Sheng Yang Lee

Effects of Cryopreservation of intact teeth on the isolated dental pulp stem cells

INTRODUCTION Human dental pulp stem cells (DPSCs) have been reported to be useful material for future regenerative medicine. Clinically, cryopreservation of intact teeth can successfully preserve the periodontal ligament for future autotransplantation; however, the effects of cryopreservation procedure on the properties of DPSCs are still unclear. The aim of this study was to test whether DPSCs isolated from cryopreserved teeth can express stem cell-specific markers. METHODS In this study, a novel programmable freezer coupled to a magnetic field was used to perform the cryopreservation experiments. The tested DPSCs were isolated from magnetically cryopreserved and non-cryopreserved fresh teeth with an enzyme digestion procedure. The success rate of isolation, growth curves, morphology, stem cell-specific markers, and the differentiation capacity of the isolated cells were evaluated and compared. RESULTS The isolation rate of dental pulp cells from magnetically cryopreserved teeth was 73%. After culture for 5 generations, there was no significant difference in cell viability between cells isolated from magnetically cryopreserved teeth and those isolated from fresh teeth. There were also no visible differences between the 2 groups of dental pulp cells in morphology, expression of stem cell markers, or osteogenic and adipogenic differentiations. CONCLUSIONS The results suggest that cryopreserved whole teeth can be used for autotransplantation and provide a viable source of DPSCs.

A novel accelerator for improving the handling properties of dental filling materials.

INTRODUCTION Mineral trioxide aggregate (MTA) fulfills many of the ideal properties of a root end filling material and repair material for furcal perforation. However, its low cohesive property often makes it difficult to handle. To improve the handling properties of MTA root canal filling materials, MTA-like cement was made, and calcium lactate gluconate (CLG) aqueous solution was used to shorten the setting time and enhance the paste viscosity. METHODS CLG solution was prepared by mixing lactic acid, glucono delta lactone, and calcium oxide by wet process. The crystalline property of the CLG powder was characterized by x-ray diffraction. The MTA-like cements were prepared by mixing Portland cement/bismuth oxide/gypsum (75/20/5); ProRoot white MTA (Dentsply Tulsa Dental, Tulsa, OK) was used as a control group. The influence of various liquid phases on initial setting time, handling properties, and pH value were investigated by a Vicat needle, questionnaire of operational hand feel, and pH meter, respectively. RESULTS By using 23.1 wt% CLG solutions as a liquid phase, the setting time of white MTA was significantly decreased from 155.5 +/- 5.0 to 12.3 +/- 2.5 minutes. The pH values for hydrated white MTA with deionized water and 23.1 wt% CLG solutions were 12.29 +/- 0.02 and 11.81 +/- 0.04 at 72 hours. CONCLUSIONS The results suggest that the addition of amorphous CLG-based liquid phase provides improvement in sealing ability as well as clinical manageability of dental filling materials.

Factors influencing the resonance frequency of dental implants

PURPOSE Resonance frequency (RF) analysis has been used by several investigators to assess the boundary conditions of dental implants. However, a scientific investigation of the association between the structural condition of the alveolar bone and the dynamic behavior of dental implants has not yet been reported. The aim of this study was to assess the factors influencing the RF of dental implants using an in vitro modal analysis. MATERIALS AND METHODS Resonant vibration within implants was induced by an impulse-force hammer. The induced vibration signal was subsequently detected using an acoustic microphone and analyzed by fast Fourier transform. The resultant data were further analyzed to test the statistical effects of the embedding-material boundary height, thickness, and density on the RF values of the sample implants. RESULTS Significant changes (P <.05) in RF values were revealed for implants embedded within a high-density block when decreasing boundary height reached 6, 5, and 4 mm, at respective thickness increments of 10, 15, and 20 mm. For analogous low-density samples, significant changes (P <.05) in RF values were found when respective decreasing boundary height reached 6, 4, and 3 mm. CONCLUSIONS Our findings indicate that boundary height, width, and density factors can influence the RF of dental implants and that a lower boundary density and greater boundary thickness can lead to more obvious RF changes.

Three-dimensional finite element analysis of subdural hematoma.

BACKGROUND Head motion, an important factor in acute subdural hematoma (ASDH), can be broken down into translational and rotational elements. We used three-dimensional finite element analysis to examine the thresholds of angular and tangential acceleration required to tear bridging veins in humans during head impact. METHODS The lengths of midsagittal and parasagittal bridging veins were calculated first. To assess the effect of translational and rotational acceleration, the strain of each vein was then computed under three different motions. The threshold of ASDH was expressed in terms of tangential and rotational acceleration. RESULTS Deformation-angle histories of the midsagittal and parasagittal bridging veins showed that veins that drain forward into the superior sinus at a 130-degree angle incurred the greatest stretch strain during occipital impact. In the midsagittal plane, pure rotation induced greater stretch strain on these veins (14.4%) than pure translation (2.5%) or combined translation and rotation motion (10.4%). A tangential acceleration of 3,912.9 G or an angular acceleration of 71.2 krad/s2 seemed to approximate the threshold for ASDH in the human midsagittal plane, whereas 5,010.9 G and 97.4 krad/s2 approximated the threshold in the parasagittal plane. CONCLUSION Impact direction and orientation of bridging veins are both important factors in ASDH. Threshold criteria for ASDH can be expressed in terms of tangential and rotational acceleration.

Magnetic cryopreservation for dental pulp stem cells

Magnetic cryopreservation has been successfully used for tooth banking with satisfactory implantation outcomes, suggesting that the method preserves human periodontal ligament cells and dental pulp stem cells (DPSCs). Therefore, magnetic cryopreservation may be applied for the preservation of DPSCs; however, this method has not been evaluated yet. A reliable cryopreservation method for live-cell preservation is important for the clinical applications of regenerative medicine. The conventional slow-freezing procedure with 10% dimethylsulfoxide (DMSO) may not be appropriate for stem cell-based therapies because DMSO is cytotoxic. The objective of this study was to investigate whether magnetic cryopreservation can be applied for DPSC cryopreservation. Cells isolated from human dental pulp were subjected to magnetic cryopreservation. Postthawing cell viability, adhesion, proliferation, expression of markers for mesenchymal stem cells (MSCs), differentiation ability of magnetically cryopreserved DPSCs and DNA stability were compared to those of cells subjected to the conventional slow-freezing method. The results indicated that a serum-free cryopreservation medium (SFM) containing 3% DMSO is optimal for magnetic cryopreservation. Post-thaw magnetically cryopreserved DPSCs express MSC markers, and perform osteogenesis and adipogenesis after induction similarly to fresh MSCs. No significant DNA damage was found in magnetically cryopreserved DPSCs. Magnetic cryopreservation is thus a reliable and effective method for storage of DPSCs. The smaller amount of DMSO required in SFM for cryopreservation is beneficial for the clinical applications of post-thaw cells in regenerative medicine.

Finite element analysis of brain contusion: An indirect impact study

The mechanism of brain contusion has been investigated using a series of three-dimensional (3D) finite element analyses. A head injury model was used to simulate forward and backward rotation around the upper cervical vertebra. Intracranial pressure and shear stress responses were calculated and compared. The results obtained with this model support the predictions of cavitation theory that a pressure gradient develops in the brain during indirect impact. Contrecoup pressure-time histories in the parasagittal plane demonstrated that an indirect impact induced a smaller intracranial pressure (−53.7 kPa for backward rotation, and −65.5 kPa for forward rotation) than that caused by a direct impact. In addition, negative pressures induced by indirect impact to the head were not high enough to form cavitation bubbles, which can damage the brain tissue. Simulations predicted that a decrease in skull deformation had a large effect in reducing the intracranial pressure. However, the areas of high shear stress concentration were consistent with those of clinical observations. The findings of this study suggest that shear strain theory appears to better account for the clinical findings in head injury when the head is subjected to an indirect impact.

Influence of hydrogen charging on the formation of nanostructural titania by anodizing with cathodic pretreatment

The purpose of the present study was to evaluate the influences of titanium hydride on the formation of nanostructural titanium oxide by electrochemical treatment. The physico-chemical surface properties were investigated by scanning electron microscopy, cross-sectional transmission electron microscopy, thin film X-ray diffractometry, and X-ray photoelectron spectroscopy. Nanoporous structures were formed after anodization with cathodic pretreatments. The titanium hydride is formed by cathodic pretreatments. Titanium hydride was a sacrificial layer on titanium following anodization. The sacrificial layer has a γ-TiH 2 phase. The γ-TiH 2 is a tetragonal nanostructure and its lattice constant is a = 3.12 nm. Furthermore, it was formed within titanium matrices during cathodization. The nanostructural γ-TiH 2 decomposes after anodization. Furthermore, the nanoporous Ti formed by dissolution of TiH 2 was changed to nanoporous TiO 2 . The TiH 2 plays an important role in forming nanoporous TiO 2 . The triangle-like γ-TiH 2 was observed on the Ti matrix and grain boundary. In the γ-Ti matrix, an γ-Ti → γ-TiH 2 transition occurred during cathodization. The anodization with cathodic pretreatment not only produces titanium hydride layer, but also results in formation of nanostructural titanium oxide. Nanoporous titania can be enhanced osseointegration of implant such as orthopedic and dental implants.

Enhancement of Biocompatibility on Bioactive Titanium Surface by Low-Temperature Plasma Treatment

The surface of implantable biomaterials directly contacts the host tissue and is critical in determining biocompatibility. To improve implant integration, interfacial reactions must be controlled to minimize nonspecific adsorption of proteins, and tissue-healing phenomena can be controlled. The purpose of this study was to develop a new method of functionalizing titanium surfaces by plasma treatment. The covalent immobilization of bioactive organic molecules and the bioactivities in vitro were assessed by transmission electron microscopy (TEM), atomic force spectroscopy (AFM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay as indices of cellular cytotoxicity. Argon plasma removed all of the adsorbed contaminants and impurities. Plasma-cleaned titanium surfaces showed better bioactive performances than untreated titanium surfaces. The analytical results reveal that plasma-cleaned titanium surfaces provide a clean and reproducible starting condition for further plasma treatments to create well-controlled surface layers. Allylamine was ionized by plasma treatment, and acted as a medium to link albumin. Cells demonstrated a good spread, and a wide attachment was attained on the Albu-Ti plate. Cell attachment and growth were shown to be influenced by the surface properties. The plasma treatment process plays an important role in facilitating tissue healing. This process not only provides a clean titanium surface, but also leads to surface amination on plasma-treated titanium surfaces. Surface cleaning by ion bombardment and surface modification by plasma polymerization are believed to remove contamination on titanium surfaces and thus promote tissue healing.

Dental Stem Cells and Tooth Banking for Regenerative Medicine

Abstract Stem cell (SC) therapy has a promising future for tissue regenerative medicine. However, because SC technology is still in its infancy, interdisciplinary cooperation is needed to achieve successful clinical applications. Dental SCs have drawn attention in recent years because of their accessibility, plasticity, and high proliferative ability. Several types of dental SCs have been identified, including dental pulp SCs from adult human dental pulp, SCs from human primary exfoliated deciduous teeth, periodontal ligament SCs, and dental follicle SCs from human third molars. Similar to mesenchymal SCs, these dental SCs can undergo self-renewal and have multipotent differentiation ability, but do not have the ethical issues associated with other sources of SCs. Therefore, appropriate preservation procedures for dental SCs and teeth are now needed. Here, we discuss the opportunities for tooth-banking (as it is now clinically feasible and commercially available), the advantages and limitations of current cryopreservation techniques for dental SCs/teeth or tissues, and the current status of tooth banks.

Mechanobiology of MG63 osteoblast-like cells adaptation to static magnetic forces.

The aim of this study was to explore the biophysical effects of static magnetic field on osteoblastic cells. MG63 cells were exposed to 0.25 and 0.4-T static magnetic fields (SMF). The cell cycle effects were tested by flow cytometry. The differentiation of the cells was assessed by detecting the changes in prostaglandin E2, osteocalcin, and extracellular matrix expression. Membrane fluidity was used to evaluate the alterations in the biophysical properties of cellular membranes after the SMF simulations. Our results show that SMF exposure increases prostaglandin E2 level and extracellular matrix express in MG63 cells. On the other hand, MG63 cells exposed to 0.4-T SMF exhibited a significant decrease in membrane fluidity at 8 h. Based on these findings, it appears reasonable to suggest that SMF affect osteoblastic maturation by increasing membrane rigidity and then inducing differentiation pathway.