Fig. 1

a Toluidine blue staining of primary cultures of hPDLSCs observed by light microscopy. The cells show mainly a spindle-shaped appearance with long cytoplasmatic processes, euchromatic nuclei with one or more nucleoli and rough endoplasmic reticulum profiles. Original magnification: 40×. b Proliferation rate is assessed by MTT assay in five hPDLSCs grown with xeno-free medium. The results are expressed as mean ± SEM of three independent experiments, and five replicates for each experimental point. The proliferation rate is measured as the absorbance detected at 650 nm OD. c The hPDLSCs, induced to osteogenic differentiation and stained with Alizarin Red S, show a characteristic arrangement; after 4 weeks the cells break off from the bottom plate and several areas of high levels of mineralization referred to as bone nodules are evident. Original magnification: 10×. d The bar graph shows mRNA levels, determined by real-time PCR, of osteo-related genes, i.e., alkaline phosphatase (ALP) and Runt-related transcription factor-2 (RUNX2) at 7 days of culture. e Adipogenic commitment has been evaluated by the appearance of oil-red O-positive lipid vacuoles. Original magnification: 40×. f The adipo-related genes, i.e., fatty acid binding protein 4 (FABP4) and peroxisome proliferator-activated receptor γ (PPARγ), analyzed by real-time PCR are shown. g Alcian blue staining of the chondrogenic pellets obtained from hPDLSCs indicating the chondrogenic differentiation. h Effect of chondro-inductive medium on the expression of chondrogenic differentiation-related genes, such as aggrecan (ACAN) and collagen type II (COL2A1), was analyzed by real-time PCR. **p < 0.05. Scale bars = 10 μm. For each experiment a representative image has been shown