This literature review is concerned with the ability of personal oral hygiene and mechanical instrumentation to establish and maintain periodontal health. Clinical, microbiologic, and histologic responses to non-surgical therapy are evaluated to provide guidelines for expected treatment results. Factors that may limit the effectiveness of non-surgical therapy as a closed procedure are also addressed. These include length of therapy, skill of therapists, patient compliance, responsibility of clinician for maintenance, and disease activity status of the patient.