Which of the following is most likely to be affected in a patient with Stage III periodontitis?

In a patient with Stage III periodontitis, the supporting bone structure is significantly affected. This stage of periodontitis is characterized by a considerable loss of alveolar bone, which supports the teeth. When periodontitis progresses to this level, it can lead to deep periodontal pockets and further tooth mobility due to the compromised bone support.

The other options focus on areas that are less directly impacted by the advanced disease severity found in Stage III. Soft tissue involvement may occur, but the hallmark of Stage III is more about the destruction of supporting structures, which surpasses mere soft tissue changes. Similarly, while occlusal surfaces can be influenced due to shifting teeth as bone loss occurs, they are not as primary a concern in terms of damage as the supporting bone itself. Dental pulp health typically remains intact until significant issues like abscesses develop, which is not a defining characteristic of Stage III periodontitis. Therefore, supporting bone structure loss aligns closely with the severity and consequences characteristic of this advanced stage of periodontal disease.