The radiographic bone defect noted on the maxillary left 1st bicuspid is best described as:

• A. 2-wall infrabony defect
• B. 1-wall defect
• C. 3-wall infrabony defect
• D. Horizontal bone loss

Answer: (A)

Understanding osseous defects involves recognizing vertical (infrabony) bone loss and counting how many bony walls remain around the defect. An infrabony defect has its base below the crest of the alveolar bone, and the “walls” are the cortical bone still present around it.

In this scenario, the radiograph shows a vertical, angular loss of bone around the maxillary left first premolar with two bony walls still intact. That means two walls remain, while the third wall is missing, which fits a two-wall infrabony defect. Such defects are typical when bone loss occurs interproximally or along two supporting walls rather than around the tooth in a uniform circle.

A one-wall defect would have only a single wall remaining, which isn’t the case here. A three-wall infrabony defect would present as a crater with three walls around the defect, which isn’t indicated. Horizontal bone loss implies a uniform, saddle-like reduction around the tooth without a distinct vertical angulation, which also isn’t what's described.

So, the description aligns with a two-wall infrabony defect because the defect is vertical with two remaining osseous walls.