Micro Implant Loading Timing Of Animal Studies

Recently in the orthodontic field micro-implant as a new anchorage means has been successfully used to clinic and popularized quickly.But the insufficient stability is still restricting its development and maturity.There are many relative factors that influenced the stability such as implant,orthodontics and host etc,of which loading time after implant is inserted is one of the most important factors.Although researches and exploration have been performed,there are different arguments on the best loading time of implant anchorage.So this experiment will do the further study.Objective:To establish a sheep jaw-anchorage implant animal experiment model,detect the shear strength of the interface between implant and bone,histologically observe implant-bone interface,analyze the effect of different loading time on the implant stability in order to provide the theory for clinical application and foundational research.Method:four male sheep served as experimental animal.64 micro-screw implants were inserted vertically into dental alveoli of molar region in maxilla and edentulous area in the middle of mandible(4 in every quadrant of every sheep's jaw) to establish animal model.All implants were randomly divided into four groups,the implants without loaded were observed four weeks as group A that was regarded control group,the other three groups were divided according to different healing time before loading(immediately loading as group B,loading after 2w as group C,loading after 4w as group D),the force of 200g was added by nickel-titanium coil spring reciprocation drawing between two adjacent implants.The animals of group B,C and D were sacrificed after loaded for four weeks.The animals of group A were sacrificed after four weeks too.The maxillary and mandibular specimen with implants were dissected,the maxillary specimens were formalin-fixed and used to grinded bone-implant slices and special stain by methylene so as to histologically observe healing mode of implant-bone interface by light microscope.The mandibular specimens were packed with physiologic saline gauze,the shear strength of the interface between implant and bone was measured by INSTRON 5544.The data was statistically dealed with by SPSS 11.5 to analyze the difference of groups and the correlation of loading time and shear strength.Results:①All implants did not loose and dropped except that two adjacent implants of group B loosed because of infection.Individuals inclined slightly but stabilized.②With increase of the load,some implants continued inclining but kept stable until the max shear strength,it was shown that the neck of implants bent to some extent.③There is general difference of the shear strength among four groups(P＜0.05).There is no significantly difference of the shear strength between group A and group B.The shear strength of samples in group C,D are significantly greater than that in group A and B,loading time and shear strength are positive linear correlation (r=0.975,P＜0.01).④From the longitudinal grinded bond slices with implants it could be shown that:the implants and their surrounding tissue integrated firmly,there are no significantly difference between pressure side and tension side on the middle and root of the implant,there are differences of amount of bone integration between two sides on the neck..From the transverse grinded slices of implant neck we can find that the major integration mode of implant-bone interface of group A and D is osseointegration,the amount osseointegration of group D is more than A.The major integration mode of implant-bone interface of group B and C is the formation of fibrous tissue,the surrounding bone tissue regenerated towards the implants.Conclusion:①when implants are loaded the distribution of the stress concentrate on the neck of the implant.②At first the healing mode of implant interface is the integration of fibrous tissue, then is osseointegration.With the healing time lasting,the strength of integration between implant and surrounding tissue increase.③Loading time has some influence on the stability of implant anchorage.During this experimental observation when the implants were loaded after four weeks the strength of integration between implant and surrounding tissue is the greatest, which is benefit for the stability of implant anchorage.While the implant were Loaded too early, the major healing mode of interface is the formation of fibrous tissue,which is disadvantageous to the stability of implant anchorage.