Molecular Dynamics Study on Docking of A3/A1 and Interdomain Interactions / 医用生物力学

Objective To investigate the interaction between von Willebrand factor (vWF) A1 and A3 domain, and type 2 M mutant W1745C-A3 effect on thermal stability and mechanical stability of A3/A1. Methods The crystal structures of A1 and A3 were downloaded from Protein Data Base (PDB). The wild-type (WT) A3/A1 structure was obtained by using SwarmDock Server, then W1745C-A3/A1 mutant was constructed by replacing the Trp1745 with Cys1745 in A3/A1. Through steered molecular dynamics simulation, formation and evolution of hydrogen bond and salt bridge between A1 and A3 interfaces were observed, and the differences in conformation, disrupted force and dissociation time between WT-A3/A1 and W1745C-A3/A1 were compared. Results There were 5 pairs of hydrogen bonds with survival rate > 0-2 and 1 pair of salt bridge with survival rate > 0-5 between A1 and A2. The W1745C-A3/A1 complex could withstand greater disrupted force and longer dissociation time compared with WT-A3/A1, by improving the stability of hydrogen bonds and increasing 1 pair of stable salt bridge. Conclusions The interaction between A1 and A3 would hinder the binding sites of A1 to GPIbα, and the W1745C-A3 mutation would further reduce the affinity of A1 to platelets. These results provide references for revealing the molecular mechanism of von Willebrand diseases in the clinic and developing the corresponding drugs targeted to hemostasis disorders.

Comparison of mechanical and biological properties of zirconia and titanium alloy orthodontic micro-implants / 대한치과교정학회지

OBJECTIVE: The aim of this study was to compare the initial stability as insertion and removal torque and the clinical applicability of novel orthodontic zirconia micro-implants made using a powder injection molding (PIM) technique with those parameters in conventional titanium micro-implants. METHODS: Sixty zirconia and 60 titanium micro-implants of similar design (diameter, 1.6 mm; length, 8.0 mm) were inserted perpendicularly in solid polyurethane foam with varying densities of 20 pounds per cubic foot (pcf), 30 pcf, and 40 pcf. Primary stability was measured as maximum insertion torque (MIT) and maximum removal torque (MRT). To investigate clinical applicability, compressive and tensile forces were recorded at 0.01, 0.02, and 0.03 mm displacement of the implants at angles of 0°, 10°, 20°, 30°, and 40°. The biocompatibility of zirconia micro-implants was assessed via an experimental animal study. RESULTS: There were no statistically significant differences between zirconia micro-implants and titanium alloy implants with regard to MIT, MRT, or the amount of movement in the angulated lateral displacement test. As angulation increased, the mean compressive and tensile forces required to displace both types of micro-implants increased substantially at all distances. The average bone-to-implant contact ratio of prototype zirconia micro-implants was 56.88 ± 6.72%. CONCLUSIONS: Zirconia micro-implants showed initial stability and clinical applicability for diverse orthodontic treatments comparable to that of titanium micro-implants under compressive and tensile forces.

The effect of the thread depth on the mechanical properties of the dental implant

PURPOSE: This study aimed to evaluate the effect of implant thread depth on primary stability in low density bone. MATERIALS AND METHODS: The insertion torque was measured by inserting Ti implants with different thread depths into solid rigid polyurethane blocks (Sawbones) with three different bone densities (0.16 g/cm3, 0.24 g/cm3, and 0.32 g/cm3). The insertion torque value was evaluated with a surgical engine. The static compressive strength was measured with a universal testing machine (UTM) and the Ti implants were aligned at 30degrees against the loading direction of the UTM. After the static compressive strength test, the Ti implants were analyzed with a Measurescope. RESULTS: The Ti implants with deeper thread depth showed statistically higher mean insertion torque values (P.05). After the static compressive strength, the thread shape of the Ti implants with deeper thread depth did not show any breakage but did show deformation of the implant body and abutment. CONCLUSION: The implants with deeper thread depth had higher mean insertion torque values but not lower compressive strength. The deep threads had a mechanical stability. Implants with deeper thread depth may increase the primary stability in areas of poor quality bone without decreasing mechanical strength.

The effect of the thread depth on the mechanical properties of the dental implant

PURPOSE: This study aimed to evaluate the effect of implant thread depth on primary stability in low density bone. MATERIALS AND METHODS: The insertion torque was measured by inserting Ti implants with different thread depths into solid rigid polyurethane blocks (Sawbones) with three different bone densities (0.16 g/cm3, 0.24 g/cm3, and 0.32 g/cm3). The insertion torque value was evaluated with a surgical engine. The static compressive strength was measured with a universal testing machine (UTM) and the Ti implants were aligned at 30degrees against the loading direction of the UTM. After the static compressive strength test, the Ti implants were analyzed with a Measurescope. RESULTS: The Ti implants with deeper thread depth showed statistically higher mean insertion torque values (P.05). After the static compressive strength, the thread shape of the Ti implants with deeper thread depth did not show any breakage but did show deformation of the implant body and abutment. CONCLUSION: The implants with deeper thread depth had higher mean insertion torque values but not lower compressive strength. The deep threads had a mechanical stability. Implants with deeper thread depth may increase the primary stability in areas of poor quality bone without decreasing mechanical strength.

Effects of spondylolysis on mechanical stability of upper lumbar vertebrae / 医用生物力学

Objective To study the stability of upper lumbar vertebra in spondylolysis by measuring the upper vertebra pressure on lumbar spondylolysis models. Method Nine fresh frozen human lumbar spinal specimens were used as experimental models. The pressure on upper vertebral discs of lumbar vertebrae was measured by the material testing machine (MTS 858 Bionix test system)with extension, flexion and axial, bilateral compression being applied on two groups of specimens: 1) intact spine; 2) lumbar spondylolysis. Results Compared with the intact specimens, the pressure of upper lumbar vertebra in spondylolysis was increased by 1.3％，1.5％，1.7％ in axial compression with 600, 800, 1 000 N (the differences were not significant (P＞0.05)), by 20.97％，24.45％，28.79％ in 15°of extension with 300, 500, 700N (the differences were significant (P < 0.01)), by 14.15％，17.86％，24.92％ in 15°of flexion with 300, 500, 700N (the differences were significant (P < 0.01)), by 3.54％，2.12％，1.14％ in 15°of bilateral compression with 300, 500, 700N (the differences were not significant (P＞0.05)). Conclusions Lumbar spondylolysis has a significant mechanical influence on lumbar spine not only at the involved level but also at the upper adjacent level, which can affect the stability of lumbar spine correspondingly.

Clinical Application and Surgical Results of Hollow Cage(RABEA(TM)) without Bone Graft in the One-Segment Cervical Spinal Interbody Fusion

OBJECTIVE: The authors report a result of application of cervical hollow cage(RABEA(TM)) without bone graft to the patients of one-level cervical spondylosis or acute cervical disc herniation to fill and stabilize a vacant space following anterior decompression. METHODS: Twenty-one patients from May 1999 to April 2001 had been taken procedure with cervical hollow cage system following anterior decompression and there had been no additional bone graft or screw fixation or fusion. Pain relief and clinical outcome were evaluated, and the intervertebral disc height and segmental angle for radiological assessment were examined. All patient were followed up for 12 months at least. RESULTS: The result was excellent in 14 cases(66.7%), good in 6 cases(28.6%) and poor in 1 case(4.8%). In the lateral projection, the mean of preoperative disc height and segmental angle were significantly improved after surgery and maintained during follow-up periods. No abnormal displacement were recorded at dynamic flexion and extension lateral X-ray and no cage rotation or retropulsion was noted in follow-up periods. Three patients(14.3%) was observed to subside of disc height on the postoperative periods and only one of their patients was dissatisfied with surgery. CONCLUSION: Cervical hollow cage is simple to perform and reduces the operation time. Besides clinical improvement, it improves mechanical stability and radiological profile as the physiologic level. The cervical hollow cage might be an alternative to traditional cervical interbody fusion with bone graft.

Clinical, Physical Stability and Histological Biocompatibility of Experimental Seoul Type Keratoprosthesis

In cases that penetrating keratoplasty do not help to improve vision, keratoprosthesis implantation is necessary. This study was performed to assess clinical and mechanical stability of Seoul type-keratoprosthesis[SKPro], bio-compatibility and effect of amniotic membrane transplantation on clinical and mechanical stability of SKPro. SKPro consists of an optic portion made of PMMA, a skirt of Gore-tex or polyurethane and a haptic of prolene. The skirt of SKPro was covered with recipient conjunctiva completely at postoperative 1 month and melting of covered conjunctiva and exposure of skirt developed at postoperative 2 months and progressed slowly to postoperative 6 months. But retroprosthetic membrane formation, extrusion of SKPro, posterior segment complication such as retinal detachment did not develop and transplanted SKPro showed relatively good clinical stability during 6 months. Pressure loading test showed relatively good mechanical stability under high pressure at postoperative 2 months. Histologic study showed moderate inflammatory reaction and abnormal pattern of collagen and extracellular matrix in lamellar pocket and anterior flap. There was no deposit of collagen in Gore-tex skirt. But histology of posterior flap of lamellar pocket was nearly normal. Group that was transplanted with amniotic membrane twice showed more better stability than once and without amniotic membrane transplantation on clinical and mechanical stability.

Clinical, Physical Stability and Histological Biocompatibility of Experimental Seoul Type Keratoprosthesis

In cases that penetrating keratoplasty do not help to improve vision, keratoprosthesis implantation is necessary. This study was performed to assess clinical and mechanical stability of Seoul type-keratoprosthesis[SKPro], bio-compatibility and effect of amniotic membrane transplantation on clinical and mechanical stability of SKPro. SKPro consists of an optic portion made of PMMA, a skirt of Gore-tex or polyurethane and a haptic of prolene. The skirt of SKPro was covered with recipient conjunctiva completely at postoperative 1 month and melting of covered conjunctiva and exposure of skirt developed at postoperative 2 months and progressed slowly to postoperative 6 months. But retroprosthetic membrane formation, extrusion of SKPro, posterior segment complication such as retinal detachment did not develop and transplanted SKPro showed relatively good clinical stability during 6 months. Pressure loading test showed relatively good mechanical stability under high pressure at postoperative 2 months. Histologic study showed moderate inflammatory reaction and abnormal pattern of collagen and extracellular matrix in lamellar pocket and anterior flap. There was no deposit of collagen in Gore-tex skirt. But histology of posterior flap of lamellar pocket was nearly normal. Group that was transplanted with amniotic membrane twice showed more better stability than once and without amniotic membrane transplantation on clinical and mechanical stability.

The Biomechanical Study for the Initial Stability of Porous - coated Acetabular Components in Total Hip Arthroplasty / 대한정형외과학회잡지

The purpose of this study was to investigate the gaps of bone-acetabular component interface, the initial mechanical stability and the effects of adjuvant screw fixation in the press-fitted two different shaped porous-coated acetabular components. Semi-hemispherical Harris-Galante II cup and full hemispherical Trilogy cup were press-fitted with or without adjuvant screw fixation in 40 bovine femur. The gaps of bone-implant interface were measured in each radiography of all specimen and axial compression tests and rotational stability tests were performed using servohydraulic tension-compression machine. There was significantly smaller gap at polar 1/3 region in the specimen implanted with Trilogy cup. But the adjuvant screw fixation did not affect the amount of gap. There was no significant statistical difference in axial load and rotational stability test in each situations of fixation. This study demonstrates that the initial mechanical stability is not influenced by the shape of semi-hemispherical Harris-Galante II cup and full hemispherical Trilogy cup and also independent of adjuvant screw fixation. But smaller gap of Trilogy cup at the polar 1/3 region indicates the possibility that less amout of wear debris of polyethylene or metal will be deposited and therefore less osteolysis or cup loosening will occur, but this hypothesis should be confirmed by the long-term clinical follow-up.