American Journal of Orthodontics and Dentofacial OrthopedicsVolume 131, Number 4

Readers’ forum 445

practice might not eliminate bias just as found in treatedsamples. Cooperative patients take the spotlight. Over rela-tively short periods of treatment, a control sample is notneeded. When superimposing on cranial base, if the secondfilm shows elevation of the molar root, we can assumeintrusion and extrapolate the amount to be added frommatched growth measurements.

The fact that 30 article abstracts fulfilled the initialselection criteria and 29 were later rejected because ofmethodological issues smacks of evaluation error. Many ofthese authors might disagree with your methods and imposi-tions. The pores in your investigative filter open and close atwill, and not by scientific design.

I am fully aware of the tremendous effort you put forthand respect that. I provide comments to spread light and notflame. May they help you become a laser for our specialty andnot a lantern.

Wayne G. WatsonLa Jolla, Calif

Am J Orthod Dentofacial Orthop 2007;131:444-50889-5406/$32.00Copyright © 2007 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2007.01.007

Authors’ responseWe thank Dr Watson for taking time to comment on our

systematic review.1 We respect his point of view, but wedisagree with the points he raised.

His first point regarded the use of the centroid instead ofpoints located in molar crowns and roots. He questioned thatthe use of the centroid is unreliable. Any cephalometric pointhas been known to have an inherent location error. Thecentroid for a molar must be defined by locating a few pointsin the tooth crown and root, and then the centroid can befound. What we question and considered a reason for exclu-sion was the use of individual crown or root points to quantifyintrusion. Changes in the molar inclination would haveartificially created a sense of intrusion or extrusion. Weclearly defined this in the introduction and the methods withthe corresponding references. In the case of the article byFirouz et al,2 we contacted the senior author for clarificationabout the method used to evaluate molar intrusion. Differentapproaches to localize the tooth centroid have been previ-ously reported,3-5 all making some theoretical assumptions.The use of teeth and bony structures as suggested by Bjork’sstudies6 does not contradict what we did. The question is howtrue intrusion is measured.

Because we intended to measure only tooth movement(molar intrusion), we decided that superimposition of thebone base was more appropriate. This factors out changesproduced by growth at distant sites or by translatory move-ment.7

Adding search terms for all possible orthodontic appli-ances that could produce molar intrusion would make thesearch unmanageable. Our search strategy followed estab-lished principles of evidence-based dentistry and focused on

identifying any indication of tooth intrusion in the abstract,

title, text, and key words. Electronic database searches are byno means a perfect tool. Hand searching is a well-acceptedprocedure to ensure that any relevant articles not identified bythe electronic search are included.8,9

Dr Watson’s 1972 article used a small sample size (n �14) with a descriptive approach and data analysis limited tomeans and standard deviations and no control group. Unfor-tunately, the article represents a low level of evidence and didnot meet the criteria for inclusion in our systematic review.Furthermore, a subjective assessment such as Dr Watson’sstatement that 5 mm of intrusion could be observed for agiven patient does not form the basis of evidence-baseddentistry.

Finally, a main reason for publishing is to provide aforum for discussion and exchange of knowledge. In thisregard, we appreciate Dr Watson’s intention to discuss whathe considered research flaws. He wisely stated that anydiscussion is a learning experience for everybody. We are,however, confident that we followed the current principles ofsystematic reviews in the context of evidence-based dentistry.

Julia NgPaul W. Major

Carlos Flores-MirLondon, Ontario and Edmonton, Alberta, Canada

Am J Orthod Dentofacial Orthop 2007;131:4450889-5406/$32.00Copyright © 2007 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2007.02.046

REFERENCES

1. Ng J, Major PW, Flores-Mir C. True molar intrusion attainedduring orthodontic treatment: a systematic review. Am J OrthodDentofacial Orthop 2006;130:709-14.

2. Firouz M, Zernik J, Nanda R. Dental and orthopedic effects ofhigh-pull headgear in treatment of Class II, Division 1 malocclu-sion. Am J Orthod Dentofacial Orthop 1992;102:197-205.

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

4. Kinzel J, Aberschek P, Mischak I, Droschl H. Study of the extentof torque, protrusion and intrusion of the incisors in the context ofClass II, Division 2 treatment in adults. J Orofac Orthop 2002;63:283-99.

5. 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.

6. Bjork A, Skieller V. Facial development and tooth eruption. Animplant study at the age of puberty. Am J Orthod 1972;62:339-83.

7. Bishara SE, Athanasiou AE. Cephalometric methods for assess-ment of dentofacial changes. In: Athanasiou AE, editor. Orthodon-tic cephalometry. St Louis: Mosby-Wolfe; 1995. p.105-24.

8. Helmer D, Savoie I, Green C, Kazanjian Z. Evidence-basedpractice: extending the search to find material for the systematicreview. Bull Med Libr Assoc 2001;89:346-52.

9. Corall CJ, Wyer PJ, Zick LS, Bockrath CR. How to find evidencewhen you need it, part I: databases, search programs, and search

strategies. Ann Emerg Med 2002;39:302-6.