Periodontitis Classification
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Direct answer
Since the 2017 World Workshop, periodontitis is one disease described along two axes: a stage (I to IV) recording severity and treatment complexity, and a grade (A, B or C) recording the speed of progression and responsiveness to risk factors. Staging rests on clinical attachment loss, radiographic bone level and lost teeth, bumped upward by complexity findings such as furcation involvement; grading rests on bone loss divided by age, direct radiographic evidence of progression, and two modifiers — smoking of 10 or more cigarettes per day and HbA1c of 7.0 per cent or more, which push the grade to C. Extent is appended as localized when under 30 per cent of teeth are involved and generalized at 30 per cent or more. The familiar split into chronic and aggressive periodontitis has been dropped because it did not hold up biologically.
What you must remember
- Stage I: attachment loss at or under 4 mm, radiographic bone loss mostly coronal third (under 15 per cent), probing at or under 4 mm.
- Stage II: attachment loss at or under 5 mm, bone loss confined to the coronal third (15–33 per cent), no tooth loss from periodontitis.
- Stage III: attachment loss of 6 mm or more, bone loss extending to the mid-third or beyond, tooth loss of 5 or fewer teeth, plus furcation involvement and vertical defects.
- Stage IV: adds 6 or more teeth lost, masticatory dysfunction, bite collapse and fewer than 20 remaining teeth.
- Extent descriptors: localized under 30 per cent of teeth, generalized 30 per cent or more, with a molar–incisor pattern descriptor replacing the old localised aggressive label.
- Grade formula: bone loss percentage divided by age — under 0.25 is grade A, 0.25 to 1.0 is B, above 1.0 is C; default is B, shifted by the evidence.
- Grade C modifiers: smoking at least 10 cigarettes per day and diabetes with HbA1c at or above 7.0 per cent.
- The 2017 framework's other categories: periodontal health and gingivitis; necrotising diseases (gingivitis, periodontitis, stomatitis, noma); periodontitis as a manifestation of systemic disease (Papillon–Lefevre, leukaemia); abscesses; perio-endo lesions; mucogingival deformities; traumatic occlusal forces.
Staging one patient, end to end
A 48-year-old smoker of 20 cigarettes a day with type 2 diabetes (HbA1c 8.2 per cent) presents with generalized 6–8 mm pockets, radiographs showing 40 per cent bone loss, a function-involved lower right first molar, and six teeth already lost to periodontitis. Severity first: attachment loss of 6 mm or more plus bone loss beyond the coronal third points to Stage III, but six teeth lost and drifting anteriors with chewing dysfunction lift it to Stage IV, generalized extent. Now grade: 40 per cent bone loss over 48 years gives a ratio of 0.83, inside the B band, but both modifiers apply — 20 cigarettes exceeds the 10-per-day threshold and HbA1c 8.2 exceeds 7.0 — so the grade moves to C. The final label — Stage IV, Grade C, generalized periodontitis — dictates complex interdisciplinary treatment, prosthetic planning and recalls measured in weeks. Contrast a 30-year-old with the same ratio but no modifiers: grade B, longer recall. Stage decides what you do; grade decides how closely you watch.
Where answers lose marks
Marks go when stage and grade swap jobs — writing that grade is based on attachment loss, or that staging includes smoking. Stage is what has happened to the dentition; grade is how fast it is happening and why. The second error is staging from probing depth instead of clinical attachment level; in a mouth with recession, the two diverge widely and the classification follows attachment. Third, the extent cut-off is 30 per cent of teeth, not the number of teeth, and "aggressive periodontitis" is no longer a formal category — the young patient with a molar–incisor pattern is described by extent and pattern, with grade C capturing the rapidity. Finally, the exam loves the two grade C modifiers; candidates who quote only smoking forget the HbA1c threshold of 7.0 per cent.
Frequently asked questions
What parameters determine the stage of periodontitis?
Clinical attachment loss, radiographic bone loss and number of teeth lost, with complexity factors — furcations, vertical defects, biting dysfunction — raising the stage.
How is the grade of periodontitis calculated?
Primarily as radiographic bone loss percentage divided by age (under 0.25 gives A, 0.25–1.0 gives B, above 1.0 gives C), modified by documented progression and by risk factors.
What is the extent threshold between localized and generalized periodontitis?
30 per cent of teeth — below it localized, at or above it generalized, with a molar–incisor pattern descriptor available for classic presentations.
Which two risk factors force a grade of C?
Smoking of 10 or more cigarettes per day and diabetes with HbA1c of 7.0 per cent or above.
What replaced aggressive periodontitis in the 2017 classification?
A single disease entity with stage, grade and extent descriptors; rapid young-onset destruction is now expressed as grade C with a molar–incisor pattern.