Abstract: Radix entomolaris（RE）is a supernumerary distolingual root of mandibular molars, mainly in mandibular first molars. RE is partly or completely attached to the distal root of mandibular molars. RE is an usually small short root with a hook, which gratly increase the difficulty of root canal treatment for mandibular first molars. An awareness and identification of the RE can contribute to the successful outcome of root canal treatment in mandibular first molars. Recent years, more and more knowledge for RE is known by us, and there is many
research about RE. This article is a review about the research of RE in mandibular first molars.