Endodontic retreatment in large and small straight canals

The change in original canal size and location after canal preparation and after reinstrumentation using a step-back technique was studied in small and large canals with less than 20-degree curvature. Teeth were mounted in jigs and then sectioned. The jig permitted the sectioned teeth to be repositioned exactly. Slides were made of the canal in the coronal, middle, and apical at the following intervals: before instrumentation, after instrumentation, and after reinstrumentation. The increase in canal area and the direction of movement was measured. The data were analyzed by ANOVA and Duncan's multiple range test. The results showed: (a) All canal areas increased after retreatment. The retreated apical canal increased in area significantly more (25.4%) than middle (4.0%) or coronal (3.0%) regardless of whether the canal was large or small. (b) The retreated canals tended to move in the same direction they moved after first instrumentation.