Effects of thread depth, taper shape, and taper length on the mechanical properties of mini-implants

Upper Midline Correction Using the Mesial-Distalslider

AIM

The purpose of the present study is the three-dimensional (3D) analysis of molar and incisor movements that occur during the correction of the upper midline deviation by using the Mesial-Distalslider appliance.

MATERIALS AND METHODS

A total of 20 consecutive patients (12 women and 8 men; mean age 19.6 ± 11.1 years) were selected from the Orthodontic Department of Heinrich-Heine University of Düsseldorf. To correct the upper midline deviation (>2 mm), the patients were treated with asymmetric mechanics (mesialization on one side and distalization on the contralateral side) with the aid of Mesial-Distalslider. Dental casts were taken for each patient before (T0) and after the treatment (T1). The casts were 3D digitized and the models were superimposed on the palatal anterior region. Three-dimensional molar movements and sagittal incisor movements (proclination and retroclination) were assessed for T0 and T1.

RESULTS

At the end of the treatment, the total movements of the molars resulted in 4.5 ± 2.2 mm (antero-posterior direction), -0.4 ± 2.4 mm (transverse direction) and 0.3 ± 0.9 mm (vertical direction) on the mesialization side, and -2.4 ± 1.7 mm (antero-posterior direction), -0.5 ± 1.5 mm (transverse direction) and 0.2 ± 1.4 mm (vertical direction) on the distalization side. Incisor displacement was 0.9 mm ± 1.7 (mesialization side) and 0.6 mm ± 0.7 (distalization side).

CONCLUSION

The Mesial-Distalslider appliance could be considered a valuable tool in orthodontic treatment for upper midline correction. Within the limits of a retrospective study, asymmetric molar movements appeared possible without clinically relevant anchorage loss.

Evaluation of mechanical properties and morphology of miniscrews Ti6Al4V cold worked versus annealed in artificial bones

PURPOSE

This study aimed to evaluate the influence of different manufacturing procedures (Eli annealed - hot work versus cold worked - cold work) of the raw material under mechanical properties and morphological characteristics of orthodontic miniscrews (MS).

MATERIAL AND METHODS

Thirty MS were randomly separated into 3 types (n=10) according to manufacturer and manufacturing process of the raw material: type A - SIN® annealed (control group); type B - Dentfix® annealed; and, type C - Dentfix® cold worked. MI were inserted in artificial bone blocks, through the manufacturer's specific manual key attached to the digital torquemeter stabilized via custom device. Data of fracture's occurrence was performed using Fisher's exact test. Comparisons between the other two types regarding insertion torque and removal torque were performed using the Mann-Whitney test. Data of fracture torque, shear stress, normal stress and torque ratio was submitted to Kruskal Wallis and Dunn tests (α=0.05). Representative images of surface morphology and fractures were selected.

RESULTS

Type C showed statistically the lowest fracture torque (N.cm) (26.11±0.41) (P=0.0012) and highest torque ratio (%) (98.74±0.85) (P=0.0007). Type C showed statistically higher calculated shear (MPa) (2,432.73±508.41) and normal stress (MPa) (1,403.86±293.39) than type B and type A, showing that they differed in relation to the mechanical strength of the material with which they were made (P=0.0007).

CONCLUSION

Type A fractured completely inside the most apical bone. Type B and type C fractured closer to the transmucosal profile. Cold worked process should be more prone to fractures than those annealed raw manufactured.

Functionality testing of an innovative biomechanically optimized and surface-modified orthodontic mini-screw-a comparative study

PURPOSE

The failure rate of orthodontic mini-screws depends strongly on primary stability and, thus, on insertion torque. Further improvement regarding the failure rate might be achieved by modifying the surface coating. Therefore, the aim of the study was to investigate the stability of a newly designed and surface-modified orthodontic mini-screw in beagle dogs.

METHODS

Newly designed mini-screws coated either with DOTIZE® or DOTIZE®-copper (DOT GmbH, Rostock, Germany; each: n = 24) were inserted in the mandibles of eight beagle dogs for a duration of 8 months. Insertion and removal torque were measured. These data were compared to values generated by using the artificial bone material Sawbones® (Sawbones Europe AB, Malmö, Sweden). Experiments with and without torque limitation (each: n = 5) were run. The bone-to-implant contact rate and the amount of bone between the threads were examined. Statistical significance was set at P < 0.05.

RESULTS

The success rates of the in vivo study reached high levels with 95.3% for the DOTIZE-coated and 90.5% for the DOTIZE-copper-coated screws, whereas the insertion and removal torque did not differ between the coatings. During insertion, a torque limitation of 20 Ncm was necessary to ensure that the recommended limit was not exceeded. The insertion in Sawbones without torque limitation revealed a significantly higher torque compared to torque-limited insertion (18.2 ± 1.3 Ncm, 23.6 ± 1.3 Ncm). Bending occurred (n = 5) in the thread-free part of the mini-screw.

CONCLUSIONS

Surface coating might be able to improve the performance of orthodontic mini-screws. The study showed high success rates and stable mini-screws until the end of observation. Further investigations are necessary.

Failure rates and factors associated with infrazygomatic crestal orthodontic implants - A prospective study

Objective

Infrazygomatic crestal (IZC) implants have gained increased popularity over the past few years. Hardly any studies have been done to assess the rate and reasons for failure of IZCs. This prospective study was planned and designed with the primary objective of assessing the rate of failure of bone-screws (BS) placed in the infrazygomatic crest. In continuation, the secondary objective was to assess the factors that were associated with the failure.

Materials and methods

The study was carried out by taking a detailed case history, (age, gender, vertical skeletal pattern, medical history), photographic records, radiographs, and clinical examination of a total of 32 randomly selected. patients of south indian origin who required infrazygomatic implants bilaterally as the choice of anchorage conservation to retract their incisors. All selected subjects were required to take a PA Cephalogram after the implant placement. The age of the patients ranged from 18 to 33 with an average age of 25 years. The patient log was maintained which included the treatment mechanics, status of oral hygiene, stability of implants, time of loading of the implant, presence of inflammation and time of failure of implant. The angulation of implant was measured on a digital PA cephalogram using Nemoceph software. These parameters were examined to evaluate independent and dependent variables using the Chi-Square test and Fischer's exact test.

Result

A failure rate 28.1% for IZC placed in the infrazygomatic crest region was observed. Patients with a high mandibular plane angle, poor oral hygiene, immediately loaded implant, peri-implantitis, and severe clinical mobility showed higher failure rates. Variables such as age, gender, sagittal skeletal pattern, length of the implant, type of movement, occluso-gingival position, method of force application, and angle of placement were not significantly associated with implant failure.

Conclusion

Oral hygiene and peri-screw inflammation must be controlled to minimize the failure of bone screws placed in the infrazygomatic crest region. Loading of the implant should be done after a latent period of two weeks. A higher failure rate was observed in patients with vertical growth pattern.

Effect of thread depth and thread pitch on the primary stability of miniscrews receiving a torque load : A finite element analysis

PURPOSE

We have been developing a new type of miniscrew to specifically withstand orthodontic torque load. This study aimed to investigate the effect of thread depth and thread pitch on the primary stability of these miniscrews if stressed with torque load.

METHODS

Finite element analysis (FEA) was used to evaluate the primary stability of the miniscrews. For thread depth analysis, the thread depth was set to 0.1-0.4 mm to construct 7 models. For thread pitch analysis, the thread pitch was set to 0.4-1.0 mm to construct another 7 models. A torque load of 6 Nmm was applied to the miniscrew, and the other parameters were kept constant for the analyses. Maximum equivalent stress (Max EQV) of cortical bone and maximum displacement of the miniscrews (Max DM) were the indicators for primary stability of the miniscrew in the 14 models.

RESULTS

In the thread depth analysis, Max DM increased as the miniscrew thread depth increased, while Max EQV was smallest in model 3 (thread depth = 0.2, Max EQV = 8.91 MPa). In the pitch analysis, with an increase of the thread pitch, Max DM generally exhibited a trend to increase, while Max EQV of cortical bone showed a general trend to decrease.

CONCLUSION

Considering the data of Max DM and Max EQV, the most appropriate thread depth and thread pitch of the miniscrews in our model was 0.2 and 0.7 mm, respectively. This knowledge may effectively improve the primary stability of newly developed miniscrews.

Investigation of periodontal status and bacterial composition aroundmini-implants

INTRODUCTION

Mini-implants are now widely used in orthodontic treatment. Soft-tissue inflammation around the mini-implant is an important factor affecting its stability. This study aimed to investigate the periodontal status and the bacterial composition around mini-implants.

METHODS

A total of 79 mini-implants in 40 patients (aged 18-45 years) were evaluated in this study. The mini-implant probing depth (mPD), mini-implant gingival sulcus bleeding index (mBI), mini-implant plaque index (mPLI), and the composition of the supragingival and subgingival plaque around the mini-implants were recorded. After Congo red staining, the bacteria were classified and counted under a light microscope.

RESULTS

The mPLI and mBI around mini-implants in the infrazygomatic crest were higher than those in the buccal shelf and interradicular area. The mPD was higher on the coronal site of the mini-implant than on the mesial, distal, and apical sites in the infrazygomatic crest. The mPLI around the mini-implant was positively correlated with the mBI, and the mBI was positively correlated with the mPD. The supragingival and subgingival bacterial composition around the mini-implants was similar to that of natural teeth. Compared with supragingival bacterial composition, the subgingival bacteria of mini-implants had a significantly lower proportion of cocci and a higher proportion of bacilli and spirochetes.

CONCLUSIONS

The bacteria composition of the plaque and the location are important factors in the inflammation around mini-implants. Similar to natural teeth, mini-implants require health maintenance to prevent inflammation of the surrounding soft tissue and maintain stability.

How Does Orthodontic Mini-Implant Thread Minidesign Influence the Stability?—Systematic Review with Meta-Analysis

Background: Clinical guidelines are lacking for the use of orthodontic mini-implants (OMIs) in terms of scientific evidence referring to the choice of proper mini-design. Thus, the present study aimed to investigate to what extent orthodontic mini-implant thread design influences its stability. Methods: Search was conducted in five search engines on 10 May. Quality assessment was performed using study type specific scales. Whenever possible, meta-analysis was performed. Results: The search strategy identified 118 potential articles. Twenty papers were subjected to qualitative analysis and data from 8 papers—to meta-analysis. Studies included were characterized by high or medium quality. Four studies were considered as low quality. No clinical studies considering the number of threads, threads depth, or TSF have been found in the literature. Conclusions: Minidesign of OMIs seems to influence their stability in the bone. Thread pitch seems to be of special importance for OMIs retention—the more dense thread—the better stability. Thread depth seems to be of low importance for OMIs stability. There is no clear scientific evidence for optimal thread shape factor. Studies present in the literature vary greatly in study design and results reporting. Research received no external funding. Study protocol number in PROSPERO database: CRD42022340970.

Optimization Analysis of Two-Factor Continuous Variable between Thread Depth and Pitch of Microimplant under Toque Force

Microimplant, an anchorage device, is widely applied in clinical orthodontic treatment. Since tooth torque is required to be controlled during orthodontic tooth movement, a novel microimplant needs to be developed to apply better torque force during orthodontic. In this study, the optimal value ranges of thread depth and pitch under toque force were studied for choosing microimplant with relevant value ranges in clinical design from biomechanical perspective. Finite element analysis (FEA) and optimization design technology were used for accessing the optimal value ranges of thread depth and pitch under toque force. Thread depth (D) (0.1 mm to 0.4 mm) and pitch (P) (0.4 mm to 1 mm) were used as continuous variables, with the other parameters as constant, and the optimal value ranges were obtained by analyzing the tangent slope and sensitivity of the response curve. When a torque force of 6 Nmm was applied on the microimplant, the maximum equivalent stress (Max EQV) of cortical bone and maximum displacements (Max DM) of microimplant were analysis indexes. When 0.55 mm ≤ P ≤ 1 mm, the Max EQV of cortical bone was relatively smaller with less variation range. When 0.1 mm ≤ D ≤ 0.35 mm, the Max DM of microimplant was relatively smaller with less variation range. So in conclusion, the initial stability of microimplants with pitch 0.55 mm ≤ P ≤ 1 mm and thread depth 0.1 mm ≤ D ≤ 0.35 mm was better with the torque force applied.

Bone quality affects stability of orthodontic miniscrews

The objective of this study was to evaluate the effect of bone–miniscrew contact percentage (BMC%) and bone quality and quantity on orthodontic miniscrew stability and the maximum insertion torque value (ITV). Orthodontic miniscrews of five different dimensions and several bovine iliac bone specimens were used in the evaluation. Miniscrews of each dimension group were inserted into 20 positions in bovine iliac bone specimens. The experiment was divided into three parts: (1) Bone quality and quantity were evaluated using cone-beam computed tomography (CBCT) and microcomputed tomography. (2) The 3D BMC% was calculated. (3) The ITVs during miniscrew insertion were recorded to evaluate the stability of the orthodontic miniscrews. The results indicated that longer and thicker miniscrews enabled higher ITVs. CBCT was used to accurately measure cortical bone thickness (r = 0.939, P < 0.05) and to predict the bone volume fraction of cancellous bone (r = 0.752, P < 0.05). BMC% was significantly influenced by miniscrew length. The contribution of cortical bone thickness to the ITV is greater than that of cancellous bone structure, and the contribution of cortical bone thickness to BMC% is greater than that of cancellous bone structure. Finally, the higher is BMC%, the greater is the ITV. This study concludes that use of CBCT may predict the mechanical stability of orthodontic miniscrews.

Construction of Customized Palatal Orthodontic Devices on Skeletal Anchorage Using Biomechanical Modeling

Orthodontic implants have been developed for the implementation of skeletal anchorage and are effectively used in the design of individual orthodontic devices. However, despite a significant amount of clinical research, the biomechanical aspects of the use of skeletal anchorage have not been adequately studied. The aim of this work was to numerically investigate the stress-strain state of the developed palatal orthodontic device supported by mini-implants. Four possible options for the placement of mini-implants in the bone were analyzed. The effect of a chewing load of 100 N on the bite plane was investigated. The study was carried out using biomechanical modeling based on the finite element method. The installation of the palatal orthodontic device fixed on mini-implants with an individual bite plane positioned on was simulated. The dependence of equivalent stresses and deformation changes on the number and location of the supporting mini-implants of the palatal orthodontic device was investigated. Two materials (titanium alloy and stainless steel) of the palatal orthodontic device were also investigated. The choice of a successful treatment option was based on the developed biomechanical criteria for assessing the surgical treatment success. Application of the criteria made it possible to estimate the stability and strength of fixation of each of the considered mini-implants installation options. As a result, options for the mini-implants optimal placement were identified (the first and the fourth which provide distributed front and side support of the device), as well as the preferred material (titanium alloy) for the manufacture of the palatal orthodontic device.

Finite element simulation and statistical investigation of an orthodontic mini-implant's stability in a novel screw design

One of the essential aspects of the mini-implant's successful application is its stability after being installed in the bone. The stability of the mini-implant affected the most by its geometry. In the present research, the effect of the geometry-related parameters of the mini-implant on its lateral displacement is investigated by Finite Element (FE) modeling using ABAQUS software. The parameters studied include length, diameter, pitch, and depth of the screw threads; besides, length and angle of the conical section. The Taguchi method was used to prevent many experiments. The mesh convergence tests and experimental tests confirmed the FE model quantitatively and qualitatively. Mean of means and variance analysis determined the parameters significance and their contribution on the stability. The screw diameter and length have the most contribution to mini-implant' displacement. The effect of screw pitch was less than that for length and diameter. The conical section improved the initial stability by creating compressive stress and additional friction in its surrounding bone. No significant effects on the stability of the mini-implant have been observed for the non-threaded part. By examining the effect of thread depth on its stability by defining the ratio of thread depth to the internal diameter and to maintain the strength of the screw the optimal value for internal to external ratio is set at about 0.7.

Effect of Different Head Hole Position on the Rotational Resistance and Stability of Orthodontic Miniscrews: A Three-Dimensional Finite Element Study

The orthodontic miniscrew is driven into bone in a clockwise direction. Counter-clockwise rotational force applied to the implanted miniscrew can degrade the stability. The purpose of this three-dimensional finite element study was to figure out the effect of shifting the miniscrew head hole position from the long axis. Two miniscrew models were developed, one with the head hole at the long axis and the other with an eccentric hole position. One degree of counter-clockwise rotation was applied to both groups, and the maximum Von-Mises stress and moment was measured under various wire insertion angles from −60° to +60°. All Von-Mises stress and moments increased with an increase in rotational angle or wire insertion angle. The increasing slope of moment in the eccentric hole group was significantly higher than that in the centric hole group. Although the maximum Von-Mises stress was higher in the eccentric hole group, the distribution of stress was not very different from the centric hole group. As the positive wire insertion angles generated a higher moment under a counter-clockwise rotational force, it is recommended to place the head hole considering the implanting direction of the miniscrew. Clinically, multidirectional and higher forces can be applied to the miniscrew with an eccentric head hole position.

Miniscrew-assisted rapid palatal expansion (MARPE): how to achieve greater stability. In vitro study

Objective:

Assess the influence of mono- and bicortical anchorage and diameter of mini-implants (MIs) on the primary stability of these devices.

Methods:

60 self-drilling MIs were distributed in six groups according to diameter (1.5mm, 1.8mm or 2.0mm) and type of anchorage (monocortical and bicortical) in bovine rib. The primary stability was evaluated by insertion torque, micromobility and pull-out strength tests. ANOVA and/or Tukey analysis were used to conduct intergroup comparisons (p< 0.05). Non-parametric statistics (Kruskal-Wallis and Mann-Whitney) were performed when normality was not found (p< 0.05).

Results:

MIs with larger diameters and bicortical anchorage showed greater primary stability regarding insertion torque (p< 0.05) and micromobility (p< 0.05). Only MI diameter had an effect on the pull-out strength test. Larger diameter MIs presented better retention in pull-out strength tests (p< 0.001), regardless of mono- or bicortical anchorage.

Conclusions:

MI primary stability is dependent on its diameter and type of anchorage. Bicortical anchorage showed greater stability when compared with monocortical anchorage, independently of other variables.

Evaluation of Bone-Implant Interface Stress and Strain Using Heterogeneous Mandibular Bone Properties Based on Different Empirical Correlations

Objectives  The purpose of this study was to compare methods used for calculating heterogeneous patient-specific bone properties used in finite element analysis (FEA), in the field of implant dentistry, with the method based on homogenous bone properties.

Materials and Methods  In this study, three-dimensional (3D) computed tomography data of an edentulous patient were processed to create a finite element model, and five identical 3D implant models were created and distributed throughout the dental arch. Based on the calculation methods used for bone material assignment, four groups—groups I to IV—were defined. Groups I to III relied on heterogeneous bone property assignment based on different equations, whereas group IV relied on homogenous bone properties. Finally, 150 N vertical and 60-degree-inclined forces were applied at the top of the implant abutments to calculate the von Mises stress and strain.

Results  Groups I and II presented the highest stress and strain values, respectively. Based on the implant location, differences were observed between the stress values of group I, II, and III compared with group IV; however, no clear order was noted. Accordingly, variable von Mises stress and strain reactions at the bone–implant interface were observed among the heterogeneous bone property groups when compared with the homogenous property group results at the same implant positions.

Conclusion  Although the use of heterogeneous bone properties as material assignments in FEA studies seem promising for patient-specific analysis, the variations between their results raise doubts about their reliability. The results were influenced by implants’ locations leading to misleading clinical simulations.

Evaluation of stability of three different mini-implants, based on thread shape factor and numerical analysis of stress around mini-implants with different insertion angle, with relation to en-masse retraction force

Objectives:

Assess the stability of three different mini-implants, based on thread shape factor (TSF), and evaluate stresses at the mini-implant site and surrounding cortical bone on application of retraction force, at two different insertion angles.

Methods:

Mini-implants of three different diameters (M1 - Orthoimplant, 1.8mm), (M2 - Tomas, 1.6mm) and (M3 - Vector TAS, 1.4mm) and length of 8mm were used. Using scanning electronic microscopy, the mean thread depth, pitch and relationship between the two (TSF) were calculated. The mini-implants were loaded into a synthetic bone block and the pull-out strength was tested. One way ANOVA and Tukey post-hoc tests were used to compare the pull-out strength of mini-implants. P values < 0.05 were considered statistically significant. Finite element models (FEM) were constructed with insertion angulation at 90° and 60°, with retraction force of 150 g. The results were analyzed using ANSYS software.

Results:

Statistically significant difference was found among all the three mini-implants for thread depth and pitch (< 0.001). Statistically significant higher pull-out force value was seen for Orthoimplant. The stress distribution level in mini-implant and surrounding bone was observed to be smaller for Orthoimplant.

Conclusion:

Orthoimplant mini-implants have more favorable geometric characteristics among the three types, and less stress with 90°angulation.

Change in Pull-Out Force during Resorption of Magnesium Compression Screws for Osteosynthesis of Mandibular Condylar Fractures

BACKGROUND

Magnesium has been used as degradable fixation material for osteosynthesis, but it seems that mechanical strength is still a current issue in these fixations. The aim of this study was to evaluate the axial pull-out force of compression headless screws made of magnesium alloy during their resorption.

METHODS

The tests included screws made for osteosynthesis of the mandible head: 2.2 mm diameter magnesium alloy MgYREZr (42 screws) and 2.5 mm diameter polylactic-co-glycolic acid (PLGA) (42 pieces, control). The screws were resorbed in Sørensen's buffer for 2, 4, 8, 12, and 16 weeks, and force was measured as the screw was pulled out from the polyurethane block.

RESULTS

The force needed to pull the screw out was significantly higher for MgYREZr screws than for PLGA ones (p < 0.01). Within eight weeks, the pull-out force for MgYREZr significantly decreased to one third of its initial value (p < 0.01). The dynamics of this decrease were greater than those of the pull-out force for PLGA screws (p < 0.05). After these eight weeks, the values for metal and polymer screws equalized. It seems that the described reduction of force requires taking into account when using magnesium screws. This will provide more stable resorbable metallic osteosynthesis.

[The experimental study of a Russian orthodontic mini-screw]

BACKGROUND

The aim of this research is the experimental study measuring stability of the orthodontic miniscrews «Turbo» designed in Russia in comparison with its foreign analogues, namely, «Vector Tas» (USA) and «BioRay» (Taiwan).

MATERIAL AND METHODS

Four self-drilling orthodontic miniscrews of each manufacturer, i.e. «Vector Tas», USA, (10-mm length, 2-mm diameter), «BioRay», Taiwan, (10-mm length, 2-mm diameter), «Turbo», Russia, (9-mm length, 2-mm diameter), a total of 12 items, were inserted into native pig mandible sample. Their stability was estimated by torques using a dynamometer (Zahoransky AG, Germany) and «Periotest» device («Periotest M», Germany). This experiment was conducted in native pig mandible sample immediately after the screws' placement and in 7 days after loading at an angle 70°.

RESULTS

After application of a load, the decreased torque values and increased Periotest values were registered in all orthodontic miniscrews.

CONCLUSION

Orthodontic miniscrews «Turbo» designed in Russia are slightly inferior to «VectorTas» miniscrews and superior to «BioRay» miniscrews in primary stability and stability after 7 days under loading.

Mechanical Evaluation of the Stability of One or Two Miniscrews under Loading on Synthetic Bone

The aim of the present study was to evaluate the primary stability of a two-miniscrew system inserted into a synthetic bone and to compare the system with the traditional one. Forty-five bi-layered polyurethane blocks were used to simulate maxillary cancellous and cortical bone densities. Samples were randomly assigned to three groups—one-miniscrew system (Group A, N = 23), two-miniscrew system (Group B, N = 22) and archwire-only (Group C, N = 10). A total of 67 new miniscrews were subdivided into Group A (23 singles) and Group B (22 couples). 30 mm of 19″ × 25″ archwires were tied to the miniscrew. The load was applied perpendicularly to the archwire. Maximum Load Value (MLV), Yield Load (YL) and Loosening Load (LL) were recorded for each group. The YL of Group B and C had a mean value respectively of 4.189 ± 0.390 N and 3.652 ± 0.064 N. The MLV of Group A, B and C had a mean value respectively of 1.871 ± 0.318N, of 4.843 ± 0.515 N and 4.150 ± 0.086 N. The LL of Group A and B had a mean value respectively of 1.871 ± 0.318 N and of 2.294 ± 0.333 N. A two- temporary anchorage device (TAD) system is on average stiffer than a one-TAD system under orthodontic loading.

A Custom-Made Orthodontic Mini-Implant-Effect of Insertion Angle and Cortical Bone Thickness on Stress Distribution with a Complex In Vitro and In Vivo Biosafety Profile

BACKGROUND

Orthodontic mini-implant failure is a debatable subject in clinical practice. However, the most important parameter to evaluate the success rate of mini-implant is the primary stability, which is mainly influenced by cortical bone thickness (CBT) and insertion angle.

MATERIALS AND METHODS

Three-dimensional finite element models of the maxilla were created and a custom-made, self-drilling, tapered mini-implant was designed. For the pull-out test, 12 simulations were performed, sequentially increasing the thickness of the cortical bone (1, 1.5 and 2 mm) and the insertion angle (30°, 60°, 90°, 120°). For the force analysis, 24 simulations were performed using an experimental orthodontic traction force of 2 N both in the horizontal and vertical axis.

RESULTS

Insertion angle and CBT have significant impact on force reaction values (p < 0.05). Cortical bone stress had the lowest value when the mini-implant had a 30° insertion angle and the highest value when the implant had a 120° insertion angle, while the CBT was 1 mm. Cortical bone stress had the lowest value with an insertion angle of 90° and the highest value when the implant was inserted at an angle of 30°, while the CBT was 2 mm independent of the force direction. Regarding the biosafety profile of the mini-implant alloy, the present results reveal that the custom-made mini-implant presents good biocompatibility.

CONCLUSIONS

When the CBT is reduced, we recommend inclined insertion while, when the CBT is appropriate, perpendicular insertion is advised.

Influence of Orthodontic Anchor Screw Anchorage Method on the Stability of Artificial Bone: An In Vitro Study

This study aims to compare the torque values for various lengths of the titanium-based orthodontic anchor screw (OAS), different anchorage methods and varying artificial bone densities after predrilling. Furthermore, the effects of these parameters on bone stability are evaluated. A total of 144 OASs were prepared with a diameter of 1.6 mm and heights of 6, 8 and 10 mm. Artificial bones were selected according to their density, corresponding to Grades 50, 40 and 30. Torque values for the automatic device and manual anchorage methods exhibited a statistically significant difference for the same-sized OAS, according to the bone density of the artificial bones (p < 0.05). However, when insertion torque was at the maximum rotations, there was no significant difference in the torque values for the Grade 30 artificial bone (p > 0.05). When the torque values of both anchorage methods were statistically compared with the mean difference for each group, the results of the manual anchorage method were significantly higher than those of the automatic device anchorage method (p < 0.05). A statistically significant difference was observed in the bone stability resulting from different OAS anchorage methods and artificial bone lengths. These findings suggest that the automatic anchorage method should be used when fixing the OAS.

Thread shape affects the stress distribution of torque force on miniscrews: a finite element analysis

This study aimed to investigate the effect of miniscrews thread shape on the stress distribution receiving a torque load. Seven thread shapes (S,V1,V2,B1,B2,R1,R2) models were constructed and a 6 Nmm-torque load was applied. The order of maximum equivalent stress (EQV) value was V1 > V2 > B1 > R1 > R2 > B2 > S. The order of maximum displacement of miniscrew (Max DM) value was S > B2 > R1 = V1 > B1 > V2 > R2. Model R2 may be the most appropriate thread shape affording a torque force.

Effect of the positional relationship between the interference screw and the tendon graft in the bone tunnel in ligament reconstruction

PURPOSE

To reveal the effects of the positional and length relationships between the interference screws (ISs) and the tendon graft in the bone tunnel on the fixation strength in ligament reconstruction.

METHODS

We compared three IS positions on the anterior (the Anterior group) or posterior (the Posterior group) or side (the Side group) of the tendon graft in relation to the pullout direction. The tendon graft was pulled at 0°, 30°, 60°, and 90° to the bone tunnel, and the maximum pullout load at each angle was compared among the groups. We also investigated the relationship between the length of the tendon graft and the length of the IS in the bone tunnel. The direction of the pullout force was the same as that of the Anterior group, and the maximum load was compared between groups in which the tendon graft was longer or shorter than the IS.

RESULTS

The maximum loads of the Anterior group were significantly greater than those of the Posterior and Side groups at the traction angles of 30° and 60°, respectively. An IS shorter than the tendon graft was found to provide significantly superior fixation strength compared to an IS longer than the tendon graft.

CONCLUSIONS

Better fixation strength was achieved when the IS was placed on the side of the anchorage tunnel on which the tendon graft was loaded and the IS was shorter than the tendon graft.

Design of a new magnesium-based anterior cruciate ligament interference screw using finite element analysis

Background/objective

In anterior cruciate ligament ​reconstruction, a tendon graft, anchored by interference screws (IFSs), is frequently used as a replacement for the damaged ligament. Generally, IFSs are classified as being either metallic or polymeric. Metallic screws have sharp threads that lacerate the graft, preventing solid fixation. These constructs are difficult to image ​and can limit bone--screw integration because of the higher stiffness of the screw. Polymeric materials are often a better match to bone's material properties, but lack the strength needed to hold grafts in place. Magnesium (Mg) is a material of great promise for orthopaedic applications. Mg has mechanical properties similar to bone, ability to be seen on magnetic resonance imagings, and promotes bone healing. However, questions still remain regarding the strength of Mg-based screws. Previous ex vivo ​animal experiments found stripping of the screw drive when the full torque was applied to Mg screws during surgery, preventing full insertion and poor graft fixation. The similar design of the Mg screw led to questions regarding the relationship between material properties and design, and the ultimate impact on mechanical behaviour. Thus, the objective of this study was to analyze the stresses in the screw head, a key factor in the stripping mechanism of IFS, then use that information to improve screw design, for this material.

Methods

Using finite element analysis, a comparison study of six drive designs (hexagonal, quadrangle, torx, trigonal, trilobe, and turbine) was performed. This was followed by a parametric analysis to determine appropriate drive depth and drive width.

Results

It was observed that with a typical torque (2 ​Nm) used for screw insertion during anterior cruciate ligament reconstruction, the maximum von Mises and shear stress values were concentrated in the corners or turns of the drive, which could lead to stripping if the values were greater than the yield stress of Mg (193 ​MPa). With a four-time ​increase in drive depth to be fully driven and a 30% greater drive width, these maximum stress values were significantly decreased by more than 75%.

Conclusion

It was concluded that improving the design of a Mg-based screw may increase surgical success rates, by decreasing device failure at insertion.

The translational potential of this article

The results of this work have the potential to improve designs of degradable IFSs, allowing for greater torque to be applied and thus greater screw fixation between host bone and the graft. Such a fixation will allow greater integration, better patient healing, and ultimately improved patient outcomes.

Investigation of the optimal design of orthodontic mini-implants based on the primary stability: A finite element analysis

Background. The design of an orthodontic mini-implant is a significant factor in determining its primary stability and its clinical success. The aim of this study was to measure the relative effect of mini-implant design factors on primary stability of orthodontic mini-implants.

Methods. Thirty-two 3-dimensional assemblies of mini-implant models with their surrounding bone were generated using finite element analysis software. The maximum displacement of each mini-implant model was measured as they were loaded with a 2-N horizontal force. Employing Taguchi’s design of experiments as a statistical method, the contribution of each design factor to primary stability was calculated. As a result of the great effect of the upper diameter and length, to better detect the impact of the remaining design factors, another set of 25 models with a fixed amount of length and diameter was generated and evaluated.

Results. The diameter and length showed a great impact on the primary stability in the first set of experiments (P<0.05). According to the second set of experiments, increased taper angle in the threaded and non-threaded area decreased the primary stability. There was also an optimum amount of 2.5 mm for threaded taper length beyond which the primary stability decreased.

Conclusion. It is advisable to increase the diameter and length if primary stability is at risk. In the second place, a minimum amount of taper angle, both in the threaded and non-threaded area with an approximate proportion of 20% of threaded taper length to MI length, would be desirable for MIs with a moderate size.

Enhancing osseointegration of titanium implants through large-grit sandblasting combined with micro-arc oxidation surface modification

PURPOSE

The demand for titanium dental implants has risen sharply. However, the clinical success rate of implant surgery needs to be improved. In this paper, we report a novel surface modification strategy, large-grit sandblasting combined with micro-arc oxidation (SL-MAO), aiming to promote peri-implant bone formation and osseointegration of titanium implants.

MATERIALS AND METHODS

Modified titanium samples were prepared by large-grit sandblasting and acid etching (SLA), micro-arc oxidation (MAO), and SL-MAO. The resulting topographical changes and chemical composition of the samples were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively, and the biocompatibility and bioactivity were analyzed by bone-marrow mesenchymal stem cells (BMMSC) adhesion tests. Modified titanium implants were also inserted into the femurs of beagle dogs, and their competence of osseointegration was appraised by quantitative histomorphometry and micro-computed-tomography (micro-CT) analyses.

RESULTS

Compared to SLA and MAO techniques, SL-MAO surface modification further enhanced titanium surfaces by creating a topographic morphology characterized by both micron-sized craters and sub-micron-scale pits, and resulted in superior chemical composition, which promoted cell adhesion, proliferation, and osteogenic differentiation. SL-MAO-modified titanium implants osseointegrated more efficiently than SLA or MAO controls, with significantly higher bone-area (BA) ratio and bone-implant contact (BIC) in the peri-implant region.

CONCLUSIONS

The SL-MAO surface modification technique optimized the surface properties of titanium implants and enhanced peri-implant bone formation and osseointegration.

EFFECT OF BONE QUALITY ON INITIAL STABILITY OF ORTHODONTIC MINISCREWS

Purpose: This study investigated the effects of the contact percentage (BMC%) of three-dimensional (3D) bone-to-miniscrew specimens in relation to host bone quality on initial miniscrew stability. Furthermore, their correlations were evaluated.

Methods: Orthodontic miniscrews (1.6[Formula: see text]mm in diameter and 11[Formula: see text]mm in length) were inserted into four types of artificial bones to measure the maximum insertion torque value (ITV). The miniscrew and artificial foam bone specimens were also scanned using microcomputed tomography, and the obtained images were imported into Mimics software to reconstruct the 3D models and calculate the BMC%. The Kruskal–Wallis test, Wilcoxon rank-sum test with Bonferroni adjustment, and Spearman correlations were applied for statistical and correlation analyses.

Results and Conclusions: Inserting the orthodontic miniscrew into artificial foam bone exhibiting higher bone quality resulted in higher maximum ITV and BMC%. The initial implant stability, quantified using ITV, was strongly positively ([Formula: see text]) and correlated with BMC%, as measured from microcomputed tomography images.

Experimental Evaluation of Screw Pullout Force and Adjacent Bone Damage According to Pedicle Screw Design Parameters in Normal and Osteoporotic Bones

This paper proposes an optimum design of the pedicle screw with respect to bone density and variables of the screw design. First, pedicle screws are designed and manufactured with design variables including the core diameter and conical angle that affect the pullout force of the pedicle screw. Variables of bone density are also classified into two groups, namely grade 10 (0.16 g/cc) with osteoporotic bone density and grade 20 (0.32 g/cc) with normal bone density. The effect of each parameter on the pullout force and relationship between the pullout force and screw designs are investigated. Furthermore, bone damage after fixation failure or insertion in the patient body is considered separately from the pullout strength. Therefore, cross sectional images of the artificial bone are observed to analyze the degree of damage after the pullout test of the pedicle screw by using micro-CT (computed tomography). The region and degree of bone damage are quantitatively analyzed. The effects of the core diameter and conical angle of the pedicle screw on the pulling force, bone damage, and fracture behavior are analyzed via the aforementioned experiments and analysis. An optimal pedicle screw design is suggested based on the experimental results.

Reliability of Orthodontic Miniscrews: Bending and Maximum Load of Different Ti-6Al-4V Titanium and Stainless Steel Temporary Anchorage Devices (TADs)

Temporary anchorage devices (TADs) have been introduced into orthodontic clinical practice in order to allow tooth movements while avoiding strain on adjacent teeth. Miniscrews are available in the market with different diameters and materials. Accordingly, the purpose of the present report was to measure and compare the forces to bend and fracture different mini implants. Ti-6Al-4V titanium and stainless steel TADs of different manufacturers (Spider ScrewHDC; Mini Implants⁻Leone; Benefit⁻Orteam; Storm⁻Kristal) were evaluated. Two different diameters (1.5 mm and 2.0 mm) were tested. The sample included 10 unused specimens for each group, blocked in an Instron Universal Testing Machine, and a shear load was applied at the neck of the miniscrew. The force to bend the miniscrew was measured at 0.1 mm and 0.2 mm deflections. Also, the maximum force before screw fracture was recorded. Data were submitted for statistical analysis. Results showed significantly higher forces for 2.0 mm than 1.5 mm screws, both at 0.1 mm and 0.2 mm deflections and at maximum load. Moreover, no significant differences were reported between titanium and stainless steel miniscrews of equal diameters.

Reliability of Orthodontic Miniscrews: Bending and Maximum Load of Different Ti-6Al-4V Titanium and Stainless Steel Temporary Anchorage Devices (TADs)

Temporary anchorage devices (TADs) have been introduced into orthodontic clinical practice in order to allow tooth movements while avoiding strain on adjacent teeth. Miniscrews are available in the market with different diameters and materials. Accordingly, the purpose of the present report was to measure and compare the forces to bend and fracture different mini implants. Ti-6Al-4V titanium and stainless steel TADs of different manufacturers (Spider ScrewHDC; Mini Implants⁻Leone; Benefit⁻Orteam; Storm⁻Kristal) were evaluated. Two different diameters (1.5 mm and 2.0 mm) were tested. The sample included 10 unused specimens for each group, blocked in an Instron Universal Testing Machine, and a shear load was applied at the neck of the miniscrew. The force to bend the miniscrew was measured at 0.1 mm and 0.2 mm deflections. Also, the maximum force before screw fracture was recorded. Data were submitted for statistical analysis. Results showed significantly higher forces for 2.0 mm than 1.5 mm screws, both at 0.1 mm and 0.2 mm deflections and at maximum load. Moreover, no significant differences were reported between titanium and stainless steel miniscrews of equal diameters.

Influence of geometric design characteristics on primary stability of orthodontic miniscrews

OBJECTIVE

Aim of the present study was to investigate the influence of geometric design characteristics on primary stability of orthodontic miniscrews.

MATERIALS AND METHODS

Forty self-drilling miniscrews with different geometric design characteristics were divided into the following groups (n = 10): group I-Tomas® (Dentaurum, Germany), group II-AbsoAnchor® (Dentos, Korea), group III-HUBIT® miniscrew (HUBIT, Korea), group IV-Creative® (China). The four types were conical miniscrews with 1.6 mm diameter and 6.0 mm length. The miniscrews were manually inserted perpendicular to cow ribs until the full thread length was reached with the help of a 1.3 mm predrilled pilot hole. Each miniscrew was evaluated using scanning electron microscope. Linear and angular measurements were taken using Photoshop CS3 software. Miniscrew stability was measured by the Periotest® and pullout test.

RESULTS

All linear and angular measurements of the geometric characteristics showed significant differences between the four groups (p ≤ 0.001). Results of the pullout test showed significant differences between the four groups (p ≤ 0.001), while the Periotest® values showed no significant differences (p = 0.122). A multiple linear regression analysis revealed the significant predictors for higher pullout: a larger flank, a higher value for the thread angle, lead angle, and apical face angle (p ≤ 0.001).

CONCLUSIONS

Orthodontic miniscrews' geometric design characteristics significantly affected the primary stability. Larger pitch width, flank, thread angle, apical face angle, and/or lead angle led to higher primary stability. Smaller a thread shape factor (TSF) also improved primary stability. Varying these characteristics may enhance miniscrew design.

Finite element analysis of dental implants with validation: to what extent can we expect the model to predict biological phenomena? A literature review and proposal for classification of a validation process

A literature review of finite element analysis (FEA) studies of dental implants with their model validation process was performed to establish the criteria for evaluating validation methods with respect to their similarity to biological behavior. An electronic literature search of PubMed was conducted up to January 2017 using the Medical Subject Headings “dental implants” and “finite element analysis.” After accessing the full texts, the context of each article was searched using the words “valid” and “validation” and articles in which these words appeared were read to determine whether they met the inclusion criteria for the review. Of 601 articles published from 1997 to 2016, 48 that met the eligibility criteria were selected. The articles were categorized according to their validation method as follows: in vivo experiments in humans (n = 1) and other animals (n = 3), model experiments (n = 32), others’ clinical data and past literature (n = 9), and other software (n = 2). Validation techniques with a high level of sufficiency and efficiency are still rare in FEA studies of dental implants. High-level validation, especially using in vivo experiments tied to an accurate finite element method, needs to become an established part of FEA studies. The recognition of a validation process should be considered when judging the practicality of an FEA study.

Increasing the Stability of Dental Implants: the Concept of Osseodensification

One of the most important factors that affect osseointegration is the primary stability of the implant. Dental implants inserted at the posterior region of the maxilla exhibit the lowest success rates as the low density bone in this area often jeopardize rigid fixation of the implant. Many surgical techniques have been developed to increase the primary stability of an implant placed in low density bone, such as bicortical fixation of the implant, undersized preparation of the implant bed and bone condensation by the use of osteotomes. A new promising technique, named osseodensification, has been recently developed that creates an autograft layer of condensed bone at the periphery of the implant bed by the aid of specially designed burs rotating in a clockwise and anti-clockwise direction. The purpose of this review is to emphasize that implant primary stability is strongly influenced by the surgical technique, to quote and briefly analyse the various surgical procedures laying weight to osseodensification procedure.

Does Change in Thread Shape Influence the Pull Out Strength of Mini Implants? An In vitro Study

INTRODUCTION

Mini implants form a valuable source for absolute anchorage thereby helping in achieving ideal treatment outcome. Stability of the mini implant is one of the important factors affecting the success of mini implants. Thread shape is a critical factor in the engineering design of mini implant, which affects the primary stability.

AIM

To evaluate the effects of thread shape on the pull out strength of mini implants.

MATERIALS AND METHODS

Mini implants of five different designs in thread shape (reverse buttress, buttress, 75° joint profile with flutes, trapezoidal and trapezoidal fluted) were used with 10 screws in each group. The mini implants were loaded on to the polyurethane foam block (Sawbones pacific research lab, USA) perpendicular to the surface and the pull out strength was tested using the Instrom testing machine. The control group consisted of mini implants with reverse buttress thread shape. One-way ANOVA and Tukey post-hoc tests were used to compare the pull out strength of the mini implants within as well as between the different groups.

RESULTS

The mean in the pull out tests ranged from 13.45 N (trapezoidal) to 61 N (trapezoidal fluted). The tukey post-hoc tests showed a statistically significant difference of 34.5 N between the control group and the trapezoidal fluted group. The level of statistical significance showed p< 0.05.

CONCLUSION

Trapezoidal fluted mini implants showed the highest pull out strength when compared to mini implants with other thread designs used in this study. Further studies with the use of Finite Element Method (FEM) and foam blocks of higher density would be required to evaluate the performance of this new thread design.

Evaluation of mechanical strengths of three types of mini-implants in artificial bones

We investigates the effect of the anchor area on the mechanical strengths of infrazygomatic mini-implants. Thirty mini-implants were divided into three types based on the material and shape: Type A (titanium alloy, 2.0×12 mm), Type B (stainless steel, 2.0×12 mm), and Type C (titanium alloy, 2.0×11 mm).The mini-implants were inserted at 90° and 45° into the artificial bone to a depth of 7 mm, without predrilling. The mechanical strengths [insertion torque (IT), resonance frequency (RF), and removal torque (RT)] and the anchor area were measured. We hypothesized that no correlation exists among the mechanical forces of each brand. In the 90° tests, the IT, RF, and RT of Type C (8.5 N cm, 10.2 kHz, and 6.1 N cm, respectively) were significantly higher than those of Type A (5.0 N cm, 7.7 kHz, and 4.7 N cm, respectively). In the 45° test, the RFs of Type C (9.2 kHz) was significantly higher than those of Type A (7.0 kHz) and Type B (6.7 kHz). The anchor area of the mini-implants was in the order of Type C (706 mm²)>Type B (648 mm²)>Type A (621 mm²). Type C exhibited no significant correlation in intragroup comparisons, and the hypothesis was accepted. In the 90° and 45° tests, Type C exhibited the largest anchor area and the highest mechanical strengths (IT, RF, and RT) among the three types of mini-implants. The anchor area plays a crucial role in the mechanical strength of mini-implants.

A Comparison of the Mechanical Measures Used for Assessing Orthodontic Mini-Implant Stability

PURPOSE

Mechanical loosening remains a common complication associated with mini-implant failure. The purpose of this study was to compare common mechanical measures of mini-implant stability to determine their association and reliability.

MATERIALS AND METHODS

Ninety self-drilling orthodontic mini-implants from 6 manufacturers were inserted into artificial bone blocks. Insertion torques (ITs) and Periotest values (PVs) were measured. Subsequently, mini-implants underwent pull-out testing for measures of pull-out load (POL) and screw displacement (ScrD). Stability measurements were compared using one-way ANOVA, associations among them were assessed using correlation analyses, and reliability was evaluated using coefficients of variation (COVs).

RESULTS

Variations in stability of mini-implants were found, specific to the mechanical measure used for assessment (P < 0.05). The strongest correlations were found between IT and PV (r = -0.68) and between IT and POL (r = 0.66). Overall, PV showed the greatest variability (COV: 11%-100%) compared with IT (≤11%), POL (≤4%), and ScrD (≤19%).

CONCLUSIONS

IT, PV, and POLs only agreed moderately in their assessment of mini-implant stability, and Periotest showed the least reliability in predicting mini-implant stability. As such, independent and interchangeable use of these stability measures should be avoided.

Surface analysis of 2 orthodontic mini-implants after clinical use

INTRODUCTION

The purpose of this study was to analyze the design and surface morphology of 2 brands of mini-implants before and after 12 to 18 months of clinical use.

METHODS

We studied 22 mini-implants sold in the Brazilian market by 2 companies (Forestadent, Pforzheim, Germany; and Dental Morelli, Sorocaba, São Paulo, Brazil). The surface morphology of the mini-implants was analyzed by scanning electron microscopy before and after insertion in the oral environment to aid orthodontic movement.

RESULTS

The Forestadent and the Morelli mini-implants showed different shapes (size, screw thread design), and the surface morphology changed after clinical use. The most important surface morphology alterations after clinical use were strain in several parts and fracture of the active thread part of some mini-implants.

CONCLUSIONS

The results of the analyses showed that the screw threads of the mini-implants differ in pitch, angle, and length. The mini-implants also showed differences in body design, active tip, and taper. These differences affect the performance of the mini-implants. After clinical use, all mini-implants showed surface degradation, plastic deformation, and some fractures.

Stress distributions of a bracket type orthodontic miniscrew and the surrounding bone under moment loadings: Three-dimensional finite element analysis

Objectives:

To evaluate the effect of moments and the combination of forces and moments on the mechanical properties of a bracket type miniscrew, resembling engagement of a rectangular wire by three-dimensional (3D) finite element study.

Materials and Methods:

By solid work software (Dassaunlt systems solid works, concord, Mass), a 3D miniscrew model of 6, 8, 10 mm lengths was designed and inserted in the osseous block, consisted of the cortical, and cancellous bones. The stress distributions, maximum stresses, and deflections of the miniscrew were evaluated for all parts using ANSYS (Work Bench, 2014).

Results:

As the magnitudes of the load increased from 100 to 200, 400 and 800 grf-mm, the peak of stresses in the 6 mm long miniscrew were increased from 7.7 to 61.5 Mpa. The maximum values of Von Mises in the cancellous bone were tremendously lower in comparison to the cortical bone by one hundredth. As the length of the miniscrew in contact with the bone was increased, the amounts and patterns of stress distribution in the cortical bone and the miniscrew did not change significantly.

Conclusions:

As the moment magnitude increased, the pick stresses increased linearly. The existence of cancellous bone was not significantly responsible for the stress distribution. The pattern of stress distribution did not change by the length of the miniscrew.

Finite Element Analysis of Bone Stress around Micro-Implants of Different Diameters and Lengths with Application of a Single or Composite Torque Force

Background

Stress on the bone surrounding dental micro-implants affects implant success.

Purpose

To compare the stress on the bone surrounding a micro-implant after application of a single force (SF) of 200 g or a composite force (CF) of 200 g and 6 N.mm torque.

Materials and Methods

Finite element models were developed for micro-implant diameters of 1.2, 1.6, and 2.0 mm, and lengths of 6, 8, 10, and 12 mm and either a SF or CF was applied. The maximum equivalent stress (Max EQS) of the bone surrounding the micro-implant was determined, and the relationships among type of force, diameter, and length were evaluated.

Results

The Max EQS of the CF exceeded that of the SF (P< 0.05). The effect of force on stress was related to implant diameter, but not to implant length. The larger CF led to greater instability of the micro-implant and the effect was most pronounced at an implant diameter of 1.2 mm. The use of implant diameters of 1.6 mm and 2.0 mm produced no significant difference in implant stability when either a CF or SF was applied.

Conclusion

When considering the use of an implant to perform three-dimensional control on the teeth, the implant diameter chosen should be > 1.2 mm.

Insertion angle of orthodontic mini-implants and their biomechanical performance: finite element analysis

AbstractObjectiveThe aim of this study was to assess the stresses and strains generated after the application of two types of forces (traction of 200 gf and torsion of 20 N.cm) in two types of orthodontic mini-implants inserted at different (45° and 90° to the cortical bone) angles.Material and methodthree-dimensional models of two brands of mini-implant (SIN – Sao Paulo, Brazil, and RMO – South Korea) were exported and analyzed by finite element analysis (FEA). Analyses were performed on simulations of cortical bone, cancellous bone and the screw.ResultFEA analysis showed that RMO mini-implants had greater elastic deformation when subjected to tensile and torsional forces when compared with SIN mini-implants. For both trademarks and insertion angles tested, there was greater cortical bone deformation, but with the greatest strain located on the mini-implant. Tension on the mini-implant was located in its transmucosal profile region.ConclusionWhen comparing the two brands of mini-implants by FEA, it is fair to conclude that that the larger number of threads and their greater angle of inclination resulted in less resistance to deformation and induced a higher level of tension in the mini-implant and cortical bone when subjected to forces, especially when inserted at an angle of 45º to the cortical bone.

Influence of Screw Length and Bone Thickness on the Stability of Temporary Implants

The purpose of this work was to study the influence of screw length and bone thickness on the stability of temporary implants. A total of 96 self-drilling temporary screws with two different lengths were inserted into polyurethane blocks (n = 66), bovine femurs (n = 18) and rabbit tibia (n = 12) with different cortical thicknesses (1 to 8 mm). Screws insertion in polyurethane blocks was assisted by a universal testing machine, torque peaks were collected by a digital torquemeter and bone thickness was monitored by micro-CT. The results showed that the insertion torque was significantly increased with the thickness of cortical bone from polyurethane (p < 0.0001), bovine (p = 0.0035) and rabbit (p < 0.05) sources. Cancellous bone improved significantly the mechanical implant stability. Insertion torque and insertion strength was successfully moduled by equations, based on the cortical/cancellous bone behavior. Based on the results, insertion torque and bone strength can be estimate in order to prevent failure of the cortical layer during temporary screw placement. The stability provided by a cortical thickness of 2 or 1 mm coupled to cancellous bone was deemed sufficient for temporary implants stability.

Tensile mechanical properties of swine cortical mandibular bone

Temporary orthodontic mini implants serve as anchorage devices in orthodontic treatments. Often, they are inserted in the jaw bones, between the roots of the teeth. The stability of the mini implants within the bone is one of the major factors affecting their success and, consequently, that of the orthodontic treatment. Bone mechanical properties are important for implant stability. The aim of this study was to determine the tensile properties of the alveolar and basal mandible bones in a swine model. The diametral compression test was employed to study the properties in two orthogonal directions: mesio-distal and occluso-gingival. Small cylindrical cortical bone specimens (2.6 mm diameter, 1.5 mm thickness) were obtained from 7 mandibles using a trephine drill. The sites included different locations (anterior and posterior) and aspects (buccal and lingual) for a total of 16 specimens from each mandible. The load-displacement curves were continuously monitored while loading half of the specimens in the oclluso-gingival direction and half in the mesio-distal direction. The stiffness was calculated from the linear portion of the curve. The mesio-distal direction was 31% stiffer than the occluso-gingival direction. The basal bone was 40% stiffer than the alveolar bone. The posterior zone was 46% stiffer than the anterior zone. The lingual aspect was stiffer than the buccal aspect. Although bone specimens do not behave as brittle materials, the diametral compression test can be adequately used for determining tensile behavior when only small bone specimens can be obtained. In conclusion, to obtain maximal orthodontic mini implant stability, the force components on the implants should be oriented mostly in the mesio-distal direction.

Strain of bone-implant interface and insertion torque regarding different miniscrew thread designs using an artificial bone model

OBJECTIVES

To evaluate the initial stability of dual-thread miniscrews by analyzing the strain at the bone-implant interface and insertion torque during implantation in artificial bone models with different cortical bone thicknesses.

MATERIALS AND METHODS

Insertion torque, and strain, measured with a five-element strain gauge in 1.0, 1.5, and 2.0-mm artificial cortical bone, during insertion of single- (OAS-T1507) and dual-thread (MPlant-U3) type self-drilling miniscrews were assessed.

RESULTS

Both dual- and single-thread miniscrews showed greater than 7790 μstrain for all cortical bone thicknesses, and dual-thread miniscrews reached up to 19580 μstrain in 2.00 m m cortical bone. The strain of dual-thread miniscrews increased with increasing cortical bone thicknesses of 1.0-2.0mm. For single-thread miniscrews, the maximum insertion torque was relatively constant, but maximum insertion torque increased significantly in dual-thread groups with increasing cortical bone thicknesses (P < 0.0001). The maximum insertion torque with all cortical bone thicknesses was significantly lower with single- than dual-thread types (P < 0.0001).

CONCLUSIONS

Self-drilling dual-thread miniscrews provide better initial mechanical stability, but may cause strain over the physiological bone remodelling limit at the bone-implant interface in thick cortical bone layers.

Optimal asymmetric thread for orthodontic microimplants: Laboratory and clinical evaluation

OBJECTIVES

To investigate the performance of microimplants incorporating a newly designed asymmetric thread.

MATERIALS AND METHODS

Three microimplants were compared. The control group comprised microimplants with the original v-shaped thread. The two experimental groups (Taper 1.0 and Taper 1.25) comprised prototype microimplants constructed with the new asymmetric thread; the Taper 1.25 specimens had a 1.25-mm-long and sharper tip, while the Taper 1.0 and control groups had a less sharp 1-mm tip. Two specially designed artificial bone blocks mimicking soft (maxillary) and hard (mandibular) bone were used to evaluate the microimplant insertion characteristics and postinsertion lateral stability. The peak insertion torque, insertion time, Periotest value (PTV), and torsional strength were measured. Then the microimplants were evaluated clinically over a 3-month period.

RESULTS

Significant differences in peak insertion torque, insertion time, and PTV were observed and favored the experimental groups. Although statistically insignificant, the clinical success rate was also higher in the Taper 1.25 experimental group than in the control group (87.2% vs 75.6%).

CONCLUSIONS

The better performances of the experimental microimplant, under both laboratory and clinical conditions (although statistically insignificant in the latter), demonstrate the superiority of the new asymmetric thread.

Bivariate optimization of orthodontic mini-implant thread height and pitch

PURPOSE

Mini-implants have been used as anchorage for years, but failure is common in clinical practice. Mini-implant design is a critical factor affecting its stability. The aim of this study was to evaluate the effect of continuous and simultaneous variations of thread height and pitch on the biomechanical properties of an orthodontic mini-implant.

METHOD

A 3D finite element model, composed of a posterior maxilla section and an orthodontic mini-implant, was created. Mini-implant thread height ranged from 0.10 to 0.40 mm, and thread pitch ranged from 0.50 to 2.00 mm. Effects of the implant thread height and pitch on the maximum Von Mises stresses in maxilla and mini-implant, as well as maximum displacements in the mini-implant, were evaluated by a finite element method. Bivariate analysis was used to determine the optimal range of thread height and pitch.

RESULTS

Variation of thread height and pitch decreased the maximum Von Mises stresses in cortical bone, cancellous bone and mini-implant by 54.9, 78.4 and 23.6 %, respectively. The maximum displacement in the mini-implant decreased by 21.8 %.

CONCLUSION

Maxillary stress and mini-implant stability were influenced by mini-implant thread height and pitch. Increased thread height with a thread pitch of 1.20 mm was better for orthodontic mini-implant in the maxillary posterior region. Thread height played a more significant role than the thread pitch in reducing maxillary stress and enhancing orthodontic mini-implant stability.