on root canal shaping

The aim of this study was to investigate the possible relationship between interfacial forces, duration of instrumentation and effectiveness of root c anal shaping by filing. All factors were standardised except the manner of manipulation of the files and the dependent variables (interfacial force an d duration of filing). The outcome measured was the final prepared canal sh ape. The study tested the hypothesis that if interfacial forces and duratio n of filing had predictive value for effective canal shaping, a relationshi p between them should be apparent. If it was not, it could be inferred that the remaining uncontrollable variable, "manner of file manipulation" had a dominating influence. 18 operators used a standard filing technique to ins trument a root canal each in single rooted teeth matched for anatomy. The t eeth were mounted in a custom-made transducer designed to measure laterally applied interfacial forces between file and dentine. The length of time ta ken with each instrument in the series was measured giving a total duration of instrumentation. The final canal shape measured by standardised "before " and "after" radiographic images of the roots was judged against an "ideal " canal shape calculated from the size of instruments used and based on the preliminary canal shape. Although some trends were revealed, no obvious re lationship was demonstrated between interfacial force, duration of filing a nd final canal shape. Operators clearly used a range of interfacial forces characteristic for each individual and for the different file sizes. Both l ight and heavy forces could produce a satisfactory canal shape. Use of ligh t or heavy forces did not obviously affect speed of preparation. Tactile di scrimination was not dependent on use of light or heavy forces. It was infe rred that the "manner of file manipulation" remained undefined and was prob ably the dominant factor influencing outcome of canal shaping.