Neglecting to clean the chuck for a long time is very dangerous because wax, gypsum, etc., accumulates in the chuck and the bur is caught insecurely, causing a run-out. In order to minimize the risk of causing chuck malfunction, please do regular maintenance as follows.
Open the ring and turn the chuck counterclock wise with provided spanner wrench to remove the chuck.
Clean the chuck insertion area of the handpiece with a cotton swab. Please do not conduct air blowing as derbis will lodge into the bearings, which results in heat generation and early abrasion of bearings.