J Korean Assoc Oral Maxillofac Surg 2024; 50(5): 253~258
Analysis of postsurgical relapse patterns in one-jaw surgery: skeletal factors and clustering analysis in patients with mandibular setback
Jong-Wan Kim1, Nam-Ki Lee2, Pil-Young Yun3, Jong-Ho Lee4, Hye-Young Sim5
1Department of Orthodontics, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Departments of 2Orthodontics and 3Oral and Maxillofacial Surgery, Section of Dentistry, Seoul National University Bundang Hospital, Seongnam, 4Oral Oncology Clinic, Research Institute and Hospital, National Cancer Center, Goyang, 5Department of Dentistry, SMG-SNU Boramae Medical Center, Seoul, Korea
Hye-Young Sim
Department of Dentistry, SMG-SNU Boramae Medical Center, 20 Boramaero 5-gil, Dongjak-gu, Seoul 07061, Korea
TEL: +82-2-840-2493
E-mail: orthodo@hanmail.net
ORCID: https://orcid.org/0000-0002-3338-4245
Received June 5, 2024; Revised July 8, 2024; Accepted July 14, 2024.; Published online October 31, 2024.
© Korean Association of Oral and Maxillofacial Surgeons. All rights reserved.

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.
 Abstract
Objectives: To compare presurgical skeletal factors and postsurgical relapse patterns between more relapsed (MR) and less relapsed (LR) groups.
Materials and Methods: This study retrospectively examined patients who underwent mandibular setback surgery, classifying them into two groups based on the amount of relapse of the pogonion using K-means analysis. Comparisons were conducted by analyzing cephalometric radiographs presurgically (T0), at 1-month post-surgery (T1), and immediately after orthodontic treatment (T2).
Results: The MR group at T0 had a lower articular angle and AB to the mandibular plane angle (MPA), higher gonial angle, shorter anterior and posterior facial heights, and shorter Frankfort horizontal plane to the upper incisor and first molar. The articular angle in the MR group increased postoperatively. The Frankfort MPA (FMA) did not differ significantly between the MR and LR groups.
Conclusion: Acute articular angle and short facial height with a high gonial angle in the presurgical stage can predict surgical relapse regardless of the FMA.
Keywords: Prognathism, Orthognathic surgery, Recurrence
I. Introduction

Mandibular setback surgery is primarily recommended in cases of severe mandibular prognathism. This surgery was developed from several techniques such as sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy after mandibular body osteotomy in the 1900s1,2.

Although surgical treatment can improve the profile of patients with mandibular prognathism, surgical relapse should be considered to achieve stable surgical results because environmental factors, such as muscular forces around the mandible and tongue and surgical factors including bone fixation methods, amounts of surgical correction, and surgical technique may affect stability3-5. Other factors, such as condylar displacement and rotation of the proximal segments, can affect surgical relapse6.

A previous study demonstrated that surgical relapse may be related to skeletal facial patterns7, which could be relevant to the masticatory muscles, surgical design, and amount of mandibular setback4. However, there are several challenges in determination of the relationship between amount of surgical relapse and surgical correction8-11.

In this study, presurgical skeletal factors and postsurgical relapse patterns were compared between more relapsed (MR) and less relapsed (LR) groups, which were classified using clustering analysis. Furthermore, the factors contributing to relapse after orthognathic surgery were investigated.

II. Materials and Methods

The study included 25 patients (15 males and 10 females) who underwent mandibular setback one-jaw surgery at Seoul National University Bundang Hospital. Patients with mandibular asymmetry were excluded. The mean patient age was 25.6 years. The SSRO for correction of mandibular prognathism was performed in all these patients. The average amount of mandibular setback was 7.41±4.45 mm. Plates and monocortical screws were used for osseous fixation, and intermaxillary fixation was applied with a stainless steel wire for 2 weeks. Functional jaw exercises were prescribed to patients for 2 weeks after intermaxillary fixation release.

Lateral cephalograms of each patient were obtained presurgically (T0), at 1 month after surgery (T1), and immediately after orthodontic treatment (T2) for analysis. The cephalogram analysis program NUSMA for Ceph was used in each of three sessions by two orthodontists. The landmarks, reference planes, and variables comprising the linear and angular measurements are shown in Fig. 1, 2.

The horizontal measurements for the analysis of anterior and posterior changes were the distance between each landmark point and the perpendicular line of the sella (S) to the Frankfort horizontal (FH) plane (S-perp) line, mandibular body length, SNB angle, and AB to the MPA. Vertical measurements included the distance from the FH plane to each landmark point and the posterior and anterior facial heights. To evaluate rotational changes in the mandible, the articular angle, gonial angle, and Frankfort-mandibular plane angle (FMA) were measured.

To analyze the upper and lower anterior tooth axes, the angle between the long axis of the U1 and the FH plane, angle between the lower incisor and mandibular plane, angle between the FH plane and the upper or lower occlusal plane, and distance between the U1 tip and the mesiobuccal cusp tip of the U6 were measured.

Statistical analysis was performed using K-means clustering to classify the patients into the MR and LR groups. The values at T0 were analyzed using an independent t-test to compare presurgical skeletal factors between the MR and LR groups. Other measurements of surgical changes (T1-T0) and postsurgical relapse (T2-T1) were analyzed using an independent t-test. Statistical significance was set at P<0.05.

This study was conducted in accordance with the tenets of the Declaration of Helsinki and approved by the Institutional Review Board (IRB) of Bundang Hospital (IRB No. B-1302-192-101).

III. Results

Anterior and posterior relapse distances of the Pog were 4.45±1.26 mm in the MR group and 1.34±1.07 mm in the LR group, which were classified by K-means clustering analysis with measurements of S-perp to Pog.(Table 1) There were 12 and 13 patients in the MR and LR groups, respectively.

Presurgical (T0) factors that were significantly different between the MR and LR groups were the AB to the MPA in the mandibular anterior and posterior measurements, FH plane to Pog, FH plane to Me, posterior facial height, and anterior facial height in vertical measurements, articular angle and gonial angle in angular measurements, and FH to U1 and FH to U6 in dental measurements.(Table 2)

The MR group exhibited a shorter presurgical vertical orientation compared to the LR group. Although the FMA angle of the MR group did not significantly differ from that of the LR group, the articular angle was larger and the gonial angle was smaller in the MR group.

Mandibular anterior and posterior measurements, such as the AB to the MPA, were significantly different between the MR and LR groups.

The measurements related to surgical changes (T1-T0) were not significantly different between the MR and LR groups, except for those of the AB to the MPA and articular angle, as shown in Table 3.

In postsurgical relapse, the MR group exhibited significant decrease in FH to Pog and FH to Me and significant increase in S-perp to Pog, S-perp to Me, and SNB (P<0.05). The articular angle and AB to the MPA in the MR group decreased more than those in the LR group. The UI to the FH and the FH to the upper occlusal plane in the MR group were significantly different from those in the LR group, as shown in Table 4 (P<0.05).

IV. Discussion

In this study, presurgical skeletal factors, including presurgical orthodontic period and postsurgical relapse patterns, were analyzed between the MR and LR groups, classified using clustering analysis.

The MR group exhibited mandibular anterior relapse even though the mandibular body length was shorter than that in the LR group at T0. The amount of surgical change and relapse of mandibular body length were similar in the groups. These results demonstrated that other presurgical factors may affect surgical relapse in patients with mandibular prognathism. The MR group revealed different skeletal patterns, with a vertically shorter face than that of the LR group. The FH to the Pog, FH to the Me, and anterior and posterior facial heights were significantly lower in the MR group compared to the LR group. This pattern was observed in the dental measurements of FH to UI (mm) and FH to U6 (mm). Although the gonial angle in the MR group was larger than that in LR group, the articular angle in the MR group was smaller than that in the LR group. A high gonial angle can induce an increase in the total mandibular length from the articulare to the Me or Pog. A smaller articular angle could result in shorter facial height anteriorly and posteriorly, which may indicate a shorter facial height with a longer mandibular length. In addition, this led to a decrease in the AB to the MPA.

During surgery, the MR group tended to exhibit larger posterior shifts of the Pog, Me, and B points and smaller decrease in the mandibular body length in the anterior and posterior measurements of the mandible. The greater tendency for posterior mandibular movement in the MR group, without a greater decrease in the length of the mandibular body, likely is related to a greater increase in the articular angle during surgery. In both groups, the articular angle increased, but the MR group revealed a significant increase, indicating that the posterior movement of the mandible created larger positional changes with an increasing articular angle compared to a reduction in the length of the mandible in that group.

Although the shape of the face in the MR group could be narrow at the front, this facial pattern may be brachyfacial, potentially resulting in strong masticatory muscles and heavy bite forces because of the low articular angle and short facial height7,12. In the MR group, an increase in the articular angle during surgery was expected to increase the resistance to the strong masticatory muscles, resulting in a higher magnitude of counterclockwise rotation of the mandible. This could cause postsurgical vertical relapse, as shown in the FH to Pog, FH to Me, and articular angle. These measurements decreased with mandibular forward relapse, as seen in previous studies that reported relation of the forward-upward rotation of the mandible after mandibular surgery to most of the forward movement of the chin13.

The FMA was not related to significant presurgical factors when classifying the facial types in this study. Postsurgical change of mandibular body length in the MR group (1.62±3.72 mm) did not significantly differ from that of the LR group (2.21±2.47 mm). The Pog and Me points were moved anteriorly approximately 4.45 mm and 5.15 mm, respectively, which were significantly larger than those in the LR group (P<0.05). This indicates that mandibular rotation after surgery due to heavy bite forces in the MR group could contribute more highly to postsurgical relapse than actual pure surgical relapse, such as an increase in the mandibular body length14. This demonstrates that postsurgical relapse could be more related to the presurgical skeletal pattern than to surgical fixation or the extent of setback surgery. Other research concerning mandibular setback surgery with a metal plate system revealed no relation to relapse in mandibular setback15. However, vertical relapse in the counterclockwise direction may occur after mandibular setback surgery and is significantly correlated with forward relapse of the chin16.

The effects of strong muscle forces were observed not only in vertical measurements, but also in U1 to FH and FH to the upper occlusal plane. The heavy bite force after surgery in the MR group may have induced changes in the upper dentition, such as labial inclination of the upper anterior teeth and counterclockwise rotation of the upper occlusal plane. In other words, upward and forward rotation of the mandible with the hinge axis of the condyle and changes in the upper occlusal plane occur frequently during occlusal settling after surgery17.

Therefore, pre-surgical skeletal factors, such as vertical measurements, articular angle, gonial angle, and AB to the MPA, could help clinicians classify the skeletal pattern, estimate the masticatory force and habit of patients, predict relapse, and create a surgical plan to reduce the relapse of mandibular setback surgery.

V. Conclusion

In conclusion, an acute articular angle and short facial height with a high gonial angle in the presurgical stage can help predict surgical relapse, regardless of the FMA. Postsurgical relapse could be more highly related to the presurgical skeletal pattern than to surgical fixation or the extent of setback surgery. Masticatory forces incurred during function and habits in the presurgical stage may affect relapse after surgery.

Authors’ Contributions

J.W.K. participated in the study design, data analysis, investigation, methodology, and writing of the original draft. N.K.L., P.Y.Y., and J.H.L. participated in the study design, data curation, and investigation. H.Y.S. participated in the study design, coordination, and revision of the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding
No funding to declare.
Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Figures
Fig. 1. Measurements for analysis. A. Mandibular anterior/posterior and angular measurements. B. Vertical measurements. C. Dental measurements.
Fig. 2. Landmarks for analysis.
Tables

Anterior and posterior relapse of Pog in the MR group and LR group by linear measurement of a perpendicular line of the sella to Pog

MR group LR group P-value
Relapse of Pog (mm) 4.45±1.26 1.34±1.07 <0.001
No. of subjects 12 13 -

(MR: more relapsed, LR: less relapsed)

Values are presented as mean±standard deviation or number only.


Presurgical (T0) cephalometric analysis of the MR group and LR group

Measurements MR group LR group Sig.


Mean SD Mean SD
Mandibular anterior and posterior measurements
S-perp to Pog (mm) 82.02 8.54 80.16 8.88 NS
S-perp to Me (mm) 76.05 8.85 73.93 9.65 NS
Mn body length (mm) 83.63 4.01 86.82 4.58 NS
SNB (°) 84.40 2.98 82.92 4.05 NS
AB to Mn plane angle (°) 55.04 4.45 60.86 4.71 0.004
Angular measurements
Articular angle (°) 139.42 6.83 146.06 8.07 0.037
Gonial angle (°) 126.19 5.87 121.25 4.44 0.026
FMA (°) 21.94 6.47 21.94 4.45 NS
Vertical measurements
FH to Pog (mm) 91.49 6.85 99.13 7.66 0.015
FH to Me (mm) 100.90 7.47 109.22 7.88 0.013
Post. facial height (mm) 88.86 8.83 97.06 7.43 0.019
Ant. facial height (mm) 133.47 8.26 142.15 8.40 0.016
Dental measurements
U1 to FH (°) 120.26 6.53 119.84 7.26 NS
IMPA (°) 83.18 9.49 86.88 6.30 NS
FH to U occlusal plane (°) 7.94 5.54 6.30 3.10 NS
FH to L occlusal plane (°) 4.22 5.68 4.46 4.23 NS
FH to U1 (mm) 57.43 4.01 61.38 4.68 0.034
FH to U6 (mm) 53.28 2.89 57.85 4.40 0.006

(MR: more relapsed, LR: less relapsed, SD: standard deviation, Sig.: significant in the independent t -test, NS: not significant, FH: Frankfort horizontal, S-perp: a line perpendiculat to FH plane through Sella, FMA: Frankfort-mandibular plane angle, Post.: posterior, Ant.: anterior, IMPA: incisor mandibular plane angle)


Cephalometric analysis of surgical changes (T1-T0) of the MR group and LR group

Measurements MR group LR group Sig.


Mean SD Mean SD
Mandibular anterior and posterior measurements
S-perp to Pog (mm) –11.58 3.20 –10.43 4.36 NS
S-perp to Me (mm) –12.19 3.46 –10.60 4.94 NS
Mn body length (mm) –7.04 4.75 –7.75 4.18 NS
SNB (°) –5.91 1.29 –4.99 1.66 NS
AB to Mn plane angle (°) 12.67 2.42 9.04 2.67 0.002
Angular measurements
Articular angle (°) 4.36 3.88 1.52 1.80 0.026
Gonial angle (°) –1.94 6.18 1.94 5.20 NS
FMA (°) 2.36 3.23 3.38 4.83 NS
Vertical measurements
FH to Pog (mm) –0.02 2.69 1.59 2.47 NS
FH to Me (mm) 0.16 2.37 –0.86 2.16 NS
Post. facial height (mm) –0.31 2.29 –0.44 4.49 NS
Ant. facial height (mm) –0.29 2.13 0.94 2.30 NS
Dental measurements
U1 to FH (°) –0.72 1.81 –1.46 3.57 NS
IMPA (°) –2.83 4.74 –1.81 3.06 NS
FH to U occlusal plane (°) 0.07 1.45 –0.06 2.11 NS
FH to L occlusal plane (°) 2.73 6.52 2.37 6.31 NS
FH to U1 (mm) 0.02 0.84 0.46 1.31 NS
FH to U6 (mm) –0.04 0.91 0.50 1.02 NS

(T1: 1 month after surgery, T0: presurgical, MR: more relapsed, LR: less relapsed, SD: standard deviation, FH: Frankfort horizontal, Sig.: significant in the independent t -test, NS: not significant, S-perp: a line perpendiculat to FH plane through Sella, FMA: Frankfort-mandibular plane angle, Post.: posterior, Ant.: anterior, IMPA: incisor mandibular plane angle)


Cephalometric analysis of postsurgical relapse (T2-T1) of the MR group and LR group

Measurements MR group LR group Sig.


Mean SD Mean SD
Mandibular anterior and posterior measurements
S-perp to Pog (mm) 4.45 1.26 1.34 1.07 <0.001
S-perp to Me (mm) 5.15 1.76 1.05 1.34 <0.001
Mn body length (mm) 1.62 3.72 2.21 2.47 NS
SNB (°) 1.93 0.79 0.75 0.68 0.001
AB to Mn plane angle (°) –4.15 2.28 –2.37 2.19 NS
Angular measurements
Articular angle (°) –3.08 2.81 –0.54 1.25 0.012
Gonial angle (°) 2.79 3.08 1.38 2.53 NS
FMA (°) –0.79 2.48 1.14 2.33 NS
Vertical measurements
FH to Pog (mm) –3.14 2.44 –1.50 0.88 0.046
FH to Me (mm) –2.64 1.66 –1.55 0.90 0.050
Post. facial height (mm) –2.46 2.62 –3.84 2.83 NS
Ant. facial height (mm) –2.58 1.52 –1.56 1.17 NS
Dental measurements
U1 to FH (°) 3.34 4.07 –0.31 4.21 0.038
IMPA (°) 0.34 6.33 1.09 3.51 NS
FH to U occlusal plane (°) –1.46 3.28 1.58 2.52 0.016
FH to L occlusal plane (°) –3.85 4.32 –1.18 3.49 NS
FH to U1 (mm) –0.86 1.70 0.28 1.10 NS
FH to U6 (mm) –0.14 0.85 –0.67 1.11 NS

(T2: immediately after orthodontic treatment, T1: 1 month after surgery, MR: more relapsed, LR: less relapsed, SD: standard deviation, Sig.: significant in the independent t -test, NS: not significant, S-perp: a line perpendiculat to FH plane through Sella, FMA: Frankfort-mandibular plane angle, FH: Frankfort horizontal, Post.: posterior, Ant.: anterior, IMPA: incisor mandibular plane angle)


References
  1. Trauner R, Obwegeser H. The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty: Part I. Surgical procedures to correct mandibular prognathism and reshaping of the chin. Oral Surg Oral Med Oral Pathol 1957;10:677-89. https://doi.org/10.1016/S0030-4220(57)80063-2.
    Pubmed CrossRef
  2. Moose SM. Surgical correction of mandibular prognathism by intra-oral sub-condylar osteotomy. Br J Oral Surg 1964;1:172-6. https://doi.org/10.1016/S0007-117X(63)80068-2.
    Pubmed CrossRef
  3. Proffit WR, Phillips C, Dann C 4th, Turvey TA. Stability after surgical-orthodontic correction of skeletal Class III malocclusion. I. Mandibular setback. Int J Adult Orthodon Orthognath Surg 1991;6:7-18.
  4. Tseng YC, Lai S, Lee HE, Chen KK, Chen CM. Are hyoid bone and tongue the risk factors contributing to postoperative relapse for mandibular prognathism? Biomed Res Int 2016;2016:5284248. https://doi.org/10.1155/2016/5284248.
    Pubmed KoreaMed CrossRef
  5. Kobayashi T, Watanabe I, Ueda K, Nakajima T. Stability of the mandible after sagittal ramus osteotomy for correction of prognathism. J Oral Maxillofac Surg 1986;44:693-7. https://doi.org/10.1016/0278-2391(86)90037-6.
    CrossRef
  6. Reitzik M. Skeletal and dental changes after surgical correction of mandibular prognathism. J Oral Surg 1980;38:109-16.
  7. Yoshida K, Rivera GA, Matsuo N, Takaishi M, Inamoto H, Kurita K. Long-term prognosis of BSSO mandibular relapse and its relation to different facial types. Angle Orthod 2000;70:220-6.
  8. Joss CU, Thüer UW. Stability of hard tissue profile after mandibular setback in sagittal split osteotomies: a longitudinal and long-term follow-up study. Eur J Orthod 2008;30:352-8. https://doi.org/10.1093/ejo/cjn008.
    Pubmed CrossRef
  9. Jakobsone G, Stenvik A, Sandvik L, Espeland L. Three-year follow-up of bimaxillary surgery to correct skeletal Class III malocclusion: stability and risk factors for relapse. Am J Orthod Dentofacial Orthop 2011;139:80-9. https://doi.org/10.1016/j.ajodo.2009.03.050.
    Pubmed CrossRef
  10. Lee JH, Kim SO, Jeon JH. The assessment of the stability in mandibular setback surgery related to spatial factors under rotational control of the proximal segment. Oral Surg Oral Med Oral Pathol Oral Radiol 2014;117:560-6. https://doi.org/10.1016/j.oooo.2014.01.012.
    Pubmed CrossRef
  11. Tseng YC, Hsu KJ, Chen KK, Wu JH, Chen CM. Relationship between frontal gap and postoperative stability in the treatment of mandibular prognathism. Biomed Res Int 2016;2016:7046361. https://doi.org/10.1155/2016/7046361.
    Pubmed KoreaMed CrossRef
  12. Ricketts RM. Philosophies and methods of facial growth prediction. Proc Found Orthod Res:11-30.
  13. Hsu SS, Huang CS, Chen PK, Ko EW, Chen YR. The stability of mandibular prognathism corrected by bilateral sagittal split osteotomies: a comparison of bi-cortical osteosynthesis and mono-cortical osteosynthesis. Int J Oral Maxillofac Surg 2012;41:142-9. https://doi.org/10.1016/j.ijom.2011.10.029.
    Pubmed CrossRef
  14. Lee NK, Kim YK, Yun PY, Kim JW. Evaluation of post-surgical relapse after mandibular setback surgery with minimal orthodontic preparation. J Craniomaxillofac Surg 2013;41:47-51. https://doi.org/10.1016/j.jcms.2012.05.010.
    Pubmed CrossRef
  15. Lee HG, Agpoon KJ, Besana AN, Lim HK, Jang HS, Lee ES. Mandibular stability using sliding or conventional four-hole plates for fixation after bilateral sagittal split ramus osteotomy for mandibular setback. Br J Oral Maxillofac Surg 2017;55:378-82. https://doi.org/10.1016/j.bjoms.2016.11.318.
    Pubmed CrossRef
  16. Kim JW, Lee NK, Yun PY, Moon SW, Kim YK. Postsurgical stability after mandibular setback surgery with minimal orthodontic preparation following upper premolar extraction. J Oral Maxillofac Surg 2013;71:1968.e1-11. https://doi.org/10.1016/j.joms.2013.07.004.
    Pubmed CrossRef
  17. Xiangdong QI, Limin MA, Shizhen Z. The influence of the closing and opening muscle groups of jaw condyle biomechanics after mandible bilateral sagittal split ramus osteotomy. J Craniomaxillofac Surg 2012;40:e159-64. https://doi.org/10.1016/j.jcms.2011.07.024.
    Pubmed CrossRef


Current Issue

31 October 2024
Vol.50 No.5 pp.241~306

This Article


Social Network Service

Services

Indexed in