Deciduous canine and permanent lateral incisor differential root resorption

When a permanent maxillary canine erupts apical to the permanent lateral in cisor and the deciduous canine, resorption typically takes place only on th e deciduous canine root. An understanding of this differential resorption c ould provide insight into the reasons for excessive iatrogenic root resorpt ion during orthodontic tooth movement. The purpose of the present study was to examine the response of roots of permanent lateral incisors and deciduo us canines to simulated resorption, and to acid and enzyme attack, reflecti ng the physiologic environment of an erupting permanent canine. Groups of m axillary permanent lateral incisor and deciduous canine roots were exposed to 5 combinations of Ten Cate demineralizing solution, Ten Cate demineraliz ing solution with EDTA, and a Type I collagenase solution. Sections of the roots were examined under a polarized light microscope. Analysis of variati on of the resulting root lesions demonstrated that the lesion depths for de ciduous canines were greater than those for permanent lateral incisors when averaged across 4 of the conditions (F-1,F-24 = 7.49, P =.0115). On averag e, deciduous canine roots demonstrated lesions 10% deeper than did permanen t lateral incisor roots. We concluded that when deciduous canine and perman ent lateral incisor roots are subjected to acid and enzyme attack, reflecti ng the physiologic environment of an erupting permanent canine, significant ly deeper demineralized lesions are seen in, the deciduous roots compared w ith the permanent roots. This finding may partially explain the differentia l root resorption during permanent tooth eruption.