The aim of this study was to investigate the response of human periodontal ligament (hPDL) fibroblasts to an intermittent compressive force and its effect on the expression of SOST, POSTN, and TGFB1. A computerized cell compressive force loading apparatus was introduced, and hPDL cells were subjected to intermittent compressive force. The changes in messenger RNA (mRNA) and protein expression were monitored by real-time polymerase chain reaction and Western blot analysis, respectively. An increased expression of SOST, POSTN, and TGFB1 was observed in a time-dependent fashion. Addition of cycloheximide, a transforming growth factor (TGF)-β inhibitor (SB431542), or a neutralizing antibody against TGF-β1 attenuated the force-induced expression of SOST and POSTN as well as sclerostin and periostin, indicating a role of TGF-β1 in the pressure-induced expression of these proteins. Enzyme-linked immunosorbent assay analysis revealed an increased level of TGF-β1 in the cell extracts but not in the medium, suggesting that intermittent compressive force promoted the accumulation of TGF-β1 in the cells or their surrounding matrix. In conclusion, an intermittent compressive force regulates SOST/POSTN expression by hPDL cells via the TGF-β1 signaling pathway. Since these proteins play important roles in the homeostasis of the periodontal tissue, our results indicate the importance of masticatory forces in this process.

Mechanical force regulates periodontal ligament cell (PDL) behavior. However, different force types lead to distinct PDL responses. Here, we report that pretreatment with an intermittent compressive force (ICF), but not a continuous compressive force (CCF), promoted human PDL (hPDL) osteogenic differentiation as determined by osteogenic marker gene expression and mineral deposition in vitro. ICF-induced osterix (OSX) expression was inhibited by cycloheximide and monensin. Although CCF and ICF significantly increased extracellular adenosine triphosphate (ATP) levels, pretreatment with exogenous ATP did not affect hPDL osteogenic differentiation. Gene-expression profiling of hPDLs subjected to CCF or ICF revealed that extracellular matrix (ECM)-receptor interaction, focal adhesion, and transforming growth factor beta (TGF-β) signaling pathway genes were commonly upregulated, while calcium signaling pathway genes were downregulated in both CCF-and ICF-treated hPDLs. The TGFB1 mRNA level was significantly increased, while those of TGFB2 and TGFB3 were decreased by ICF treatment. In contrast, CCF did not modify TGFB1 expression. Inhibiting TGF-β receptor type I or adding a TGF-β1 neutralizing antibody attenuated the ICF-induced OSX expression. Exogenous TGF-β1 pretreatment promoted hPDL osteogenic marker gene expression and mineral deposition. Additionally, pretreatment with ICF in the presence of TGF-β receptor type I inhibitor attenuated the ICF-induced mineralization. In conclusion, this study reveals the effects of ICF on osteogenic differentiation in hPDLs and implicates TGF-β signaling as one of its regulatory mechanisms.

Aim To investigate the involvement of Wnt signalling and cell cycle regulation in hard tissue formation after pulp capping with several materials in a rat molar pinpoint exposure model. Methodology Thirty‐two rat molar pulps were mechanically exposed and assigned to 4 groups according to the pulp capping materials used Ca(OH)2, mineral trioxide aggregate (MTA), Biodentine™ and an untreated control group. After 4 weeks, the teeth were collected for microcomputed tomography to quantify reparative dentine formation. Histological analysis was then performed to evaluate the quality of the reparative dentine and the dental pulp tissue inflammatory reaction. Cyclin D1 and β‐catenin expression was examined using immunofluorescence staining. The Kruskal–Wallis followed by Dunn’s multiple comparison test was performed to determine significant differences. Results The exposed dental pulps treated with Ca(OH)2, MTA and Biodentine™ exhibited reparative dentine formation near the exposure site. Fibrous tissues adjacent to the exposure site were observed in the untreated group. The microcomputed tomography evaluation of MTA and Biodentine™ groups revealed significantly greater reparative dentine formation compared with the control group (P = 0.0032 in the MTA group and P = 0.05 in the BiodentineTM group). From histological evaluations, the BiodentineTM group exhibited significantly greater reparative dentine formation grading compared with the control group (P = 0.0152). The pulp tissues treated with Ca(OH)2 and Biodentine™ exhibited a lower inflammatory score compared with those of the untreated control (P = 0.0291 in the Ca(OH)2 and P = 0.0110 in the BiodentineTM group). Ca(OH)2, MTA and Biodentine™ induced cyclin D1 expression in the dental pulp tissues adjacent to the reparative dentine. Moreover, the Biodentine™‐treated defects demonstrated β‐catenin expression in the pulp tissue adjacent to the newly formed reparative dentine, which was not observed with the other materials. Conclusion All test materials promoted dentine bridge formation and stimulated cyclin D1 expression. The favourable outcome after direct pulp capping with Biodentine™ involved Wnt/β‐catenin signalling. However, Wnt/β‐catenin signalling did not participate in the mechanism by which Ca(OH)2 and MTA promoted reparative dentine formation.

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