Analytical, oral epidemiological studies in adult 'toothbrushing' populations show that the highest prevalence of missing teeth is for molars and maxillary premolars ('key-risk' teeth). The highest prevalence of subgingival microflora, gingivitis (CPITN-1), plaque retentive factors, such as subgingival calculus and restoration overhangs (CPITN-2), and diseased pockets > 3 mm (CPITN-3-4) is found on the approximal surfaces of the same teeth ('key-risk' surfaces). Primary and secondary prevention, as well as treatment of periodontal disease should be focused on these 'key-risk' surfaces. One single, well-executed subgingival scaling and root-planning procedure in deep, diseased periodontal pockets, followed by oral hygiene training and professional mechanical tooth-cleaning (PMTC) at need-related intervals, will prevent further loss of periodontal attachment. However, if the root cementum is removed during instrumentation, and the post-treatment plaque control programme fails, microorganisms will recolonize and invade the rough exposed root dentine, resulting in recurrence of periodontitis and possibly, root caries and pulpitis. Some of these problems may be overcome by the application of new instruments and methods for self-care, PMTC, removal of overhangs, scaling and root-planing without removing 'non-diseased' cementum.