Address for correspondence: sorelolivier@wanadoo.fr Our training in dental surgery or stomato­ logy has taught us everything we need to know about teeth: their life and works. We afford them care and protection and, as od­ ontologists, reorganization. Faced by the failure of long­term results for expansion, C. Tweed conceived the idea of extracting healthy dental elements and drew up his drastic rules for the correct po­ sition of the mandibular incisor. Extraction has become consensual, but for some it amounts to voluntary mutilation. There is thus an open battle between the partisans and opponents of extraction and, beyond that, of the concept of expansion. Ricketts was one of the first to question Tweed, whom he found far too extractionist; he was not exactly challenging the concept itself, but defined an area of equilibrium, integrating function. Others, such as Korn, took up more extreme positions, describ­ ing more or less extractionless approaches, with a conservationist, natural, “organic” at­ titude more in line with the Zeitgeist: con­ serving what nature has bestowed on us is pure benefit... What is wanted, however, is precisely to change what Mother Nature provided! So, how to justify extraction? The treatment decision should be guided by the risk/benefit ratio (presuming here that the decision to undertake orthodontic treatment has a positive risk/benefit value). Assessment of extraction risk begins with the risks incurred by surgery. Moreover, ex­ traction represents an immediate, definitive and irreversible loss of dental substance; benefit has therefore to match this loss, or the risks entailed by abstention have to be unacceptable.