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 Table of Contents  
Year : 2018  |  Volume : 52  |  Issue : 6  |  Page : 157-160

An interview with Dr. Kwangchul Choy

1 Prof. and HOD, Department of Orthodontics, SRIHER, Chennai, Tamil Nadu, India
2 Prof., Department of Orthodontics, SRIHER, Chennai, Tamil Nadu, India

Date of Web Publication7-Dec-2018

Correspondence Address:
Prof. Vignesh Kailasam
Department of Orthodontics, SRIHER, Chennai, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jios.jios_192_18

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How to cite this article:
Padmanabhan S, Kailasam V. An interview with Dr. Kwangchul Choy. J Indian Orthod Soc 2018;52, Suppl S2:157-60

How to cite this URL:
Padmanabhan S, Kailasam V. An interview with Dr. Kwangchul Choy. J Indian Orthod Soc [serial online] 2018 [cited 2019 Apr 25];52, Suppl S2:157-60. Available from: http://www.jios.in/text.asp?2018/52/6/157/247054

Interviewed by Dr. Sridevi Padmanabhan (SP) and Dr. Vignesh Kailasam (VK)

  1. SP: Warm greetings from JIOS, Dr. Kwangchul Choy (KC). Our readers are familiar with the phenomenal work, you have done on temporary anchorage devices (TADs). I am sure they would also be interested in your early career and education

  2. KC: I am Kwangchul Choy, DDS, MS, PhD. I graduated and completed orthodontic training at Yonsei University and have been a research fellow and a visiting professor at University of Connecticut. Currently, I am a clinical professor at Yonsei University, as well as, an adjunct professor of Orthodontics at Ewha Womans University. I have carried out clinical and scientific research in the biomechanics of tooth movement and orthodontic appliances and have lectured around the world on biomechanics. I also maintain a private practice in Seoul.

  3. SP: Can you tell us about your initiation and your foray into TADs?

  4. KC: There were no TADs commercially available at that time. Perhaps in 2002, a surgical screw for mini plate was used. The head of the screw head was sandblasted and inserted, and then a lingual button was bonded over the head with resin. These experiments ultimately led to the publication of the book, 'The Biomechanical Foundation of Clinical Orthodontics' and over 30 papers and book chapters in the field of biomechanics.

  5. VK: What would be your guidelines for a contemporary Orthodontic graduate student, who is about to start their career with TADs?

  6. KC: TAD eliminates many side effects associated with conventional orthodontic techniques. Therefore, many Orthodontists feel that biomechanics is not so important while using TADs. That is not true. Biomechanics are still important, even while using TADs. However, it can be stated that the force system involved in conventional biomechanics are reasonably simplified, and in that way, biomechanics gets simplified, but not unnecessary with TADs. The flip side is that, since the TADs ensure more predictable tooth movement, placement of TADs and the actual prediction of the tooth movement and therefore the biomechanics becomes more important with TADs.

  7. VK: The biomechanical requirements with TADs are not given due importance in the graduate curriculum. What would be the way forward to ensure that?

  8. KC: TAD is single force appliance. This means, there is only a single force between active unit (tooth) and a reactive unit, which is the TAD [Figure 1]. The force system on the reactive unit, or so called anchorage unit is ignored because the TADs are stationary (however, Eric Liou in his landmark article proved that TADs are per se not stationary, but the point is, we can disregard the effect on the reactive unit). If we are using extension arms on active unit or reactive unit, point of force application changes, and various types of tooth movement are accomplished. However, it produces many types of side effects not only on the active unit, but also on the reactive unit. For example, consider the situation when an incisor intrusion spring is pitted against the screw on the screws on the buccal side. To activate the spring, downward force (blue arrow) is required in the incisors. The replaced equivalent force system on the screw is a downward force, and the clockwise moment is depicted in yellow arrows [Figure 2]a. The extension arm on the TAD would produce a moment on the TAD, and if the axis of the moment is parallel with the screw axis, the stability of the TAD will be vulnerable [z direction in [Figure 2]b. This would be an example why you should not ignore the force system acting on the reactive unit.

  9. VK: At what age do you start using TADs. What are your thoughts on the use of TADs on mixed dentition?
  10. Figure 1: TAD is single force appliance with two points of application on the tooth (active unit) and TAD (reactive unit)

    Click here to view
    Figure 2: (a) An extension is placed in the screw. (b) The TAD is very vulnerable by the moment in z direction

    Click here to view

    KC: I usually postpone the orthodontic treatment until permanent dentition unless patient shows skeletal problems. I would not recommend TADs on mixed dentition unless it is strictly indicated.

  11. SP: Total maxillary intrusion with TADs is now a reality. What is your recommended protocol in terms of the number of TADs and their location?

  12. KC: Intrusion of total maxillary arch by a single force is very difficult for many reasons;First, we do not know the exact location of Cres. Other variables include, the number of molars included in the arch and angulation of the incisors which can affect the location of the Cres. Further, even if exact location of the Cres is determined, just a little deviation of the single force from the Cres can result in rotation of the arch. We know the location of the center of mass of an egg; however, it is very difficult to make an egg stand on a flat table with a single force (support) [Figure 3]a. It is much easier to stand an egg with multiple forces (supports) [Figure 3]b.
    Figure 3a and b: Single and multiple supports

    Click here to view

    Therefore, if you want to intrude the maxillary dentition by translation, it requires multiple TADs. Two TADs on each side at least are required [Figure 3]b. However, increased number of TADs significantly increase the possibility of treatment failure. Suppose, even a single loss of a TAD is considered failure of the treatment, the success rate of the treatment decreases, as the number of screws increase. Assuming the success rate of a single TAD is 70%, and we have used 4 TADs, two on each side for intrusion of maxillary dentition, then the success rate of the treatment would be only 24%. This is another reason why you should avoid translation of maxillary dentition with multiple TADs. If you still need translation, you'd better rotate it in one direction, followed by the opposite direction sequentially. Therefore, my protocol and suggestion is that, it is much easier to rotate and intrude the maxillary dentition rather than attempt total maxillary dentition intrusion by translation. Hence, I would rotate the maxillary arch in one direction first, and follow it up in the opposite direction, so that there is ultimately total maxillary intrusion. Fortunately, there is not much indication for maxillary dentition intrusion by translation in non-surgical cases.

  13. VK: A few tips to prevent TADs fracture

  14. KC: Fracture of the TADs is due to the low yield strength of the material. Bending, torsion, and fatigue fracture can be produced during insertion and removal. The fracture problem is being solved by metallurgic manufacturing processes and has less to do with the technique of a clinician.

  15. VK: Do you routinely reuse the TADs for the same patient, that is, reposition the TADs?

  16. KC: No, I discard the TAD, once it is removed from the patient.

  17. SP: There is a popular belief that TADs will/has revolutionized Orthodontic treatment planning and many patients who were originally thought of as surgical patients are now being treated with TADs. Your comments.

  18. KC: Yes, I believe so. Especially in very challenging cases like asymmetry, reinforcing the posterior anchorage by TADs has greatly increased the scope of orthodontics [Figure 4]. In Korea, many patients want to improve their facial profile by retraction of the anterior teeth. However, the amount of tooth movement is limited by the amount of alveolar bone, especially in a patient with a very thin mandibular symphysis [Figure 5].
    Figure 4: Very challenging asymmetry case can be easily treated by TADs

    Click here to view
    Figure 5: Treatment of lip protrusion by retraction of anterior teeth

    Click here to view

    Hence, you should be very careful, not to move the tooth beyond the labial or lingual cortical plate of the bone.[1],[2]

  19. VK: Your book, co-authored with Prof Burstone, mentions that you would personally prefer a round base archwire when you are using a torqueing auxiliary to torque a single tooth. Can you please elaborate on that?

  20. KC: I prefer to use an anterior root spring with a long arm because it produces light and continuous torque on the teeth. If you want to use a torqueing auxiliary to a single tooth, it should allow 3rd order rotation of the tooth. Therefore, I would recommend either an undersized rectangular or round wire, never filling the slot with a full-sized wire.

  21. SP: Your thoughts on the stability of TADs treatment especially with total maxillary intrusion

  22. KC: Many clinical studies show that the intrusion of anterior teeth is quite stable in the long term. For posterior teeth intrusion, there are a wide range of individual variations. My belief is that, posterior teeth intrusion with TADs would have 10%–20% of relapse. Therefore, some over correction of total maxillary intrusion is required.

  23. SP: Mandibular molar intrusion, a challenge even with TADs?

  24. KC: Mandibular molar intrusion is possible with TADs. It should be remembered that the single force is applied at the buccal side of the Cres of mandibular molar and subsequently it tends to rotate (crown buccal, root lingual). It is very difficult to place a TAD lingually to counter-act this rotation. Therefore, if this type of rotation is not desirable, it must be resolved by placing a passive lingual arch, which in my view, would be the best solution to prevent the rotation.

  25. SP: Aligner therapy with TADs – can they coexist. In the sense, aligner therapy is now marketed for the general dental practitioner, while TADs require advanced Orthodontic knowledge in terms of Biomechanics.

  26. KC: I think, there is no reason to make any restriction of using TADs with aligners. The force system available from an aligner is very limited, even with addition of attachments. Therefore, the most important thing to understand is the inherent limitation of the force system with aligners and perhaps TADs can be complementary to completing the required force system. No matter what type of appliance you are using, understanding the underlying fundamental biomechanics is most important.

  27. VK: Your first interaction with Dr Burstone.

  28. KC: When I was a first-year resident at Yonsei University back in early 90s, I had a chance to read one of his articles, and I was instantly mesmerized by his clear mechanical explanation. I started to write letters to him with many questions, for many years and luckily, for me, I could visit him as a research fellow after I finished my graduate study. There was no email in the early 90s and it took at least two months to receive a reply from him. I still treasure those faded hand-written paper letters from Dr. Burstone.

  29. VK: Your experience with Dr Charles Burstone on writing the book.

    KC: I have been asking him to combine all his papers together and to compose an oeuvre of his life's work for many years, but he was not interested. Several years later, in 2012, he offered me the opportunity to write a book with him. The book was published 3 years later in 2015. While writing the book I visited him two times and almost 2,000 emails were shared between Dr Burstone and me. It was one of the most challenging, most exciting and the happiest moments in my life. Sadly, he could not see the publication of his life's work.

  30. VK: An interesting incident with Dr Charles Burstone

  31. KC: When I was a resident, Dr. Burstone visited Yonsei University for a 3-day course. After finishing the course, I took him to the old city of Korea for a tour. I remember, I prepared a lot of questions and bothered him for many hours after we had dinner.

  32. SP: Infra Zygomatic Crest (IZC) and Buccal Shelf Implants (BSI) vs conventional TADs – your experience; what percentage of your practice is IZCs versus conventional TADs?

  33. KC: While using IZC or BSI, the distance from the point of force application and the point of insertion is relatively long. If the line of force is acting perpendicular to the axis of the screw, and a very large moment is created on the screw, it will result in instability. I prefer using a short conventional screw, as much as possible.

  34. SP: Asian Orthodontics-the future… will it lead innovations for global orthodontics, like the way TADs have revolutionized contemporary Orthodontics?

  35. KC: One of the differences between Western and Asian orthodontic patients is that, most of the Asian patients anticipate improvement of facial appearance, such as retraction of their lips, whereas Western patients do not anticipate this. Therefore, TADs are more likely indicated for Asian patients for some aspects, and I believe many clinical experiences will lead to development of the TADs and techniques.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Wehrbein H, Bauer W, Diedrich P. Mandibular incisors, alveolar bone, and symphysis after orthodontic treatment. A retrospective study. Am J Orthod Dentofacial Orthop 1996;110:239-46.  Back to cited text no. 1
Burstone CJ, Choy K. Biomechanical Foundation of Clinical Orthodontics. Chicago, USA: Quintessence; 2015. p. 185.  Back to cited text no. 2


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]


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