With the development of so-called “non-extraction”10 treatments in contemporary orthodontics, complications in the eruption of the second molars are becoming noticeably more prevalent in our practices ranging from a simple delay of eruption, to ectopic eruption, up to retention of the second molars caused by a mechanical obstruction. Using a retrospective study of some cases and a review of the literature, we are seeking to find new diagnostic approaches in order to choose the best treatment.