Elongation or lengthening of the teeth and surrounding structures results from under-angulation. When a vertical angulation error is made using the paralleling technique, the image moves in a vertical dimension (up or down) on the receptor. To correct this error the operator must increase the vertical angulation. In other words, for the maxillary arch, the positive angulation must be increased (PID pointing down); for the mandibular arch, the negative angulation must be increased (PID pointing up).
This error can also occur when using the bisecting angle technique. Often the error is caused by the x-ray beam being perpendicular to the long axis of the teeth, rather than bisecting the angle between the teeth and the receptor.