Often, a plastic(composite/teflon/nylon) gear is used because it has damping properties. Smoothing the shock load from a single cylinder piston stroke on to the pump it is spinning . They can even offer increased life over an aluminum or steel gear, because often the softer part will imbed particulate and it will act as an abrasive against the harder material.
Also, SquadraCorse, that bike looks great, love the Martini team colors. Makes me want to Johnny Player Special my black SM.