A Quantitative Method to Assess Bristle End Form in Toothbrushes

Objectives: The aim of this investigation was to predict the ideal end rounding geometry of powered toothbrush bristles. The quality end-rounding pattern of 6 commercially available powered toothbrushes was measured against this ideal geometry. Methods: Six commercially available electric toothbrushes, were selected; Blend-a-Dent Medic 2000tp, Braun, Oral B Ultra Plaque Remover (D9), Interplak NT-6, Philips Dental Logic, HP405, Sonicare PS-1, Teledyne Water Pik SR-100E. Tufts were cut from each head and 50 bristles were attached to microscope slides. A region of interest (ROI) of each bristle tip consisting of a square box together with a second ROI of the bristle outline created within the first were captured by a camera attached to a microscope linked to a computer running the Optimas image analysis programme. A macro was written so that the circularity = (Perimeter*Perimeter)/(Area) and the rectangularity = (area/area of bounding box orientated along major axis) of each individual bristle was processed with the data entered into a spreadsheet. Results: The geometrical ideal shape for circularity is 14.92 and rectangularity is 0.62. None of the bristles measured exhibited the ideal geometrical shape given by the macro for a rounded bristle. Within the selection of bristles (n = 50), from the six different powered toothbrushes there was variability away from this ideal shape. Disparity was least between those bristles associated with the Braun D9 and the Philips with regards to, circularity and rectangularity when compared to the other powered toothbrushes. Conclusions: This study demonstrated that the use of image analysis quickly identifies those bristles that stray from the ideal geometrical shape for end rounding. This method may be used as a quality control procedure in the manufacture of both manual and powered brushes.