Risk Factors Of Affecting Stability Of Mini-implants In Clinic

Objective:Stable anchorage is the main prerequisite for successful orthodontic treatment. The anchorage quality of dental structures is often insufficient due to a periodontically-compromised. Both clinical and experimental studies have demonstrated that mini-implants were basically able to provide sufficient and stable anchorage for tooth movement during the entire time period of orthodontic therapy. And mini-implants were developed to ease the surgical insertion procedure and to allow anchorage at different positions of the alveolar bone, so their use has increased in popularity. But reports on mini-implants using in clinic demonstrated a high number of failures despite the shorter usage period. There are issues, such as placement site, age, gender, loading opportunity, mandibular plane angle, oral hygiene and so on, all of which may exert a relevant influence on the stability of mini-implant. Many researchers have investigated the risk factors for failure of mini-implants to improve the success rate, but there has been no verdict.The purposes of this study were to confirm risk factors of affecting the mini-implant stability with a long-term observation for patients, in order to improve the success rates in clinic.Materials and Methods:1 Choose Patients:Six-four patients (13 males and 51 females) were eligible for the study, who required skeletal anchorage for orthodontic therapy and had no contraindications for surgery from February 2007 to October 2010. There were 42 adults and 22 adolescents (average age of 27.2 years old). All of the patients were treated with straight-wire appliance and self-tapping mini-implants (1.5mm in diameter,8mm in length) used as orthodontic anchorage. Patients and their parents were explained advantages and disadvantages of planting mini-implants and signed operation consent.2 Preoperative Preparation and Insert Mini-implants:Patients should be made a X-ray, and the positioning device was made. After local anesthesia was administered, a pilot hole was drilled with a pre-drill into the buccal alveolar bone on mucogingival junction level with cooling waters. Finally the mini-implant was spun into the implant hole. Patients were advised to keep well oral hygiene and so on.3 Loading Time:Both sides were loaded from 100g to 200g force 8 weeks later, if the patient had seen a doctor from 2007 to 2008. The right or left side of each arch was randomly selected for immediate loading and the contralateral side was loaded 8 weeks later, if the patient had seen a doctor in 2009. Both sides were loaded immediately patients see a doctor in 2010.4 Observation and Note:Patients were checked whether their mini-implants loose or not, condition of mucosa surrounding mini-implants and oral hygiene. Mini-implants were loaded with elastic chain which replaced every four weeks. After the space-closure phase, customary orthodontic treatment proceeded without interruption. The mini-implant were easily removed without local anesthesia. Deciduous mini-implants were recorded their position and additional information, and were analysed the probable cause.5 Related Factors:It was chosen that factors may influence the stability of mini-implants in clinic. These were age (between adults and adolescents), gender, oral hygiene, parodontopathy, implant position (maxillary or mandible; the region of anterior teeth or posterior teeth), loading time, mandibular plane angle, loading direction (from occlusal surface to gingiva; mesial or distal direction) and postoperative occlusal pain.5.1 Evaluation Standard5.1.1 Plaque Index (PLI):All inspection and record were done by the same doctor. The oral hygiene was recorded fine, if PLI was 0 or 1. It was recorded middling, if PLI was 2. It was recorded inferior, if PLI was 3.5.1.2 Standard of Planting Success in Clinic:Mini-implants were not loose and could bear the orthodontic force. It could accomplish their tasks through the whole treatment process.5.1.3 Patients was classified as high mandibular plane angle, average mandibular plane angle and low mandibular plane angle by measuring mandibular plane angle (mandibular plane intersects orbitomeatal plane; FH-MP).6 Statistical Analysis:The factors related to stabilities of mini-implants were evaluated using multivariate stepwise logistic regression analysis with SPSS 13.0 statistical program and a P-value less than 0.05 was considered to be statistically significant.Results:1 164 mini-implants were inserted, and 26 of them were failed. The success rate of all mini-implants was 84.14%.128 of them were used to facilitate anterior teeth retraction.4 of them were used to facilitate posterior teeth antedisplacement.6 of them were used to depress molars.26 of them were used to depress anterior teeth.2 Only three factors were found to be significant statistical differences, such as oral hygiene(P<0.01, OR=3.873), mandibular plane angle(P<0.05, OR=4.73) and postoperative occlusal pain(P<0.01, OR=12.065).3 There was not significant statistical differences between immediate loading and delayed loading. The age, gender, parodontopathy, placement site and loading direction were not risk facters to affect stabilities of mini-implants.Conclusions:1 Mini-implants inserted in patients of high mandibular plane angle was a higher failure rate. Patients of high mandibular plane angle should be analysed thickness and hardness of cortical bone and chosen a suitable operation.2 Orthodontic force of an appropriate magnitude can thus be applied immediately after mini-implants placement without decreasing the success rate.3 If mini-implants were too close to pericementum or root, it affected stabilities of mini-implants significantly.4 The oral hygiene of patients affected stabilities of mini-implants significantly. Patients inserted mini-implant should be educated how to keep oral hygiene well.5 Patients with mild parodontopathy should not insert mini-implants until their disease controlled. Patients must keep oral hygiene well.6 It didn't affect success rate of planting significantly that mini-implants were placed in maxillary or mandible. And the implant position whether the region of anterior teeth or posterior teeth was not too.7 The age and gender of patients were not risk factors of affecting success rate of planting.