Abstract
The aim of this study was to investigate the mechanism by which periodontal ligament stem cells (PDLSCs) modulate root resorption of human deciduous teeth under mechanical stress. In this investigation, the PDLSCs were derived from deciduous and permanent teeth at different stages of root resorption. A cyclic hydraulic pressure was applied on the PDLSCs to mimic chewing forces in the oral environment. The cultured cells were characterized using osteogenic and adipogenic differentiation assays, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting analysis. The PDLSCs exhibited the ability to induce osteoclast differentiation under certain mechanical stresses. As the expressions of RUNX2, alkaline phosphatase (ALP), and osteoprotegerin (OPG) were significantly reduced, the receptor activator of the nuclear factor kappa-B ligand (RANKL) was upregulated increasing the RANKL/OPG ratio. Under hydrodynamic pressure at 0-135 kPa, the expressions of alpha 7 nicotinic acetylcholine receptors (α7 nAChR), p-GSK-3β, and active-β-catenin were markedly upregulated in PDLSCs from unresorbed deciduous teeth. Treatment with the α7 nAChR inhibitor alpha-bungarotoxin (α-BTX) and the Wnt pathway inhibitor DKK1 may reverse the mechanical stress inducing upregulation of RANKL and reduction of RUNX2, ALP, and OPG. Alizarin red staining confirmed these results. The mechanical stress applied on the deciduous tooth PDLSCs can induce osteoclastic effects through upregulation of α7 nAChR and activation of the canonical Wnt pathway. It can be suggested that chewing forces may play a major role at the beginning of the physiological root resorption of deciduous teeth.
Highlights
The physiological root resorption of deciduous teeth is one of the most important physiological changes required for the shedding of deciduous teeth and eruption of permanent teeth [1]
The α7 nAChR inhibitor alpha-bungarotoxin (α-BTX) treatment completely reversed this effect (Figures 3(e) and 3(f)). These results indicated that mechanical stress regulated the expressions of RANKL, RUNX2, alkaline phosphatase (ALP), and OPG via α7 nAChR
In order to simulate the physiologic effect of chewing forces, the periodontal ligament stem cells (PDLSCs) were loaded with variable degrees of dynamic cyclic hydraulic pressure
Summary
The physiological root resorption of deciduous teeth is one of the most important physiological changes required for the shedding of deciduous teeth and eruption of permanent teeth [1]. The physiological root resorption of deciduous teeth is closely related to the genetically programmed odontoclastic activity [2] and further supplemented by alveolar bone remodeling, dominated by osteoblasts and osteoclasts [3]. The odontoclasts have ultrastructural characteristics, enzymatic properties, and metabolic properties similar to that of osteoclasts and play a main function in the resorption of the dental hard tissues (such as dentin and cementum) [4, 5]. The physical pressure of erupting permanent teeth plays an important role in driving the root resorption of deciduous teeth [1]. The erupting force from permanent teeth affects corresponding deciduous teeth leading to root resorption [6]
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