BACKGROUND:Al ogeneic bone has anatomical appearance and biological features similar to autogenous bone, which is an excel ent biological scaffold material. Mesenchymal stem cel s originating from autogenous bone marrow have mutli-lineage differentiation potential, can differentiate into osteoblasts and chondrocyte, and thus can accelerate the formation of bone tissue and cartilage tissue. OBJECTIVE:To establish the osteogenic ability of al ogeneic bone with autogenous bone marrow mesenchymal stem cel s for repairing major mandibular defects. METHODS:The left mandibular teeth of 24 beagles were extracted, and at 2 months after wound healing, mandibular defects were made artificial y. The beagles were divided into two groups:control group treated with lyophilized al ogeneic bone, and experimental group with autogenous bone marrow mesenchymal stem cel s and lyophilized al ogeneic bone. Densitometry with CT and Micro-CT was conducted 4, 12, and 24 weeks after surgery. RESULTS AND CONCLUSION:Compared with the control group, the bone density of the mandible was significantly higher in the experimental group at 12 weeks after transplantation (P<0.05). Over time, the bone densities in the two groups were both increased, but the bone density in the experimental group was always higher than that in the control group. Bone structure parameters were progressively increased or decreased in the two groups, especial y in the experimental group. At 24 weeks after surgery, the degree of trabecular separation in regions of interest was higher in the experimental group than the control group (P<0.05), but the bone volume fraction, number of trabecular bone, and bone trabecular thickness were significantly lower in the experimental group than the control group (P<0.05). These findings indicate that bone marrow mesenchymal stem cel s are capable of accelerating the reconstruction of al ogeneic bones.

BACKGROUND:The favorable structure and biological characteristics of al ogeneic temporomandibular joint become an effective solution for condylar defect, but immunologic rejection and slow ossification are the main problem for the presence of bone al ograft. OBJECTIVE:To meet the requirements of rebuilding mandible defect by lyophilizing canine mandible. METHODS:The periosteum, soft tissue, and cartilage of 12 canine mandibles were removed. 1 mm diameter hole was dril ed with 1 to 2 cm intervals in their cortical bones with a fissure bur. After washing, they were placed into a-4 ℃ refrigerator for 12 hours, and then stored at-80℃gradual y for 1 week. The mandibles were put in a drier. When the moisture content of osseous tissue decreased to 5%, the bones were packed in aseptic environment, radio pasteurized, and stored in vacuum container at atmosphere temperature. A biomechanical test was conducted after the lyophilization. RESULTS AND CONCLUSION:The maximum shifts of lyophilized mandibles in compression and bending tests were slight according to the steep load-shift curve. The plastic zone was insignificant and fractures appeared immediately when the pressure exceeded the plastic zone. The maximum load, maximum shift, and rigidity in the compression test were (5 163.10±730.16) N, (0.78±0.19) mm and (11 069.17±1 758.12) N/mm, respectively. The data in bending test were (486.67±134.12) N, (0.67±0.15) mm and (1 151.67±256.46) N/mm, respectively. It is concluded that the dehydrated and lyophilized canine mandibles have good shape and support ability and can meet the mechanical requirements in repairing and reconstructing mandibular defect.

OBJECTIVETo investigate the effect of segmental defects reconstruction of canine mandible with allogenenic bone marrow mesenchymal stem cells (BMSC) combined with lyophilized bone.

METHODSA 30 mm segmental defect was created on the left mandibles of beagles. Beagles were randomly divided into three groups. Allogeneic bone marrow mesenchymal stem cells with lyophilized bone were used for segmental defects reconstruction in group A. Autologous bone marrow mesenchymal stem cells with freeze- dried bone were used for segmental defects reconstruction in group B. The defects of group C were repaired with lyophilized bone only. Every three beagles were sacrificed 4, 12, 24, and 48 weeks after surgery respectively. The reconstruction effect was evaluated by CT and histopathological examination.

RESULTSCT examination showed that new bones formed in group A and group B 12 weeks after surgery, but not in group C. The form of the reconstructed mandibles in the three groups recovered in 48 weeks. The small pores on the bone graft were filled with new bones in group A and group B. In group C, the pores were still evident. Histopathological examination showed that bone trabecula between allogeneic bone and autogenous bone was completely joined in group A and group B. A large number of fibrous tissue appeared around the implanted bone and new bones were formed. In group C, the lyophilized bone resorption was still not obvious, the new bone formation was significantly slower than the other two groups. There was no difference between group A and group B.

CONCLUSIONSBoth allogeneic bone marrow mesenchymal stem cells and autologous mesenchymal stem cells could accelerate the bone formation.

Allografts ; Animals ; Bone Transplantation ; Dogs ; Mandibular Reconstruction ; methods ; Mesenchymal Stem Cell Transplantation ; Osteogenesis ; Time Factors ; Tissue Engineering ; methods

Objective To design a personalized titanium mandibular prosthesis with porous and support structure, and analyze its stress distribution characteristics through finite element analysis, so as to evaluate clinical value and prospect of the prosthesis. Methods The fourth mandibular premolar and molar from the right mandible of Beagle dogs were removed. The spiral CT was taken after three-month healing, and the three-dimensional (3D) model of the mandible was established. Resection of 3 cm mandible with simulated surgical procedure and reconstruction with personalized restoration were conducted. The prosthesis consisted of abutment, pillar, solid unit, porous unit and retention unit. A personalized titanium mandibular prosthesis finite element model A was established, to analyze the prosthesis stress under loading, and further study was proceeded when the maximum stress of each part constituting the prosthesis was smaller than yield strength of its material. The finite element model B with the assembly of the prosthesis, mandible and screw was constructed and loaded with the mastication force, and the stress, strain and displacement distributions of the mandible were recorded. Results When the abutment was under 100 N vertical loading, the peak stress of the prosthesis with solid structure and porous structure was 147.03 and 75.36 MPa, respectively, which was smaller than yield strength of its material; the peak stress of the cortical bone and cancellous bone was 53.713, 4.216 7 MPa, and the strain was 3.753 6, 3.562 5, respectively; the maximum displacement of the restoration was 338.3 μm. ConclusionsTaking the canine mandible as an example, the personalized prosthesis with porous and support structure shows the uniform stress distribution and good mechanical properties through finite element analysis. The results provide a new method for the design of prosthesis for repairing mandibular defects.

Objective To investigate biomechanical properties of personalized titanium root-analogue implants with porous surface, so as to provide theoretical basis for the design and clinical implantation of such implants. Methods Based on CT data, the personalized model of root-analogue implant with porous surface was designed by using 3-matic software, and after registering it with the mandible model, the mesh was divided and material parameters were attributed. The implant was applied with 200 N loading, and the maximum stress of the implant and the stress and strain of the bone around the implant were analyzed. An appropriate clinical case was selected and the implant was implanted immediately after tooth extraction for conducting clinical evaluation. Results The peak stress of the personalized root-analogue implant with porous surface was mainly concentrated on the interface between the solid structure and the porous structure of the implant. The maximum stresses of the solid structure and porous structure were 137.710 and 37.008 MPa, respectively, which were smaller than its yield strength. The three-dimensional (3D) printed porous root-analogue implants had good initial stability immediately after implantation, with minimal trauma and similar mechanical transmission to natural teeth. This simplified the surgical process, shortened the treatment time, and had high patient satisfaction. Conclusions The 3D printed root-analogue implant with porous surface explores a new method for immediate implantation after tooth extraction.

Objective To make finite element analysis and compressive performance test on three-dimensional (3D) printed personalized poly-ether-ether-ketone (PEEK) condyle prosthesis, so as to analyze stress distribution characteristics and mechanical properties of the prosthesis, and to evaluate its clinical value and prospect. Methods The finite element models of PEEK condyle prosthesis, mandible and fixation screw were established by software such as CBCT, Mimics, Geomagic Studio, SolidWorks and ANSYS Workbench. The maximum mastication force was applied, and the maximum stress of the condyle prosthesis and screw, as well as the stress and strain of the mandible were recorded. In order to simulate the actual clinical situation, a special fixture was designed to test compression performance of the condyle prosthesis prepared by the fused deposition modeling (FDM) and selective laser sintering (SLS) at the rate of 1 mm/min. Results The peak stress of the PEEK condyle prosthesis was 10.733 MPa, which was located at the back of the condyle neck. The peak stress of 5 fixing screws was 9.707 5 MPa, which appeared on the 2# and 5# screws near the trailing edge of the mandibular ascending branch. The peak stress of both the prosthesis and the screw was smaller than its yield strength. The maximum pressure of the condyle prosthesis prepared by FDM and SLS was (3 814.7±442.6) N and (1 193.970±260.350) N, respectively. Compared with the SLS preparation, the FDM prepared prosthesis not only had higher compression strength but also better toughness. Conclusions The 3D printed personalized PEEK condyle prosthesis shows uniform stress distributions and good mechanical properties, which can provide the theoretical basis for PEEK as reconstruction material for repairing temporomandibular joint.

【Objective】 To solve the problem of insufficient hydrophilicity on the surface of polycaprolactone (PCL)/β-TCP bone tissue engineering scaffolds, NaOH etching method was used to improve the surface microstructure of 3D printed PCL/β-TCP scaffolds, further affecting their hydrophilicity and cell response. 【Methods】 PCL/β-TCP mesh scaffolds were prepared using 3D printing melt deposition molding technology, and the surface roughness of the scaffolds was modified by NaOH etching. The effects of two reaction parameters, NaOH concentration and time, on the microstructure, spectral elements, contact angle, compressive strength, and cell adhesion of the scaffolds before and after modification were observed. 【Results】 After NaOH etching, the surface microporous structure of the mesh scaffold was successfully prepared. With the increase of either NaOH concentration or time, the surface micropores of the scaffold increased while the contact angle of the material surface decreased. However, the compression strength of the etched scaffold treated with NaOH for 1 mol/L (24 h) or 10 mol/L (6 h) was not statistically significant compared to the untreated group (P>0.05). The number of cells on the etched scaffold increased, with a larger spreading area of individual cells, making it more advantageous in the adhesion and proliferation of BMSCs. 【Conclusion】 The use of NaOH etching to improve the hydrophilicity of 3D printed PCL/β-TCP bone tissue engineering scaffolds is a low-cost and effective strategy which can effectively improve the wettability and cell adhesion of the scaffolds.

【Objective】 To construct a 3D printed PLLA/β-tricalcium (PLLA/β-TCP) bone tissue engineering scaffold surface porous structure through simple treatment with NaOH solution, increase the roughness and hydrophilicity of the scaffold, and promote cell adhesion on the scaffold surface. 【Methods】 The PLLA/β-TCP mesh scaffold was prepared by 3D printing melt deposition molding technology, and the scaffold was roughed by NaOH etching. The effects of NaOH concentration and time on the scaffold were observed according to the microstructure, energy spectrum, contact angle, mechanics, and cell adhesion of the scaffold. 【Results】 The PLLA/β-TCP composite scaffold constructed by melt deposition technology had a pre-set porous structure, and the pores were interconnected. After NaOH etching, a porous structure with both macroscopic and microscopic pores was formed. The increase in any of the NaOH concentration and time parameters would lead to the increase of pore diameter and surface roughness. When the NaOH treatment parameter was 0.1 mol/L (9 h), it could significantly reduce the water contact angle on the surface of the scaffold, and had no significant effect on the compressive strength of the scaffold. In vitro cell testing showed that the surface porous composite scaffold etched with NaOH had more advantages in the adhesion and proliferation of BMSCs. 【Conclusion】 Using NaOH to process 3D printing of PLLA/β-TCP bone tissue engineering scaffolds can effectively improve the surface morphology of the scaffold, and optimize its hydrophilicity and cell adhesion.