Biomechanical and Histomorphometric Analyses of Monocortical Screws at Placement and 6 Weeks Postinsertion

Success rate of mini-implants based on side of insertion and type of jaw in adult patients undergoing orthodontic treatment – A systematic review and meta-analysis

Objectives:

To find out success rate of mini-implants based on side of insertion and type of jaw. The aim of orthodontic treatment is to maintain sufficient anchorage control to create appropriate force systems that provide the desired treatment effects. Implants have been used as skeletal anchorage devices for orthodontic purposes.

Material and Methods:

The following study is a systematic review of mini-screws as an intervention to evaluate the stability and different related clinical parameters to define the success rate (outcome) depending on the side of insertion (i.e., right side and left side) and type of jaw (i.e., maxilla and mandible following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses).

Results and Conclusion:

A total of 52 articles were extracted for qualitative synthesis among which 24 articles were reviewed for meta-analysis and the results showed that the maxilla is a better placement site for insertion of mini-implant (MI) than mandible with the odds ratio of 0.58, that is, the MI placement in the maxillary region is 58% more successful than mandibular region. The other parameter showed that the insertion of MI on the right side was more successful with the odds ratio of 0.50, that is, the insertion of MI on the right side of the jaw is 50% more successful than on the left side of the jaw.

Risk factors associated with the stability of mini-implants and mini-plates: systematic review and meta-analysis

OBJECTIVE

The objective of this systematic review is to assess the risk factors associated with the stability of mini-implants and mini-plates in patients undergoing orthodontic treatment using temporary anchorage devices.

MATERIAL AND METHODS

Search strategies were developed for each electronic database (PubMed/Medline, LILACS, Scopus, Web of Science, Embase, and Cochrane Library) and gray literature (Google Scholar, Proquest, and Open Grey). The risk of bias was assessed using the Cochrane Collaboration tool for assessing the risk of bias and Meta-Analysis of Statistics Assessment and Review Instrument. The certainty of the evidence was assessed using the GRADE tool. Meta-analyses and meta-regressions of random effects were performed for the outcomes of interest.

RESULTS

A total of 1517 articles were found, of which seven were selected for quantitative synthesis. When comparing the risk of failure between mini-implants and mini-plates, the risk values approached the threshold of statistical significance (p = 0.07) (RR = 1.83; 95% CI = 0.96-3.50; I² = 69%), showing significance after sensitivity analysis (p < 0.05) and a greater risk for mini-implants. Mandible installation presented a higher risk of failure (RR = 1.85; 95% CI = 1.17-2.91).

CONCLUSIONS

The evidence found indicates that failure in the stability is related to the type of device and that there is a greater risk by using isolated mini-implants, especially when positioned in the mandible.

CLINICAL RELEVANCE

These findings help the orthodontist and/or the surgeon to stipulate risks, learn about the predictability of techniques, and communicate with the patient in an easier way.

Comparative Evaluation of Primary Stability of Two Different Types of Orthodontic Mini-Implants

Background

The mini-implants introduced new possibilities of adequate anchorage in orthodontics. Furthermore, due to its small size, it can even be placed at relatively difficult sites with ease. Removal torque should be high to prevent implant unscrewing.

Objective

This prospective clinical trial was aimed to evaluate the insertion torque and removal torque of single-threaded and double-threaded cylindrical orthodontic mini-implants.

Materials and Methods

A total of 36 cases were randomly divided into two groups, with an equal number of patients in each group (n = 18). In Group 1 single-threaded cylindrical mini-implant was placed, and in the other group, cylindrical implants with double-threaded were placed. Maximum insertion torque (MIT) and maximum removal torques (MRTs) were recorded for both groups. Data collected were subjected to statistical analysis.

Results

MIT was found to be significantly higher than MRT for both the groups and between the groups. Intergroup comparison in the present study showed significantly higher values for MIT than MRT. Intergroup comparison of MIT showed more values for Group 2 as compared to Group 1. Similar statistically significant values were seen in terms with MRT, where double-threaded cylindrical mini-implants had more torque value than the other group.

Conclusions

Orthodontic mini screws represent effective temporary anchorage devices. Double-threaded cylindrical mini-implants have significantly higher insertion and removal torque than single-threaded mini-implants and hence better stability.

Long-term stability behavior of paramedian palatal mini-implants: A repeated cross-sectional study

INTRODUCTION

The initial stability of orthodontic mini-implants is well investigated over a period of 6 weeks. There is no clinical data available dealing with the long-term stability. The aim of this study was the assessment of long-term stability of paramedian palatal mini-implants in humans.

METHODS

Stability of 20 implants was measured after removal of the orthodontic appliance (sliding mechanics for sagittal molar movement 200 cN each side) before explantation (T4) using resonance frequency analysis (RFA). Data were compared with a matched group of 21 mini-implants assessing the stability immediately after insertion, and after 2, 4, and 6 weeks (T0-T3). The mini-implants used in this study were machined self-drilling titanium implants (2.0 × 9.0 mm). Gingival thickness at the insertion site was 1-2 mm.

RESULTS

The implant stability quotient (ISQ) values before removal of the implant at T4 were 25.2 ± 2.9 after 1.7 ± 0.2 years and did not show a statistically significant change over time compared with the initial healing group (T0-T3).

CONCLUSIONS

Comparing the stability of mini-implants just after completion of the healing period and at the end of their respective usage period revealed no significant difference. An increase of secondary stability could not be detected. The level of stability seemed to be appropriate for orthodontic anchorage.

Influence of mini-screw diameter and loading conditions on static and dynamic assessments of bone-implant contact: An animal study

OBJECTIVES

The goal was to compare static versus dynamic bone-implant interface histology of mini-screws and to evaluate its relation to diameter and load.

SETTING AND SAMPLE POPULATION

Canine animal model.

MATERIAL AND METHODS

Custom-machined, titanium alloy (Ti6AI4V) mini-screws (n = 70) of 1.60, 2.00, 3.00 and 3.75 mm diameter were placed into edentulous sites in five skeletally mature beagle dogs. Using a split-mouth design, no load (NL) was applied to one side while a 2N load (L) was applied by calibrated coil springs on the other side. Intravenous bone labels were administered 21 and 7 days prior to sacrifice. Dogs were euthanized 90 days after screw placement. Bone sections were analysed under bright-field and epifluorescent light. The region of interest was defined as the bone within the threads of the screws. The following parameters were quantified: (a) Static-bone volume/tissue volume (BV/TV %) and bone-implant contact (BIC, %); (b) Dynamic-labelled bone/bone volume (LB/BV, %), and dynamic BIC (DBIC, %).

RESULTS

BV/TV ranged from 71.2% to 85.0% of the screw surface. BIC ranged from 45.7% to 55.4% of the screw surface and was not affected by diameter (P = 0.66). In contrast, the percentage of DBIC did not vary with the applied load (P = 0.41); however, it correlated significantly with the diameter of the screw (P = 0.001).

CONCLUSION

The percentage of DBIC that is actively remodelling increases with increasing diameter of the screw. Dynamic histomorphometry is more sensitive to detecting changes in bone-implant contact when compared to static measurements.

Success rates of a skeletal anchorage system in orthodontics: A retrospective analysis

OBJECTIVES

To evaluate the premise that skeletal anchorage with SAS miniplates are highly successful and predictable for a range of complex orthodontic movements.

MATERIALS AND METHODS

This retrospective cross-sectional analysis consisted of 421 bone plates placed by one clinician in 163 patients (95 female, 68 male, mean age 29.4 years ± 12.02). Simple descriptive statistics were performed for a wide range of malocclusions and desired movements to obtain success, complication, and failure rates.

RESULTS

The success rate of skeletal anchorage system miniplates was 98.6%, where approximately 40% of cases experienced mild complications. The most common complication was soft tissue inflammation, which was amenable to focused oral hygiene and antiseptic rinses. Infection occurred in approximately 15% of patients where there was a statistically significant correlation with poor oral hygiene. The most common movements were distalization and intrusion of teeth. More than a third of the cases involved complex movements in more than one plane of space.

CONCLUSIONS

The success rate of skeletal anchorage system miniplates is high and predictable for a wide range of complex orthodontic movements.

Screw-type device diameter and orthodontic loading influence adjacent bone remodeling

OBJECTIVE

To evaluate the effect of diameter and orthodontic loading of a screw-type implantable device on bone remodeling.

MATERIALS AND METHODS

Screw-shaped devices of four distinct diameters, 1.6, 2, 3, and 3.75 mm, were placed into edentulous sites in five skeletally mature beagle dogs (n = 14/dog) following premolar extraction. Using a split-mouth design, devices on one side were loaded using calibrated 2N coil springs. Epifluorescent bone labels were administered intravenous prior to sacrifice. Bone-implant sections (∼ 70 μm) were evaluated to quantify bone formation rate (BFR), and other histomorphometric variables were assessed in the implant supporting bone.

RESULTS

The mean BFR ranged from 10.93 percent per year to 38.91 percent per year. BFR in the bone adjacent to the device was lower for the loaded 1.6-mm screws when compared with the nonloaded 1.6-mm screws (P < .01) and the loaded 2.0-, 3.0-, and 3.75-mm diameter screws (P < .01). No significant differences in BFR were noted, regardless of loading condition, between the 2.0-, 3.0-, and 3.75-mm diameter screws.

CONCLUSIONS

We detected a dramatic reduction in bone remodeling. Although orthodontic loading of 2N did not alter bone remodeling associated with screws with a 2.0-mm diameter or larger, it did decrease bone remodeling adjacent to a loaded 1.6-mm screw. The long-term effect of this diminished remodeling should be further investigated.

Temporary replacement of missing maxillary lateral incisors with orthodontic miniscrew implants in growing patients: rationale, clinical technique, and long-term results

The missing maxillary lateral incisor in adolescent patients presents an orthodontic challenge. Historically, there have been three treatment options to address this clinical problem: (1) canine substitution, (2) tooth auto-transplantation, and (3) dental restoration. Unfortunately, these methods are not without limitation. A novel treatment concept, originating in 2003 and utilizing orthodontic miniscrew implants, is presented along with the rationale, clinical technique and 8 years of follow-up.

Bone anchors--can you hitch up your wagon?

The purpose of this review was to address and understand the current status of mini-screw implants (MSI) that are used in orthodontics. Understanding the biologic adaptation of MSI to its adjacent bone is one of the critical factors to their success. The review explores factors that are associated with failure of MSI, with special focus on an understanding of osseointegration as it relates to MSI. The rationale and importance of measuring bone contact and dynamic bone remodeling in animal studies are outlined. The utility of microcomputed tomography (μCT) as a substitute for conventional histomorphometry is debated. Finally, alveolar physiology and rigidity of implants are explored to understand potential reasons for the high failure rate of MSI when compared to endosseous implants.

Mechanical influence of thread pitch on orthodontic mini-implant stability

The aim of this study was to evaluate the effect of pitch distance on the primary stability (PS) of orthodontic mini-implants (MIs) in artificial bone. Twenty experimental MIs were allocated to two groups, according to their geometric design: G1 (30o X 0.6 mm) and G2 (45o X 0.8 mm), and inserted into artificial bone of different densities: D1 (0.32 g/cm3) and D2 (0.64 g/cm3). The maximum insertion torque (IT) and removal torque (RT) values were recorded in N.cm. Loss of torque (LT) values were obtained by calculating the difference between the IT and RT. MI mobility was measured by means of a Periotest assessment. Normality and homogeneity were determined by means of the Kolmogorov-Smirnov and Shapiro-Wilk tests, respectively. A two-way ANOVA was used to detect differences between the mini-implant design and density factors. The ANOVA/Tukey tests were used to determine the intergroup difference. Higher IT values were observed for G2 (p ≤ 0.05) in D2. No statistical difference for RT was observed between the groups, whereas G2 presented higher values only for LT (p ≤ 0.05). The Periotest values (PTV) were higher for G1, in comparison with G2, in D1. G1 presented better PS in D2 (IT, RT and LT), whereas G2 was found to be more stable in D1, after evaluation with Periotest.

Flexural strength of mini-implants developed for Herbst appliance skeletal anchorage. A study in Minipigs br1 cadavers

OBJECTIVE

The present study was designed to verify if mini-implant prototypes (MIP) developed for Herbst appliance anchorage are capable of withstanding orthopedic forces, and to determine whether the flexural strength of these MIP varies depending on the site of insertion (maxilla and mandible).

METHODS

Thirteen MIP were inserted in three minipig cadavers (six in the maxilla and seven in the mandible). The specimens were prepared and submitted to mechanical testing. The mean and standard deviation were calculated for each region. A two-way Student's t test was used to compare the strength between the sites. A one-way Student's t test was performed to test the hypothesis. Orthopedic forces above 1.0 kgf were considered.

RESULTS

The MIP supported flexural strength higher than 1.0 kgf (13.8 ± 2.3 Kg, in the posterior region of the maxilla and 20.5 ± 5.2 Kg in the anterior region of the mandible) with a significantly lower flexural strength in the anterior region of the mandible (p < 0.05).

CONCLUSIONS

The MIP are capable of withstanding orthopedic forces, and are more resistant in the anterior region of the mandible than in the posterior region of the maxilla in Minipigs br1 cadavers.

A systematic review of methods for tissue analysis in animal studies on orthodontic mini-implants

Anchorage devices are increasingly used in orthodontics, and their clinical performance is directly dependent on the tissue response to these devices. This study aims to identify assessment parameters for evaluating tissue reactions around orthodontically loaded implants and to propose parameters to be included in a standardized method. Several electronic databases (PubMed, ScienceDirect, the Cochrane database) were explored for papers from January 1999 to December 2009. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement was used as a guideline for the methodology of systematic reviews. Twenty-five publications were selected from 123 potentially relevant abstracts. The selected studies mainly aimed to answer a clinical question and particularly the ability of immediate loading in orthodontics. Very few studies aimed to understand the healing mechanism around the devices leading to a lack of information on this topic. The most frequent combination of assessment methods was clinical evaluation, histology/histomorphometry and intravital bone labeling. Although the dog model is mainly used, pigs represent an interesting animal model, especially when studying devices in growing bone. Despite the extensive use of miniscrews in growing individuals, only few studies have included young subjects in their protocol. Moreover, in such studies, an oral hygiene program is absolutely necessary to avoid complications. Finite element analysis could improve the knowledge of the relationship between design and bone reaction; unfortunately, this elaborated method is complex and impossible to perform routinely. For standardization, the authors recommend to include specific criteria in study protocols when assessing tissue response to orthodontically loaded devices.

Stability of miniplates and miniscrews used for orthodontic anchorage: experience with 492 temporary anchorage devices

OBJECTIVES

The aim of this retrospective study was to evaluate systematically the potential factors that influence failure rates of temporary anchorage devices (TADs) used for orthodontic anchorage.

MATERIALS AND METHODS

Data on 492 TADs (miniplates, pre-drilling miniscrews, and self-drilling miniscrews) in 194 patients were collected. The factors related to TAD failure were evaluated using univariate analysis and multivariate forward stepwise logistic regression analysis.

RESULTS

There were no significant differences in failure rates among the TADs for the following variables: gender, type of malocclusion, facial divergency, implantation site (buccal, lingual, or crestal/midpalatal), location (anterior or posterior), method of force application (power chain or Ni-Ti coil spring), arch (upper or lower), type of soft tissue (attached gingiva or removable mucosa), and most of the cephalometric measurements that reflect dento-cranio-facial characteristics. An increased failure rate was noted for the self-drilling miniscrew type of TAD, TADs used for tooth uprighting, those inserted on bone with lower density, those associated with local inflammation of the surrounding soft tissue, those loaded within 3 weeks after insertion, and those placed in patients with greater mandibular retrusion. Failure rates of the self-drilling miniscrews installed by an oral surgeon and by an orthodontist did not differ significantly.

CONCLUSIONS

Inflammation of soft tissue surrounding a TAD and early loading within 3 weeks after insertion were the most significant factors predicting TAD failure. Both orthodontists and oral surgeons who install orthodontic TADs must undergo sufficient training to achieve clinical excellence.

Biomechanical comparison of four different miniscrew types for skeletal anchorage in the mandibulo-maxillary area

This study compared four miniscrew types for skeletal anchorage (Aarhus, FAMI, Dual Top and Spider) regarding their biomechanical properties contributing to primary stability. Insertion torque measurements and pull-out tests in axial (0 degrees ) as well as in the 20 degrees and 40 degrees direction were performed. Stiffness of the screw-bone construct was calculated from the load-displacement curve. Conic FAMI and Dual Top screws had higher insertion torques. Insertion torques were raised by drill-free insertion of FAMI and Dual Top screws. Statistically significant differences were found between the 4 screw types in pull-out tests. The highly significant differences between the four screws for peak load in the axial (0 degrees ) and 20 degrees direction were not apparent in 40 degrees angular loads. For the conical screws, peak load values increased in angular compared with axial load. The Dual Top screw achieved the highest values for peak load and stiffness. 12 Dual Top and 1 Spider screw heads fractured in the pull-out tests. A conical drill-free screw design achieves higher primary stability compared with cylindrical self-tapping screws. This effect was more obvious in insertion torque estimations rather than in pull-out tests. The Dual Top screws, although biomechanically superior to other screw types, were most prone to fractures.

Replacing animal experiments: choices, chances and challenges

Replacing animal procedures with methods such as cells and tissues in vitro, volunteer studies, physicochemical techniques and computer modelling, is driven by legislative, scientific and moral imperatives. Non-animal approaches are now considered as advanced methods that can overcome many of the limitations of animal experiments. In testing medicines and chemicals, in vitro assays have spared hundreds of thousands of animals. In contrast, academic animal use continues to rise and the concept of replacement seems less well accepted in university research. Even so, some animal procedures have been replaced in neurological, reproductive and dentistry research and progress is being made in fields such as respiratory illnesses, pain and sepsis. Systematic reviews of the transferability of animal data to the clinical setting may encourage a fresh look for novel non-animal methods and, as mainstream funding becomes available, more advances in replacement are expected.