Hyalinization and root resorption during early orthodontic tooth movement in adolescents.

The aim of this investigation was to study the hyalinization of the periodontal ligament with time and its relationship to root surface resorption after the application of an orthodontic force, reactivated weekly, of 50 cN (approximately 50 g). Fifty-six patients (18 boys and 38 girls, mean age 13.8 years) were divided into 7 groups of 8. In each patient, one premolar was moved buccally 161 with a fixed orthodontic appliance. The contralateral premolar served as a control. The experimental periods ranged from 1 to 7 weeks. Local areas of overcompression in the periodontal ligament were recorded in 33 test teeth (59%) and 2 controls (4%). Hyalinization was seen in all experimental groups, more often after the first 4 weeks of force application. Hyalinized areas were recorded opposite an intact root surface (54%) or close to and just apical or coronal to an area of root resorption (45%), and were usually located buccocervically and linguoapically, corresponding to expected pressure zones of the periodonal ligament.