failure of miniscrews

SYSTEMATIC REVIEW

Insertion torque and success of orthodonticmini-implants: A systematic review

Reint A. Meursinge Reynders,a Laura Ronchi,a Luisa Ladu,a,c Faridi van Etten-Jamaludin,b and Shandra Bipatc

Milan, Italy, and Amsterdam, The Netherlands

aPrivabCliniAmstecReseAcadeNetheThe aproduReprin20123Subm0889-Copyrhttp:/

596

Introduction: In this systematic review, we analyzed whether recommended maximum insertion torque valuesof 5 to 10 Ncm were associated with higher success rates of orthodontic mini-implants compared with mini-implants inserted with maximum insertion torque values beyond this range. Objective assessments ofstability, variables that influence maximum insertion torque values, and adverse effect of interventions werealso assessed in the studies selected for our PICO (patient problem or population, intervention, comparison,and outcomes) question. Methods: Computerized and manual searches of the literature were conducted upto February 24, 2012, for human studies that assessed these objectives. Our eligibility criteria selected studiesthat (1) used sample sizes of 10 or more, (2) recorded maximum insertion torque during the insertion of ortho-dontic mini-implants, (3) inserted implants with a diameter smaller than 2.5 mm, and (4) applied orthodonticforces for a minimum duration of 4 months. Confounding was assessed through the analysis of risk of bias,and the validity of outcomes was rated according to the GRADE approach. The Cochrane Handbook forSystematic Reviews of Interventions was our main guideline for the methodology. Results: Seven nonrandom-ized studies met the eligibility criteria. All associations between specific maximum insertion torque values andsuccess were based on literature rated as having low quality. The reasons for these judgments included subjec-tive definitions of success, poor-quality torque sensors, and high risks for selection, performance, detection, andreporting biases. A risk of multiple publication bias was also suspected. All associations between maximuminsertion torque and factors related to implant, patient, location, and surgery were rejected; few studiesreported on adverse effects. Conclusions: Currently, no evidence indicates that specific maximum insertiontorque levels are associated with higher success rates for orthodontic mini-implants. Additional research onthis topic is therefore necessary. The following guidelines for future studies are suggested: (1) systematicallyreview the animal and laboratory literature, (2) perform maximum insertion torque tests on artificial bone, (3)test associations in animal studies before conducting clinical trials, (4) test associations between maximuminsertion torque and the stability of orthodontic mini-implants with objective quantitative recordings rather thansubjective qualitative measures, (5) measure maximum insertion torque with digital sensors rather than withmechanical devices, (6) assess the stability of orthodontic mini-implants at preestablished times, (7) consultour risk-of-bias analysis, and (8) analyze the adverse effects of interventions. (Am J Orthod DentofacialOrthop 2012;142:596-614)

Many variables that affect the stability of ortho-donticmini-implants (also called temporary an-chorage devices) are still poorly understood.1-6

It has been suggested that excessive torque forces

te practice, Milan, Italy.cal librarian, Medical Library of the Academic Medical Center, University ofrdam, Amsterdam, The Netherlands.arch associate, Departments of Radiology, Epidemiology and Biostatistics,mic Medical Center, University of Amsterdam, Amsterdam, Therlands.uthors report no commercial, proprietary, or financial interest in thects or companies described in this article.t requests to: Reint A. Meursinge Reynders, Via Matteo Bandello 15,, Milan, Italy; e-mail, [email protected], October 2010; revised and accepted, June 2012.5406/$36.00ight � 2012 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2012.06.013

applied during the insertion of these devices can causenecrosis of the surrounding bone and compromise theirsuccess.2,7-9 It is therefore necessary to understand atwhat levels torque strains remain physiologic and canguarantee the stability of these implants.

Finding reliable sources for stationary anchorage haslong been a challenge for orthodontists. Orthodonticmini-implants have been introduced as promisingsolutions for this problem, but their outcomes are not al-ways consistent.4,10 These devices can loosen, becomemobile, or even migrate.5,11,12 Variables that influencetheir success rates include factors related to patient,implant, location, surgery, orthodontics, and implantmaintenance.10,13 This review will focus on insertiontorque, which is a subgroup of surgery-related factors. In-sertion torque results from frictional resistance between

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Meursinge Reynders et al 597

the screw thread and its surrounding bone and is a stan-dard to evaluate mechanical stability.14-17 Maximuminsertion torque is expressed in Newton centimeters(Ncm) and is the maximum torque value recordedduring the insertion of orthodontic mini-implants. Thestability of implants can be divided into primary and sec-ondary. The former is mechanical stabilization achievedimmediately after insertion, and the latter is attainedwhen new bone forms at the implant interface.18

To achieve initial stability, a certain level of maximuminsertion torque is necessary.2,19 Studies with dentalimplants have shown that increases in peak insertiontorque can reduce the amount of micromotion andimprove their success.18,20 However, excessive stress tothe bone can cause necrosis and local ischemia7 andmightimpede osseointegration and hence secondary stability.2

Such an association was also suggested in various clinicalstudies in the orthodontic literature.2,21-24 Animal studieshave associated higher maximum insertion torque valuesand overtightening of orthodontic mini-implantswith fractures of the cortical bone.8,9 The orthopedicliterature has shown that overtightening can damageand cause stripping of the bone, and this can lead todiminished holding strength25 with losses in pulloutstrength up to 40% to 50%.26 To control excessive stressduring the insertion of orthodontic mini-implants, torqueratchets or torque sensors have been developed.

Clinicians want to know whether specific maximuminsertion torque values are associated with highersuccess rates. If a range of safe torque levels can be iden-tified, they also want to learn which variables affect thesemeasures. Maximum insertion torque values in the rangeof 5 to 10 Ncm have been presented as the gold standardin several clinical articles,2,21,22 and Google Scholar hasrecorded over 135 citations for one of these articles.2

However, conflicting findings on this issue have alsobeen recorded in the orthodontic literature.24,27,28

Because of this disagreement and because currentlyno reviews have addressed these issues, a systematicreview was deemed appropriate. The following PICO(patient problem or population, intervention, compari-son, and outcomes) question was therefore asked: Isthe application of maximum insertion torque valuesin the range of 5 to 10 Ncm (intervention) during theinsertion of orthodontic mini-implants in patientswho require maximum anchorage during treatmentassociated with higher success rates of orthodonticmini-implants (outcomes) than those inserted withmaximum insertion torque values beyond this range(comparison)? Adverse effects of interventions and var-iables that influence insertion torque levels were alsoassessed in the studies that were selected for ourPICO question.

American Journal of Orthodontics and Dentofacial Orthoped

MATERIAL AND METHODS

The protocol for undertaking a systematic review ispresented in a flow diagram (Fig 1), based on theCochrane Handbook for Systematic Reviews of Inter-ventions,29 and the CONSORT and PRISMA state-ments.30-33

To address the objectives of this review, we definedthe selection criteria for the types of studies, interven-tions, outcomes, and timing of the results as follows.

1. Human studies with minimum samples sizes of 10were considered. Animal studies, laboratory studies,technique articles, case reports, opinion papers, re-views, and in-vitro studies were excluded.

2. Our preferred choice of research design was therandomized controlled trial, but nonrandomizedstudies with a low or moderate risk of bias werealso assessed.34 This decision was based on the justi-fications of the guidelines of theCochraneHandbookfor Systematic Reviews of Interventions34 and theCentre for Evidence Based Medicine at the Universityof Oxford in the United Kingdom.35,36 The rationalesfor including nonrandomized studies in a systematicreview are the following: (1) high-quality non-randomized studies could produce a better unbiasedeffect size compared with low-quality randomizedcontrolled trials; (2) randomized controlled trialscould be unavailable for ethical reasons; (3) non-randomized studies place the validity of the currentliterature in perspective and show the need for futureresearch; (4) findings of a review of nonrandomizedstudies might be helpful in designing subsequentstudies; (5) nonrandomized studies could revealpotential unexpected or rare harms of interven-tions34,37; and (6) the validity of nonrandomizedstudies could be upgraded for demonstratinga large treatment effect.35,36

3. If moderate- or high-quality randomized controlledtrials were identified, nonrandomized studies werenot consulted for their treatment effect, but onlyfor additional information on adverse effects ofthe intervention.34

4. Patients of either sex, in any ethnic, socioeconomic,or age group, and in any setting in need of station-ary anchorage during treatment with fixed ortho-dontic appliances were included.

5. Interventions must include inserted orthodonticmini-implants for stationary orthodontic anchor-age.

6. Interventions must include records of the maxi-mum insertion torque values during the insertionof orthodontic mini-implants. Maximum insertiontorque represents primary stability and is defined

ics November 2012 � Vol 142 � Issue 5

Establish selection criteria

Establish search methods for identification of studies

Selection of studies Present flow diagram “searching for studies”

Establish what data to extract

Data extraction Conduct subgroup analyses when indicated

Present estimate of effect for each outcome

Define types of bias specific for eligible studies

Define rating parameters for magnitude, reliability and direction of bias

Assess risk of bias for outcomes within a study across domains

Assess risk of bias across outcomes (only in case of multiple outcomes)

Define general parameters that can affect GRADE ratings

“Final” quality assessment (GRADE)

“Initial” quality assessment (GRADE)

Identify study specific factors that may affect the assessment of quality

ASSESSMENT OF RISK OF BIAS FOR OUTCOMES

CRITERIA FOR CONSIDERING STUDIES

SEARCHING FOR STUDIES

DATA COLLECTION

SUMMARY OF FINDINGS TABLE FOR EACH ELIGIBLE STUDY

Fig 1. Flow diagram for a protocol of a systematic review.29-33

598 Meursinge Reynders et al

November 2012 � Vol 142 � Issue 5 American Journal of Orthodontics and Dentofacial Orthopedics


as the maximum torque value recorded from thebeginning to the end of the insertion process oforthodontic mini-implants.15 Maximum insertiontorque is expressed in Newton centimeters and isrecorded with either mechanical or electronicscrewdrivers.

7. Interventions must include insertion of orthodonticmini-implants with a diameter smaller than 2.5 mm.This limit was chosen because larger implants wouldnot classify for specific orthodontic indications (eg,interradicular positioning). Articles on miniplateswere excluded because of their different biome-chanical characteristics.

8. Studies that applied forces for more than 120 dayswere included.38 This arbitrary time frame was cho-sen because most orthodontic objectives cannot becompleted in less than 4 months.

9. Primary and secondary outcomes as well as adverseeffects were assessed for the intervention under re-view. Eligibility was established irrespective of theoutcomes measured or reported.39

Success was selected as the primary outcome for ourquestion. The following characteristics were defined forthis parameter.

1. An orthodontic mini-implant was considered suc-cessful when it could be loaded with orthodonticforces and fulfill its anchorage objectives duringa minimum period of 4 months.

2. Orthodontic mini-implants that were lost or had be-come unusable were considered to be failures. Thisgroup also included implants that fractured at inser-tion or during orthodontic treatment.

3. The timing for this outcome assessment was dividedinto 3 time frames: short term (4-6 months), me-dium term (6 months-1 year), and long term (1year and longer).

One adverse effect, fractured implants, was also in-cluded as a primary outcome and expressed in ratios(number of fractured implants per total number of in-serted implants).

Three types of secondary outcomes were assessed: (1)subjective stability of the orthodontic mini-implants, (2)objective stability of the orthodontic mini-implants, and(3) variables that influenced maximum insertion torquevalues.

The stability of orthodontic mini-implants can bemeasured either subjectively by a clinician40 or objec-tively with various measuring devices.41,42 Immobility,mobility, and displacement were used as parameters toclassify subjective stability and defined according toa recent systematic review.10


1. Success without mobility (score 0): implants with noclinically detectable mobility that could fulfill allnecessary orthodontic anchorage objectives.

2. Success with mobility (score 1): implants that hadbecome mobile but could still fulfill all necessaryorthodontic anchorage objectives.

3. Success with displacement (score 2): implants thathad become displaced but could still fulfill all neces-sary orthodontic anchorage objectives.

4. Not specified success (score NSS): the type of suc-cess of the implants was not specified and includedscores of 0, 1, and 2.

The objective stability of orthodontic mini-implantswas measured at their removal with mechanical or digitalinstruments. Values that were specific for each instru-ment were recorded: eg, removal torque or resonancefrequency values.

Variables that might influence maximum insertiontorque values of orthodontic mini-implants were classi-fied under the following factors: implant, patient, loca-tion, and surgery. Associations between maximuminsertion torque and these parameters were tested ac-cording to the following criteria:

1. An association with maximum insertion torque wasonly considered if it was based on samples sizes of10 patients or more.

2. A proposed association with maximum insertiontorque was rejected when the article presented di-rect proof that at least 1 influencing variable wasnot controlled. Lack of information about con-founding factors was not sufficient to reject anassociation.

3. Only associations that presented theirP values and/orconfidence intervals were considered.

Adverse effects of insertion procedures of orthodon-tic mini-implants were assessed according to theguidelines in a recent systematic review.10 Adverse ef-fects included implant fracture at insertion, biologicdamage, inflammation, and pain and discomfort. Bio-logic damage was defined according to the followingparameters:

1. No biologic damage (score 0): no biologic damagehad occurred, and no correcting dental procedureswere considered necessary.

2. Reversible biologic damage (score 1): biologic dam-age that is completely reversible with simple dentalprocedures. This group included removal of hyper-plastic tissue and fractured orthodontic mini-implants that could be removed without causingirreversible damage.



3. Irreversible biologic damage (score 2): biologic dam-age that is not completely reversible with simpledental procedures. This group included tooth, nerve,sinus, and blood vessel damage; fractured mini-implants that could not be removed; and the needfor orthognathic surgery caused by uncontrolledbiomechanics with orthodontic mini-implants.

4. Not specified biologic damage (score NSBD): thebiologic damage was described, but the type ofdamage was not identified.

5. Postimplant biologic damage (score PIBD): thebiologic damage was caused by treatment with or-thodontic mini-implants but occurred or was de-tected after removal of the screw.

Inflammation was measured either within the firstmonth of implant placement or beyond this time limit,and defined as follows:

1. No inflammation: (score 0): no signs of inflamma-tion during the entire period of treatment with or-thodontic mini-implants.

2. Temporary inflammation (score 1): inflammationwas confined to the first month.

3. Continuing inflammation (score 2): inflammationlasted longer than the first month.

4. Not specified inflammation (score NSI): the durationof the inflammation was not specified.

Pain and discomfort weremeasured in thefirst 2 weeksafter implantation or beyond43 and defined as follows:

1. No pain or discomfort (score 0): no pain or discom-fort during the entire treatment period with ortho-dontic mini-implants.

2. Moderate pain or discomfort (score 1): moderatepain or discomfort noted in the first 2 weeks.

3. Severe pain or discomfort (score 2): severe pain ordiscomfort noted in the first 2 weeks.

4. Continuing pain or discomfort (score 3): pain lastinglonger than 2 weeks.

5. Not specified pain (score NSP): pain and discomfortwere described, but their quality or duration werenot specified.

Search methods for identification of studies

To find eligible studies for our PICO question, weconsulted the following electronic data bases throughFebruary 24, 2012: Google Scholar Beta, PubMed (Med-line), Embase (Ovid), CENTRAL, Science Direct, Scopus,Web of Science, LILACS, and AJOL.44-46 Eligiblereports were also searched in the grey literature,because excluding those data bases could introducepublication bias.47 For this purpose, we consultedOpen Grey, the Health Management Information

November 2012 � Vol 142 � Issue 5 American

Consortium (HMIC), and the National Technical Infor-mation Service (NTIS). The fourth author (F.E.J.), a librar-ian who specializes in computerized searches of healthscience publications at the Academic Medical Centre ofthe University of Amsterdam, assisted with the examina-tion of these databases.

Transparency and reproducibility of our searchprocess was our primary goal, and we aimed for highsensitivity and accepted low precision.44 To avoid inap-propriate exclusion, a wide variety of search terms wascombined, including the following subject headingsand keywords: orthodontics, torque, implant, mini im-plant, micro implant, microimplant, screw, mini screw,miniscrew, micro screw, microscrew, and temporary an-chorage device. For each search engine, the appropriatecharacters were used to truncate or explore the searchterms. Nouns, adjectival, and singular and plural formsof all keywords were inserted.44 Search filters wereavoided, and the Boolean NOT operator was not ap-plied.44 To analyze whether the keywords had coveredall articles on orthodontic mini-implants, the followingjournals were handsearched: American Journal ofOrthodontics & Dentofacial Orthopedics, Angle Ortho-dontist, European Journal of Orthodontics, Journal ofOrthodontics, Journal of Clinical Orthodontics, Semi-nars in Orthodontics, World Journal of Orthodontics,and International Journal of Adult Orthodontics andOrthognathic Surgery. In addition, the references ineach identified article were manually screened for arti-cles that possibly were missed by the electronic searchengines. All manual and electronic searches were soli-cited for review articles, and references found in thesereviews were screened for relevant articles.44 No lan-guage restrictions were applied in the search strategy,and pertinent articles were translated and reviewed.

To minimize the risk of missing eligible studies, 3 au-thors (R.A.M.R., L.R., L.L.), all topic experts, selected thestudies.47,48 All selection procedures were performedindependently by these reviewers. The fifth author (S.B.)guaranteed the soundness of the methodology and thestatistics of this study. To control interexamineragreement (kappa statistics), we followed the protocol inthe Cochrane Handbook for Systematic Reviews ofInterventions.47 According to this protocol, pilot testson samples of reports were used to refine and clarify theeligibility criteria and ensure that these criteria could beapplied consistently.47 Then, all titles and abstracts wereexamined to remove obviously irrelevant reports. Thefull texts of potentially relevant articles were retrievedand reviewed. Ambiguous articles were also read toprevent inappropriate exclusions. To avoid bias throughduplicate publications, special attentionwas paid to iden-tifying multiple reports from the same study.47 In case of

Journal of Orthodontics and Dentofacial Orthopedics

Records screened ( n =9480)

Records excluded (n =9443)

Studies included in qualitative synthesis

( n=7 )

Records identified through database searching

(n = 9464)

Additional records identified through other sources

(n =16)

Full-text articles assessed for eligibility

( n= 37)

Full-text articles excluded, with reasons

(n= 30)

Fig 2. PRISMA flow diagram.32,33


uncertainties, the authors of such articles were contactedfor clarification. Disagreements between authors aboutthe eligibility of articles were resolved by rereading anddiscussion. Our selection procedures are presented ina flow diagram (Fig 2).

Prior to conducting this systematic review, datacollection forms were designed and pilot tested fortheir validity. These forms included all informationabout a study: eg, details of methods, participants,settings, contexts, interventions, outcomes, variables,results, publications, and investigators.47 Although or-thodontics and implant-related factors do not influ-ence insertion torque values, they were recordedbecause they can influence success rates. Data thatcould facilitate the assessment of risk of bias werealso collected. Data extraction procedures were doneindependently by all 3 topic experts. Disagreementsbetween authors were resolved by rereading and dis-cussion. Investigators of the selected studies were con-tacted in case of uncertainty or inability to extract allnecessary information, or in case of disagreement be-tween reviewers.47 If possible, individual patient datawere sought directly from the authors.47 Subgroupanalyses were performed only if the study itself orthe individual patient data provided sufficient datato permit such assessments.49


The validity of each study was scored through theassessment of risk of bias in the results.50 Critical judg-ments were made for the following domains: multiplepublications, selection, performance, detection, attri-tion, and reporting bias. Performance bias was furthersubdivided as implant, location, surgery, orthodontics,implant maintenance, outcome assessment, operator,and duration related systematic errors. To guaranteethe transparency of these judgments, detailed informa-tion on these variables was presented. Judgments weremade on the magnitude, reliability, and direction ofbias. Descriptions and definitions of each type of biasare given in Table I. Judgments were defined as low,high, or unclear risk of bias. The Cochrane Collabora-tion50 assigns the latter score if “1) insufficient detailis reported of what happened in the study; 2) what hap-pened in the study is known, but the risk of bias is un-known; 3) an entry is not relevant to the study athand.” Domains of bias were scored as high risk onlywhen the article presented direct evidence that an entrywas at risk of systematic error. Incorporating assess-ments of risk of bias was not used as a threshold forinclusion of studies but exclusively as a possible expla-nation for differences in results.

For the assessment of the quality of a body of evi-dence, we applied the GRADE approach,51 which was


Table I. Classification scheme for the assessment of risk of bias in maximum insertion torque studies34,50

Type of bias Description of biasMultiple publication bias Judgment on duplicate or multiple publications of the same research.Selection bias Judgment on the type of sample selection concerning random sequence generation,

allocation concealment, and description of sample characteristics on outcomes.Performance bias, implants Judgment on the impact of, eg, the description, quality, and other implant-related

confounding factors on outcomes.Performance bias, patients Judgment on the impact of, eg, the number, age, physical, dental status, and other

human-related confounding factors on outcomes.Performance bias, location Judgment on the impact of, eg, the site of insertion, character of the mucosa, exposure, and

other location-related confounding factors on outcomes.Performance bias, surgery Judgment on the impact of, eg, the torquing device, flap/flapless technique, distance between

screws, direction and speed of insertion, time of insertion torque assessment, self-drilling/predrilling insertion technique, starter and full-length pilot holes, depth of insertion,axial load, stripping, and other surgery-related confounding factors on outcomes.

Performance bias, orthodontics Judgment on the impact of, eg, the type of orthodontic movement, timing and duration offorce application, the magnitude, type, and direction of the force, and otherorthodontics-related confounding factors on outcomes.

Performance bias, implant maintenance Judgment on the impact of, eg, protocols for antibiotics, chlorhexidine rinses, oral hygiene,control of peri-implantitis and mobility, and other implant maintenance-relatedconfounding factors on outcomes.

Performance bias, outcome assessment Judgment on the character and quality of outcome assessments: eg, subjective or objectivemethods of assessments on outcomes.

Performance bias, operator Judgment on the impact of operators concerning blinding on outcomes.Performance bias, duration Judgment on the duration of the intervention concerning a precise description of the

duration of the study on outcomes.Detection bias assessors Judgment on the impact of assessors concerning blinding on outcomes.Attrition bias Judgment on the impact of incomplete outcome data concerning completeness of sample,

follow-up, and data on outcomes.Reporting bias Judgment on the impact of the type of reporting concerning selective or incorrect

reporting on outcomes.


also adopted by the Cochrane Collaboration.52 Accord-ing to this grading systems, 4 levels of quality (high,moderate, low, and very low) were scored for individualoutcomes. Factors that could decrease the quality ofa body of evidence included limitations in the designof the selected studies, high risk of bias, indirectnessof evidence, unexplained heterogeneity, imprecisionof results, unit of analysis issues, and high probabilityof publication bias.35,36,49,52-55 Factors that couldupgrade the body of evidence included a largetreatment effect, or when all biases would affect themagnitude of a treatment effect in the samedirection.51,52,54 We only considered outcomes ofhigh or moderate quality.

Risk ratio and odds ratio were chosen as measures forour dichotomous primary outcomes. If indicated, unit ofanalysis issues were assessed according to the level atwhich randomization occurs and analyzed for each de-sign.49

Statistical analysis

The criteria for a meta-analysis of the summary effectsize are shown in a flow diagram (Fig 3). Such a synthesiswas conducted in the case of (1) low risk of bias in


eligible studies, (2) consistent effect sizes (treatment ef-fect) across the range of studies, (3) low reporting bias,(4) a high number of eligible studies, and (5) low hetero-geneity between studies.49,50,53 Funnel plots weredesigned to detect reporting biases. Funnel asymmetrywas assessed only when at least 10 eligible articleswere identified because, with fewer studies, the powerof this test is too low to distinguish chance from realasymmetry.46

RESULTS

A flow diagram according to the PRISMA group wasused to explain the selection procedures (Fig 2).30,32,33

No interexaminer disagreement was recorded for theinclusion of studies, indicating a kappa of 1.0. Thevarious search methods for identification of studiesfound a total of 9480 abstracts with overlap (AppendixTable I). Thirty-seven full-text articles were assessedfor eligibility; 30 were excluded. The reasons for exclu-sion are listed in Appendix Table II.47 The characteristicsof the selected studies are summarized in Table II. All ar-ticles were nonrandomized cohorts,2,21-24,27,28 and 4 ofthe 7 articles were published by the same researchgroup.2,21-23


Define criteria for justifying a meta-analysis of a summary effect:

a) Low risk of bias in studies (high or moderate quality (GRADE)b) Consistent effect size across studiesc) Low reporting biasd) A high number of studiese) Low heterogeneity between studies

Calculate the appropriate effect measures of the intervention for each study

Calculate the weight average of the intervention effect of all studies

Assess whether to conduct a fixed-effects or a random-effects meta-analysis or both

“Final” quality assessment (GRADE) of the meta-analysis

“Initial” quality assessment (GRADE)

Define general parametersthat can affect GRADE ratings

Assess heterogeneity(e) and when indicated conduct subgroup analyses and meta-regressions

Assess criteria a,b,c and d

Identify study specific factors that could affect theassessment of quality

Assess criteria a-e prior to undertaking a meta-analysis

Conduct sensitivity analyses to assess the effects of procedural decisionson findings

JUSTIFYING A META-ANALYSIS

UNDERTAKING A META-ANALYSIS

ASSESSING THE VALIDITY OF A BODY OF EVIDENCE SUMMARIZED IN A META-ANALYSIS

SUMMARY OF FINDINGS OF ALL STUDIES (FOREST PLOTS) AND ADDITIONAL TABLES AND FIGURES

Fig 3. Flow diagram for a protocol of a meta-analysis of the summary effect size.49,50,53


High heterogeneity was found between and withinthe selected articles, and large standard deviationswere recorded for the maximum insertion torque values(Table II). In most studies, the implants were inserted inpoorly defined locations, various types of screws were


used, and different surgical and orthodontic techniqueswere applied (Appendix Tables III-IX). Tests for funnelplot asymmetry were not indicated because only 7eligible studies were identified.46 Most studies measuredmaximum insertion torque with mechanical torque


Table II. Characteristics of maximum insertion torque studies

Authors and year of publication Design of study Patients (n) Implant numbers, types, and characteristicsMotoyoshi et al2 2006 Nonrandomized cohort 41 124 Biodent (tapered)

D 1.6 mmL 8 mm

Motoyoshi et al21 2007 Nonrandomized cohort 57 169 Biodent (tapered)D 1.6 mmL 8 mm


Arismendi et al27 2007 Nonrandomized cohort 9 34 Leone (cylindrical)D 1.5 and 2.0 mmL 10.0 and 12 mm

Chaddad et al24 2008 Nonrandomized cohort 10 17 Dual Top (machined and tapered)D 1.4, 1.6, and 2.0 mmL 6.0, 8.0, and 10.0 mm15 C implants (sandblasted and tapered)D 1.8 mmL 8.5 mm


Suzuki and Suzuki28 2011 Nonrandomized cohort 95 120 Sistema Nacional de Implantes (cylindrical)D 1.5 mm, L 6 and 8 mm160 ACR (tapered)D 1.5 mm, L 6 and 8 mm

MIT, Maximum insertion torque; D, diameter of the screw; L, length of the screw; PDI, predrilling insertion technique; SDI, self-drilling insertiontechnique.


sensors (Table III), but these devices cannot record inser-tion torque during the entire insertion process. Thecurves of insertion torque vs time were therefore notavailable, and possible stripping of the bone could notbe analyzed. Suzuki and Suzuki28 used a digital torquesensor but measured maximum insertion torque onlyat the final turn of the screwdriver. Success rates rangedfrom averages of 55.6% to 100%, depending on the sub-group, but the timing of these assessments variedwidely. These rates were based on a wide variety ofsubjective definitions of stability. Objective stability oforthodontic mini-implants was assessed in 3 stud-ies23,27,28 (Table III). Two of these studies recorded re-moval torque values,23,28 and 1 study measuredstability with digital calipers.27

The risk of bias analysis was conducted with rigorousprecision, because the magnitude and direction of bias isgenerally higher in nonrandomized studies than in ran-domized trials.34 All studies had 2 or more domains


scored as high risk of bias (Table IV). This score was ap-plied to selection bias in the 7 eligible studies, because allwere nonrandomized studies. High-risk scores for per-formance bias were also identified in all articles. Thistype of systematic error is specified in Table V, and addi-tional explanations for these judgments can be verifiedin Appendix Tables III through IX. Four of the 7selected articles were published by Motoyoshi et al2,21-23 (Table II). Various letters were sent to these authorsin 2010, 2011, and 2012 to inquire about individual pa-tient data and the potential overlap of studies, but theydid not reply. The domain “multiple publication bias” forthese studies was therefore scored as an unclear risk ofsystematic error (Table IV).

Associations between maximum insertion torque andsuccess are summarized in Table VI. Most of these assess-ments were based on subjective definitions of success.Chaddad et al24 found higher success rates at torquevalues above 15 Ncm, and 3 studies by Motoyoshi


Implant sites Insertion technique MITPosterior buccal alveolar bone in maxilla andmandible

PDI Maxilla: 8.3 6 3.3 NcmMandible: 10 6 3.3 Ncm

Posterior buccal alveolar bone in maxilla andmandible

PDI Adolescent, early load:Maxilla: 8.9 6 2.6 NcmMandible: 8.5 6 3.0 Ncm

Adolescent, late load:Maxilla: 7.6 6 2.7 NcmMandible: 8.8 6 3.0 Ncm

Adult, early load:Maxilla: 8.8 6 2.8 NcmMandible : 8.8 6 2.6 Ncm


PDI Success group: 8.83 6 2.83 NcmFailure group: 9.64 6 6.62 Ncm

Buccal alveolar bone in maxilla and palatal bone PDI Range, 11-25 Ncm


SDI Torquing device set at 15 Ncm


PDI Maxilla: 7.67 6 2.62 NcmMandible: 8.40 6 2.51 Ncm

Alveolar bone in maxilla and mandible and inmidpalatal suture area

PDISDI

PDI maxilla: 7.2 6 1.4 NcmPDI palate : 14.5 6 1.6 NcmPDI mandible: 12.4 6 1.2 NcmSDI maxilla: 12.1 6 3.1 NcmSDI palate: 21.1 6 2.2 NcmSDI mandible: 15.7 6 2.3 Ncm

Table II. Continued


et al2,21,23 recommended placement torques between 5and 10 Ncm. Three other articles could not associatespecific maximum insertion torque with the stability oforthodontic mini-implants.23,27,28 The quality of thebody of evidence for all associations was rated as lowaccording to the GRADE approach (Table VI). Completeinterexaminer agreement was recorded for these qualityreadings. Risk ratios were not calculated, and data werenot pooled to conduct a meta-analysis of the summaryeffect size, because of high heterogeneity, inconsistenteffect sizes, and high risk of bias across the studies (Fig 3).

Table VII summarizes variables associated with max-imum insertion torque levels. Many contrary associa-tions were presented for the same variable, but all 20proposed associations were rejected because of con-founding. Ten associations were excluded becausebone drills had modified insertion torque values to pre-established levels, thereby skewing the outcomes of thevariables under review. Adverse effects are listed in Table


VIII. Inflammation of soft tissues was recorded in 2 arti-cles24,27; 1 article reported 1 implant fracture duringinsertion and 4 during the removal of the orthodonticmini-implants.28

DISCUSSION

Variables that affect the stability of orthodonticmini-implants are both numerous and heterogeneous;this makes reviewing difficult.10 In this systematic reviewwe extracted just 1 factor (maximum insertion torque) tomake it more narrow in scope and therefore more wieldy.

To identify eligible studies, special measures were ap-plied that minimized the risk of introducing publication,location, language, and multiple publication bias. Theseprecautions implied that (1) a wide spectrum of key-words, search engines, and grey literature was consulted;(2) 3 investigators were involved; (3) no language restric-tions were applied; and (4) authors were contacted in



case of uncertainties about multiple publications from 1study.46

These selection procedures identified only non-randomized studies. Although systematic reviews focusparticularly on randomized controlled trials,56 the in-clusion of nonrandomized studies could be justifiedfor the following reasons:

1. High-quality nonrandomized studies could producea less biased estimate of effect size compared withlow-quality randomized controlled trials.53

2. Systematic reviews of nonrandomized studies candemonstrate areas where the available evidence isinsufficient and explain the need of subsequent re-search.34,57

3. They can further help to improve on the design offuture trials through the identification of relevantsubgroups.34

4. Etiologic hypotheses can generally not be tested inrandomized experiments58 and could easily be op-posed for ethical reasons.34 To answer our PICOquestion, patients should ideally be assigned to 1of 2 (or more) alternative forms of treatment. Thiswould entail, for example, predrilling implant sitesto create pilot holes with different dimensions.Such protocols would establish groups withdifferent preestablished maximum insertion torquevalues but are difficult to obtain approval by ethicsreview boards.44

5. Systematic reviews of nonrandomized studies canput citation bias in perspective. Citation metricsindicate the significance of impact of a particularstudy in its field.59 At the time of writing this sys-tematic review, Google Scholar Beta registeredover 135 citations for 1 selected article, which rec-ommended specific safe insertion torque values fororthodontic mini-implants.2 This was surprising be-cause of the high scores of bias and low quality rat-ings of this article (Tables IV-VI). This systematicreview could therefore have an important role inpreventing citation and publication bias.

6. Including nonrandomized studies could provide ad-ditional information regarding potential adverse ef-fects, because many serious harms of interventionsare unexpected or rare and do not appear duringthe period of study of a randomized controlled trial.

7. The level of evidence of nonrandomized studies canbe upgraded for demonstrating large effects.35,36

This criterion could not be applied, because noselected study had such an outcome.

It was hypothesized that maximum insertion torquevalues of 5 to 10 Ncm were associated with higher suc-cess rates of orthodontic mini-implants. We found no


evidence to support this hypothesis. This finding wasconfirmed by studies that assessed a possible associationbetween specific maximum insertion torque values andobjective measures of stability.23,27,28

Three studies foundapositive answer toour PICOques-tion,2,21,22 but opposing outcomes were also recorded byother research groups.24,28 This heterogeneity was causedby 3 factors: (1) differences in materials and methodsbetween studies (Tables II and III; Appendix Tables III-IX), (2) different definitions of success and stability, and(3) lack of control of confounding factors and thereforehigh risk of systematic error for various domains (TablesIV and V).

The assessment of risk of bias is considered the cor-nerstone of a systematic review and was therefore usedas a framework to explain conflicting outcomes. We rec-ommend consulting the following analysis for the designof future trials for this PICO question.

The inclusion of several publications of a single studycould lead to overestimation of the effects of an inter-vention.46 Four studies appeared to be almost identi-cal.2,21,23 Their authors were frequently contacted in2010, 2011, and 2012 but did not respond to ourcorrespondence. Because we had no direct proof thatthese articles represented 1 study, the relatively mildunclear risk of bias score was assigned (Table IV).

Susceptibility to selectionbias is theprincipal differencebetween randomized trials and nonrandomized studies.34

No information on selection procedures was presented inthe eligible articles, and the risk of heterogeneous samplingand “cherry-picking”was therefore high. Samples had dis-proportionate divisions of the sexes, with more femalesubjects and a wide range of ages (Appendix Table IV).

Eight subdivisions of performance bias were identi-fied. All selected studies scored at least 3 of these entriesas high risk of bias (Table V). Confounding factors in-cluded the following:

1. Grouping of implants of different types and dimen-sions24,27 (Appendix Table III).

2. Heterogeneous sites of insertion of orthodonticmini-implants (Appendix Table V).

3. Uncontrolled surgery-related factors (AppendixTables VI and VII). Different torque sensors wereused in the selected studies, and no informationon the calibration of these devices was presented.Most studies measured maximum insertion torquevalues with mechanical torque drivers. Recordingswith these devices are subject to error, becauseaxial load and the position and posture of theclinician can affect their readings.15 Also, they lackprecision and can be damaged over time duringthe sterilization process.60 Furthermore, mechanical


Table IV. Risk of bias in maximum insertion torque studies34,47,50

Authors Multiple publication bias Selection bias Performance bias Detection bias Attrition bias Reporting biasMotoyoshi et al2 Unclear High High Unclear Unclear LowMotoyoshi et al21 Unclear High High Unclear Unclear HighMotoyoshi et al22 Unclear High High High Unclear HighArismendi et al27 Low High High Unclear Low LowChaddad et al24 Low High High High Unclear LowMotoyoshi et al23 Unclear High High Unclear Low HighSuzuki and Suzuki28 Low High High High Low High

Unclear: The Cochrane Collaboration50 assigns the latter score if “1) insufficient detail is reported of what happened in the study; 2) what happenedin the study is known, but the risk of bias is unknown; 3) an entry is not relevant to the study at hand.”

Table III. Success and stability in maximum insertion torque studies

AuthorsTorquingdevice

Time of successmeasurement

Success rate andsubjective stability of OMIs Objective stability of OMIs

Motoyoshi et al2 Mechanical 6 months or more 85.5% (score NSS) NDMotoyoshi et al21 Mechanical 6 months or more Early load, adolescents: 63.8% (score 0);

range: 55.6%-71.4%Late load, adolescents: 97.2% (score 0);

range: 90.9%-100%Early load, adults: 91.9% (score 0);

range: 85%-100%Success rates combined: 85.2% (score 0);

range: 55.6%-100%

ND

Motoyoshi et al22 Mechanical 6 months or more 87.4% (score 0);range: 85.7%-90.9 %

ND

Arismendi et al27 ND Mean, 6.5 monthsRange, 3-9 months

97.1% (score 1) Mobility of 0.6 mm or more:At 3 months: 3% of OMIsAt 8 months: 13.6% of OMIs

Chaddad et al24 Mechanical 150 days Machined implants: 82.5% (score 0)Surface treated: 93.5% (score 0)Success rates combined 87.5% (score 0)

ND

Motoyoshi et al23 Mechanical Mean, 23.1 6 6.7 months 90.45% (score 1) Removal torque:Maxilla: 4.37 6 2.20 NcmMandible: 4.09 6 1.90 Ncm

Suzuki and Suzuki28 Digital 44 6 11 weeks Predrilling group, 94.16% (NSS)Self-drilling group, 92.5% (NSS)

Removal torque:15.8 6 3.6 to 26.9 6 2.0 Ncm

Subjective stability: score 0, success without mobility; score 1, success with mobility; score 2, success with displacement;NSS, not specified success(includes scores 0-2).OMIs, Orthodontic mini-implants; ND, not described.

Table V. Risk of performance bias in maximum insertion torque studies34,47,50

AuthorsImplant-

related biasLocation-related bias

Surgery-related bias

Orthodontics-related bias

Implantmaintenance-related bias

Outcomeassessment-related bias

Operator-related bias

Duration-related bias

Motoyoshi et al2 Low High High Unclear Unclear High Unclear HighMotoyoshi et al21 Low High High Unclear Unclear High Unclear HighMotoyoshi et al22 Low High High Unclear Unclear High Unclear HighArismendi et al27 High High High High Unclear Low Low HighChaddad et al24 High High High High Unclear High High LowMotoyoshi et al23 Low High High Unclear Unclear Unclear Unclear HighSuzuki and Suzuki28 Low High High Unclear Unclear Unclear Unclear High

Unclear: The Cochrane Collaboration50 assigns “unclear” risk of bias if “1) insufficient detail is reported of what happened in the study; 2) whathappened in the study is known, but the risk of bias is unknown; 3) an entry is not relevant to the study at hand.”


American Journal of Orthodontics and Dentofacial Orthopedics November 2012 � Vol 142 � Issue 5

Table VI. Summary of findings of associations between maximum insertion torque and success or stability

Association between MIT and success and character of statistical significanceStudies proposingthis association Quality (GRADE)

Mandible:MIT 5-10 Ncm higher success rates than MIT .10*or\5 Ncm (NS)

Maxilla:MIT 5-10 Ncm higher success rates than MIT .10* or\5 Ncm*

Motoyoshi et al2 Low

Adolescent, early load:MIT 5-10 Ncm higher success rates than MIT .10* or\5 Ncm* in the maxilla, with nodifferences in the mandible, and the sum of maxilla and mandible combined

Adolescent, late load:Association between success rates and MIT was not analyzed, because of high success rates

Adult, early load:MIT 5-10 Ncm higher success rates than MIT .10 Ncm in the maxilla,* and the sum of maxillaand mandible combined*

Motoyoshi et al21 Low

MIT 8-10 Ncm higher success rates than implants with MIT .10*or\8 Ncm* Motoyoshi et al22 LowNo association between MIT and stability of OMIs Arismendi et al27 LowMIT .15 Ncm higher success rates than MIT\15 Ncm* Chaddad et al24 LowNo significant correlation between MIT and removal torque Motoyoshi et al23 LowNo significant difference in MIT values between successful and failed OMIs in both PDI andSDI groups (NS)

Suzuki and Suzuki28 Low

MIT, Maximum insertion torque; OMIs, orthodontic mini-implants; PDI, predrilling insertion technique; SDI, self-drilling insertion technique; NS,not significantly different.*P\0.05.


torque drivers record only 1 insertion torque value atthe final rotation of the screw and cannot registerintermediate torque values during the insertion oforthordontic mini-implants. Information on possi-ble stripping of the bone was therefore lacking.Stripping of bone threads reduces the pulloutstrength of screws by 40% or more and thereforesignificantly affects their holding power.25,26

Digital torque sensors, on the other hand, canpresent a graph of the insertion torque valuesduring the entire insertion procedure and provideimmediate information when stripping occurs.Based on this information, the surgeon can decideto change the length or the diameter of the screw,place the screw in another location, or modify theloading protocol.

4. Lack of homogeneity in the orthodontic protocols(Appendix Table VIII). Precise descriptions of thetype of orthodontic movement, timing of force ap-plication, magnitude, type, duration, and directionof orthodontic forces were often lacking.

5. Poorly defined implant maintenance protocols.6. The outcome assessments were subjective (Table

III). Subjective judgments of success—eg, rated byat least 1 clinician—were presented in most of thestudies and can introduce bias. To prevent confu-sion in future studies, we propose distinguishingbetween “success” and “stability” of orthodonticmini-implants. The former parameter should be de-


fined as the ability of a mini-implant to fulfill allpreestablished anchorage objectives and should beregistered at the completion of these goals. Successshould not be used for testing associations with in-dependent variables because treatment objectives inorthodontics are rarely completed under the sameconditions and within the same time intervals. Fur-thermore, success is a qualitative subjective measureand therefore less reliable. Stability, on the otherhand, is an objective quantitative value that canbe recorded with objective measuring devices, eg,periotest,61,62 resonance frequency analysis,63,64

removal torque recordings,15,23 or pullout tests65

(the latter is not feasible in human subjects). Mostof these tests can be conducted at preset timesand are not conditioned by the duration of a partic-ular treatment. It has been shown that orthodonticmini-implants osseointegrate,8,9,28,66,67 andinformation on objective stability at differenttimes could help clinicians with the application ofappropriate loading protocols.

7. Lack of clarity about blinding of the operators(Table V). Operator-related bias was rated as unclearfor most studies. This parameter was not consideredin our quality rating, because blinding during surgi-cal procedures is generally difficult to accomplish.

8. The duration of the application of forces variedwidely and was often poorly defined (Table III).Assessments of success at random times could


Table VII. Summary of findings of variables associated with maximum insertion torque

Association with MITStudies proposing

association with MITRejected associations and

reasons for rejectionImplant-related factorsSame MIT in machined and surface treated screws (NS) Chaddad et al24 Rejected (a,b,c,d)Patient-related factorsMIT and sex: no Motoyoshi et al23 Rejected (c,d,e)Higher MIT with increasing age* Motoyoshi et al23 Rejected (c,d,e)MIT and age: no Motoyoshi et al21 Rejected (d,e)Location-related factorsSame MIT on left and right sided in the success group (NS) Motoyoshi et al2 Rejected (c,d)Same MIT on left and right sided (NS) Motoyoshi et al21 Rejected (d,e)Same MIT on left and right sided (NS) Motoyoshi et al23 Rejected (c,d,e)Higher MIT with increasing cortical bone thickness in maxilla* Motoyoshi et al23 Rejected (c,d,e)Higher MIT with increasing cortical bone thickness for the maxilla andmandible combinedy

Motoyoshi et al22 Rejected (c,d)

MIT and cortical bone thickness in mandible: no Motoyoshi et al23 Rejected (c,d,e)Higher MIT in mandible than maxillay Motoyoshi et al2 Rejected (c,d)Higher MIT in mandible than maxilla* Motoyoshi et al22 Rejected (c,d)Same MIT in maxilla and mandible Motoyoshi et al21 Rejected (d,e)Same MIT in maxilla and mandible Motoyoshi et al23 Rejected (c,d,e)Higher MIT on palatal side compared with buccal side* Arismendi et al27 Rejected (a,b,c,e)Higher MIT in midpalatal suture than in dentoalveolar area in maxilla in thepredrilling and self-drilling groups*

Suzuki and Suzuki28 Rejected (b,c,d)

Higher MIT in the dentoalveolar area in the mandible than in the maxilla in thepredrilling and self-drilling groups*

Suzuki and Suzuki28 Rejected (c,d)

No difference in MIT values between the mandible and midpalatal suture in thepredrilling group (NS)

Suzuki and Suzuki28 Rejected (b,c,d)

Higher MIT in midpalatal suture than in mandible in the self-drilling group* Suzuki and Suzuki28 Rejected (b,c,d)Surgery-related factorsHigher MIT in self-drilling insertion group compared with the predrillinginsertion groupz

Suzuki and Suzuki28 Rejected (c,d)

Total 20 associations 20 rejected

MIT, Maximum insertion torque; NS, not significantly different.Rejection criteria: a, number of implants\10; b, implant-related factors were not controlled; c, patient-related factors were not controlled; d,location-related factors were not controlled; e, bone drills had modified MIT values to preestablished levels.*P\0.05; yP\0.01; zP\0.001.

Table VIII. Adverse effects of inserting orthodontic mini-implants in maximum insertion torque studies

Authors Implant fractureBiologicdamage Inflammation Pain and discomfort

Motoyoshi et al2 ND ND ND NDMotoyoshi et al21 ND ND ND NDMotoyoshi et al22 ND ND ND NDArismendi et al27 ND ND 32.3% (score 2) entire treatment

periodND

Chaddad et al24 ND ND 6.25% (score 1) (for 14 days)6.25% (score 2) (for 85 days)

20% (score 1)

Motoyoshi et al23 ND ND ND NDSuzuki and Suzuki28 1 during insertion and

4 during removal of implantson a total of 280 implants

ND ND ND

ND, Not described.Inflammation: score 1, temporary inflammation; score 2, continuing inflammation.Pain and discomfort: score 1, moderate pain and discomfort.




introduce an additional variable because osseointe-gration of implants is time-dependent; studies thatare stopped at random time intervals could underes-timate or overestimate the effects of interven-tions50; and certain types of adverse effects, suchas root resorption, can be missed in the case of earlystopping.50

Although blinding of operators during surgical pro-cedures is difficult to accomplish, masking of outcomeassessors is relatively simple, because success can bemeasured by an operator not familiar with the objectivesof the study. Most selected articles, however, scored un-clear or with a high risk for detection bias.

Incomplete outcome data, due to attrition (fractureof implants or dropouts), raise the possibility that an ob-served effect is biased.50 It is important to consider boththe missing data and the reasons for the missing data.50

Attrition bias was rated as unclear in 4 studies (Table IV).Selective reporting indicates that certain outcomes

on the basis of their results are included or withheldfrom publication.50 One article presented only successrates for specific maximum insertion torque values with-out reporting the number of implants.21 Two articles didnot specify the recommended maximum insertiontorque values separately for each jaw22,28; in anotherarticle, the numbers did not add up.23 These 4 articleswere therefore rated as having a high risk of reportingbias (Table IV).

Variables that influence maximum insertion torquevalues were divided into implant-, patient-, location-,and surgery-related factors (Table VII). Rejection criteriawere discussed according to these categories. Animaland laboratory studies were consulted to compare find-ings.

Chaddad et al24 found no differences in maximuminsertion torque levels in machined screws comparedwith surface-treated screws. This association was re-jected, because confounding factors were poorly con-trolled (Table VII). Animal studies on implant-relatedfactors have shown that the surface treatment,15

form,4,8 and diameter8 of orthodontic mini-implantswere associated with maximum insertion torquevalues. These findings have been confirmed in labora-tory studies on animal and artificial bone and have im-portant implications.16,42,68 Small changes in 1variable could cause excessive bone strains orinsufficient holding power. This was confirmed bytomographic and histomorphometric analyses in ananimal study in which greater microdamage wasregistered: cortical bone cracks, when orthodonticmini-implants with larger diameters and taperedshapes were inserted.8


Sex, age, and physical and dental statuses are part ofthis group of variables. Motoyoshi et al23 found signifi-cantly higher maximum insertion torque values withincreasing age. This was expected, because bone densi-ties in adolescents are lower than those of young adults.However, in another article from the same researchgroup, no differences in maximum insertion torquevalues were recorded between age groups (Table VII).21

These opposing associations were both rejected, becausevariables related to patient and location were not con-trolled. In addition, insertion torque values were ad-justed with bone drills to preestablished torque levels.These procedures jeopardized an unbiased assessmentof a possible association between insertion torque andage. A proposed association between maximum inser-tion torque and sex was rejected for similar reasons.23

Differences in sex should be considered because corticalbone thickness can vary between the sexes.69

Left and right differences, cortical bone thickness,and various insertion sites in the maxilla and mandiblewere assessed for associations with specific maximuminsertion torque levels. All associations between maxi-mum insertion torque and location-related factorswere rejected because of confounding. Many of theseassociations had opposing outcomes; this explains thepoor control of confounding factors and possibly thelack of homogeneity of implant site selection withinand between studies. Precise identification of these sitesis essential because cortical bone thickness can even varyaccording to the distance from the alveolar crest.69 An-imal studies have shown higher maximum insertiontorque values in the mandible compared with the max-illa, and higher recordings were also registered withincreasing cortical bone thickness.4,15,70 Theseassociations require further confirmation fromcarefully designed artificial bone and animal studies.

Animal studies have shown that predrilling or self-drilling surgical techniques and the diameter of the pilothole can significantly influence maximum insertiontorque values.70,71 By modifying these variables,clinicians can insert orthodontic mini-implants with de-sired maximum insertion torque levels and thereby ob-tain appropriate primary stability in sites with eitherstiff or fragile bone. Surgical procedures can also bemodified to lower insertion torque values to preventfractures of orthodontic mini-implants.72 Only 1surgery-related association with maximum insertiontorque was presented, but it was rejected because ofconfounding (Table VII).

Adverse effects of insertion of orthodontic mini-implants were assessed in only 3 studies. To achievea balanced perspective, assessments of both primaryand negative outcomes of interventions are necessary.73



Definitions of adverse outcomes and their intensitiesshould be precisely recorded because they can varyacross studies.47 Adverse effects were assessed accordingto the guidelines of a recent systematic review10; we rec-ommend this framework for future articles. Follow-upstudies of adverse outcomes of interventions are alsonecessary for the assessment of the long-term conse-quences of root and nerve damage, or sinus and nasalcavity perforations, for example.

Before authors set up a randomized controlled trial,we suggest that they adopt rigorous research protocolswith the following sequence:

1. Systematically review the laboratory and animal lit-erature to assess how implant-, location-, or sur-gery-related factors influence maximum insertiontorque.

2. If these reviews provide insufficient answers, eachfactor should be isolated and tested for its effecton maximum insertion torque values and thereforeprimary stability. Most of this initial research canbe conducted on laboratory models. Artificial bonewould be the material of choice, because it has sim-ilarmechanical properties as human cancellous bonebut is more homogeneous.74 ASTM Internationalhas therefore chosen polyurethane foams for testinginsertion torque of medical bone screws.74

3. When a good understanding of the variables that in-fluence primary stability is obtained, specific maxi-mum insertion torque values can be tested forsecondary stability in animal studies.

4. In a subsequent phase, the effect of loading vs non-loading and other orthodontic-related factors canbe investigated.

High-precision sensors are necessary to record maxi-mum insertion torque values. Digital sensors are recom-mended over mechanical devices because they canrecord consecutive insertion torque levels at high-frequency intervals and therefore provide an immediatecurve of these values. This information can inform theclinician instantly about the risk of implant fracture,the quality of the bone, root contact, excessive tighten-ing, and possibly stripping of the bone.9 Because successis a subjective qualitative value of stability, it should notbe tested for associations with independent variables.Only objective quantitative recordings of stability shouldbe assessed for possible associations with maximum in-sertion torque.

Exchange of such objective readings betweenclinicians and research groups can speed up our under-standing of variables that influence the stability oforthodontic mini-implants in an exponential way. Reg-istrations of primary and secondary failure rates are


also necessary. These rates and their timings can provideimportant information on initial and secondary stability,because there is currently no consensus on whether orwhen an interface between the bone and the orthodonticmini-implant has formed.75 To achieve a balanced per-spective, adverse effects should be scored and handledwith the same rigor as the assessment of primary out-comes.

CONCLUSIONS

1. Currently, there is no evidence to recommendspecific maximum insertion torque levels to obtainhigher success rates of orthodontic mini-implants.We found that an association between specificmaximum insertion torque values and success oforthodontic mini-implants was analyzed only innonrandomized studies of low quality.

2. Success is a subjective qualitative recording ofstability and should not be considered as a reliablemeasure for testing associations with maximum in-sertion torque. On the other hand, recordings withobjective measuring devices should be applied forsuch assessments and should become the goldstandard for testing associations between the stabil-ity of orthodontic mini-implants and independentvariables.

3. Subsequent studies should record maximum inser-tion torque values with digital torque sensors andnot with mechanical devices.

4. Numerous associations were proposed betweenmaximum insertion torque levels and implant-, pa-tient-, location-, and surgery-related factors, but allwere rejected by our selection criteria. The many op-posing associations confirmed the heterogeneitywithin and between studies and the lack of controlof confounding factors.

5. We presented the risk of multiple publication biasand showed the need of retrieving individual patientdata from each eligible study.

6. This systematic review could be considered a nega-tive study, because no evidence-based conclusionscould be drawn. Although studies with significantresults are more likely to be published, the contribu-tion of negative (a misnomer) articles is as importantas the former studies, because they have an impor-tant role for placing the validity of the current liter-ature in perspective.46,76-79 They can further controlcitation and publication bias, show the need forfuture studies, and help in designing such research.

7. Future research on our PICO question should payspecial attention to controlling the various formsof bias that were identified because the probability



that a research claim is true strongly depends onsystematic error.

8. Recordings of adverse effects during mini-implantinsertion were generally sparse. Precise definitionsof adverse effects and their character and intensityshould become part of every future researchprotocol.73

We wish to extend special thanks to Dr. Louis Keith atNorthwestern University, Mary Kreinbring at the ADA li-brary, and Rossella Bassi.

SUPPLEMENTARY DATA

Supplementary data associated with this article canbe found, in the online version, at http://dx.doi.org/10.1016/j.ajodo.2012.06.013.

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Appendix Table I. Abstracts retrieved by electronic searching, hand searching, and reference searching* with subjectheadings and keywords: orthodontics, torque, implant, mini implant, micro implant, microimplant, screw, mini screw,miniscrew, micro screw, microscrew, and temporary anchorage devicey

Source of records Date of search Abstracts per search engine (n)Google Scholar Beta 24-02-2012 7922PubMed (Medline) 24-02-2012 111Embase (Ovid) Week 7 2012 824CENTRAL 24-02-2012 26Science Direct 24-02-2012 239Scopus 24-02-2012 154Web of Science 24-02-2012 162LILACS 24-02-2012 26AJOL 24-02-2012 0Grey literature 24-02-2012 0 additional abstracts to all found under Google ScholarHand searching 24-02-2012 5References, review articles 24-02-2012 3References, selected articles 24-02-2012 8Total 9480 with overlapping articles

*All search strategies were copied and pasted from the original without retyping, since this could have introduced errors.44 yFor each search engine,the appropriate characters were used to truncate or explore search terms.

Appendix Table II. Articles excluded by the selection criteria (n 5 30)

Authors Year of publication Reason for exclusionOhmae et al1 2001 BB€uchter et al2 2005 BHuja et al3 2005 BYano et al4 2006 BMorais et al5 2007 BWu et al6 2007 BSerra et al7 2008 BIijima et al8 2008 CKim et al9 2008 BChen et al10 2008 ATsaousidis and Bauss11 2008 AKim et al12 2008 ASu et al13 2009 CChang et al14 2009 BZhao et al15 2009 BWu et al16 2009 BDao et al17 2009 BHembree et al18 2009 BChen et al19 2009 BKang et al20 2009 BMortensen et al21 2009 BViwattanatipa et al22 2009 ASantiago et al23 2009 AMo et al24 2010 BKim et al25 2010 AZhang et al26 2010 BAsscherickx et al27 2010 DHong et al28 2011 CHong et al29 2011 CPark et al30 2011 E

Exclusion criteria: A, human study that did not assess insertion torque values; B, animal study; C, laboratory study; D, human study with implantdiameter .2.5 mm; E, human study on dental implants.

Meursinge Reynders et al 614.e1


Appendix Table III. Implant-related factors in maximum insertion torque studies

AuthorsImplant typeand number Design

Diameter (D)Length (L)

Additionalcharacteristics Material Finishing Sterilization

Motoyoshi et al2 124 Biodent Tapered D 1.6 mmL 8 mm

ND Titanium ND ND


ND Titanium ND ND


ND Titanium ND ND

Arismendi et al27 34 Leone Cylindrical D 1.5 and 2.0 mmL 10.0 and 12 mm

ND Stainless steel ND ND

Chaddad et al24 17 Dual top Dual Top: machinedand tapered

Dual Top:D 1.4, 1.6, 2.0 mmL 6.0, 8.0, 10.0 mm

ND Titanium ND ND

Chaddad et al24 15 C implant C implant: surfacetreated and tapered

C implant:D 1.8 mmL 8.5 mm

ND Titanium ND ND


ND Titanium ND ND

Suzuki and Suzuki28 120 SistemaNacional deImplantes

Cylindrical PDS D 1.5 mmL 6 and 8 mm

ND Titanium ND ND

Suzuki and Suzuki28 160 ACR Tapered SDS D 1.5 mmL 6 and 8 mm

ND Titanium ND ND

SDS, Self-drilling screws; PDS, predrilling screws; ND, not described.

Appendix Table IV. Patient-related factors in maximum insertion torque studies

AuthorsNumber of patients, sex,and number of implants Age (y) Physical status Dental status

Motoyoshi et al2 4 males (10 implants)37 females (114 implants)

Average: 24.9 6 6.5Range: 13.3-42.8

ND ND

Motoyoshi et al21 Adolescents: 83 implants6 males and 24 femalesAdults: 86 implants3 males and 24 females

Adolescents: mean, 15.9 6 1.9;range: 11.7-18.9

Adults: mean, 26.2 6 5.6;range: 20.4-36.1

ND ND


Average: 24.4 6 6.5Range: 14.6-42.8

ND ND

Arismendi et al27 9 patients (34 implants)Sex ND

ND No systemicdisease

No periodontalproblems

Chaddad et al24 10 patients (32 implants)Sex ND

Range: 13-65 Healthy ND


Average: 26.1 6 8.4Range: 13.9-63.5

ND ND

Suzuki and Suzuki28 40 males and 55 females290 implants

Average: 25.6 6 6.7Range: 12-46.6

ND ND

ND, Not described.

614.e2 Meursinge Reynders et al


Appendix Table VII. Surgery-related factors in maximum insertion torque studies

Authors Insertion technique Starter pilot hole Full-length pilot hole Insertion depth Axial load Stripping or stallingMotoyoshi et al2 PDI ND D 1.3 mm

Full lengthFull length ND NM

Motoyoshi et al21 PDI ND D 1, 1.3, 1.4 mmFull length

Full length ND NM

Motoyoshi et al22 PDI ND D 1.3 mmFull length

Full length ND NM

Arismendi et al27 PDI ND D 1.1, 1.3, 1.5, 1.7 mmFull length

Full length ND NM

Chaddad et al24 SDI Yes NA ND ND NMMotoyoshi et al23 PDI ND D 1.0, 1.3, 1.4 mm

Length NDND ND NM

Suzuki and Suzuki28 PDI and SDI SDI: NoPDI: Yes

PDI: full length ND ND NM

D, Diameter; SDI, self-drilling insertion technique; PDI, predrilling insertion technique; ND, not described;NA, not applicable; NM, not measured.

Appendix Table V. Location-related factors in maximum insertion torque studies

Authors Implant siteKeratinized/nonkeratinized

mucosa Exposed or closedMotoyoshi et al2 Posterior buccal alveolar bone in maxilla and mandible ND NDMotoyoshi et al21 Posterior buccal alveolar bone in maxilla and mandible Keratinized gingiva NDMotoyoshi et al22 Posterior buccal alveolar bone in maxilla and mandible ND NDArismendi et al27 Buccal alveolar bone in maxilla and palatal bone Both NDChaddad et al24 Posterior buccal alveolar bone in maxilla and mandible Both NDMotoyoshi et al23 Posterior buccal alveolar bone in maxilla and mandible ND NDSuzuki and Suzuki28 Alveolar bone in maxilla and mandible and in midpalatal suture area Keratinized gingiva Exposed

ND, Not described.

Appendix Table VI. Surgery-related factors in maximum insertion torque studies

Authors Torquing deviceFlap or flapless

surgeryDistance between

screws Direction of insertionInsertionspeed

Assessment ofinsertion torque

Motoyoshi et al2 Mechanical Flapless NA ND ND At final turnMotoyoshi et al21 Mechanical Flapless NA 30� to the long

axis of the toothND ND

Motoyoshi et al22 Mechanical Flapless NA ND ND NDArismendi et al27 ND Flapless NA 30�-60� ND NDChaddad et al24 Mechanical Flapless NA ND ND NDMotoyoshi et al23 Mechanical Flapless NA ND ND At final turnSuzuki and Suzuki28 Digital Flapless NA ND ND At final turn

ND, Not described; NA, not applicable.



Appendix Table VIII. Orthodontics-related factors in maximum insertion torque studies

AuthorsType of orthodontic

movementTiming of forceapplication Force magnitude Type of force

Duration of forceapplication

Directionof force

Motoyoshi et al2 Retraction of anteriorteeth in both jaws

Immediate (at surgery) \200 g ND 6 months or more ND


Early load, adolescents:Average: 2.6 weeksLate load, adolescents:Average: 13.2 weeksEarly load, adults:Average: 2.2 weeks

Approximately 200 g Continuous 6 months or more ND


Immediate (at surgery) ND ND 6 months or more ND

Arismendi et al27 Intrusion of maxillarymolars

8 days after surgery 42.4-84.9 g Intermittent 6.5 monthsRange: 3-9 months

Diagonal tovertical

Chaddad et al24 Various movementsin both jaws

Immediate (at surgery) 50-250 g Both 150 days ND

Motoyoshi et al23 ND Immediate (at surgery) \200 g ND 23.1 6 6.7 months NDSuzuki and Suzuki28 Retraction of anterior

teeth in both jawsAfter minimum healing

period of 2 weeks50 g Continuous 44 6 11 weeks ND

ND, Not described.

Appendix Table IX. Implant maintenance-related factors in maximum insertion torque studies

AuthorsAntibioticprotocol

Chlorhexidineprotocol

Oral hygieneprotocol

Peri-implantitisprotocol Mobility protocol

Motoyoshi et al2 3 days PI ND ND ND NDMotoyoshi et al21 3 days PI ND ND ND NDMotoyoshi et al22 3 days PI ND ND ND NDArismendi et al27 ND ND ND ND First week and then

every monthChaddad et al24 ND 1 week PI ND ND NDMotoyoshi et al23 3 days PI ND ND ND NDSuzuki and Suzuki28 ND ND ND ND ND

PI, Postimplant placement; ND, not described.

614.e4 Meursinge Reynders et al


REFERENCES OF EXCLUDED ARTICLES

1. Ohmae M, Saito S, Morohashi T, Seki K, Qu H, Kanomi R, et al. Aclinical and histological evaluation of titanium mini-implants asanchors for orthodontic intrusion in the beagle dog. Am J OrthodDentofacial Orthop 2001;119:489-97.

2. B€uchter A, Wiechmann D, Koerdt S, Wiesmann HP, Piffko J,Meyer U. Load-related implant reaction of mini-implants usedfor orthodontic anchorage. Clin Oral Implants Res 2005;16:473-9.

3. Huja SS, Litsky AS, Beck FM, Johnson KA, Larsen PE. Pull-outstrength of monocortical screws placed in the maxillae and man-dibles of dogs. Am J Orthod Dentofacial Orthop 2005;127:307-13.

4. Yano S, Motoyoshi M, Uemura M, Ono A, Shimizu N. Tapered or-thodontic miniscrews induce bone-screw cohesion following im-mediate loading. Eur J Orthod 2006;28:541-6.

5. Morais LS, Serra GG, Muller CA, Andrade LR, Palermo EF, Elias CN,et al. Titanium alloy mini-implants for orthodontic anchorage: im-mediate loading and metal ion release. Acta Biomater 2007;3:331-9.

6. Wu JC, Huang JN, Zhao SF. Bicortical microimplant with 2 anchor-age heads for mesial movement of posterior tooth in the beagledog. Am J Orthod Dentofacial Orthop 2007;132:353-9.

7. Serra G, Morais LS, Elias CN, Meyers MA, Andrade L, Muller C, et al.Sequential bone healing of immediately loaded mini-implants. AmJ Orthod Dentofacial Orthop 2008;134:44-52.

8. Iijima M, Muguruma T, Brantley WA, Okayama M, Yuasa T,Mizoguchi I. Torsional properties and microstructures of mini-screw implants. Am J Orthod Dentofacial Orthop 2008;134:333.e1-6.

9. Kim JW, Baek SH, Kim TW, Chang YI. Comparison of stability be-tween cylindrical and conical type mini-implants. Angle Orthod2008;78:692-8.

10. Chen YJ, Chang HH, Lin HY, Lai EH, Hung HC, Yao CC. Stability ofminiplates and miniscrews used for orthodontic anchorage: expe-rience with 492 temporary anchorage devices. Clin Oral ImplantsRes 2008;19:1188-96.

11. Tsaousidis G, Bauss O. Influence of insertion site on the failurerates of orthodontic miniscrews. J Orofac Orthop 2008;69:349-56.

12. Kim SH, Cho JH, Chung KR, Kook YA, Nelson G. Removal torquevalues of surface-treatedmini-implants after loading. Am J OrthodDentofacial Orthop 2008;134:36-43.

13. Su YY, Wilmes B, H€onscheid R, Drescher D. Comparison of self-tapping and self-drilling orthodontic mini-implants: an animalstudy of insertion torque and displacement under lateral loading.Int J Oral Maxillofac Implants 2009;24:404-11.

14. Chang CS, Lee TM, Chang CH, Liu JK. The effect of microroughsurface treatment on miniscrews used as orthodontic anchors.Clin Oral Implants Res 2009;20:1178-84.

15. Zhao L, Xu Z, Yang Z, Wei X, Tang T, Zhao Z. Orthodontic mini-implant stability in different healing times before loading: a micro-scopic computerized tomographic and biomechanical analysis. OralSurg Oral Med Oral Pathol Oral Radiol Endod 2009;108:196-202.

16. Wu J, Bai YX, Wang BK. Biomechanical and histomorphometriccharacterization of osseointegration during mini-screw healingin rabbit tibiae. Angle Orthod 2009;79:558-63.

17. Dao V, Renjen R, Prasad HS, Rohrer MD, Maganzini AL, Kraut RA.Cementum, pulp, periodontal ligament, and bone response afterdirect injury with orthodontic anchorage screws: a histomorpho-logic study in an animal model. J Oral Maxillofac Surg 2009;67:2440-5.

18. Hembree M, Buschang PH, Carrillo R, Spears R, Rossouw PE. Ef-fects of intentional damage of the roots and surrounding struc-tures with miniscrew implants. Am J Orthod Dentofacial Orthop2009;135:280.e1-9.

19. Chen Y, Kang ST, Bae SM, Kyung HM. Clinical and histologic anal-ysis of the stability of microimplants with immediate orthodonticloading in dogs. Am J Orthod Dentofacial Orthop 2009;136:260-7.

20. Kang YG, Kim JY, Lee YJ, Chung KR, Park YG. Stability of mini-screws invading the dental roots and their impact on the paraden-tal tissues in beagles. Angle Orthod 2009;79:248-55.

21. Mortensen MG, Buschang PH, Oliver DR, Kyung HM, Behrents RG.Stability of immediately loaded 3- and 6-mm miniscrew implantsin beagle dogs—a pilot study. Am J Orthod Dentofacial Orthop2009;136:251-9.

22. Viwattanatipa N, Thanakitcharu S, Uttraravichien A, Pitiphat W.Survival analyses of surgical miniscrews as orthodontic anchorage.Am J Orthod Dentofacial Orthop 2009;136:29-36.

23. Santiago RC, de Paula FO, Fraga MR, Picorelli Assis NM, Vitral RW.Correlation between miniscrew stability and bone mineral densityin orthodontic patients. Am J Orthod Dentofacial Orthop 2009;136:243-50.

24. Mo SS, Kim SH, Kook YA, Jeong DM, Chung KR, Nelson G. Resis-tance to immediate orthodontic loading of surface-treated mini-implants. Angle Orthod 2010;80:123-9.

25. Kim YH, Yang SM, Kim S, Lee JY, Kim KE, Gianelly AA, et al. Mid-palatal miniscrews for orthodontic anchorage: factors affectingclinical success. Am J Orthod Dentofacial Orthop 2010;137:66-72.

26. Zhang L, Zhao Z, Li Y, Wu J, Zheng L, Tang T. Osseointegration oforthodontic micro-screws after immediate and early loading. An-gle Orthod 2010;80:354-60.

27. Asscherickx K, Vannet BV, Bottenberg P, Wehrbein H,Sabzevar MM. Clinical observations and success rates of palatalimplants. Am J Orthod Dentofacial Orthop 2010;137:114-22.

28. Hong C, Lee H, Webster R, Kwak J, Wu BM, Moon W. Stabilitycomparison between commercially available mini-implants anda novel design: part 1. Angle Orthod 2011;81:692-9.

29. Hong C, Truong P, Song HN, Wu BM, Moon W. Mechanical stabil-ity assessment of novel orthodontic mini-implant designs: part 2.Angle Orthod 2011;81:1001-9.

30. Park KJ, Kwon JY, Kim SK, Heo SJ, Koak JY, Lee JH, et al. Therelationship between implant stability quotient values and im-plant insertion variables: a clinical study. J Oral Rehabil 2012;39:151-9.



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