Influence of mechanical compression on human periodontal ligament fibroblasts and osteoblasts

The aim of this study was to investigate and compare the changes in human periodontal ligament fibroblasts (HPdLFs) and osteoblasts (HOBs) after the application of compressive force (CF) at two different strengths in vitro. HPdLF and HOB were exposed to CF with various strengths (5 and 10 %) using a Flexercell Compression Unit for 12 h in vitro. Viability was detected via 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide (MTT) and apoptosis rate by transferase dUTP nick end labeling (TUNEL) assay. The gene expression of alkaline phosphatase (ALP), osteocalcin (OCN), osteoprotegerin (OPG), and receptor activator of NF-kappa B ligand (RANKL) was analyzed using reverse transcriptase polymerase chain reaction (RT-PCR). Osteopontin (OPN), matrix metalloproteinase-8 (MMP-8), and tissue inhibition of metalloproteinase-1 (TIMP-1) were quantified by an ELISA. Ten percent CF decreased viability, particularly in HOBs, but did not induce increased apoptosis. ALP gene expression increased the most after 5 % CF in HPdLFs and after 10 % CF in HOB. OCN was not affected by CF in either cell line. The highest RANKL/OPG ratio was measured after 5 % CF in both cell lines. OPN was upregulated in HOB by 5 %. HPdLFs showed an upregulation of MMP-8-synthesis and an increased MMP-8/TIMP-1 ratio. HOBs have a greater effect on bone remodeling through the upregulation of OPN, whereas HPdLFs facilitate orthodontic tooth movement by influencing the extracellular matrix via the MMP-8/TIMP-1 ratio. High CF in orthodontics should be avoided to prevent tissue damage, whereas moderate CF enables active tissue remodeling and tooth movement.