Quick answer: Stage periodontitis using clinical attachment loss (CAL) or radiographic bone loss (RBL) — Stage I (CAL 1–2mm), Stage II (CAL 3–4mm), Stage III or IV (CAL ≥5mm), with Stage IV requiring specific complexity factors like masticatory dysfunction. Grade A–C based on rate of progression evidence, starting at Grade B and adjusting for modifiers. Use our free periodontal staging calculator to classify any case systematically.
Why the 2018 Classification Changed Everything
The 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases, co-sponsored by the American Academy of Periodontology (AAP) and the European Federation of Periodontology (EFP), produced the most significant update to periodontal disease classification since 1999. Published in the June 2018 supplement of the Journal of Periodontology and Journal of Clinical Periodontology (Tonetti, Greenwell & Kornman et al.), it replaced the chronic/aggressive subdivision with a single multidimensional staging and grading framework.
The critical change: aggressive and chronic periodontitis no longer exist as separate categories. All forms of periodontitis are now classified under a single “Periodontitis” umbrella, differentiated by Stage (severity) and Grade (risk of progression) rather than clinical behaviour pattern.
The Three-Step Process for Staging and Grading
The AAP released a simplified three-step workflow for clinical application:
- Step 1 — Initial case overview: Obtain radiographs, probing depths, and missing tooth count. Determine if findings suggest Stage I/II (mild-moderate) or Stage III/IV (severe-very severe).
- Step 2 — Establish Stage: Determine severity using CAL or RBL, then check for complexity factors that upgrade the stage.
- Step 3 — Establish Grade: Start at Grade B, then assess for direct and indirect evidence to shift to A or C, and apply systemic modifiers.
Step 2: Establishing the Stage — Complete Guide
Primary Staging Criteria — Use Highest CAL or RBL Interdentally
| Stage | Severity | CAL Interdental | RBL | Max Probing Depth | Tooth Loss (Perio) |
|---|---|---|---|---|---|
| Stage I | Initial | 1–2 mm | Coronal third (<15%) | ≤4 mm | No tooth loss |
| Stage II | Moderate | 3–4 mm | Coronal third (15–33%) | ≤5 mm | No tooth loss |
| Stage III | Severe | ≥5 mm | Extending to middle or apical third (>33%) | ≥6 mm | ≤4 teeth lost |
| Stage IV | Very severe | ≥5 mm | Extending to middle or apical third (>33%) | ≥6 mm | ≥5 teeth lost |
Important rules:
- Use the worst site interdentally — the highest CAL or greatest RBL observed anywhere in the mouth.
- CAL and RBL are alternative criteria — use whichever is available. If both are available, use the one that gives the highest stage.
- Tooth loss counts only teeth lost due to periodontal causes — not extractions for other reasons, trauma, or prosthodontic planning.
Complexity Factors — When They Override Primary Criteria
Complexity factors can upgrade a Stage I to Stage II, or Stage II to Stage III. They represent features that increase treatment complexity beyond what the primary CAL/RBL would suggest. Any one complexity factor from Stage III or IV list upgrades the stage to that level.
| Stage II Complexity Factors | Stage III Complexity Factors | Stage IV Complexity Factors |
|---|---|---|
| Maximum probing depth ≥5 mm Vertical bone loss ≥3 mm Furcation involvement Class II or III Moderate ridge defect | Vertical bone loss ≥3 mm Furcation Class II or III Moderate ridge defect Max probing depth ≥6 mm Less than 20 remaining teeth (10 opposing pairs) | Masticatory dysfunction Secondary occlusal trauma (mobility ≥2) Severe ridge defect Bite collapse, flaring, drifting Less than 10 remaining teeth (5 opposing pairs) |
Stage III vs Stage IV — The Critical Distinction
This is the most commonly confused differentiation in the 2018 classification. Both Stage III and IV share the same primary severity criteria (CAL ≥5mm, RBL extending beyond the coronal third). The distinction is:
- Stage III: Severe disease but tooth retention is still possible with appropriate therapy. Up to 4 teeth lost due to periodontal causes.
- Stage IV: Severe disease with masticatory dysfunction — the periodontitis has progressed to the point that the chewing apparatus is compromised. Five or more teeth lost due to periodontal causes, OR complexity factors indicating bite collapse, flaring/drifting, or severe secondary occlusal trauma.
Ask yourself: “Has this patient’s periodontitis compromised their ability to chew effectively?” If yes, Stage IV. If the disease is severe but chewing function is preserved, Stage III.
Step 3: Establishing the Grade — Complete Guide
Grading assesses the rate and risk of disease progression, the patient’s responsiveness to therapy, and the potential systemic impact of the disease. There are three grades: A (slow), B (moderate), C (rapid).
Start at Grade B — Then Adjust
The most important clinical rule: start with the assumption of Grade B for every patient, then seek specific evidence to shift to Grade A (slower) or Grade C (faster). This prevents over- or under-grading based on insufficient evidence.
Direct Evidence of Progression Rate
| Evidence | Grade A | Grade B | Grade C |
|---|---|---|---|
| Longitudinal data (radiographs over time) | No loss over 5 years | <2 mm loss over 5 years | ≥2 mm loss over 5 years |
| % RBL ÷ Age | <0.25 | 0.25–1.0 | >1.0 |
The % RBL ÷ Age calculation is a practical way to estimate progression rate when longitudinal records are unavailable. Example: A 40-year-old with 25% RBL = 25 ÷ 40 = 0.625 → Grade B range.
Indirect Evidence (Biomarkers of Risk)
| Evidence | Grade A | Grade B | Grade C |
|---|---|---|---|
| Case phenotype | Heavy biofilm with low levels of destruction | Destruction consistent with biofilm deposits | Destruction exceeds what biofilm alone would predict — molar/incisor pattern |
Grade Modifiers — These Can Override Primary Grade
Even if direct/indirect evidence suggests Grade A or B, the presence of grade modifiers automatically shifts the patient to Grade C:
| Modifier | Grade C Threshold |
|---|---|
| Smoking | ≥10 cigarettes per day (any smoking → Grade B minimum; ≥10/day → Grade C) |
| Diabetes (HbA1c) | HbA1c ≥7% in diabetic patient → Grade C; HbA1c <7% (controlled) → Grade B modifier |
Additional Grade C risk factors supported by evidence include: obesity, physical inactivity, stress, depression, and certain medications — but smoking and diabetes are the two with the strongest evidence and the two specifically incorporated into the classification framework.
Extent and Distribution
After staging and grading, describe the extent:
- Localised: <30% of teeth involved
- Generalised: ≥30% of teeth involved
- Molar/incisor pattern: When periodontitis affects primarily first molars and incisors — this pattern (previously labelled “aggressive”) is now simply described as extent within the staging/grading framework
Critical rule: A patient receives ONE stage and ONE grade for their entire dentition — not different stages for different areas. The stage is determined by the worst site; the grade reflects the overall disease trajectory. Do not write “Generalised Stage II with Localised Stage III” — this is incorrect.
Complete Case Examples
Case 1 — 45-year-old non-smoker, no systemic disease
- Maximum CAL: 4 mm interdentally
- RBL: Coronal third, approximately 20%
- No furcation involvement, no vertical bone loss >3mm
- No tooth loss
- % RBL ÷ age = 20 ÷ 45 = 0.44
- Diagnosis: Generalised Periodontitis, Stage II, Grade B
Case 2 — 58-year-old, smoker (15 cigarettes/day), HbA1c 8.2%
- Maximum CAL: 6 mm
- RBL: Extending to middle third, 40%
- Furcation Class II (#14, #19)
- 3 teeth lost due to periodontal disease
- Bite collapse present posteriorly
- % RBL ÷ age = 40 ÷ 58 = 0.69 (Grade B range — but modifiers apply)
- Grade modifier: Smoking ≥10/day → Grade C. Diabetes HbA1c ≥7% → Grade C
- Diagnosis: Generalised Periodontitis, Stage III, Grade C
Free Periodontal Staging Calculator
Use our free periodontal staging and grading calculator to classify any case systematically. Enter CAL, RBL, probing depth, tooth loss, complexity factors, and systemic modifiers — the calculator applies the 2018 AAP classification framework step by step and generates a complete case documentation template. No login required.
→ Open the free Periodontal Staging Calculator
Frequently Asked Questions
What is the difference between Stage III and Stage IV periodontitis?
Both share the same primary severity (CAL ≥5mm, RBL extending beyond the coronal third). Stage IV is differentiated by masticatory dysfunction — bite collapse, flaring/drifting, secondary occlusal trauma (mobility ≥2), or loss of five or more teeth due to periodontal disease. Stage III is severe but chewing function remains intact.
How do I determine the grade when I have no longitudinal radiographs?
Use the % RBL ÷ age calculation as indirect evidence of progression rate. Start at Grade B and adjust based on this ratio, case phenotype, and systemic modifiers. If the patient smokes ≥10 cigarettes/day or has poorly controlled diabetes (HbA1c ≥7%), grade as C regardless of other evidence.
Can a patient’s stage change after treatment?
The stage is generally considered permanent — it reflects the maximum disease severity ever reached. However, complexity factors that drove the stage can be resolved (e.g., furcation repair, tooth replacement), in which case the complexity level may regress. The stage itself does not decrease, but it can be noted as “Stage III, reduced periodontium in a stable patient.”
Does the 2018 classification still use “aggressive periodontitis”?
No. Aggressive periodontitis was eliminated in the 2018 classification. What was previously called aggressive periodontitis — characterised by rapid attachment loss, molar/incisor pattern, and often a familial aggregation — is now classified as Periodontitis with the molar/incisor extent pattern, typically at Stage III or IV, Grade C with rapid progression evidence.
Is a non-smoker with controlled diabetes still Grade B?
Yes. Well-controlled diabetes (HbA1c <7%) is a risk modifier that keeps the patient at Grade B minimum — it does not automatically trigger Grade C. Only poorly controlled diabetes (HbA1c ≥7%) is a Grade C modifier per the 2018 framework.
References
- Tonetti MS, Greenwell H, Kornman KS. Staging and grading of periodontitis: Framework and proposal of a new classification and case definition. J Periodontol. 2018;89 Suppl 1:S159-S172. PMID: 29926952.
- Caton JG, Armitage G, Berglundh T, et al. A new classification scheme for periodontal and peri-implant diseases and conditions. J Periodontol. 2018;89 Suppl 1:S1-S8. PMID: 29926489.
- Papapanou PN, Sanz M, Buduneli N, et al. Periodontitis: Consensus report of workgroup 2 of the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions. J Periodontol. 2018;89 Suppl 1:S173-S182. PMID: 29926951.
- Chapple ILC, Mealey BL, Van Dyke TE, et al. Periodontal health and gingival diseases and conditions on an intact and a reduced periodontium. J Periodontol. 2018;89 Suppl 1:S74-S84. PMID: 29926953.
Written by Nikhil Mahajan, PT, MPT | Last reviewed: May 2026 | Free Periodontal Staging Calculator →