Periodontitis is advanced gum disease, a chronic inflammatory condition. It occurs when the body’s response to bacterial plaque leads to the breakdown of specialized tissues surrounding the tooth root. This destructive process ultimately targets the jawbone supporting the teeth. The pattern of bone loss is not uniform, creating specific anatomical defects that require different diagnostic and treatment approaches. The way the supporting alveolar bone is lost is a fundamental distinction for dental professionals.
The Formation of Periodontal Pockets
Healthy gum tissue forms a shallow space around the tooth called the gingival sulcus, typically 1 to 3 millimeters deep. Bacterial plaque triggers an inflammatory response known as gingivitis, the initial stage of gum disease. If inflammation persists, the infection extends downward, destroying the connective tissue fibers anchoring the gum to the tooth root. This detachment allows the epithelial lining to migrate down the root surface.
This deepening creates a measurable space known as a periodontal pocket. The pocket allows aggressive bacteria to accumulate, fueling a vicious cycle of inflammation and tissue destruction. As the pocket deepens, the body’s immune response starts to resorb the underlying alveolar bone. The specific relationship between the base of this pocket and the remaining alveolar bone crest determines the classification of the resulting defect.
Suprabony and Infrabony Defects Defined
Bone defects are classified entirely on the anatomical position of the base of the periodontal pocket relative to the adjacent alveolar bone crest.
Suprabony Defects
A suprabony defect occurs when the bottom of the pocket is located coronal (above) the level of the remaining alveolar bone crest. This defect is associated with horizontal bone loss, which is the most common pattern seen in periodontitis. Horizontal bone loss means the bone height is reduced in a relatively even manner across the width of the jawbone, maintaining a crest that is mostly perpendicular to the tooth surface.
Infrabony Defects
An infrabony defect, also known as a vertical or intrabony defect, is defined by the base of the pocket being located apical (below) the level of the adjacent alveolar bone crest. This pattern of loss creates a trough, crater, or bowl-shaped area of missing bone that angles down the root surface. The distinct morphology of an infrabony defect is classified by the number of bony walls remaining around the defect space: three-wall, two-wall, or one-wall defects.
The number and configuration of remaining walls is a significant factor in determining the potential for bone regeneration. The three-wall defect is the most favorable for treatment, as it is surrounded by bone on three sides, offering containment for new bone growth. A one-wall defect, often called a hemiseptal defect, is the least contained and presents a greater challenge for predictable bone repair. The shape and depth of the defect directly influence the biological environment and the likelihood of successful repair.
How Dentists Identify These Conditions
Differentiating between suprabony and infrabony defects requires clinical examination combined with radiographic imaging. The initial step is periodontal probing, using a specialized instrument to measure the pocket depth from the gum margin to the attachment point on the root. This measurement determines the vertical extent of the soft tissue lesion and helps locate the base of the pocket. Probing alone, however, cannot reveal the underlying bone morphology.
Dental X-rays are subsequently used to visualize the supporting bone structure. Horizontal bone loss associated with suprabony defects appears as a generalized reduction in bone height. The remaining bone crest is largely parallel to the line connecting the cementoenamel junctions (CEJ) of adjacent teeth. In contrast, infrabony defects appear on a radiograph as distinct, angular, or wedge-shaped radiolucencies extending down the side of the root.
While X-rays are highly informative, they provide only a two-dimensional view. They can sometimes obscure the true three-dimensional shape and number of walls of an infrabony defect due to the superimposition of bone structures. For the most precise diagnosis, especially before complex surgical intervention, the exact defect morphology is often confirmed by direct visual inspection during a surgical procedure. Accurate identification of the defect type is necessary to select the most effective treatment approach.
Treatment Strategies Based on Defect Type
The anatomical distinction between the two defect types dictates the strategy for correcting the resulting bone and soft tissue loss.
Suprabony Defect Treatment
Treatment for suprabony defects aims primarily at pocket elimination to create a biologically maintainable environment. This often begins with non-surgical therapy such as Scaling and Root Planing (SRP) to remove plaque and calculus from the exposed root surface. If deep pockets persist, surgical intervention may involve resective procedures, such as osseous surgery. In osseous surgery, the bone is reshaped and the gum tissue is repositioned to reduce the pocket depth.
Infrabony Defect Treatment
For infrabony defects, the treatment goal shifts from simply reducing the pocket to actively regenerating the lost tissue, including alveolar bone, cementum, and periodontal ligament. The contained nature of many infrabony defects makes them biologically suited for regenerative procedures. These techniques utilize bone grafts, barrier membranes for Guided Tissue Regeneration (GTR), or biological agents to rebuild lost support. Narrow and deep infrabony defects, especially those with three remaining bony walls, respond most favorably to regenerative surgery. The specific geometry of the vertical defect directly influences the prognosis and the choice to pursue complex regenerative surgery over simpler resective methods.