24.1 The 2018 Classification and Periodontal Health
Key Takeaways
- The 2018 classification defines periodontitis by stage for severity and complexity and by grade for rate of progression.
- Clinical periodontal health on an intact periodontium requires no interdental attachment loss, probing depths of 3 mm or less and bleeding on probing under 10%.
- A treated periodontitis patient with bleeding under 10% and no site of 4 mm or more bleeding is described as stable, never as cured.
- Gingivitis on a reduced periodontium is distinguished from recurrent periodontitis by the absence of further attachment loss.
- Localised gingivitis is 10% to 30% bleeding sites and generalised gingivitis is more than 30%.
1. The 2018 International Classification Framework
The 2018 Classification replaced the 1999 Armitage system, eliminating ambiguous designations such as "chronic" and "aggressive" periodontitis in favour of a unified disease entity (Periodontitis) characterized by multi-dimensional Staging (anatomical severity, tissue loss, and complexity of management) and Grading (biological rate of progression, responsiveness to therapy, and systemic health impact).
2018 EFP/AAP / BSP Classification Architecture
│
├── 1. Periodontal Health, Gingival Diseases & Conditions
│ ├── Periodontal Health & Gingival Health (Intact vs Reduced Periodontium)
│ ├── Dental Plaque-Induced Gingivitis (Biofilm alone or mediated by risk factors)
│ └── Non-Plaque-Induced Gingival Diseases (Genetic, infections, mucocutaneous, reactive, neoplasms)
│
├── 2. Periodontitis
│ ├── Necrotizing Periodontal Diseases (Necrotizing gingivitis, necrotizing periodontitis, necrotizing stomatitis)
│ ├── Periodontitis as a Manifestation of Systemic Diseases (e.g., Papillon-Lefèvre, Chediak-Higashi, Down syndrome)
│ └── Periodontitis (Characterised by Staging [I–IV], Grading [A–C], and Extent [Localised/Generalised/Molar-Incisor])
│
├── 3. Periodontal Manifestations of Systemic Diseases & Developmental/Acquired Conditions
│ ├── Systemic disorders affecting periodontal supporting apparatus
│ ├── Mucogingival deformities and conditions (Recession, phenotype, lack of keratinised tissue)
│ ├── Traumatic occlusal forces (Primary vs Secondary occlusal trauma)
│ └── Tooth- and prosthesis-related factors (Enamel pearls, cervical margins, biological width impingement)
│
└── 4. Peri-Implant Diseases and Conditions
├── Peri-Implant Health
├── Peri-Implant Mucositis (Biofilm-induced inflammation, BOP, absence of bone loss)
├── Peri-Implantitis (Inflammation, BOP/suppuration, increased probing depths, progressive crestal bone loss)
└── Peri-Implant Soft and Hard Tissue Deficiencies
2. Periodontal Health and Gingivitis: Intact vs Reduced Periodontium
A pivotal advancement of the 2018 Classification is the explicit differentiation between an intact periodontium (no historical loss of periodontal attachment or alveolar bone) and a reduced periodontium (historical loss of attachment and bone). A reduced periodontium is further sub-classified based on whether the patient has a verifiable history of periodontitis.
The Three Clinical Scenarios
- Intact Periodontium: No clinical attachment loss (CAL = 0), no radiographic alveolar bone loss. Anatomical structures remain coronal to the cemento-enamel junction (CEJ).
- Reduced Periodontium in a Non-Periodontitis Patient: Demonstrable CAL and bone loss arising secondary to non-periodontitis aetiologies, such as surgical crown lengthening, horizontal toothbrush abrasion, orthodontic tipping, or surgical flap exposure during impacted tooth extraction. No active or historical periodontitis.
- Successfully Treated Stable Periodontitis Patient on a Reduced Periodontium: A patient with historical periodontitis who has achieved therapeutic stability following cause-related therapy, characterized by resolution of pocketing and absence of progressive tissue breakdown.
| Clinical Parameter | Intact Periodontium | Reduced Periodontium (Non-Periodontitis) | Reduced Periodontium (Successfully Treated Periodontitis) |
|---|---|---|---|
| Interdental CAL | None ($0\text{ mm}$) | Present (Non-periodontitis origin) | Present (Historical periodontitis origin) |
| Probing Pocket Depth (PPD) | $\le 3\text{ mm}$ | $\le 3\text{ mm}$ | $\le 4\text{ mm}$ (no $4\text{ mm}$ site with BOP) |
| Bleeding on Probing (BOP) - Health | $< 10%$ of sites | $< 10%$ of sites | $< 10%$ of sites |
| Bleeding on Probing (BOP) - Gingivitis | $\ge 10%$ of sites | $\ge 10%$ of sites | $\ge 10%$ of sites (with PPD $\le 4\text{ mm}$) |
| Radiographic Bone Loss (RBL) | Absent | Absent or secondary to trauma/surgery | Present (Coronal, middle, or apical third) |
Bleeding on Probing (BOP) Thresholds for Gingival Diseases
Bleeding on probing, elicited using a standardized, light probing force of approximately $0.20-0.25\text{ N}$ ($20-25\text{ g}$), is the primary objective clinical criterion for assessing gingival vascular inflammation:
- Clinical Periodontal Health: $< 10%$ of probing sites elicit bleeding.
- Localised Gingivitis: $10%\text{ to }30%$ of probing sites elicit bleeding, with no periodontitis pocketing.
- Generalised Gingivitis: $> 30%$ of probing sites elicit bleeding, with no periodontitis pocketing.
[!IMPORTANT] The Critical Distinction on a Reduced Periodontium in Treated Periodontitis: In a patient previously treated for periodontitis who currently maintains a reduced periodontium:
- Periodontal Stability (Health): PPD $\le 4\text{ mm}$, BOP $< 10%$, and no $4\text{ mm}$ site exhibiting bleeding on probing.
- Gingival Inflammation on a Reduced Periodontium: PPD $\le 4\text{ mm}$, BOP $\ge 10%$, but no $4\text{ mm}$ site exhibiting bleeding on probing. This represents gingival catarrhal inflammation without active destructive attachment loss.
- Recurrent / Unstable Periodontitis: The presence of any site with PPD $\ge 4\text{ mm}$ that bleeds on probing, or any site with PPD $\ge 5\text{ mm}$ regardless of BOP. Such sites represent active periodontal pockets requiring reinstitution of subgingival instrumentation.
Why the Classification Changed
The 2018 classification replaced the 1999 system for reasons candidates are expected to be able to state. The old distinction between chronic and aggressive periodontitis could not be applied reliably, because the two forms shared pathophysiology and their clinical separation depended on age and rate of progression that were rarely documented. The new system replaces them with a single disease, periodontitis, described by stage — severity and anticipated complexity of management — and grade — the rate of progression and the risk of further progression. It also introduced a formal category of peri-implant diseases and conditions, which the 1999 classification lacked, and defined periodontal health on both an intact and a reduced periodontium.
Health, Gingivitis and the Treated Patient
The clinically useful innovation is the recognition that a successfully treated periodontitis patient does not return to being a healthy patient; they become a patient with periodontitis in remission on a reduced periodontium, requiring lifelong supportive care. Three scenarios must be distinguished. A patient with an intact periodontium and minimal bleeding has gingival health. A patient with a reduced periodontium without a history of periodontitis — for example after recession or crown lengthening — can also have gingival health. A patient with a reduced periodontium with a history of periodontitis who now has shallow pockets and low bleeding scores has stable disease, not health, and remains at higher risk of recurrence.
Bleeding on probing is the objective marker used to make these judgements. Gingival health is defined by bleeding at less than 10 per cent of sites; localised gingivitis by bleeding at 10 to 30 per cent of sites; and generalised gingivitis by bleeding at more than 30 per cent of sites. These thresholds are examinable numbers, and they are also the thresholds by which the success of treatment is judged at re-evaluation.