What is the AAP 2018 periodontal staging and grading system?

The AAP 2018 periodontal staging and grading system was introduced by the 2018 World Workshop on Classification of Periodontal and Peri-Implant Diseases. It classifies periodontitis using Stage (I–IV) to describe disease severity and complexity, and Grade (A–C) to describe the rate of progression and risk factors. Stage is based on radiographic bone loss, probing depth, and tooth loss. Grade is based on bone loss rate, smoking, and diabetes control.

What is Stage III vs Stage IV periodontitis?

Stage III periodontitis: radiographic bone loss greater than 33% of root length, probing depth ≥ 6 mm, vertical bone loss ≥ 3 mm, Class II or III furcation involvement, or tooth loss of up to 4 teeth due to periodontitis. Stage IV adds the complexity factors of masticatory dysfunction, bite collapse, flaring/drifting, less than 20 remaining teeth, or need for complex multidisciplinary rehabilitation.

What makes periodontitis Grade C?

Periodontitis is classified as Grade C (rapid progression) when any of the following are present: bone loss > 2 mm in 5 years, bone loss % divided by age greater than 1.0, heavy smoking (≥ 10 cigarettes/day), or uncontrolled diabetes (HbA1c ≥ 7%). Grade C indicates rapid disease progression and highest systemic risk.

What is radiographic bone loss percentage for periodontal staging?

Radiographic bone loss percentage for periodontal staging: Stage I = less than 15% bone loss; Stage II = 15–33% bone loss from the CEJ; Stage III = greater than 33% bone loss or bone loss extending to the middle or apical third of the root. Bone loss percentage is calculated relative to root length on periapical radiographs.

What is the AAP 2018 periodontal staging and grading system?

The AAP 2018 periodontal staging and grading system was introduced by the 2018 World Workshop on Classification of Periodontal and Peri-Implant Diseases. It classifies periodontitis using Stage (I–IV) to describe disease severity and complexity, and Grade (A–C) to describe the rate of progression and risk factors. Stage is based on radiographic bone loss, probing depth, and tooth loss. Grade is based on bone loss rate, smoking, and diabetes control.

What is Stage III vs Stage IV periodontitis?

Stage III periodontitis: radiographic bone loss greater than 33% of root length, probing depth ≥ 6 mm, vertical bone loss ≥ 3 mm, Class II or III furcation involvement, or tooth loss of up to 4 teeth due to periodontitis. Stage IV adds the complexity factors of masticatory dysfunction, bite collapse, flaring/drifting, less than 20 remaining teeth, or need for complex multidisciplinary rehabilitation.

What makes periodontitis Grade C?

Periodontitis is classified as Grade C (rapid progression) when any of the following are present: bone loss > 2 mm in 5 years, bone loss % divided by age greater than 1.0, heavy smoking (≥ 10 cigarettes/day), or uncontrolled diabetes (HbA1c ≥ 7%). Grade C indicates rapid disease progression and highest systemic risk.

What is radiographic bone loss percentage for periodontal staging?

Radiographic bone loss percentage for periodontal staging: Stage I = less than 15% bone loss; Stage II = 15–33% bone loss from the CEJ; Stage III = greater than 33% bone loss or bone loss extending to the middle or apical third of the root. Bone loss percentage is calculated relative to root length on periapical radiographs.

Periodontal Staging and Grading Calculator | AAP 2018 Classification Tool

Periodontal Staging & Grading Calculator

Enter clinical parameters to classify periodontitis using the AAP/EFP 2018 World Workshop system. Determines Stage (I–IV) by severity and Grade (A–C) by progression rate, with complete charting documentation.

Clinically reviewed by Dr. Nikhil Mahajan, PT, MPT · Jan 15, 2025

AAP 2018 Periodontal Staging — Complete Reference

Stage	Severity	Radiographic Bone Loss	Max Probing Depth	Tooth Loss	Complexity Factors
Stage I	Mild	Less than 15% (coronal third)	Maximum probing depth ≤ 4 mm	No tooth loss due to periodontitis	No complexity factors
Stage II	Moderate	15–33% (coronal third)	Maximum probing depth ≤ 5 mm	No tooth loss due to periodontitis	Furcation Class I or II; vertical bone loss < 3 mm; horizontal bone loss pattern
Stage III	Severe with potential for tooth loss	Greater than 33% (extending to middle or apical third)	Maximum probing depth ≥ 6 mm	Tooth loss ≤ 4 teeth due to periodontitis	Furcation Class II or III; vertical bone loss ≥ 3 mm; ridge defect; Class I–II mobility; masticatory dysfunction less than Stage IV
Stage IV	Severe with tooth loss and masticatory dysfunction	Greater than 33% (extending to middle or apical third)	Maximum probing depth ≥ 6 mm	Tooth loss ≥ 5 teeth due to periodontitis	Masticatory dysfunction; secondary occlusal trauma; bite collapse; flaring and drifting; less than 20 remaining teeth (10 opposing pairs); need for complex multidisciplinary rehabilitation

Stage

Severity

Radiographic Bone Loss

Max Probing Depth

Tooth Loss

Complexity Factors

Stage I

Mild

Less than 15% (coronal third)

Maximum probing depth ≤ 4 mm

No tooth loss due to periodontitis

No complexity factors

Stage II

Moderate

15–33% (coronal third)

Maximum probing depth ≤ 5 mm

No tooth loss due to periodontitis

Furcation Class I or II; vertical bone loss < 3 mm; horizontal bone loss pattern

Stage III

Severe with potential for tooth loss

Greater than 33% (extending to middle or apical third)

Maximum probing depth ≥ 6 mm

Tooth loss ≤ 4 teeth due to periodontitis

Furcation Class II or III; vertical bone loss ≥ 3 mm; ridge defect; Class I–II mobility; masticatory dysfunction less than Stage IV

Stage IV

Severe with tooth loss and masticatory dysfunction

Greater than 33% (extending to middle or apical third)

Maximum probing depth ≥ 6 mm

Tooth loss ≥ 5 teeth due to periodontitis

Masticatory dysfunction; secondary occlusal trauma; bite collapse; flaring and drifting; less than 20 remaining teeth (10 opposing pairs); need for complex multidisciplinary rehabilitation

AAP 2018 Periodontal Grading — Complete Reference

Grade	Progression	Bone Loss Rate	BL% ÷ Age	Smoking	Diabetes
Grade A	Slow Progression	< 0.25 mm/year (< 2 mm over 5 years)	Bone loss % / age < 0.25	Non-smoker	No diabetes or normoglycemic
Grade B	Moderate Progression	< 2 mm over 5 years	Bone loss % / age between 0.25 and 1.0	Smoker — less than 10 cigarettes/day	Controlled diabetes — HbA1c < 7.0%
Grade C	Rapid Progression	≥ 2 mm over 5 years	Bone loss % / age ≥ 1.0	Heavy smoker — ≥ 10 cigarettes/day	Uncontrolled diabetes — HbA1c ≥ 7.0%

Grade

Progression

Bone Loss Rate

BL% ÷ Age

Smoking

Diabetes

Grade A

Slow Progression

< 0.25 mm/year (< 2 mm over 5 years)

Bone loss % / age < 0.25

Non-smoker

No diabetes or normoglycemic

Grade B

Moderate Progression

< 2 mm over 5 years

Bone loss % / age between 0.25 and 1.0

Smoker — less than 10 cigarettes/day

Controlled diabetes — HbA1c < 7.0%

Grade C

Rapid Progression

≥ 2 mm over 5 years

Bone loss % / age ≥ 1.0

Heavy smoker — ≥ 10 cigarettes/day

Uncontrolled diabetes — HbA1c ≥ 7.0%

The AAP 2018 Periodontal Staging and Grading System

The 2018 World Workshop on the Classification of Periodontal and Peri-Implant Diseases, co-organized by the American Academy of Periodontology (AAP) and the European Federation of Periodontology (EFP), introduced a new multidimensional classification system for periodontitis. Published by Tonetti, Greenwell, and Kornman (2018), this framework replaced the previous chronic/aggressive/generalized/localized classification with a Stage (I–IV) and Grade (A–C) system that better captures disease complexity, risk, and systemic impact.

Understanding Periodontal Stage (I–IV)

The Stage is determined by the severity and complexity of the disease:

Stage I (Mild): Radiographic bone loss less than 15% of root length; maximum probing depth ≤ 4 mm; no tooth loss due to periodontitis; no complexity factors. Responds well to standard non-surgical periodontal therapy.
Stage II (Moderate): Bone loss 15–33%; maximum probing depth ≤ 5 mm; no tooth loss due to periodontitis; horizontal bone loss pattern; Furcation Class I or II. Non-surgical therapy typically successful.
Stage III (Severe): Bone loss exceeding 33% or extending to middle/apical third; maximum probing depth ≥ 6 mm; tooth loss ≤ 4 teeth due to periodontitis; vertical bone loss ≥ 3 mm; Furcation Class II or III. Often requires surgical intervention.
Stage IV (Very Severe): Same bone loss as Stage III plus complexity factors including masticatory dysfunction, bite collapse, flaring and drifting, fewer than 20 remaining teeth (10 opposing pairs), or tooth loss ≥ 5 teeth. Requires complex multidisciplinary rehabilitation.

Understanding Periodontal Grade (A–C)

The Grade reflects the rate of progression and systemic risk factors:

Grade A (Slow progression): No longitudinal evidence of bone loss; bone loss %/age less than 0.25; non-smoker; no diabetes or normoglycemic. Best prognosis — respond to standard treatment and maintain stability.
Grade B (Moderate progression): Less than 2 mm bone loss over 5 years; bone loss %/age 0.25–1.0; smoker less than 10 cigarettes/day; controlled diabetes (HbA1c < 7%). Risk factors present but manageable with treatment and lifestyle modification.
Grade C (Rapid progression): 2 mm or more bone loss over 5 years; bone loss %/age ≥ 1.0; heavy smoker (≥ 10 cigarettes/day); uncontrolled diabetes (HbA1c ≥ 7%). Highest systemic risk — modify treatment plan to address risk factors aggressively.

The "Worst Factor Rules" — How to Determine Grade

Grade is determined by the worst (highest-level) risk factor present. For example, a patient who is a non-smoker (Grade A modifier) but has uncontrolled diabetes (HbA1c ≥ 7%, Grade C modifier) is classified as Grade C overall. Similarly, Stage is determined by the most severe parameter — a patient with bone loss below 33% (Stage II) but a probing depth of 6 mm or furcation Class III involvement is classified as Stage III.

Differences from the Previous AAP Classification

Previous system: "Chronic periodontitis" and "Aggressive periodontitis" as separate entities — now both are classified as "Periodontitis" with Stage and Grade reflecting characteristics previously used to separate them
"Generalized/Localized" is now an extent descriptor added to the Stage-Grade classification
The new system explicitly captures systemic risk factors (diabetes, smoking) in the Grade, linking periodontal diagnosis directly to systemic health management
Complexity factors in Stages III and IV now drive treatment planning toward surgical intervention and multidisciplinary rehabilitation

Dr. Nikhil Mahajan, PT, MPT Clinical Reviewer · Reviewed January 15, 2025 · View credentials

Frequently Asked Questions

Can a patient's periodontal stage change over time?

Stage can only progress upward — periodontitis is a chronic progressive disease and once bone is lost, Stage does not regress downward even after successful treatment. A Stage III patient who responds to treatment remains Stage III but achieves a "stable" status. Grade, however, can improve — if a patient quits smoking or achieves better glycemic control (HbA1c), their Grade may be reclassified from C to B or A, reflecting reduced progression risk and better treatment response.

What does "extent" mean in the AAP classification?

Extent describes how many teeth are affected: Localized = less than 30% of teeth affected; Generalized = 30% or more of teeth affected; Molar-incisor pattern = a specific pattern that may indicate a particular pathogenesis. Extent is added as a descriptor to the Stage-Grade classification — for example, "Generalized Stage III Grade C Periodontitis." This calculator currently focuses on Stage and Grade — document extent separately based on full-mouth probing chart.

How is bone loss percentage calculated for staging?

Bone loss percentage for periodontal staging is calculated on periapical radiographs: % BL = (distance from CEJ to bone crest ÷ root length) × 100. For the Grade BL%/age calculation: divide the bone loss percentage by the patient's age. For example, a 40-year-old with 20% bone loss: BL%/age = 20/40 = 0.5 — this falls in Grade B range (0.25–1.0). Standardized paralleling technique radiographs are required for accurate measurement.

Is Stage IV the same as advanced periodontitis?

Stage IV is equivalent to what was previously called "advanced" or "severe" periodontitis in older classifications, but it adds specific complexity criteria that trigger the Stage IV designation. The defining feature of Stage IV versus Stage III is not just bone loss severity, but the presence of masticatory dysfunction (bite collapse, drifting, loss of posterior support) or tooth loss of 5 or more teeth due to periodontitis — factors that require complex, often multidisciplinary rehabilitation rather than standard periodontal surgery alone.