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J Clin Dent. 2004;15(1):22-7.

Bristle end-rounding in toothbrushes: a comparison of different evaluation techniques, bristle position and viewing angle.

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Department of Operative Dentistry and Periodontology, University School of Dental Medicine, Charité-Universitätsmedizin, Berlin, Germany.



Numerous studies using various evaluation techniques have shown substantial variations in the degree of bristle end-roundness of commercially available toothbrushes. The aim of the present study was to compare the effects of the examination angle, the bristle selection and two analyzing techniques assessing bristle end-rounding measurements.


The study was conducted in two parts. Part One used five randomly selected tufts from 20 brushes that were scanned with an electron micrograph (SEM; 45x) at two viewing angles (45 degrees and 90 degrees). Those bristle tips that were visible on both viewing angles were then judged by 1) a direct comparison to a grading scale, and 2) a shape factor (SF) analysis. In Part Two of the study, SEM images of five bristles from different tufts obtained from 40 brushes were taken at a viewing angle of 45 degrees, and five bristles from different locations within a tuft were also judged by both the direct comparison to a grading scale method, and the SF analysis, to assess bristle location.


The SF values and the direct comparison percentage of rounded bristles did not differ because of the viewing angle (45 degrees or 90 degrees; p > 0.05; Mann-Whitney test), but differed significantly at various SF thresholds (percentage of bristles above or below a certain degree of end-roundness) when bristles from Part One were compared to Part Two (p < 0.01, adjusted chi-square-test). Location of the bristles from either the edge of a tuft or those located in the inner part had no effect on the assessments (p > 0.05). The results from the subjective direct comparison grading did not differ from those found with the SF analysis (p > 0.05).


SF analysis is a time-consuming method for assessing bristle end-rounding, and can be as accurately done by direct comparison to a grading scale. One viewing angle (45 degrees) of bristles from different locations within a tuft can also be used to accurately assess a brush's level of end-roundness.

[Indexed for MEDLINE]

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