The circadian expression of osteogenic factors in periodontal tissue loading mechanical force: new concepts of the personalized orthodontic care

Abstract

Objective The need for orthodontic treatment continues to increase. Strategies that shorten the treatment course and reduce discomfort are most welcome in clinic. Circadian rhythm plays important role in various physiological processes, including bone formation. This study intended to depict a possible circadian releasing property of the osteogenic factors within the periodontal tissue during orthodontic treatment, which may direct a more efficient and satisfactory orthodontic treatment to the patient. Methods Primary periodontal ligament cells (PDLCs) were obtained from the Sprague-Dawley (SD) rats. An equibiaxial strain value of 12% was applied on rat PDLCs (rPDLCs). After 2 h stimuli of 10 −7 M dexamethasone (DX), the osteogenic genes' expressions were detected by real-time polymerase chain reaction (RT-PCR) at Zeitgeber times 0, 4, 8, 12, 16, 20, and 24. An orthodontic appliance was placed on 45 SD rats. Animals were maintained under 12-h light/dark periods and euthanized at 9 time points over the diurnal cycle. The orthodontic sensitive tissues of the mesial root of the maxillary first molar were collected for RT-PCR and immunohistological assay. Results The rPDLCs displayed typical fibroblastic spindle shape, and subcultured steadily in vitro. Induced by DX, the mRNA expression of Col-1, OPN, and IBSP within the loaded/unloaded rPDLCs oscillated as that of the main clock gene Per-1. The osteogenic genes' expressions as well as the protein releases sustained a circadian oscillation trend in vivo. Conclusions This study indicates the existence of a circadian rhythm of the osteogenic factors within the orthodontic sensitive tissues, which highlights the importance of precise timing of force loading in further orthodontic treatment. Thus, a periodicity pattern of orthodontic traction at night may prove a more efficient tooth movement while minimizing the treatment window and discomfort complains.

Effect of Dexamethasone Infiltration on Periodontal Ligament After Experimental Molar Luxation in Rats

“…Furthermore, it was recorded by Hakki et al, 2009 27 that the addition of dexamethasone to FGF2 to cultured periodontal ligament cells would enhance the periodontal regeneration. While the sole addition of dexamethasone induced biomineralization and osteogenic differentiation 31 .An observation that also explains the elevated means of alkaline phosphatase expression in the current study. Dexamethasone was demonstrated to improve periodontal healing in research work which is confirmed by the elevated level of FGF2 in the present study.…”

“…They suggested that corticosteroids in general could be effective in stimulation of periodontal ligament recovery 28 . Moreover, the organized spindle shape of fibroblasts demonstrated in the current interval of the treated group was also recorded by other researchers' in vitro studies 27,31 . However, the herein results of the treated group were not in accordance with Choi et al, as they reported that dexamethasone treatment induced the production of DKK-1 gene by periodontal ligament stem cells in vitro which in turn inhibited the growth of human periodontal ligament stem cells 17 .…”

Dynamic study into autophagy and apoptosis during orthodontic tooth movement

“…Orthodontic mechanical force can be roughly divided into traction force and compression force, and it can affect the biological behavior of PDLCs ( 20 , 21 ). Moreover, it has been reported that PDL hyalinization, bone density and bone turnover can affect the rate of OTM ( 22 ).…”

Circadian rhythms affect bone reconstruction by regulating bone energy metabolism

“…Recent studies revealed a relationship between circadian rhythm and osteogenesis and osteoclastogenesis. The study found that under the effect of the peripheral nervous system, bone-related genes and bone absorption-related genes show periodic expression patterns [ 32 ]. Circadian time cues in bone affect osteoblast and osteoclast differentiation, and bone transformation markers exhibit circadian changes [ 33 ] (Fig.…”

“…In addition to Bmal1 , Clock , Cry and Per are also the main genes of the molecular clocks. Recent studies also showed that Cry2 and Per2 affect multiple mechanisms of adjusting bone volume [ 32 ]. Cry2 affects osteoclast activity [ 46 ].…”