Final answer:
The resolution of periodontal inflammation is the best criterion for evaluating the success of periodontal treatment, as it signifies a halt in disease progression and damage to oral structures.
Step-by-step explanation:
The single best criterion for evaluating the success of periodontal debridement and root planing as well as oral hygiene 4 to 6 weeks after treatment is the resolution of periodontal inflammation. While reduction in pocket depth, improvement in gingival bleeding, and decrease in plaque accumulation are all important indicators of improved periodontal health, the resolution of inflammation signifies that the immediate threat to periodontal structures has been addressed.
Periodontal inflammation is a critical factor that leads to the destruction of the supporting structures of the teeth, including the gums and bone. Thus, its resolution indicates a successful halt in disease progression.