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KJO Korean Journal of Orthodontics

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pISSN 2234-7518
eISSN 2005-372X

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Korean J Orthod 2025; 55(1): 1-2   https://doi.org/10.4041/kjod55.0001RF

First Published Date January 25, 2025, Publication Date January 25, 2025

Copyright © The Korean Association of Orthodontists.

READER’S FORUM

Soo Hyun Nam

Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea

Body

Bin Xu, Jung-Jin Park, Jin Bai, Seong-Hun Kim

Effect of bone-borne maxillary skeletal expanders on cranial and circummaxillary sutures: A cone-beam computed tomography study.

- Korean J Orthod 2024;54:346-358

Questions

I appreciate the author’s hard work on the study. To gain a deeper understanding of your work, I have a few inquiries.

Q1. It was explained that, compared to the ATOZ expander, the C-expander causes a reduction in the width of the circumscribed zygomatic suture due to the rotation of the naso-maxillo-zygomatic complex around the frontonasal suture as a center of rotation during expansion. Why the C-expander shows less effect on the bone and a more pronounced rotational effect on the complex compared to the ATOZ expander?

Q2. What is the clinical significance of the difference between two appliances in terms of showing opposing trends in the changes of circumscribed zygomatic suture width before and after expansion?

Q3. In clinical practice, under what circumstances would it be advantageous to use a C-expander type or an ATOZ expander type, respectively?

Questioned by

Soo Hyun Nam

Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea

Answers

I am glad to receive your questions.

A1. Since the C-expander has a miniscrew on the palatal slope and the basic direction of expansion is lateral push movement, it rotates around the fronto-nasal suture or fronto-zygomatic suture, so that part is compressed and narrowed, whereas the ATOZ can exert continuous force to show even changes in the entire circum-maxillary suture and the anchor site that exerts force is more superior than the C-expander, gradually inducing circum-maxillary suture changes. Therefore, unlike the C-expander that applies lateral force to the left and right alveolus and rotates around the fronto-nasal suture, the effect of overall bilateral volume up is shown.1 Therefore, clinically, the ATOZ can have the best effect on midface volume up, followed by the C-expander, and the maxillary skeletal expander (MSE) is thought to have less effect on midface volume up.

A2. For patients with Class III malocclusion in early age, a wider suture may be more advantageous for treatment,2,3 and these two types of orthodontic appliances have different effects on the circummaxillary sutures. Therefore, orthodontic appliances that can widen circummaxillary sutures may be more beneficial for the treatment of patients with maxillary deficiency. In adult patients, the widening of the circumscribed zygomatic sutures during maxillary expansion may increase facial width, reduce facial contour sharpness, and potentially diminish midface aesthetics. This is particularly critical for patients with high aesthetic demands and sensitivity to facial changes, such as those with a broad facial type or hypodivergent patients. In such cases, caution is advised when using maxillary expansion devices like the MSE, which may increase zygomatic width during maxillary expansion. From this perspective, the C- and ATOZ expander offers a more favorable alternative.4,5

A3. According to research on C-expanders and ATOZ, we can find that C-expanders and ATOZ can produce significant maxillary bone expansion.5,6 For patients who simply need to open the maxillary palatal suture, we can use both. However, the C-expander orthodontic appliance requires patient cooperation during activation, so patients need to have high compliance, while the ATOZ is different, as it stores strength in the appliance and does not require patient cooperation for a certain period. According to research, ATOZ can enlarge some circummaxillary sutures and had the largest skeletal effects. While in the C-expander, there were some differences, expansion effects both in skeletal expansion and alveolar bone bending. Therefore, for patients who need more skeletal expansion effects with maxilla transverse deficiency, ATOZ expander is recommended for treatment.

The ATOZ expander does not induce breakage of suture interdigitation through rapid expansion. Instead, it applies sufficient orthopedic force to maintain pressure until the suture interdigitation loosens due to bone remodeling. Therefore, there is a lag phase that requires time until the midpalatal suture (MPS) separates. The T1 stage represents the active stage of expansion, during which data was collected. Due to the characteristics of the ATOZ expander, there are cases where the MPS expansion amount appears as zero during the lag phase. Overall, compared to general hyrax-type expanders that cause suture rupture or tearing rapidly, the reaction time of the MPS is longer. For this reason, in the comparison between T0 and T1, the overall expansion amount of the MPS appears smaller.6

In the future, if data is obtained at the T2 stage (just before or after removing the ATOZ following full-range expansion) for research, it is expected that greater skeletal changes will be observed with the ATOZ. Follow-up studies are also planned to confirm that inducing a more response in the circum-maxillary sutures improves the stability of maxillary transverse deficiency treatment outcomes.

Replied by

Jung-Jin Park, Jin Bai, Seong-Hun Kim

Department of Orthodontics, School of Dentistry, Kyung Hee University, Seoul, Korea

References

  1. Jin B, Choi JY, Kim SH. The design of bone-borne maxillary expander affects the different dentoalveolar inclination and expansion pattern: a CBCT study. Semin Orthod 2024. [Epub ahead of print] https://doi.org/10.1053/j.sodo.2024.05.002
    CrossRef
  2. Choi JY, Choo H, Oh SH, Park JH, Chung KR, Kim SH. Finite element analysis of C-expanders with different vertical vectors of anchor screws. Am J Orthod Dentofacial Orthop 2021;159:799-807. https://doi.org/10.1016/j.ajodo.2020.02.024
    Pubmed CrossRef
  3. Pithon MM, Santos NL, Santos CR, Baião FC, Pinheiro MC, Matos Neto M, et al. Is alternate rapid maxillary expansion and constriction an effective protocol in the treatment of Class III malocclusion? A systematic review. Dental Press J Orthod 2016;21:34-42. https://doi.org/10.1590/2177-6709.21.6.034-042.oar
    Pubmed KoreaMed CrossRef
  4. Büyükçavuş MH. Alternate rapid maxillary expansion and constriction (Alt-RAMEC) protocol: a comprehensive literature review. Turk J Orthod 2019;32:47-51. https://doi.org/10.5152/turkjorthod.2019.18021
    Pubmed KoreaMed CrossRef
  5. Paredes N, Gargoum A, Dominguez-Mompell R, Colak O, Bui J, Duong T, et al. Pattern of microimplant displacement during maxillary skeletal expander treatment: a cone-beam computed tomography study. Korean J Orthod 2023;53:289-97. https://doi.org/10.4041/kjod23.056
    Pubmed KoreaMed CrossRef
  6. Xu B, Park JJ, Bai J, Kim SH. Effect of bone-borne maxillary skeletal expanders on cranial and circummaxillary sutures: a cone-beam computed tomography study. Korean J Orthod 2024;54:346-58. https://doi.org/10.4041/kjod24.180
    Pubmed KoreaMed CrossRef

Article

Reader’s Forum

Korean J Orthod 2025; 55(1): 1-2   https://doi.org/10.4041/kjod55.0001RF

First Published Date January 25, 2025, Publication Date January 25, 2025

Copyright © The Korean Association of Orthodontists.

READER’S FORUM

Soo Hyun Nam

Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Body

Bin Xu, Jung-Jin Park, Jin Bai, Seong-Hun Kim

Effect of bone-borne maxillary skeletal expanders on cranial and circummaxillary sutures: A cone-beam computed tomography study.

- Korean J Orthod 2024;54:346-358

Questions

I appreciate the author’s hard work on the study. To gain a deeper understanding of your work, I have a few inquiries.

Q1. It was explained that, compared to the ATOZ expander, the C-expander causes a reduction in the width of the circumscribed zygomatic suture due to the rotation of the naso-maxillo-zygomatic complex around the frontonasal suture as a center of rotation during expansion. Why the C-expander shows less effect on the bone and a more pronounced rotational effect on the complex compared to the ATOZ expander?

Q2. What is the clinical significance of the difference between two appliances in terms of showing opposing trends in the changes of circumscribed zygomatic suture width before and after expansion?

Q3. In clinical practice, under what circumstances would it be advantageous to use a C-expander type or an ATOZ expander type, respectively?

Questioned by

Soo Hyun Nam

Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea

Answers

I am glad to receive your questions.

A1. Since the C-expander has a miniscrew on the palatal slope and the basic direction of expansion is lateral push movement, it rotates around the fronto-nasal suture or fronto-zygomatic suture, so that part is compressed and narrowed, whereas the ATOZ can exert continuous force to show even changes in the entire circum-maxillary suture and the anchor site that exerts force is more superior than the C-expander, gradually inducing circum-maxillary suture changes. Therefore, unlike the C-expander that applies lateral force to the left and right alveolus and rotates around the fronto-nasal suture, the effect of overall bilateral volume up is shown.1 Therefore, clinically, the ATOZ can have the best effect on midface volume up, followed by the C-expander, and the maxillary skeletal expander (MSE) is thought to have less effect on midface volume up.

A2. For patients with Class III malocclusion in early age, a wider suture may be more advantageous for treatment,2,3 and these two types of orthodontic appliances have different effects on the circummaxillary sutures. Therefore, orthodontic appliances that can widen circummaxillary sutures may be more beneficial for the treatment of patients with maxillary deficiency. In adult patients, the widening of the circumscribed zygomatic sutures during maxillary expansion may increase facial width, reduce facial contour sharpness, and potentially diminish midface aesthetics. This is particularly critical for patients with high aesthetic demands and sensitivity to facial changes, such as those with a broad facial type or hypodivergent patients. In such cases, caution is advised when using maxillary expansion devices like the MSE, which may increase zygomatic width during maxillary expansion. From this perspective, the C- and ATOZ expander offers a more favorable alternative.4,5

A3. According to research on C-expanders and ATOZ, we can find that C-expanders and ATOZ can produce significant maxillary bone expansion.5,6 For patients who simply need to open the maxillary palatal suture, we can use both. However, the C-expander orthodontic appliance requires patient cooperation during activation, so patients need to have high compliance, while the ATOZ is different, as it stores strength in the appliance and does not require patient cooperation for a certain period. According to research, ATOZ can enlarge some circummaxillary sutures and had the largest skeletal effects. While in the C-expander, there were some differences, expansion effects both in skeletal expansion and alveolar bone bending. Therefore, for patients who need more skeletal expansion effects with maxilla transverse deficiency, ATOZ expander is recommended for treatment.

The ATOZ expander does not induce breakage of suture interdigitation through rapid expansion. Instead, it applies sufficient orthopedic force to maintain pressure until the suture interdigitation loosens due to bone remodeling. Therefore, there is a lag phase that requires time until the midpalatal suture (MPS) separates. The T1 stage represents the active stage of expansion, during which data was collected. Due to the characteristics of the ATOZ expander, there are cases where the MPS expansion amount appears as zero during the lag phase. Overall, compared to general hyrax-type expanders that cause suture rupture or tearing rapidly, the reaction time of the MPS is longer. For this reason, in the comparison between T0 and T1, the overall expansion amount of the MPS appears smaller.6

In the future, if data is obtained at the T2 stage (just before or after removing the ATOZ following full-range expansion) for research, it is expected that greater skeletal changes will be observed with the ATOZ. Follow-up studies are also planned to confirm that inducing a more response in the circum-maxillary sutures improves the stability of maxillary transverse deficiency treatment outcomes.

Replied by

Jung-Jin Park, Jin Bai, Seong-Hun Kim

Department of Orthodontics, School of Dentistry, Kyung Hee University, Seoul, Korea

References

  1. Jin B, Choi JY, Kim SH. The design of bone-borne maxillary expander affects the different dentoalveolar inclination and expansion pattern: a CBCT study. Semin Orthod 2024. [Epub ahead of print] https://doi.org/10.1053/j.sodo.2024.05.002
    CrossRef
  2. Choi JY, Choo H, Oh SH, Park JH, Chung KR, Kim SH. Finite element analysis of C-expanders with different vertical vectors of anchor screws. Am J Orthod Dentofacial Orthop 2021;159:799-807. https://doi.org/10.1016/j.ajodo.2020.02.024
    Pubmed CrossRef
  3. Pithon MM, Santos NL, Santos CR, Baião FC, Pinheiro MC, Matos Neto M, et al. Is alternate rapid maxillary expansion and constriction an effective protocol in the treatment of Class III malocclusion? A systematic review. Dental Press J Orthod 2016;21:34-42. https://doi.org/10.1590/2177-6709.21.6.034-042.oar
    Pubmed KoreaMed CrossRef
  4. Büyükçavuş MH. Alternate rapid maxillary expansion and constriction (Alt-RAMEC) protocol: a comprehensive literature review. Turk J Orthod 2019;32:47-51. https://doi.org/10.5152/turkjorthod.2019.18021
    Pubmed KoreaMed CrossRef
  5. Paredes N, Gargoum A, Dominguez-Mompell R, Colak O, Bui J, Duong T, et al. Pattern of microimplant displacement during maxillary skeletal expander treatment: a cone-beam computed tomography study. Korean J Orthod 2023;53:289-97. https://doi.org/10.4041/kjod23.056
    Pubmed KoreaMed CrossRef
  6. Xu B, Park JJ, Bai J, Kim SH. Effect of bone-borne maxillary skeletal expanders on cranial and circummaxillary sutures: a cone-beam computed tomography study. Korean J Orthod 2024;54:346-58. https://doi.org/10.4041/kjod24.180
    Pubmed KoreaMed CrossRef