If the instrument head cannot be rotated to an up or down position, then most likely tooth debris has become cemented in the gap created when the shaft is extended (pull out position) to rotate the shaft. To loosen, spray inside of the gap with WD-40 or Brake cleaner, then lubricate with 3 in 1 oil. Forcibly loosen and resume using in both upper and lower position. This gap should be oiled bi-monthly to prevent build-up of debris.