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

The Orthodontic Mini-Implants Failures Based on Patient Outcomes: Systematic Review

Anchorage is a challenge and essential issue for an orthodontist in determining the success of orthodontic treatment. Orthodontic anchorage is defined as resistance to unwanted tooth movement. Mini-implant is one of the devices that can be used as an anchor in orthodontic treatment. Many cases have reported successful treatment using mini-implant, but there are cases where mini-implants may fail. Failure of mini-implants can affect orthodontic treatment, and it is known that several factors may lead to mini-implant loss in orthodontic treatment. This systematic review aimed to determine the factors influencing mini-implant failure in orthodontic treatment. Articles were selected from electronic databases (PubMed, Google Scholar, The Cochrane Library, ScienceDirect) from January 2015 until 2023 according to the PRISMA method (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) under the PEOS (Population-Exposure-Outcome-StudyType) framework questions for systematic review. The study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (CRD42022337684). All data collected were in English, and filtering was done by eliminating duplicate data, meta-analysis, case reports, case series, mini-reviews, and animal studies. The analysis was further divided into three groups, that is, patient-related, implant-related, and operator-related and operator-related (A graphical abstract provided as a Supplementary information [available in the online version]). Twenty-one articles were identified according to the inclusion criteria in the form of retrospective, prospective, in vivo, and randomized controlled trial studies. Mini-implant failures due to patient-related showed six etiological factors, failures due to implant-related had eight etiological factors, and only one factor was operator-related, which may lead to mini-implant failure. The data was extracted without a computerized system and only in English. Mini-implant failure can be caused by many factors; we could not accuse one major factor as a cause. However, the quality or condition of the bones and oral hygiene are factors that play a significant role in obtaining the stability of implants. Mini-implant failure is highly influenced by poor oral hygiene and peri-implant inflammation. Comprehensive diagnostic prior to mini-implant insertion should be appropriately considered. This systematic review describes several factors that can influence mini-implant failure, divided into three groups: patient-related, implant-related, and operator-related (A graphical abstract provided as a Supplementary information [available in the online version]).

Effects of low-level laser therapy on orthodontic miniscrew stability: a systematic review

BACKGROUND

Miniscrews as auxiliary anchorage devices in orthodontic treatment have definite advantages and efficacy. The aim of the present study was to investigate the scientific evidence including randomized controlled trials (RCTs) or controlled clinical trials (CCTs) to support the application of low-level laser therapy to improve miniscrews stability in orthodontic treatment.

METHODS

An extensive literature research was conducted with the Cochrane Library, PubMed, EMBASE, Web of Science and ScienceDirect without language limitations. All searches were inclusive until June 2020. The Cochrane Risk of Bias Tool was used to assess the risk of bias (RoB) in the included RCTs.

RESULTS

Through the electronic searches, 428 titles and abstracts were identified. From these, 4 articles were retrieved for review, and 3 of these met the inclusion criteria. Two RCTs reported increased miniscrews stability with low-intensity laser therapy, but the other one reported no difference. Except one study assessed as "high risk of bias" the other two were rated as "low risk of bias".

CONCLUSION

There is insufficient evidence to support or refute the effectiveness of LLLT for improvement of miniscrew stability. Further studies with a better study design, reliable evaluation method, comprehensive evaluation intervals and appropriate loading protocol are required to provide more reliable evidence for the clinical application of LLLT.

Evidence-based selection of orthodontic miniscrews, increasing their success rate in the mandibular buccal shelf. A randomized, prospective clinical trial

Background

Skeletal anchorage has made it possible to perform complex orthodontic tooth movements that are difficult or even impossible to achieve with conventional orthodontic treatment. Mandibular buccal shelf miniscrews, used for distalization, play a particularly important role in treatment of Class III malocclusion. Unfortunately, stability of the miniscrews placed in the mandible is still considered at higher risk of failure compared to other intraoral locations. The aim of our study was to determine the influence of the miniscrew size on their long-term stability, occurrence of oral mucosa inflammation and pain lasting over 48 h after implantation.

Methods

184 Absoanchor^® miniscrews (Dentos, South Korea) in two sizes: SH2018-10 (length 10 mm, ø 1.8–2.0 mm) and SH1514-08 (length 8 mm, ø 1.4–1.5 mm) were inserted in the mandibular buccal shelf in 92 Caucasians aged 20–50 years, diagnosed with Class III malocclusion that required en-masse distalization of the mandibular dentition. Data was statistically analyzed with the level of significance set at p = .05.

Results

91.3% of the SH2018-10 and 75% of the SH1514-08 miniscrews were stable, and this difference was statistically significant (p < .05). Inflammation of the oral mucosa was noticed around both types of miniscrews and affected 50% of the SH2018-10 and 26.09% of the SH1514-08 group (p < .05). Pain lasting longer than 48 h after implantation was related to 60.87% and 20.65% of the SH2018-10 and the SH1514-08 miniscrews (p < .05), respectively. Inflammation associated with larger SH2018-10 miniscrews did not affect their stability (p > .05), contrary to the SH1514-08 ones (p < .05). When inflammation was present, the overall success rate declined to 64.29%, from 94.74% noted for TADs without inflammation. According to the log-rank test, smaller TADs failed significantly sooner than the larger ones (p = .002).

Conclusion

Larger SH2018-10 miniscrews are the anchorage of choice for the mandibular buccal shelf, despite triggering inflammation and long-lasting pain significantly more often than the smaller ones. Therefore, this issue should be discussed with every patient prior to miniscrew use. Trial registration ID: ClinicalTrials.gov Identifier: NCT05280678 Date of Registration: 15/03/2022. Retrospectively registered.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A Scoping Review about the Characteristics and Success-Failure Rates of Temporary Anchorage Devices in Orthodontics

This study synthesized the scientific evidence concerning the main characteristics of the Temporary Anchorage Devices (TADs) used in orthodontics and reported the success-failure rates during treatment. For that means, this scoping review collected articles from previous research. A complementary search was carried out in the databases PubMed-MEDLINE, Scopus, LILACS, and EMBASE, focusing on original studies published from 2010 to 2020. We analyzed the main characteristics of the publications. As a result, 103 articles were included. Most of the research was conducted among different groups, who needed TADs principally in the maxilla and an interradicular location between the second premolar and first molar. AbsoAnchor, Dentos Inc., Daegu, Korea, was the most used brand of TADs. The most common characteristics of the devices and biomechanics were a diameter and length of 1.6 mm and 8 mm, a self-drilled system, a closed technique for placement, immediate loading, and forces that ranged between 40 and 800 g. Of the studies, 47.6% showed success rates ≥90%. In conclusion, high success rates were found for TADs, and differences were found according to sociodemographic and clinical variables. The studies showed variability in methodological design, and scientific publications were concentrated in certain countries. We recommend further scientific research on TADs using more standardized designs.

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

OBJECTIVE

This study aims to evaluate success factors implicated in clinical orthodontic miniscrew stability after their interradicular placement in maxilla.

MATERIALS AND METHODS

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 ± 1.7 years) 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.

RESULTS

The average success rate was 88%. The principal factors implicated in the failure rate were miniscrew length, MIT values and type of gingiva. Specifically, 8 mm 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 (≤ 8 mm for higher failure rates). For others, MIT values of 5-10 Ncm are linked to higher failure rates (p < 0.05).

CONCLUSION

Orthodontic miniscrews inserted in the maxilla display good success rates. However, clinicians should be discouraged from using miniscrews of length ≤ 8 mm and MIT values < 10 Ncm, even with longer miniscrews.

CLINICAL RELEVANCE

Information about factors related to failure rate of miniscrews placed at posterior maxillary interradicular sites is given.

Long-term evaluation of factors affecting removal torque of microimplants

Background

The current study aimed to evaluate factors affecting the long-term stability of microimplants using removal torque and the correlation between removal torque and clinical variables.

Materials and methods

This research evaluated 703 microimplants placed in 354 patients (mean age: 30.4 ± 12.1 years). The removal torque was evaluated according to various clinical variables including sex, age, placement site, microimplant size, and placement method (self-drilling versus pre-drilling). Pearson correlation and stepwise multiple linear regression analyses were performed to investigate different variables and their association with removal torque.

Results

The mean removal torque was significantly higher in the mandible (4.46 N cm) than in the maxilla (3.73 N cm). The values in the posterior teeth/retromolar areas were significantly higher than those in the anterior teeth area. There were no significant difference in terms of sex. Teenagers had a lower removal torque than older adults in the mandible, but not in the maxilla. Microimplants with a greater length and diameter, except for those with a greater diameter in the maxilla, was associated with a higher removal torque. Regardless of placement torque, the removal torque convergently reached approximately 4 N cm in both placement methods. The removal torque was significantly correlated with screw length in the self-drilling group and with diameter in the pre-drilling group.

Conclusions

Removal torque was related with placement site, age, placement method, and length and diameter of microimplants.

Optimal Implantation Site of Orthodontic Micro-Screws in the Mandibular Anterior Region Based on CBCT

Background: To determine the optimal implantation site of orthodontic micro-screws based on cone beam computed tomography (CBCT) analysis in the mandibular anterior tooth region, provide a theoretical basis for orthodontic implant placement and improve post-implantation stability.

Methods: Forty patients who underwent CBCT scanning were selected for this study. CBCT scanning was applied to measure the interradicular distance, buccolingual dimension, labial cortical bone thickness and lingual cortical bone thickness between mandibular anterior teeth at planes 2, 4, 6, and 8 mm below the alveolar ridge crest. The data were measured and collected to obtain a comprehensive evaluation of the specific site conditions of the alveolar bone.

Results: The interradicular distance, buccolingual dimension and labial cortical bone thickness between the mandibular anterior teeth were positively correlated with the distance below the alveolar ridge crest (below 8 mm). The interradicular distance, buccolingual dimension, labial cortical bone thickness, and lingual cortical bone thickness were all greater than those in other areas between the lateral incisor root and canine incisor root 4, 6, and 8 mm below the alveolar ridge crest.

Conclusion: The area between the lateral incisor root and the canine incisor root in planes 4, 6, and 8 mm from the alveolar ridge crest can be used as safe sites for implantation, while 8 mm below the alveolar ridge crest can be the optimal implantation site. An optimal implantation site can be 8 mm below the alveolar ridge crest between the lateral incisor root and the canine incisor root.

RFA measurements of survival midpalatal orthodontic mini-implants in comparison to initial healing period

Background

In dental implantology, the development of stability over time is a well-investigated topic. In case of orthodontic mini-implants, quantitative data for long-term stability is not available yet. This study aims to clinically investigate the long-term stability of mini-implants inserted in the midsagittal suture of the anterior palate. Moreover, the influence of the length of implants was elucidated. The stability of 2 × 9 and 2 × 11 mm mini-implants after orthodontic treatment (9 mm, 2.84 years ± 1.25 years; 11 mm, 3.17 years ± 0.96 years) was assessed by resonance frequency analysis (RFA). The obtained long-term pieces of data were compared with each other (9 mm vs 11 mm), as well as with the data from the matched early stability groups, to assess the initial and early secondary stability after the insertion from previous clinical trials.

Results

For both lengths, the long-term stability (2 × 9 mm, 25.12 ± 7.11, n = 21; 2 × 11 mm, 24.39 ± 5.82, n = 18) was significantly lower than primary stability (2 × 9 mm, 36.14 ± 6.08, n = 19; 2 × 11 mm, 33.35 ± 3.53, n = 20). The differences within the groups disappeared over the initial healing period: after 4 weeks for the 2 × 9 mm implants and after 2 weeks for the 2 × 11 mm implants. Also, the 2 × 9 mm and 2 × 11 mm implants showed comparable long-term stability values.

Conclusion

The stability of midpalatal mini-implants does not change in the long term after the initial healing period. Moreover, 2 × 9 mm mini-implants seem to be appropriate for orthodontic anchorage, as the stability of 2 × 11 mm implants is not higher. Therefore, owing to lower invasiveness, 2 × 9 mm implants should be preferred.

Distance to alveolar crestal bone: a critical factor in the success of orthodontic mini-implants

Background

To evaluate the success rate of orthodontic mini-implant (MI) in relation to implant characteristics, mainly implant distance to alveolar crestal bone (AC) and root proximity (RP) to adjacent teeth.

Methods

Two hundred sixty MIs (209 in maxilla, 51 in mandible) were categorized into success (n = 229) and failure (n = 31) groups. Distances from MI to the most adjacent tooth (DT) and to AC level (DC) were measured on periapical radiographs taken with the orthoradial projection technique. Appropriate statistical tests (chi-square, t test, logistic regression) were applied.

Results

DC measurements were statistically significantly greater in the success group (7.46 ± 1.7 mm) compared to 3.43 ± 0.81 mm in the failure group. Root proximity was not associated with miniscrew failure. Patient age, mini-implant site, and DC were significant predictors of mini-implant failure (p < 0.001), which decreased significantly with increasing age (Coef = − 0.345; p = 0.013) and when the mini-implant was placed between premolars (p = 0.028) or between premolar and first molar (p = 0.045). The probability of failure also decreased with increasing DC distance (Coef = − 3.595; p < 0.001).

Conclusion

The distance to alveolar crest was strongly associated with long-term stability. More apical placement of the MI from the crest would be compatible with a denser and thicker bucco-lingual/palatal bone level.

Miniscrews failure rate in orthodontics: systematic review and meta-analysis

Background

Miniscrews in orthodontics have been mainly used for anchorage without patient compliance in orthodontic treatment. The literature has reported changing failure rates.

Objective

The aim of this review was to provide a precise estimation of miniscrew failure rate and the possible risk factors of the mechanically-retained miniscrews.

Search method

Electronic search in database was undertaken up to July 2017 through the Cochrane Database of Systematic Reviews, MEDLINE, Scopus, and Ovid. Additional searching for on-going and unpublished data, hand search of relevant journals and grey lietraure were also undertaken, authors were contacted, and reference lists screened.

Eligibility criteria

Randomised controlled trials (RCTs) and prospective cohort studies (PCSs), published in English were obtained, which reported the failure rate of miniscrews, as orthodontic anchorage, with less than 2 mm diameter.

Data collection and analysis

Blind and induplicate study selection, data extraction, and risk of bias assessment were undertaken in this research. Failure rates and relevant risk factors of miniscrews with the corresponding 95 per cent confidence intervals (CIs) were calculated by using the random-effects model. The heterogeneity across the studies was assessed using the I2 and Chi2 test. The risk of bias was assessed using Cochrane risk of bias and Newcastle-Ottawa Scale. Subgroup and sensitivity analyses were performed in order to test the robustness of the results in meta-analysis.

Results

The 16 RCTs and 30 PCSs were included in this research. Five studies were not included in the meta-analysis due to a lack of the statistical information needed to compute the effect sizes. About 3250 miniscrews from 41 studies were pooled in a random-effect model. The overall failure rate of miniscrews was 13.5 per cent (95% CI 11.5-15.9). Subgroup analysis showed that miniscrews 'diameter, length and design, patient age, and jaw of insertion had minimal effect on rate of miniscrews failure while the type of the gingivae and smoking had statistically significant effect.

Conclusion

Miniscrews have an acceptably low failure rate. The findings should be interpreted with caution due to high-level of heterogeneity and unbalanced groups in the included studies. High quality randomized clinical trial with large sample sizes are required to support the findings of this review.

Role of anatomical sites and correlated risk factors on the survival of orthodontic miniscrew implants: a systematic review and meta-analysis

Objectives

The aim of this review was to systematically evaluate the failure rates of miniscrews related to their specific insertion site and explore the insertion site dependent risk factors contributing to their failure.

Search methods

An electronic search was conducted in the Cochrane Central Register of Controlled Trials (CENTRAL), Web of Knowledge, Scopus, MEDLINE and PubMed up to October 2017. A comprehensive manual search was also performed.

Eligibility criteria

Randomised clinical trials and prospective non-randomised studies, reporting a minimum of 20 inserted miniscrews in a specific insertion site and reporting the miniscrews’ failure rate in that insertion site, were included.

Data collection and analysis

Study selection, data extraction and quality assessment were performed independently by two reviewers. Studies were sub-grouped according to the insertion site, and the failure rates for every individual insertion site were analysed using a random-effects model with corresponding 95% confidence interval. Sensitivity analyses were performed in order to test the robustness of the reported results.

Results

Overall, 61 studies were included in the quantitative synthesis. Palatal sites had failure rates of 1.3% (95% CI 0.3–6), 4.8% (95% CI 1.6–13.4) and 5.5% (95% CI 2.8–10.7) for the midpalatal, paramedian and parapalatal insertion sites, respectively. The failure rates for the maxillary buccal sites were 9.2% (95% CI 7.4–11.4), 9.7% (95% CI 5.1–17.6) and 16.4% (95% CI 4.9–42.5) for the interradicular miniscrews inserted between maxillary first molars and second premolars and between maxillary canines and lateral incisors, and those inserted in the zygomatic buttress respectively. The failure rates for the mandibular buccal insertion sites were 13.5% (95% CI 7.3–23.6) and 9.9% (95% CI 4.9–19.1) for the interradicular miniscrews inserted between mandibular first molars and second premolars and between mandibular canines and first premolars, respectively. The risk of failure increased when the miniscrews contacted the roots, with a risk ratio of 8.7 (95% CI 5.1–14.7).

Conclusions

Orthodontic miniscrew implants provide acceptable success rates that vary among the explored insertion sites. Very low to low quality of evidence suggests that miniscrews inserted in midpalatal locations have a failure rate of 1.3% and those inserted in the zygomatic buttress have a failure rate of 16.4%. Moderate quality of evidence indicates that root contact significantly contributes to the failure of interradicular miniscrews placed between the first molars and second premolars. Results should be interpreted with caution due to methodological drawbacks in some of the included studies.

Electronic supplementary material

The online version of this article (10.1186/s40510-018-0225-1) contains supplementary material, which is available to authorized users.

Influence of antibiotic prophylaxis on the stability of orthodontic microimplants: A pilot randomized controlled trial

INTRODUCTION

The aims of this 2-arm parallel pilot randomized controlled trial were to investigate the influence of antibiotic prophylaxis on the stability of orthodontic microimplants and to evaluate the efficacy of systemic inflammatory marker measurements in detecting infections in tissues surrounding microscrews.

METHODS

Orthodontic patients requiring en-masse distalization in the maxilla received antibiotics or a placebo before microimplant placement. Eligibility criteria included 13 years of age, and good general and oral health. Exclusion criteria comprised allergy to antibiotics, severe systemic allergy, heart and kidney diseases, and recent antibiotic treatment. Stability of the microimplants was the primary outcome; inflammation of the tissues surrounding the microscrews, pain related to the microimplantation, and serum levels of inflammatory markers were the secondary outcomes. Randomization in a 1:1 ratio was performed by auxilliary staff via a flip of a coin between 2 participants of the same sex and developmental stage, and the "winner" was allocated to the intervention group. Pharmaceutically prepared identical capsules with either amoxicillin (intervention) or glucose (control) given 1 hour before microimplant placement according to the allocation provided blinding of the participants. Subsequently, 1 clinician unaware of the allocation inserted the microimplants and assessed the outcomes, which simultaneously blinded the operator-assessor. Blood samples for laboratory analysis of inflammatory markers were collected a day before and 1, 3, and 7 days postoperatively.

RESULTS

Out of 80 participants initially assessed for eligibility, 41 received the randomized allocation. Three patients were lost to follow-up. Eventually, data of 18 and 20 participants (mean age, 20.4 ± 5.9 years) were available for analysis in the intervention and control groups, in which 1 and 2 patients lost a microimplant, respectively, resulting in odds ratio of 0.53 (95% confidence interval [CI], 0.0084-11.23; P = 1.0). The odds ratio for inflammation development was 1.22 (95% CI, 0.34-4.38), and the odds ratio for feeling milder pain was 1.174 (95% CI, 0.350-3.941) in the intervention compared with the control group, but the result was not statistically significant (P = 0.758; P = 0.795, respectively). The inflammatory marker levels did not increase due to either microimplantation (procalcitonin, P = 0.445; C-reactive protein, P = 0.4) or peri-implantitis. Antibiotic prophylaxis slightly decreased the levels of the biomarkers in the intervention group; however, the results were not statistically significant (P = 0.68; P = 0.908, respectively). No harms caused by the microimplantation procedure or drug intake were noted.

CONCLUSIONS

Antibiotics provided no benefit in terms of microimplant stability, inflammation of soft tissues, or postoperative pain in our pilot sample. Measurements of serum levels of inflammatory markers were inefficient in detecting soft tissue inflammations. These initial results should be interpreted with caution until validated by a large multicenter definitive trial.

REGISTRATION

This trial was not registered.

PROTOCOL

The protocol was not published before trial commencement.

FUNDING

The trial was funded by Wroclaw Medical University; grant number pbmn91 and supported by Diagnostyka.

Prognosis of primary and secondary insertions of orthodontic miniscrews: What we have learned from 500 implants

INTRODUCTION

Although the success of using orthodontic miniscrews for primary insertion has been reported in the literature, few studies have followed up on secondary insertions after failure of the first insertion. In this study, we investigated not only the primary but also secondary success rates of miniscrews and considered the risk factors influencing their stability.

METHODS

Five hundred miniscrews were inserted for orthodontic anchorage in 240 patients. Ninety-eight miniscrews lacked stability; thus, 77 of these were removed and reinserted. We calculated and compared the primary and secondary success rates of insertion. Moreover, we investigated which clinical parameters affected the stability of miniscrews.

RESULTS

The success rate of secondary insertion (44.2%) was significantly lower than that of primary insertion (80.4%). The screw length and jaw receiving the insertion were significantly associated with the stability of miniscrews. The 8.0-mm miniscrews were significantly more stable than the 6.0-mm miniscrews, and the success rate for insertions into the maxilla was significantly higher than that for the mandible.

CONCLUSIONS

Secondary insertions lack stability; therefore, clinicians should be aware of the reduced success rate of reinsertion and know the risk factors to avoid failure of secondary insertions.

Risk factors associated with the failure of miniscrews - A ten-year cross sectional study

The aims of this study were to identify (1) patient-related factors (sex, age, craniofacial pattern and smoking habit), (2) miniscrews implants (MSI)-related factors (length and diameter) and (3) location-related factors [bone (maxilla or mandible) and area (buccal, lingual and alveolar ridge)] that may be associated with MSI loss of stability. A total of 1356 MSI were installed in 570 patients (423 females and 147 males) with mean age of 42.7 during a 10-year period and were clinically evaluated once a month until the end of the proposed movement. Length (5, 7, 9 and 11 mm) and diameter (1.3, 1.4 and 1.6 mm) of the MSI were selected according to insertion site. The evidence of clinical mobility during treatment or fracture during insertion was considered as failure. A total success rate of 89.1% was observed. There was no statistically significant difference in loss of stability when considering age, sex, craniofacial pattern or smoking habit. Considering diameter, there was no statistically significant difference (p = 0.645), but the shorter miniscrews (5 mm) showed higher failure rates (p < 0.001) than the longer ones. There were more loses (p < 0.001) in the mandible than in the maxilla, but the area (buccal, lingual or alveolar ridge) did not interfere in the results (p = 0,421). It can be concluded that MSIs are effective for skeletal anchorage in orthodontics. Patient-related factors, such as sex, age, smoking habit and craniofacial pattern, did not affect MSI success. However, the use of shorter MSIs (5 mm) was inversely proportional to failure probability, and loss of stability was greater in the mandible.

[Bone-based anchorage failure]

The aim of this article is to list the circumstances likely to give rise to failure of orthodontic temporary bone-supported anchorage and, hence, to attempt to define criteria for correct miniscrew usage. Our study was based on a review of the literature and analyses of clinical cases. Our findings show that, with a sound knowledge of the indications for screw selection and positioning and of the insertion protocols combined with a clear understanding of orthodontic mechanics, bone-based anchorage can henceforth provide orthodontists with an essential tool to enable formerly unachievable dental movements and to stabilize unwanted movements, thus making treatment both more reliable and more effective.