[The cytotoxicity of N48 NdFeB magnets coated with titanium-nitride].

PURPOSE: To evaluate the effect of N48 NdFeB magnets coated with titanium-nitride on the growth and apoptosis of L929 mouse fibroblast cells, and to determine the material biocompatibility. METHODS: The NdFeB magnets coated with titanium-nitride, bare NdFeB magnets and ordinary brackets were put into RPMI-1640 to prepare fusions. L929 mouse fibroblast cells were cultivated in the negative control liquid, positive control liquid, 100%, 50% and 25% sample fusions, respectively. The cell proliferation vitality was detected by MTT assay and the relative growth rate was calculated.Cell scatter diagrams of the negative control liquid, 100% titanium-nitride coated magnets fusion and bare magnets fusion were detected by flow cytometry Annexin V/PI double staining method. The ratios of normal cells, early apoptosis, advanced apoptosis and necrosis cells were calculated. The results were analyzed for paired t test using SPSS11.5 software package. RESULTS: The toxic levels of N48 NdFeB coated with titanium-nitride were ranked as 0-1. The toxic levels of bare magnets were ranked as 2. The cell scatter diagrams showed that there was no significant difference in living cell, early apoptosis and necrosis between magnets coated with titanium-nitride and control group. But there was significant difference between the bare magnets group and control group. CONCLUSION: The N48 NdFeB magnets coated with titanium-nitride have good biocompatibility.

[Evaluation of three dimensional orthodontic force produced by magnet of fix appliance].

PURPOSE: To analyze the feature and magnitude of three dimensional orthodontic force produced by the magnet of fix appliance. METHODS: Forces detected by universal fatigue test system included the attractive and repulsive,the inclined and rotated orthodontic forces of two magnets in different air gaps, and the integrated inclined and rotated orthodontic forces of two magnets and NiTi wire. RESULTS: The attractive and repulsive forces of two magnets were 4.68 to 0.45 N and 3.00 to 0.40 N respectively in the air gaps of 0 to 5 mm. The inclined orthodontic forces were 1.54 to 1.67 N, 0.63 to 0.69 N, 0.47 to 0.54 N when the magnets were vertically inclined 10 degrees to 40 degrees in the air gaps of 0, 1, 2mm. The rotated orthodontic forces were 0.97 to 1.32 N, 0.53 to 0.59 N, 0.39 to 0.48 N when the magnets were horizontally rotated 10 degrees to 40 degrees in the air gaps of 0, 1, 2mm. The integrated orthodontic force of two magnets and 0.014-inch NiTi wire was 0.32 to 0.5 N when the magnets was vertically inclined 10 degrees to 40 degrees in the air gap of 4 mm. The integrated orthodontic force of two magnets and 0.012-inch NiTi wire was 0.32 to 0.39 N when the magnets were horizontally rotated 10 degrees to 40 degrees in the air gap of 3 mm. CONCLUSION: Magnets made into orthodontic brackets to some extent could replace the mechanical orthodontic force produced by orthodontic wires and elastics.

[Quantitative study of osteoclastic related factors in the process of bone reconstruction].

OBJECTIVE: To detect the expression of osteoclast related factors, tumor necrosis factor-alpha (TNF-alpha), receptor activator of NF-kappaB ligand (RANKL) and tartrate-resistant acid phosphatase (TRAP), in the process of bone remodeling. METHODS: 8-week-old male C57BL/6J mice were employed in this study to detect the expression of osteoclast related factors by real time PCR. RESULTS: TNF-alpha, RANKL and TRAP were up regulated in the process of bone remodeling, they reached the peak on day 2, 5 and 10 individually after injury. CONCLUSION: Osteoclast related factors also participate in bone remodeling, which depends on the delicate balance between bone formation and bone resorption.

[Quantitative study of alkaline phosphatase and osteocalcin in the process of new bone].

OBJECTIVE: Alkaline phosphatase (ALP) and osteocalcin (OC) are the markers of new bone formation. Quantitative study of ALP and OC in the process of new bone formation helps to understand the ongoing of this cascade and contributes to make diagnosis in clinical treatment. METHODS: 8-week-old male C57BL/6J mice and primary osteoblasts from neonatal C57BL/6J mice calvaria were used in this experiment. HE staining, Northern blot and Real Time PCR methods were employed to detect the histological changes and the expression pattern of ALP and OC. RESULTS: In vivo study showed that after fracture the expressions of both ALP and OC kept on increasing which were peaked on the 10 day, then started decreasing gradually. In vitro study on primary osteoblasts showed that the expressions of ALP and OC reached peak on the 14th day in differentiation culture medium and started decreasing from this time point till the 21st day. CONCLUSION: The expression of ALP and OC in the process of new bone formation parallels with the development of osteoblasts, it increases with the differentiation of osteoblasts and becomes decreasing with the maturation of osteoblasts. The reciprocal relationship between the expression pattern of ALP and OC and development of osteoblast helps to maintain homeostasis.

[Evaluating the integrated force induced by high quality magnet and elastics in orthodontic fixed appliance].

PURPOSE: To investigate the stability and effective working distance of integrated forces induced by high quality magnet and elastics in orthodontic fixed appliance. METHODS: N48 NdFeB magnets resembling brackets in size and volume were combined with 1/8, 3/16, 1/4, and 3/8 inch orthodontic elastics respectively to induce integrated forces that had super-long working distance. Magnetic, elastic, and integrated forces were tested by universal material test system and curves of the forces were draw. The characteristics of integrated forces, complementary effects of magnetic and elastic forces, and the proportion between elastic and magnetic forces in integrated forces at different extension distances were analyzed. Unpaired t test was used to analyze the differences between integrated and elastic forces. RESULTS: With the increase of the extension distance, the magnitude of the magnetic forces decreased significantly and the elastic forces increased in a liner manner, while the integrated forces were stable and changed mildly. Four kinds of integrated forces achieved 86 g, 138 g, 163 g, and 192 g stable forces within super-long distance respectively. Magnetic forces accounted for 34.94%-93.98% of the integrated force at 3 mm distance, 12.60%-37.89% at 6 mm distance, and only 2.69%-5.98% at 12 mm distance. The differences between four integrated forces and elastic forces at 3 mm (P<0.01), 6 mm (P<0.01), and 9 mm distance (P<0.05) were significant. CONCLUSION: Integrated forces composed of magnetic and elastic forces were a new ideal stable orthodontic force with super-long working distance.