A Research Of Three Different Methods In The Preparation Of Molar's Curved Root Canals

Aim:The purpose of this study is to observe the effect of stainless steel K-files combined with Gates-Glidden bur (G-G bur) in the preparation of severe curved canal, in addition, to compare with the effect of rotary Ni-Ti Profile and stainless steel K-files singly used in it. It should provide the theory elements to use the files in clinic.Methods:497 severe curved canals (25-45degree) of 401 teeth were chosen from 389 pulpitis and apical periodontitis cases in clinic.with 15# K file insert in root and radiography with ODIS-1 type of oral digital imaging system, survey root length. According to the method of Schneider to measure the root canals curvature.All root canals divided into three groups randomly.Group A:Sequence used 1#,2# and 3#G-G bur to expand the canal orifices, processing each G-G bur with the cursor, each G-G bur drill down the depth lessen 2mm, all the root canal for crown present a funnel.Use stainless steel K file to prepare the root tip segment to the major point file 30#, the method is step-back technique. Every increaseing a file size the length decreases 1mm until 40# file, and shaped the root canal with 30# K file every time, keep the root canal unobstructed and smooth.Group B:Using rotary Ni-Ti Profile to prepare root canal by step-down technique. Profile. OS (0.05-0.08) for the root canal of crown segment, and Profile.06 (0.06) to prepare the root canal of central segment, Profile.04(0.04)to prepare root tip segment.Group C:Using stainless steel K-files to prepare root canal by step-back technique. All molar's severe curved root canals were cleaned by ultrasound with medium power. Results:(1) comparison of average curvature pre-and post-preparation: comparison between groups:there was no statistic difference (P>0.05) in Group A, B, and C before preparation; Group A and B have no statistic difference (P>0.05) post-preparation, however, Group C showed a greater change compared to group A and B in average curvature (P< 0.05). comparison in each group:the difference of Group A and B have a statistical significance (P<0.01), while Group C in the opposite position. (2) average time of preparation:groups paired comparison:the difference between group A and B have no statistical significance(P> 0.05), in the opposite way, group A and C, group B and C displayed a statistic difference (P<0.05). (3) comparison of fracture instrument: interclass comparison revealed that differences between A, B, and C have statistical significance(P<0.05). Group B had the highest incidence rate of fracture, and Group A had the lowest one.(4) comparison of shaping ledge:the difference between group A and B have no statistical significance(P>0.05), however, Group C showed a significant difference to group A and B (P<0.05). Severe pain:Group C was higher than group A and B, but there were no statistic differences in three groups.Conclusion:Using the combination of G-G bur and stainless steel K-file to prepare severe curved canal have a similar alteration with rotary Ni-Ti profile in curvature, which lead to a nice shaping of root canal. Inversely after stainless steel K-file singly used, curvature of canal slightly changed, result in a shape below the mark; In efficiency of preparation, combination of G-G bur and stainless steel K-file has advantages, same as rotary Ni-Ti profile, while stainless steel K-file singly used is in the backward place; Rotary Ni-Ti profile have a higher rate of fracture instrument than stainless steel K-files; it is easier for stainless steel K-file singly used to shape a ledge during preparation, and to occur severe pain after preparation.