All of the following are reasons for cone cut except:
Cone cut:

Cause: Cone of radiation not covering the area of interest, not using film holders. Correction: Make sure that the cone is properly centered over the area of interest and the film, both vertically and horizontally.
Cause: PID not properly aligned with the periapical film holder. Correction: Position the PID carefully. If a film holder with an aiming ring is used, make sure that the PID and the aiming ring are aligned.
Cause: Top of the film not immersed in the developing solution. Correction: Maintain the level of the solution in the processing tanks and make sure that the film is completely immersed during processing.
Cone of radiation not covering the area of interest
PID not properly aligned with periapical film holder
Top of the film not immersed in the developing solution
Not enough film showing below or above the crowns of the teeth