Assessment of Esophageal Reconstruction via Bioreactor Cultivation of a Synthetic Scaffold in a Canine Model

Objectives@#. Using tissue-engineered materials for esophageal reconstruction is a technically challenging task in animals that requires bioreactor training to enhance cellular reactivity. There have been many attempts at esophageal tissue engineering, but the success rate has been limited due to difficulty in initial epithelialization in the special environment of peristalsis. The purpose of this study was to evaluate the potential of an artificial esophagus that can enhance the regeneration of esophageal mucosa and muscle through the optimal combination of a double-layered polymeric scaffold and a custom-designed mesenchymal stem cell-based bioreactor system in a canine model. @*Methods@#. We fabricated a novel double-layered scaffold as a tissue-engineered esophagus using an electrospinning technique. Prior to transplantation, human-derived mesenchymal stem cells were seeded into the lumen of the scaffold, and bioreactor cultivation was performed to enhance cellular reactivity. After 3 days of cultivation using the bioreactor system, tissue-engineered artificial esophagus was transplanted into a partial esophageal defect (5×3 cm-long resection) in a canine model. @*Results@#. Scanning electron microscopy (SEM) showed that the electrospun fibers in a tubular scaffold were randomly and circumferentially located toward the inner and outer surfaces. Complete recovery of the esophageal mucosa was confirmed by endoscopic analysis and SEM. Esophagogastroduodenoscopy and computed tomography also showed that there were no signs of leakage or stricture and that there was a normal lumen with complete epithelialization. Significant regeneration of the mucosal layer was observed by keratin-5 immunostaining. Alpha-smooth muscle actin immunostaining showed significantly greater esophageal muscle regeneration at 12 months than at 6 months. @*Conclusion@#. Custom-designed bioreactor cultured electrospun polyurethane scaffolds can be a promising approach for esophageal tissue engineering.

A Platform for Studying of the Three-Dimensional Migration of Hematopoietic Stem/Progenitor Cells

Background@#Hematopoietic stem/progenitor cells (HSPCs) have the property to return to the bone marrow, which is believed to be critical in situations such as HSPC transplantation. This property plays an important role in the stemness, viability, and proliferation of HSPCs, also. However, most in vitro models so far have not sufficiently simulated the complicate environment. Here, we proposed a three-dimensional experimental platform for the quantitative study of the migration of HSPCs. @*Methods@#After encapsulating osteoblasts (OBs) in alginate beads, we quantified the migration of HSPCs into the beads due to the physical environment using digital image processing. Intermittent hydrostatic pressure (IHP) was used to mimic the mechanical environment of human bone marrow without using any biochemical factors. The expression of stromal cell-derived factor 1 (SDF-1) under IHP was measured. @*Results@#The results showed that the presence of OBs in the hydrogel scaffold initiate the movement of HSPCs. Furthermore, the IHP promotes the migration of HSPCs, even without the addition of any biochemical factors, and the results were confirmed by measuring SDF-1 levels. @*Conclusion@#We believe this suggested three-dimensional experimental platform consisting of a simulated in vivo physical environment and encapsulated OBs should contribute to in vitro migration studies used to investigate the effects of other external factors.

A Platform for Studying of the Three-Dimensional Migration of Hematopoietic Stem/Progenitor Cells

Background@#Hematopoietic stem/progenitor cells (HSPCs) have the property to return to the bone marrow, which is believed to be critical in situations such as HSPC transplantation. This property plays an important role in the stemness, viability, and proliferation of HSPCs, also. However, most in vitro models so far have not sufficiently simulated the complicate environment. Here, we proposed a three-dimensional experimental platform for the quantitative study of the migration of HSPCs. @*Methods@#After encapsulating osteoblasts (OBs) in alginate beads, we quantified the migration of HSPCs into the beads due to the physical environment using digital image processing. Intermittent hydrostatic pressure (IHP) was used to mimic the mechanical environment of human bone marrow without using any biochemical factors. The expression of stromal cell-derived factor 1 (SDF-1) under IHP was measured. @*Results@#The results showed that the presence of OBs in the hydrogel scaffold initiate the movement of HSPCs. Furthermore, the IHP promotes the migration of HSPCs, even without the addition of any biochemical factors, and the results were confirmed by measuring SDF-1 levels. @*Conclusion@#We believe this suggested three-dimensional experimental platform consisting of a simulated in vivo physical environment and encapsulated OBs should contribute to in vitro migration studies used to investigate the effects of other external factors.

The Effects of Epigallocatechin-3-Gallate and Mechanical Stimulation on Osteogenic Differentiation of Human Mesenchymal Stem Cells: Individual or Synergistic Effects

This study aims to investigate the roles and effects of EGCG (epigallocatechin-3-gallate) during the osteogenic differentiation of human mesenchymal stem cells (hMSCs) in vitro. Recent studies have shown that proper mechanical stimuli can induce osteogenic differentiation of hMSCs apart from biochemical factors. In this study, the hMSC cultures were subjected to: (1) 25 uM EGCG alone or (2) 3% mechanical stretching (0.2 Hz for 4 h/day for 4 days) or (3) in combination with 3% mechanical stretching (0.2 Hz for 4 h/day for 4 days). The two factors were applied to the cell cultures separately and in combination to investigate the individual and synergistic effect of both mechanical stimulation and ECGC in the osteogenic differentiation of hMSCs. Utilizing real time PCR, we measured various osteogenic markers and even those related to intracellular signalings. Further investigation of mitochondria was performed that mitochondria biogenesis, antioxidant capacity, and morphological related markers were measured. hMSCs were to be osteogenic or myogenic differentiated when they were under 3% stretching only. However, when EGCG was applied along with stretching they were to be osteogenic differentiated rather than to be myogenic differentiated. This was supported by evaluating intracellular signalings: BMP-2 and VEGF. Therefore, the synergistical effects of simultaneous employment of stretching and EGCG on osteogenic differentiation were confirmed. Moreover, simultaneous employment was found positive in mitochondria biogenesis, antioxidant capacity, and morphological changes. Through this study, we came into the conclusion that the combination of proper mechanical stretching, 3% in this study, and EGCG promote osteogenic differentiation. Reflecting that EGCG can be obtained from plants not from the chemical syntheses, it is worth to be studied further either by animal tests or long-term experiments for clinical applications.

PCL/β-TCP Composite Scaffolds Exhibit Positive Osteogenic Differentiation with Mechanical Stimulation

We investigated the use of Polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP) composites with applied mechanical stimulation as scaffold for bone tissue engineering. PCL-based three-dimensional (3D) structures were fabricated in a solvent-free process using a 3D-printing technique. The mass fraction of β-TCP was varied in the range 0–30%, and the structure and compressive modulus of the specimens was characterized. The shape and interconnectivity of the pores was found to be satisfactory, and the compressive modulus of the specimens was comparable with that of human trabecular bone. Human mesenchymal stem cells were seeded on the composites, and various biological evaluations were performed over 9 days. With a mass fraction of β-TCP of 30%, differentiation began earlier; however, the cell proliferation rate was lower. Through the use of mechanical stimulation, however, the proliferation rate recovered, and was comparable with that of the other groups. This stimulation effect was also observed in ECM generation and other biological assays. With mechanical stimulation, expression of osteogenic markers was lower on samples with a β-TCP content of 10 wt% than without β-TCP; however, with mechanical stimulation, the sample with a β-TCP content of 30 wt% exhibited significantly greater expression of those markers than the other samples. We found that mechanical stimulation and the addition of β-TCP interacted closely, and that a mass fraction of β-TCP of 30% was particularly useful as a bone tissue scaffold when accompanied by mechanical stimulation.

Distinguishing Tendon and Ligament Fibroblasts Based on ¹H Nuclear Magnetic Resonance Spectroscopy

Tendon and ligament (T/L) have been known to be obviously different from each other in tissue level. However, due to the overlapping gene markers, distinction in cellular level has not been clearly verified yet. Recently, the use of nuclear magnetic resonance (NMR) spectroscopy has shown the potential to detect biological markers in cellular level. Therefore, in this study we applied a non-invasive technique based on NMR spectroscopy to establish biomarkers to distinguish between T/L fibroblasts. In addition the cellular morphologies and gene expression patterns were also investigated for comparison through optical microscopy and real-time polymerase chain reaction (PCR). No difference was observed from morphology and real-time PCR results, either as expected. However, we found clear differences in their metabolomic spectra using ¹H NMR spectroscopy. The calculated integral values of fatty acids (with chemical shifts at ~0.9, 1.26, 1.59, 2.05, 2.25, and 2.81 ppm), lactate (~1.33 ppm), and leucine (~2.72 ppm) were significantly different between the two types of fibroblasts. To be specific tendon group exhibited higher level of the metabolite than ligament group. In conclusion, in-cell metabolomic evaluation by NMR technique used in this study is believed to provide a promising tool in distinguishing cell types, especially T/L cells, which cannot be classified by conventional biological assays.

Effects of Mechanical Stimulation and Scaffolds for Nucleus Pulposus Replacement of Intervertebral Disc / 대한정형외과연구학회지

PURPOSE: In this study, we investigated the potential of injectable hydrogel scaffolds for the regeneration of nucleus pulposus. MATERIALS AND METHODS: We prepared injectable hydrogels [Chitosan-Pluronic (CP), CP/Osteogenic Protein-1 (CP/OP-1), CP/Gly-Arg-Gly-Asp-Ser (CP/GRGDS), CP/GRGDS/OP-1] for this study. One of the four potential materials was selected through the cell viability tests. For each material, primary cultured nucleus pulposus (NP) cells from New Zealand rabbits were seeded onto each material. For the investigation of the effects of mechanical stimulation, the commercially available bioreactor was used. 0.2 MPa of intermittent hydrostatic pressure was imposed for 3 days after 7th day of seeding with the pattern of 2 min and 15 min for stimulating and resting, respectively. The specimens were harvested at 1, 10, 14 day after seeding for analyses. RESULTS: The MTT assay for 5 days revealed that CP/OP-1 group showed significant increase. The other two groups (CP/GRGDS and CP/GRGDS/OP-1) showed that the proliferation rate increased until 3 days after culture, while it decreased on day 5. The mechanical stimuli induced higher amounts of DNA measured in CP/OP- 1 on day 5 after culture. However, no significant difference was observed between two groups. CONCLUSION: We came to the conclusions that the biochemical environment as well as mechanical stimulation may play an important role in regenerating nucleus pulposus matrix, especially in CP/OP-1 in this study. However, further study are recommended in relation to mechanical effects as well as biochemical conditions.

Biocompatibility Evaluation of Heat-treated Mineralized Porcine Cancellous Bone : Using Animal & Clinical Study / 대한정형외과연구학회지

PURPOSE: In our previous study, the authors developed high heat-treated mineralized porcine cancellous bone(TS-GBB, TaeSan Green Bone Block) as bone-substitute. So we projected that this experiments about TSGBB would prove its safety about problems after transplants, and its stability in mechanical strength as the human bone-substitute. MATERIALS AND METHODS: Highly heat-treated mineralized porcine cancellous bone was made. The chemical, mechanical, and morphological properties were evaluated through various tests. Animal study Total 31 New Zealand White rabbits were randomly selected. Bony defect on medial side of the proximal tibia was made. TS-GBB was implanted into the defect area in experimental group, while it was not inserted in control group. For stable fixation self-designed plate of stainless steel was used in both groups. At 2, 8, and 24 weeks, radiological evaluation was performed to measure new bone formation. At 4 and 16 weeks, clinical laboratory tests were performed. Mechanical shear tests were performed for control and experimental groups at 2, 8, and 16 weeks after operation. Also, histological observations were performed by H & E staining at 2 and 16 weeks after operation. Clinical experiments With the approval of IRB in Pusan Paik Hospital of Inje University and Hwasoon Hospital of Chunnam National University, the clinical trials were processed. After harvesting iliac bone for auto grafts from the 40 patients, 20 for each hospital, the TS-GBB were inserted to the donor site. ESR, CRP, WBC count were performed at postoperative time immediately, 1 week, 4 weeks, and 12 weeks to examine possible infection. At 12 weeks after operation, additional X-ray and CT observation were performed. RESULTS: Animal study At all laboratory finding, two group did not indicate a significant difference. At radiologic evaluation, we could comfirm that bone defect size was small gradually by new bone formation in the control group but new bone formation degree was more smaller and slower compared to the TS-GBB group. And at result of biological dynamic stiffness experiments, at postoperative 16 weeks, maximum load at breakage of control group showed to approximately 70% in normal tibia's that. But, maximum load at breakage or yield of TS-GBB group showed to more than 95% in normal tibia's that. In histologic examination, at postoperative 16 weeks, we comfirmed that in control group atypical bony tissue existed in defect site. On the other side, in TS-GBB group new bone formation formed in uniform. Clinical experiments In 20 cases of Inje University, absorption rate was slow a little at 1 case, but the others absorbed normally. In 17 cases of Hwasun Hospital of Chunnam National University, we comfirmed in grade 3 about TS-GBB's absorption and new bone formation at 16 case. At only 1 case, degree of TS-GBB's absorption and new bone formation was poor. In clinical chemistry tests to evaluate the safety, 19 of 20 patients who participated in the experiment in Pusan Paik hospital showed no specific abnormality and showed similar result to preoperative laboratory. In 1 case at postoperative 12 weeks, CRP was elevated, at 16 weeks this patient showed in normal value in ESR, CRP, and WBC count. In 20 patients of Hwasun Hospital all showed similar results to preoperative laboratory in clinical chemistry tests. CONCLUSION: We think that TS-GBB is the suitable material for regeneration of bone defect site as xenograft of clinical bone substitute.

Effects of Nanofiber Alignment and Strain Direction on Cellular Activities of Human ACL Fibroblasts / 대한정형외과연구학회지

PURPOSE: The effects of fiber alignment and direction of mechanical strain on the ECM generation of human ACL fibroblast were assessed. MATERIALS AND METHODS: The aligned nanofiber was fabricated using electrospinning with a rotating target. The amounts of collagen on aligned and randomly oriented structures were compared. To evaluate the effect of strain direction, 5% uniaxial strain (0.2 Hz) was applied to fibroblasts seeded on parallel aligned, vertically aligned to the strain direction, and randomly oriented nanofiber sheets. The amounts of collagen produced were measured 2 days after halting the strain application. RESULTS: The fibroblasts on the aligned nanofiber were spindle-shaped and oriented in the direction of the fibers. Significantly more collagen (22.5+/-2.7 ug/ngDNA) was synthesized on the aligned nanofiber than the randomly oriented (14.5+/-3.2 ug/ngDNA). And the amounts of collagen produced were increased by 150% and 50% approximately with the longitudinal and perpendicular cyclic strain, respectively. CONCLUSION: The aligned nanofiber scaffold used in this study constitutes a promising base material for tissue-engineered ligament in that it provides a more biomimetic structure, including the preferable mechanical environment.

The Influence of Androgen Deficiency and Osteopenia on Fracture Healing in Orchiectomized Rats / 대한정형외과학회잡지

PURPOSE: The purpose of this study was to evaluate the effect of testosterone deficiency and osteopenia on fracture healing using orchiectomized adult rats. MATERIALS AND METHODS: Fifty-two 3 month old male rats were used. Animals were divided into 3 groups. Group 1 received sham operations and groups 2 and 3 were orchiectomized. At 4 weeks, right tibial shaft fractures were administered in all animals. Afterwards in group 3, testosterone was injected intra-peritoneally for 4 weeks. After 8 weeks of breeding, animals were sacrified for morphometrical, histopathological and biomechanical testing. RESULTS: No nonunion or delayed union was observed. Differences in tibial volumes and circumferences between the fracture site and the corresponding contralateral site were less in groups 2 and 3 than in group 1, with statistical significance. The yield strength and the trabecular area of the fractured tibiae were significantly lower in group 2, but group 3 and group 1 were similar. CONCLUSION: Even though there was no evidence of compromised fracture healing, both of the androgen deficiency and osteopenia induced by orchiectomy negatively influenced callus volume and strength. But osteopenia did not influece callus strength. The above results demonstrate the positive effect of testosterone injection on fracture healing.

A Study on the Potential of Hydroxyapatite Based Bioactive Bone Cement / 대한정형외과연구학회지

Study on the Potential of Hydroxapatite Based Bioactive Bone Cement PURPOSE: The purpose of this study is to propose a new bioactive bone cement (BBC) composed of bone powder (hydroxyapatite; HA), chitosan powder, and currently available polymethylmethacrylate (PMMA) bone cement for use in orthopaedic surgeries such as vertebroplasty or bone filler. MATERIALS AND METHODS: Three types of proposed BBCs and a currently available commercial PMMA were tested. In vitro studies the surface morphology, chemical composition, changes in pH value along the time, exothermic temperatures, intrusion and cellular responses were investigated. SEM, radiological and histological examinations were performed in animal studies. RESULTS: The major components of BBCs were C, O, Ca, P, Cl, Si, S, Ba and Mg. The pH values in BBCs decreased after 1 day, however they eventually reached 7.2-7.4. The water absorbency, weight loss, and porosity in BBCs increased more than PMMA more than during degradation (p<0.05). However, the compressive Young's moduli and ultimate compressive strength (UCS) of BBCs were lower than those of PMMA (<0.05). The exothermic temperatures of the BBCs were considerably lower than that of PMMA (p<0.05). In view of setting time, it takes relatively longer for BBCII and III to be solidified than PMMA (p<0.05). The intrusion tests showed that the BBCs were more intrusive than PMMA (p<0.05). The cell proliferation test on BBCII showed that the BBCII was more preferable than the PMMA. No cytotoxic characteristics were found in all BBCs. In the animal test, BBC II was more biocompatible as well as osteoconductible than the PMMA. CONCLUSION: The results of in vitro and animal studies indicated that the proposed BBCs have a potential of clinical application as replacement of the current PMMA bone cements.

The Biomechanical Responses of Intervertebral Disc due to Degenerative Change in Porcine Lumbar Spine / 대한정형외과연구학회지

PURPOSE: The biomechanical responses of degenerative porcine intervertebral disc were compared with those MATERIALS AND METHODS: Two groups were set; Group A (44.0+/-2.8 months old, female) and Group B (6.2 +/-1.3 months old, female). Histological (H&E stain) observations were carried out to see the degeneration for both groups. Then biomechanical responses were investigated by measuring height changes in disc, intradiscal pressure values and relaxation time for each specimen under axial compressive loads. RESULTS: Degenerative changes were confirmed through H&E staining in Group A. The ratios of the nucleus pulposus area to total area were 14.7+/-4.5% and 29.2+/-6.0% in Group A and B, respectively (p=0.000). The decrease rates in disc height were 12.1+/-3.3% and 21.6+/-7.6%, in Group A and B, respectively under the axial compression of 740 N (p=0.000). No significant difference in intradiscal pressure measured in anterior zone between-groups except at axial load of 740N (p> 0.05). However, significant difference in pressure was found in posterolateral zone when the load was 542 N and higher (542 N: p=0.015, 740 N: p=0.010). The average relaxation time for Group A was significantly longer than that for Group B at 740N, i.e., at maximum load (anterior: p=0.010, posterolateral: p=0.014). CONCLUSION: Different biomechanical responses in degenerative disc were confirmed. They are 1) less flexible, 2) slower in energy relaxation under axial loading, and 3) larger portion of the external load were taken up at posterior part of annulus fibrous, especially in degenerative disc.

Circumferential Bending Test of Lumbar 4-5 Segment and Biomechanical Investigation of Stability for Anterior Lumbar Interbody Cages and Supplemental Posterior Instrumentation / 대한척추외과학회지

STUDY DESIGN: Compare the effectiveness of three types of cages used in each case separately with that of cages supplemented by posterior fixation such as transfacet screws and transpedicular screws. OBJECTIVES: To determine whether any important information could be obtained when anterolateral and/or posterolateral bending is imposed. SUMMARY OF LITERATURE REVIEW: Most lumbar spine biomechanical bending tests have been performed on flexion-extension and lateral bending only. MATERIALS AND METHODS: Flexibility was tested through the unconstrained eccentric compression-bending of isolated L4-L5 motion segments. A total of sixteen fresh frozen human cadaveric lumbosacral spine specimens(range of ages : 42+/-13 years 12 males and 4 females) were tested in this investigation. In each case bending load was applied in flexion(0 degree direction), then in 30 degree increments around the transverse plane until flexion was repeated at the 360 degree loading direction. Specimens underwent anterior interbody instrumentation with three different types of cage at L4-5 in three groups, respectively. After testing the interbody fusion constructs, the L4-L5 segments were first stabilized posteriorly using transfacet screws and then retested using transpedicular screw instrumentation. RESULTS: In the intact model, the increase in deflection angle was twice compared with that of the previous point starting from 120 degree up to 150 degree. The pure extensional motion showed the largest deflection angles which are 3.5 times higher than those in pure flexion in average. All three types of cages showed the similar results that were obtained from the intact model.

Chemical, Structural & Osteoconductive Properties of Mineralized Porcine Cancellous Bone / 대한정형외과연구학회지

PURPOSE: The purpose of this study is to determine the efficacy of bioactive hydroxyapatite obtained from the porcine cancellous bone for the treatment of bone defect and nonunion. MATERIALS AND METHODS: Porcine cancellous bones were heat-treated at 1300degrees C for 2 hours. The chemical compositions, calcium to phosphate ratio and microstructures of mineralized porcine bone were examined. For in vivo implantation, bone defects were made on the anteromedial aspects of proximal tibia in 7 beagle dogs and theses artificial bones were inserted. Plain X-ray was taken at every 2 weeks interval for radiologic evaluation. At 12 weeks, specimens were evaluated histologyically with hematoxylin and eosin stain. RESULTS: The composition and morphology of mineralized porcine cancellous bone were similar to those of heat-treated human cancellous bone. Radiographs showed union at the host bone-bone block interfaces. At 12 weeks, all uniform and substantial new bone formation were observed. CONCLUSION: This mineralization technique has several advantages such as no disease transmission, no immune reaction, excellent biocompatibility, and cost-effectiveness. Consequently, mineralized porcine cancellous bone showed an effective osteoconductivity.

A Finite Element Analysis on the Effectiveness and Ideal Positions of the Tansfixators in Pedicle Screw Instrumentation / 대한정형외과연구학회지

Recent studies suggest that addition of transfixators to pedicle screw instrumentation enhances rotational stability of the constructs. However, the effectiveness of the transfixators along with their ideal numbers and positions still remains unclear. In this study, finite element analysis was performed to suggest the most effective positions of the transfixators based on their numbers. For this purpose, a finite element model of a spinal segment(L3-5) with total vertebrectomy at L4 and pedicle screw instrumentation was developed. The finite element model was made with 3-D 8 node solid elements so that they are more realistic and closer to the actual human vertebrae than the preciously published models. On this model, the transfixator(s) were placed along the pre-determined position(s) along the rod while its number was varied between 1 and 2. Appropriate boundary conditions were designated and rotational moment of 6.4 Nm was applied both in axial rotation and lateral bending. Improvement in rotational stability due to addition of the transfixator(s) was calculated as the percent decrease in motion relative to the case without. Results suggested that with one transfixator the rotational stability increased by the average of 19.0% and 6.1% against axial rotation and lateral bending, respectively. With two, the corresponding improvements were 32.3% and 10.7%. Against axial rotation, it was most effective when transfixator was placed at the middle of the rod(22.9%) for one transfixator and at the 1/3 and 2/3 sites along the rod(35.8%) for two. Against lateral bending, the ideal position(s) were at the proximal end(10.7%) for one transfixator and at the proximal and distal ends of the construct(17.7%) for two. It was also found that adding of a transfixator was more sensitive against lateral bending than against axial rotation(78% versus 64%). In conclusion, base on our biomechanical results, it can be suggested that the ideal positions for the ators are located at the equidistance from the both ends of the rod against axial rotation and at the both ends against lateral bending.

A Biomechanical Analysis of Surgical Procedures for Osteonecrosis of the Femoral Head using Three-Dimensional Finite Element Method: A Parametrical Analysis by Varying Physiological Loading Conditions / 대한정형외과연구학회지

Many operative procedures for osteonecrosis of the femoral head(ONFH) have been proposed, but their clinical results remain controversial to many clinicians. Recently, a new surgical procedure that incorporates cementation with polymethylmethacrylate(PMMA) after core drilling has been tried clinically. In this study, a finite element method (FEM) was employed to analyze and compare various surgical procedures of ONFH to provide a biomechanical insight by varying physiological loading conditions. Our finite element models were constructed for this purpose they included normal, necrotic, core decompressed, fibular bone grafted, and cementation models. The extent of necrotic region was determined based upon the average CT-scan data from 10 patients. The physiological load directions and magnitudes during the gait cycle were selected at the stage of heel-strike, toe-off, and average stance. The von Mises stresses were calculated and volumetric percentages of the necrotic region under different levels of stresses were analyzed for each model. Our results indicated that there were substantial increase of the necrotic region subjected to the high stress level (beyond 11 MPa) and decrease in the low stress level (below 5 MPa) with the core decompression model, an indication of a malignant stress transfer pattern. On the other hand, the exact opposite pattern of stress transfer was noted with the fibular bone graft and cementation methods suggesting that they could provide structural integrity within the necrotic region.

Finite element method modeling for individual malocclusions: development and application of the basic algorithm / 대한치과교정학회지

The purpose of this study is to devlop the basic algorithm for the finite slsment method modeling of indivdual malocclusions. Usully, a great deal of time js spent in preprocessiong. To reduce the time required, we developed a stsndardized proccrdure for measuring the position of each tooth and a program to automatically preprocess. The following procedures were carride to complete this study. 1. Twenty-eigth teeth mofphologies were constructed three- dimensionally for the finite element analysis and saved as separate files. 2. Standard brackets were attached so that the FA points conincide with the center of the brackets. 3. The study model of a patient was made. 4. Using the study model, the crown inclination, and the vertical distance from the tip of a tooth was measured by using specially designed tools. 5. The arch form was determined from a picture of the model with an image processing technique. 6. The meadured data were input as a rotational matrix. 7. The program provides an output file containing the necessary information about the three-dimensional position of teeth, which is applicable to several finite element programs commonly used. The program for basic algorithm was made with Turbo-C and the subsequent outfile was applied to ANSYS. This standatdized model measuring procedure and the program reduce the time required, espccially for preprocessing and can be applied to other malocclusions easily.

Mechanical Analysis of the Excimer Laser Photorefractive Keratectomy

This study proposed a mechanical model of the excimer laser photorefractive keratectomy(PRK) for myopia patients utilizing finite element method, which is a simulation technique widely used in engineering fields. The outcomes of the surgery depends on many factors, which are also dependent on each other. In this study, some mechanical factors are selected and the effects of the selected factors on the surgical results were analyzed. One of the important factors in the finite element analysis is the mechanical properties of the object. The representative characteristic of the human cornea is that it shows highly nonlinear property in the stress-strain relationship like most soft tissues in the human body. Therefore, the nonliear property was adopted in this study. Other important mechanical properties which affect the outcomes of the surgery are: a preoperative thickness, intraocular pressure, diameter of ablation zone and the depth of ablation. With various changes of the those mechanical factors, the outcomes of the surgery were predicted using the finite element method. The results show the qualitative agreement with clinical outcomes also promising agreement quantitatively. Therefore, this study shows a potential of the finite element method in clinical application of excimer laser PRK.