EFFECT OF TIP DESIGN OF NICKEL-TITANIUM AND STAINLESS-STEEL FILES ON ROOT-CANAL PREPARATION

The purpose of this study was to evaluate the effect of modified and n on-modified tip designs of both stainless steel and nickel-titanium en dodontic hand files on root canal preparation. Root canals of mesial r oots of extracted mandibular molars were prepared using a quarter-turn -pull technique. The experimental design permitted comparison of the e ffects of nickel-titanium alloy construction or file tip modification alone, with effects when these two factors were incorporated into a si ngle file design. Transportation, centering ratio, and dentin removal were evaluated using a modified Bramante technique. Nickel-titanium fi les, regardless of tip design, remained significantly move centered an d demonstrated less apical transportation than stainless steel files a t size 25. When instrumentation was continued to size 40 apically with step-back, there were no significant differences in transportation in the apical or coronal sections. However, during instrumentation to si ze 40 with step-back, the combination of modified tip and nickel-titan ium alloy produced significantly more transportation and dentin remova l, as well as greater deviation from the center at the mid-root level than did other file designs. Thus, of the file design parameters evalu ated in this study, construction from nickel-titanium was most importa nt in defining canal configuration at small file sizes in the apical r egion. Although the combination of nickel-titanium and modified tip de sign resulted in more transportation at larger file sizes in the midro ot region, such alterations in canal configuration may be of little im portance clinically. Nonetheless, it is suggested that other factors, such as tactile sensation and instrumentation technique, should be con sidered as important as the type of alloy or tip design.