ORIGINAL ARTICLE

True incisor intrusion attained duringorthodontic treatment: A systematic reviewand meta-analysisJulia Ng,a Paul W. Major,b Giseon Heo,c and Carlos Flores-Mird

London, Ontario, and Edmonton, Alberta, Canada

Introduction: The purpose of this meta-analysis was to quantify the amount of true incisor intrusion attainedduring orthodontic treatment. Methods: Electronic databases (PubMed, Medline, Medline In-Process &Other Non-Indexed Citations, all EBM reviews [Cochrane Database of Systematic Reviews, ASP JournalClub, DARE, and CCTR], Embase, Web of Science, and Lilacs) were searched with the help of a senior healthsciences librarian. The goal was to identify clinical trials that assessed true incisor intrusion throughcephalometric analysis and factored out craniofacial growth when required. From the selected abstracts,original articles were retrieved, and their references were hand searched for missing articles. Results:Twenty-eight articles met the initial inclusion criteria, but 24 were rejected because they did not quantify trueincisor intrusion or factor out normal growth impact when required. The remaining 4 articles showed that trueincisor intrusion is attainable (0.26 to 1.88 mm for the maxillary incisors and –0.19 to 2.84 mm for themandibular incisors) but with large variability depending on the appliance used. A meta-analysis with resultsfrom the 2 articles that used the segmental technique was completed. The combined mean estimates ofintrusion and 95% CI were 1.46 mm (1.05-1.86 mm) for the maxillary incisors and 1.90 mm (1.22-2.57 mm)for the mandibular incisors. Conclusions: True incisor intrusion is achievable in both arches, but the clinicalsignificance of the magnitude of true intrusion as the sole treatment option is questionable for patients withsevere deepbite. In nongrowing patients, the segmented arch technique can produce 1.5 mm of incisorintrusion in the maxillary arch and 1.9 mm in the mandibular arch. (Am J Orthod Dentofacial Orthop 2005;128:

212-9)

Deep overbite is a common component of mal-occlusion in adults and children.1 It can becorrected with various treatment modalities,

but the best option will depend on the patient’s char-acteristics and the treatment objectives. Esthetic con-siderations are also important in deepbite treatment.

Nonsurgical treatment alternatives include molarextrusion, incisor intrusion, or a combination of both.1-6

In patients with vertical growth tendencies, opening thebite by extruding the posterior occlusion would not berecommended. For these patients, true incisor intrusionis the treatment of choice.2

aResident, Graduate Orthodontic Program, University of Western Ontario,London, Ontario, Canada.bProfessor and director of Orthodontic Graduate Program, University ofAlberta, Edmonton, Alberta, Canada.cAssociate professor of statistics, Orthodontic Graduate Program, University ofAlberta, Edmonton, Alberta, Canada.dPostdoctoral fellow, Orthodontic Graduate Program, University of Alberta,Edmonton, Alberta, Canada.Reprint requests to: Dr Carlos Flores-Mir, Faculty of Medicine and Dentistry,Room 4051A, Dentistry/Pharmacy Centre, University of Alberta, Edmonton,Alberta, Canada T6G 2N8; e-mail, carlosflores@ualberta.ca.Submitted, January 2004; revised and accepted, April 2004.0889-5406/$30.00Copyright © 2005 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2004.04.025

212

Differential growth of the maxilla and mandible cancontribute to overbite correction in children4; in adults,orthognathic surgery might be required in conjunctionwith orthodontic tooth movement.1

Labial tipping of incisors gives the clinical impres-sion of deepbite correction because it influences thevertical incisal edge position.3,7,8 Therefore, incisaledge and root apex are not good reference pointsbecause they are not independent of tooth inclinationchanges. The incisor centroid, defined as a point on thelongitudinal axis of the tooth that is independent of anychange in inclination, is the reference point of choice.9

Different approaches to localize the centroid have beenreported4,9-11 that make some theoretical assumptions.

A reference plane relative to the centroid must alsobe used to evaluate whether true intrusion has beenachieved; for the maxillary incisors, the palatal planeand, for the mandibular incisors, the mandibular planeare used as craniofacial reference structures.4,6,9 Theuse of study models rather than lateral cephalometricradiographs would not allow the evaluation of trueintrusion via the centroid.

Reports differ on the amount of attainable incisor

intrusion.3,4,6,9-32 True intrusion is difficult to achieve

found i

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 128, Number 2

Ng et al 213

and assess, yet it is frequently used in deepbite treat-ment; therefore, a systematic review of the availableevidence about the amount of true incisor intrusionattainable is recommended.

The purpose of this systematic review was toquantify the amount of true incisor intrusion attained inorthodontic patients and to evaluate its clinical signif-icance.

MATERIAL AND METHODS

Initial inclusion criteria for this systematic reviewwere human clinical trials and intrusion of permanentincisors determined through cephalometric radiographsuperimpositions. To find the appropriate articles, asearch was first conducted in the following databases:Medline (1966 to week 4 of February 2004); PubMed(1966 to week 4 of February 2004); Medline In-Process& Other Non-Indexed Citations (March 8, 2004); allEBM reviews (Cochrane Database of Systematic Re-views, ASP Journal Club, DARE, and CCTR) (tofourth quarter 2003); Embase (1988 to week 10 of2004); Web of Science (1975 to March 6, 2004); andLilacs (1982 to February 2004). The main terms used inthe search were tooth movement, orthodontics, intru-sion, and incisor. Specific related terms for each data-base (Table I) were selected with the help of a seniorlibrarian who specialized in health-sciences databases.

Eligibility of the selected studies was determined byreading the abstracts of the articles identified by thesearch. All articles that appeared to meet the inclusioncriteria were selected, and the actual articles collected.The selection process was done independently by 2

Table I. Database search strategy and sensitivity of the

Database Keywords

PubMed (1) orthodon*; (2) incis*; (3) intru*;(5) limit to human

Medline (1) orthodon$; (2) incis$; (3) intru$;(5) limit to human

Medline In-Process &other nonindexedcitations

(1) orthodon$; (2) incis$; (3) intru$;(5) limit to human

Web of Science (TS�intrusion and TS�incis*) and Ttooth); DocType�Article; Languaglanguages; Database(s)�SCI-EXPAA&HCI

Embase (1) orthodon$; (2) incis$; (3) intru$;(5) limit to human

All EBM reviews (1) orthodon$; (2) incis$; (3) intru$;incisor and intrusionLilacs

*Percentages do not add up to 100% because same references were

researchers (J.N. and C.F.), and their results were

compared to identify discrepancies. The only exceptionwas the Lilacs database, which was evaluated by only 1researcher (C.F.) because of language knowledge. If theabstract did not provide enough information to make adecision, the actual article was obtained. In cases ofdisagreement, a mutual decision was made. The refer-ence lists of the retrieved articles were also hand-searched for additional relevant publications that mighthave been missed in the database searches.

When information was required for discussion orstatistical analysis that was not specifically stated in thearticle, the authors were asked to provide it.

The complete selected articles were independentlyevaluated by 3 researchers (J.N., P.M., C.F.). A con-sensus was reached about which articles to include inthe systematic review and the meta-analysis. Articlesthat did not report true incisor intrusion and did notfactor out growth when required were rejected. Trueintrusion was considered met when the study used thecentroid of the incisors as the reference point toquantify the movement of the incisor vertically in thedentoalveolar bone. Although measurement error isneeded for a correct interpretation of the clinicalsignificance of the findings, it was not considered areason to reject an article.

If 2 or more articles evaluating the same techniquecould be found, a meta-analysis was planned.

RESULTS

Medline identified 149 articles, PubMed 143, theEBM reviews 3, Embase 6, Web of Science 63, andLilacs 19. The PubMed database search included al-

onic databases used

Results Selected

% of totalselected abstracts

(27)*

, and 3; 149 25 92.6

, and 3; 143 18 66.7

, and 3; 2 0 0

th or

, SSCI,

63 7 25.9

, and 3; 6 1 3.7

, and 3 8 6 22.219 0 0

n several databases.

electr

(4) 1, 2

(4) 1, 2

(4) 1, 2

S�(teee�AllNDED

(4) 1, 2

(4) 1, 2

most all references found in Medline and all Embase

American Journal of Orthodontics and Dentofacial OrthopedicsAugust 2005

214 Ng et al

and Web of Science references. Use of the Lilacsdatabase permitted the inclusion of articles in Spanishthat do not normally appear in the English databases.None of the Lilacs references appeared in the PubMedsearch. Of the total number of abstracts identified in theelectronic databases, only a small percentage fulfilledthe inclusion criteria (Table I). PubMed obtained thegreatest diversity of abstracts but did not include allabstracts from the other databases. Medline and Web ofScience found 2 references that were not in PubMed. Inthe case of Medline, 88.9% of the selected referenceswere included in PubMed, and 71.4% from Web ofScience. No abstracts were selected from the EBMreviews or the Lilacs databases.

Twenty-eight articles that fulfilled the initial selec-tion criteria were identified. Of these, 24 were laterrejected because of methodological issues, as statedin Table II. Various studies3,10,12-18,20,22-24,26,27,29-32

were rejected because true intrusion was not evalu-ated. Some of them also did not consider verticalgrowth impact when children or adolescents wereevaluated.10,14,15,18,20-23,25,26,28-30,32,33 One study19

was not considered in the final selection because the

Table II. Studies that fulfilled selection criteria but wererejected

Year AuthorsReason to

reject

1980 Otto et al3 1,31982 Pancherz12 11986 Abdel-Kader13 1,31989 Dake and Sinclair14 1,2,31990 Lew15 1,21991 Ball and Hunt16 11992 Dermaut et al17 1,31992 Goerigk et al18 1,2,31992 Weiland et al19 41995 Everdi and Ozkan20 1,21995 Xu et al21 2,31996 Costopoulos and Nanda33 21997 Weiland et al10 1,21998 Parker and Harris22 1,2,31998 Stucki and Ingervall23 1,21999 AlQabandi et al. 24 11999 Covell et al25 2,31999 Pearson and Pearson26 1,22000 Dincer et al27 12000 Liu et al28 2,32000 Reddy et al29 1,22001 Heinig and Goz30 1,22001 Uçüncü et al31 12002 Stromeyer et al32 1,2

1, True intrusion not evaluated; 2, effect of growth not considered; 3,no error of measurements stated; 4, same data reported later.

same data were reported later.6

Only 4 articles4,6,9,11 fulfilled all selection criteriaand were finally used for the systematic review. Asummary of the sample size, study design, method oftreatment, and method of incisor intrusion from each ofthese studies is shown in Table III.

Hans et al4 compared incisor intrusion in 45 chil-dren (mean age, 10.3 years; SD 1.8) treated withcervical headgear/tandem mechanics and 50 children(mean age, 11.3 years; SD 1.6) treated with Bionatorappliances against 40 (mean age, 10.4 years; SD 1.8)and 48 (mean age, 12.1 years; SD 1.5) control subjects,respectively. The “tandem” mechanics in the maxillaryarch consisted of a 2 x 4 lever arch, cinched back andgabled 1 mm anterior to the molar band. Archwire sizeand angulation of the gable bend were not specified. Inthe mandibular arch, a “tandem yoke” was inserted intoround tubes on the first molars, and the archwire wastied directly to the mandibular incisors with steelligatures. Placement of gable bends and archwire sizeswere not specified. Class III elastics were used with theheadgear to develop arch length. With headgear/tandemmechanics, statistically significant (P � .001) maxil-lary incisor intrusion of 1.88 mm (SD 2.08 mm) wasachieved, but not mandibular incisor intrusion. With thebionator, statistically significant (P � .001) maxillaryincisor intrusion of 0.88 mm (SD 2.05) and statisticallysignificant (P � .01) mandibular incisor intrusion of0.53 mm (SD 2.40) were achieved. No comparison wasmade regarding initial craniofacial and dental valuesbetween treatment groups. The standard deviationswere calculated from the reported standard error of themeans. No measurement errors for these intrusionvalues were stated. An attempt was made to reach theoriginal authors to get these values, but no reply wasreceived. Facial type was reported to affect mandibularintrusion for the bionator group.

Weiland et al6 studied 25 adults (mean age, 23.3years; range, 18-35.3) treated with a continuous arch-wire technique and 25 adults (mean age, 24.6 years;range, 18.7-40.3) treated with a Burstone segmentedarch technique. According to the authors, an intrusiveforce of 10 to15 g per tooth was applied in both groups.The technique used for determining intrusive force wasnot provided. They reported that both methods signif-icantly reduced deepbites. The continuous archwiretechnique did so by extrusion of the maxillary andmandibular molars, with a resultant posterior rotationof the mandible and an increase in the lower anteriorfacial height. Statistically significant (P � .01) man-dibular incisor intrusion of 1.03 mm (SD 1.55) wasreported in the continuous archwire group. Maxillaryincisor intrusion in the continuous archwire group was

not significant (P � .05). In contrast, the segmented

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 128, Number 2

Ng et al 215

arch technique reduced the overbite primarily by sta-tistically significant (P � .001) intrusion of the maxil-lary and mandibular incisors with minimal molar ex-trusion. Maxillary incisor intrusion was 1.50 mm (SD1.28), and mandibular incisor intrusion was 1.72 mm(SD 1.91). No measurement error for the intrusionvalues was stated. The authors told us that no measure-ment errors were calculated.

Hong et al11 evaluated the amount of mandibularincisor intrusion attained in 8 women (mean age, 25.8years; range 22-30.8) undergoing lingual orthodonticswith 0.016 x 0.016-in stainless steel reverse curvemushroom arches (10° tip back bends distal to caninesand premolars). The mean pretreatment overbite valuewas 3.9 mm (SD 1.51; range 2.4-5.9). The attainedintrusion was 1.5 mm (SD 0.53). The reported mea-surement error was 0.20 mm.

Kinzel et al9 studied the amount of incisorintrusion in 25 Class II Division 2 adults (mean age,26.2 years; SD 5.2) treated with fixed appliances.Both arches exhibited incisor intrusion (maxillaryarch, 1.14 mm, SD 1.20; mandibular arch, 1.17 mm,SD 2.27). When only incisor intrusion by the seg-

Table III. Studies included for review that fulfilled sele

Author Sample characteristics Method error

Hans et al4 Nonrandom; 95 deepbitepatients (58 boys, 37girls); HG/tandemgroup:10.3 years (SD1.8), bionator group:11.3 years (SD 1.6),control group A: 10.4years (SD1.8), controlgroup B: 11.2 years(SD1.5)

Not numericallystated, onlyhow it wascalculated

Weiland et al6 Nonrandom; 50 deepbitepatients (13 men, 37women); continuousarchwire 23.3 years(18-35.3); segmentedarchwire mean age �25.6 years (18.7-40.3)

Not stated

Hong et al11 Nonrandom; 8 women;25.8 years (22-30.8)

0.2 mm

Kinzel et al9 Nonrandom; 25 Class IIDivision 2 patients (7men, 18 women);different techniques26.2 years (5.2)

0.2 mm

mented arch technique was considered, the amounts

of intrusion were 1.37 mm (SD 1.31) for the maxil-lary incisors and 2.71 mm (SD 2.33) for the mandib-ular incisors (SD calculated from Table 3 of theoriginal article). The article provided only descrip-tive statistics with the assumption that incisor intru-sion was statistically significant. The reported mea-surement error for the intrusion values was less than0.20 mm. No comparison was made of initial cranio-facial and dental values between both treatmentgroups.

A summary of the mean intrusion values and theirrespective standard deviations from the selected articlesis given in Table IV. None of the selected studiesreported adverse effects of their treatments.

The 2 studies6,9 that used the segmented archtechnique were included in a fixed-effects meta-analy-sis34 to evaluate the amount of incisor intrusion. Theestimate was given a weight inversely proportional toits precision. The study of Weiland et al6 has a higherweight because the SD is smaller and the sample sizelarger relative to Kinzel et al.9 The combined meanestimates and 95% CI were 1.46 mm (CI 1.05-1.86) forthe maxillary incisor and 1.90 mm (CI 1.22-2.57) of

criteria

Treatment Study designMethod of intrusion

evaluation

G/tandem (28 boys,girls)atched controls (24ys, 16 girls)onator (30 boys,girls)atched controls (28ys, 20 girls)

Retrospective;T1�initialT2�final

Center of resistance ofmaxillary/mandibularincisor relative tocreated plane

ntinuous archwiremen, 17 women)gmented archwiretients (5 men, 20men)

Retrospective;T1�initialT2�final

Centroid of max/mandincisor relative tonasion-sella line ormandibular plane

ngual orthodonticsth reverse curveshroom arch

Prospective;T1�initialT2�afterinitialintrusion

Midpoint betweenincisal edge and rootapex relative tomandibular plane

ults treated withferent fixedpliances

Retrospective;T1�initialT2�finalT3�follow-up(some)

Centroid of maxillary/mandibular incisorrelative to palataland mandibularplanes

ction

45 H17

40 mbo

50 bi20

48 mbo

25 co(8

25 sepawo

All liwimu

25 addifap

intrusion for the mandibular incisor.

American Journal of Orthodontics and Dentofacial OrthopedicsAugust 2005

216 Ng et al

DISCUSSION

From the 4 studies that met all selection criteria,it was evident that true incisor intrusion was achiev-able, especially with the segmented arch technique.The clinical significance of the reported mean values,however, might be questionable when the largevariances are considered. The amount of intrusionattained in clinical situations could be influenced bydental arch, individual patient considerations, andchosen mechanics.

Hans et al,4 Hong et al,11 and Kinzel et al9 did notreport statistical comparisons of pretreatment groups todemonstrate equivalency of their sample composition.There could have been a selection bias in the analysisand interpretation of the reported results. If the initialvalues of deepbite were different, the amount of re-quired incisor intrusion would also have been different.Furthermore, skeletal pattern could influence the rela-tive incisor intrusion versus the molar extrusion inoverbite reduction. In some cases, altered incisor incli-nation might be a treatment objective; this would havean influence on the required amount of incisor intrusionin subjects with the same amount of overbite. Cautionshould be exercised in interpreting the clinical signifi-cance of differences in incisor intrusion between tech-niques reported in these studies.

The selected studies used different appliances forincisor intrusion, making it difficult to compare andassess which was the best appliance or technique forincisor intrusion. Hans et al4 used appliances (head-gear/tandem mechanics and bionator) not primarilydeveloped for precise dental movements. Weiland et al6

and Hong et al11 used continuous fixed appliances,which are undetermined force systems, making thespecific quantification of the force levels and vectors offorce difficult to control or determine.1,2,35-38 OnlyKinzel et al9 and Weiland et al6 used the segmentedarch technique for adult subjects and approximately thesame treatment times.

Interestingly, there was more mandibular than max-

Table IV. Mean values (SD) of true incisor intrusion in

Study Technique

Hans et al4Headgear/tandemBionator

Weiland et al6Continuous archSegmented arch

Hong et al11 Continuous arch

Kinzel et al9VariousSegmented arch

illary incisor intrusion in both studies, although, for

Kinzel et al,9 the difference was significantly differentbetween arches. Reitan and Rygh39 stated that, inadults, mandibular incisor intrusion is readily achievedcompared with maxillary incisor intrusion. Anotherconsideration could be that often there is a greater needfor mandibular intrusion.

Differences in the reference planes selected todetermine the amount of incisor intrusion probably didnot contribute to the different results. Hans et al,4

Kinzel et al,9 and Hong et al11 used the palatal or themandibular plane as the reference to evaluate theamount of maxillary or mandibular incisor intrusion,respectively. Weiland et al6 used the nasion-sella lineinstead of the palatal plane. The use of the centroid andan adequate superimposition technique makes the se-lection of the reference plane noninfluential.

No comparison of incisor intrusion could be madebetween samples of adults6,9,11 and children4 becauseof the different techniques used. It is expected thatdental movements in growing patients are more easilyaccomplished.40

Nineteen studies3,10,12-18,20,22-24,26,27,29-32 that metthe initial selection criteria were rejected because theydid not evaluate true intrusion. Instead of using thecentroid of the incisor, most used the incisal edge or theroot apex to measure the amount of intrusion. Using thelatter 2 reference points would not allow one todistinguish true intrusion from inclination of the incisaledges or crown apexes; this could create a falseperception of intrusion. The final selected studies4,6,9,11

evaluated true incisor intrusion. They used the centroidof the incisor and measured its distance from either themaxillary or mandibular plane to assess the amount ofintrusion.

Some rejected studies10,14,15,18,20-23,25,26,28-30,32,33

did not factor out normal vertical growth in growingchildren. The amount of true incisor intrusion mighthave been greater than what was reported because ofvertical growth of the maxilla or mandible simulta-neous to the actual intrusion mechanics; this creates a

ted articles

xillary incisor (mm)D, no. of subjects)

Mandibular incisor (mm)(SD; no. of subjects)

1.88 (2.08; 45) �0.19 (1.54; 45)0.88 (2.05; 50) 0.53 (2.40; 50)0.26 (1.55; 25) 1.03 (1.50; 25)1.50 (1.28; 25) 1.72 (1.91; 25)Not measured 1.5 (0.53; 8)1.14 (1.20; 25) 1.17 (2.27; 25)1.37 (1.31; 14) 2.71 (2.33; 8)

selec

Ma(S

theoretical bias to report less intrusion. In the study by

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 128, Number 2

Ng et al 217

Hans et al,4 with children as the subjects, a controlgroup of the same age accounted for the effects ofvertical growth of the maxilla and the mandible.

Many3,13,14,17,18,21,22,25,28 of the 24 rejected studiesand 2 of the selected4,6 studies did not state measure-ment error. This made the interpretation of the clinicalsignificance of the findings and subsequent conclusionsquestionable.

A meta-analysis of the amount of incisor intrusionwith the segmented arch technique was made. A meta-analysis is a statistical approach to combine the resultsfrom separate but similar studies to provide an overallquantitative summary of the effect of interest.41 Whenintrusion of incisors would be indicated, such as elon-gated incisors or periodontal bone loss of the incisors,42

the segmented arch technique has been reported as thetreatment of choice. According to the meta-analysisresults, about 1.5 mm of maxillary incisor intrusion and1.9 mm of mandibular incisor intrusion is routinelyattainable. The small margin of error (0.4 mm for themaxillary incisors and 0.7 mm for the mandibularincisors) obtained in the meta-analysis makes it clearthat the technique worked consistently. In the analysisof the present findings, consideration must be given tothe small sample in the meta-analysis. Two studies6,9

evaluated only adult patients, not adolescents; it mightnot be not possible to extrapolate the values to youngerpopulations.

A theoretical limitation for the amount of incisorintrusion exists based on the proximity of the roots tothe cortical bone; this limits the amount of intrusionattainable in some cases. No clinically significant (0.4mm) root resorption was caused by incisor intrusion upto 4 mm with a segmented arch technique comparedwith a control group with full fixed appliances.33

Careful planning of the technical procedures could limitthe negative side effects.2,39 Individual patient charac-teristics are also important factors to be consideredwhen incisor intrusion is required.

Caution should be exercised with meta-analysisresults because of publication bias, methodologicalheterogeneity and quality between studies, and lack ofindependence between the selected studies.41 In thiscase, only 2 articles were finally selected for themeta-analysis, both with very small sample sizes, butwith statistical homogeneity. Unfortunately, neitherstudy was a randomized clinical trial, which wouldhave been the best study for a meta-analysis.41

There is no clear explanation for the finding thatmandibular incisor intrusion was greater than maxillaryincisor intrusion. Bone density is greater in the anteriorpart of the mandible than in the anterior part of the

maxilla.43 This would favor intrusion mechanics in the

maxilla. The smaller root-bone area interaction associ-ated with mandibular teeth should be compensated bycontrolling force magnitude. Use of suboptimal forcelevels, different patient-specific intrusion requirements(lack of randomization of patient assignment), anddifferent treatment durations could account for thedifferential amount of intrusion between maxillary andmandibular incisors. The 0.45-mm difference in intru-sion between arches is most likely not clinically signif-icant.

To avoid a possible language bias in this systematicreview, non-English literature was considered eventhough less significant results and poorer methodolo-gies were expected.44,45 The exclusion of 1 trial couldhave important effects on the conclusions in meta-analyses or systematic reviews with fewer than 5trials.46 Our results showed that searching in Lilacs forSpanish studies altered the final selection of articlesbased on the selection criteria. Two articles in Chi-nese21,28 and 1 in German19 were selected initially,based on their English abstracts, but were later rejectedafter reading the full articles in their original languages.The selection of articles for systematic reviews ormeta-analysis from only commonly used databases(Medline or Pubmed) is not supported by our findings.

Based on the selected articles, an average of only 1to 2 mm of true incisor intrusion was achieved. Theexception was Kinzel et al,9 who achieved 2.71 mm ofmandibular incisor intrusion but on a small sample.Based on these few studies, it is difficult to assesswhether incisor intrusion is easier in adolescents or inadults. It is also difficult to conclude which appliance isbest for incisor intrusion because the studies useddifferent appliances, thus preventing comparisons. Ap-parently, incisor intrusion is easier in the mandibulararch, although its clinical significance is questionable.

Because the initial amount of incisor intrusionrequired was not clearly stated in the articles, the actualmaximum intrusion value attainable could not be de-termined. Clinical goals set by orthodontists determinehow much intrusion is required. Therefore, a quantifi-cation of the total true intrusion attainable is notfeasible with the information available.

Future studies should be conducted with the formatof randomized clinical trials to quantify the amount ofincisor intrusion with the least number of confoundingvariables (random patient selection, controlled treat-ment times and forces, and similar initial intrusionrequirements). Also, further studies in adolescent sam-ples factoring out normal growth are required to com-pare the amount of attainable incisor intrusion against

adult samples.

American Journal of Orthodontics and Dentofacial OrthopedicsAugust 2005

218 Ng et al

CONCLUSIONS

Under the limitations of the number of availablestudies and total samples for this systematic review, thefollowing conclusions could be made:

1. True incisor intrusion can be accomplished in botharches. However, the feasibility of true incisorintrusion alone for the correction of severe deepbitehas not been established.

2. The amount of true intrusion attainable differsbetween the arches, although the clinical signifi-cance of the difference is questionable.

3. The segmented arch technique in nongrowing pa-tients produced 1.5 mm maxillary incisor intrusionand 1.9 mm mandibular incisor intrusion.

We thank Linda Seale for her assistance in thedatabase search and Dr Futhang Zhang for translatingthe Chinese articles.

REFERENCES

1. Nanda R. Correction of deep overbite in adults. Dent Clin NorthAm 1997;41:67-87.

2. Burstone CR. Deep overbite correction by intrusion. Am JOrthod 1977;72:1-22.

3. Otto RL, Anholm JM, Engel GA. A comparative analysis ofintrusion of incisor teeth achieved in adults and children accord-ing to facial type. Am J Orthod 1980;77:437-46.

4. Hans MG, Kishiyama C, Parker SH, Wolf GR, Noachtar R.Cephalometric evaluation of two treatment strategies for deepoverbite correction. Angle Orthod 1994:265-74.

5. Davidovitch M, Rebellato J. Two-couple orthodontic appliancesystems utility arches: a two-couple intrusion arch. SeminOrthod 1995;1:25-30.

6. Weiland FJ, Bantleon HP, Droschl H. Evaluation of continuousarch and segmented arch leveling techniques in adult patients—aclinical study. Am J Orthod Dentofacial Orthop 1996;110:647-52.

7. Engel G, Cornforth G, Damerell JM, Gordon J, Levy P, McAlp-ine J, et al. Treatment of deep-bite cases. Am J Orthod 1980;77:1-13.

8. Barton KA. Overbite changes in the Begg and edgewise tech-niques. Am J Orthod 1972;62:48-55.

9. Kinzel J, Aberschek P, Mischak I, Droschl H. Study of the extentof torque, protrusion and intrusion of the incisors in the contextof Class II, division 2 treatment in adults. J Orofac Orthop2002;63:283-99.

10. Weiland FJ, Ingervall B, Bantleon HP, Droacht H. Initial effectsof treatment of Class II malocclusion with the Herren activator,activator-headgear combination, and Jasper jumper. Am J OrthodDentofacial Orthop 1997;112:19-27.

11. Hong RK, Hong HP, Koh HS. Effect of reverse curve mushroomarchwire on lower incisors in adult patients: a prospective study.Angle Orthod 2001;71:425-32.

12. Pancherz H. Vertical dentofacial changes during Herbst appli-ance treatment. A cephalometric investigation. Swed Dent JSuppl 1982;15:189-96.

13. Abdel-Kader HM. Clinical crown length and reduction in over-jet, overbite, and dental height with orthodontic treatment. Am J

Orthod 1986;89:246-50.

14. Dake ML, Sinclair PM. A comparison of the Ricketts andTweed-type arch leveling techniques. Am J Orthod DentofacialOrthop 1989;95:72-8.

15. Lew K. Intrusion and apical resorption of mandibular incisors inBegg treatment: anchorage bend or curve? Aust Orthod J1990;11:164-8.

16. Ball JV, Hunt NP. The effect of Andresen, Harvold, and Beggtreatment on overbite and molar eruption. Eur J Orthod 1991;13:53-8.

17. Dermaut LR, van den Eynde F, de Pauw G. Skeletal anddento-alveolar changes as a result of headgear activator therapyrelated to different vertical growth patterns. Eur J Orthod1992;14:140-6.

18. Goerigk B, Diedrich P, Wehrbein H. [Intrusion of the anteriorteeth with the segmented-arch technique of Burstone–a clinicalstudy]. Fortschr Kieferorthop 1992;53:16-25.

19. Weiland F, Bantleon HP, Droschl H. [The orthodontic treatmentof deepbite in adults–a comparison of the straight-wire applianceand the segmented arch technique]. Fortschr Kieferorthop 1992;53:153-60.

20. Erverdi N, Ozkan G. A cephalometric investigation of the effectsof the elastic bite-block in the treatment of Class II Division 1malocclusions. Eur J Orthod 1995;17:375-84.

21. Xu T, Lin J, Huang J. [The changing of orofacial structure by biteopening with Begg technique]. Zhonghua Kou Qiang Yi Xue ZaZhi 1995;30:13-16, 63.

22. Parker RJ, Harris EF. Directions of orthodontic tooth movementsassociated with external apical root resorption of the maxillarycentral incisor. Am J Orthod Dentofacial Orthop 1998;114:677-83.

23. Stucki N, Ingervall B. The use of the Jasper jumper for thecorrection of Class II malocclusion in the young permanentdentition. Eur J Orthod 1998;20:271-81.

24. AlQabandi AK, Sadowsky C, BeGole EA. A comparison of theeffects of rectangular and round arch wires in leveling the curveof Spee. Am J Orthod Dentofacial Orthop 1999;116:522-9.

25. Covell DA Jr., Trammell DW, Boero RP, West R. A cephalo-metric study of Class II Division 1 malocclusions treated with theJasper jumper appliance. Angle Orthod 1999;69:311-20.

26. Pearson LE, Pearson BL. Rapid maxillary expansion with incisorintrusion: a study of vertical control. Am J Orthod DentofacialOrthop 1999;115:576-82.

27. Dincer M, Gulsen A, Turk T. The retraction of upper incisorswith the PG retraction system. Eur J Orthod 2000;22:33-41.

28. Liu D, Bai D, Wang C, Sun W, Guo J, Xi R. [Simultaneousintrusion and retraction of the anterior teeth using a three-piecebase arch]. Hua Xi Kou Qiang Yi Xue Za Zhi 2000;18:168-70.

29. Reddy P, Kharbanda OP, Duggal R, Parkash H. Skeletal anddental changes with nonextraction Begg mechanotherapy inpatients with Class II Division 1 malocclusion. Am J OrthodDentofacial Orthop 2000;118:641-8.

30. Heinig N, Goz G. Clinical application and effects of the Forsusspring. A study of a new Herbst hybrid. J Orofac Orthop2001;62:436-50.

31. Ucuncu N, Turk T, Carels C. Comparison of modified Teuscherand van Beek functional appliance therapies in high-angle cases.J Orofac Orthop 2001;62:224-37.

32. Stromeyer EL, Caruso JM, DeVincenzo JP. A cephalometricstudy of the Class II correction effects of the Eureka Spring.Angle Orthod 2002;72:203-10.

33. Costopoulos G, Nanda R. An evaluation of root resorptionincident to orthodontic intrusion. Am J Orthod Dentofacial

Orthop 1996;109:543-8.

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 128, Number 2

Ng et al 219

34. Sutton AJ. Methods for meta-analysis in medical research. NewYork: John Wiley; 2000.

35. Braun S, Marcotte MR. Rationale of the segmented approach toorthodontic treatment. Am J Orthod Dentofacial Orthop 1995;108:1-8.

36. Raboud DW, Faulkner MG, Lipsett AW, Haberstock DL. Three-dimensional effects in retraction appliance design. Am J OrthodDentofacial Orthop 1997;112:378-92.

37. Raboud D, Faulkner G, Lipsett B, Haberstock D. Three-dimen-sional force systems from vertically activated orthodontic loops.Am J Orthod Dentofacial Orthop 2001;119:21-9.

38. Kuhlberg AJ, Priebe D. Testing force systems and biomechan-ics—measured tooth movements from differential moment clos-ing loops. Angle Orthod 2003;73:270-80.

39. Reitan K, Rygh P. Biomechanical principles and reactions. In:Graber TM, Vanrsdall R, editors. Orthodontics. current princi-ples and techniques. Saint Louis: Mosby Year Book; 1994. p.96-192.

40. Reitan K. Biomechanical principles and reactions. In: Graber TM,

Swain BF, editors. Current orthodontic principles and techniques.Saint Louis: C. V. Mosby; 1985. p. 101-92.

41. Petrie A, Bulman JS, Osborn JF. Further statistics in dentistry.Part 8: Systematic reviews and meta-analyses. Br Dent J 2003;194:73-8.

42. Melsen B, Agerbaek N, Markenstam G. Intrusion of incisors inadult patients with marginal bone loss. Am J Orthod DentofacialOrthop 1989;96:232-41.

43. Norton MR, Gamble C. Bone classification: an objective scale ofbone density using the computerized tomography scan. Clin OralImplants Res 2001;12:79-84.

44. Juni P, Holenstein F, Sterne J, Bartlett C, Egger M. Direction andimpact of language bias in meta-analyses of controlled trials:empirical study. Int J Epidemiol 2002;31:115-23.

45. Bigby M, Williams H. Appraising systematic reviews andmeta-analyses. Arch Dermatol 2003;139:795-8.

46. Sutton AJ, Duval SJ, Tweedie RL, Abrams KR, Jones DR.Empirical assessment of effect of publication bias on meta-analyses. Br Med J 2000;320:1574-7.

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