The original histological investigation that forms the basis of our present understanding of tooth movement was carried out on dogs by the Swedish dentist Carl Sandstedt at the Karolinska Institute, Stockholm. His findings were published in 1901 as a monograph in Swedish, and shortly after his death in 1904, as three articles in German entitled ‘Einige Beiträge zur Theorie der Zahnregulierung’. Sandstedt observed that the bone was deposited on the alveolar wall of the tension side with both heavy and light forces, new bone spicules following the orientation of the periodontal fibres. On the pressure side, with light forces, osteoclasts resorbed the surface of the alveolar bone, but heavy forces compressed the periodontal ligament resulting in hyalinization—the formation of localized cell-free areas. At these sites, bone removal resulted from undermining resorption by osteoclasts from adjacent marrow spaces. He also observed root resorption and commented on the centre of rotation of the teeth. No English version of Sandstedt’s research has ever been published, and in view of its importance, one of us (DB) has translated his three articles from the original German. The aim was to persuade an orthodontic journal to publish the articles in full—however, weighing-in at 21 000 words, the impracticality of this plan soon became clear. We concluded that excerpts from the text plus commentary would be the most practical solution. Where possible and without materially changing the intended meaning, we have translated the German text into something resembling contemporary English, accompanied by the original 16 figures.