Periodontal Staging and Grading: The Complete Chart (Stages I–IV, Grades A–C)
Key takeaways
- Periodontitis is classified by stage (I–IV, how severe and complex the disease is) and grade (A–C, how fast it is progressing), under the 2017 AAP/EFP classification.
- Stage is driven mainly by interdental clinical attachment loss (CAL) at the worst site, radiographic bone loss, and tooth loss due to periodontitis.
- Grade starts at B by default and moves to A or C based on evidence of progression, the bone loss-to-age ratio, smoking, and diabetes.
- Accurate staging depends on a complete, accurate perio chart – every site, every visit.
This guide walks through the full periodontal staging and grading chart, shows how to apply it step by step, and explains where your perio chart data comes in.
Periodontal disease stages: the staging chart
Staging is based on severity (attachment and bone loss), complexity (factors that make treatment harder), and extent (how many teeth are involved). Severity is assessed at the site with the greatest loss. Complexity factors can move a case up a stage, but never down.
| Stage I Initial |
Stage II Moderate |
Stage III Severe |
Stage IV Advanced |
|
|---|---|---|---|---|
| Interdental CAL (worst site) | 1–2 mm | 3–4 mm | ≥5 mm | ≥5 mm |
| Radiographic bone loss | Coronal third (<15%) | Coronal third (15–33%) | Middle third of root or beyond | Middle third of root or beyond |
| Tooth loss due to periodontitis | None | None | ≤4 teeth | ≥5 teeth |
| Complexity | Max probing depth ≤4 mm; mostly horizontal bone loss | Max probing depth ≤5 mm; mostly horizontal bone loss | Probing depth ≥6 mm; vertical bone loss ≥3 mm; Class II or III furcation; moderate ridge defect | Stage III factors plus need for complex rehabilitation: masticatory dysfunction, secondary occlusal trauma (mobility ≥2), severe ridge defect, bite collapse, drifting, flaring, fewer than 20 remaining teeth (10 opposing pairs) |
| Extent | Localized (fewer than 30% of teeth involved), generalized (30% or more), or molar/incisor pattern | |||
Stage I periodontitis (initial)
The earliest stage of periodontitis: 1–2 mm of interdental attachment loss, bone loss limited to the coronal 15% of the root, and probing depths no deeper than 4 mm. Stage I sits at the border between gingivitis and periodontitis, which is why consistent charting matters so much – small changes from one visit to the next are what reveal it.
Stage II periodontitis (moderate)
Attachment loss of 3–4 mm, bone loss in the coronal third (15–33%), no teeth lost to periodontitis, and maximum probing depths up to 5 mm with mostly horizontal bone loss.
Stage III periodontitis (severe, with potential for tooth loss)
Attachment loss of 5 mm or more and bone loss reaching the middle third of the root. Up to four teeth may have been lost to periodontitis. Complexity factors such as probing depths of 6 mm or more, vertical bone loss of 3 mm or more, Class II or III furcation involvement, or a moderate ridge defect also place a case in Stage III.
Stage IV periodontitis (advanced, with potential loss of the dentition)
Everything in Stage III, plus five or more teeth lost to periodontitis or the need for complex rehabilitation – for example masticatory dysfunction, secondary occlusal trauma with mobility of degree 2 or more, bite collapse, drifting or flaring, or fewer than 20 remaining teeth.
Periodontitis grading: grades A, B and C
Grading estimates the rate of progression and the patient’s risk of future progression. Start every case at Grade B (moderate rate), then shift to Grade A or C if you have evidence.
| Grade A Slow |
Grade B Moderate |
Grade C Rapid |
|
|---|---|---|---|
| Direct evidence: bone loss or CAL over 5 years | No loss | <2 mm | ≥2 mm |
| Indirect evidence: % bone loss / age | <0.25 | 0.25–1.0 | >1.0 |
| Case phenotype | Heavy biofilm with low levels of destruction | Destruction in line with biofilm deposits | Destruction out of proportion to biofilm; rapid progression or early-onset patterns |
| Risk factor: smoking | Non-smoker | <10 cigarettes/day | ≥10 cigarettes/day |
| Risk factor: diabetes | Normoglycemic, no diagnosis of diabetes | HbA1c <7.0% in a patient with diabetes | HbA1c ≥7.0% in a patient with diabetes |
Risk factors can only move a grade up. A patient who would otherwise be Grade A but smokes 10 or more cigarettes a day becomes Grade C.
How to calculate the bone loss-to-age ratio
Take the percentage of radiographic bone loss at the worst site and divide it by the patient’s age. A 50-year-old with 25% bone loss has a ratio of 0.5 (25 ÷ 50), which points to Grade B. The same 25% bone loss in a 20-year-old gives 1.25 – Grade C.
How to stage and grade a case, step by step
- Confirm it’s periodontitis. A patient is a periodontitis case when interdental CAL is detectable at two or more non-adjacent teeth, or buccal/oral CAL of 3 mm or more with pocketing over 3 mm is detectable at two or more teeth – and the loss can’t be explained by other causes such as trauma, a vertical root fracture, or an endodontic lesion.
- Find the worst interdental site on the perio chart and note its CAL.
- Check radiographs for the percentage of bone loss at that site.
- Count teeth lost to periodontitis.
- Assign the initial stage from CAL (or bone loss if CAL isn’t available), then adjust for complexity – deep pockets, vertical defects, furcations, mobility, and rehabilitation needs.
- Describe the extent: localized, generalized, or molar/incisor pattern.
- Assign the grade: start at B, use direct evidence from previous charts and radiographs if you have it, otherwise the bone loss-to-age ratio, then apply smoking and diabetes modifiers.
Example: A 45-year-old patient who smokes 15 cigarettes a day has a worst-site interdental CAL of 6 mm, bone loss into the middle third of the root, one 7 mm pocket, and no teeth lost to periodontitis. Seven of 28 teeth (25%) are affected. Diagnosis: Periodontitis, Stage III, localized, Grade C (smoking 10 or more per day).
Gingivitis vs. Stage I periodontitis
Under the same classification, gingivitis on an intact periodontium is defined by bleeding on probing at 10% or more of sites with probing depths of 3 mm or less and no attachment loss. Bleeding at 10–30% of sites is localized gingivitis; more than 30% is generalized. Once attachment loss appears at the interdental level, the case moves into periodontitis – usually Stage I.
Why staging starts with the perio chart
Almost every input in the staging and grading chart comes from your periodontal charting: CAL at the worst site, probing depths, furcation involvement, mobility, and – for grading – how those numbers have changed since the last exam. A chart with skipped sites or estimated numbers produces an unreliable diagnosis, and it’s much harder to show progression when previous charts are incomplete.
That’s the practical case for charting every site at every comprehensive exam. If you need a refresher on the fundamentals, see our complete guide to perio charting and how to calculate CAL and record furcation and mobility.
Get the data staging depends on – every site, every visit
With Denti.AI Voice Perio, hygienists speak pocket depths, bleeding, recession, furcation and mobility as they probe, and the perio chart fills in on screen. A full-mouth chart takes about 5 minutes, saves straight to your practice management system, and comes with a patient-friendly oral health report. Denti.AI Voice Perio also includes AAP staging support, so the numbers you chart turn into a clear picture for the patient. Voice Perio is part of OneStop Clinical, together with Denti.AI Scribe for AI clinical notes.
Communicating stage and grade to patients
“Stage III, Grade C” means a lot to a clinician and very little to a patient. A visual report that shows which areas are healthy, which are bleeding, and where pockets are deepening makes the conversation far easier – and helps patients understand why treatment is recommended. Show the same report again at the next visit so patients can see what has improved.
Frequently asked questions
What are the 4 stages of periodontal disease?
Under the 2017 AAP/EFP classification, periodontitis has four stages: Stage I (initial, 1–2 mm interdental CAL), Stage II (moderate, 3–4 mm CAL), Stage III (severe, 5 mm or more CAL with up to 4 teeth lost to periodontitis), and Stage IV (advanced, 5 mm or more CAL with 5 or more teeth lost or a need for complex rehabilitation).
What is the difference between staging and grading in periodontitis?
Staging describes how severe and complex the disease is right now, based mainly on attachment loss, bone loss, tooth loss and complexity factors. Grading estimates how fast the disease is progressing and the risk of future progression, based on evidence of past progression, the bone loss-to-age ratio, smoking and diabetes.
What grade should I start with?
Start every case at Grade B (moderate rate of progression), then move to Grade A or Grade C if direct evidence, the bone loss-to-age ratio, or risk factors such as smoking and diabetes support it.
How do you calculate the bone loss-to-age ratio?
Divide the percentage of radiographic bone loss at the worst site by the patient’s age. Below 0.25 suggests Grade A, 0.25–1.0 suggests Grade B, and above 1.0 suggests Grade C.
What is the difference between localized and generalized periodontitis?
Localized periodontitis involves fewer than 30% of teeth; generalized periodontitis involves 30% or more. A molar/incisor pattern is described separately.
Shelly Mendoza is a results-driven executive with 25+ years in the dental industry. Starting as a dental assistant, she brings deep clinical and operational insight to every leadership role. She has led multi-site DSO operations, implemented scalable systems, and earned multiple President’s Club honors. Shelly is passionate about workflow solutions that boost team efficiency and elevate the patient experience.
