“…However, it is still a challenge to accurately quantify 3D experimental variables such as root resorption and bone formation. It is known that the mechanical stimuli for orthodontic responses are the 3D distributed stresses/strains on the root and bone-PDL (periodontal ligament) interface (Andersen et al, 1991a;Andersen, Pedersen & Melsen, 1991b;Cattaneo, Dalstra & Melsen, 2005;Davidovitch, 1991;Fukui, 1993;Jones et al, 2001;Katona et al, 1995;Kawarizadeh et al, 2003a;Kawarizadeh et al, 2004;Krishnan & Davidovitch, 2006;Melsen, 1999;Melsen, 2001;Middleton, Jones & Wilson, 1996;Provatidis, 2002;Roberts, Goodwin & Heiner, 1981;Rygh, 1976;Toms et al, 2002;Wright & Yettram, 1979). Histology provides only 2D data and the results greatly depend on the choice of the representative sections, as well as choice of method of root resorption assessment.…”