Su-Jin Ahn

Magnetic nanocomposite scaffolds combined with static magnetic field in the stimulation of osteoblastic differentiation and bone formation.

Magnetism has recently been implicated to play significant roles in the regulation of cell responses. Allowing cells to experience a magnetic field applied externally or scaffolding them in a material with intrinsic magnetic properties has been a possible way of utilizing magnetism. Here we aim to investigate the combined effects of the external static magnetic field (SMF) with magnetic nanocomposite scaffold made of polycaprolactone/magnetic nanoparticles on the osteoblastic functions and bone formation. The SMF synergized with the magnetic scaffolds in the osteoblastic differentiation of primary mouse calvarium osteoblasts, including the expression of bone-associated genes (Runx2 and Osterix) and alkaline phosphatase activity. The synergism was demonstrated in the activation of integrin signaling pathways, such as focal adhesion kinase, paxillin, RhoA, mitogen-activated protein kinase, and nuclear factor-kappaB, as well as in the up-regulation of bone morphogenetic protein-2 and phosphorylation of Smad1/5/8. Furthermore, the SMF/magnetic scaffold-stimulated osteoblasts promoted the angiogenic responses of endothelial cells, including the expression of vascular endothelial growth factor and angiogenin-1 genes and the formation of capillary tubes. When the magnetic scaffolds were implanted in mouse calvarium defects, the application of SMF significantly enhanced the new bone formation at 6 weeks, as revealed by the histological and micro-computed tomographic analyses. Current findings suggest that the combinatory application of external (SMF) and internal (scaffold) magnetism can be a promising tool to regenerative engineering of bone.

Differences in implant stability associated with various methods of preparation of the implant bed: An in vitro study

STATEMENT OF PROBLEM It is difficult to achieve the primary stability necessary for immediate loading in the posterior maxilla because of thin cortical bone, low density trabecular bone, and inadequate bone height due to the presence of the maxillary sinus. PURPOSE The purpose of this study was to examine the primary stability of dental implants placed by using different methods of preparation for in vitro monocortical and bicortical models of the posterior maxilla. MATERIAL AND METHODS Sixty screw-shaped implants (4.0 × 10 mm) were inserted into solid rigid polyurethane blocks. The implants were divided into 6 groups (n=10) to test 2 variables: 1) location (monocortical or bicortical block) and 2) preparation method (standard preparation, underpreparation, or the osteotome technique). The insertion and removal torques were measured and resonance frequency analysis (RFA) was performed to determine the primary stability of each implant. Insertion and removal torque data were analyzed by 2-way ANOVA, followed by the post hoc Tukey HSD multiple comparison test. RFA data were analyzed by 2-way and 1-way ANOVAs and the Tukey HSD multiple comparison test (α=.05). The Pearson correlation analysis was also performed to examine correlations among the values. RESULTS The preparation method had a significant effect on insertion torque, RFA value, and removal torque; however location had a significant effect only on the removal torque (P<.001). There was a significant interaction between location and preparation method for RFA values (P=.045) and a significant difference in standard preparation method according to the location (P=.039); however, there was no significant difference in underpreparation (P=1.00) and osteotome technique (P=1.00). Statistically significant correlations were found between insertion torque and RFA values (r=0.529, P< .001), insertion torque and removal torque values (r=0.517, P< .001), and removal torque and RFA values (r=0.481, P<.001). CONCLUSIONS Underpreparation and bicortical fixation significantly increased implant stability and the osteotome technique decreased implant stability in synthetic bone models that mimicked the posterior maxillary region. The primary stability values had statistically significant correlations to each other.

Effects of moderate intensity static magnetic fields on human bone marrow-derived mesenchymal stem cells.

This study aimed to explore effects of static magnetic fields (SMFs) of moderate intensity (3-50 mT) as biophysical stimulators of proliferation and osteoblastic differentiation of human bone marrow-derived mesenchymal stem cells (MSCs). MSCs were exposed to SMFs of three intensities: 3, 15, and 50 mT. Proliferation was assessed by cell counting and bromodeoxyuridine incorporation, and differentiation by measuring alkaline phosphatase (ALP) activity, calcium content, mineralized nodule formation, and transcripts of osteogenic markers. Moderate intensity SMFs increased cell proliferation, ALP activity, calcium release, and mineralized nodule formation in a dose- and time-dependent manner, which peaked at 15 mT. In the same manner, they upregulated expression of osteogenic marker genes such as ALP, bone sialoprotein 2 (BSP2), collagen1a1 (COL1a1), osteocalcin (OCN), osteonectin (ON), osteopontin (OPN), osterix (OSX), and runt-related transcription factor 2 (RUNX2) with peak at 15 mT after 14 or 21 days of exposure. Results demonstrate that moderate intensity SMFs promote proliferation and osteoblastic differentiation of MSCs. This effect could help to improve MSC responses during osseointegration between a dental implant and surrounding bone.

Texture direction of combined microgrooves and submicroscale topographies of titanium substrata influence adhesion, proliferation, and differentiation in human primary cells

OBJECTIVE This study aimed to identify the optimal micro- and submicroscale topographies of titanium (Ti) substrata that would most significantly influence adhesion, proliferation, and other activities of these cells. DESIGN Truncated V-shaped microgrooves in 60 μm-wide and 10 μm-deep cross-sections with 0°, 30°, 60°, or 90° angles between the microgrooves and ridge-top submicroscale texture were created on the Ti substrata (designated NE60/10-0°, NE60/10-30°, NE60/10-60° and NE60/10-90°, respectively). Ground titanium with submicroscale texture but with no microgrooves was used as the control substratum, NE0. Scanning electron microscopic observation and the assays determining the cell adhesion, cell proliferation and osteoblast differentiation were performed. RESULTS Cells more actively migrated into the microgrooves on NE60/10-30° than into the microgrooves on any other substrata tested, suggesting that the cells utilise the increased surface area of the substrata at the microscale level. NE60/10-0° and NE60/10-30° substrata generally enhanced adhesion, proliferation, alkaline phosphatase activity, and osteoblast differentiation of human primary cells when compared to other Ti substrata, and significant correlations were observed between these cellular activities. CONCLUSIONS Here, we show that the contact guidance of human primary cells grown on Ti substrata can be controlled more by specific submicroscale textures on ridge tops than by the dimensions of surface microgrooves only. Also, the degree of angles created between the submicroscale textures and microgrooves on Ti substrata significantly affect cell adhesion, proliferation and differentiation in human primary cells.

The Effects of a Static Magnetic Field on Bone Formation Around a Sandblasted, Large-Grit, Acid-Etched–Treated Titanium Implant

The purpose of this study was to compare the bone formation around commercial sandblasted, large-grit, acid-etched (SLA)–treated titanium implants with or without a neodymium magnet in a rabbit tibia through histomorphometric analysis. Commercial SLA-treated implants with or without neodymium magnets were placed in 10 rabbits. After incising the flat part of the rabbits tibia and installation of the specimens of titanium implants, the nonmagnet group was stitched without magnet insertion. On the other hand, the magnet group was inserted with neodymium magnet, fixed with pattern resin, and stitched. At 3 and 6 weeks after surgery, the animals were sacrificed, and the specimens were obtained. Undecalcified specimens were prepared for histomorphometric analysis of the bone-to-implant contact ratio (BIC) and bone volume (BV). The histomorphometric findings of the cortical bone showed that the mean BVs of the magnet group (3 weeks, 75.99%; 6 weeks, 82.94%) were higher than those of the nonmagnet group (3 week...

Histomorphometric Analysis and Removal Torque of Small Diameter Implants With Alternative Surface Treatments and Different Designs

This study was designed to investigate the histomorphometric and biomechanical comparison of small-diameter implants with different designs. These implants can be placed surgically in narrow bone spaces, such as the lower incisor region, that have low occlusal loading. Specimens of screw-shaped pin implants were designed for the study. These specimen implants were divided into 6 groups: group 1, machined implants; group 2, resorbable blast media (RBM)-treated implants; group 3, machined implants with a long vertical groove; group 4, RBM-treated implants with a long vertical groove; group 5, RBM-treated implants with a vertical groove on the upper thread; and group 6, RBM-treated implants with a vertical groove on the lower trunk. The specimen implants were placed surgically on the medial side of the rabbit tibia. Animals were sacrificed 2, 4, and 8 weeks after surgery. The removal torque was measured and tissues were prepared for histologic and histomorphometric analysis. The bone-to-implant contact and the percentage of the bone area inside the threads were measured. RBM-treated implants with vertical groove groups showed significantly higher values of removal torque, bone-implant contact, and bone area rate than the ones of machined surface groups.

Tumor Necrosis Factor-α Induces Matrix Metalloproteinases-3, -10, and -13 in Human Periodontal Ligament Cells

BACKGROUND Various biologic mediators, including matrix metalloproteinases (MMPs), that are implicated in periodontal tissue breakdown can be induced by cytokines. MMPs are known to degrade periodontal ligament attachment, and bone matrix proteins and tissue inhibitors of metalloproteinase (TIMPs) inhibit the activity of MMPs. The aim of this study is to investigate the effect of tumor necrosis factor (TNF)-α on the expression of MMPs in human periodontal ligament (PDL) cells in vitro and establish which MMPs are expressed specifically in response to that stimulus. METHODS Cultured PDL cells were stimulated with TNF-α and analyzed with an MMP antibody array. Real-time polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and western blot with cell lysate and zymography were used to measure messenger RNA (mRNA) and protein levels of MMP-3, -10, and -13. To examine TNF receptor (TNFR) expression, PDL cells were examined by flow cytometry, and expression of MMP-3, -10, and -13 was observed after blocking the TNFR with an antagonist. Results from real-time PCR, ELISA, and western blot were analyzed by paired t test. RESULTS The antibody array showed that the protein most strongly upregulated by TNF-α stimulation was MMP-3, followed by MMP-13 and MMP-10. The TNF-α receptor blocker specifically inhibited expression of MMP-3 and -13. In addition, TNF-α increased levels of MMP mRNAs in MMP-3, -13, and -10 (in decreasing order). However, ELISAs showed that MMP-13 was the most upregulated protein, followed by MMP-10 and MMP-3. Western blotting indicated that TNF-α increased MMP-3 and -13 levels but had no significant effect on the level of MMP-10, and zymography showed that TNF-α increased the activities of all forms of MMP-3 and -13, but MMP-10 was not detected. Flow cytometry demonstrated that the majority of PDL cells expressed TNFR1. CONCLUSIONS TNF-α (10 ng/mL) upregulates levels of MMP-3, -10, and -13 in human PDL cells. These results suggest that these proteins play an important role in the inflammation of PDLs.

Effect of etched microgrooves on hydrophilicity of titanium and osteoblast responses: A pilot study

PURPOSE The aim of this pilot study was to investigate the effect of etched microgrooves on the hydrophilicity of Ti and osteoblast responses. MATERIAL AND METHODS Microgrooves were applied on Ti to have 15 and 60 µm width, and 3.5 and 10 µm depth by photolithography, respectively. Further acid etching was applied to create Ti surfaces with etched microgrooves. Both smooth- and acid-etched Ti were used as the controls. The hydrophilicity of Ti was analyzed by determining contact angles. Cell proliferation and osteogenic activity of MC3T3 mouse preosteoblasts were analyzed by bromodeoxyuridine assay and alkaline phosphatase (ALP) activity test, respectively. One-way ANOVA, Pearsons correlation analysis and multiple regression analysis were used for statistics. RESULTS Etched microgrooves significantly increased the hydrophilicity of Ti compared to the smooth Ti. 60 µm-wide etched microgrooves significantly enhanced cell proliferation, whereas the osteogenic activity showed statistically non-significant differences between groups. Result of the osteogenic activity significantly correlated with those of hydrophilicity and cell proliferation. Hydrophilicity was determined to be an influential factor on osteogenic activity. CONCLUSION This study indicates that increase in hydrophilicity of Ti caused by etched microgrooves acts as an influential factor on osteogenic activity. However, statistically non-significant increase in the ALP activity suggests further investigation.

Comparison of the microhardness and morphology of five different retrograde filling materials in aqueous and dry conditions.

The purpose of the present study was to compare the effect of dry and aqueous conditions on the surface morphology and surface hardness of five materials 24 h after being used as fillings without initial setting time in dry condition. The five materials were ProRoot mineral trioxide aggregate (MTA), super EBA, intermediate restorative materials (IRM), zinc oxide eugenol (ZOE), and amalgam. To evaluate microhardness, the five materials were submitted to the Vickers microhardness (VHN) test. We used a scanning electron microscope (Steroscan 440, Leica Cambridge, England) to observe the microstructural morphology of the five different materials. The VHN of MTA soaked in water showed five times lower than that of MTA soaked in dry condition. On the other hand, super EBA was less influenced by the medium of storage compared with the other materials. Scanning electron microscope (SEM) images showed the similar results with microhardness tests. The surface of MTA soaked in water appeared to be unstable compared with that of dry condition while super EBA showed similarly smooth surface in both conditions (aqueous and dry). In conclusion, the physical property of MTA is reduced after storage in water; however, super EBA is less influenced by aqueous condition.

Influence of the connection design and titanium grades of the implant complex on resistance under static loading

PURPOSE The purpose of this study was to evaluate the resistance to deformation under static overloading by measuring yield and fracture strength, and to analyze the failure characteristics of implant assemblies made of different titanium grades and connections. MATERIALS AND METHODS Six groups of implant assemblies were fabricated according to ISO 14801 (n=10). These consisted of the combinations of 3 platform connections (external, internal, and morse tapered) and 2 materials (titanium grade 2 and titanium grade 4). Yield strength and fracture strength were evaluated with a computer-controlled Universal Testing Machine, and failed implant assemblies were classified and analyzed by optical microscopy. The data were analyzed using the One-way analysis of variance (ANOVA) and Students t-test with the level of significance at P=.05. RESULTS The group IT4S had the significantly highest values and group IT2 the lowest, for both yield strength and fracture strength. Groups IT4N and ET4 had similar yield and fracture strengths despite having different connection designs. Group MT2 and group IT2 had significant differences in yield and fracture strength although they were made by the same material as titanium grade 2. The implant system of the similar fixture-abutment interfaces and the same materials showed the similar characteristics of deformation. CONCLUSION A longer internal connection and titanium grade 4 of the implant system is advantageous for static overloading condition. However, it is not only the connection design that affects the stability. The strength of the titanium grade as material is also important since it affects the implant stability. When using the implant system made of titanium grade 2, a larger diameter fixture should be selected in order to provide enough strength to withstand overloading.