Effect of Different Parameters of In Vitro Static Tensile Strain on Human Periodontal Ligament Cells Simulating the Tension Side of Orthodontic Tooth Movement.

Changyun Sun,Sven Otto,Mila Janjic Rankovic,Uwe Baumert,Andrea Wichelhaus,Thomas Stocker,Matthias Folwaczny

doi:10.3390/ijms23031525

Abstract

This study aimed to investigate the effects of different magnitudes and durations of static tensile strain on human periodontal ligament cells (hPDLCs), focusing on osteogenesis, mechanosensing and inflammation. Static tensile strain magnitudes of 0%, 3%, 6%, 10%, 15% and 20% were applied to hPDLCs for 1, 2 and 3 days. Cell viability was confirmed via live/dead cell staining. Reference genes were tested by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and assessed. The expressions of TNFRSF11B, ALPL, RUNX2, BGLAP, SP7, FOS, IL6, PTGS2, TNF, IL1B, IL8, IL10 and PGE2 were analyzed by RT-qPCR and/or enzyme-linked immunosorbent assay (ELISA). ALPL and RUNX2 both peaked after 1 day, reaching their maximum at 3%, whereas BGLAP peaked after 3 days with its maximum at 10%. SP7 peaked after 1 day at 6%, 10% and 15%. FOS peaked after 3 days with its maximum at 3%, 6% and 15%. The expressions of IL6 and PTGS2 both peaked after 1 day, with their minimum at 10%. PGE2 peaked after 1 day (maximum at 20%). The ELISA of IL6 peaked after 3 days, with the minimum at 10%. In summary, the lower magnitudes promoted osteogenesis and caused less inflammation, while the higher magnitudes inhibited osteogenesis and enhanced inflammation. Among all magnitudes, 10% generally caused a lower level of inflammation with a higher level of osteogenesis.

Highlights

The aim of orthodontic tooth movement (OTM) is to align malpositioned teeth by applying external forces (“orthodontic forces”) to the teeth and stimulating bone remodeling [1]
Inflammation is regulated by a large array of mediator molecules [3], including pro-inflammatory molecules such as interleukin 1B (IL1B), tumor necrosis factor (TNF), interleukin 6 (IL6) and interleukin 8 (IL8), as well as prostaglandin-endoperoxide synthase 2 (PTGS2; known as COX2), prostaglandin E2 (PGE2) and anti-inflammatory molecules such as interleukin 10 (IL10) [4]
Light orthodontic forces seem to be beneficial for coordinated bone remodeling and the maintenance of periodontal tissue homeostasis, enabling efficient tooth movement

Summary

Introduction

The aim of orthodontic tooth movement (OTM) is to align malpositioned teeth by applying external forces (“orthodontic forces”) to the teeth and stimulating bone remodeling [1]. Located between the teeth and the alveolar bone, the human periodontal ligament (hPDL) and the cells it contains play an essential role in withstanding mechanical forces in physiological, pathological and therapeutical conditions, e.g., orthodontic treatment [2]. During OTM, mechanical stimulation triggers complex aseptic inflammatory cellular and molecular processes causing the remodeling of the surrounding tissues, leading to bone resorption on the compression side and bone formation on the tension side. Various molecules mediating osteoclasto/osteoblastogenesis are upregulated at different stages of bone remodeling during this aseptic inflammatory process [5], including transcription factors (e.g., Runt-related transcription factor 2 (RUNX2) and SP7, known as osterix) [6–8] and early or late osteoblastic marker genes such as alkaline phosphatase (ALPL), bone-matrix protein-bone gamma-carboxyglutamate protein (BGLAP, known as osteocalcin) [9], as well as receptor activator of nuclear factor kappa ligand (RANKL) and osteoprotegerin (OPG) [10]. Its dimerization with JUN forms the heterodimeric activator protein 1 (AP1), which binds to different promoters of osteoblast-specific genes, activating the proliferation and differentiation of osteoblasts in periodontal tissue [2,11]

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