READERS' FORUM

Letter to the editor*

Biased look at self-ligation

The August 2010 "Ask Us" article was not an impartiallook at self-ligation (Marshall SD, Currier GF, Hatch

NE, Huang GJ, Nah HD, Owens SE, et al. Self-ligatingbracket claims. Am J Orthod Dentofacial Orthop2010;138:128-31). Two of the references cited disputingthe formation of buccal bone had errors in study designsand were suspect because of regional accelerated phe-nomena. A well-designed thesis was dismissed. Was thisbecause it found self-ligating arch expansion to be similarto that of rapid palatal expansion? A textbook chapter wasreferred to as “a few case reports.” Their conclusion of thestability of expansion is at odds with the authors, whostated that “there are treatments which may be effective,but for which a high level of evidence may not be found.”Could this be said of self-ligation?

On efficiency, they implied that 20 seconds per wireremoval is insignificant. In a practice of 50 patients perday, at only 20 seconds, 4 days a week, 48 weeksa year, the difference is 192 patient visits, or 1 week ofpatient care. That is substantial, and removing wires isfaster than placing them.

They noted a meta-analysis of self-ligation vs con-ventional ligation that showed 1.5� less maxillary incisorproclination with self-ligating brackets. These in-vivodata suggest that crowding is alleviated by buccal ex-pansion and molar “distalization,” not the incisor flaringseen with traditional systems. This was not mentioned.

Friction and binding were addressed with a recentlyacquired disdain for in-vitro studies. They warned thatin-vitro studies do not replicate in-vivo conditions.The review cited supports findings of reduced unwantedside effects of friction described in the in-vivo discus-sions. They implied that in-vitro studies’ positive resultson reduced friction with self-ligation are contrived,whereas there is an emphasis on Burrows, whose premiseis counter to all fundamentals of self-ligation; theadvantage of self-ligation is accomplished by usingsmall round wires, not the large rectangular wires usedin Burrows’ biased report.

They attempted to discredit excellent research byBadawi et al by comparing it with Burrows’ obvious sup-port of traditional ligation. The next studies cited sup-port the use of small round wires in a large lumen toprovide more predictable forces and fewer unwanted

*The viewpoints expressed are solely those of the author(s) and do not reflectthose of the editor(s), publisher(s), or Association.

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forces from the outset, but this concept was lost onthe authors.

On pain levels associated with self-ligating systems,they downplayed that initial archwires are less painfuland emphasized that the second archwire is morepainful. However, they failed to mention that the earlygeneration brackets used required pliers that causedmild discomfort to open and close slides. The secondwire was larger than any practitioner of self-ligationwould consider placing today and occurred without re-gard to malalignment. This in-vivo study failed to followprotocols and data gleaned from in-vitro studies! Nowonder patients found them painful.

It has been stated that a competent clinician usesclinical judgment, “developed from sound experienceand bolstered by, but not based exclusively on, system-atic scientific evidence.”1 The authors said that “thischallenge requires knowledge of the strength of theevidence of these claims.” I suggest that their challengeincludes experience with self-ligations, not solely thejudgment of a band of authorities on scientific evidencewho might suffer from a proficiency bias leading toinaccurate interpretation of the literature.

David E. PaquetteCharlotte, NC

Am J Orthod Dentofacial Orthop 2011;139:5740889-5406/$36.00Copyright � 2011 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2011.03.008

REFERENCE

1. Ackerman JL, Kean MR, Ackerman MB. Evidence-bolsteredorthodontics. Aust Orthod J 2006;22:69-70.

Author’s response

Claims of treatment (appliance) superiority must beanalyzed rationally and dispassionately. Otherwise,

scientific truth might be lost in the smoke of heatedargument without resolution.

To assess the evidence for or against the claims ofsuperiority made by self-ligating bracket (SLB)manufacturers (and advocates), we asked: are therepeer-reviewed data to support these claims? Are thedata independently confirmed? We then commentedon evidence strength based on the available answers.Briefly:

Readers' forum 575

� Do SLBs “grow” buccal bone? Evidence showingwhether this phenomenon occurs, or does not occur,in response to treatment with SLBs is weak and notpeer-reviewed, and should be interpreted with cau-tion. Additional well-designed peer-reviewed studiesare needed to answer this question. These are facts.

Currently, it is inappropriate for SLB manufacturersto make this claim.

� Is SLB expansion comparable with RME plus fixed ap-pliances? Although the thesis making this comparisonis often cited as published in a peer-reviewed journal,it was not peer-reviewed. Our assertion is true: “nopeer-reviewed scientific evidence supports thisclaim.”

� Is SLB expansion stable in the long term? You’vetaken this sentence out of context: “there are treat-ments which may be effective, but for which a highlevel of evidence may not be found.” Evidence forpostretention stability after RME and fixed appliancesis not the “highest” because there are no randomizedclinical trials involving this intervention. Evidence forlong-term stability of SLB expansion is, at present,anecdotal.

� Are SLBs more effective? The meta-analysis findingof 1.5� less mandibular incisor proclination for SLBtreatment was questioned in a recent AJO-DO“Reader’s forum.”1 The authors of the meta-analysisresponded by stating that “we do not considerour conclusions to be robust, and they could beinfluenced greatly by just a couple of additional,well-conducted trials.” We agree. Additionalwell-designed studies are needed.

� Do SLBs reduce friction? We did not imply that in-vitro results on friction are “contrived.” Dr Burrows’evaluation of Thorstenson and Kusy’s work hasshed light on data from in-vitro friction studies.2

Our statement, “At this time, the exact role offrictional forces opposing motion of a bracket alongan archwire in vivo is not clear, and the relationshipbetween bracket-archwire friction and tooth move-ment remains to be elucidated,” is accurate and fair.

� Are SLBs less painful? We did not “downplay” infor-mation on pain perception. We pointed out studyweaknesses. Our statement, “At this time, additionalstudies are needed to fairly and fully answer thisclaim,” is accurate and unbiased.

We would never suggest that clinical judgment is“based exclusively on systematic scientific evidence.”Evidence-based practice requires equal weight for 3domains: the best available scientific evidence, theorthodontist’s clinical skills and judgment, and each

American Journal of Orthodontics and Dentofacial Orthoped

patient’s needs and preferences. In my practice, clinicalskill and judgment with SLB systems result in excellentoutcomes for my patients (my proficiency bias notwith-standing). However, I also take the responsibility toinform my patients that the best available scientificevidence lacks sufficient strength to support 12 of the14 most notable claims made for these bracket systems.

Steve MarshallIowa City, Iowa

Am J Orthod Dentofacial Orthop 2011;139:574-50889-5406/$36.00Copyright � 2011 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2011.03.009

REFERENCES

1. Kaklamanos EG, Athanasiou AE. Systematic review of self-ligatingbrackets. Am J Orthod Dentofacial Orthop 2011;139:145-6.

2. Burrow SJ. Friction and resistance to sliding in orthodontics:A critical review. Am J Orthod Dentofacial Orthop 2009;135:442-7.

Image superimposition method in toothmovement and arch dimension changesevaluation

We read with interest Min-Young Cho and col-leagues’ article on three-dimensional (3D) analysis

of tooth movement and arch dimension changes bysuperimposing 3D virtual images (Cho MY, Choi JH,Lee SP, Baek SH. Three-dimensional analysis of thetooth movement and arch dimension changes in ClassI malocclusions treated with first premolar extractions:a guideline for virtual treatment planning. Am J OrthodDentofacial Orthop 2010;138:747-57). As the 3D imagesuperimposition method is more widely used in ortho-dontic studies, there are 2 aspects of this method towhich we want to draw attention.

In orthodontic evaluation and tooth movement anal-ysis, clinicians are interested in the final position of thecrown, as well as the kinetic manner of root movement.Root movement control determines the orthodontic pro-cedure, and the final position of the crown determinesthe esthetic and functional outcomes.

Three-dimensional images of tooth and arch are thesubstructure of 3D image superimposition methods.Computed tomography (CT) and optical scans are 2ways commonly used for 3D image reconstruction. Anoptical scan, which has higher resolution, can provideonly the image of tooth crown, whereas the CT scancan provide the images of both crown and root withrelatively lower resolution. Can we find a way to geta comprehensive 3D image that has the information

ics May 2011 � Vol 139 � Issue 5