The Lid’s Off the Box Again

Having just had submitted a completely revised chapter on Periodontal Microbiology for the second edition of my textbook which is due early next year, I’ve read with interest an editorial (or Perspective) by Professor Mike Curtis about a new study by Brazilian microbiologists/periodontists Perez-Chaparro et al. (2014) in the Journal of Dental Research, a systematic review of 41 studies on newly identified pathogens associated with periodontitis. As far as I understand, none was longitudinal. Curtis remembers the days (in the 1980s and 1990s) when periodontal investigators not intimately involved in what was going on in oral microbiology disrespectfully (“scornfully”) called “their microbiology colleagues – ‘The Bug of the Month Club’ – intended to convey the inappropriate promotion of this apparently bewildering array of periodontal pathogen new kids on the block.”

What is called by Perez-Chaparro et al. (2014) as “modern era” of oral microbiology, i.e. the past 12 years, was covered after the focused question had been asked, “What is the weight of evidence for the existence of newly identified periodontal pathogens based on association studies?”

There is no discussion in the paper about the basically erroneous prerequisite, Socransky’s modification of Koch’s postulates in 1979 when he paradigmatically had suggested “criteria for the infectious agents in dental caries and periodontal disease. Unfortunately, Perez-Chaparro et al. further reduced the claimed evidence for pathogenic potential to,

(1) The organism should be present in higher prevalence and/or levels in disease than in health (“association” studies), and

(2) Its suppression or elimination should reduce or stop disease progression (“elimination” studies).

They concede that, so far, “elimination” studies are missing for new pathogen candidates, so “strong” evidence for “true new periodontal pathogens” is missing but, based on “association” studies, moderate evidence might have emerged. But that is not the fact.

My grave concern is that a 35-year-old concept of identifying oral pathogens, which, at the time, was mainly based on Koch’s postulates which were largely diluted (but included also evidence from host response, animal experimentation, and the identification of virulence factors, neither of which is even mentioned in the paper by Perez-Chaparro et al.), must not be valid today anymore; despite the fact that they were helpful in the identification of cultivable microorganisms as potential periodontal candidates in the 1980s. Unfortunately, Socransky (1979) did not base his criteria on somewhat earlier concepts for proving causality of complex diseases such as periodontitis, namely Bradford Hill’s criteria of 1965, which had identified temporality as crucial.

As long as temporal association has not been established, there is no, let alone “moderate”, evidence for a role of newly identified bacteria listed in Table 3 as periodontal pathogens.

Table 3 of the paper by Perez-Chaparro et al. (2014). A claim is made that the evidence for newly identified periodontal pathogens in the etiology of periodontitis is weighted based on

Table 3 of the paper by Perez-Chaparro et al. (2014). A claim is made that the evidence for newly identified periodontal pathogens in the etiology of periodontitis is weighted based on “association studies.”

20 August 2014 @ 12:15 pm.

Last modified August 22, 2014.

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