A compressor wheel assembly comprises a compressor wheel mounted to a rotating shaft, extending through a bore provided along the rotational axis of wheel. Method of using such compositions for the cleaning and polishing of dental enamel, such methods including the step of applying such oral care compositions to the teeth of a user. The control bits are appropriately selected to provide the desired rotation-cum-reversal with just the 2n\xd7n array of multiplexers, and can themselves be generated by appropriate logic gates. The first and second memory cell transistor is provided in a first active region. According to the present invention, vibration-proof rollers are installed inside a roller frame instead of conventional rollers and the shock absorption bridge is fixed between the main frame and the roller frame, thereby absorbing an external shock in two steps and thus enhancing ride comfort. The third and fourth vertical support bars are spaced a substantially equal distance from the longitudinal axis.