W&H Perfecta 900 Instructions For Use Manual page 35

15. Cleaning / changing the chuck LA-66 (optional)
Chuck key, spanner, cleaning brush are located on the underside of the handpiece holder .

Turn the front sheath clockwise up to the limit stop .
Unscrew the tip anti-clockwise .

Insert the chuck key up to the limit stop in the chuck and unscrew anticlockwise .
Hold the shaft firmly with the spanner .

Remove the chuck .
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