This author’s ingeniousness expressed itself in his publications and in many appliances conceived and improved by him, signs of his great passion in our speciality.

In occasion of the "9th International Medical Congress" in 1887, he presented "The Angle System of Regulation and Retention" after which he made many other publications.  In these, he disagreed with Farrar and his intermittent force theory, while underlining the importance of post-treatment retention and condemning orthodontic extractions.  The palatal expander, conceived by him, became very famous and popular.  In his article published in Dental Cosmos in 1899 he wrote that it is better to talk about a "malocclusion” rather than “dental irregularity”.  He explained: “There will not be irregularity of teeth if the occlusion is perfect.  So first the treatment will consider the malocclusion and will try to eliminate it.”

In "Some Basic Principles in Orthodontia" (International Dental Journal, 1903), Angle explained the principles on which orthodontics should be founded.  These consisted of:   (a) considering dental apparatus in its complexity, (b) giving the right importance to first molars and to canines, and (c) if a preference should be given to one arch it must be the lower.  His antero-posterior interdental classification system, still used nowadays, was presented during the 4th Annual Meeting of American Society of Orthodontics in 1905 in a communication entitled "Upper first molar as basis of diagnosis in Orthodontia". This study by Angle represents a milestone in the profession because for the first time the concept of diagnostic arrangement based on science was discussed and it opened the way to etiological research of malocclusions. Angle was firmly persuaded that the first upper molars always erupt in a fixed, constant position on the facial bulk and so he identified normal occlusion as that which presents the lower molar half a cusp anterior in occlusion.  Always in contrast to Farrar's thinking, and a fervent supporter of continuous and light forces, in many lessons and publications he emphasised the importance of histological studies in the orthodontist’s curriculum to better understand osseous growth and the stability of the results of the treatment.

 Angle also suggested the redundancy of dental extractions since he was convinced that palatal expansion could resolve every case.  Accordingly he dedicated himself to the invention of numerous appliances, which he never patented. The stability of the first upper molar and the “ad libitum” expansion of the maxilla were his greatest mistakes for which all Angle’s theories were later hardly criticised especially because obtaining good occlusion was considered a condition which had the power to restore a satisfactory facial aesthetic.

However Angle’s merits rest great in consideration of the times in which he lived (the first cephalometrical analysis was performed in 1930), but also and especially for the passion he took in the attempt to give dignity and autonomy to the orthodontic speciality. These concepts and ideas were performed by the American universities after many years and still seem to be not understood by many Italian universities.