Yanpu Liu

Tisssue responses in corticotomy- and osteotomy-assisted tooth movements in rats: histology and immunostaining.

INTRODUCTION The purpose of this histologic study was to examine underlying cellular responses to corticotomy- and osteotomy-assisted tooth movements. METHODS Thirty-six rats were divided into 5 groups: corticotomy-assisted tooth movement (CO + TM), sham corticotomy without tooth movement (CO alone), osteotomy-assisted tooth movement (OS + TM), sham osteotomy without tooth movement (OS alone), and unassisted tooth movement (TM alone). Standard orthodontic springs were activated to produce mesial tooth movement. The rats were killed at 3, 21, and 60 days after activation for osteoclast and blood vessel counts, and immunostaining with proliferating cell nuclear antigen (PCNA), transforming growth factor beta 1 (TGF beta 1), vascular endothelial growth factor (VEGF), and osteocalcin were performed. RESULTS The CO + TM group had significantly more osteoclasts at 3 days (P <0.005) compared with the OS + TM group. The alveolar bone surrounding the dental roots was replaced with multicellular tissue at 21 days in the CO + TM group but was intact in the OS + TM group with the exception of a distal distraction site. At day 21, immunostaining with PCNA, TGF beta 1, VEGF, and osteocalcin occurred at the mesial border of bone in the CO + TM group, whereas a diffuse pattern was observed in the distal distraction sites at 21 and 60 days in the OS + TM group. CONCLUSIONS Corticotomy-assisted tooth movement produced transient bone resorption around the dental roots under tension; this was replaced by fibrous tissue after 21 days and by bone after 60 days. Osteotomy-assisted tooth movement resembled distraction osteogenesis and did not pass through a stage of regional bone resorption.

Accurate reconstruction of discontinuous mandible using a reverse engineering/computer-aided design/rapid prototyping technique: a preliminary clinical study.

PURPOSE To improve the reconstructive surgical outcome of a discontinuous mandibular defect, we used reverse engineering (RE), computer-aided design (CAD), and rapid prototyping (RP) technique to fabricate customized mandibular trays to precisely restore the mandibular defects. Autogenous bone grafting was also used to restore the bony continuity for occlusion rehabilitation. PATIENTS AND METHODS Six patients who had undergone block resection of the mandible underwent reconstruction using a custom titanium tray combining autogenous iliac grafts. The custom titanium tray was made using a RE/CAD/RP technique. A virtual 3-dimensional model was obtained by spiral computed tomography scanning. The opposite side of the mandible was mirrored to cover the defect area to restore excellent facial symmetry. A bone grafting tray was designed from the mirrored image and manufactured using RP processing and casting. The mandibular defects were restored using the trays in combination of autologous iliac grafting. An implant denture was made for 1 of the 6 patients at 24 weeks postoperatively for occlusion rehabilitation. RESULTS The trays fabricated using this technique fit well in all 6 patients. The reconstructive procedures were easy and time saving. Satisfactory facial symmetry was restored. No severe complications occurred in the 5 patients without occlusion rehabilitation during a mean 50-month follow-up period. The reconstruction in the patient with occlusion lasted for only 1 year and failed eventually because of bone resorption and infection. CONCLUSIONS Mandibular reconstruction was facilitated using the RE/CAD/RP technique. Satisfactory esthetic results were achieved. However, the rigidity of the cast tray could cause severe stress shielding to the grafts, which could lead to disuse atrophy. Therefore, some modification is needed for functional reconstruction.

Engineering scaffold‐free bone tissue using bone marrow stromal cell sheets

The use of exogenous scaffolds to engineer bone tissue faces several drawbacks including insufficient biological activity, potential immunogenicity, elevated inflammatory reaction, fluctuating degradation rate, and low cell‐attachment efficiency. To circumvent these limitations, we sought to engineer large scaffold‐free bone tissue using cell sheets. We harvested intact cell sheets from bone marrow stromal cells using a continuous culture method and a scraping technique. The cell sheets were then rolled and fabricated into large constructs. Finally, the constructs were implanted into the subcutaneous pockets of nude mice. The cells within the sheet maintained in vitro osteogenic potential after osteoblast differentiation. Computed tomography scans and histological examination confirmed new bone formation in vivo. Additionally, the engineered bone exhibited enhanced compressive strength. Our results indicate that the BMSC sheets can facilitate the formation of functional three‐dimensional bone tissue without the use of exogenous scaffolds. Hence, the study provides an intriguing alternative strategy for bone repair.

Platelet-rich plasma – A promising cell carrier for micro-invasive articular cartilage repair

Due to the limited regenerative capacity of cartilage tissues, articular cartilage defect caused by various lesions remains a problem to be resolved. Tissue engineering provided a valuable alternative to current therapeutic approaches, which is expected to greatly reduce the need of joint replacement. Scaffold, acting as cell carrier, plays an important role in maintaining cells in defect sites, thus facilitates the chondrogenesis. However, an open operation is often needed to implant the cell/scaffold composite, to find a less invasive way to delivering the complex into the defect site would be desirable. Different from synthetic and other nature derived scaffold, platelet-rich plasma (PRP) is a fraction of plasma which contains multiple growth factors and could be clotted when mixed with thrombin. Therefore, we hypothesized that PRP could be used as an autologous cell carrier to inject and fix chondrocytes into the defect site of articular cartilage. With the assistance of arthroscope, the defect could be precisely located, and injectable PRP-Cell composite would make the operation micro-invasive and simple.

Enhancing bone formation by transplantation of a scaffold‐free tissue‐engineered periosteum in a rabbit model

OBJECTIVES The periosteum plays an important role in bone regeneration. However, the harvesting of autogenous periosteum is associated with disadvantages such as donor site morbidity and limited donor sources. This study uses an osteogenic predifferentiated cell sheet to fabricate a scaffold-free tissue-engineered periosteum (TEP). MATERIAL AND METHODS We generated an osteogenic predifferentiated cell sheet from rabbit bone marrow stromal cells (BMSCs) using a continuous culture system and harvested it using a scraping technique. Then, the in vitro characterization of the sheet was investigated using microscopy investigation, quantitative analysis of alkaline phosphatase (ALP) activity, and RT-PCR. Next, we demonstrated the in vivo osteogenic potential of the engineered sheet in ectopic sites together with a porous β-tricalcium phosphate ceramic. Finally, we evaluated its efficiency in treating delayed fracture healing after wrapping the cell sheet around the mandible in a rabbit model. RESULTS The engineered periosteum showed sporadic mineralized nodules, elevated ALP activity, and up-regulated gene expression of osteogenic markers. After implantation in the subcutaneous pockets of the donor rabbits, the in vivo bone-forming capability of the engineered periosteum was confirmed by histological examinations. Additionally, when wrapping the engineered periosteum around a mandibular fracture gap, we observed improved bone healing and reduced amounts of fibrous tissue at the fracture site. CONCLUSION The osteogenic predifferentiated BMSC sheet can act as a scaffold-free TEP to facilitate bone regeneration. Hence, our study provides a promising strategy for enhancing bone regeneration in clinical settings.

CAD/CAM surface templates as an alternative to the intermediate wafer in orthognathic surgery

OBJECTIVE A new simple technique using a pair of surface templates fabricated by CAD/CAM technique as an alternative to the use of intermediate surgical wafer is presented. STUDY DESIGN A patient with transverse maxillary cant and maxillary midline deviation was scanned using computed tomography (CT) to create a 3D model of the maxillofacial bone. Eight virtual cylindrical markers were placed on the selected locations of maxilla. Subsequently, the locations of these cylinders were expressed as drill holes in the preosteotomy templates. The maxillary segment was separated and repositioned in the computer according to preoperative plans. Postosteotomy surface templates were then designed and resin templates were fabricated by a rapid prototyping machine. After investing and casting, metal templates were fabricated. At the beginning of operation, surgical fixation holes on the maxilla were drilled with the preosteotomy templates. Once maxillary osteotomy and segmentation were finished, screws were placed through the holes in the postosteotomy templates into the predrilled holes on the bone correspondingly, and maxillary segments were fixed with the titanium plates. RESULTS After the postosteotomy templates were positioned and fixed, the maxillary segment was placed to the desired position. Maxillary transverse cant and midline deviation were corrected as the preoperative plan and simulation. CONCLUSION The use of the surface templates before and after osteotomy as an alternative to intermediate wafer in orthognathic surgery can minimize labor and errors contained in the traditional way, reducing preoperative work as well as a reduction in operation time.

A new hypothesis of mechanisms of traumatic ankylosis of temporomandibular joint

Temporomandibular joint (TMJ) ankylosis is a disease that severely affects the human health. Although it is well known that trauma is the most common cause of TMJ ankylosis, the mechanisms by which the traumatic TMJ ankylosis develops are unclear. The existing hypothesis is not convincing in explaining the genesis of traumatic TMJ ankylosis. We make a hypothesis that the distraction osteogenesis (DO) of the lateral pterygoid muscle combining with the dislocated and damaged disc is an important factor in genesis of traumatic TMJ ankylosis. If this hypothesis is verified, it will be helpful for the prevention of traumatic TMJ ankylosis and change the principle of management of sagittal fracture of mandibular condyle (SFMC).

Engineering injectable bone using bone marrow stromal cell aggregates.

With the increasing popularity of minimally invasive surgery, to develop an injectable bone would be highly preferable for the repair of bone nonunions and defects. However, the use of dissociated cells and exogenous carriers to construct injectable bone faces several drawbacks. To circumvent these limitations, we first harvested a cell sheet from rabbit bone marrow stromal cells using a continuous culture method and a scraping technique. The obtained sheet was then cut into fragments of multicellular aggregates, each of which was composed of a certain number of cells, extracellular matrix, and intercellular connections. The aggregates showed apparent mineralization properties, high alkaline phosphatase activity, increased osteocalcin content, and upregulated bone markers, implying their in vitro osteogenic potential. Then, serum-free medium (the control group), dissociated cell suspension (the cell group), and suspension of multicellular aggregates (the aggregate group) were injected subcutaneously on the back of the nude mice to evaluate ectopic bone formation. The results revealed that the aggregate group showed significantly larger and denser bone at the injection sites than the cell group, whereas bone formation did not occur in the control group. Additionally, when injecting them locally into the mandibular fracture gap of delayed healing in a rabbit model, we observed the most improved bone healing in the aggregate group. More cells survive and retain at the injection sites in the aggregate group than that in the cell group postoperatively. Our study indicates that the multicellular aggregates might be considered a promising strategy to generate injectable bone tissue and improve the efficacy of cell therapy.

Optimal design of thread height and width on an immediately loaded cylinder implant: A finite element analysis

In this study, we used a finite element method to evaluate the maximum Von Mises stresses in jaw bones of immediately loaded implant with different thread heights and widths, and the maximum displacements in implant-abutment complex. The implant thread height ranged from 0.20 to 0.60 mm, and the thread width ranged from 0.10 to 0.40 mm. Compared to those in standard designed implants, the maximum Von Mises stresses in cortical and cancellous bones with axially loaded implants decreased by 18.85% and 47.46%, respectively, and by 16.38% and 63.46%, respectively in buccolingually loaded implants. The maximum displacement of implant-abutment complex loaded axially and buccolingually decreased by 13.78% and 6.97%, respectively. These results indicated that thread height played more important roles in affecting bone stresses and implant-abutment complex stability than thread width. Immediately loaded cylinder implants with thread height exceeding 0.44 mm and width ranging from 0.19 to 0.23 mm caused the lowest stresses to the type B/2 bone.

Local injection of nerve growth factor via a hydrogel enhances bone formation during mandibular distraction osteogenesis

OBJECTIVE The objective of this study was to evaluate the effects of the injectable NGF-carrying collagen/nano-hydroxyapatite/alginate hydrogel on the bone formation in a rabbit mandibular distraction osteogenesis model. STUDY DESIGN Thirty-five New Zealand white rabbits underwent bilateral madibular distraction osteogenesis at a rate of 0.75 mm/12 h for 6 days. The rabbits were divided into 4 groups: group 1 received injections of collagen/nano-hydroxyapatite/alginate hydrogel containing hNGFβ; groups 2, 3, and 4 received injections of hNGFβ, Col/nHA/Alg hydrogel, and saline, respectively. The injections were performed on both sides of the mandible at the end of the lengthening phase. All the animals were killed at a consolidation time of 14 days. RESULTS No difference in regenerate bone dimensions was observed among the 4 groups. Bone mineral density, the maximum load, and the bone volume/total volume of the new bone in the distraction gap in group 1 was significantly greater (P < .05) than in the other 3 groups. CONCLUSIONS Application of the Col/nHA/Alg hydrogel as an NGF delivery during the consolidation phase of distraction osteogenesis increased regeneration and new bone formation.