Ki-Tae Koo

Alveolar Bone Regeneration by Transplantation of Periodontal Ligament Stem Cells and Bone Marrow Stem Cells in a Canine Peri-Implant Defect Model: A Pilot Study

BACKGROUND The present study was undertaken to evaluate the potential of periodontal ligament stem cells (PDLSCs) and bone marrow SCs (BMSCs) on alveolar bone regeneration in a canine peri-implant defect model. METHODS Four adult, male beagle dogs were used in this study. Autologous BMSCs from the iliac crests and PDLSCs from extracted teeth were cultured. Three months after extraction, BMSC- and PDLSC-loaded hydroxyapatite/beta-tricalcium phosphate (HA/TCP) (test groups) and cell-free HA/TCP (control group) were implanted in three rectangular, saddle-like peri-implant defects, respectively. The left side of the mandible was initially prepared, and after 8 weeks, the right side was also prepared. The animals were sacrificed after an 8-week healing period. Undecalcified ground sections were prepared. New bone formation and bone-to-implant contact (BIC) were measured histomorphometrically. BMSCs and PDLSCs were fluorescently labeled and traced. RESULTS Alveolar bone regeneration in surgically created peri-implant saddle-like defects was more effective in test groups than the control group. The BMSC group had the highest new bone formation (34.99% and 40.17% at healing times of 8 and 16 weeks, respectively) followed by the PDLSC group (31.90% and 36.51%) and control group (23.13% and 28.36%), respectively. Test groups exhibited a significantly higher new bone formation than the control group at 8 weeks, but the same was true for only the BMSC group at 16 weeks (P <0.05). Fluorescently labeled cells were identified adjacent to HA/TCP carriers and, partly, near connective tissues and osteoids. CONCLUSION This study demonstrated the feasibility of using stem cell-mediated bone regeneration to treat peri-implant defects.

Dual Delivery of rhPDGF-BB and Bone Marrow Mesenchymal Stromal Cells Expressing the BMP2 Gene Enhance Bone Formation in a Critical-Sized Defect Model

Bone tissue healing is a dynamic, orchestrated process that relies on multiple growth factors and cell types. Platelet-derived growth factor-BB (PDGF-BB) is released from platelets at wound sites and induces cellular migration and proliferation necessary for bone regeneration in the early healing process. Bone morphogenetic protein-2 (BMP-2), the most potent osteogenic differentiation inducer, directs new bone formation at the sites of bone defects. This study evaluated a combinatorial treatment protocol of PDGF-BB and BMP-2 on bone healing in a critical-sized defect model. To mimic the bone tissue healing process, a dual delivery approach was designed to deliver the rhPDGF-BB protein transiently during the early healing phase, whereas BMP-2 was supplied by rat bone marrow stromal cells (BMSCs) transfected with an adenoviral vector containing the BMP2 gene (AdBMP2) for prolonged release throughout the healing process. In in vitro experiments, the dual delivery of rhPDGF-BB and BMP2 significantly enhanced cell proliferation. However, the osteogenic differentiation of BMSCs was significantly suppressed even though the amount of BMP-2 secreted by the AdBMP2-transfected BMSCs was not significantly affected by the rhPDGF-BB treatment. In addition, dual delivery inhibited the mRNA expression of BMP receptor type II and Noggin in BMSCs. In in vivo experiments, critical-sized calvarial defects in rats showed enhanced bone regeneration by dual delivery of autologous AdBMP2-transfected BMSCs and rhPDGF-BB in both the amount of new bone formed and the bone mineral density. These enhancements in bone regeneration were greater than those observed in the group treated with AdBMP2-transfected BMSCs alone. In conclusion, the dual delivery of rhPDGF-BB and AdBMP2-transfected BMSCs improved the quality of the regenerated bone, possibly due to the modulation of PDGF-BB on BMP-2-induced osteogenesis.

The Effect of Internal Versus External Abutment Connection Modes on Crestal Bone Changes Around Dental Implants: A Radiographic Analysis

BACKGROUND To the best of our knowledge, the influence of external versus internal implant-abutment connections on crestal bone remodeling has not been reported. The aim of the present study is to investigate the influence of the abutment connection on peri-implant crestal bone levels (CBLs) using radiographic recordings. METHODS Radiographic recordings from 40 single-tooth implants (20 external and 20 internal octagonal connections; one implant/patient) in 40 patients (15 males and 25 females; mean age: 54.3 years) were selected for analyses. The radiographic evaluation included the following: 1) linear bone change (LBC); 2) dimensional change (DC); and 3) angle between the implant and adjacent bone (AIB). Differences in LBC, DC, and AIB between implant placement and 1 year after loading for each system were evaluated using a paired t test. Comparison of LBC, DC, and AIB between systems at 1 year after loading was done using analysis of covariance. The significance level was set at P ≤0.05. RESULTS Radiographic CBLs (LBCs) were reduced at 1 year after loading compared to those at implant placement to reach statistical significance for the external connection (P = 0.000) but not the internal connection (P = 0.939). CBL changes were significantly greater for the external compared to the internal connection (P = 0.000). Similarly, the DC for the external connection was significantly greater compared to that for the internal connection (P = 0.004). CONCLUSION Within the limitations of this study, the implant-abutment connection technology appears to have a significant impact on peri-implant CBLs, with the external connection paralleled by a significant reduction of CBLs.

Effect of implant drill characteristics on heat generation in osteotomy sites: a pilot study

OBJECTIVES The objective of this study was to evaluate the effect of drill-bone contact area on bone temperature during osteotomy preparation. MATERIAL AND METHODS Conventional triflute Ø3.6 mm drills were modified with the intent to reduce frictional heat induction. The peripheral dimensions of the drill were reduced 0.15, 0.35 and 0.5 mm to evaluate the effect of surface area on induction of frictional heat between the drill and bone/cutting debris (parameter A). Also, the lateral cutting surface of the drill was set to 0.1, 2 and 7.5 mm to estimate heat induced by direct function of the drill (parameter B). A non-modified triflute drill (parameter A: 0 mm; parameter B: 15 mm) served as control. Thus, nine drills with different A/B combinations vs. one control were tested in artificial bone. Real-time temperature changes (during drilling and withdrawing) were assessed using an infrared thermal imager. Each drilling procedure was performed up to 20 times. Thermal image data were transferred to a PC for simultaneous analysis. RESULTS Mean temperature changes for all modified drill combinations were smaller than for the control (P<0.001). The effects of parameters A and B were statistically significant (P<0.001). There was a significant interaction effect between the two parameters (P<0.001) showing that the effect of parameter A on the mean temperature changes is different depending on the values of parameter B. As the dimensions of parameter B decreased, the temperature change during drilling also decreased. However, a tendency for the temperature to increase or decrease by parameter A was not observed. CONCLUSIONS Within the limitations of this pilot study, the observations herein suggest that reduction in contact area between the drill and bone reduces heat induction. Further studies to optimize drill/bone contact dimensions are needed.

Ex vivo bone morphogenetic protein 2 gene delivery using periodontal ligament stem cells for enhanced re-osseointegration in the regenerative treatment of peri-implantitis

Peri-implantitis is a chronic inflammatory process with advanced bone loss and impaired healing potential. For peri-implantitis treatment, tissue engineering can be applied to enhance bone regeneration of peri-implant defects. This study aimed to evaluate ex vivo bone morphogenetic protein 2 (BMP2) gene delivery using canine periodontal ligament stem cells (PDLSCs) for regeneration of peri-implantitis defects. Canine PDLSCs were transduced with adenoviral vectors containing BMP2 (BMP2/PDLSCs). After peri-implantitis was induced by ligature placement in six beagle dogs, regenerative procedures were performed; hydroxyapatite (HA) particles and collagen gel with autologous canine PDLSCs (PDLSC group) or BMP2/PDLSCs (BMP/PDLSC group) or without cells (control group) were grafted into the defects and covered by an absorbable membrane. Three months later, the animals were sacrificed. In vitro, BMP2/PDLSCs showed similar levels of stem cell properties to PDLSCs, such as colony-forming efficiency and expression of MSC markers STRO-1 and CD 146. BMP2/PDLSCs produced BMP-2 until day 21 at a concentration of 4-8 ng/mL. In vivo, the BMP2/PDLSC group showed significantly more new bone formation and re-osseointegration in peri-implantitis defects compared to the other groups. In conclusion, ex vivo BMP2 gene delivery using PDLSCs enhanced new bone formation and re-osseointegration in peri-implantitis defects.

Evaluation of the correlation between insertion torque and primary stability of dental implants using a block bone test

Purpose Implant stability at the time of surgery is crucial for the long-term success of dental implants. Primary stability is considered of paramount importance to achieve osseointegration. The purpose of the present study was to investigate the correlation between the insertion torque and primary stability of dental implants using artificial bone blocks with different bone densities and compositions to mimic different circumstances that are encountered in routine daily clinical settings. Methods In order to validate the objectives, various sized holes were made in bone blocks with different bone densities (#10, #20, #30, #40, and #50) using a surgical drill and insertion torque together with implant stability quotient (ISQ) values that were measured using the Osstell Mentor. The experimental groups under evaluation were subdivided into 5 subgroups according to the circumstances. Results In group 1, the mean insertion torque and ISQ values increased as the density of the bone blocks increased. For group 2, the mean insertion torque values decreased as the final drill size expanded, but this was not the case for the ISQ values. The mean insertion torque values in group 3 increased with the thickness of the cortical bone, and the same was true for the ISQ values. For group 4, the mean insertion torque values increased as the cancellous bone density increased, but the correlation with the ISQ values was weak. Finally, in group 5, the mean insertion torque decreased as the final drill size increased, but the correlation with the ISQ value was weak. Conclusions Within the limitations of the study, it was concluded that primary stability does not simply depend on the insertion torque, but also on the bone quality.

Evaluation of single-tooth implants in the second molar region: a 5-year life-table analysis of a retrospective study.

BACKGROUND To our knowledge, no study has evaluated the success or survival rate of single-tooth implants that replaced missing maxillary and mandibular second molars. The purpose of the present study was to evaluate the 1- to 5-year cumulative survival rate (CSR) for single-tooth implants placed in the second molar region and the effects of associated factors. METHODS Four hundred eighty-nine patients (298 males and 191 females; age range: 23 to 91 years; mean age: 47 years) who were admitted to the Seoul National University Dental Hospital between March 2003 and July 2008 and treated with single-tooth implants in the second molar region (227 maxillary implants and 294 mandibular implants; total: 521 implants) were included in the study. Thirty-two subjects received two implants each. A 1- to 5-year CSR was calculated using a life-table analysis. A comparison of CSRs between maxillary versus mandibular implants, one-stage versus two-stage implants, short (<or=8.5 mm) versus long (>10 mm) implants, and standard-diameter (<or=4.0 mm) versus wide-diameter (>or=5.0 mm) implants was performed using Wilcoxon (Gehan) statistics. P <0.05 was considered significant. RESULTS Fifteen of the 521 implants were lost between insertion and the follow-up examinations. The 1- to 5-year CSR was 95.1%. There were no statistically significant differences in CSRs between implants placed in maxillas and mandibles (96.3% versus 94.9%, respectively; P = 0.084), one- and two-stage implants (95.6% versus 94.7%, respectively; P = 0.267), short and long implants (100% versus 95.1%, respectively; P = 0.582), and standard- and wide-diameter implants (93.8% versus 96.8%, respectively; P = 0.065). CONCLUSIONS Within the limitations of the study, the placement of single-tooth implants in the second molar region was an effective and reliable treatment modality. Also, associated factors such as implant diameter, length, and location (the maxilla versus the mandible) may not have an impact on the long-term success of implants.

Biological effects of a semiconductor diode laser on human periodontal ligament fibroblasts.

Purpose It has been reported that low-level semiconductor diode lasers could enhance the wound healing process. The periodontal ligament is crucial for maintaining the tooth and surrounding tissues in periodontal wound healing. While low-level semiconductor diode lasers have been used in low-level laser therapy, there have been few reports on their effects on periodontal ligament fibroblasts (PDLFs). We performed this study to investigate the biological effects of semiconductor diode lasers on human PDLFs. Methods Human PDLFs were cultured and irradiated with a gallium-aluminum-arsenate (GaAlAs) semiconductor diode laser of which the wavelength was 810 nm. The power output was fixed at 500 mW in the continuous wave mode with various energy fluencies, which were 1.97, 3.94, and 5.91 J/cm2. A culture of PDLFs without laser irradiation was regarded as a control. Then, cells were additionally incubated in 72 hours for MTS assay and an alkaline phosphatase (ALPase) activity test. At 48 hours post-laser irradiation, western blot analysis was performed to determine extracellular signal-regulated kinase (ERK) activity. ANOVA was used to assess the significance level of the differences among groups (P<0.05). Results At all energy fluencies of laser irradiation, PDLFs proliferation gradually increased for 72 hours without any significant differences compared with the control over the entire period taken together. However, an increment of cell proliferation significantly greater than in the control occurred between 24 and 48 hours at laser irradiation settings of 1.97 and 3.94 J/cm2 (P<0.05). The highest ALPase activity was found at 48 and 72 hours post-laser irradiation with 3.94 J/cm2 energy fluency (P<0.05). The phosphorylated ERK level was more prominent at 3.94 J/cm2 energy fluency than in the control. Conclusions The present study demonstrated that the GaAlAs semiconductor diode laser promoted proliferation and differentiation of human PDLFs.

Immunomodulatory effect of canine periodontal ligament stem cells on allogenic and xenogenic peripheral blood mononuclear cells

Purpose The aim of this study was to investigate the immunomodulatory effects of canine periodontal ligament stem cells on allogenic and xenogenic immune cells in vitro. Methods Mixed cell cultures consisting of canine stem cells (periodontal ligament stem cells and bone marrow stem cells) and allogenic canine/xenogenic human peripheral blood mononuclear cells (PBMCs) were established following the addition of phytohemagglutinin. The proliferation of PBMCs was evaluated using the MTS assay. The cell division of PBMCs was analyzed using the CFSE assay. The apoptosis of PBMCs was assessed using the trypan blue uptake method. Results Periodontal ligament stem cells and bone marrow stem cells inhibited the proliferation of allogenic and xenogenic PBMCs. Both periodontal ligament stem cells and bone marrow stem cells suppressed the cell division of PBMCs despite the existence of a mitogen. No significant differences in the percentages of apoptotic PBMCs were found among the groups. Conclusions Canine periodontal ligament stem cells have an immunomodulatory effect on allogenic and xenogenic PBMCs. This effect is not a product of apoptosis of PBMCs but is caused by the inhibition of cell division of PBMCs.

Ex vivo bone morphogenetic protein‐2 gene delivery using gingival fibroblasts promotes bone regeneration in rats

AIM The aim of the present study was to investigate bone regeneration following ex vivo bone morphogenetic protein-2 (BMP-2) gene delivery using human gingival fibroblasts (HGFs) in rat calvarial defects. MATERIALS AND METHODS An 8 mm craniotomy defect was created in Sprague-Dawley rats. The animals were divided into four groups: (1) non-grafted group, the defect was left empty; (2) collagen matrix group, the defect was filled with collagen matrix only; (3) HGF group, the defect was filled with non-transduced HGFs on collagen matrix; (4) BMP-2/HGF group, the defect was filled with BMP-2 gene-transduced HGFs on collagen matrix. Animals were sacrificed at 2 and 4 weeks after surgery, and micro-computed tomographic and histologic observations were performed. RESULTS The BMP-2/HGF group showed promoted osseous healing of calvarial defects, as compared with the other groups. At both 2 and 4 weeks, regenerated bone area was significantly greater in the BMP-2/HGF group than the other three groups. Quite a few number of transplanted HGFs were observed within the regenerated bone tissues. CONCLUSIONS The results of this study suggest that ex vivo BMP-2 gene delivery induces prominent bone regeneration in vivo and HGFs may be useful as target cells for ex vivo gene therapy.