Effect of placement angle on the stability of loaded titanium microscrews: a microcomputed tomographic and biomechanical analysis

Comparative analysis of anchorage strength and histomorphometric changes after implantation of miniscrews in adults and adolescents: an experimental study in Beagles

OBJECTIVES

This study aimed to explore the differences in anchorage strength and histomorphometric changes in orthodontic miniscrews between adult and adolescent beagles.

MATERIAL AND METHOD

Six adult beagles and six young beagles were used as experimental subjects, and eight miniscrews were symmetrically placed in the posterior mandible of each dog. Measurement of the displacement (mm) of two adjacent miniscrews after load application was performed to compare the anchorage strength between the adult and adolescent groups. Three intravital bone fluorochromes (oxytetracycline, calcein green, xylenol orange) were administered postoperatively to mark the active bone-forming surface. Subsequently, the mineral apposition rate and bone-implant contact ratio were measured for dynamic and static histomorphometry. Finally, the expression levels of the RANKL/OPG ratio were evaluated by immunohistochemistry.

RESULTS

The average displacement of miniscrews in the adult group was significantly less than that in the adolescent group after load application. For histomorphometry analysis, the mineral exposure rate in the adolescent group was higher than that in the adult group with or without force application. In addition, more fractures and new bone formation but deceased bone-implant contact ratios were observed in the adolescent group than in the adult group. The ratio of RANKL/OPG expression increased more in the adolescent group than in the adult group.

CONCLUSION

Miniscrews do not remain in the same position as skeletal anchors, and the amount of displacement was higher in adolescent group than that in adult group, reflecting the weaker anchorage strength of miniscrews in adolescents due to the higher bone turnover rate and active bone remodelling. Therefore, it is feasible to apply orthodontic loading to the miniscrews in adult patients earlier, even immediately, but it is recommended to wait a period for the adolescents.

Analysis for Predictors of Failure of Orthodontic Mini-implant Using Patient-Specific Finite Element Models

In this study, we analyzed the clinical factors and mechanical parameters for predicting orthodontic mini-implant (OMI) failure in the mandible, which has different properties from the maxilla. A patient-specific finite element analysis was applied to 32 OMIs (6 failures and 26 successes) implanted between the mandibular second premolars and first molars used for anchorage. The peak stress and strain parameters were calculated for each sample. A logistic regression of the failure (vs. success) of OMIs on the mechanical parameters in the models was conducted. In addition, the influence of clinical factors on the mechanical parameters considered to be related to OMI failure was examined by a regression analysis. The mechanical parameter which best predicts OMI failure in the mandible was found to be a minimum principal strain of between 0.5 to 1.0 mm from the OMI surface (R² = 0.8033). The results indicate the patient's bone density, distance between the OMIs and adjacent root, and vertical implantation angle of the OMIs are potential clinical predictors of OMI failure in the mandible.

Miniscrews for orthodontic anchorage: analysis of risk factors correlated with the progressive susceptibility to failure

INTRODUCTION

The phenomenon of orthodontic anchorage miniscrews loosening after being implanted several times happens in daily clinical practice, and the reasons need to be traced. This study aimed to investigate the underlying risk factors influencing the progressive susceptibility of orthodontic miniscrews to failure.

METHODS

Overall, 889 miniscrews were successively inserted into 347 patients because some loosened or fell off once, twice, or more before achieving their purposes. The number of miniscrew failures (ie, once, twice, or more) was defined as progressive susceptibility to failure. The clinical indicators were assessed via univariate analysis, multicollinearity diagnosis, and Poisson log-linear regression model with stepwise calculation to screen out.

RESULTS

The progressive susceptibility of miniscrews to failure was proved to be affected by the age of patients, the onset of force application, site of placement, and appliance type. Age and onset of force application presented a negative relationship with susceptibility. Miniscrews inserted in the palatal region appeared to be more stable than the forepart of the arch. In contrast, the retromaxillary and retromandibular areas obtained the lowest stability. The patients with fixed appliances were more unlikely to suffer progressive failure than removable appliances. In addition, the larger number of screws inserted in each patient, the greater probability of failure.

CONCLUSIONS

Younger people with removable appliances that miniscrews inserted in the retromaxillary or retromandibular regions and earlier onsets of loading had a higher progressive susceptibility to loosening. Meanwhile, the failure rate was elevated with the increasing number of screws per patient received.

Effect of miniscrew insertion angle in the maxillary buccal plate on its clinical survival: a randomized clinical trial

INTRODUCTION

This study sought to assess the effect of miniscrew insertion angle (vertical and oblique) on its clinical survival under shearing forces in orthodontic patients undergoing canine retraction.

MATERIALS AND METHODS

In this split-mouth randomized controlled clinical trial, 50 miniscrews were placed bilaterally in 25 patients with 45° and 90° insertion angles relative to a line perpendicular to the occlusal plane distal to the maxillary first premolar extraction site. Allocation of insertion angles to the right/left side was random using the Random Allocation Software. The patients, clinician, and statistician were blinded to the allocation of miniscrews to the side of jaw. The patients were followed-up monthly for 6 months. The primary outcome was the clinical survival of miniscrews, which was evaluated at each follow-up session. The secondary outcomes were the miniscrew stability based on the Periotest value (PTV) and the level of pain experienced by patients at 1, 12, and 24 h, and 7 days after miniscrew placement using a visual analog scale (VAS). Data were analyzed using paired t-test, repeated measures ANOVA, and McNemar's test.

RESULTS

The clinical survival rate of miniscrews placed at 90° and 45° angles was 76% and 88%, respectively. This difference was not statistically significant (P = 0.375). No significant difference was noted between the two groups regarding the PTV or the pain score either (P > 0.05).

CONCLUSION

Clinically, the insertion angle of miniscrews (90° versus 45° relative to a line perpendicular to the occlusal plane) has no significant effect on the miniscrew survival rate or stability during orthodontic treatment.

TRIAL REGISTRATION

This trial was registered at www.irct.ir ( IRCT20190901044659N1 ).

PROTOCOL

The protocol was published after trial commencement.

Stress distribution patterns in mini-implant and bone in the infra-zygomatic crest region at different angulations: A finite element study

PURPOSE

To evaluate, using the finite element method (FEM), von Mises stress patterns produced both in a mini-implant (MI) and the infra-zygomatic crest region (IZC) at different placement angles and force magnitudes.

MATERIAL AND METHODS

FEM modeling of an infra-zygomatic crest MI, of dimensions 2 mm × 12 mm, was designed and placed in the IZC bone. The MI was inserted at 50°, 60°, 70°, 80°, and 90° angulations to the IZC surface. Simulated orthodontic forces of magnitudes 8, 9, 10, 11, and 12 oz were applied to the MI head. Von Mises stress and magnitude both in the MI and surrounding bone were measured.

RESULTS

Von Mises stress in the MI and bone was maximum at 90°. Least stresses were observed at 50° and 60° angulations. As force magnitude increased, von Mises stress increased linearly. Maximum stresses in the MI and bone were observed when loads were 12 oz and minimum stresses were observed at 8 oz.

CONCLUSION

To achieve optimum primary stability, angles of insertion between 50° and 60° are recommended in the IZC region. Highest von Mises stress values were detected in the MI, followed by cortical and cancellous bone. Also, loading force between 8 and 12 oz exerted stresses below the tolerable threshold of bone and MI. Hence, proper placement of MI in IZC using these findings might provide better biomechanical stability during retraction and may help in preserving the bone-implant interface.

Simulation of miniscrew-root distance available for molar distalization depending on the miniscrew insertion angle and vertical facial type

Objective

The purpose of this study was to evaluate the effects of miniscrew insertion angle and vertical facial type on the interradicular miniscrew–root distance available for molar distalization.

Materials and methods

Cone-beam computed tomography images of 60 adults with skeletal Class I occlusion exhibiting hyperdivergent (n = 20), normodivergent (n = 20), and hypodivergent (n = 20) facial types were used. Placement of a 6-mm long, 1.5-mm diameter, tapered miniscrew was simulated at a site 4 mm apical to the cementoenamel junction, with insertion angles of 0°, 30°, 45°, and 60° relative to the transverse occlusal plane. The shortest linear distance between the miniscrew and anterior root at four interradicular sites was measured: maxillary second premolar and first molar (Mx 5–6), maxillary first and second molars (Mx 6–7), mandibular second premolar and first molar (Mn 5–6), and mandibular first and second molars (Mn 6–7).

Results

Miniscrew–root distance significantly increased as the insertion angle increased from 0° to 60°. In the mandible, the distances significantly differed among vertical facial types, increasing in the following order: hyperdivergent, normodivergent, and hypodivergent. The minimum mean distance was found in the Mx 6–7 (30°; 0.86±0.35 mm), and the maximum mean distance was found in the Mn 5–6 (60°; 2.64±0.56 mm). The rates of miniscrews located buccally outside the root distalization path were up to 70% and 55% when the miniscrews were placed at 60° insertion angles in the Mx 5–6 and Mn 5–6 regions, respectively.

Conclusions

Miniscrew–root distance increased significantly with the increased insertion angle, and the amount of increase was affected by the miniscrew placement site and vertical facial type. To ensure adequate distalization of the posterior segment, the miniscrew should be inserted at an angle in the interradicular area between the second premolar and first molar.

The ideal insertion angle after immediate loading in Jeil, Storm, and Thunder miniscrews: A 3D-FEM study

OBJECTIVE

The miniscrew is effectively used to provide additional anchorage for orthodontic purposes. The aim of this study was to identify an optimal insertion angle for Jeil, Storm, and Thunder miniscrews on stress distribution at the bone miniscrew interface.

MATERIALS AND METHODS

To perform 3-dimensional finite element model analysis, a 3-dimensional model with a bone block was constructed with type D2 of bone quality, and with miniscrews of Storm, Thunder, Jeil, with the diameter of 2, 1.5. 1.6mm and length 15.9, 12.4, 14.4mm respectively. The miniscrews were inserted at 15° 30°, 45°, 60°, 75° and 90° to the bone surface. A simulated horizontal orthodontic force of 200 gram was applied to the centre of the miniscrews head in all models, and stress distribution and its magnitude were evaluated with a 3-dimensional finite element analysis program.

RESULTS

In the cancellous bone, minimum stress was found at placement angles of 90° for Jeil and Storm, which was 0.37 and 0.39MPa respectively, and 15° for Thunder, which was 0.85MPa. The maximum von Mises stresses in the cancellous bone for Jeil was at 60°, which was 0.92MPa, and for Thunder at 90°, which was 1.3MPa.

CONCLUSION

Each miniscrew has an ideal insertion angle, optimal insertion positions were found within 90° for Jeil and for Storm but 15° for Thunder. Clinical significance 3-dimensional finite element analysis confirmed that each miniscrew has an ideal insertion angle according to its characteristics.

Evaluation of stress generation on the cortical bone and the palatal micro-implant complex during the implant-supported en masse retraction in lingual orthodontic technique using the FEM: Original research

Background. This study aimed to evaluate and analyze the distribution of stresses on the palatal micro-implants and the cortical bone at the micro-implant site with optimal orthodontic retraction force in lingual orthodontics. Methods. ANSYS 12.1 software was used to construct the finite element model of the maxillary bone, teeth and the periodontal ligament along with the lingual bracket set-up with wire and the micro-implant. Six- and 8-mm micro-implants were constructed. The final model consisted of 99190 nodes and 324364 elements. A 200-gram of retraction force was applied from the micro-implant to the anterior retraction hook. The micro-implant was embedded between the second premolar and the first molar. Hyper-view software was used to get the results in X-Y-Z dimensions. Results. The maximum von Mises stresses detected were 52.543 MPa for 6-mm micro-implant and 54.489 MPa for 8-mm micro-implant. Maximum stress was at the neck of the micro-implant. The 8-mm implant model showed 6×10-3 mm of lingual displacement. The least displacement of 1×10-3 mm was noticed for both the implant models in the apico-occlusal direction. The maximum von Mises stresses in the cortical bone at the micro-implant site was 18.875 MPa for 6-mm micro-implant and 21.551 MPa for 8-mm micro-implant. Conclusion. Six-mm micro-implant can be the choice for the implant-supported lingual orthodontic retraction as it produced minimal stresses on the cortical bone, and the initial stress displacements produced on the micro-implant were also minimal.

Stress distributions in peri-miniscrew areas from cylindrical and tapered miniscrews inserted at different angles

Objective

The purpose of this study was to analyze stress distributions in the roots, periodontal ligaments (PDLs), and bones around cylindrical and tapered miniscrews inserted at different angles using a finite element analysis.

Methods

We created a three-dimensional (3D) maxilla model of a dentition with extracted first premolars and used 2 types of miniscrews (tapered and cylindrical) with 1.45-mm diameters and 8-mm lengths. The miniscrews were inserted at 30°, 60°, and 90° angles with respect to the bone surface. A simulated horizontal orthodontic force of 2 N was applied to the miniscrew heads. Then, the stress distributions, magnitudes during miniscrew placement, and force applications were analyzed with a 3D finite element analysis.

Results

Stresses were primarily absorbed by cortical bone. Moreover, very little stress was transmitted to the roots, PDLs, and cancellous bone. During cylindrical miniscrew insertion, the maximum von Mises stress increased as insertion angle decreased. Tapered miniscrews exhibited greater maximum von Mises stress than cylindrical miniscrews. During force application, maximum von Mises stresses increased in both groups as insertion angles decreased.

Conclusions

For both cylindrical and tapered miniscrew designs, placement as perpendicular to the bone surface as possible is recommended to reduce stress in the surrounding bone.

Comparison of transverse changes during maxillary expansion with 4-point bone-borne and tooth-borne maxillary expanders

INTRODUCTION

The purposes of this study were to evaluate and compare the dentoskeletal changes concurrent with 4-point bone-borne and tooth-borne rapid maxillary expanders in growing children.

METHODS

The study was conducted with 20 growing girls (ages, 12 ± 0.6 years) with posterior crossbite. They were divided into 2 equal groups; patients in one group were treated with a tooth-borne maxillary hyrax expander (TBME), and those in the other group received a bone-borne maxillary hyrax expander (BBME) anchored directly to the palatal bone. Changes were assessed using cone-beam computed tomography. Images were taken before and immediately after expansion.

RESULTS

Superimpositions of the 3-dimensional palatal images showed significant increases in skeletal widths at the canine, first premolar, and first molar areas in both groups. The TBME group had greater nasal width expansion. Regarding the transverse dentolinear measurements, significant increases were seen in both groups, whereas the TBME group showed a greater increase than the BBME group. Significant increases in the dentoangular measurements were seen in the TBME group only and were significantly greater than in the BBME group at the first premolars.

CONCLUSIONS

There were significant increases in facial and maxillary widths for the BBME group and in nasal width for the TBME group. Both expanders produced basal bone expansion at the level of the hard palate. The TBMEs produced more dental expansion, buccal rolling, and a greater increase in nasal width than did the BBMEs.

Orthodontic Microimplants Assisted Intrusion of Supra-erupted Maxillary Molar Enabling Osseointegrated Implant Supported Mandibular Prosthesis: Case Reports

Loss of mandibular molars, when not replaced in time, are usually associated with overeruption of maxillary molars. To provide prosthetic replacement for missing lower posteriors, over erupted maxillary teeth have been intruded in past with great difficulty in adults with conventional orthodontics, along with associated problems of root resorption. Currently orthodontic microimplants provide stable intraoral anchorage, allow predictable maxillary molar intrusion enabling reestablishment of functional posterior occlusion with mandibular implant supported prosthesis, thereby reducing need for prosthetic crown reduction in maxillary arch. The added advantage of microimplant is it enables use of sectional appliance in area of concern instead of full arch bracketed appliance which an adult may not accept. The case reports demonstrates, overerupted maxillary molars were intruded using orthodontic microimplants to enable prosthetic rehabilitation of mandibular dentition by osseointegrated implant supported prosthesis. The second case report also demonstrates use of CBCT scan in planning and execution.

Effect of placement angle on the stability of loaded titanium microscrews in beagle jaws

OBJECTIVE

To evaluate the effect of insertion angle on stability of loaded titanium microscrews in beagle jaws.

MATERIALS AND METHODS

Forty-eight microscrews were inserted at four different angles (30°, 50°, 70°, and 90°) into the intraradicular zones of the mandibular first molars and third premolars of 12 beagles and immediately loaded with a force of 2 N for 8 weeks. Microcomputed tomography (micro-CT) and biomechanical pull-out tests were used to assess osseointegration of the interface.

RESULTS

All micro-CT parameters and maximum pull-out force (FMAX) of the microscrews were affected by insertion angles of microscrews. Higher micro-CT parameters and FMAX were seen for implants inserted at angles between 50° and 70° (P < .05). Excessive oblique and vertical insertion angles resulted in reduced stability (P < .05).

CONCLUSION

An insertion angle of 50° to 70° is more favorable than excessive oblique or vertical angles to achieve stability of microscrews.

Biomechanical evaluation of an orthodontic miniimplant used with revolving (translation and rotation) temporary anchorage device by finite element analysis and experimental testing

PURPOSE

To evaluate the biomechanical interactions of a miniimplant using a temporary anchorage device (TAD) for orthodontic traction.

MATERIALS AND METHODS

A miniimplant was designed with dual thread (DT) with a TAD that can be connected optionally onto the miniimplant with 60-degree switching unit and an extended arm for tying orthodontic wire. Finite element analysis was used to calculate the relative miniimplant displacement and bone strain under immediate load (500 gW) on behalf of the maximum lateral force during orthodontic treatment. The TAD removal forces were measured by pullout testing.

RESULTS

Simulated results showed that the maximum von Mises bone strain concentrated at the cervical regions around the miniimplant. The corresponding strain value in DT miniimplant assembled with TAD was greater than those for DT and single-thread implants with 2.24 and 1.73 times, respectively. Small relative miniimplant displacement (<20 μm) was found in all cases. The TAD removal force remained larger than 2 times the finger-pulling force (9.3 N) after 5 repeated removal tests.

CONCLUSION

The DT miniimplant connected with TAD can provide translation and rotation features to change the angles and directions of orthodontic tractions for most effective anchorage preparation.

Biomechanical evaluation of an orthodontic mini-implant with plastic removal cap: an in-vitro experimental testing

This study evaluates the biomechanical interactions of a mini-implant using a plastic revolving cap (PRC) with translation/rotation features for optional orthodontic traction. An orthodontic mini-implant and the PRC consisting of a hexagon connection onto mini-implant with 60 degree switching unit and an extended arm to provide orthodontic wire tied at different positions. The PRC removal force was measured by pull-out testing. The PRC removal force remained larger than three times the finger pulling force (9.3N) after 5 repeated removal tests. The results for the PRC resistant testing showed that the PRC rotational resistant force (20.31±0.83N) is larger than the maximum traction force (about 4.9N) for orthodontic treatment. The mini-implant used with PRC can provide translation and rotation features to change the angles and directions of orthodontic tractions for most effective anchorage preparation under safety consideration.