Factors affecting stresses in cortical bone around miniscrew implants: A three-dimensional finite element study

Objective:To evaluate various types of stress in cortical bone around miniscrew implants using finite element analysis.Materials and Methods:Twenty-six three-dimensional assemblies of miniscrew models placed in alveolar bone blocks were constructed using Abaqus (Dassault Systèmes Simulia Corp, Providence, RI), a commercial finite element analysis software package. The model variables included implant design factors and bone-related factors. All miniscrew implants were loaded in the mesial direction with a linear force equal to 2 N. Peak von Mises and principal stress values in cortical bone were compared between the different models for each factor.Results:The results demonstrated that some factors affected the stresses in bone (implant diameter, implant head length, thread size, and elastic modulus of cancellous bone), while other factors did not (thread shape, thread pitch, and cortical bone thickness).Conclusions:Miniscrew implant diameter, head length, and thread size as well as the elastic modulus of cancellous bone affect the stresses in cortical bone layer surrounding the miniscrew implant and may therefore affect its stability.     

Primary loading of palatal implants for orthodontic anchorage--a pilot animal study.

OBJECTIVES: This study aimed at evaluating the clinical performance and osseointegration of short orthodontic implants immediately loaded with orthodontic forces. MATERIAL AND METHODS: The investigation was designed as an experimental animal study. Eight palatal implants of the Ortho-system were immediately loaded with 100 cN after palatal insertion in 4 female German shepherd dogs. Xylene orange and calcein green were used for polychrome sequential labelling. Histological preparation utilized the cutting and grinding technique. Outcome variables were clinical implant success, histological osseointegration and bone-to-implant contact rates. RESULTS: All (8/8) implants were clinically successful and stable when the animals were sacrificed. One implant showed fibrous encapsulation and was histologically classified as "failed" for "osseointegration". Upon morphometrical analysis, bone to implant contact rates for newly formed or remodelled bone were 19% at 4 weeks and 26% at 6 months. The fluorochrome labelling indicated substantial mineral apposition on the surface of the implants at the end of the first and the second postoperative months. CONCLUSION: This study revealed borderline reliability of osseointegration for immediately loaded palatal implants but reasonable bone formation at the 4th postoperative week. Thus, two clinical concepts are both supported: early orthodontic loading after 4 weeks as well as improvement of primary stability to provide a biomechanical basis for immediate orthodontic loading.     

Optimal force magnitude loaded to orthodontic microimplants: A finite element analysis

Objective:To find an optimal force that can be loaded onto an orthodontic microimplant to fulfill the biomechanical demands of orthodontic treatment without diminishing the stability of the microimplant.Materials and Methods:Using the finite element analysis method, 3-D computer-aided design models of a microimplant and four cylindrical bone pieces (incorporating cortical bone thicknesses of 0.5, 1.2, 2.0, and 3.0 mm) into which the microimplant was inserted were used. Various force magnitudes of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 N were then horizontally and separately applied to the microimplant head as inserted into the different bone assemblies. For each bone/force assembly tested, peak stresses developed at areas of intimate contact with the microimplant along the force direction were then calculated using regression analysis and compared with a threshold value at which pathologic bone resorption might develop.Results:The resulting peak stresses showed that bone pieces with thicker cortical bone tolerated higher force magnitudes better than did thinner ones. For cortical bone thicknesses of 0.5, 1.2, 2.0, and 3.0 mm, the maximum force magnitudes that could be applied safely were 3.75, 4.1, 4.3, and 4.45 N, respectively.Conclusions: For the purpose of diminishing orthodontic microimplant failure, an optimal force that can be safely loaded onto a microimplant should not exceed a value of around 3.75–4.5 N.     

Is trabecular bone related to primary stability of miniscrews?

Objective: To compare the primary stability of miniscrews inserted into bone blocks of different bone mineral densities (BMDs) with and without cortical bone, and investigate whether some trabecular properties could influence primary stability.Materials and Methods:Fifty-two bone blocks were extracted from fresh bovine pelvic bone. Four groups were created based on bone type (iliac or pubic region) and presence or absence of cortical bone. Specimens were micro-computed tomography imaged to evaluate trabecular thickness, trabecular number, trabecular separation, bone volume density (BV/TV), BMD, and cortical thickness. Miniscrews 1.4 mm in diameter and 6 mm long were inserted into the bone blocks, and primary stability was evaluated by insertion torque (IT), mini-implant mobility (PTV), and pull-out strength (PS).Results:Intergroup comparison showed lower levels of primary stability when the BMD of trabecular bone was lower and in the absence of cortical bone (P ≤ .05). The Pearson correlation test showed correlation between trabecular number, trabecular thickness, BV/TV, trabecular BMD, total BMD, and IT, PTV, and PS. There was correlation between cortical thickness and IT and PS (P ≤ .05).Conclusion:Cancellous bone plays an important role in primary stability of mini-implants in the presence or absence of cortical bone.     

Palatal implants in adolescents: a histological evaluation in beagle dogs

Objectives: Small osseointegrated implants inserted in the palate provide a reliable anchorage control during orthodontic treatment. When these implants are inserted in the median palatal suture in adolescents, there might be interference with normal transverse development of the maxilla. The aim of this study was to determine histometrically the influence of implants inserted in the median palatal suture in adolescent beagle dogs on transverse maxillary development and to determine the amount of osseointegration of unloaded palatal implants in the median palatal suture in adolescent beagle dogs.
Material and methods: Two palatal implants were inserted in the median palatal suture in four of five adolescent beagle dogs. The experimental period took 25 weeks, and the dogs were subjected to a scheme of sequential point labelling with vital stains every 6 weeks. Insertion sites were examined microscopically and histometric analysis was performed.
Results and discussion: Both anterior width and posterior width were wider in the control dog as compared with the average in the test dogs, 3.7% and 9.5%, respectively. After loss of a palatal implant, immediate repair of the bone in the suture area could be observed. In the posterior region, the repaired suture looked more like a suture in the infantile stage in humans, instead of having a sinusoidal course, as was observed in the control dog and in adolescent humans. The amount of osseointegration varied from 43% to 64.3%.
Conclusion: The results of this study support the idea that in adolescents, palatal implants should not be inserted in the median palatal suture because of possible growth impairment (transverse maxillary development). The amount of osseointegration of unloaded palatal implants in the median palatal suture in adolescent dogs is less as compared with dental implants in dogs and loaded palatal implants in adult humans.     

Locating the center of resistance of maxillary anterior teeth retracted by Double J Retractor with palatal miniscrews

Objective:To locate the center of resistance of six maxillary anterior teeth retracted by the Double J Retractor (DJR) and to find the optimal position of palatal miniscrews.Materials and Methods:The three-dimensional (3D) finite element model included 12 teeth with two first premolars extracted. The DJR was modeled as a 3D beam element. The miniscrew was sagittally placed between the second premolar and the first molar, and the vertical position of the miniscrew was established at five conditions: 6, 7, 8, 9, and 10 mm apically from the cervical line of the first molar. The length of the retraction lever arm was determined according to the position of the miniscrew, for the direction of retraction force to be parallel to the maxillary occlusal plane. The 3D finite element method was used to determine the location of the center of resistance of the maxillary anterior teeth by visualizing the tooth displacement and stress distribution.Results:As the miniscrew was located apically, the stress spread out to the root apex and the adjacent alveolar bone. At the 8-mm level of miniscrews, a bodily-like parallel retraction could be obtained with DJR.Conclusion:In this study, the center of resistance of the six maxillary anterior teeth retracted by DJR with palatal miniscrews was estimated to be 12.2 mm apically from the incisal edge of the central incisor.     

Histomorphometric Evaluation of Cortical Bone Thickness Surrounding Miniscrew for Orthodontic Anchorage

Background: Recently, the use of miniscrews as an anchorage device has become a routine approach in the orthodontic field. However, there is no report that has analyzed the healing process of the miniscrew, such as the thickness of the cortical bone, in the past. Purpose: In the present study, to histologically assess the healing process of the osseous tissue surrounding miniscrews used as an orthodontic anchorage, the change in the thickness of the cortical bone was analyzed after 3, 6, and 12 weeks after the placement. Furthermore, the change in the bone‐implant contact in different regions of the miniscrew during the initial healing period was also investigated. Materials and Methods: Ninety‐six miniscrews were placed in eight beagle dogs. After 3, 6, and 12 weeks of healing, a force of 200–300 g was applied to the force‐applied groups for 12 weeks. Non‐forced groups remained in the jaw without force application. Results: In the non‐forced groups, a significant amount of cortical bone was formed at the head of the miniscrew at the initial stage of the healing process in the maxilla. However, less cortical bone formation was observed in the mandible. After the force application, increased bone formation was observed within 1 mm of the miniscrew compared to other regions in both jaws. In the mandible, significantly less cortical bone was observed 3 and 6 weeks after the force application. Bone‐implant contact revealed that the osseous tissue surrounding the miniscrew matured from the apex toward the head of the miniscrew. Conclusion: We suggest that this sufficient amount of cortical bone at the initial stage of healing enables the immediate loading in miniscrews to resist against orthodontic force. Furthermore, less amount of cortical bone formed at the head of the miniscrew may be one reason for the higher failure rate in the mandible.     

Orthodontic load on short maxillary implants with reduced sink depth: an experimental study

Objective: The aim of this study was to investigate experimentally the positional stability and histomorphometric findings of length‐reduced temporary anchorage devices (Orthosystem^®, length: 4 mm) with reduced sink depth. Material and methods: For this purpose, four maxillary pre‐molars (₂P₂, ₃P₃) were extracted from each of four foxhounds. After a 16‐week alveolar healing period, 16 implants (four per dog) were inserted into the edentulous areas. Four implants (one per dog) were placed simultaneously in the mid‐palatal area. The implants were intentionally submerged to about three‐quarters of their length. After a 10‐week unloaded implant healing period, the implants in the P3 areas and the palate were loaded (test implants) by means of transpalatal bars fixed on the implants in the P3 areas and Sentalloy traction springs (～2 N continuous force) inserted mid‐sagittally between palatal implants and bars (force application period: 24 weeks). The implants in the P2 areas served as controls. Results: Clinical measurements and histological evaluation revealed positional stability of the loaded fixtures. Alveolar control implants (ACI) were inserted to a mean depth of 3.2 mm, alveolar test implants (ATI) to 3.3 mm and palatal test implants (PTI) to 2.6 mm. The mean direct bone contact percentage values were 71.3% (ACI), 79.6% (ATI) and 72.2% (PTI). Conclusion: These results suggest that, probably due to the relatively high percentage of bone contact with implant surface, only 3 mm of intrabony implant length is sufficient to retain positional stability during long‐term orthodontic loading.     

骨皮质厚度及植入角度对支抗种植钉影响的三维有限元分析

目的:探讨不同骨皮质厚度和不同植入角度对支抗种植钉应力分布的影响及位移变化。方法:建立简单的颌骨及支抗种植钉的三维有限元模型,在不同的骨皮质厚度为0.5mm-3mm和不同的植入角度30°-90°下分别植入支抗种植钉(直径1.6mm、长8mm),在支抗种植钉的头部施加200g力,力的方向与骨面平行,得到模型中的应力和位移,并进行分析。结果:模型中颌骨最大应力均发生在支抗种植钉的颈部,集中分布在1mm的深度范围内。随着骨皮质厚度的增加骨皮质应力减小,当厚度为0.5mm时骨皮质应力较大,从21.00MPa(植入角度70°)到37.88MPa(植入角度30°);骨皮质厚度为1mm时(除外植入角度为≤50°)应力<28MPa。植入角度对骨皮质应力变化影响较大,植入角度为60°、70°时应力较小。颌骨最大位移发生在受支抗种植钉拉压的两侧,支抗种植钉最大位移在其顶部,当骨皮质厚度为0.5mm时,支抗种植钉的位移最大,当骨皮质厚度≥1mm时,骨皮质厚度的变化对位移的影响不显著,植入角度为70°时支抗种植钉位移最小。结论:骨皮质厚度会影响骨皮质和骨松质的应力,临床植入支抗种植钉时应该避开骨皮质较薄的区域,植入区域骨皮质厚度应≥...     

不同垂直骨面型成人微螺钉种植体常植入区骨皮质厚度分析

目的 探讨不同垂直骨面型成人上下颌骨后牙区微螺钉种植体拟植入部位的骨皮质厚度,为临床植入微螺钉种植体提供参考.方法 57例正畸成人患者,髙角组20例、均角组22例、低角组15例;拍摄头颅CBCT,在三维重建模型上测量上颌骨颊、腭侧及下颌骨颊侧骨皮质厚度,进行统计学分析.结果 3组间多数测量部位平均骨皮质厚度的差异均有统计学意义(P<0.05),且高角组的平均骨皮质厚度最小,低角组的平均骨皮质厚度最大.结论 髙角患者在上颌后牙区植入微螺钉种植体需谨慎.     

Success of miniscrews used as anchorage for orthodontic treatment: analysis of different factors

ObjectivesTo examine factors involved in clinical success of miniscrew implants used for orthodontic anchorage in the upper jaw.Materials and methodsOne hundred and forty-four patients (93 females and 51 males) were fitted with a total of 324 miniscrew implants of two different morphologies (cylindrical and conical), and of different lengths and diameters. The clinical factors examined were screw length, side of insertion, miniscrew shape and diameter, bone quality, skeletal type, and relationship between bone quality and skeletal type and patient age.ResultsThe mean overall success rate of the implants was 91.4%. The length and shape of the miniscrews significantly influenced the success rate, whereas side of insertion (left or right), screw diameter and skeletal type showed no significant effects. Poor (soft) bone quality and good (hard) bone quality are risk factors for miniscrew failure, with the best results obtained when the screws are inserted into bone of medium quality (10-15 Ncm).ConclusionIn the posterior areas of the upper jaw, long, conical miniscrews showed a significantly greater success rate. An insertion torque of 10 Ncm to 15 Ncm is also a significant index of higher success rate.     

Factors affecting stresses in cortical bone around miniscrew implants

Abstract Objective: To evaluate various types of stress in cortical bone around miniscrew implants using finite element analysis. Materials and Methods: Twenty-six three-dimensional assemblies of miniscrew models placed in alveolar bone blocks were constructed using Abaqus (Dassault Systèmes Simulia Corp, Providence, RI), a commercial finite element analysis software package. The model variables included implant design factors and bone-related factors. All miniscrew implants were loaded in the mesial direction with a linear force equal to 2 N. Peak von Mises and principal stress values in cortical bone were compared between the different models for each factor. Results: The results demonstrated that some factors affected the stresses in bone (implant diameter, implant head length, thread size, and elastic modulus of cancellous bone), while other factors did not (thread shape, thread pitch, and cortical bone thickness). Conclusions: Miniscrew implant diameter, head length, and thread size as well as the elastic modulus of cancellous bone affect the stresses in cortical bone layer surrounding the miniscrew implant and may therefore affect its stability.     

Bone mineral density: Methods of measurement and its influence on primary stability of miniscrews

Objective:To verify whether bone mineral density (BMD) of cortical bone, trabecular bone, and total bone influence the primary stability of orthodontic miniscrews and to verify whether there is a correlation between the measurement of BMD by cone-beam computed tomography (CBCT) and central dual-energy x-ray absorptiometry (DEXA).Materials and Methods:Twenty bovine bone sections were extracted from the pubic and iliac bones from regions with cortical thicknesses of approximately 1 mm. The BMD of the total bone block was evaluated using two methods: CBCT and DEXA. The BMD of cortical, trabecular, and total bone in the region of interest (ROI) were also evaluated by CBCT. After scanning the bone blocks, 20 self-drilling miniscrews (INP®) 1.4 mm in diameter and 6 mm long were inserted into them. The peak implant insertion torque (IT) was registered. After this, the pull-out test (PS) was performed and the maximum force registered. The Pearson correlation test was applied to verify the correlations between variables.Results:The BMD of the total bone block verified by CBCT and DEXA showed a positive and strong correlation (r  =  0.866, P  =  .000). The BMD of the ROI for cortical bone influenced the IT (r  =  0.518, P  =  .40) and the PS of miniscrews (r  =  0.713, P  =  .001, Table 2). However, the total bone BMD (verified by CBCT and DEXA) and trabecular bone BMD presented weak and not statistically significant correlations with primary stability.Conclusions:There was a positive correlation between total bone block BMD measured by DEXA and CBCT. The cortical BMD influenced the IT and PS.     

Evaluation of miniscrew stability using an automatic embedding auxiliary skeletal anchorage device

Objective:To clarify the in vivo effect of an automatic embedding device on miniscrew stability.Materials and Methods:42 miniscrews were implanted into rabbit femurs. The miniscrews with the novel auxiliary device formed the auxiliary group (n = 11 at 4 weeks; n = 11 at 8 weeks) and the miniscrews without the auxiliary device formed the nonauxiliary control group (n = 9 at 4 weeks; n = 11 at 8 weeks). Cortical bone thickness, distance from the cortical bone surface to the miniscrew head, and implantation depth of the spike were measured using micro-computed tomography. The mechanical retention force was evaluated by measuring the displacement of the miniscrew head after it was loaded perpendicular to its long axis. In the lateral displacement test, effects of the auxiliary (with vs without auxiliary), and time (4 vs 8 weeks) were assessed using the Brunner–Langer nonparametric analysis of longitudinal data in factorial experiments.Results:The mean implantation depth of the spike in the auxiliary group at 4 and 8 weeks was 0.28 mm (median: 0.33; SD: 0.12) and 0.37 mm (median: 0.33; SD: 0.19), respectively. The retention force was approximately 2.0 to 2.8 and 1.6 to 1.8 times greater in the auxiliary group than in the nonauxiliary group at 4 and 8 weeks, respectively.Conclusions:The auxiliary device improved the mechanical retention force without the need to increase miniscrew length or diameter. This may enable the safe use of miniscrews in difficult areas.     

Factors influencing the stability of miniscrews. A retrospective study on 300 miniscrews

The aim of this study was to investigate, over a period of approximately 3 years, the reactions to orthodontic loading of a type V titanium miniscrew. In this retrospective study, conducted in a private practice, the records of 300 miniscrews inserted in 132 consecutive patients (80 females, 60.6 percent) by the same surgeon were evaluated. The mean age of the patients was 23.2 years. Three types of miniscrews (type A: diameter 1.5 mm, length 9 mm; type B: diameter 1.5 mm, length 11 mm; and type C: diameter 1.3 mm, length 11 mm) were used. The clinical variables evaluated included the loading time and location of the miniscrew in relation to the gingiva and root. The success rates with different variables were compared using chi-square or Fisher's exact test where appropriate. A cumulative survival rate of 81 percent (243/300) was found using Kaplan-Meier analysis, with an optimum success rate for the 1.3 mm wide miniscrew inserted in the attached gingiva, with immediate loading applied. Cox proportional hazard regression showed significant differences between success rate and the following parameters: gender, loading time, gingival or bone localization, and diameter of the miniscrews. Considering the clinically controllable parameters, and within the limits of this retrospective study, 1.3 mm diameter miniscrews inserted in attached gingiva and immediately loaded had the most favourable prognosis.     

Anatomic site evaluation of the palatal bone for temporary orthodontic anchorage devices

Objectives: The aim of the present study was to assess the micromorphologic characteristics of the palatal bone from an implantologic standpoint.
Materials and Methods: The material consisted of tissue blocks of autopsy material from 22 subjects (18 males, three females) between 18 and 63 years of age. The specimens comprised the anterior median palatal region from 5 to 10 mm behind the incisive foramen. They were prepared in the transversal plane according to ground thin-section technology. The midpalatal area as well as an area of 3 mm bilateral to the midline were assessed, and a classification of quantitative palatal bone availability was developed.
Results: The findings could be divided into three classes: (1) class I palatal bone consists almost of compact bone; (2) class II cortical bone layer on oral and nasal sides of palate, broad compact bone in the suture area (≥3 mm), loose trabecular bone lateral to the suture area; and (3) class III cortical bone on oral and nasal side, thin compact bone in the suture area (<3 mm) and loose-structured trabecular bone lateral to the suture area. In most sections (72.7%), class I characteristics were found (16 subjects). 18.2% of sections were assigned to class II (four subjects) and only 9.1% of sections were assigned to class III (two subjects).
Conclusion: These results document that in most cases a good primary stability of temporary orthodontic anchorage devices should be achieved in the midpalatal and paramedian area of the anterior palate, as the bone quantity available is high.     

Cross-sectional evaluation of the prevalence and factors associated with soft tissue scarring after the removal of miniscrews

Objective:To investigate the prevalence of distinguishable soft tissue scarring after the removal of temporary anchorage devices (TADs) such as orthodontic miniscrews and to analyze the factors associated with scar formation.Materials and Methods:The prevalence of soft tissue scarring in 66 patients (202 miniscrew removal sites) was clinically investigated at least 1 year after miniscrew removal. To determine the clinical factors associated with soft tissue scar formation, miniscrew stability; host factors including age, gender, and gingival biotype; and miniscrew-related factors such as insertion site, vertical position, and insertion period were evaluated.Results:The prevalence of a distinguishable scar remaining at least 1 year after miniscrew removal was 44.6%. Patients with flat gingiva showed a significantly higher prevalence of soft tissue scar formation than did those with pronounced scalloped gingiva (P < .05). Maxillary buccal removal sites showed a significantly higher prevalence of soft tissue scar formation than did those in the mandible or palatal slope (P < .05). Miniscrew sites at the alveolar mucosa showed a significantly lower prevalence of soft tissue scar formation than did those in the mucogingival junction or the attached gingiva (P < .01).Conclusion:The prevalence of distinguishable scarring after miniscrew removal was fairly high. On the basis of our results, patients with flat gingiva and buccal interdental gingival insertion sites are more susceptible to scar formation.     

国产微型钛钉正畸支抗即刻负载稳定性的实验研究

目的:评估国产微型钛钉种植支抗即刻负载稳定性。方法:随机选择犬下颌骨的一侧为实验组即加力组,另一侧为对照组即不加力组,植入国产微型钛钉各两颗。实验组钛钉间施力200克。三个月后处死动物,分别测量实验组、对照组钛钉间的位移变化及种植体—骨界面剪切力。结果:实验组钛钉间位移平均减少0.47mm;对照组几无变化;实验组种植体-骨界面剪切力明显大于对照组,平均为367.42牛顿。结论:国产微型钛钉作为种植支抗可满足临床要求。     

Immediate loading of implants used for orthodontic anchorage

The healing around an immediately loaded screw was described and related to the bone type, manner of loading and observation time. In four adult macaca fasicularis monkeys, 16 titanium vanadium screws were inserted into the infrazygomatic crest and two in the symphysis region. Immediately after insertion, screws were loaded with 25- and 50-g Sentalloy springs extending to the canines. Following an observation period of 1, 2, 4 and 6 months, the screws and the surrounding bone were removed. Undecalcified serial sections perpendicular to the long axis were made and the degree of osseointegration studied. Two of the screws were lost immediately after insertion. Of the remaining screws, osseointegration was present around all, but two. The integration was independent of bone type, trabecular or cortical, but increased with time. Based on the results of this study, the use of screws described in the report can be recommended as anchorage units in cases where conventional anchorage is not possible.     

Bone‐to‐implant contact of orthodontic horizontal implants in humans subjected to loading

Implant‐based anchorage in orthodontics is increasingly obtaining significance. In this study, implants were temporarily inserted into the mid‐palatal and the mandibular retromolar areas in humans for orthodontic anchorage. Histological analysis of the implant‐bone interface was performed following the retrieval of implants which were subjected to prolonged oblique orthodontic loading. The results of the histomorphometric evaluation indicated that all the implants serving for orthodontic anchorage were well integrated into the bone despite the prolonged application of the orthodontic loading. Hence, it may be concluded that small‐size, one‐part transmucosal implants with a self-tapping thread and an SLA surface seemed to provide adequate anchorage for orthodontic therapy. Furthermore, the successful integration and the subsequent oblique loading of these orthodontic implants provide evidence that continuous forces in the order of magnitude of 2–6 N are compatible with the maintenance of osseointegration.