2D Evaluation of Condylar Vertical Positional Changes and Stability after Bilateral Sagittal Split Osteotomy

Syeda Fathimuz Zahara; Nandish Shetty; Pooja Harish

doi:10.4103/jofs.jofs_28_21

ORIGINAL ARTICLE

Year : 2021 | Volume : 13 | Issue : 2 | Page : 85-89

2D Evaluation of Condylar Vertical Positional Changes and Stability after Bilateral Sagittal Split Osteotomy

Syeda Fathimuz Zahara, Nandish Shetty, Pooja Harish
Department of Orthodontics and Dentofacial Orthopaedics, Yenepoya Dental College, Yenepoya (Deemed to be) University, Manglore, Karnataka, India

Date of Submission	27-Jan-2021
Date of Acceptance	22-Oct-2021
Date of Web Publication	14-Jan-2022

Correspondence Address:
Syeda Fathimuz Zahara
Department of Orthodontics and Dentofacial Orthopaedics, Yenepoya Dental College, Yenepoya (Deemed to be) University, Manglore 575018, Karnataka
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jofs.jofs_28_21

Abstract

Introduction: The purpose of this study was to evaluate the condylar vertical positional changes and stability after the bilateral sagittal split osteotomy (BSSO) setback procedure for class III malocclusions. Materials and methods: This was a retrospective study comprising lateral cephalograms of 11 patients with 8 males and 3 females who had undergone BSSO, without additional surgery. Manual superimposition was performed with the Frankfurt horizontal plane as a reference. Condylar vertical, linear, and angular positional changes, and chin position were considered. To compare pre- and postsurgical statistics paired t test was used. Significance was set at P-value <0.05. Results: Two angular and three linear parameters showed statistically significant changes. The articular angle, gonial angle, the mandibular plane angle, and Ramal height decreased, Pogonion-Nasion parallel to Sella-Nasion increased postsurgically. Conclusion: There were significant condylar changes and the rigid fixation method provided maximum stability after the BSSO surgical procedure.

Keywords: BSSO, class III malocclusion, condyle, stability

How to cite this article:
Zahara SF, Shetty N, Harish P. 2D Evaluation of Condylar Vertical Positional Changes and Stability after Bilateral Sagittal Split Osteotomy. J Orofac Sci 2021;13:85-9

How to cite this URL:
Zahara SF, Shetty N, Harish P. 2D Evaluation of Condylar Vertical Positional Changes and Stability after Bilateral Sagittal Split Osteotomy. J Orofac Sci [serial online] 2021 [cited 2023 Jun 9];13:85-9. Available from: https://www.jofs.in/text.asp?2021/13/2/85/335849

Introduction

Bilateral sagittal split osteotomy (BSSO) is a surgical procedure introduced as a treatment modality by Trauner and Obwegeser for the correction of mandibular prognathism.^[1] This modality of correction for class III malocclusions had given the best results in the patients who cannot be treated by any of the camouflage methods. There are numerous indications for the application of this technique which gave way for several modifications in this procedure.^[2]

Mandibular osteotomies, used in the single jaw or bimaxillary surgery, initiate an adaptation mechanism in the temporomandibular joint (TMJ). Mandibular osteotomies may often alter the condylar position, which leads to different load distributions in the TMJ. Adaptation mechanisms in the TMJ may trigger bone remodeling with structural changes that may result in an altered shape of the condyle.^[3]

Condylar changes are observed in terms of a progressive alteration of condylar shape and a decrease in mass. As a result, most patients exhibit a decrease in posterior facial height and retrognathism. Although the cause is unknown, condylar resorption has been associated with various systemic diseases, trauma, neoplasia, orthodontic treatment, and orthognathic surgery. The BSSO may cause alteration of the position of the condyle in the fossa.^[4]

Several authors have suggested that the type of fixation also can influence the condylar position. Stroster and Pangrazio-Kulbersh noted greater condylar displacement after a BSSO fixed with rigid fixation than with wire osteosynthesis.^[5] Kundert and Hadjianghelou believed there was a greater displacement of the condyles when rigid fixation was used.^[6] Previous clinical studies on this subject have not been randomized. The purpose of this retrospective study was to evaluate and compare condylar position changes in patients who had undergone the BSSO setback procedure and also to evaluate the stability with rigid fixation.

Materials and Methods

The retrospective study comprised 11 patients with 8 males and 3 females of age group 17 to 25 years with 7 vertical and 4 horizontal growth patterns, who had mandibular prognathism. Ethical clearance was obtained for the study from YEC 2. Ethical approval for this study was provided by Yenepoya Ethical Committee-2 with protocol number YEC2/518 of Yenepoya (Deemed to be) University, Manglore on 23^rd October 2020. It was a short-term study, carried out using inclusion and exclusion criteria. Records that fulfill the criteria are taken. The digital lateral cephalometric radiographs are obtained from a machine planmeca taken at the department of oral medicine and radiology Yenepoya (Deemed to be) University, Yenepoya Dental College, Mangalore, as a part of treatment procedure for orthodontic treatment.

Patients orthodontically treated with fixed mechanotherapy, the patients who underwent BSSO setback procedure without additional surgeries, patients with no TMJ disorders, skeletal and dental class III molar relation, and reverse jet of more than 5 mm were included in the study. Patients with a history of systemic or metabolic disorders (as per the records) that interfere in bone healing, radiographs with gross facial asymmetry and deformities, radiographs with cleft lip and palate, and distorted radiographs were excluded from the study.

The obtained radiographs include before orthodontic treatment, that is, pretreatment cephalograms (T0) and postsurgical (after 3 months of surgery) (T1). The amount of setback considered was in a range of 5 to 9 mm and an average was taken as 6 mm. Manual tracing was performed using acetate sheets attached to the radiographs and 0.5 mm lead pencil and mandibular landmarks are traced with Frankfurt horizontal (FH) plane as a reference. The parameters assessed in lateral cephalograms to obtain condylar changes include [Figure 1]: (1) Ramus inclination: the angle between the posterior line of the ramus (articulare point–ramus down point) and the FH line, (2) Saddle angle, (3) Articular angle, (4) Gonial angle, (5) Mandibular plane angle, and (6) Ramal height [condylion (Co) to Gonion (Go)].

Figure 1 (A) Ramus inclination. (B) Saddle angle. (C) Articular angle. (D) Gonial angle. (E) Mandibular plane angle. (F) Ramal height. (G) Pog-N perpendicular to SN. (H) Pog-N parallel to SN.

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The stability is obtained from the parameters assessed in lateral cephalograms that is [Figure 1].

Pogonion-Nasion (Pog-N) parallel to Sella-Nasion (SN): the distance between Pog and N on a line parallel to SN.
Pog-N perpendicular to Sella-Nasion (SN): the distance between Pog and N on a line perpendicular to SN.
Ramus inclination: the angle between the posterior line of the ramus (articulare point–ramus down point) and the FH line. Each radiograph was evaluated and manually superimposed to compare changes in terms of angulation and height.

As per the records, at the time of fixation, the dental arch of the distal segment was secured to titanium, a long miniplate (four holes/bur 8 mm, thickness 0.55 mm) and four screws (2 mm * 8 mm; Würzburg titanium miniplate system; Leibinger Co., Freiburg, Germany) were placed monocortically in the mandibular angle region in each side through a transcutaneous approach.

Method error was evaluated for locating the reference points and superimposing the lateral cephalograms and measuring the parameters of all 11 subjects for intra- and interexaminer errors. The formula of Dahlberg was used in the calculations, where d is the difference between two registrations of a pair and n is the number of double registrations. The method error amounted to 0.5 mm.

The obtained results were analyzed using IBM SPSS Statistics for Windows software (version 23 IBM corp., Armonk, NY). Estimation was carried out using G* power for analysis of variance. At 10% level of significance and 80% power with effect size 0.508 from pooled standard deviation (SD) 3.6. The descriptive statistics were used to obtain mean and SD for continuous data paired t test was performed to analyze the changes in pre- and postsurgery. The data are shown as mean (SD) with a 95% confidence interval. Differences were considered significant if the probability was less than 0.05. (i.e., P < 0.05).

Results

The mean values of articular angle, gonial angle, the mandibular plane angle, and Ramal height decreased, Pog-N parallel to SN increased postsurgically. There were statistically significant changes noted. The paired t test showed a significant difference [Table 1].

Table 1 Significant values of the parameters considered for the study

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Discussion

This retrospective study was designed to determine the condylar changes in terms of angulation, height, and to determine the stability after mandibular setback surgery. The mandibular setback with an average of 6 mm was considered among 7 males and 4 females.

Early skeletal relapse has been linked to postoperative instability and intersegment movement at the osteotomy site. This so-called “osteotomy slippage” can occur if the “rigid fixation” is inadequate. It has been reported to occur before bony union has been established, and can be measured as a change in mandibular corpus length.^[7],[8] In our study, mandibular corpus length [Figure 2] decreased 2.5 mm during surgery but almost fully returned to its preoperative length (71 mm, P = 0.03). In contrast to Franco et al.,^[9] who did not find any osteotomy slippage in the first 3 years postoperatively, our results show that there is osteotomy slippage after mandibular setback surgery, probably contributing to early skeletal relapse. The muscular factor is regarded as being most important in postoperative relapse following mandibular setback.^[10] Many authors have presented various techniques to reduce postoperative relapse.^[11],[12] Epker^[2] presented the short lingual osteotomy technique. This modification prevented excessive bleeding, avascular necrosis or infection, and postoperative swelling.^[14],[15] Certain reports have mentioned the potential for error during cephalometric measurements. MacIntosh^[16] and Karabouta and Martis (1984)^[17] believed that a change of 41 mm could be regarded as a meaningful relapse. Pepersack and Chausse^[13] defined relapse as a change in the mandibular segment on the occlusal plane of over 1.5 mm. In our study, each cephalometric radiograph was traced by the same operator; the landmarks, and the linear and the angular measurements were calculated manually. Freihofer and Petresevic^[18] said that there was a maximum error of 11° in angular measurement and a maximum error of 1 mm in linear measurement.

Figure 2 Comparison of all the parameters with their significance.

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Another mechanism contributing to early relapse is condylar displacement and clockwise rotation of the proximal segment, which occurs in connection with condylar repositioning during surgery.^[19] This positional change of the proximal segment lengthens the pterygomasseteric muscle sling, stretching the lateral muscle attachments. At the same time, the posterior movement of the distal segment places the medial attachments under tension. The stretched mandibular musculature thus tends to return the ramus to its original inclination when function resumes, and therefore skeletal relapse may occur. A vertical change of the Go in an inferior direction is indicative of condylar displacement. The posterior rotation of the ramus becomes visible as the inclination increases. Our results showed that the condylar height decreased indicating that there was condylar displacement.^[20] During surgery, Go also moved posteriorly, with an increase in mandibular ramus inclination indicating a proximal segment rotation (7.72°). Proffit et al.^[21],[22] observed a strong relapse tendency due to condylar displacement 1 year after mandibular setback. Komori et al.^[23] found that the degree of proximal segment anteroposterior rotation was a significant factor in distal segment relapse at an early postoperative stage. In those studies, a measurable increase of the ramus length was associated with rotation of the proximal segment. Subsequently, Mobarak et al.^[24] made a similar observation in a 3-year follow-up after mandibular setback, confirming a positive correlation between proximal segment rotation, condylar displacement, and mandibular skeletal relapse. Our results, and those from the other studies mentioned earlier, indicate that surgical rotation of the proximal segment occurs in most cases of mandibular setback. In addition, the proximal segment rotation in our study was not contributed by early skeletal relapse. The results of our study show no further skeletal relapse after a month of observation. However, there was a continuous decrease of mandibular ramus length. The decrease in mandibular plane angle and gonial angle confirmed that a remodeling process occurred at the osteotomy site in the angular region of the mandible. The postoperative changes of the mandible seemed to be part of a continuous process, which is an indication that the prognathic mandible is part of a functional interrelation. These observations may verify Moss theory that hard-tissue morphology is a result of the functional requirements of an area.

Changes in condylar position after orthognathic surgery are a matter of concern. Historically, fixation using a single upper border wire was advocated. However, this resulted in a forward rotation of the condylar fragment and an associated unaesthetic notch at the lower border on many occasions. The Epker modification was suggested to prevent this. Lower border wiring has been used, not only to enhance stability but also to maintain the position of the proximal fragment and place the condyle in the fossa as accurately as possible. It also has been advocated that no fixation of any kind be used to allow the condyles to settle in the most favorable position. Changes in intercondylar angle and width after BSSO advancement or setback may influence TMJ function.^[25] Intercondylar width tends to decrease after mandibular setback and to increase after mandibular advancement. A study showed that a bent plate was more effective than a straight plate for postoperative temporomandibular disorder (TMD).^[26] Titanium plates and screws were used for fixation as in our study. Orthognathic surgery is associated with a wide range of TMD symptoms. Among 280 patients undergoing orthognathic surgery without rigid fixation, Karabouta and Martis^[12] found that 40.8% had TMD preoperatively. After BSSO, the incidence decreased to 11.1%, including the development of new symptoms in 3.7% of the patients. Rigid fixation of the mandible during orthognathic surgery may or may not lead to a higher incidence of TMD when compared with wire (nonrigid) fixation. Timmis et al.^[27] found a significant reduction in the incidence of masticatory dysfunction with screw fixation in 28 patients who underwent BSSO, but Feinerman and Pieuch^[19] reported that masticatory muscle pain and TMJ clicking improved with rigid fixation and worsened with non-rigid fixation. Thus, some authors have reported that the fixation method is related to postoperative TMD.

In orthognathic surgery, bone fragments are usually fixed with the use of metallic plates and screws. Recently, the use of resorbable materials to stabilize the maxillofacial skeleton has been reported. Synthetic polymers have had a considerable impact on orthognathic procedures. Bioabsorbable polymers currently used to produce osteo-fixation devices include homopolymers and copolymers.

Conclusion

There was an increase in the mean values of the parameters, paired t test showed significant changes in pre- and postsurgery. So according to the study, we can conclude that after the BSSO setback procedure,

There were significant changes in condylar angulation and height.
The rigid fixation method provided maximum stability postoperatively.

Limitations of the study

As it is a two-dimensional study, the exact condylar changes could not be recorded and further three-dimensional studies can be carried out to analyze the changes that might occur.
Long-term follow-up studies must be conducted to analyze the stability after BSSO setback surgeries.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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