| Objective: Anchorage is the key factor that affects orthodontic treatmenteffect. The mini-implants not only provide reliable anchorage effect but alsoexpand the scope of orthodontic treatment, ever since they have been used asadditional orthodontic anchorage. Compared with conventional dentalimplants, mini-implants have more advantages such as small volume, flexibleimplant placement, simple surgery procedure, easy to remove and so on. Butthe small size also impacts on the stability of mini-implants, sheddingsituation often occurs. The stability and the loading time of implants havebecome hotspots of many scholars.The stability of the mini-implants includes the initial stability afterinsertion and biological stability during the treatment. The initial stabilitymeans the tightness of implants and the surrounding bone tissue, while thebiological stability refers the osseointegration degree of implant-boneinterface. The main clinical indicators are insertion torque value and removaltorque value. Researches suggest that good initial stability of mini-implants isa necessary condition of the biological stability. The removal torque is theresistance during the pulling out process, and it could estimate the stability ofimplant quantitative. However, the factors influencing the biological stabilityof mini-implants are not clear.The doctors and patients wish the implants could afford orthodonticforce as soon as possible, as the implants are temporary anchorage device.Nowadays, the loading time divides into immediate loading, early loading anddelay loading. Some scholars suggest that a healing period is necessary toensure a sufficient time for osseointegration, while the others believe that thereis significant relationship between initial stability and success rate of implants.Mini-implants could endure immediate and early loading as long as good initial stability of mini-implants can be ensured. And the formation ofosseointegration has no relationship with healing period. However, there arerare prospective studies which are self-control in the patient’s oral cavity.This study is a prospective study. In the study, we measured themaximum insertion torque values (MIT) and maximum removal torque values(MRT), analyzed the relationship between the stability and the factors such asloading time, MIT and MRT insertion position on its own control, detect therecommended MIT range and the influence of insertion position and loadingtime on the stability of mini-implants, to guide the clinical application andimprove the success rate of mini-implant anchorage.Methods:1Select The Patients:31patients (4males and27females, age range from11to43) were eligible for the study, who required rigid bone anchorage fororthodontic therapy from October2010to October2012. All of thepatients were treated with straight-wire appliance and self-tappingmini-implants (1.5mm in diameter,8mm in length) used as orthodonticanchorage. Excluding surgical contraindications, patients and their parentswere explained the risks of inserting mini-implants and signed operationconsent.2Preoperative Preparation and Surgical Progress: Patients should be made aX-ray. And the positioning device should be made. Disinfection of oral andmaxillofacial, after local anesthesia was administered, a pilot hole wasdrilled with a pre-drill into the buccal alveolar bone on the level ofmucogingival junction cooling physiological saline constantly. Finallyscrew the mini-implant into the pilot hole in clockwise and measure theinsertion torque values with screw drive. Patients were advised to keep welloral hygiene and so on. There was no need to take antibiotics generally.3Loading Time and The Orthodontic Force Level: Selecting the implants forimmediate loading, early loading or delay loading. The orthodontic forceapplied to the implants is mainly about100~200N.4Observation and Note: Patients were checked their oral hygiene, the condition of mini-implants and mucosa surrounding per implant. Load andrecord the force according to the plan every four weeks. After thespace-closure and evaluated by the experienced doctor, remove themini-implants in counterclockwise. And then measure and record theremoval torque values. Failed mini-implants were recorded including theirposition and surrounding tissues condition. Try to analyze the reasons.5Standard of Planting Success in Clinic: Mini-implants were not loose andcould bear the orthodontic force. It could accomplish their tasks through thewhole treatment process.6Statistical Analysis: Analysis the collated data with SPSS16.0software.Analyze the success rate of mini-implants and the range of MIT and MRT.Detect the effect of loading times and locations on the success rate byChi-square test. Discus the impact of locations on MIT and MRT byN-independent samples Kruskal Wallis H test. Analyze the relationshipbetween MRT and loading times, unloading period by N-independentsamples Kruskal Wallis H test also. And last detect the influence of loadingperiod on MRT by2-independent samples Mann-Whitney test.Result:1Success rate: There are91mini-implants in the experiment, and81of themwere successful. The success rate was89.0%.2Loading time: The success rate of mini-implants by immediate, early anddelay loading were87.1%,78.1%and100%respectively. There wasstatistical difference between various loading times(P=0.012﹤0.05). Thesuccess rate of implants by early loading was lower than delay loading(P=0.012﹤0.05).3Implant position: The success rates of various locations has no significantstatistical difference.4MIT: The locations had no effect on MIT. The MIT of successful mini-implants was8.07±0.69Ncm,95%CI was6.63~9.51Ncm.5MRT: The MRT of successful mini-implants was7.67±0.51Ncm,95%CIwas6.65~8.70Ncm. 6Implant position and MRT: There were statistical differences between MRTin various locations. MRT of mandible was higher than maxilla(P=0.00﹤0.05). And the posterior MRT was higher than anterior region (P=0.02﹤0.05).But there was no difference between left and right.7Loading time and MRT: The MRT of immediate, early and delay loadingmini-implants were6.96±0.92Ncm,8.06±1.05Ncm and7.85±0.71Ncmrespectively. There was no statistical difference (P=0.46﹥0.05).8Loading period and MRT: The MRT of0~12month loading periodmini-implants(7.02±0.60Ncm)was lower than12month(9.37±1.00Ncm)(P=0.046﹤0.05).9Unloading period and MRT: The MRT of0~3month,3~6month and morethan6month unloading period mini-implants has no statistical difference(P=0.85﹥0.05).Conclusions:1The success rate of all mini-implant in the experiment was89.13%. Therewas no relationship between the locations and success rate.2Loading time influenced the success rate of mini-implants. The success rateof mini-implants by early loading was significantly lower than delayloading. It suggested that doctors should decide the loading time basing onthe condition of implants, and avoid early loading.3The ideal MIT was6~10Ncm, it has no relationship with insertion locations.The implants could load immediately when MIT was in the range.4Loading time and unloading period before removal has no influence on MRTof mandible was higher than maxilla, MRT of the posterior was higher thananterior region. And the longer loading period caused higher MRT. |
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