| Objective:In order to study the stability of the microimplant anchorage for clinical application and foundational research, we placed titanium alloy and stainless steel microimplants in the jaws of dogs,to study the bone remodeling with histological observation,to measure the Bone Contact Ratio (BCR) and detect the shear strength between the microimplant and bone interface.Method:Thirty-two titanium alloy microimplants and thirty-two stainless steel microimplants were placed in the jaws of eight adult male mongrel dogs. Selecting one side of the maxilla randomly,one titanium alloy microimplant was inserted vertically into the furcation of the third premolar (P3) and one stainless steel microimplant was inserted vertically into the furcation of the first molar(M1),and so as the contralateral side of the mandible.Then we inserted another microimplant at the same location with the same method in the leftover jaws. Approximate 200g of constant force was loaded immediately between two microimplants in the same side of maxilla or mandible with nickel-titanium coil springs therapy.Two dogs were sacrificed after 4 and 12 weeks for histology. The specimens were dehydrated by ascending series of ethanol and then embedded in methyl methacrylate resin.Undercalcified sections longitudinal to the implant were randomly divided into two parts to stained with toluidine blue and methylene blue-basic fuchsin stain for histological observation and measurement of the BCR between microimplant and bone interface.Two dogs were sacrificed after 4 and 12 weeks for detecting the shear strength between microimplant and bone interface.Using the factor analysis to analyze the data by SPSS 13.0.Results:1.All microimplants did not loose and lost,and the gum tissues around the implants showed no obvious inflammatory response.Individuals inclined slightly in each group but all kept stable. 2.Observing the slice of the X-ray with naked eye,all microimplants did not have damage to the surrounding bone tissues and teeth.3.Under the light microscope:after loaded 4 weeks,both microimplants combined with the bone loosely and intermittently,and we could see more of osteoblasts and osteoid-like tissues,occasionally osteoclasts;after loaded 12 weeks,both microimplants combined with the bone firmly and successively,and we could occasionally find osteoblasts and osteoid-like tissues,barely osteoclasts.4.The result of the statistical analysis suggested:The time had prominent influence both on the BCR and the shear force (P<0.05),and the BCR and the shear force were both bigger after 4 weeks than 12 weeks by comparing means;the type of the microimplant also had prominent influence on both the BCR and the shear force (P<0.05),and the BCR and the shear force of titanium alloy microimplant were both bigger than stainless steel microimplant by comparing means;The interaction between the type of the microimplant and the time didn't have influence on both the BCR and the shear force,and the differences both had no statistics meaning(P>0.05).5.During the shear stress test,some implants continued inclining but kept stable when the loading enforced until the max shear strength,and it was shown that the neck of implants bent to some extent when spun out.Conclusion:1.The healing modes of both microimplants were the fibro-osseous integrations when immediately loaded.With the healing time lasting,the strength of integration between implant and surrounding tissue increased.2.The titanium alloy microimplant was more stable than the stainless steel microimplant as an orthodontic anchorage,but they could both keep stable in this experiment.With time lasting,their stabilities increased.3.When implant was loaded,the distribution of the stress concentrated on the neck of the implant. |
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