Which type of periodontal bony defect has the best prognosis for regenerative therapy?

Periodontal bony defects are classified by the number of remaining bony walls surrounding the defect. A three-wall (intrabony) defect has the best prognosis for periodontal regeneration because three bony walls provide maximum support for new bone formation, contain the graft material, and allow blood supply from multiple directions. Two-wall defects (craters) have intermediate prognosis. One-wall defects have the poorest prognosis because only one wall remains to support regeneration. The three-wall defect provides an ideal environment for guided tissue regeneration (GTR), bone grafting, or biologic agents such as enamel matrix derivative (EMD).