Final answer:
Inform the patient that deep probing depths in periodontitis may require additional treatments beyond nonsurgical therapy, such as surgical intervention or local antibiotics, and emphasize the importance of good oral hygiene and regular periodontal maintenance.
Step-by-step explanation:
During nonsurgical therapy for a patient with periodontitis, encountering multiple sites with probing depths exceeding 6 mm where root surfaces cannot be thoroughly instrumented is a clinical concern. You should inform the patient that such depths can harbor bacteria and potentially complicate their periodontal disease. Explain that when root surfaces cannot be completely cleaned through nonsurgical methods, additional treatment such as surgical intervention, local delivery of antibiotics, or other advanced periodontal therapies may be necessary. It's crucial to convey that maintaining good oral hygiene at home and regular periodontal maintenance visits are essential for managing their condition.