Length Of Miniscrew Research Articles

A biomechanical investigation of miniscrews placed on a mandible for temporary anchorage; a patient-specific finite element analysis

Miniscrews are temporary skeletal anchorage devices that are widely used in orthodontic treatment, and their success depends on the placement area, angle, technique, and screw dimensions. This study aimed to investigate the effects of miniscrew lengths, insertion angles, and force directions on a mandible model consisting of teeth, cortical and cancellous bones. One Dental Volumetric Tomography (DVT) scan from a patient who had miniscrews were used for mandibular bone modeling to perform finite element analysis. The model variables included miniscrew lengths (6, 8, and 10 mm), insertion angles (−15°, 45°, 60°, and 90°), and force directions (30°, 45°, and 60°). The minimum and maximum stresses were calculated as 18.61 and 37.11 MPa at 6 mm and 10 mm, respectively. According to the insertion angles, the lowest stress was observed at 60°, while the highest stress was found at 15° in the ventral direction. At force directions, the lowest stress was at 60°, and the highest stress was at 45°. However, there were no significant differences in insertion angles and force directions. A statistically significant difference was determined in miniscrew length. As a result, the best result was calculated to be 6 mm inserted at a 60° angle, which could induce the lowest stress. Increasing the miniscrew length will increase the stress on the mandible. In addition, because of the higher force direction, stress decreases with shorter power arms.

How palatal vault morphology and screw length influence the accuracy of dynamic computer-guided orthodontic miniscrew insertion. A prospective clinical study

ObjectivesThe aim of this study was to evaluate the influence of palatal vault morphology and screw length on the accuracy of miniscrew insertion in dynamic computer-assisted surgery (d-CAS). MethodsTwenty-four subjects were allocated into three groups, according to their palatal vault morphology (Group A: medium; Group B: steep/high; Group C: low/flat) and the length of miniscrew used. For each subject, two miniscrews were inserted using a dynamic navigation system. To assess the accuracy of insertion, a postoperative CBCT was performed, and the pre- and post-operative scans were superimposed. Five variables were evaluated: Entry-3D, Entry-2D, Apex-3D, Apex-vertical and angular deviation. Descriptive statistics, Shapiro-wilk, Kruskal-Wallis and Dunn's tests were used for the statistical analysis. The level of significance was P ≤ 0.05. ResultsThe mean angular deviation values revealed strong discrepancies amongst the groups (Group A:7.11°±5.70°; Group B:13.30°±7.76°; Group C:4.92°±3.15°) and significant differences were found regarding the Apex-3D (P = 0.036) and angular deviations (P = 0.008). A Dunn's test revealed differences in angular deviation between the medium and high/steep palate group (P = 0.004), and between low/flat and high/steep palate group (P = 0.01) but did not confirm any significant difference in the Apex-3D parameter (Group A-B P = 0.10; Group B-C, P = 0.053; Group A-C, P = 1.00). No significant differences were found regarding the length of the miniscrews. ConclusionsPalatal vault morphology is a factor that influences the accuracy of miniscrew insertion in d-CAS. In subjects with steep and high palatal vaults, insertion accuracy is lower when considering the angular deviation value. Miniscrew length does not influence accuracy. Clinical significanceAlthough computer-guided surgery assists the clinician in preventing damage to nearby anatomical structures, individual anatomical variability is a crucial variable. In subjects with a high/steep palate, greater attention should be paid during the planning phase in order to allow for a wide margin from adjacent anatomical structures to achieve better outcomes.

Reliability and safety of miniscrew insertion planning with the use of lateral cephalograms assessed on corresponding cone-beam computer tomography images.

Recently, lateral cephalograms have been proposed for guided miniscrew insertion planning. Therefore, the aim was to assess the reliability and safety of such planning on corresponding cone-beam computer tomography (CBCT) images. Intraoral scans, lateral cephalograms, and CBCT images of 52 subjects (even sexes distribution), aged 15.1 ± 2.5 years, were included. Miniscrew (n = 104) insertion planning was performed using lateral cephalograms superimposed on the maxillary intraoral scans, while the assessment of their bicortical placement, length in bone, contact with adjacent teeth, incisive canal, and nasal floor perforation was done on corresponding superimposed CBCT images. Moreover, maxillary incisor inclination, crowding, and the maxillary intercanine width were measured. The overall miniscrew length in bone was 7.2 ± 1.3mm. Bicortical placement was seen in 58.7% of the sample (38.5% of subjects). Incisive canal and nasal floor perforation was seen in 25% and 21.2% of subjects, respectively. No contact of the miniscrew with adjacent teeth was recorded. A negative significant interaction was seen between the miniscrew length in bone, the percentage of total miniscrew length and maxillary anterior teeth crowding (β, -0.10, P = .047 and β, -0.90, P = .006, respectively). Moreover, a positive significant interaction was seen between the incisive canal perforation and maxillary anterior teeth crowding (OR = 1.32, P = .021). Exclusion of subjects with impacted teeth. Miniscrew insertion planning using lateral cephalograms, despite being safe in preventing contact with adjacent teeth, is limited in achieving bicortical placement and insufficient in completely avoiding incisive canal and nasal floor perforation.

Does the Miniscrew Length, Insertion Level, and Insertion Force Make a Difference on the Stress and Strain Distribution Across the Alveolar Bone? A Finite Element Study

Objective The aim of this study was to evaluate, using the finite element method (FEM), the stresses generated on various parts of the mini-screw and on the bone resulting from the insertion of mini-screws of varying lengths and under different forces. Materials and Methods Three-dimensional models of mini-screws (1.6 × 6, 8, and 10 mm) and bone (mandible cortical bone thickness of 2 mm) were constructed and simulated using FEM. The mini-screws were inserted using force loads of 10 and 20 Ncm, and stress evaluation was carried out on screws and bone. The stress evaluation was also performed across different levels of insertion (at the point of insertion, half-insertion, and full insertion). Results A direct correlation between the force applied and the stresses on the body of the screws was observed. There was an inverse relationship between the length of the mini-screw and the resulting stress on the bone with the highest stress of 14.58 Mpa with 6 mm long and the minimum stress of 3.81 Mpa with longer mini-screws. On application of different force magnitudes, the stress levels increased linearly with a change in the length. The highest stresses on the bone were observed only when the screw was fully inserted in the bone. Conclusion When mini-screws of different lengths were inserted using different magnitudes of forces, the stress levels increased linearly on the bone. A combination of longer mini-screw and lesser force magnitude used during insertion produced less stress on the bone.

Do the miniscrews of the prefabricated systems for the “appliance first” protocol of miniscrew-assisted rapid palatal expansion have lengths that meet the palatal thickness of patients?

In the "appliance first" protocol of miniscrew-assisted rapid palatal expansion, the prefabricated shape of the expanders limits the potential locations for miniscrew placement. Considering the influence of palatal thickness on the selection of the optimal length of miniscrews, this study aimed to evaluate the thickness of both bone and mucosa of the palate of patients aged 6-65 years and suggest optimal lengths of miniscrews for this approach. Two hundred and eighty-two cone-beam computed tomography of patients of both sexes were divided into 3 groups according to age. The thicknesses of bone and mucosa were measured in the anterior and posterior regions of the palate. Males showed a greater thickness of palatal bone than females. The thickness of both bone and mucosa was greater in the anterior region of the palate. The young patients showed greater bone thickness than adults and mature adults. The mature adults showed thinner bone thickness in the posterior region of the palate and greater mucosal thickness along the palate than young patients and adults. Development of miniscrews with longer thread lengths is necessary. Miniscrews with a 3-mm thread length would prevent excessive extravasation in the posterior region of the palate. The thickness of both bone and mucosa of the palate is variable and influenced by sex and age. Manufacturing additional miniscrews with different lengths of thread is suggested to achieve bicortical anchorage in patients undergoing the "appliance first" protocol of miniscrew-assisted rapid palatal expansion.

Evaluation of bone depth, cortical bone, and mucosa thickness of palatal posterior supra-alveolar insertion site for miniscrew placement

BackgroundThe use of palatal miniscrew offers the possibility to improve the effectiveness of orthodontic expansion devices. Palatal expanders supported by miniscrew can be applied with different clinical protocols. Some authors proposed the use of four palatal miniscrews during miniscrew-supported palatal expansion to maximize skeletal effects in young adults’ treatment. However, bone availability decreases in the posterior paramedian palatal regions, making the positioning of the two-posterior paramedian palatal miniscrews challenging, when it is performed avoiding nasal cavities invasion. Some authors proposed miniscrews insertion in a specific region located laterally to the palatal process of the maxillary bone, and apically relatively to the dento-alveolar process. The aim of this study was to evaluate the bone thickness, cortical bone thickness, and mucosae depth of this anatomical site that, in this study, was defined as palatal posterior supra-alveolar insertion site.ResultsThe evaluation of bone availability of palatal posterior supra-alveolar insertion site at different antero-posterior levels showed that the maximum amount of total bone thickness was found between the second premolar and the first molar. At this level total bone, thickness is significantly (p < .05) greater compared to the other sagittal sites and it offers on average around 2 mm of extra bone depth for miniscrew placement. Cortical bone thickness is adequate for primary miniscrew stability. Overall, cortical bone thickness considered at different insertion sites showed significant statistically (p < .05) differences. The findings of this study showed that palatal mucosa is particularly thick with average values ranging from 4 to 7 mm, and its extension ultimately affects miniscrew length selection. Palatal mucosa thickness showed no clinically significant differences comparing different sagittal and vertical insertion sites. Data also showed that palatal mucosal thickness slightly significantly increases (p < .05) with the inclination of the insertion axis relative to the occlusal plane. Finally, study findings showed that vertical growth pattern can significantly affect considered outcomes (p < .05).ConclusionsPalatal posterior supra-alveolar insertion site is an appropriate site for posterior insertion of palatal miniscrews. Considering high anatomical variation preliminary CBCT evaluation is important to achieve optimal miniscrew placement.

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.

Analysis of biological and structural factors implicated in the clinical success of orthodontic miniscrews at posterior maxillary interradicular sites.

This study aims to evaluate success factors implicated in clinical orthodontic miniscrew stability after their interradicular placement in maxilla. Six hundred seventy-six miniscrews were inserted in maxillary interradicular sites in a sample of 276 patients (109 males and 167 females; mean age 19 ± 1.7years) and immediately loaded. Percentage failure rate was recorded, and the influence of the following factors was investigated: structural (miniscrew length, diameter and body shape), operative (side of insertion site, pilot hole drilling or not) and biological (maximal insertion torque [MIT] and type of gingiva). A chi-square test with Monte Carlo correction was performed to detect the influence of these variables on the failure rate of orthodontic miniscrews. Then both multivariate logistic regression and post hoc analysis were performed, followed by classification and regression tree (CART) analysis. The average success rate was 88%. The principal factors implicated in the failure rate were miniscrew length, MIT values and type of gingiva. Specifically, 8mm miniscrew length, alveolar mucosa and 5-10 Ncm MIT values were linked to higher failure rates. According to CART, the main variable influencing failure is miniscrew length (≤ 8mm for higher failure rates). For others, MIT values of 5-10 Ncm are linked to higher failure rates (p < 0.05). Orthodontic miniscrews inserted in the maxilla display good success rates. However, clinicians should be discouraged from using miniscrews of length ≤ 8mm and MIT values < 10 Ncm, even with longer miniscrews. Information about factors related to failure rate of miniscrews placed at posterior maxillary interradicular sites is given.

Periotest Evaluation of Stability after Insertion of Temporary Anchorage Device

Introduction: Skeletal anchorage devices was developed for absolute anchorage during orthodontictreatment. Because of immediate loading on orthodontic miniscrews, early stability became a essentialrequirement for loading forces on miniscrews.Objective: The aim of this study was to evaluate the early stability of the miniscrews after two weeks ofinsertion and the effect of the length and the side of insertion of the miniscrews on its stability using Periotestdevice.Material and Method: Thirty- three orthodontic patients in a collage clinic were recruited who requiredbilateral miniscrews for orthodontic anchorage. Under local anesthesia, each patient received two miniscrewsin the maxillary buccal area (one side 1.6x8mm and the other side 1.6x10mm). after two week early stabilitymeasured using Periotest device.Results: There was no significant different in stability of miniscrew between right and lift sides and betweenshort and long miniscrews.Conclusion: length of miniscrew and side of insertion do not affect the early stability of miniscrew.

Effects of Intrabony Length and Cortical Bone Density on the Primary Stability of Orthodontic Miniscrews.

Miniscrews have gained recent popularity as temporary anchorage devices in orthodontic treatments, where failure due to sinus perforations or damage to the neighboring roots have increased. Issues regarding miniscrews in insufficient interradicular space must also be resolved. This study aimed to evaluate the primary stability of miniscrews shorter than 6 mm and their feasibility in artificial bone with densities of 30, 40, and 50 pounds per cubic foot (pcf). The primary stability was evaluated by adjusting the intrabony miniscrew length, based on several physical properties: maximum insertion torque (MIT), maximum removal torque (MRT), removal angular momentum (RAM), horizontal resistance, and micromotion. The MIT and micromotion results demonstrated that the intrabony length of a miniscrew significantly affected its stability in low-density cortical bone, unlike cases with a higher cortical bone density (p < 0.05). The horizontal resistance, MRT, and RAM were affected by the intrabony length, regardless of the bone density (p < 0.05). Thus, the primary stability of miniscrews was affected by both the cortical bone density and intrabony length. The effect of the intrabony length was more significant in low-density cortical bone, where the implantation depth increased as more energy was required to remove the miniscrew. This facilitated higher resistance and a lower risk of falling out.

The thickness of posterior buccal attached gingiva at common miniscrew insertion sites in subjects with different facial types

The purpose of this study was to assess the thicknesses of maxillary and mandibular posterior buccal approximal attached gingiva at common miniscrew insertion sites, which has critical importance in determining miniscrew length, in subjects with different facial types. One hundred seventy-four subjects with no transversal skeletal discrepancy were included in this study. The facial types of these subjects were evaluated in the sagittal and vertical directions. In the sagittal direction, the subjects were assigned into 3 groups: skeletal Class I, II, and III. Also, each of these groups was divided into subgroups in the vertical direction: low angle, norm, and high angle. Transgingival probing was used to measure the thickness of the buccal attached gingiva. The thickness of the buccal attached gingiva between the second premolar-first molar ranged from 1.18±0.33 to 1.46±0.28 mm and from 1.28±0.30 to 1.58±0.37 mm in the maxilla and mandible, respectively. The thickness of the buccal attached gingiva between the first-second molars ranged from 1.31±0.41 to 1.60±0.62 mm and from 1.36±0.43 to 1.72±0.52 mm in the maxilla and mandible, respectively. In terms of the thicknesses of the buccal attached gingiva of second premolar-first molar and first-second molars, no statistically significant difference was found between subjects with different facial types. It was determined that the thicknesses of maxillary and mandibular posterior buccal approximal attached gingiva varied between 1.18-1.72. At this point, the insertion of miniscrews of 7-8mm in length was recommended for maxillary and mandibular posterior buccal regions, in order to obtain adequate insertion depth.

The effect of miniscrew length and bone density on anchorage resistance: An in vitro study

With conventional anchorage, it is usually hard to accomplish a satisfactory result with an absolute anchorage, and this limitation could be resolved by the usage of mini-screw. The successful rate of miniscrew usage depends on its stability, which was determined by its length, bone density, cortical bone thickness, the insertion technique, the insertion angle, and the applied loads. To observe the effect of miniscrew length and bone density on anchorage resistance. Thirty pieces of miniscrew with 1.6mm in diameter were divided into three groups based on its length (n=10): 10mm (L), 8mm (M), and 6mm (S). Each group was further divided into 2 sub-groups: to be planted in optimal density bovine ribs (L1, M1, S1) and to be planted in low-density bovine ribs (L2, M2, S2). The density of bovine ribs was measured by CBCT. After the insertion of miniscrews based on respective groups, tensile test was done by means of Autograf Univerval Testing Machine to measure its stability. The data recorded was analysed using the Least Significant Difference (LSD) Fisher's test. The results of this study showed that L1 provided the greatest stability than other groups. On the other hand, the least stability was found in S2. The length of miniscrew and the density of bone affect the stability of miniscrew. In bone with optimum density, 10mm and 8mm miniscrew equipped good anchorage resistance while in bone with low-density only 10mm miniscrew provided favourable anchorage resistance.

Effect Of changing various parameters on stress distribution in mini-screws and surrounding alveolar bone: a three dimensional finite element analysis

Aim: The purpose of the study was to clarify and evaluate the effects of various force magnitudes and mini-screw length, diameter and insertion angle on the stress distribution of the mini-screw and the surrounding bone utilizing a three dimensional finite element analysis. Methods: We created a three dimensional finite element model simulating various clinical situations where mini-screws with different diameters (1.5 and 2 mm), lengths (9, 11 and 13 mm) and insertion angles (45o and 90o) were utilized under various force magnitudes (200 and 250gm). The resultant deformations and stresses from the applied loading were analyzed with a 3D FEM according to maximum values of total deformations and Von Mises stress. Results: The Von Mises stresses in both the mini-screw and the cortical bone in obliquely inserted 1.5 mm diameter screws with 200 gm and 250gm force were higher than those with 2 mm diameter screws. The Von Mises stresses in the spongy bone in both the vertically and obliquely inserted 1.5 and 2 mm diameter screws with 200gm and 250gm force were higher with the 2 mm diameter screws. The maximum compressive stress and equivalent micro-strain in cortical bone was evident with screw dimensions 13mm length and 2mm diameter under an oblique force magnitude of 250 gm. The Von Mises stresses in the spongy bone in obliquely inserted 1.5 and 2 mm diameter screws with 200gm and 250gm force were higher with the 2 mm diameter screws The maximum stress (Von Mises) generated in the miniscrew and cortical bone in all the simulated finite element models was 72.77 and 13.52 MPa respectively. Conclusion: Increase in the mini-screw diameter with both vertical and oblique insertion reduced the deformations and stresses within the mini-screw and cortical bone but increased the deformations and stresses within the spongy bone. Increase in the mini-screw length with vertical insertion had negligible effect. The deformation and stress values within the cortical bone were higher in oblique insertion than vertical insertion with both (200 and 250 gm) force

Influence of changing various parameters in miniscrew-assisted rapid palatal expansion: A three-dimensional finite element analysis.

ObjectiveThis study aimed to analyze the effect of changing various parameters of the bone-borne rapid palatal expander (RPE) using the finite element method (FEM).MethodsIn eight experimental groups, we investigated the effect of the number, position, and length of miniscrews; positional changes of the expander; and changes in the hook length on maxillary expansion. In finite element analysis, we compared the magnitude and distribution of stress, and the displacement changes following expansion of the bone-borne RPE.ResultsWhen we compared the number and position of miniscrews, placing miniscrews in the anterior and posterior sides was advantageous for maxillary expansion in terms of stress distribution and displacement changes. Miniscrew length did not significantly affect stress distribution and displacement changes. Furthermore, anteroposterior displacement of the expander did not significantly affect transverse maxillary expansion but had various effects on vertical changes of the maxilla. The maxilla rotated clockwise when the miniscrews were placed in the anterior region. The hook length of the expander did not show consistent results in terms of changes in stress distribution and magnitude or in displacement changes.ConclusionsThe findings of this study suggest that changes in the location and length of the miniscrews and displacement of the bone-borne RPE could affect the pattern of the maxillary expansion, depending on the combination of these factors.

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

To clarify the in vivo effect of an automatic embedding device on miniscrew stability. 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. 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. 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.

Pain and discomfort experience after miniscrew insertion as an anchorage device in orthodontic patients

Introduction: The aim of this study was to evaluate the degree of pain and discomfort experienced for 1 week after miniscrew insertion using a questionnaire survey. Materials and Methods: Thirty-nine miniscrews were inserted in the mandible and maxilla of 33 patients with a self-drilling JB head type miniscrew under local anesthesia. Patients were asked to rate the degree of pain and discomfort experienced on a visual analog scale (VAS) after 1 hour, 12 hours, 1 day, and 1 week . Data were analyzed using the Statistical Package for the Social Sciences version 22 software. Repeated measures analysis of variance (ANOVA) with considering the jaw, side of insertion, and length of miniscrew as a between subject factor was used. Results: There was no significant association between the length of miniscrew (P = 0.448), the jaw (P = 0.870), and the side of the insertion (P = 0.346) and causing pain. The maximum degree of pain experience was in 1 hour after insertion that was 48.79 mm in VAS scores, which started to decrease significantly after 12 hours, 1 day, and 1 week as the minimum intensity of the pain was 1 week after the miniscrew insertion that was 2.31 mm in VAS scores. Conclusion: On the basis of the patient responses, it can be concluded that miniscrew could be an acceptable option in orthodontic treatments.

A study of success rate of miniscrew implants as temporary anchorage devices in singapore.

Objective. To find out the success rate of miniscrew implants in the National Dental Centre of Singapore (NDCS) and the impact of patient-related, location-related, and miniscrew implant-related factors. Materials and Methods. Two hundred and eighty-five orthodontic miniscrew implants were examined from NDCS patient records. Eleven variables were analysed to see if there is any association with success. Outcome was measured twice, immediately after surgery prior to orthodontic loading (T1) and 12 months after surgery (T2). The outcome at T2 was assessed 12 months after the miniscrew's insertion date or after its use as a temporary anchorage device has ceased. Results. Overall success rate was 94.7% at T1 and 83.3% at T2. Multivariate analysis revealed only the length of miniscrew implant to be significantly associated with success at both T1 (P = 0.002) and T2 (P = 0.030). Miniscrew implants with lengths of 10–12 mm had the highest success rate (98.0%) compared to other lengths, and this is statistically significant (P = 0.035). At T2, lengths of 10–12 mm had significantly (P = 0.013) higher success rates (93.5%) compared to 6-7 mm (76.7%) and 8 mm (82.1%) miniscrew implants. Conclusion. Multivariate statistical analyses of 11 variables demonstrate that length of miniscrew implant is significant in determining success.

Inferior Level of Maxillary Sinus and Cortical Bone Thickness at Maxillary Posterior Quadrant, in Three Different Growth Patterns: 3D-Computed Tomographic Study

Objective of this retrospective study was to measure cortical bone thickness and lowest level of maxillary sinus at maxillary posterior quadrant in different growth pattern (hypodivergent, average, and hyperdivergent) at prospective microimplant placement sites in order to understand both safety and stability aspects of microimplant placement by using cone-beam 3-dimensional computed tomographic images. In posterior quadrant, vertical distance from cementoenamel junction to lowest level of maxillary sinus at interradicular region was measured. Buccal cortical bone thickness was measured at 3 different vertical levels at interradicular space. The cortical bone thickness was found more at sinus floor level and above it than below the sinus floor. In perspective of miniscrew placement, study shows that maxillary sinus floor is safer with average and hyperdivergent growth pattern than hypodivergent growth pattern. In the proximity of maxillary sinus floor, 1 mm or more cortical bone can be expected in maxillary posterior region in average and hyperdivergent growth patterns. However, it was thicker in hypodivergent than hyperdivergent growth patterns. Hypodivergent patients require either more horizontal insertion (more parallel to occlusal plane) or shorter length of miniscrew to avoid damage to maxillary sinus.

Effects of orthodontic miniscrew placement angle and structure on the stress distribution at the bone miniscrew interface – A 3D finite element analysis

The study was conducted to evaluate the effects of orthodontic miniscrew placement angle and structure in terms of length and diameter on stress distribution at the bone miniscrew interface. 10 FE models were created representing miniscrews inserted in the buccal alveolar bone between the maxillary first molar and second premolar to simulate varying angulations of miniscrew placement (90°, 60°, 45°, 30°) to the long axis of the maxillary first molar, varying length (6mm, 8mm, 10mm, 12mm) and varying diameter (1.2mm, 1.3mm, 1.4mm, 1.5mm). In order to simulate retraction forces an identical force of 200 g was applied perpendicular to the long axis of the miniscrew in all the models. Finite Element Modeling Analysis was used to analyze the stress distribution at the bone miniscrew interface. Minimum and maximum stress in the miniscrew was generated at placement angles of 30° and 90° respectively. In the bone minimum and maximum stress was found at placement angles of 90° and 30° respectively. On increasing the miniscrew diameter stress in both the miniscrew and the bone decreased. There was no difference found in the stress distribution patterns with varying miniscrew length. Based on stress patterns, biomechanical stability of the miniscrew is enhanced by a placement angle of 90° to the long axis of the first maxillary molar and a diameter of 1.5 mm for the site selected in this study while miniscrew length has no implication on its stability.

Evaluation of the Effects of Different Surface Configurations on Stability of Miniscrews

Introduction. The aim of this study was to analyze the effects of screw design and force application on the stability of miniscrews, using RTT, SEM, and histomorphometric analyses. Materials and Methods. Eighty cylindrical, self-drilling, and Ti6Al4V alloy miniscrews (1,6 × 6 mm) were used. Four mini-screws were inserted in fibulas of each rabbit, and 115 G of force was immediately applied. Four miniscrews were inserted in the other fibula, on which no force was applied. Eight weeks after insertion, osseointegration between miniscrew and the surrounding bone was evaluated by the histomorphometric analyses, SEM, and RTT. Kruskal-Wallis and the paired t-tests were used for statistical analysis. Results. Values obtained from Group I were significantly higher than those of the other loaded groups (P < .05). There were no differences in RTT scores among Groups II, III, and IV. Similar findings were also observed for unloaded mini-screws. There was no significant difference between Groups I and IC, while the differences between loaded and unloaded controls for each miniscrew were statistically significant. Conclusions. Immediate loading of miniscrews does not impair screw stability. Also, the diameter of miniscrew and more frequent thread pitches have a positive effect on stability; however, length of miniscrews does not have a significant effect on the stability.