The Research On Time-validity Of The Stability Of Miniscrews Near The Extraction Wound Under Mechanical Loading

In orthodontic treatment,anchorage control is one of the most importantfactors in successful orthodontic treatment. Miniscrews as dental anchorageare extensively used because of some unique advantages： small size,ease ofplacement and removal, lower medical cost, minimal discomfort and thepossibility of immediate or early loading.The cases with severe congestionor bimaxillary protrusion usually been extracted tooth to get enoughspace.Miniscrews often implanted near the extraction wound as the absoluteanchorage.Previous research indicated that the miniscrews near theextraction wound can remain stable at no load condition. However,thevarious situation of clinical and histological after the miniscrews near theextraction wound under loading has yet to be further exploration andresearch.objective:Established animal model to research on the stability ofimplanted microscrews near the extraction wound under different loadingperiod.methods:1.Beagle’s maxillary interradicular safe zones were studied to make miniscrew implantation safer by CBCT and anatomical way.2.Beagles were used to estabolish the animal experimental model.9beagles were randomly divided into3groups, each group of three.The P3was extracted in advance in each dog. The experimental miniscrews wereimplanted near the P3area and the control miniscrews were implanted nearthe P4,M1area. Miniscrews were loaded100g force after healing3weeks,after1,4,8weeks to execute animals and harvest specimens.3.The influence of extraction on bone metabolism of the interface wasstudied through living fluorescence staining techniques at different healingtimes after miniscrew loading.Oxytetracycline,Calcein,Xylenol orangewere used to mark new bone formation and calcification after loadingimmediately,1,2,3,4,7weeks.4.The influence of extraction on bone remodeling process of theinterface was studied through Micro CT,histomorphological observationand histomorphometric calculation analysis at different healing times afterminiscrew loading.Results:1.Zones of mesiodistal width measurement larger than4.7mmwere between the mesial and distal roots P2at8mm from the CEJ, the mesialand distal roots P3,P4at6-8mm from the CEJ respectively. The buccolingualdimension measurement larger than7mm were between P1and P2,themesial and distal roots P2,P3,P4at2-6mm from the CEJ.2.There was no obvious fluorescent strips after1week loading.Three fluorescent strips appeared in the interface after loading4,8weeksrespectively.The inner layer was yellow, the median layer was green andthe outer was red. The calcification of bone deposition rate betweenexperimental group and control group after loading4,8weeks has statisticalsignificance.3.BV/TV of control group was higher than those of experimental groupafter loading4,8weeks respectively.Tb.N and Tb.Sp demonstratedsignificant statistical difference after loading1,4weeks respectively.4.Interface for histological observation: The most active bonereconstruction after loading4weeks,bone reconstruction speed is greaterthan the experimental group in the control group.The bone tabular wasmature at the implant-bone interface of two groups after loading8weeks.conclusions:1.The beagle’s maxillary posterior region can be used toestablished animal model.In the maxillary posterior region,the optimal sitesfor implanting between P1and P2at the4-6mm level from the CEJ,themesial and distal roots of P2,P3at the6-8mm level,the mesial and distalroots of P4at the4-8mm level from the CEJ.2.The implant-bone interface reconstruction speed as the extension ofload cycle presented increasing trend.In the early load, bone absorption inexperimental group greater than that in control group.But in the subsequenttime bone formation rapidly enhance.It is prompted that early of extractionhealing has negative influence of implant-bone interface. 3.Continued strength of4to8weeks,the trabecular bone volumefraction (BV/TV), bone trabecular number (Tb. N), bone contact rate (BIC)were increased over time,bone trabecular separation degree(Tb.Sp) wasdecreased, mechanical loading throughout the healing process has apositive impact in bone healing.4.Hard tissue slicing technology and traditional decalcified technologycan mutual complement each other in histology observation.Livingfluorescence dyeing technology can dynamically observe implant-boneinterface of bone integration.Micro CT to make up for the deficiency of thetraditional decalcified section technology, is a rapid, non-destructive, fullyaccurate reflection of implant-bone interface in the form of trabecular boneand effective inspection method.Based on these findigs,Through multi-layer longitudinal analysis ofminiscrew near the extraction wound loaded under different loadingperiod.we can see that in the case of early loading,the miniscrew during theinitiation of loading has the lowest stability.Continued strength of4to8weeks,bone reconstruction active,BIC increase, the stability of theminscrews enhance.Therefore,we suggested the miniscrews near theextraction wound was loaded safer after healing4weeks.