Age Effect On OPG And OPGL Expression In Periodontal Ligament Cells During Orthodontic Tooth Movement

Objective:To compare the difference of OPG and OPGL expression and its ratio in rat periodontal ligament (PDL) cells during orthodontic tooth movement between young and aged rats and to explore the possible mechanism of the age-related difference in orthodontic bone remodeling.Method:The orthodontic tooth movement of right upper molars was performed in four-week (juvenile) and 24-week (adult) SD rats. The expression of OPG and OPGL protein on the pressure side was detected by immunohistochemical staining technique at 1, 3, 5, 7, 10, 14d after applying orthodontic force and 21d ( removing applied orthodontic force at 14d). Orthodontic tooth movement (OTM) was determined by measuring the space between the maxillary first and second molars on tracings of the roentgenograms at 14d. Statistical analyses were carried out with the SPSS11.0 software, the level of significance was set to P<0.05.Result:1. On day 3 after tooth movement, OPGL expression positive cells on the pressure side of the young rats were much stronger than that of aged ones. On day 5 and 7 after tooth movement, the expression of OPGL was remarkably increased in both young and aged rats. At the same time, a large amount of osteoclasts appeared. On day 10 and 14 after tooth movement, the expression of OPGL decreased gradually in all rats. On day 21 (applied orthodontic force was removed at 14d), the expression of OPGL was weak for all rats. There were several osteoblasts located in the related bone resorbing lacunae of young rat alveolar bones.2.There were no remarkable change in OPG expression positive cells on the pressure side after applied orthodontic force in both young and aged rats.3. On day 1 and 3 after tooth movement, the ratio of OPGL to OPG has remarkable change on the pressure side between the young and aged rats, but it has no remarkable change at 5, 7, 10, 14, 21d.4.There was significant difference (P﹤0.05) in OTM (median) between young rats(0.85mm) and aged rats(0.40mm).Conclusion:The ratio of OPGL to OPG was closely related with age under orthodontic force. OPGL/OPG plays an important role in alveolar bone remodeling. The transformation of the expression of OPGL/OPG in periodontal tissues by aging factors may be the molecular mechanism, which results in adult orthodontic characteristics.