Study Of Micro-screw's Stability In Different Healing Time Before Loading

Correct anchorage design and control are very important to orthodontic clinical work.It is very difficult to get absolute and stable anchorage in traditional ways.And anchorage loss is the main reason to effect the orthodontic treatment.Micro-screw can provide stable and efficient anchorage control and require minimal compliance,which led to the expansion of MIA technology.These is a high success rate for micro-screw both in animal experiments and clinical work.But we still don't catch on all the reasons micro-screw fails.Micro-screw's stability can be influenced by many factors.And the healing time is regarded as one of the most important factor. Most research has been performed in laboratory animals to determine the waiting time necessary before applying forces to the implant. But the answer is amphibolous.These are two reasons:The first is that the microscrew's stability can be influenced by many factors which have complementary effects.The second is that we have not mastered the whole process how healing time influences the stability of micro-screws.Immediate loading,two weeks and four weeks,the three different healing time were chosen in our study.And a consecutive research was carried on in four aspects:the displacement of micro-screws,the biomechanics test(pull-out test),the interface research between micro-screw and surrounding osseous tissue,the osteogenesis related protein expression.In the study,we investigated loading factor besides time factor.And had a thoroughly research on how healing time influences the stability of micro-screws.Results:1. All the micro-screws with different healing time(immediate loading, 2 weeks and 4 weeks) were good and efficient anchorage when teeth movement.But they were not absolute anchorage. And the displacement of three groups was different.2. Each micro-screw with different healing time could meet the orthodontic clinical work from the view of biomechanics.The value of Pull-out test was no different between the 2-week healing time group and the 4-week healing time group.But they were significantly greater than the immediate loading group.3. All the micro-screws with different healing time showed the good biological compatibility.We found osseointegration and fibrous tissue in the interface between micro-screw and osseous tissue.The osseointegration was different among the three different healing time groups. The highest osseointegration was found in the 4-week healing time group and the lowest osseointegration in the immediate loading group.4. The protein OC and TGF-β1 were found to be lower expression when the micro-screws were loaded with 100g for 1 week,which was significant in immediate loading group.Based on our study and clinical request ,we prefer to the 2-week healing time. If there are some other factors influcing the stability,we can add the stability of micro-screws by prolonging the healing time.We think the factors of influencing stability can be divided two parts according to the findings. One is time factor before loading and the other is loading factor. Loading factor can be regarded as the more important factor. It is a key role to the micro-screw's stability. And it can change the enviroment where bone remodels by changing the micromovement of micro-screws.This is one of the focus of further study.