Osteogenic differentiation of periodontal fibroblasts is dependent on the strength of mechanical strain

Objective: During orthodontic therapy the correct strength of mechanical strain plays a key role for bone remodelling during tooth movement. Aim of this study was to investigate the osteogenic differentiation of human periodontal ligament fibroblasts (HPdLF) depending on the applied strength of mechanical strain compared to osteoblasts (HOB). Design: HPdLF and HOB were loaded with different strengths (1%, 5% and 10%) of static mechanical strain (SMS) for 12 h in vitro. Viability was verified by MTT and apoptosis by TUNEL assay. Gene expression of cyclin D1, collagen type-1 (COL-I), alkaline phosphatase (ALP), osteocalcin, osteoprotegerin (OPG) and receptor activator of the NF-kappa B ligand (RANKL) were investigated using RT-PCR. OPG and RANKL synthesis was measured by ELISA and ALP activity by colorimetric assay. Results: 10% of SMS led to a decrease in cell viability of both cells lines, but no increased rate of apoptosis. RT-PCR showed the highest increase of cyclin D1 expression for HPdLF and HOB when applied to 5% of SMS, and HOB showed a doubling of COL-I gene expression. HPdLF and HOB showed a strength-dependent synthesis of OPG and ALP activity, whereas HOB demonstrated a decrease in OPG synthesis and ALP activity when applied to 10% of SMS. Conclusion: Osteogenic differentiation of HPdLF correlates with increasing strength of SMS. HOB show decreased activity when applied to high SMS, demonstrating potential damage to the bone remodelling due to strain of high strength. SMS up to 5% provides the best conditions for bone formation at the tension site of tooth movement. (C) 2013 Published by Elsevier Ltd.