Which statement about the base of suprabony and infrabony pockets is correct?

The correct statement is that both the base of a suprabony pocket being above the alveolar crest and the base of an infrabony pocket being below the alveolar crest hold true in the context of periodontal disease.

In a suprabony pocket, the base of the pocket lies above the level of the alveolar crest, meaning that the inflammation and destructive process of periodontitis have extended the pocket formation without the loss of bone that would position the base below the crest. This is typically seen in horizontal bone loss scenarios where the supporting alveolar bone is maintained but the soft tissue has receded.

Conversely, in an infrabony pocket, the base of the pocket is located below the level of the alveolar crest. This reflects a more advanced stage of periodontal disease where vertical bone loss has occurred. The resulting infrabony pocket typically signifies that there has been significant destruction of the osseous support of the tooth, leading to the pocket extending below the bony margin.

Thus, both statements correctly describe the positioning of the base of suprabony and infrabony pockets relative to the alveolar crest, confirming that both are true.