APICAL EXTENT OF ROTARY CANAL INSTRUMENTATION WITH AN APEX-LOCATING HANDPIECE IN-VITRO

Problem. The Tri Auto ZX (J. Morita Co., Kyoto, Japan) is a cordless e ndodontic handpiece with a built-in apex locator that is programmed to reverse the direction of rotation when the file reaches a predetermin ed apical level or when torque becomes excessive. Objective. nle purpo se of this investigation was to examine the apical extent of rotary ca nal instrumentation and the ability to maintain apical constriction wi th the Tri Auto ZX at different automated settings. Study design. In 6 0 extracted teeth, canals were measured to the apical constriction, fi rst visually and then electronically with the Tri Auto ZX; then they w ere instrumented with nickel titanium rotary files. For the instrument ation, the automatic apical reverse mechanism of the handpiece was set to 1, 1.5, or 2; these settings correspond to different distances fro m the apical foramen. Instrumentation was carried out apically until r otation was reversed by the automatic apical reverse function; the ins trumented length was then measured, and the canal was filled with gutt a-percha and sealer. The integrity of the apical constriction was asse ssed by exposing the apical 4 mm of the canal and observing the dentin -cementum junction. Paired t-tests were used to compare the visually m easured length, the electronically measured length, and the instrument ed length for each tooth. Results. On average, the electronically meas ured length was 0.54 mm shorter than the visually measured length (p < 0.05). When the automatic apical reverse mechanism's setting was 1, t he instrumented length was 0.1 mm shorter than the electronically meas ured length; when the setting was 1.5, the instrumented length was 0.3 6 mm shorter than the electronically measured length (p < 0.01). Resul ts were inconsistent when the setting was 2. Conclusion. Instrumentati on with the automatic apical reverse feature set at 1 consistently app roximated the apical constriction; however, the constriction was frequ ently enlarged.