Background: Retaining teeth in their proper alignment after orthodontic treatment can be highly challenging. This study aimed to estimate the effectiveness of locally injected melatonin in improving bone remodelling and reducing post-orthodontic relapse.&nbsp; 
 
Methods: The third incisors on the right and left quadrants of six sheep were removed and the second and fourth incisors were brought close together by using a sectional orthodontic appliance. Melatonin solution was injected near and parallel to the mesial surface of the second incisor and the distal surface of the fourth incisor on one quadrant while the other quadrant received 1% dimethyl sulphoxide as a control. Four weeks later, the orthodontic appliance was debonded and the teeth were allowed to move back. By utilizing digital analysis, the relapse distance of the approximated incisors was measured at 21 and 42 days respectively after appliance removal. Histological and mRNA expression analysis of osteogenic marker (Runx2) were conducted to evaluate the periodontal space width and the surrounding alveolar bone of the melatonin-treated and control side incisors.&nbsp; 
 
Result: clinical and histological measurements showed that the approximated incisors in the melatonin-treated quadrant had a significantly shorter relapse distance (p&le;0.05), significantly smaller periodontal ligament width (p&le;0.05) and significantly larger new bone area formation (p&le;0.05) than in the control quadrant. The mRNA expression level of the osteogenic marker (Runx2) was significantly larger (p&le;0.05) in the melatonin-treated quadrant than in the control quadrant. The outcomes of this research suggest that melatonin can enhance bone remodelling and reduce post-orthodontic relapse in sheep.

Impact of Local Melatonin Application on Expression Level of Osteogenic Marker (Runx2) and Post-orthodontic Relapse in Ovine Model: A Split Mouth Study