1990 年 10 巻 4 号 p. 421-428
The shaping of straight and curved canals produced by rotational instrumentational techniques was evaluated in 22 human molar root canals which were prepared in vitro. The technique for rotational instrumentation featured only clockwise rotations. The results were collected from pre-and postoperative radiographs as well as from scanning electron microscopic analysis of longitudinally ground sections of the roots and of the enlarging instruments. Each preparation was evaluated in terms of its curvature, flow, taper, apical design, and wall surface appearance. The instruments were examined for signs of physical deformation. Rotational techniques in straight canals did not alter the original shape of the canal. The results in moderately curved canals were inconsistent. The results of apical misshapings, perforations, and poor flow in severely curved canals were consistent. The presence of smear layer, debris, and instrument striations on the walls of the canals were observed regardless of the type of canal. Enlarging instruments showed areas of unwinding, blunting, and remaining dentin chips. This study has shown that the reaming technique is reliable only in shaping straight canals. In curved canals, the deleterious effects of reaming on the shape of the preparation were evident. This study suggests that the rotational techniques should be used discriminately as it not only significantly alters canal curvature but it also causes the physical deterioration of the enlarging instruments regardless of the type of canal they were used in.