Fracture resistance of commonly used self-drilling orthodontic mini-implants

Objective:To investigate the fracture resistance of six commonly used self-drilling orthodontic mini-implants by comparing their respective fracture torques during insertion.Materials and Methods:Ninety self-drilling mini-implants from six manufacturers (Aarhus, Dual-Top, OrthoEasy, Tomas-pin, Unitek, and VectorTAS), with diameters ranging from 1.4 to 1.8 mm, were inserted into acrylic blocks using a custom-made insertion device. Insertion torques were measured using a 6-degree-of-freedom load cell fixed to the base of the acrylic blocks, and peak torques experienced at the time of fracture for each of the mini-implants were recorded. One-way analysis of variance (α  =  .05) was used to compare the fracture torques among the six different groups.Results:Statistical analysis revealed significant differences (P < .05) in the peak fracture torques among mini-implant groups. Mean fracture torques ranked as follows: Unitek (72 Ncm) > Tomas-pin (36 Ncm) > Dual-Top (32 Ncm) ≈ VectorTAS (31 Ncm) > OrthoEasy (28 Ncm) > Aarhus (25 Ncm), with significant differences found between all manufacturers, except for Dual-Top and VectorTAS.Conclusions:Mini-implants tested showed a wide range of torque at fracture depending on the manufacturer, with only a weak correlation between mini-implant diameter and fracture resistance. This torque should be considered at the time of mini-implant insertion to minimize the risk of implant fracture, especially in areas of high-density bone without predrilling.     

Assessment of damping capacity as an index of root proximity in self-drilling orthodontic mini-implants

Objectives

This study aims to investigate orthodontic mini-implant root proximity, placement torque, and damping capacity and to determine whether placement torque and damping capacity (Periotest value (PTV)) are useful indices for the estimation of mini-implant root proximity.

Materials and methods

The root proximity of 143 orthodontic mini-implants (1.6 mm diameter, 8 mm screw thread length) was evaluated in 79 patients (24 males, 55 females; mean age, 22.5?±?8 years) using cone-beam computed tomography. The placement torque and PTV of each implant were determined using a torque tester and the Periotest, respectively. Variability in these values according to root proximity was evaluated.

Results

PTVs of mini-implants with multiple (two or more) points of contact between the root and implant were significantly larger than those of mini-implants with no root contact in the self-drilling group. Placement torque did not differ significantly according to root proximity. In the self-drilling group, the odds ratio for root contact was 20.82 (P?=?0.000) for a PTV >6.

Conclusions

Placement torque could not be used to estimate root proximity. The PTV was significantly affected by root proximity in the self-drilling group.

Clinical relevance

A threshold of PTV >6 could be applied clinically for the estimation of self-drilling mini-implant root proximity.     

Clinical indices for orthodontic mini-implants

Orthodontic mini-implants were recently developed and have been widely used in clinics. However, loosening of mini-implants, as well as infection and swelling of mucosal tissue at the placement site, are often observed during orthodontic treatment. Thus, clinical indices are greatly needed for the safe use of orthodontic mini-implants. This article presents information on mini-implants and offers suggestions on indications, placement technique, optimum design, and evaluation of the placement site for mini-implants. The author concludes that 1) mini-implants should be left in the placement site for 3 months before loading to allow for a healing period, which increases the success rate in adolescent patients, 2) placement torque should be considered when tightening mini-implants into bone, as excessively high or low torque results in low stability, 3) mini-implants with optimal screws should be placed in the correct position, and 4) a prepared site should be established in an area with a cortical bone thickness of greater than 1.0 mm, to improve the success rate. Finally, the vector of orthodontic forces in the arrangement with the center of resistance of the entire dental arch should be considered when developing treatment goals.     

Evaluation of the palatal bone for placement of orthodontic mini-implants in Japanese adults

Mini-implants are increasingly being used for orthodontic anchorage in the palate. The anatomical structure of the jaw must be properly evaluated prior to use; however, there are a few research reports providing basic data regarding the palate. Bone thickness was measured and bone morphology evaluated in the palates of Japanese people. The palates of five Japanese adult cadavers and 15 skulls were examined. The samples were imaged and measured using the micro-CT system. In the mid-palatine suture region, the cortical bone had a complex mesh-like structure and was thicker than surrounding areas. Cortical bone thickness varied depending on the site. The mid-palatine suture region is an ideal site for mini-implant insertion; however, because bone and cortical bone thickness markedly decrease in the lateral region, careful attention should be paid when inserting mini-implants in the mid-palatine suture.     

A stent fabricated on a selectively colored stereolithographic model for placement of orthodontic mini-implants

The purpose of this report is to present a new method for placing orthodontic mini-implants using a stent fabricated on a selectively colored stereolithographic model. A stent was fabricated that incorporated a guide groove drilled in accordance with the planned direction of the mini-implant. Tooth crowns, gingiva, tooth roots, and the maxillary sinuses were clearly identified in the stereolithographic model. As a result, the stent could be fabricated while taking into account the anatomic characteristics of both the bone interior and the dental surface. A stent fabricated on the selectively colored stereolithographic model is suggested to be a promising device for guiding placement of orthodontic mini-implants adjacent to the tooth roots and the maxillary sinuses.     

Angled-predrilling depth and mini-implant shape effects on the mechanical properties of self-drilling orthodontic mini-implants during the angled insertion procedure

Abstract Objective: To investigate the effects of orthodontic mini-implant (OMI) shape and angled-predrilling depth on the mechanical properties of OMIs during the angled insertion procedure. Materials and Methods: A total of 30 OMIs (self-drilling type, 7?mm in length) were allocated into six groups according to the OMI shape (cylindrical or tapered) and angled-predrilling depth (control, 1.5-mm and 4.0-mm angled-predrilling; predrilled with 1-mm-diameter drill-bit), as follows: C-con, C-1.5, C-4.0, T-con, T-1.5, and T-4.0 groups (N = 5 per group). The OMIs were installed at an angle of 60° in double-layer artificial bone blocks that simulated the cortical and cancellous bone (Sawbone?). Total insertion time (TIT), maximum insertion torque (MIT), total insertion energy (TIE), and inclination of the time-torque graph (INC) were measured. Results: Within the same shape group, angled-predrilling had a shorter TIT than did the control (control vs 1.5; control vs 4.0; all P < .05). MIT and TIE decreased in the order of control, 1.5-mm, and 4.0-mm angled-predrilling (control vs 1.5; 1.5 vs 4.0; all P < .05), but INC increased from control to 1.5-mm angled-predrilling and decreased from 1.5-mm to 4.0-mm angled-predrilling within the same shape group (control vs 1.5, 1.5 vs 4.0; all P < .05). The MIT of the tapered group was greater than that of the cylindrical group (C-con vs T-con, C-1.5 vs T-1.5; all P < .05, C-4.0 vs T-4.0; P < .01). In the same angled-predrilling depth, no differences were observed in TIE between the cylindrical and tapered groups (C-1.5 vs T-1.5, C-4.0 vs T-4.0; all P > .05). Conclusions: In angled-predrilling insertion of OMIs into thick cortical bone, tapered OMIs might be a better choice than cylindrical OMIs for increasing primary stability because of higher MIT and similar TIE values.     

The application of mini-implants for orthodontic anchorage

The aim of this study was to explore the use of mini-implants for skeletal anchorage, and to assess their stability and the causes of failure. Forty-five mini-implants were used in orthodontic treatment. The diameter of the implants was 2mm, and their lengths were 8, 10, 12 and 14mm. The drill procedure was directly through the cortical bone without any incision or flap operation. Two weeks later, a force of 100-200g was applied by an elastometric chain or NiTi coil spring. Risk factors for the failure of mini-implants were examined statistically using the Chi-square or Fisher exact test as applicable. The average placement time of a mini-implant was about 10-15min. Four mini-implants loosened after orthodontic force loading. The overall success rate was 91.1%. The location of the implant was the significant factor related to failure. In conclusion, the mini-implants are easy to insert for skeletal anchorage and could be successful in the control of tooth movement.     

Long-term durability of orthodontic mini-implants

The current study aimed at examining surface and chemical composition changes of retrieved mini-implants after different periods of service as aids of anchorage for orthodontic patients. This study examined 72 retrieved orthodontic self-tapping and self-drilling mini-implants, 1.7 mm in diameter and 8 mm in length (OrthoEasy system, Forestadent, Pforzheim, Germany) from 36 adult orthodontic patients (18 men and 18 women, mean age = 23 years). The retrieved mini-implants were divided into 3 groups according to service period: 3–6 months (3M–6M) group, 6–12 months (6M–12M) group, and 12–24 months (12M–24M) group, with 24 mini-implants in each group. The control group (As Received) comprised of 24 unused mini-implants of the same type (AR group). All mini-implant heads and threaded bodies were examined for chemical characterization and topographical features by SEM–EDS. The average weight percentages for the following elements Ti, Al, and O₂ were obtained and compared among the 4 groups. There was significant decrease in titanium content and deterioration for the surface properties for all parts of the mini-implants after being used inside patients’ oral cavities for more than 6 months p < 0.05. The period of mini-implant service inside patients’ oral cavities should not exceed 6 months.     

Mechanical anisotropy of orthodontic mini-implants

This study investigated stress distribution in the bone around orthodontic mini-implants using the finite element method and determined the difference in the stress distribution for different loading directions to identify risk factors for the loosening of mini-implants. Three-dimensional finite element models were constructed for conventional and cervical threadless mini-implants with cortical bone 1 or 3 mm thick. The authors calculated the compressive stresses on the bone elements and evaluated stress distribution according to the loading direction. Directional dependency (i.e. mechanical anisotropy) was observed with the conventional mini-implant model. The compressive stress ranged from –31 to –55 MPa depending on the loading direction. In the cervical threadless model, mechanical anisotropy disappeared and the stress was reduced. Cortical bone thickness had no influence in either model. One of the risk factors for mini-implant failure might be related to mechanical anisotropy. This report suggests ways for clinicians to avoid overload traction force when conventional mini-implants are used. The cervical threadless mini-implant can reduce mechanical anisotropy to facilitate successful placement. Inserting a conventional screw deeply beyond the threaded part might be useful in stabilizing a mini-implant.     

Effect of cortical bone thickness and implant placement torque on stability of orthodontic mini-implants

PURPOSE: To examine the relationship between cortical bone thickness, inter-root distance (horizontal space), distance from alveolar crest to the bottom of maxillary sinus (vertical space) at the prepared site, and implant placement torque and the success rate of mini-implants placed for orthodontic anchorage. MATERIALS AND METHODS: After computerized tomography examination, mini-implants 1.6 mm wide and 8 mm long were placed in the posterior alveolar bone. The mini-implant was judged a success when orthodontic force could be applied for at least 6 months without pain or clinically detectable mobility. The unpaired t test was performed to examine differences between the success and failure groups. The chi-square analysis or Fisher exact probability test was used to compare the implant success according to placement torque, location, and patient gender. P values less than .05 were considered significant. RESULTS: The subjects included 4 males (11 implants) and 28 females (76 implants) who ranged in age from 14.6 to 42.8 years. The success rate of the 87 implants was 87.4%. Cortical bone thickness was significantly greater in the success group (1.42 +/- 0.59 mm vs 0.97 +/- 0.31 mm, P = .015). The success rate was significantly higher in the group with an implant placement torque of 8 to 10 Ncm (100%) as compared to implants with higher or lower placement torques. The odds ratio for failure of the mini-implant was 6.93 (P = .047) when the cortical bone thickness was less than 1.0 mm relative to 1.0 mm or more. CONCLUSION: A relationship between stability after implant placement and the width and height of the peri-implant bone was not demonstrated. The prepared site should have a cortical bone thickness of at least 1.0 mm, and the placement torque should be controlled up to 10 Ncm.     

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锁[牙合]可发生于单侧或双侧,分为正锁[牙合]和反锁牙合。处于游离端位置的第二磨牙区锁[牙合]的矫治一直是正畸治疗中的一个难点。本文主要介绍了利用微小种植体支抗腭移或颊移上颌后牙,颊移下颌后牙解决第二磨牙区正、反锁[牙合]的方法,并对如何解决矫治中会出现的锁[牙合]伴上下后牙近中倾斜、拥挤的情况进行了详细描述。     

Application of orthodontic mini-implants in adolescents

The aim of this study was to determine the success rate of mini-implants in adolescents, and also whether a latent period is necessary and the optimum placement torque in an attempt to improve the success rate in adolescent patients. There were 57 orthodontic patients involved in the study, with ages ranging from 11.7 to 36.1 years, who underwent surgery to insert mini-implants (169 implants). When a mini-implant endured an orthodontic force applied for 6 months or more without any mobility, it was considered a success. The success rate was 63.8% in the early-load group (less than 1-month latent period) of adolescents, 97.2% in the late-load group (3-month latent period) of adolescents and 91.9% in the adult group. The success rate of the early-load group of adolescents was significantly inferior to those of the other groups (P<0.01). In measurements of the placement torque in adolescents, the success rate of the 5-10 N cm group was significantly higher than the other groups only in the maxilla of the early-load group. Although the optimum torque could not be defined, a latent period of 3 months before loading is recommended to improve the success rate of the mini-implant when placed in the alveolar bone in adolescent patients.     

Mechanical strength of orthodontic infrazygomatic mini-implants

Orthodontic anchorages have recently been reinforced by newly developed mini-implants. The aim of the present study was to investigate the mechanical strengths of infrazygomatic mini-implants. We measured the insertion torque and pull-out strength of three brands of infrazygomatic mini-implants (AbsoAnchors, Bioray, and Lomas). All three mini-implants were 2 mm in diameter, and five of each brand were manually driven 6 mm into artificial bone. Significant differences among the brands were investigated with Kruskal-Wallis tests. We found no significant relationship between insertion torque and pull-out strength in any individual brand. Among the three brands of infrazygomatic mini-implants, we found no significant difference in mechanical strength. The design of an infrazygomatic mini-implant may be the most important factor determining its mechanical strength.     

腭部不同微种植体植入位置的骨质情况研究

目的:研究腭部骨质情况,提供腭部微种植植入参考图。方法:硬腭部测量时,纳入148例研究对象;腭侧牙槽骨测量时,筛选出其中的86名研究对象,使用CBCT分别测量其骨质情况。结果:硬腭部的骨质厚度在前磨牙间冠状面处最大;腭侧牙根间间距随着远离牙槽嵴顶而逐渐增加。结论:硬腭部微种植体植入部位推荐在前磨牙间冠状面植入。腭侧牙槽骨前牙区推荐在侧切牙与尖牙间距离牙槽嵴顶6 mm以上水平植入;前磨牙区推荐在距离牙槽嵴顶4 mm以上水平植入;磨牙区推荐斜形植入,高于牙槽嵴顶8 mm时需注意上颌窦的影响。     

不同微型种植体稳定性比较的动物实验

目的评价自攻型和助攻型正畸微型种植体的稳定性，探讨两种种植体生物力学的差别。方法将自攻型组与助攻型组正畸微型种植体（每组各28枚）种植于两只狗的上下颌骨颊侧根间区，植入时测量最高植入转矩，即刻负载水平力约1．96N，持续9周后取出种植体，测量最高去除转矩。结果上、下颌自攻型组最高植入转矩[分别为（5．6±1．1）N·cm和（8．7±2．3）N·cm]均明显高于助攻型组[分别为（3．5±2．1）N·cm和（7．4±1．1）N·cm]，差异均有统计学意义（P〈0．05）。上、下颌自攻型组最高去除转矩[分别为（-6．5±2．2）N·cm和（-7．1±2．0）N·cm]均高于助攻型组[分别为（-5．7±2．3）N·cm和（-6．1±0．5）N·cm]，差异均无统计学意义（P〉0．05）。自攻型组成功率为92．9％，助攻型组成功率为86．7％。结论自攻型种植体有较高的初期稳定性，适于种植在上颌骨及下颌骨骨皮质较薄的部位。     

Friction heat during self-drilling of an orthodontic miniscrew

The aim of this study was to measure the heat generated when using a self-drilling miniscrew at speeds of 50, 100, 150, and 250 rpm. Specimens were classified into two groups: in the thin group the cortical bone thickness was 1.2 ± 0.02 mm on average and in the thick group it was 2.0 ± 0.03 mm on average. The thin group was used to model maxillary bone and the thick group to model mandibular bone in humans. The temperature in the 1.2-mm and 2.0-mm cortical bone specimens was measured according to revolution speed. As the revolution speed increased, the temperature significantly increased in both bone thicknesses. The temperature increased significantly more in the thicker cortical bone. The temperature increase in the 2.0-mm thick bone at 250 rpm exceeded 10 °C, regarded as the threshold for bone damage in this study; other temperature increases were below this threshold. Installing self-drilling screws at high speeds with an implanter is not recommended; low speeds of less than 150 rpm should be used.     

正畸微种植体支抗的三维有限元研究进展

近年来,微种植体支抗在口腔正畸临床实践中的应用逐渐增多.与传统支抗相比,微种植体支抗体积较小且相对价格低廉、操作简便,能够解决更多疑难病例,但却仍然存在一定的失败率.为了进一步提高其稳定性,本文对国内外学者关于微种植体结构设计、骨质量、植体材料、正畸力载荷以及植入角度的有限元研究进行综述,进一步明确这些因素对于微种植体稳定性的影响,为微种植体支抗能够更加高效的应用于临床提供依据.