Tobias K. Boehm (October 24, 2025)
Periodontal probe inside a gum pocket. (Dr. Boehm)
One of the rituals of getting a check-up at a dentist is having your gums checked for signs of gum disease. This involves a dentist, hygienist, or another staff member probing the gums with a metal probe and calling out various numbers. These numbers are entered into a chart that looks like this:
Example of a paper-based periodontal chart (Dr. Boehm)
The chart may be paper-based or an electronic version of it, but it always will have the same setup of numbers, symbols and teeth. In this series, we break down what these numbers and symbols mean.
In this article, we describe the terms “pocketing”, “pocket depths” and “probing depths”. We also will describe what these numbers mean and how it may affect treatment decisions for gum disease.
What is measured here?
Measuring with a periodontal probe. GM = tip of gum tissue next to tooth (“gingival margin”). SB = where tissue attaches to tooth. PD = probing depth, the distance between GM and SB measured in millimeters (Dr. Boehm)
Typically, there is a little space between the gum tissue and the underlying tooth surface where the gums and the teeth meet. You can also think of it as a little tissue fold where the gum tissue folds inward to attach to the underlying tooth. The size of this space can be measured with a periodontal probe, as seen in the picture above. This probe has markings on it to allow dental providers measuring the size of this space. The design of this probe can vary, depending on the preferences of a given dental office or dental provider. But all have in common that they resemble small rulers that can be dipped into this little space.
Typically, with healthy gums, the space is shallow and only a few millimeters deep. If the gum tissue appears healthy and the space is shallow, the space is called a “sulcus” or “periodontal sulcus”.
If the space is deeper than a few millimeters, the space is called a pocket. Usually, most dental providers call this space a pocket if the depth is 5 mm or more.
Therefore, “pocketing” means that there are pockets, or the space between gums and teeth is at least 5 mm deep. “Pocket depth” means that there is a pocket that is at least 5 mm deep. “Probing depth” simply describes the depth of the space between gums and teeth.
When measuring probing depths, providers usually round up to the next highest number. In the picture shown above, the probe inserts 5 to 6 mm into the space between gum and tooth, so the measurement is “6” mm. Therefore, the probing depth is 6 mm, and this would be considered a pocket with a pocket depth of 6 mm.
Typically, dental providers check the periodontal sulcus around each tooth and record the highest measurement in 6 areas around each tooth, just as shown in the chart above.
What do the numbers mean?
Generally, low numbers (i.e. “1”, “2”, “3”) suggest healthy gums and high numbers (i.e. “5”, “6”,…) suggest gum disease. In most dental practices, these numbers refer to probing depths. Occasionally, and most likely in a periodontal specialist office, these numbers can also be measures of “attachment level” or “clinical attachment (level)”. But generally, 3 digit numbers (i.e. “3 2 3”) stand for probing depths and may be labeled as “PD”.
How does probing depth affect my gum treatment?
Dentists use these measurements to judge your risk for further gum disease and determine what treatment to recommend. Based on past experience and training, dentists pick a cut-off for probing depths after which they recommend more aggressive treatment for gum disease. Dental insurance uses these numbers to justify approving or denying certain types of treatment for gum disease. For example, dental insurance typically covers deep cleanings (i.e. “scaling and root planing”) if there are probing depths greater than 4 mm but will likely deny it if probing depths are 3 mm or less, provided deep cleanings have not been done within a few years.
Probing depths are just one of many factors dentists consider when recommending gum treatment. Therefore, interpreting what a particular probing depth means for treatment is different for different dentists, different patients and different teeth. Because each patient and each tooth is unique, there is no universal guideline that suggests treatments for a given probing depth. Yet, many clinical studies in the 1970s and 1980s suggested minimum probing depths where the tested gum treatment produced improved tooth support (as measured in “clinical attachment level”). For example, Lindhe and others called this “critical probing depth” and identified that non-surgical treatment alone (“scaling and root planing”) on average lead to improved tooth support for probing depths deeper than 2.9 mm. Combined non-surgical and surgical treatment produced improved tooth support for probing depths greater than 4.2 mm (1).
Periodontists learn about these studies during residency and form their interpretation of probing depths in similar ways. While each periodontist likely has developed their own “critical probing depths” to guide treatment decisions, they are probably not too different from my own interpretation that follows here:
- 1 – 3 mm: Likely healthy gums. Likely needs only preventive care such as regular checkup and cleaning (“prophylaxis”)
- 4 – 5 mm: May have gum disease. May need deep cleaning (“scaling and root planing”). Probably has risk for worsening gum disease, may need shorter intervals between cleanings. Gum surgery could be used to address persistently deep 5 mm pockets if needed.
- 6 – 7 mm: Likely has significant gum disease. Likely requires deep cleaning, and probably gum surgery or other forms of advanced treatments
- 8 – 9 mm: Likely has significant gum disease with possibility of tooth loss. Preventing tooth loss will likely require variety of non-surgical and surgical procedures. Tooth removal may be a better option, as suggested by researchers at the University of Michigan (2).
- 10 mm and above: May be a combination of gum and root canal infection (“combined periodontal-endodontic infection”). Tooth loss is likely without treatment. Saving tooth likely requires many dental procedures and collaboration between specialists and still may not be successful. It likely is best to remove affected tooth right away.
While this is my own interpretation of probing depth values, it likely is similar to that of other dentists or periodontists and it can help you as patient to understand where treatment recommendations come from. As patient, you can ask what your probing depths are and ask for recommendations to improve them.
When should I be concerned about probing depths?
Generally, any deep probing depth is a concern. Most dentists will recommend some form of treatment if probing depths reach 5 mm or greater.
What conditions cause deep probing depths?
Deep probing depths usually are a sign of gum disease such as gingivitis or periodontitis. Deep probing depths around dental implants can be a sign of gum disease specific to implants such as peri-implantitis and perimucositis.
Occasionally, other conditions may lead to increased probing depths such as:
- Impacted teeth, with gum tissue still covering part of the tooth
- Altered passive eruption, where thick gum tissue still covers part of the tooth
- Tipped teeth
- Excess soft tissue towards the back of the mouth covering parts of teeth
The conditions are readily identified during dental exams and distinguised from gum diseases.
How should probing depth numbers change during treatment?
Generally, probing depths should improve and become smaller during periodontal treatment. The goal in periodontal treatment is to reduce inflammation in the gums (“periodontal tissues”) so that there is less chance of losing additional tooth support and bone. Low probing depths suggest low inflammation. Probing depths often reduce some after scaling and root planing, and should further decrease with gum surgery and removal of hopelessly infected teeth.
When should probing depths be measured?
Probing depths are typically measured during the initial dental visit and at check up visits. If probing depths are low and the oral tissues appear healthy, measuring probing depths once or twice a year is enough. For patients who have had significant gum disease such as periodontitis, measuring the probing depths every 2 to 4 months may be useful to detect worsening of gum disease (3).
I have dental implants. Do I need to get probing depths measured around these implants?
Dental associations around the world recommend checking dental implants regularly for signs of gum disease including probing around implants (4, 5). Measuring the probing depths around dental implants is essential for detecting gum diseases such as peri-implantitis and perimucositis (6).
While there was some concern that probing with a metal probe could damage the surface of implants, using a typical metal periodontal probe is unlikely to produce significant damage to dental implants (7). Dental providers may use plastic probes to probe around dental implants to avoid this risk alltogether.
Why does gum pocketing develop?
Gum pockets usually develop as consequence of gum disease. In gum disease, changes in the microbial flora around teeth cause inflammation in the gums. Inflammation in the gums leads to tissue swelling, and the tissue swelling creates a deeper space between teeth and gums. In addition, inflammation damages the gum tissue attachment to teeth, allowing for deeper penetration of periodontal probes into the tissue, resulting in greater depth readings. As time goes on, microbes invade the damaged tissue attachment, causing the gum tissue to further separate from the tooth and the base of the pocket to become deeper. Eventually, persistent inflammation also destroys the underlying bone supporting the tooth, allowing the pocket floor to creep down towards the root tip of the tooth. Since tooth roots of molars are about 10 mm long, a pocket of 10 mm means that the pocket floor likely reached the tip of the root and there is complete loss of tooth support. At that point the tooth usually becomes loose, and this is the reason why teeth with pockets of 10 mm or more most often are just removed during treatment.
About the author:
Tobias K. Boehm, DDS, PhD, MBA, PC, DABP, DICOI, FGDIA is the founder of The Dental Institute, executive director at The Defeating Epilepsy Foundation and a professor at Western University of Health Sciences where he teaches and practices a periodontal specialist.
References:
(1) Lindhe J, Socransky SS, Nyman S, Haffajee A, Westfelt E. “Critical probing depths” in periodontal therapy. J Clin Periodontol. 1982 Jul;9(4):323-36. doi: 10.1111/j.1600-051x.1982.tb02099.x. PMID: 6764782.
(2) Avila G, Galindo-Moreno P, Soehren S, Misch CE, Morelli T, Wang HL. A novel decision-making process for tooth retention or extraction. J Periodontol. 2009 Mar;80(3):476-91. doi: 10.1902/jop.2009.080454. PMID: 19254132.
(3) Trombelli L, Simonelli A, Franceschetti G, Maietti E, Farina R. What periodontal recall interval is supported by evidence? Periodontol 2000. 2020 Oct;84(1):124-133. doi: 10.1111/prd.12340. PMID: 32844410.
(4) Todescan S, Lavigne S, Kelekis-Cholakis A. Guidance for the maintenance care of dental implants: clinical review. J Can Dent Assoc. 2012;78:c107. PMID: 23306040.
(5) Louropoulou A, van der Weijden F. De richtlijnen voor parodontale en peri-implantaire ontstekingen [The Dutch guidelines for prevention and treatment of periodontal and peri-implant diseases]. Ned Tijdschr Tandheelkd. 2021 Dec;128(12):585-592. Dutch. doi: 10.5177/ntvt.2021.12.21122. PMID: 34859973.
(6) Renvert S, Persson GR, Pirih FQ, Camargo PM. Peri-implant health, peri-implant mucositis, and peri-implantitis: Case definitions and diagnostic considerations. J Clin Periodontol. 2018 Jun;45 Suppl 20:S278-S285. doi: 10.1111/jcpe.12956. PMID: 29926496.
(7) Folwaczny M, Rudolf T, Frasheri I, Betthäuser M. Ultrastructural changes of smooth and rough titanium implant surfaces induced by metal and plastic periodontal probes. Clin Oral Investig. 2021 Jan;25(1):105-114. doi: 10.1007/s00784-020-03341-1. Epub 2020 Jun 21. Erratum in: Clin Oral Investig. 2022 Jan;26(1):1101. doi: 10.1007/s00784-021-04216-9. PMID: 32564141; PMCID: PMC8590678.