Lefoulon introduced the term "orthodontia" in this book, and went into more detail and recorded more notable advances in the practice of orthodontics than any of his predecessors.

"Lefoulon introduced treatment without extraction. He had the happy idea of treatment both by an elastic excentric force (lingual spring) and by an elastic concentric force (vestibular spring). He was the first to obtain transversal maxillary expansion" (Dechaume & Huard, Histoire illustrée de l'art dentaire, p. 76). Hoffmann-Axthelm, History of Dentistry, pp. 364-65. Weinberger, History of Orthodontics 253-71. Digital facsimile from the Internet Archive at this link.