Clean lime scale buildup from a Moen showerhead by removing the fixture from the wall pipe, immersing it in distilled white vinegar overnight, scrubbing with an old toothbrush, reinstalling it and running cold water through it for a few minutes. The acidity of the vinegar dissolves the mineral deposits without harming the finish of the showerhead.
Remove the showerhead by grasping it where it joins the wall pipe and turning it counterclockwise. If it does not turn easily, wrap a rag around the chrome and use a wrench to loosen it. If the showerhead and pipe are a single unit, leave it in place, and fill a large plastic bag with vinegar to submerge it. Secure the bag with a rubber band and clean the fixture the next morning. Place a removable showerhead in a pot, and add vinegar to cover it.
Scrub with the brush to remove any remaining surface deposits, and insert a toothpick into the holes to loosen any accumulations there. Rinse in cold water to remove the vinegar.
Wrap Teflon plumbing tape around the threads of the wall pipe and screw the showerhead back in place. Turn the shower control knob to cold, and turn on the water to blast away any remaining mineral deposits. Check around the joint for water leaks, and tighten the showerhead if necessary.