Dr. Kornman and colleagues’ reading list of highly cited and otherwise classic papers, which had shaped modern Periodontology, has been published by AAP’s Journal of Periodontology this month, and has been widely welcomed by likewise practitioners and undergraduate and postgraduate teachers. At the same time, scientists have noted time and again that frequent quotation does not mean high quality of a paper but often rather mainstream. I have discussed, in a previous post, several seminal papers in oral microbiology and risk assessment which were missing in Dr. Kornman’s list but which have had a considerable impact at the time when published. In their topic #3, Kornman et al.  point to the fact that,
3. Periodontal diseases encompass multiple conditions of the teeth-supporting tissues, including periodontitis which involves multiple entities with different etiologies, different clinical and biological characteristics, and different treatment needs
When discussing with colleagues the current classification system of periodontal diseases and conditions there is hardly anybody who won’t find the 1999 consensus as regards the differentiation between chronic and aggressive periodontitis anything else than awkward. The brief introductory remarks of the 1999 consensus workshop which has been published in a now dozed off AAP enterprise (Annals of Periodontology) by Armitage (1999)  has got an impressive 2,124 citations. Two of the three remaining highly cited papers had been listed also under the risk factor theme (#2) while the paper by Löe and Silness (1963)  has described a methodological issue and, no wonder, has therefore been cited 4,161 times. While two of the three consensus papers (derived from reading lists of several U.S. graduate programs) won’t exactly fit under the topic, the classic paper by Löe et al. (1986)  on natural history of periodontal disease in man (which seems to differ in different parts of the world) had been cited an impressive 609 times (as assessed on 27 January 2014). I am missing a bit the controversy which had emerged in the aftermath of the 1999 World Workshop on the classification of periodontal diseases and conditions. For instance the much clarifying paper by Baelum and Lopez (2003)  who point to the complete outdated conception of (re-)defining a syndrome (i.e., periodontitis) essentialistically (i.e., “as if it has an independent existence”). Although the paper has been quoted just 47 times it had made a huge intellectual impact. It certainly has (or should have) played a role in both undergraduate and postgraduate teaching. A couple of years later, Van der Velden (2005)  (quoted 47 times) in entertaining the inappropriateness of the “essentialistic” idea for classifying periodontitis, and favoring a nominalistic approach, quotes Scadding (1996),
“Essentialist definitions [of diseases] typically start ‘X is . . .’, implying a priori the existence of something that can be identified as X.
“The essentialist’s hankering after a unified concept of diseases as a class of agents causing illness, is mistaken and misleading for several good reasons: many diseases remain of unknown cause; known causes are of diverse types; causation may be complex, with interplay of several factors, intrinsic; and, more generally, an effect – the disease – should not be confused with its own ’cause’.” 
On the occasion of the celebration of AAP’s 100th anniversary this year, a reading list of highly cited and otherwise classic papers has been assembled by the editor-in-chief of the Journal of Periodontology, Dr. Kenneth S. Kornman, and AAP’s Drs. Paul B. Robertson and Ray C. Williams . Authors admit that there are undoubtedly some omissions. They offer possible reasons,
For example, some important papers in the early years of periodontology may not have been highly cited because there were many fewer papers published at that time and therefore fewer opportunities to cite the paper. Similarly, some papers may have influenced clinical management of patients but did not lead to additional published work that might cite the earlier findings.
While the papers are listed within eleven themes, or unifying principles, each theme, it is promised, will be the basis for a commentary to be published during the year 2014 in the Journal of Periodontology.
I had a brief look at the extensive list and want to share with readers of my blog some ideas (and obviously missing papers) which came instantly to my mind.
Theme I. Bacteria play a critical role in the pathogenesis of periodontal disease
It appears that two groups of scientists dominate the list of highly cited papers, groups in which Jørgen Slots (6 out of 20 papers, and an additional 2 out of 4 “consensus papers of importance”) and the late Sigmund S. Socransky (9 papers plus 1) were principal investigators (the two did not collaborate). Both are known to have or have had a strong bias toward specific bacteria, or groups of bacteria, being involved in the pathogenesis of periodontitis or certain forms thereof. Advances in the microbiology of periodontal diseases definitely accelerated after Sig Socransky had published a not-so-often quoted paper in which he had tried to mitigate Robert Koch’s postulates, which were formulated almost a century earlier in 1884 and which ultimately proved Mycobacterium tuberculosis as cause of tuberculosis. Socransky’s paper on “Criteria for the infectious agents in dental caries and periodontal disease”  had been quoted, according to Google Scholar, just 94 times (as accessed on 22 Jan 2014), but had nevertheless an immense impact on how allegedly pivotal clinical studies had been designed in the 1980s and 1990s in order to “prove” that certain species or groups of species were involved in the etiology of both oral diseases.
Socransky (1979) mentions four criteria for the determination of an oral pathogen when he intentionally deviates from Koch’s: association with disease, the effect of elimination of the organism, the host response, and animal pathogenicity. This has sparked later dozens of studies by his group and hundreds all over the world which used thereby suggested study designs. Certainly, they ultimately led to a deeper understanding of the highly complex human oral microbiome. And in turn, the importance of certain periodontal pathogens had to be put into relation.