Portenier I, Lutz F, Barbakow F
Department of Preventive Dentistry, Periodontology and Cariology, School of Dentistry, University of Zurich, Switzerland.
Int Endod J. 1998 Mar;31(2):103-11. doi: 10.1046/j.1365-2591.1998.00116.x.
This study measured in vitro the displacement of natural canal centres in 18 human teeth before and after shaping by the step-back or Lightspeed techniques. Experimental roots (n = 9 per group), embedded in clear plastic, were cross-sectioned using a 0.1-mm-thick band saw at distances 1.25 mm, 3.25 mm and 5.25 mm from the apices. A stereo microscope was used to take 35 mm slides of the cut surfaces of the sectioned roots and canals. The slides of the uninstrumented canals were scanned into a computer and saved. Each sectioned root was then reassembled and the canals shaped by the step-back or Lightspeed technique. File size 40 and instrument size 50 were selected as the master apical file and master apical rotary for the step-back and Lightspeed groups, respectively. The 18 prepared canals were photographed, and the 35 mm slides scanned and computer stored as previously. This allowed the positions of the pre- and postinstrumented roots to be electronically superimposed for subsequent analyses. Displacements of the root canal centres before and after preparation were assessed in relation to the cross-sectional diameter of the files or instruments used. In addition, increases in cross-sectional area of the root canals after preparation were evaluated in relation to the cross-sectional area of the files or instruments used. Engine-driven nickel-titanium Lightspeed instruments caused significantly less (P < 0.001) displacement of the canal centres, so roots in the Lightspeed group remained better centred than those in the step-back group. The mean cross-sectional area after preparation in the Lightspeed group was significantly less (P < 0.001) than that recorded in the step-back group. Clinically, this implies less apical transportation and less dentine destruction with the Lightspeed technique than with the step-back technique.
本研究在体外测量了18颗人牙在采用逐步后退法或LightSpeed技术进行根管预备前后天然根管中心的移位情况。将实验牙根（每组9颗）嵌入透明塑料中，使用0.1毫米厚的带锯在距根尖1.25毫米、3.25毫米和5.25毫米处进行横断面切割。使用体视显微镜拍摄切割后的牙根和根管断面的35毫米幻灯片。将未预备根管的幻灯片扫描到计算机中并保存。然后将每个切割后的牙根重新组装，并用逐步后退法或LightSpeed技术对根管进行预备。分别选择40号锉和50号器械作为逐步后退组和LightSpeed组的主尖锉和主尖旋转器械。对18个预备后的根管进行拍照，并将35毫米幻灯片如前所述进行扫描并存储在计算机中。这使得预备前和预备后牙根的位置能够进行电子叠加，以便后续分析。根据所使用的锉或器械的横断面直径评估预备前后根管中心的移位情况。此外，根据所使用的锉或器械的横断面积评估预备后根管横断面积的增加情况。电动镍钛LightSpeed器械导致根管中心的移位明显更少（P < 0.001），因此LightSpeed组的牙根比逐步后退组的牙根保持更好的中心定位。LightSpeed组预备后的平均横断面积明显小于（P < 0.001）逐步后退组记录的横断面积。临床上，这意味着与逐步后退技术相比，LightSpeed技术导致的根尖偏移和牙本质破坏更少。
