Impact of insertion depth and predrilling diameter on primary stability of orthodontic mini-implants

The evolution of robotics: research and application progress of dental implant robotic systems

The use of robots to augment human capabilities and assist in work has long been an aspiration. Robotics has been developing since the 1960s when the first industrial robot was introduced. As technology has advanced, robotic-assisted surgery has shown numerous advantages, including more precision, efficiency, minimal invasiveness, and safety than is possible with conventional techniques, which are research hotspots and cutting-edge trends. This article reviewed the history of medical robot development and seminal research papers about current research progress. Taking the autonomous dental implant robotic system as an example, the advantages and prospects of medical robotic systems would be discussed which would provide a reference for future research.

Success rate of infrazygomatic miniscrews considering their design and insertion techniques. A review

Miniscrews offer the possibility of performing dental movements, minimizing unwanted side effects and enhancing effectiveness. Extra-alveolar miniscrews are ideal as they provide excellent primary stability and avoid anatomical structures. However, in some cases the primary stability is lost before achieving the success of the mechanics used and thus, the most likely causes of failure should be determined. The purpose of this review was to analyze the success rate of infrazygomatic miniscrews, considering their design and the insertion techniques used. Data collection of this literature review was carried out by searching PubMed, Wiley, Google Scholar sites, SCIELO, Elsevier and Dialnet for publication made from 2003 to June 2022. The search was carried out on June 10th, 2022 and the following keywords were used; infrazygomatic crest, miniscrews, anchorage and stability. Different topics were analyzed and discussed highlighting their clinical relevance. After analyzing the 798 articles, 566 were excluded. The remaining articles were re-analyzed and 153 articles were excluded for the title or abstract and 33 articles were excluded for the methodology. Finally, 46 items remained. After thoroughly analyzing all the articles included, this study concluded that the alloy of the miniscrew (stainless steel or titanium), perforation of the maxillary sinus and the placement area (adhered mucosa or mobile mucosa) do not influence the survival of the miniscrew. The evidence also indicates that the percentage of failure is lower in infrazygomatic compared to intraradicular miniscrews. Orthodontists can confidently and safely include infrazygomatic miniscrew in different orthodontic procedures.

Evaluation of Optimal Sites for the Insertion of Orthodontic Mini Implants at Mandibular Symphysis Region through Cone-Beam Computed Tomography

This study aims to evaluate the overall bone thickness (OBT) and cortical bone thickness (CBT) of mandibular symphysis and to determine the optimal sites for the insertion of orthodontic mini implants. Cone-beam computed tomography (CBCT) images of 32 patients were included in this study. The sample was further categorized into three facial types: low-, average-, and high-angle. OBT and CBT were measured at the mandibular symphysis region. All measurements were performed at six different heights from the cementoenamel junction [CEJ] and at seven different angles to the occlusal plane. Analysis of variance (ANOVA) was used for statistical comparison and a p value less than 0.05 was considered statistically significant. Our results revealed that neither OBT nor CBT was influenced by age or sex, except for the observation that CBT was significantly greater in adults than in adolescents. OBT and CBT were significantly greater in low-angle cases than in average- and high-angle cases. Both OBT and CBT were significantly influenced by insertion locations, heights and angles, and their interactions. CBT and OBT were greatest at the location between two lower central incisors, and became greater with increases in insertion height and angle. Both recommended and optimal insertion sites were mapped. The mandibular symphysis region was suitable for the placement of orthodontic mini implants. The optimal insertion site was 6–10 mm apical to the CEJ between two lower central incisors, with an insertion angle being 0–60 degrees to the occlusal plane.

Robotic Applications in Orthodontics: Changing the Face of Contemporary Clinical Care

The last decade (2010-2021) has witnessed the evolution of robotic applications in orthodontics. This review scopes and analyzes published orthodontic literature in eight different domains: (1) robotic dental assistants; (2) robotics in diagnosis and simulation of orthodontic problems; (3) robotics in orthodontic patient education, teaching, and training; (4) wire bending and customized appliance robotics; (5) nanorobots/microrobots for acceleration of tooth movement and for remote monitoring; (6) robotics in maxillofacial surgeries and implant placement; (7) automated aligner production robotics; and (8) TMD rehabilitative robotics. A total of 1,150 records were searched, of which 124 potentially relevant articles were retrieved in full. 87 studies met the selection criteria following screening and were included in the scoping review. The review found that studies pertaining to arch wire bending and customized appliance robots, simulative robots for diagnosis, and surgical robots have been important areas of research in the last decade (32%, 22%, and 16%). Rehabilitative robots and nanorobots are quite promising and have been considerably reported in the orthodontic literature (13%, 9%). On the other hand, assistive robots, automated aligner production robots, and patient robots need more scientific data to be gathered in the future (1%, 1%, and 6%). Technological readiness of different robotic applications in orthodontics was further assessed. The presented eight domains of robotic technologies were assigned to an estimated technological readiness level according to the information given in the publications. Wire bending robots, TMD robots, nanorobots, and aligner production robots have reached the highest levels of technological readiness: 9; diagnostic robots and patient robots reached level 7, whereas surgical robots and assistive robots reached lower levels of readiness: 4 and 3, respectively.

Influence of bone density, screw size and surgical procedure on orthodontic mini-implant placement - part B: implant stability

This in vitro study aimed to investigate the influence of bone density, implant size, and surgical procedure on the primary stability (PS) of orthodontic mini-implants (OMIs). In total, 640 OMIs of various sizes (2.0 × 7, 2.3 × 7, 2.0 × 11 and 2.3 × 11 mm) were inserted in the artificial bone of different densities (D1-D4). Placement was performed with an insertion angle of 90° or 60° to the bone surface and in 320 cases without predrilling, which resulted in 64 groups. PS was measured on the basis of implant stability quotient (ISQ) and insertion torque (IT). With regard to all possible influencing parameters, the mean PS differed between 39.20 and 60.00 (ISQ), and 10.00 and 39.00 Ncm (IT). The effect of OMI size and surgical procedure was dependent on bone quality. For example, implant size had less effect in high-density bone and was stronger with decreasing density. Overall, implant length had a greater influence than the diameter, and a high correlation was found among both PS measurement techniques. Therefore, a suitable choice of implant size and surgical protocol with regard to bone density can positively influence PS. In principle, ISQ and IT are suitable for measuring OMI stability.

Influence of bone density, screw size and surgical procedure on orthodontic mini-implant placement - part A: temperature development

The aim of this in vitro study was to determine the influence of bone density, orthodontic mini-implant (OMI) size, and the surgical procedure on temperature increase during implant site osteotomy and placement. OMIs of different sizes (2.0×7, 2.3×7, 2.0×11, and 2.3×11mm) were placed in artificial bone blocks of different densities (D1-D4). Optionally, the drilling and insertion angle was 90° or 60° to the bone surface. A total of 640 OMIs were inserted, and predrilling was performed in 320 cases. All insertions were done without irrigation with an axial load of 20N, which resulted in 64 groups. Temperature measurements were performed during implant site preparation and placement using Type-K-thermocouples. Mean temperature increase differed for OMI osteotomy between 1.38°C and 8.75°C and placement between 3.8°C and 18.74°C, respectively. Critical thermal increase was especially reached during placement using long implants. Increasing bone density and implant size (diameter <length) correlated with thermal increase. Predrilling and angulated implant placement resulted in less heat development. Critical temperature behaviour in high-density bone could be partially responsible for the high failure rates of OMI placement in the lower jaw. The influence of the implant size on temperature development should be considered when selecting an OMI.

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.

Bone and cortical bone characteristics of mandibular retromolar trigone and anterior ramus region for miniscrew insertion in adults

INTRODUCTION

The aim of this study was to evaluate bone depth, cortical bone thickness, and vestibulolingual bone dimension of the mandibular retromolar trigone and anterior ramus region to evaluate what are its most suitable sites for miniscrew insertion in adults.

METHODS

The sample included cone-beam computerized tomography (CBCT) records of 60 adult subjects retrospectively evaluated. All CBCT examinations were performed with the use of an i-CAT CBCT scanner (Imaging Sciences International). Each exam was converted into DICOM format and processed with the use of Osirix Medical Imaging software. On reproducible sagittal scan views, bone depth and cortical bone thickness were evaluated on specific lines parallel and at a 45° angle to the occlusal plane, and at 3 mm and at 6 mm distance from it. Vestibulolingual bone dimension was computed in 4 different cross-section scans and at 3 different levels of depth (0, 6, and 11 mm).

RESULTS

All of the considered insertion sites showed on average more than 10 mm of bone depth. Inferential statistics showed significantly (P <0.05) greater bone depth (+3 mm) in cross-sectional scans parallel to the occlusal plane compared with those at a 45° angle to it. Cortical bone thickness showed average values from 3 mm to 5 mm. Vestibulolingual bone dimension showed a significant (P <0.05) reduction (-10 mm) in the posterior region of retromolar region. No significant differences were found between subjects with and without third molars.

CONCLUSIONS

The retromolar trigone and anterior ramus region showed enough bone quantity and adequate bone quality for safe miniscrew insertion in adults.

3-Dimensional characterization of cortical bone microdamage following placement of orthodontic microimplants using Optical Coherence Tomography

Microimplants are being used extensively in clinical practice to achieve absolute anchorage. Success of microimplant mainly depend on its primary stability onto the cortical bone surface and the associated Microdamage of the cortical bone during insertion procedure leads to many a microimplants to fail and dislodge from the cortical bone leading to its failure. Even though, previous studies showed occurrence of microdamage in the cortical bone, they were mainly 2-dimension studies or studies that were invasive to the host. In the present study, we used a non-invasive, non-ionizing imaging technique- Optical Coherence Tomography (OCT), to image and analyze the presence of microdamage along the cortical bone surrounding the microimplant. We inserted 80 microimplants in two different methods (drill and drill free method) and in two different angulations onto the cortical bone surface. Images were obtained in both 2D and 3D imaging modes. In the images, microdamage in form of microcracks on the cortical bone surface around the bone-microimplant interface and micro-elevations of the cortical bone in angulated microimplant insertions and the presence of bone debris due to screwing motion of the microimplant on insertion can be appreciated visually and quantitatively through the depth intensity profile analysis of the images.

Bone and cortical bone thickness of mandibular buccal shelf for mini-screw insertion in adults

OBJECTIVE

To analyze the buccal bone thickness, bone depth, and cortical bone depth of the mandibular buccal shelf (MBS) to determine the most suitable sites of the MBS for mini-screw insertion.

MATERIALS AND METHODS

The sample included cone-beam computed tomographic (CBCT) records of 30 adult subjects (mean age 30.9 ± 7.0 years) evaluated retrospectively. All CBCT examinations were performed with the i-CAT CBCT scanner. Each exam was converted into DICOM format and processed with OsiriX Medical Imaging software. Proper view sections of the MBS were obtained for quantitative and qualitative evaluation of bone characteristics.

RESULTS

Mesial and distal second molar root scan sections showed enough buccal bone for mini-screw insertion. The evaluation of bone depth was performed at 4 and 6 mm buccally to the cementoenamel junction. The mesial root of the mandibular second molar at 4 and 6 mm showed average bone depths of 18.51 mm and 14.14 mm, respectively. The distal root of the mandibular second molar showed average bone depths of 19.91 mm and 16.5 mm, respectively. All sites showed cortical bone depth thickness greater than 2 mm.

CONCLUSIONS

Specific sites of the MBS offer enough bone quantity and adequate bone quality for mini-screw insertion. The insertion site with the optimal anatomic characteristics is the buccal bone corresponding to the distal root of second molar, with screw insertion 4 mm buccal to the cementoenamel junction. Considering the cortical bone thickness of optimal insertion sites, pre-drilling is always recommended in order to avoid high insertion torque.

Influence of Manual Screwdriver Design in Combination With and Without Predrilling on Insertion Torque of Orthodontic Mini-Implants

PURPOSE

The study focused on the influence of screwdriver design in combination with and without predrilling a pilot hole of inner implant diameter on insertion torque of orthodontic mini-implants, controlling for cortical thickness and vertical insertion force as cofactors.

METHODS

One hundred twenty mini-implants (Forestadent) of 1.7 mm in diameter and 6 and 8 mm in length were manually inserted into 120 swine rib bone samples. Maximal insertion torque as a measure of primary stability and vertical force were measured. The study included procedures with and without pilot hole and different screwdriver handles and shaft length and 2 implant lengths.

RESULTS

Design of manual screwdriver does not modify insertion torque to a significant extent. In multiple linear regression model, significant predictors of insertion torque are thicker cortical bone (explaining 16.6% of variability), higher vertical force at maximal torque (13.5%), 6-mm implant length (2.5%), and the presence of pilot hole (2.3%).

CONCLUSIONS

Handle type and shaft length of manual screwdriver do not significantly influence insertion torque, whereas predrilling a pilot hole has low impact on torque values of manually inserted self-drilling orthodontic mini-implants.

Orthodontic mini-implant stability at different insertion depths : Sensitivity of three stability measurement methods

OBJECTIVES

The purpose of this work was to evaluate the influence of insertion depth on the stability of orthodontic mini-implants. Sensitivity of three different methods to measure implant stability based on differences in insertion depth were determined.

METHODS

A total of 82 mini-implants (2 × 9 mm) were inserted into pelvic bone of Swabian Hall pigs. Each implant was inserted stepwise to depths of 4, 5, 6, 7, and 8 mm. At each of these depths, three different methods were used to measure implant stability, including maximum insertion torque (MIT), resonance frequency analysis (RFA), and Periotest(®). Differences between the recorded values were statistically analyzed and the methods tested for correlations.

RESULTS

Almost linear changes from each insertion depth were measured with the values of RFA [implant stability quotient (ISQ) values range from 1-100], which increased from 6.95 ± 2.85 ISQ at 4 mm to 34.63 ± 5.51 ISQ at 8 mm, and with those of Periotest(®) [periotest values (PTV) range from -8 to 50], which decreased from 13.24 ± 4.03 PTV to -2.89 ± 1.87 PTV. Both methods were found to record highly significant (p < 0.0001) changes for each additional millimeter of insertion depth. The MIT increased significantly (p < 0.0001) from 153.67 ± 69.32 Nmm to 261 ± 103.73 Nmm between 4 and 5 mm of insertion depth but no further significant changes were observed as the implants were driven deeper. The RFA and Periotest(®) values were highly correlated (r = -0.907).

CONCLUSIONS

Mini-implant stability varies significantly with insertion depth. The RFA and the Periotest(®) yielded a linear relationship between stability and insertion depth. MIT does not appear to be an adequate method to determine implant stability based on insertion depth.

Torque Loss After Miniscrew Placement: An In-Vitro Study Followed by a Clinical Trial

To evaluate torque loss a week after insertion, both in an in vivo and an in vitro experimental setup were designed. In the in vivo setup a total of 29 miniscrews were placed in 20 patients who underwent orthodontic treatment. Maximum insertion torque (MIT) was evaluated at insertion time (T1). A week later, insertion torque was measured again by applying a quarter turn (T2); no load was applied on the screw during the first week. In the in vitro setup a total of 20 miniscrews were placed in pig rib bone samples. MIT was evaluated at insertion time (T1). Bone samples were kept in saline solution and controlled environment for a week during which the solution was refreshed every day. Afterwards, torque was measured again by applying a quarter turn (T2). The comparison of MIT over time was done calculating the percentage difference of the torque values between pre- and post-treatment and using the parametric two independent samples t-test or the non-parametric Mann–Whitney test. After a week unloaded miniscrews showed a mean loss of rotational torque of 36.3% and 40.9% in in vitro and in in vivo conditions, respectively. No statistical differences were found between the two different setups. Torque loss was observed after the first week in both study models; in vitro experimental setup provided a reliable study model for studying torque variation during the first week after insertion.

Evaluation of Fracture Resistance of Orthodontic Mini-implants in the Transmucosal Profile Region

AIM

This study sought to compare the fracture resistance of three trademarked orthodontic mini-implants in the transmucosal profile region. Thirty-six mini-implants of three different brands, separated into groups I, II and III, were tested. Each group consisted of 12 mini-implants of 6 mm in length. The mean diameter and length of the transmucosal profile of the mini-implants were 1.90 and 2.0 mm in group I, 1.77 and 1.0 mm in group II and 1.50 and 1.0 mm in group III, respectively. The tests were performed on a universal testing machine in compression mode, with a 2,000 kgf load, a speed of 4.0 mm per minute and a chisel-shaped active tip, which acted cross-sectionally on the transmucosal profile. Single-criterion analysis of variance was used to compare the three brands. A significance level of 5% and test power of 80% were adopted. The mean fracture resistance achieved by the mini-implants was 172.03 ± 25.59 N for group I, 162.35 ± 30.81 N for group II and 139.69 ± 42.99 N for group III. There was no statistically significant difference in mean fracture resistance among the tested mini-implant brands.

CONCLUSION

The transmucosal profile diameter does not seem to be a deciding factor in the choice of mini-implants to minimize the risk of fractures.

CLINICAL SIGNIFICANCE

Although being an in vitro study it is possible to believe that this new brand has a very satisfactory resistance to fracture and enables its use with great efficiency.

Effect of the length of orthodontic mini-screw implants on their long-term stability: a prospective study

OBJECTIVE

To analyze the influence of the length of temporary intraoral skeletal anchorage devices (TISAD/TAD) on their long-term stability in the mandible in a homogenous group of patients.

MATERIALS AND METHODS

A group of generally healthy patients of the same gender (female) and with a statistically insignificant age difference (20-29 years) highly homogenous with respect to known factors affecting the success rate of TISAD/TAD was evaluated. One type of TISAD/TAD was applied (6- or 8-mm long). Each patient received both 6- and 8-mm-long TISAD/TAD in randomly selected mandibular quadrants: left or right. The long-term success rate of TISAD/TAD was analyzed.

RESULTS

The 8-mm orthodontic mini-screw implants were significantly more stable than the 6-mm ones in the analyzed group.

CONCLUSION

The length of the TISAD/TAD may be one of the factors that can affect the long-term success rate in the mandibles of 20- to 29-year-old women.

Microdamage generation by tapered and cylindrical mini-screw implants after pilot drilling

OBJECTIVE

To investigate the relationship between mini-screw implant (MSI) diameter (1.6 vs 2.0 mm) and shape (tapered vs cylindrical) and the amount of microdamage generated during insertion.

MATERIALS AND METHODS

Thirty-six cylindrical and 36 tapered MSIs, 6 mm long, were used in this study. Half of each shape was 1.6 mm in diameter, while the other half was 2.0 mm. After pilot drilling, four and five MSIs were inserted, respectively, into fresh cadaveric maxillae and mandibles of dogs. Bone blocks containing the MSIs were sectioned and ground parallel to the MSI axis. Epifluorescent microscopy was used to measure overall cortical thickness, crack length, and crack number adjacent to the MSI. Crack density and total microdamage burden per surface length were calculated. Three-way analysis of variance (ANOVA) was used to test the effects of jaw, and MSI shape and diameter. Pairwise comparisons were made to control the overall significance level at 5%.

RESULTS

The larger (2.0 vs 1.6 mm) cylindrical MSIs increased the numbers, lengths, and densities of microcracks, and the total microdamage burden. The same diameter cylindrical and tapered MSIs generated a similar number of cracks and crack lengths. More total microdamage burden was created by the 2.0-mm cylindrical than the 2.0-mm tapered MSIs. Although higher crack densities were produced by the insertion of 1.6-mm tapered MSIs, there was no difference in total microdamage burden induced by 1.6-mm tapered and 1.6-mm cylindrical MSIs.

CONCLUSIONS

Pilot drilling is effective in reducing microdamage during insertion of tapered MSIs. To prevent excessive microdamage, large diameter and cylindrical MSIs should be avoided.

Treatment efficiency of mini-implant-borne distalization depending on age and second-molar eruption

OBJECTIVE

The aim of this study was to evaluate the efficiency of molar distalization depending on age and second-molar eruption using the Beneslider.

MATERIALS AND METHODS

Treatment of 51 patients (mean age 17.8 ± 9.6 years) was investigated retrospectively by means of pre- and posttreatment cephalograms. Patients were divided into three groups: 14 children with unerupted upper second molars (group 1), 23 adolescents with second molar in place (group 2), and 14 adults (group 3). The distalization forces applied were 2.4 N in group 1 and 5.0 N in groups 2 and 3. Treatment changes were evaluated and examined statistically for significant differences.

RESULTS

In all patients a Class I molar relationship was achieved. All mini-implants remained stable during treatment. Mean distalization distance as measured by the displacement of the center of resistance was 3.6 ± 1.9 mm (range 1.2-8.5 mm depending on treatment needs). Since no significant tipping was detected, the type of movement can be described as bodily movement. Mean overall distalization speed was 0.6 ± 0.4 mm per month. There were no statistical differences between the groups.

CONCLUSION

We found the Beneslider to be an effective appliance that enables bodily distalization in adequate treatment time. The higher resistance due to erupted second molars can be compensated by the use of higher forces without significantly reducing distalization speed.

Systematic review of mini-implant displacement under orthodontic loading

A growing number of studies have reported that mini-implants do not remain in exactly the same position during treatment, although they remain stable. The aim of this review was to collect data regarding primary displacement immediately straight after loading and secondary displacement over time. A systematic review was performed to investigate primary and secondary displacement. The amount and type of displacement were recorded. A total of 27 studies were included. Sixteen in vitro studies or studies using finite element analysis addressed primary displacement, and nine clinical studies and two animal studies addressed secondary displacement. Significant primary displacement was detected (6.4–24.4 µm) for relevant orthodontic forces (0.5–2.5 N). The mean secondary displacement ranged from 0 to 2.7 mm for entire mini-implants. The maximum values for each clinical study ranged from 1.0 to 4.1 mm for the head, 1.0 to 1.5 for the body and 1.0 to 1.92 mm for the tail part. The most frequent type of movement was controlled tipping or bodily movement. Primary displacement did not reach a clinically significant level. However, clinicians can expect relevant secondary displacement in the direction of force. Consequently, decentralized insertion within the inter-radicular space, away from force direction, might be favourable. More evidence is needed to provide quantitative recommendations.

Insertion torque and orthodontic mini-implants: A systematic review of the artificial bone literature

This article systematically reviewed the literature to (1) identify variables that were associated with maximum insertion torque values during the insertion of orthodontic mini-implants into artificial bone, (2) quantify such associations and (3) assess adverse effects of this procedure. Computerized and manual searches were conducted up to 24 February 2012. Selection criteria included studies that (1) recorded maximum insertion torque during the insertion of orthodontic mini-implants into artificial bone, (2) used sample sizes of five screws or more, (3) assessed maximum insertion torque with electronic torque sensors, and (4) used orthodontic mini-implants with a diameter smaller than 2.5 mm. ASTM Standards F543-07ε1 and F1839-08ε1 and the Cochrane Handbook for Systematic Reviews were used as guidelines for this systematic review. Quality assessments were rated according to the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach. A total of 23 studies were selected, many of which were multiple publications of the same study. Many domains in the risk of bias assessments were scored as “high” or “unclear” risk of bias. A wide variety of implant, test block, and insertion procedure–related associations with maximum insertion torque were recorded. The quality of most outcomes was classified as “moderate.” Outcomes could not be combined in a meta-analysis because of high risk of bias, poor standardization, high heterogeneity, or inconsistency in direction of outcomes within or between studies. Adverse effects were only assessed in one study. Future studies should control publication bias, consult existing standards for conducting torque tests, and focus on transparent reporting.

Insertion torque, pull-out strength and cortical bone thickness in contact with orthodontic mini-implants at different insertion angles

This study aimed to evaluate biomechanical behaviour of inclined orthodontic mini-implants by analyzing its insertion torque (IT), axial pull-out strength (APS), and cortical bone thickness in contact with mini-implant (CBTC). A total of 102 mini-implants were inserted at 90 degree, 60 degree, and 45 degree to the surface of synthetic bone. Peak IT was measured, and the mini-implants were aligned with the mechanical testing machine to record the APS. The cortical bone thickness in contact with each mini-implant was measured after the pull-out test and the data were subjected to statistical analyses. The 45 degree group had a significantly higher IT compared with the 90 degree group (P < 0.05). There was a statistically significant increase in the average of cortical bone thickness in CBTC across the three groups (P < 0.05). A negative correlation between the angulation and the CBTC (r = -0.95, P < 0.05) and a positive correlation between the APS and the CBTC were observed (r = 0.34, P < 0.05). Mini-implants that are inserted more inclined to the surface of the bone provide greater IT and an increased contact with the cortical bone. The greater the CBTC, the greater is the APS.

Effects of repeated sterilization cycles on primary stability of orthodontic mini-screws

OBJECTIVE

To determine if repeated sterilization has deleterious effects on the clinical stability of mini-screws.

MATERIALS AND METHODS

Thirty each of the following mini-screws were tested: Aarhus (American Orthodontics, Sheboygan, Wisc), VectorTAS (Ormco Corporation, Orange, Calif), Dual-Top (RMO, Denver, Colo), and Ortho Anchor (KLS Martin, Jacksonville, Fla). Controls were sterilized once using a steam autoclave (Statim 5000, SciCan USA, Canonsburg, Pa). Each group of mini-screws was divided into three groups: the control (n = 10) and two test groups (n  =10, each). Test groups were cycled five and 10 times respectively. All screws were inserted into custom-designed synthetic blocks that simulated mandibular bone. Maximum insertion torque and lateral displacement force data were recorded and subjected to statistical testing. Two-way analysis of variance (ANOVA) and three-way mixed ANOVA were used for statistical analyses for maximum insertion torque data and lateral displacement force data, respectively. Level of significance was established at P < .05.

RESULTS

Insertion torque values displayed significant differences between both of the groups and sterilization cycles (P < .05). Significant differences were observed between American Aarhus mini-screws and both RMO and KLS Martin mini-screws. Ormco Vector mini-screws also differed significantly from the KLS Martin mini-screws in this comparison (P < .05). For lateral displacement, there was a significant main effect of groups, F(1,36) = 14.5 (P < .05). Significant differences were observed between American Aarhus mini-screws and all three of the other groups (P < .05).

CONCLUSIONS

The examined groups displayed statistical differences of variable quality that may not affect their clinical stability.

Miniscrew design and bone characteristics: an experimental study of primary stability

INTRODUCTION

The purpose of this study was to evaluate the correlations between bone characteristics, orthodontic miniscrew designs, and primary stability.

METHODS

Four different miniscrews were placed in pig ribs. The miniscrews were first scanned with a scanning electron microscope to obtain measurable images of their threads. Subsequently, the maximum insertion torque of the screws and the maximum load value in the pullout force tests were measured; furthermore, bone specimen characteristics were analyzed by using cone-beam computed tomography. For each bone sample, the insertion site cortical thickness as well as both cortical and marrow bone density were evaluated. The nonparametric Kendall rank correlation (tau) was used to evaluate the strength of the associations among the characteristics measured. The nonparametric Kruskall-Wallis test was used to evaluate the differences among the groups, and post-hoc comparisons were assessed by using the Nemenyi-Damico-Wolfe-Dunn test.

RESULTS

A significant dependence was found between pitch and maximum insertion torque (tau, -0.49). Positive correlations were also found between pullout force and maximum insertion torque (tau, 0.64), cortical thickness (tau, 0.36), and marrow bone density (tau, 0.35).

CONCLUSIONS

In this in-vitro experimental study, strong correlations were observed among miniscrew geometry, bone characteristics, and primary stability.

[Improvement of mini-implant stability in orthodontics]

Orthodontists are continuing to increase the use of mini-implants as a source of skeletal anchorage. However, the relatively high 16.4% rate of their failures remains a problem. An analysis of articles in the literature on the loss of mini-implants shows that larger size anchorage screws and plates inserted in the anterior and median regions of the hard palate are highly stable and, accordingly, contribute to a high rate of optimum orthodontic outcomes. It is the reliability of the mini-implant/skeletal structure couple that is the principal factor in this success. With mini-implants whose heads possess internal threads, orthodontists can attach different types of stable, screwed-in abutments. And with long plates with specifically designed perforations splinting two mini-implants together, orthodontists can further increase the stability of this artificial anchorage. By employing a system with pre-fabricated components orthodontists can quickly create skeletal anchorage adaptable to the mechanics of different techniques.

Measurement of mini-implant stability using resonance frequency analysis

OBJECTIVE

To investigate whether resonance frequency analysis (RFA) is suitable to measure orthodontic mini-implant stability. Implant size significantly affects the level of resonance frequency. Regarding the operating mode of RFA, it has to be proven whether the resonance frequency of mini-implants in bone fits the range of frequency emitted by the Osstell ISQ device.

MATERIAL AND METHODS

For this purpose the SmartPegs in the Osstell ISQ device were modified to fit with the inner screw thread of orthodontic mini-implants, and 110 mini-implants were inserted into porcine pelvic bone. RFA was performed parallel and perpendicular to the run of superficial bone fibers. A suitability test, Periotest, was also performed in the same directions. Compacta thickness was measured using cone-beam computed tomography. Correlation tests and linear regression analysis were carried out between the three methods.

RESULTS

The RFA showed a mean Implant Stability Quotient value of 36.36 ± 2.67, and the Periotest mean value was -2.10 ± 1.17. The differences between the two directions of measurement were statistically significant (P > .001) for RFA and the Periotest. There was a high correlation between RFA and the Periotest (r  =  -0.90) and between RFA and compacta thickness (r  =  0.71). The comparison between the Periotest and compacta thickness showed a correlation coefficient of r  =  -0.64.

CONCLUSION

The present results suggest that RFA is feasible as a measurement method for orthodontic mini-implant stability. As a consequence, it could be used for clinical evaluation of current stability and allow stability-related loading of mini-implants to reduce the failure rate.

Influence of different implant materials on the primary stability of orthodontic mini-implants

This study evaluates the influence of different implant materials on the primary stability of orthodontic mini-implants by measuring the resonance frequency. Twenty-five orthodontic mini-implants with a diameter of 2 mm were used. The first group contained stainless steel mini-implants with two different lengths (10 and 12 mm). The second group included titanium alloy mini-implants with two different lengths (10 and 12 mm) and stainless steel mini-implants 10 mm in length. The mini-implants were inserted into artificial bones with a 2-mm-thick cortical layer and 40 or 20 lb/ft(3) trabecular bone density at insertion depths of 2, 4, and 6 mm. The resonance frequency of the mini-implants in the artificial bone was detected with the Implomates(®) device. Data were analyzed by two-way analysis of variance followed by the Tukey honestly significant difference test (α = 0.05). Greater insertion depth resulted in higher resonance frequency, whereas longer mini-implants showed lower resonance frequency values. However, resonance frequency was not influenced by the implant materials titanium alloy or stainless steel. Therefore, the primary stability of a mini-implant is influenced by insertion depth and not by implant material. Insertion depth is extremely important for primary implant stability and is critical for treatment success.

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

INTRODUCTION

The primary stability of a mini-implant is critical, since most orthodontic mini-implant failures occur at an early stage. As orthodontic mini-implants have restrictions in diameter and length, an optimal design of the shape is important for sufficient primary stability. The purpose of this study was to investigate the influence of various mini-implants design factors, including thread depth, degree of taper, and taper length on insertion torque, pullout strength, stiffness, and screw displacement before failure.

METHODS

Finite element analyses were conducted first for identification of optimal design parameters. Four types of mini-implants with different design parameters were then custom manufactured and tested mechanically. All mechanical tests were performed in artificial bone with homogenous density to remove the variability associated with bone.

RESULTS

Finite element results showed that, for mini-implants with a fixed external diameter of 2 mm, a thread length of 9.82 mm, and a pitch of 0.75 mm, those with greater thread depths, smaller taper degrees, and shorter taper lengths generated higher maximum stresses on the bone and thread elements. These mini-implants also had larger relative displacements. Maximum pullout resistance was attained with a core/external diameter ratio of 0.68. All mechanical results were compatible with the findings in the finite element analyses.

CONCLUSIONS

Modification of the mini-implant design can substantially affect the mechanical properties. The finite element method is an effective tool to identify optimal design parameters and allow for improved mini-implant designs.

Fracture resistance of orthodontic mini-implants: a biomechanical in vitro study

Sufficient primary stability is of importance for the survival of orthodontic mini-implants. This means that adequate torque has to be achieved during insertion. However, as moments exceeding the fracture resistance of a mini-implant may result in their fracture, the maximum torque load capacity should be known. In this study, the threshold torque values resulting in the fracture of various mini-implant types and diameters were evaluated. Forty-one different mini-implants with diameters ranging from 1.3 to 2.0 mm (Aarhus screw, Abso Anchor, Ancora, Bone screw, Dual Top, Lomas, MAS, O.S.A.S, Ortho Easy, Spider Screw, and Tomas pin) were inserted in acrylic glass by a robot system. Ten specimens of each mini-implant type were tested. The insertion torque was measured and the maximum torque at the time of mini-implant fracture was evaluated. Significance of the mean value differences was evaluated by Kruskal-Wallis tests. Fracture moments varied depending on the diameter of the mini-implants. The measured values ranged from 108.9 Nmm (MAS 1.3×11 mm) to 640.9 Nmm (Lomas 2.0×11 mm). The differences were highly statistically significant (P<0.001). The risk of mini-implant fracture should be borne in mind at the time of insertion, especially if mini-implants with a small diameter are employed. To minimize the risk of fracture, pre-drilling should be carried out if the mini-implants are to be inserted at a site with a high bone density.