Namsik Oh

In vivo study on hydroxyapatite scaffolds with trabecular architecture for bone repair.

The objective of this research was to investigate the bone formation and angio-conductive potential of hydroxyapatite (HA) scaffolds closely matched to trabecular bone in a canine segmental defect after 3 and 12 weeks post implantation. Histomorphometric comparisons were made between naturally forming trabecular bone (control) and defects implanted with scaffolds fabricated with micro-size (M-HA) and nano-size HA (N-HA) ceramic surfaces. Scaffold architecture was similar to trabecular bone formed in control defects at 3 weeks. No significant differences were identified between the two HA scaffolds; however, significant bone in-growth was observed by 12 weeks with 43.9 +/- 4.1% and 50.4 +/- 8.8% of the cross-sectional area filled with mineralized bone in M-HA and N-HA scaffolds, respectively. Partially organized, lamellar collagen fibrils were identified by birefringence under cross-polarized light at both 3 and 12 weeks post implantation. Substantial blood vessel infiltration was identified in the scaffolds and compared with the distribution and diameter of vessels in the surrounding cortical bone. Vessels were less numerous but significantly larger than native cortical Haversian and Volkmann canals reflecting the scaffold architecture where open spaces allowed interconnected channels of bone to form. This study demonstrated the potential of trabecular bone modeled, highly porous and interconnected, HA scaffolds for regenerative orthopedics.

An in vivo comparison of working length determination by only root-ZX apex locator versus combining root-ZX apex locator with radiographs using a new impression technique

OBJECTIVE The objective of this study was to compare, in vivo, the accuracy of working length determination using only the Root-ZX electronic apex locator versus adjusting Root-ZX measurements after obtaining a working length radiograph. STUDY DESIGN The working length was determined in 25 premolar root canals using Root-ZX and K-files were fixed at these positions. Radiographs were acquired and interpreted, and the recorded working length measurement was adjusted, if necessary, for a combined measurement. The teeth were then extracted in an effort to determine the position of the file tip to the root canal constriction. On the basis of the position of the file tip to the apical foramen, polyvinylsiloxane impressions of the root apex were taken, or the root was imbedded in acrylic resin and ground in order to measure the position of the file tip to the apical constriction. RESULTS The Root-ZX alone detected the apical constriction within +/- 0.5 mm in 84% of the samples (21 of 25 canals). However, 96% (24 of 25 canals) were within this range when the combination of Root-ZX and radiographs was used. We noted no statistical significance between these 2 methods (P > .05). CONCLUSION Using a Root ZX Electronic Apex Locator combined with radiographs is recommended for the determination of working length, although there was no statistical significance between those 2 groups in this study.

Factors influencing osteoblast maturation on microgrooved titanium substrata

In this study, we demonstrate surfaces with various dimensions of microgrooves fabricated by photolithography and subsequent acid etching that enhance various characteristics of titanium. Microgrooves with truncated V-shape in cross-section from 15 to 90 microm widths enabled us to report their exclusive effects on altering the surface chemistry and on enhancing the surface hydrophilicity, serum protein adsorption and osteoblast maturation on titanium substrata in a microgroove dimension-dependent manner. Further, acid etching and measurement direction separately affected the surface hydrophilicity results. By multiple correlation and regression analyses, surface chemistry, surface hydrophilicity and serum protein adsorption were determined to be the significant influential factors on osteoblast maturation. Within the limitations of this study, we conclude that combined submicron- and microtopography with relevant micro-dimension and structure enhance various characteristics of titanium, including surface hydrophilicity, which act as the essential factors influencing the osteoblast maturation on microgrooved titanium substrata.

Effects of bone marrow-derived mesenchymal stem cells and platelet-rich plasma on bone regeneration for osseointegration of dental implants: Preliminary study in canine three-wall intrabony defects

Tissue engineering has been applied to overcome the obstacles encountered with bone regeneration for the placement of dental implants. The purpose of this study was to determine the bone formation ability of human bone marrow-derived mesenchymal stem cells (BMMSCs) and platelet-rich plasma (PRP) when applied separately or together to the intrabony defect around dental implants with a porous hydroxyapatite (HA) scaffold. Standardized three-wall intrabony defects (4 × 4 × 4 mm) were created at the mesial of each dental implant site in four mongrel dogs. Defects were then grafted with the following materials: HA + BMMSCs (HS group), HA + PRP (HP group), HA + BMMSCs + PRP (HSP group), and HA scaffold alone (HA group). The level of bone formation (bone density) and osseointegration (bone-to-implant contact [BIC]) in bone defects around the implants were evaluated by histological and histometric analysis at 6 and 12 weeks after the placement of implants. HA, HS, HP, and HSP groups generally showed an increase in bone density and BIC between 6 and 12 weeks, except BIC in the HS group. Although no statistically significant differences were found among HA, HS, HP, and HSP groups (p > 0.05), the highest level of bone density and BIC were observed in the HSP group after the 12-week healing period. Furthermore, the level of bone maturation was higher in the HSP group than in the other groups as determined histologically. The findings of this preliminary study suggest that BMMSCs and PRP combined with HA scaffold may provide additional therapeutic effects on bone regeneration and improve osseointegration in bone defects around dental implants.

Surface microgrooves and acid etching on titanium substrata alter various cell behaviors of cultured human gingival fibroblasts.

OBJECTIVE This study aimed to investigate the influence of surface microgrooves and acid etching on titanium substrata on cell proliferation and gene expression of cultured human gingival fibroblasts. MATERIAL AND METHODS Ti substrata with various dimensions of microgrooves and further acid etching comprised four experimental groups (E15/3.5, E30/5, E60/10, and E90/15), whereas smooth and acid etched Ti discs were both used as control (NE0 and E0). The chemical composition of the control and experimental cp Ti substrata was analyzed by X-ray photoelectron spectroscopy (XPS). Cell proliferation, gene expression, and protein expression of cultured human gingival fibroblasts were analyzed between all groups using bromodeoxyuridine (BrdU) assay, reverse-transcriptase polymerase chain reaction (RT-PCR), and Western blotting, respectively. RESULTS The XPS results showed that the Ti substrata used in this study showed no significant differences in the expression of surface chemical composition. BrdU assay showed that cell proliferation was significantly increased in E60/10 compared with that in any other group. In RT-PCR, E60/10 was noted to increase the expression of various genes involved in cell-matrix adhesion and adhesion-dependent cell cycle progression. In Western blotting, increased expression of fibronectin and Rho A was noted in E60/10 compared with that in NE0 or E15/3.5. CONCLUSION This study indicates that surface microgrooves 60 mum in width and 10 mum in depth, and further acid etching on Ti substrata trigger the proliferation and alter the expression of both genes and proteins in cultured human gingival fibroblasts.

Influence of etched microgrooves of uniform dimension on in vitro responses of human gingival fibroblasts

OBJECTIVE The purpose of this study was to investigate the influence of titanium (Ti) substrata with etched surface microgrooves on in vitro responses of human gingival fibroblasts. MATERIAL AND METHODS Commercially pure Ti discs with surface microgrooves 15, 30, and 60 microm in width were fabricated using photolithography. Microgrooves 15 microm in widths were designed to be 3.5 microm in depth, whereas microgrooves 30 and 60 microm in width varied between 5 and 10 microm in depth. The entire surface of the microgrooved Ti substrata was further acid etched and used as the five experimental groups in this study (E15/3.5, E30/5, E30/10, E60/5, and E60/10), whereas the smooth and acid-etched Ti discs were both used as the control (NE0 and E0). Human gingival fibroblasts were cultured on all groups of substrata on successive timelines. Fibroblast adhesion and morphology was analyzed using confocal laser scanning microscopy (CLSM). Cell adhesion and proliferation were analyzed and compared using crystal violet staining and sulforhodamine B protein staining assays, respectively. RESULTS In CLSM, the cells in E30/10 and E60/10 were observed to be able to readily descend into and form focal adhesions inside the microgrooves, whereas the cells in E15/3.5 were mostly found on the ridge tops. Cell adhesion was significantly increased in E60/10 compared with that in NE0 or E0 at 4-h incubation. Cell proliferation was significantly increased in E60/10 and E15/3.5 compared with NE0 or E0 after 72 and 96 h of culture. CONCLUSION This study indicates that Ti substrata with etched microgrooves 60 microm in width and 10 microm in depth significantly enhance human gingival fibroblast adhesion and proliferation.

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.

Synergistic effect of bone marrow-derived mesenchymal stem cells and platelet-rich plasma on bone regeneration of calvarial defects in rabbits

Bone tissue regeneration techniques include tissue engineering approaches which employ mesenchymal stem cells as an osteogenic agent for bone repair. Recent studies have demonstrated that tissue engineering scaffolds and growth factors can support cell proliferation, bone formation, and bone tissue repair in lost bone tissue. Furthermore, many studies have suggested that platelet-rich plasma (PRP) can improve bone regeneration due to the numerous growth factors that it contains. This study was performed to investigate the influence of bone marrow-derived mesenchymal stem cells (BMMSCs) and PRP on bone regeneration of calvarial defects in rabbits. Hydroxyapatite (HA) was used as a scaffold for bone regeneration. There were three groups in this experiment: 1) HA loaded with BMMSCs (HS group), 2) HA loaded with PRP (HP group), and 3) HA loaded with BMMSCs and PRP (HSP group). Two circular bony defects (6 mm in diameter) were made in rabbit calvaria using a trephine bur. BMMSCs and PRP with a HA scaffold (diameter 5.5 mm, height 3 mm) were applied to each defect. The animals were sacrificed after 2 weeks, 4 weeks and 8 weeks. The level of their ability of osteogenesis was evaluated through histological and histomorphometric analyses. High-quality bone regeneration was observed in the HSP group. The percentage of new bone area around the scaffolds was higher in the HSP group than it was in the other groups (HS and HP group), especially at 8 weeks (HS, 72.5±15 %; HP, 85.8±14 %; HSP, 98.8±2.5%). In addition, the level of bone maturation was higher in the HSP group than in the other groups. The results of this study show that PRP has a positive effect on bone generation. HA with a combination of BMMSCs and PRP can enhance bone regeneration. In addition, the growth factor capacity of PRP may affect the differentiation of BMMSCs and promote bone formation.

Clinical evaluations of cast gold alloy, machinable zirconia, and semiprecious alloy crowns: A multicenter study.

STATEMENT OF PROBLEM Few studies have compared the marginal and internal fits of crowns fabricated from machinable palladium-silver-indium (Pd-Ag-In) semiprecious metal alloy. PURPOSE The purpose of this clinical study was to evaluate and compare the marginal and internal fits of machined Pd-Ag-In alloy, zirconia, and cast gold crowns. MATERIAL AND METHODS A prospective clinical trial was performed on 35 participants and 52 abutment teeth at 2 centers. Individuals requiring prosthetic restorations were treated with gold alloy or zirconia crowns (2 control groups) or Pd-Ag-In alloy crowns (experimental group). A replica technique was used to evaluate the marginal and internal fits. The buccolingual and mesiodistal cross-sections were measured, and a noninferiority comparison was conducted. RESULTS The mean marginal gaps were 68.2 μm for the gold crowns, 75.4 μm for the zirconia crowns, and 76.9 μm for the Pd-Ag-In alloy crowns. In the 5 cross-sections other than the distal cross-section, the 2-sided 95% confidence limits for the differences between the Pd-Ag-In alloy crowns and the 2 control groups were not larger than the 25-μm noninferiority margin. The control groups displayed smaller internal gaps in the line angle and occlusal spaces compared with the Pd-Ag-In crown group. CONCLUSION The marginal gaps of machinable Pd-Ag-In alloy crowns did not meet the noninferiority criterion in the distal margin compared with zirconia and gold alloy crowns. Nonetheless, all 3 crowns had clinically applicable precision.

Secondary closure of an extraction socket using the double-membrane guided bone regeneration technique with immediate implant placement

Purpose Immediate implantation presents challenges regarding site healing, osseointegration, and obtaining complete soft-tissue coverage of the extraction socket, especially in the posterior area. This last issue is addressed herein using the double-membrane (collagen membrane+high-density polytetrafluoroethylene [dPTFE] membrane) technique in two clinical cases of posterior immediate implant placement. Methods An implant was placed immediately after atraumatically extracting the maxillary posterior tooth. The gap between the coronal portion of the fixture and the adjacent bony walls was filled with allograft material. In addition, a collagen membrane (lower) and dPTFE membrane (upper) were placed in a layer-by-layer manner to enable the closure of the extraction socket without a primary flap closure, thus facilitating the preservation of keratinized mucosa. The upper dPTFE membrane was left exposed for 4 weeks, after which the membrane was gently removed using forceps without flap elevation. Results There was considerable plaque deposition on the outer surface of the dPTFE membrane but not on the inner surface. Moreover, scanning electron microscopy of the removed membrane revealed only a small amount of bacteria on the inner surface of the membrane. The peri-implant tissue was favorable both clinically and radiographically after a conventional dental-implant healing period. Conclusions Secondary closure of the extraction socket and immediate guided bone regeneration using the double-membrane technique may produce a good clinical outcome after immediate placement of a dental implant in the posterior area.