Determination of root canal curvatures before and after canal preparation (part 1): a literature review.

The continuing development of methods and materials for root canal preparation is resulting in enhanced preparation techniques with only minor alterations to the canal morphology. Improved evaluation methods are required for differentiated assessment of these innovations. One criterion for assessment of the preparation quality of curved root canals is preparation-induced straightening of the canal. The first canal curvature measurements served to divide teeth into different curvature classes. However, their actual execution represented mere angular measurement rather than root curvature assessment. This purely graphic method lacked precision, nor could it be readily applied to all tooth groups. Further developments of that method resulted in it being applicable to molars and to canals with multiple curvatures. Some years ago, the graphically determined curvature radius was added as a further parameter to measurement of the canal deviation angle, thus permitting a curvature to be correctly described for the first time in geometric and analytic terms. The first mathematically accurate description was presented by Dobó-Nagy et al., who correctly described the mean canal curvature in a two-dimensional image in concrete terms by means of fourth-degree polynomial functions. Recent developments in the application of microcomputed tomography of extracted teeth permit non-destructive three-dimensional assessment of root canal configurations. It remains to be seen whether this resource-intensive form of in vitro examination can assert itself.