Understanding the 2017 AAP Periodontitis Classification: A Deep Dive into Grading

Navigating the complexities of periodontal disease requires a precise and predictive diagnostic framework. The 2017 American Academy of Periodontology (AAP) classification system introduced a multidimensional approach that not only identifies the severity and extent of periodontitis (Staging) but also assesses its rate of progression and potential response to therapy (Grading). Understanding the grading system is crucial for dental professionals to create personalized treatment plans and predict long-term outcomes for their patients. This guide will explore the essential parameters used in periodontal grading, providing clarity on how we classify the disease as Grade A, B, or C.

The Purpose of Periodontal Grading

Periodontal grading aims to estimate the future risk of periodontitis progression and its potential impact on both oral and systemic health. It provides a dynamic, forward-looking assessment that complements the more static snapshot provided by staging. The three grades are:

Grade A: Slow Rate of Progression
Grade B: Moderate Rate of Progression
Grade C: Rapid Rate of Progression

By default, every patient diagnosed with periodontitis begins at Grade B. Clinicians then seek evidence to shift the patient to either Grade A or Grade C. This determination is based on a primary criterion and the presence of specific grade modifiers.

Primary Criterion: Assessing the Rate of Progression

The core of the grading system lies in evaluating how quickly the disease has advanced. This can be done using either direct or indirect evidence.

Direct Evidence: A Look into the Past

The most reliable method for determining the rate of progression is through direct, longitudinal evidence. This involves comparing historical dental records, specifically radiographic images and periodontal charting, over a period of up to five years. By analyzing these records, a clinician can directly observe the amount of bone loss or clinical attachment loss (CAL) that has occurred over time.

Evidence of No Progression: If records show no loss of bone or attachment over five years, the patient qualifies for Grade A (Slow).
Evidence of Moderate Progression: If the patient has experienced less than 2 mm of loss over five years, they are classified as Grade B (Moderate).
Evidence of Rapid Progression: If the records indicate 2 mm or more of bone or attachment loss within five years, the patient is assigned Grade C (Rapid).

While direct evidence is the gold standard, its availability is often limited. Many new patients arrive without previous records, or existing records may be of poor diagnostic quality. In these common scenarios, clinicians must rely on indirect evidence.

Indirect Evidence: Making an Educated Assessment

When direct evidence is unavailable, the AAP provides two methods for indirectly assessing the rate of progression. These methods use currently available data to infer the disease’s aggressiveness.

1. Bone Loss Divided by Age

This metric provides a powerful insight into the aggressiveness of the disease relative to the patient’s age. It works by calculating the percentage of radiographic bone loss at the most affected tooth and dividing that number by the patient’s age. This ratio helps contextualize the destruction. For instance, seeing 50% bone loss in a 20-year-old is far more alarming than seeing the same amount in a 70-year-old, indicating a much more rapid disease process.

Ratio < 0.25: Suggests Grade A (Slow).
Ratio 0.25 to 1.0: Suggests Grade B (Moderate).
Ratio > 1.0: Suggests Grade C (Rapid).

2. Case Phenotype: Biofilm vs. Destruction

This assessment looks at the relationship between the amount of microbial biofilm (plaque and calculus) present and the severity of the periodontal destruction. It evaluates the host’s inflammatory response. Some individuals may have substantial biofilm deposits with minimal bone loss, suggesting a resilient host response. Conversely, others may exhibit severe destruction with surprisingly little biofilm, indicating a highly susceptible host whose immune system overreacts to the bacterial challenge.

Heavy Biofilm, Low Destruction: This phenotype points toward Grade A (Slow).
Destruction Commensurate with Biofilm: This is the expected finding and aligns with Grade B (Moderate).
Low Biofilm, High Destruction: This pattern is a hallmark of a hyper-inflammatory response and warrants a classification of Grade C (Rapid).

Grade Modifiers: Recognizing Critical Risk Factors

Beyond the primary criterion, the grading system incorporates established risk factors that are known to negatively influence the progression of periodontitis. These “grade modifiers” can elevate a patient’s grade, reflecting their increased risk profile. The two primary grade modifiers are smoking and diabetes.

Smoking

Cigarette smoking is one of the most significant risk factors for periodontitis. It impairs the body’s immune response, masks clinical signs like bleeding on probing due to vasoconstriction, and hinders healing after therapy. The grading system quantifies this risk based on the number of cigarettes smoked per day.

Non-Smoker: No grade modification.
Smoker (<10 cigarettes/day): Automatically classifies the patient as Grade B.
Smoker (≥10 cigarettes/day): Automatically classifies the patient as Grade C.

Diabetes Mellitus

Poorly controlled diabetes significantly worsens periodontal disease. Elevated blood sugar levels (hyperglycemia) lead to an exaggerated inflammatory response, impaired wound healing, and compromised immune function. The level of glycemic control, measured by the HbA1c test, is used as a grade modifier.

Normoglycemic / No Diabetes: No grade modification.
Diabetic with HbA1c < 7.0%: The patient is classified as Grade B, reflecting moderate control.
Diabetic with HbA1c ≥ 7.0%: Poor glycemic control elevates the patient to Grade C.

The Evolving Landscape: Emerging Factors and Systemic Impact

The field of periodontology is constantly evolving, and the AAP acknowledges that our understanding of risk is growing. The 2017 guidelines also highlight emerging risk factors and systemic markers that may be incorporated into future iterations of the grading system. These include:

Obesity: Adipose tissue is metabolically active and produces pro-inflammatory cytokines that contribute to systemic inflammation, exacerbating periodontitis.
Stress: Chronic stress can dysregulate the immune system, making an individual more susceptible to inflammatory diseases.
Genetic Factors: Certain genetic polymorphisms can predispose individuals to a more aggressive inflammatory response to bacterial plaque.
Nutrition and Physical Activity: Lifestyle factors play a critical role in modulating inflammation and overall health, which directly impacts periodontal status.

Furthermore, the classification system introduces the concept of assessing the systemic inflammatory burden. This involves looking at biomarkers like high-sensitivity C-reactive protein (hs-CRP), a well-known marker for systemic inflammation. Elevated levels could indicate that the patient’s periodontitis is contributing significantly to their overall inflammatory load, increasing their risk for other systemic conditions like cardiovascular disease. The analysis of biomarkers in saliva, gingival crevicular fluid, or serum represents the next frontier in providing a highly personalized risk assessment for periodontitis progression and its systemic consequences.

Conclusion: A Comprehensive Approach to Patient Care

The AAP grading system provides a robust, evidence-based framework for assessing the risk and progression of periodontitis. By integrating direct and indirect evidence with critical risk modifiers like smoking and diabetes, clinicians can move beyond a simple diagnosis to create a highly tailored treatment strategy. This comprehensive assessment not only predicts the trajectory of a patient’s oral health but also acknowledges the profound connection between periodontal disease and systemic well-being. As our understanding of risk factors and biomarkers continues to grow, this grading system will undoubtedly evolve, paving the way for even more precise and proactive patient care.