[Establishment and experimental study of alveolar preservation before dental implantation in Beagle dogs].

PURPOSE: To establish the model of alveolar ridge preservation after tooth extraction for dental implant replacement, and to observe the effect of tissue engineered bone on osseointegration. METHODS: Isolated BMSCs were expanded and osteogenically induced in vitro. The tissue engineering complex was constructed with BMSCs/A-PCPC in vitro. Six extraction sockets, with three on each side, were created in the mandibles of four Beagle dogs by extracting the second, third and fourth premolars. BMSCs/A-PCPC were placed on one side of the extraction sockets, while autogenous bone, A-PCPC and nothing were placed on the other side as control. X-ray and CT scans were conducted 1day, 4 and 12 weeks after operation to detect the change of the alveolar ridge. The bone of sockets were harvested at 8-week post-implantation and subject to histological for evaluating. SPSS17.0 software package was used for data analysis. RESULTS: Radiographs demonstrated higher radiodensity in group of complex than in simple materials group, autogenous bone group after 4 weeks. Hard tissue biopsy at 12-week showed that bone activity of BMSCs/A-PCPC complex was better than the other groups. Spiral CT analysis showed that alveolar ridge of each group experienced a certain degree of absorption. At 12-week, the alveolar ridge height reduction values in A-PCPC group was smaller than in A-PCPC group, autogenous bone group and blank group (P<0.05). CONCLUSION: The BMSCs/A-PCPC complex is favorable for preservation of alveolar ridge.

[Response of bone morphogenetic protein-2 and basic fibroblast growth factor in bone marrow stromal cells in ectopic and in situ bone formation].

OBJECTIVE: We ascertained the effect of bone morphogenetic protein-2 (BMP-2) and basic fibroblast growth factor (bFGF) by a series of experiments: Proliferation and differentiation of bone marrow stromal cells (BMSCs) in vitro, ectopic and in situ bone formation and loaded porous calcium phosphate cement (CPC) on the repair of bone defects around dental implants. METHODS: BMSCs from Beagle dogs were cultured in vitro with basic culture medium containing BMP-2, bFGF, and BMP-2+bFGF. Proliferation and differentiation of BMSCs were quantified using methyl thiazolyl tetrazolium (MTT) and alkaline phosphatase (ALP) test. The CPC seeded with BMSCs and BMP-2, bFGF, combined BMP-2 with bFGF were implanted subcutaneously into nude rats in ectopic bone formation, and were implanted into critical-sized bone defects of Beagle dogs in the in situ bone formation. The bone formation was detected by histology examination and quantified using an image analysis system. Polychrome sequential fluorescent labels and fluorescence histological examinations of undecalcified sections were performed post-operatively. RESULTS: It was determined that BMP-2+bFGF promoted BMSCs statistically significant proliferation and differentiation compared to either BMP-2 or bFGF in vitro. The CPC with BMP-2+bFGF group yielded more bone than those with either BMP-2 or bFGF in ectopic bone formation test. The percentages of newly ectopic formed bone were higher in the BMP-2+bFGF group (48.79% +/- 11.31%) than those in other groups (BMP-2 group, 30.71% +/- 10.85%; bFGF group, 27.33% +/- 9.67%; and the control group, 10.65% +/- 6.05%). Undecalcified showed that new bone was actively formed in the BMP-2+bFGF group after 12 weeks in the in situ bone formation test. The bone mineralization apposition rate (MAR) was better in the BMP-2+bFGF group than in other groups (P<0.01). CONCLUSION: BMP-2 combined with bFGF are more effective than one alone in promoting the formation of new bone.

Repairing critical-sized calvarial defects with BMSCs modified by a constitutively active form of hypoxia-inducible factor-1α and a phosphate cement scaffold.

Tissue engineering combined with gene therapy represents a promising approach for bone regeneration. The Hypoxia-inducible factor-1α (HIF-1α) gene is a pivotal regulator of vascular reactivity and angiogenesis. Our recent study has showed that HIF-1α could promote osteogenesis of bone mesenchymal stem cells (BMSCs) using a gene point mutant technique. To optimize the function of HIF-1α on inducing stem cells, another constitutively active form of HIF-1α (CA5) was constructed with truncation mutant method and its therapeutic potential on critical-sized bone defects was evaluated with calcium-magnesium phosphate cement (CMPC) scaffold in a rat model. BMSCs were treated with Lenti (lentivirus) -CA5, Lenti-WT (wild-type HIF-1α), and Lenti-LacZ. These genetically modified BMSCs were then combined with CMPC scaffolds to repair critical-sized calvarial defects in rats. The results showed that the overexpression of HIF-1α obviously enhanced the mRNA and protein expression of osteogenic markers in vitro and robust new bone formation with the higher local bone mineral density (BMD) was found in vivo in the CA5 and WT groups. Furthermore, CA5 showed significantly greater stability and osteogenic activity in BMSCs compared with WT. These data suggest that BMSCs transduced with truncation mutanted HIF-1α gene can promote the overexpression of osteogenic markers. CMPC could serve as a potential substrate for HIF-1α gene modified tissue engineered bone to repair critical sized bony defects.

[Stress distribution of two kinds of fixed prosthese supported by four or six dental implants in edentulous mandible].

PURPOSE: To investigate the stress distribution of 2 kinds of distal cantilevered fixed prostheses supported by 4 or 6 dental implants in edentulous mandible with three-dimensional finite element method. METHODS: The first design was 4 implants supported fixed prostheses with 6mm distal cantilever; the second design was 6 implants supported fixed prostheses with 6mm distal cantilever. Vertical force of 100 N was applied to the distal cantilever of fixed prostheses. RESULTS: The bone stress was concentrated at the cortex of mandible. The maximum bone stress was at the cortex near the second implants from the point that the vertical force was applied. The maximum implant stress was at the terminal and medium implant-prostheses interface. CONCLUSIONS: The bone around the terminal implant is easily to absorb and the terminal and medium implants are easily to fracture. The maximum stress of the implants and prostheses of two kinds of design are almost same(239Mpa). Two kinds of design can be applied in the clinic. 6 mm distal cantilevered fixed prostheses supported by 6 implants have the less bone stress than 4 mm distal cantilevered fixed prostheses in edentulous mandible.