An added inertia resonant system (12) for a power toothbrush (10) comprises a drive shaft (16), a drive system (22), and at least one inertial weight member (24). The drive shaft (16) has a principal axis (26) that defines a center of rotation. The drive system (22) imparts a reciprocating motion to the drive shaft (16) about the principal axis (26). The at least one inertial weight member (24) couples to the drive shaft (16) and comprises a planar material having a complex shape balanced along an x-, y- and z-axis to enable the drive system (22) to achieve low power, high amplitude motion of the drive shaft (16) when placed under user loading. A method for providing added inertia in a resonant system for a power toothbrush is also disclosed.
