Milestones in periodontal research and the remaining critical issues.

A significant recent development in periodontal research has been the convergence of basic and clinical research resulting in a logarithmic increase in the rate of progress. Scientific consensus has been reached in many areas. In most populations, moderate to severe periodontitis affects a relatively small segment of adults who are at high risk. The microbial etiology is accepted and the identity of the major pathogenic bacterial species is known. The mechanisms through which resistant individuals successfully fend off the microbial challenge are known, and the immuno-inflammatory pathways activated by bacteria that underlie destruction of the alveolar bone and the connective tissues of the periodontium are reasonably well understood. The evidence shows that these pathways are held in common by all forms of periodontitis. Therapeutic modulation of these pathways is now possible, and new treatments based on such modulation are now becoming available. Although bacteria are essential for disease to occur, they are insufficient; a susceptible host is also necessary. Host susceptibility, disease progression and response to treatment are determined predominantly by heredity and environmental and acquired risk factors. Some of these can be changed while others are immutable. Concepts and procedures for treatment are generally scientifically based and appropriately applied. Preventive measures are largely successful and widely practiced in industrialized countries. Clearly, control of these ancient chronic diseases is now within our reach. In spite of the tremendous progress, many unresolved issues remain. The purpose of this paper is to summarize some of the major accomplishments of periodontal research, and identify and discuss some of the more important critical issues that still need to be addressed.