Purpose: In severe cases of periodontitis or dental trauma, periodontal tissues including alveolar bone and periodontal ligament (PDL) are destroyed, and so novel therapy by cell implantation to reconstruct the damaged periodontal tissue is strongly required. Human dental pulp (DP) tissue, which has an abundant population of DP stem cells (DPSC), is believed to be a promising source of cells for regenerative medicine in various medical fields. Recently, matrix elasticity has been shown to regulate the differential fate of stem cells. Therefore, in the present study, we investigated whether DPSCs could convert to PDL-like cells by perceiving matrix elasticity, and possess the potential to regenerate periodontal tissues.

 Method: Primary human DP cells, PDL cells, DPSCs and PDL stem cells (PDLSCs) were isolated from healthy patients. Gene expression was analyzed by quantitative RT-PCR. Osteogenic, adipogenic and chondrogenic induction assays were examined by alizarin red S staining, oil red O staining and alcian blue staining, respectively. Expression of cell surface markers was analyzed using a flow cytometer. Bone slices (depth 10 mm×width 10 mm×height 3 mm) were created from mandibular bone of healthy swine. Rat GFP-expressing DP cells were transplanted in the tooth socket of a rat tooth replantation model, and homing of transplanted DP cells in PDL tissue was investigated by immunohistochemical staining.

 Results: Primary PDL cells showed higher expression levels of PDL-related markers such as Periostin, Col-1, and α-SMA than those of primary DP cells by quantitative RT-PCR. DPSCs and PDLSCs showed pluripotency, and also expressed mesenchymal stem cell markers, such as CD73, CD90, CD105, CD146, and CD166 similarly to PDLSCs examined by flow cytometric analysis. PDLSCs also highly expressed Periostin, Col-1, and α-SMA compared to DPSCs by quantitative RT-PCR. DPSCs cultured on bone slices for 2 weeks enhanced gene expression of Periostin, Col-1, and α-SMA at similar levels to PDLSCs. In addition, transplanted rat GFP-positive DP cells were detected in PDL tissue around the replanted tooth in the rat tooth replantation model.

 Conclusion: DPSCs cultured on bone tissue increased the expression of PDL-related genes, suggesting that DPSCs might be a useful source of cells for PDL tissue regeneration.

 Purpose: To investigate the antimicrobial effects of surface pre-reacted glass ionomer (S-PRG) filler eluate containing several ions including fluoride, strontium and boron on polymicrobial biofilm grown from stimulated saliva.

 Methods: Stimulated saliva was obtained from a healthy donor. S-PRG eluate was obtained by suspending S-PRG filler in distilled water. Polymicrobial biofilm was grown under anaerobic conditions at 37℃ on glass coverslips suspended for 10 h in buffered McBain 2005 medium containing the saliva, then in fresh medium without saliva for a further 14 h. They were then suspended under anaerobic conditions for a further 24 h in buffered McBain 2005 medium with either S-PRG eluate containing 110.5 ppm fluoride (the PRG group), NaF solution at 110.5 ppm F (the NaF group) or nothing (the Cont group). Colony-forming units (CFU) were counted at 48 h, 0 h being the start of cultivation, and statistically analyzed (one-way ANOVA, Games-Howell, p<0.05). Also at 48 h, the total amounts of bacteria in the biofilms and amounts of Streptococcus, Actinomyces and Veillonella identified by their 16S rRNA were analyzed.

 Results: CFU was lower in the PRG group than in the Cont and NaF groups. Total 16S rRNA level was lower in the PRG group than in the Cont and NaF groups (Cont: 8.24×10⁹, NaF: 4.68×10⁹, PRG: 8.30×10⁸). There was no difference in total 16S rRNA levels between the Cont and NaF groups. The 16S rRNA levels of Streptococcus, Actinomyces and Veillonella were lower in the PRG group than in the other two groups (Streptococcus: Cont: 2.10×10⁹, NaF: 1.19×10⁹, PRG: 3.83×10⁸, Actinomyces: Cont: 8.69×10⁶, NaF: 3.27×10⁶, PRG: 4.23×10⁵, Veillonella: Cont: 2.06×10⁹, NaF: 1.90×10⁹, PRG: 7.58×10⁷).

 Conclusion: Ions in S-PRG eluate not only suppressed total viable bacteria in the biofilms but also the initial colonizers of the biofilms.

 Purpose: In this study, we compared anti-demineralization of dentin by a conventional glass ionomer cement with that of a newly developed glass ionomer cement with a glass containing zinc, fluoride and calcium using transverse microradiography (TMR). We also analyzed the elements incorporated in the dentin using an electron probe micro-analyzer (EPMA).

 Method: Eighteen samples of bovine root dentin were divided equally into three groups. The F7 group was covered by a 100 μm-thick Teflon sheet with a 2×3 mm cut-out onto which Fuji Ⅶ conventional glass ionomer cement was then pressed. The C10 group was similarly covered but ZincF-C10 cement was applied. The cements had been prepared according to the manufacturer’s instructions. The Teflon sheet and excess cement were removed after five minutes. The third group, the control, was not treated with cement. The entire surfaces of all 18 samples, except for a 2×3 mm area on each sample, were painted with acid-resistant varnish. In the F7 and C10 samples, the 2×3 mm area was adjacent to the cement. Each group of samples was fixed to the bottom of a separate container and demineralized by leaving for four days at 37℃ covered in acidic solution (1.5 mmol/l CaCl₂, 0.9 mmol/l KH₂PO₄, 50 mmol/l acetic acid, 0.1 ppm F, pH 5.0) which was refreshed every 24 hours. Sections 300 μm in thickness were prepared and examined by TMR. The mineral profiles and integrated mineral loss (IML) of lesions in each group were analyzed by dedicated software. Fluoride concentration of each demineralization solution was also measured. Statistical analysis of IML was performed with one-way ANOVA and Tukey’s test at p<0.05. Elements (Ca, P, F, Zn) incorporated into the demineralized dentin of C10 were detected on the cut surface by EPMA.

 Results: Compared to the other two groups, the C10 group showed higher mineral volume% in the surface layer and in the lesions, indicating that IML of C10 was significantly lower than for the other groups (p<0.05). EPMA line profiles of the C10 specimens showed Zn in an extremely thin region at the dentin surface, and F was incorporated at a depth of 40 μm from the surface. Ca and P had similar line profiles to the TMR profile. The concentration of fluoride was higher in demineralization solution of C10 than in that of F7.

 Conclusion: Glass ionomer cement containing zinc glass is more effective than conventional glass ionomer cement at reducing demineralization of dentin.

 Purpose: The aim of this study was to examine the clinical efficacy of swept-source optical coherence tomography (SS-OCT) for measuring the refractive index of metal-free restoration materials, for which accurate measurements are difficult to obtain by conventional refractometry.

 Methods: Twenty-five specimens with dimensions of 10×10×1.0 mm (vertical×side×thickness) were used, consisting of five specimens each of five types of material: ESTELITE BLOCK (EB), IPS Empress CAD (IEP), IPS e-max CAD (IEM), VITA SUPRINITY for KaVo ARCTICA (VS), and NACERA pearl 1 (NA). Eight areas on each specimen were randomly selected as measuring points. The refractive index was calculated from the optical path length (OPL) and the actual thickness obtained by the OPL matching method. The mean refractive index was then calculated based on the data from each type of metal-free restoration material. To investigate whether the thickness of the specimen influenced the refractive index, simple regression analyses were performed.

 Results: The refractive index of NA, which is difficult to measure by conventional refractometry, was 2.227 (±0.023), a significantly higher value (p<0.05) than that of the other materials (-1.5). All of the materials exhibited a negative correlation between the thickness and the refractive index by simple regression analysis.

 Conclusion: Refractive index measurement of the metal-free restoration materials was possible via SS-OCT, including for NA (zirconia), which cannot be measured by conventional refractometry due to its high refractive index. In this study, we confirmed that the refractive index obtained by SS-OCT is influenced by the specimen thickness. It is suggested that by measuring the refractive index of the material in advance and digitizing the refractive index data, the actual thickness of the material can easily be measured at the chair-side. We suggest that SS-OCT has wide potential in clinical applications, not limited to its value as an imaging technique.

 Purpose: When particles of bioactive glass (BAG) containing strontium (Sr) are implanted into calvarial defects of rats, osteogenesis is promoted in comparison with BAG particles without Sr. In order to avoid washing away or dissolution of the particles by bleeding at the bone defects, we made a hardened material that consisted of BAG particles and γ-poly-glutamic acid (γ-PGA). The purpose of this study was to verify maintenance of the disc and to compare the osteogenic properties of the BAG discs containing or not containing Sr, and to clarify the effect of Sr released from the disc on promoting osteogenesis.

 Method: BAG (Sr0) containing 53SiO₂-20CaO-23Na₂O-4P₂O₅ (wt%) and BAG (Sr100) containing 53SiO₂-20SrO-23Na₂O-4P₂O₅ (wt%) were prepared, and some powders (particle size ≤40 μm) were made. The powders and 5%γ-PGA were then mixed and hardened to obtain the discs (2 mm thickness, 6 mm diameter). Calvarial defects of 6 mm diameter were made surgically in 12-week-old Sprague Dawley rats. The discs of Sr0 or Sr100 were implanted into the defects; nothing was implanted in the control group. At 1, 2 and 3 months after the operation, the animals were examined by taking micro-CT photographs. After taking micro-CT photographs for 3 months, rats were sacrificed and the formation of new bone was analyzed histomorphometrically by optical microscopy.

 Results: The surgical defect area of the control group slightly decreased. The Sr0 discs did not disintegrate and were maintained in the bone defects. New X-ray opaque materials were not observed in the bone defects of the Sr0 disc group. The Sr100 discs did not disintegrate and were maintained in the bone defects. Small granular X-ray opaque materials were observed on the surfaces of the discs. New X-ray opaque materials were noted on the dura mater. At 3 months after the operation, new bone formation was hardly seen at the center of the calvarial defects of the control group. New bone formation was not observed around the Sr0 discs or at the center of the defects. New bone formation was observed at the surfaces of the Sr100 discs, and on the dura mater. New bone formation of the Sr100 disc group increased significantly compared with that in the control group and the Sr0 disc group.

 Conclusion: The present study suggested that BAG discs containing Sr should be maintained in bone defects, and that Sr released from the discs enhances osteogenesis in rat calvarial defects.