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López R, Baelum V. Community Dent Oral Epidemiol 2012; 40: 385–395

Nosology classifies diseases. Despite this being at the heart of conventional medicine, such groupings of diseases are sometimes little more than a label ascribed to a collection of observations. But where does this leave the patient when the cause or the cacophony of signs and symptoms are ambiguous?

During the past 25 years, there have been more than ten different periodontal disease classification systems. Within this backdrop, the authors of this paper make the following assertions: 1) the present periodontal disease classifications 'obstruct(s) our understanding of the disease', 2) the veracity of any classification should be predicated on 'well-documented differences in the management of each entity', 3) treatment outcomes must have an evidence base, and 4) more subtly, the 'need for a distinction between therapy and prevention is therefore less clear than one might think'. It is mooted that the 'prevailing idea that the periodontal disease classification should be based on etiology' should be abandoned. The present largely reductionist approach to classifications of periodontal disease is bad science. Furthermore from a moral perspective, the authors of this paper argue that such a model promulgates a 'high-risk strategy' ('targeted rescue operation' for the 'deviant minority') which perpetuates the unacceptable culture of 'victim-blaming'.

The authors consider periodontal disease should be looked at from the 'ecosocial premise of embodiment.' In this, the 'central focus is on how people literally embody – biologically – social conditions, thereby generating inequitable population distributions of health' (see Krieger N. In Anderson N B (ed) Encyclopedia of health and behaviour). And this chimes with the author's 'nominalistic disease concept' for periodontal disease (denying the existence of universals). This paper urges both the practitioner and scholar to look at periodontal disease from a 'widespread exposure to smaller risks' as opposed to 'the confined exposure to a few large risks'.

The simple message from this challenging paper is that a classification of disease, including periodontal disease, is only valuable if it drives the therapeutic imperative.