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A periodontal probe is an instrument in dentistry commonly used in the dental armamentarium. It is usually long, thin, and blunted at the end. The primary purpose of a periodontal probe is to measure pocket depths around a tooth in order to establish the state of health of the periodontium. There are markings inscribed onto the head of the instrument to make measurements more accurate and easier for a dentist.

Michigan O probe with Williams markings (left) and Naber's probe with shades alternating every 3 mm (right).

Proper use of the periodontal probe is necessary to maintain accuracy. The tip of the instrument is placed with light pressure into the gingival sulcus, which is an area of potential space between a tooth and the surrounding tissue. It is important to keep the periodontal probe parallel to the contours of the root of the tooth and to insert the probe down to the base of the pocket. This results in obscuring a section of the periodontal probe's tip. The first marking visible above the pocket indicates the measurement of the pocket depth. It has been found that the average, healthy pocket depth is around 3 mm. Depths greater than 3 mm can be associated with "attachment loss" of the tooth to the surrounding alveolar bone, which is a characteristic found in periodontitis. Pocket depths greater than 3 mm can also be a sign of gingival hyperplasia.

There are many different types of periodontal probes, and each has their own manner of indicating measurements on the tip of the instrument. For example, the Michigan O probe with Williams markings has circumferential lines at 1 mm, 2 mm, 3 mm, 5 mm, 7 mm, 8 mm, 9 mm, and 10 mm. The PCP12 probe with Marquis markings has alternating shades every 3 mm. Unlike the previous two mentioned, the Naber's probe is curved, and it is used for measuring into the furcation area between the roots of a tooth.

The periodontal probe can also be used to measure other dental instruments and tooth preparations during restorative procedures.

• Summit, James B., J. William Robbins, and Richard S. Schwartz. "Fundamentals of Operative Dentistry: A Contemporary Approach." 2nd edition. Carol Stream, Illinois, Quintessence Publishing Co, Inc, 2001. ISBN 0-86715-382-2.

• Video of the use of a periodontal probe hosted on Wichita State University's website