Bristle stiffness is varied by allowing a support beam (22, 66, 80) that carries the bristles (54, 55, 68, 82, 84) to undergo torsional movement in response to brushing action. Torsional movement is achieved by allowing the support beam to be disconnected to the brush head along at least portions of the length of the support beam. In particularly preferred embodiments, brushes employing the varying stiffness techniques are made with bristle sub-assemblies that have at least one row of bristles connected to a base string or similar structure that functions as a support beam. The base string can be connected across an opening in the brush, and is thus connected at its opposite ends, or it can be connected at any number of spaced intervals, the number and length of spacing being selected to achieve a desired degree of stiffness.