Association between bilateral sagittal split osteotomy setback and autorotation of the mandible

Syeda Fathimuz Zahara; Nandish Shetty; Pooja Harish; Akhter Husain

doi:10.4103/ijds.ijds_41_22

ORIGINAL ARTICLE

Year : 2023 | Volume : 15 | Issue : 1 | Page : 37-39

Association between bilateral sagittal split osteotomy setback and autorotation of the mandible

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

Date of Submission	13-Apr-2022
Date of Decision	28-Sep-2022
Date of Acceptance	09-Oct-2022
Date of Web Publication	17-Feb-2023

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

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/ijds.ijds_41_22

Abstract

Introduction: The study aimed to evaluate the autorotation for Class III malocclusions after the bilateral sagittal split osteotomy (BSSO) setback procedure. Methodology: This retrospective study includes lateral cephalograms of eight males and three females total of 11 patients who had undergone BSSO, without any other additional surgeries. The Frankfurt-Horizontal (F-H) plane was used as a reference and manual superimposition was done. Considering stable mandibular landmarks, reference line perpendicular (RLp) and reference line (RL) were drawn as x and y coordinates, respectively. Pre- and postsurgical statistics were used to compare using paired t-test where P < 0.05 was set for statistical significance. Results: Superimposed tracings showed no significant difference in pre- and postsurgical treatments. There was no statistically significant amount of autorotation after the BSSO setback procedure (P = 0.714). Conclusion: Hence, BSSO setback surgery will not cause any significant amount of autorotation of the mandible. If autorotation is required it must be incorporated into treatment planning.

Keywords: Angle's Class III malocclusion, autorotation, bilateral sagittal split osteotomy, mandible

How to cite this article:
Zahara SF, Shetty N, Harish P, Husain A. Association between bilateral sagittal split osteotomy setback and autorotation of the mandible. Indian J Dent Sci 2023;15:37-9

How to cite this URL:
Zahara SF, Shetty N, Harish P, Husain A. Association between bilateral sagittal split osteotomy setback and autorotation of the mandible. Indian J Dent Sci [serial online] 2023 [cited 2023 Nov 28];15:37-9. Available from: http://www.ijds.in/text.asp?2023/15/1/37/369894

Introduction

The bilateral sagittal split osteotomy (BSSO) procedure had various modifications after it was described by Trauner and Obwegeser.^[1] The modifications advocated by Dal Pont,^[2] Hunsuck,^[3] and Epker^[4] have reduced the “lingual and buccal cortical plate fracture” and “lingual cortical plate fracture” as complications.^[5]

During the entire opening movement through a single center of rotation, the mandible does not rotate. It can be characterized as different centers of the rotations with multiple arches of circles. Mandibular rotation is therefore relevant for a particular movement of the jaw.^[6]

This study aimed to evaluate the autorotation of the mandible in a BSSO setback procedure and also to know the direction of autorotation, either clockwise or counterclockwise to aid in diagnosis and treatment planning.

Methodology

This retrospective study included 11 individuals with mandibular prognathism comprising, three females and eight males between 17 and 25 years with growth patterns of seven vertical and four horizontal. After obtaining ethical clearance for the study, lateral cephalograms were obtained from a machine Planmeca ProMax™ using Agfa Nx software from the department of oral medicine and radiology.

Patients included in the study were treated orthodontically by fixed mechanotherapy. They underwent only the BSSO setback procedure of reverse jet of more than 5 mm without additional surgeries and were Skeletal and dental Class III molar relation with no temporomandibular joint disorders. As per the records, patients with a history of systemic or metabolic disorders which interfere with bone healing and distorted radiographs, radiographs with facial asymmetry, cleft lip and palate, and facial deformities were excluded.

The radiographs included presurgical cephalograms (T0) that are, before orthodontic treatment and postsurgical (after 3 months of surgery as T1).

Five to nine millimeter (average 6 mm) amount of setback was considered. The acetate sheets were attached to the radiographs and a 0.5 mm lead pencil was used for tracing.

The tracings were drawn as shown in [Figure 1]. A reference line perpendicular (RLp) was drawn perpendicular to the stable reference point as sella which was considered as y-coordinate and another reference line (RL) was drawn passing through the tip of the central incisor to the distobuccal cusp of first molars which was considered as an x-coordinate axis. Pre- and postsurgical tracings were manually superimposed [Figure 2] and evaluated for the degree of variation.

Figure 1: Measurement of mandibular rotation where RLP represents a perpendicular from stable point sella as y-coordinate and RL represents a line passing through the tip of central incisor to the distobuccal cusp of first molars which was considered as x-coordinate axis

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Figure 2: Superimposition of pre- and postsurgical tracing where black tracing represents presurgical and blue represents postsurgical

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For locating reference points along with superimposition of the lateral cephalograms to measure the parameters of 11 subjects, method error was evaluated for intra and interexaminer errors. Dahlberg formula was used in the calculations: N is the number of double registrations, and d is the difference between two registrations of a pair; 0.5 mm of method error was calculated.

Operative technique used

According to the records, the surgical procedure described by Epker^[4] was carried out. Horizontal cuts were made for the osteotomy at the mandibular body at the ascending ramus. Vertical cuts were used for wedge osteotomies. Rigid intermaxillary fixation was used after surgery.

Results

The standard deviation (SD) and mean values were tabulated. The The IBM SPSS (version 23 IBM Corp.,Armonk,NY) Statistics for Windows software was used for statistical analysis. Using G*Power for the t-test estimation was done with 0.508 as the effect size from pooled SD 3.6 at 80% power and 10% level of significance. Mean and SD for continuous data were used to obtain descriptive statistics. To analyze the changes in pre- and postsurgery, paired t-test was performed. The data were shown as mean (SD) with a 95% confidence interval. Differences were considered significant if the probability was <0.05 (i.e., P < 0.05).

From the statistical analysis of the paired t-test [Table 1], the data showed a P = 0.714 which is not a statistically significant value and shows that no significant amount of autorotation has occurred in any direction during BSSO setback procedure and the mean value of presurgical was 85.09 and postsurgical was 85.27 and SD of 1.60.

Table 1: The obtained values of the parameter considered for the study

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Discussion

Wessberg et al.^[7] termed occlusal programming feedback mechanism where autorotation of the mandible is a biological phenomenon which is regulated by the central nervous system. According to a study by Mobarak et al.,^[8] there was a clockwise rotation of the ramal segments after the BSSO setback procedure with no autorotation. Our study showed backward and downward rotation in the mandible by 0.2° which was not statistically significant (P = 0.714). Our study showed increased mandibular rotation in vertical growers similar to Mojdehi et al.,^[9] where there was increased ramal length as well as mandibular rotation in vertical growers. The small sample size and use of lateral cephalograms were the limitations of our study. More samples and advanced diagnostic aids would have provided better justification.

The palpatory method is the common method used for finding the rotation center of the mandible.^[6] A study by Grant^[10] and also by Baragar and Osborn^[11] in the biomechanical literature questioned the representation of the average center of mandibular rotation using the center of the condyle for small movements close to occlusion.

We have used the cephalometric center as described by Ruf et al.,^[12] in his study where Bjork and Skiller's method was used in calculating the amount of mandibular rotation using the superimposition of the tracings. Bailey et al.,^[13] studies showed that there was a backward placement of B point and pogonion and Gonion. Our study also showed similar results which helped in the correction of the skeletal pattern.

According to the study by Jokić et al.,^[14] there was a forward and downward rotation in the mandible which improved the soft-tissue profile. Our study had shown similar results, thereby giving rise to improvement in the lower anterior soft-tissue profile. Schendel et al.^[15] had shown a reduction in lower face height and the maxillary incisor exposure amount postsurgically. Our study also showed that there was an improvement in maxillary incisor exposure resulting in an improved facial profile.

Conclusion

There is no statistically and clinically significant amount of autorotation after the BSSO setback procedure
The mandible showed clockwise rotation by 0.2° which is statistically not significant
The growth pattern does not have an influence on the autorotation of the mandible significantly
Since BSSO setback surgery itself does not cause autorotation, the required amount and direction of autorotation must be planned and incorporated during treatment planning.

Limitations of the study

The sample size is inadequate
Less literature is available hence more studies might be required for further understanding
Long-term observation is needed.

Ethical statement

Ethical approval was obtained from the Ethical Committee of Yenepoya Dental College (YEC-2/518).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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