Functional Stiffness Characteristics of Toothbrush Bristles

¹ Metropolitan General Hospital, Western Reserve University School of Dentistry, Cleveland, Ohio

An analysis of individual bristle stiffness quality of toothbrushes was made. Approximate theoretical solutions showed that bristles which are simultaneously compressed and forced laterally have at least two distinct stiffness characteristics. Lateral stiffness to lateral loads depends on end compression forces and bristle physical properties. Lateral stiffness to endwise loads depends on lateral load, end force, and bristle properties. Stiffness to lateral loads is very small compared to stiffness to endwise loads, and controls brushing effectiveness.

An elastic definition, which depends on bristle forces and deflections, was used to prove that the Euler critical buckling load for slender columns is a satisfactory standard bristle characteristic which may be used as a design guide for bristle stiffness quality. This reference value depends on bristle material, cross-sectional shape, dimensions, type of load, and nature of end support. Toothbrush tuft stiffness is not predicted, but is easily obtainable as a summation of the theoretical stiffness qualities of individual bristles.