Periodontitis is a chronic inflammatory disease that affects the gums and the bone supporting the teeth. It begins when bacterial plaque triggers inflammation, which, if untreated, destroys the underlying connective tissue and alveolar bone. Dental professionals use a standardized classification system (staging and grading) to accurately diagnose the condition because periodontitis varies widely in severity. This system is necessary for establishing a precise diagnosis, determining the patient’s outlook, and creating an effective, tailored treatment plan.
Understanding Clinical Measurements
Dental professionals use specific, measurable metrics to assess the degree of tissue destruction caused by periodontitis. The most common measurement is the periodontal pocket depth (PPD), which is measured using a thin, calibrated probe inserted between the gum and the tooth surface. A healthy sulcus, the space between the tooth and gum, typically measures 3 millimeters or less without bleeding upon probing.
A periodontal pocket forms when the inflammatory process causes the gum attachment to detach from the tooth root surface, deepening the sulcus. A measurement of 6 millimeters signifies a deep pocket, indicating substantial tissue loss and presenting a challenge for routine cleaning by the patient. PPD alone is not the definitive measure of disease severity, however, because it can be influenced by gum swelling or inflammation.
The gold standard for determining the true extent of tissue destruction is the Clinical Attachment Loss (CAL). CAL is the distance measured from the cemento-enamel junction to the base of the periodontal pocket. This measurement directly reflects the irreversible loss of supporting tissue around the tooth. While pocket depth (PPD) measures the depth of the space at the time of measurement, CAL measures the actual amount of historical damage that has occurred.
The Four Stages of Periodontitis
The current classification system, established by the 2017 World Workshop, uses CAL and radiographic bone loss (RBL) to assign one of four stages. Staging classifies the severity and extent of the disease, moving from initial damage to advanced tissue loss. The initial stage is determined by the worst affected site in the mouth.
Stage I periodontitis represents the initial or mild form of the disease, where the interdental CAL is only 1 to 2 millimeters. Radiographs typically show bone loss limited to the coronal third of the root, with a maximum of 15 percent bone loss. At this stage, the maximum probing depth is usually 4 millimeters or less, and no teeth have been lost due to the condition.
Stage II is classified as moderate periodontitis, indicated by an interdental CAL of 3 to 4 millimeters. Radiographic bone loss has progressed further, affecting 15 to 33 percent of the coronal third of the root. The complexity of managing the case remains relatively low, with maximum probing depths generally not exceeding 5 millimeters.
Stage III and Stage IV represent severe and advanced periodontitis, respectively, both beginning with an interdental CAL of 5 millimeters or more. Radiographically, bone loss extends to the middle third of the root or beyond. The primary difference between these two stages lies in the complexity of treatment and the number of teeth lost. Stage III may involve the loss of up to four teeth, while Stage IV is reserved for cases with five or more teeth lost or those requiring complex, extensive rehabilitation.
Determining Complex Disease Progression
While Clinical Attachment Loss primarily determines the initial severity stage, specific local factors can dramatically increase the complexity of the case, causing the classification to shift to a higher stage. These complexity factors reflect the difficulty of treatment and the prognosis for the affected tooth. A periodontal probing depth of 6 millimeters or greater is one specific complexity factor that automatically elevates the disease classification.
If a patient meets Stage I or Stage II criteria based on CAL but presents with at least one site measuring a probing depth of 6 millimeters, the diagnosis is automatically reclassified to Stage III. A deep pocket of 6 millimeters or more is too complex for non-surgical treatment alone and often requires surgical intervention. This shift occurs because the deeper pocket prevents proper cleaning of the root surface, necessitating a more advanced treatment plan.
Other complexity factors that can shift a case to Stage III or IV include vertical bone defects of 3 millimeters or greater or Class II or III furcation involvement (bone loss between the roots of multi-rooted teeth). Stage IV classification requires complexity factors so severe they necessitate complex rehabilitation, such as secondary occlusal trauma, bite collapse, or fewer than 20 remaining teeth. Thus, a 6-millimeter pocket depth is a threshold defining significant local complexity. This factor places the case at a minimum of Stage III periodontitis, regardless of a lesser initial CAL measurement.