Abstract: A periodontal probe instrument for measuring the depth of the gingival sulcus and periodontal pockets. A probe extending from a handle of the instrument includes a transparent portion which is insertable into the periodontal pocket. An optical fiber extends through the probe and may be retracted until its end is barely visible at the gingival line. A potentiometer driven by the retraction mechanism for the fiber generates an electrical output signal having a voltage proportional to the position of the fiber to provide a measure of the pocket depth. The signal is used to digitally display and print each measurement that is taken.