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Khalighinejad N, Aminoshariae MR et al. J Endod 2016;42: 1427–1434

In this muddled paper, the results were given in the discussion, the direction of association was unclear, and although causation was touched on, there was no mention of the Bradford Hill Criteria.

But there was an abundance on plausibility (the mechanism that links cause and effect). For example, these authors cite a paper that found interleukin 6 and tumo(u)r necrosis factor can increase insulin resistance but then state '...the current evidence is inconclusive and insufficient to suggest an association' between diabetes and endodontic disease. The key observation was that there was a link between endodontic pathology and CVD, and CVD and endodontic disease. Only those studies looking for associations between CVD and endodontic disease showed a low level of bias. The quality of studies looking for other such links with identified systemic disease such as chronic liver disease, haemophilia and bone mineral density were poor. In this systematic review, 16 articles were interrogated. It was not possible to carry out a meta analysis due to study heterogeneity.