Root curvature: differences among dental morphotypes and modifications after mechanical instrumentation

Background:This study was designed to describe a method for measuring root curvature of extractedteeth, compare root curvature of four different dental morphotypes before mechanical instrumentation, andmeasure root curvature after mechanical instrumentation.Methods:Fifty-five maxillary (14 central incisors, 13 lateral incisors, 14 cuspids, 14 premolars) extractedteeth were analyzed. Measurements were recorded on the horizontal plane at the most apical point of thecemento-enamel junction (CEJ). A 4 mm wide root portion on the buccal aspect was selected and recordedon this plane. A digital scanner traced the circle coinciding with the profile of this root portion and calcu-lated its radius, arc, chord, and arrow (i.e., the perpendicular bisector of the chord). Since root curvatureis the inverse of the radius (1/r), the radius was related to root curvature; the arc to the mesio-distal dimen-sion of the root portion; and the reduction of the arrow to root flattening after mechanical instrumentation.The measurements were recorded four times: before treatment (baseline), after polishing, after a first rootplaning, and after a second root planing. The radii of each dental morphotype (upper central incisors, upperlateral incisors, upper canines, upper premolars) recorded in the first measurement were calculated and usedfor the statistical analyses: one-way analysis of variance (ANOVA) test and the Tukey multiple comparisonmethod were used to study the curvature. The measurements of the radius, the arc, and the arrow at thefour times were used for the statistical analyses: the two-way ANOVA test and the Tukey multiple comparisonmethod were applied in the study of the root modifications after mechanical instrumentation. The accuracyand reliability of the method were also evaluated.Results:The mean radii of the four dental morphotypes were: central incisors: 3.613±0.258 mm; lateralincisors: 2.558±0.256 mm; canines: 2.822±0.238 mm; and premolars: 2.321±0.179 mm. The statisticalanalyses revealed differences among central incisors, canines, lateral incisors, and premolars. There wasno statistically significant difference between lateral incisors and premolars. Regarding the root modifica-tions after mechanical treatment, the radius did not show statistically significant differences in any of thecomparisons. The arc and the arrow did not show significant differences between baseline and polishing,while they did show significant differences after the second root planing.Conclusions:This study indicates that: 1) the method of measuring is accurate and reliable; 2) there arestatistically significant differences among the root curvatures of different dental morphotypes; and 3) polish-ing did not modify the root. A vigorous root planing did not modify root curvature, but it did reduce themesio-distal dimension and flatten the root surface slightly.