A replacement head for an electric toothbrush has a simplified drive construction and desired bristle carrier retention. The replacement head includes a tubular neck with a head at one end and a brush shaft disposed within the neck. An eccentric extension extends from the brush shaft parallel with the longitudinal axis and an axial extension extends parallel to the eccentric extension. The eccentric extension engages the bristle carrier to drive the bristle carrier. The brush shaft, including the eccentric extension and the axial extension, may be formed together as a single unitary piece. A pin may extend through pin retention openings in the head and a pin slot in the bristle carrier in a direction transverse to both the longitudinal axis and the carrier rotation axis to retain the bristle carrier on the head.