Interdental Bone Height as the Determinant of Root Coverage: The Cairo 2011 Paradigm

To understand why interdental bone governs surgical success, one must examine surgical microvascular biology. When an autogenous connective tissue graft is sutured over an exposed root, the root surface itself possesses zero blood vessels (it is avascular mineralized dentin).

The transplanted tissue can survive only if it receives collateral blood supply diffusing from adjacent tissues. The primary vascular donors are the two lateral interdental papillae flanking the receded tooth. These papillae are supported directly by the underlying interdental alveolar bone crest.

The Cairo classification of gingival recession defects categorizes tissue loss based on the relationship between facial attachment loss and interdental clinical attachment levels. Recession Type 1 (RT1) exhibits facial recession with zero loss of interproximal clinical attachment, representing an ideal candidate for 100% root coverage.

Dr. Cairo categorized recession defects into three distinct groups based on the relationship between buccal and interdental Clinical Attachment Level (CAL):

Recession Type 1 (RT1): Gingival recession with zero interdental clinical attachment loss. The interdental bone is at its full physiological height. Complete 100% root coverage is biologically predictable. Recession Type 2 (RT2): Gingival recession accompanied by interdental attachment loss, but the interdental loss is less than or equal to the buccal recession. Complete coverage is unattainable, but partial coverage up to the interdental bone height is predictable. Recession Type 3 (RT3): Interdental attachment loss is greater than buccal loss; root coverage is biologically impossible.

Recession Type 2 (RT2) defects feature facial recession accompanied by interdental attachment loss that is less than or equal to the facial loss. In RT2 defects, partial root coverage can be achieved, but complete 100% soft-tissue restoration is limited by the reduced interdental bone height.

The beauty of the Cairo classification is that it removes guesswork and protects patients from unrealistic promises. If a patient presents with an RT1 defect, the surgeon can confidently aim for complete cosmetic root coverage and restoration of the original gumline.

If the defect is RT2, the periodontist reframes the surgical goals before picking up a scalpel. The patient is informed that 60% to 70% coverage will be achieved, and that the primary purpose of surgery is augmenting attached tissue thickness to stop progressive tooth loss and eliminate sensitivity. In RT3, surgery focuses strictly on non-surgical stabilization.

Recession Type 3 (RT3) defects present severe interdental attachment loss that exceeds the extent of facial recession, typically caused by advanced periodontitis. Complete surgical root coverage in Cairo RT3 defects is biologically impossible because there is no interproximal vascular bone scaffold to nourish an advanced tissue flap.

For over three decades, the 1985 Miller classification was the standard system used to categorize gingival recession. However, Miller's system relied on the mucogingival junction—a landmark that can be ambiguous or absent—and suffered from poor inter-examiner reproducibility.

In 2011, Cairo and colleagues introduced a paradigm shift based entirely on objective clinical measurements of interproximal clinical attachment loss. The Cairo system recognizes that the interdental bone height and papilla integrity represent the true biological foundation for root coverage.

Cairo RT1 defects feature zero interproximal attachment loss; RT2 defects feature interproximal loss less than or equal to buccal loss; and RT3 defects feature interproximal loss greater than buccal loss. This objective framework provides unparalleled predictive accuracy for surgical outcomes.

The central biological principle established by the Cairo classification is that soft tissue cannot predictably survive coronal to the underlying interproximal bone crest. When a surgical flap is coronally advanced over an avascular root, its collateral blood supply is derived from the adjacent interdental vascular plexuses.

In RT1 defects, the intact interproximal bone and papilla provide a rich, multi-directional blood supply that nourishes the advanced flap, enabling complete root coverage. In RT2 defects, where interdental bone has resorbed, the vascular bed is reduced, and the newly formed gingival margin will heal only up to the level of the interdental attachment.

Understanding this biological ceiling prevents clinicians from promising unachievable complete coverage in patients with underlying interdental bone loss.