Is inferior border osteotomy beneficial in bilateral sagittal split osteotomy? A retrospective clinical study

doi:10.21203/rs.3.rs-4298672/v1

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Is inferior border osteotomy beneficial in bilateral sagittal split osteotomy? A retrospective clinical study

https://doi.org/10.21203/rs.3.rs-4298672/v1

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Background

To investigate the effect of lower border osteotomy on the lingual split pattern and inferior alveolar nerve (IAN) in bilateral sagittal split osteotomy (BSSO).

Materials and Methods

The study comprised 32 patients (64 operated sides) who underwent BSSO due to dentofacial abnormalities. In the mandible, 32 sides (the conventional group) received standard BSSO surgery, while 32 sides (the modified group) additionally received lower border osteotomy. The split difficulty of the mandible, the lingual split pattern, and the recovery status of the IAN were evaluated.

Results

Mandibular split difficulty showed a statistically significant difference favoring the modified group (p = 0.032). The mean numbness level of the modified group following surgery was lower than that of the conventional group (p = 0.019). Although there was no statistically significant difference between the two groups regarding lingual fracture pattern, the rate of type 1 fracture was higher in the modified group (p = 0.089).

Conclusion

The additional lower border osteotomy makes the split procedure easier. The modification resulted in an increased incidence of type 1 lingual fracture pattern. The neurosensory recovery capacity of the IAN in the postoperative period is higher in modified group.

Sagittal split

inferior border osteotomy

split pattern

Bilateral sagittal split osteotomy (BSSO) is one of the most commonly used techniques in orthognathic surgery for the correction of mandibular skeletal abnormalities (1). Trauner and Obwegeser first proposed the original approach about 70 years ago, which Dal Pont, Hunsuck, Epker, Wolford and David later modified (2–7). These modifications have increased the stability and predictability of postoperative outcomes while reducing the frequency of intraoperative and postoperative complications. They have also reduced the frequency of intraoperative and postoperative complications and improved the stability and predictability of postoperative outcomes. Despite these developments, BSSO demands technical accuracy, and complications still occur (1, 8, 9). Injuries to the inferior alveolar nerve (IAN) constitute one of the most common and widely documented complications of BSSO. Permanent nerve damage in the IAN can occur in approximately 5–10% of patients after BSSO surgery (9–11). Due to the IAN injury, permanent anesthesia, hyperesthesia, or allodynia could appear in the lower lip and chin area after the surgery. These neurosensory disturbances may be caused by due to incorrect osteotomy procedures, severe nerve manipulation, wrong fixation screw placement, massive mandibular advancements, nerve compression by bone spiculae, or bad splits. Although this complication usually resolves within a year, permanent nerve damage may be seen in some cases. Since the BSSO is an elective approach, great caution should be taken to reduce the possibility of complications (1, 12, 13).

Another complication that might arise during BSSO surgery is a bad split, which is referred to as the unfavorable and unpredictable form of mandibular osteotomy fracture. The incidence of bad splits ranges from 2–14.6% per split site (14). Due to the inability to visually check the lingual split pattern during the segmental separation stage of BSSO procedures, IAN injury may occur during the postoperative period (8, 13). Inadequate osteotomies frequently lead to the bad split. Additionally, a bad split may also develop after a superficial osteotomy to protect the IAN during surgery (15). In the postoperative phase, a bad split may cause bone integrity to be impaired, which could then result in infection and bone sequestration (14). Therefore, to reduce potential problems, the technical details and reliability of each modification of BSSO should be reviewed (12).

According to some authors, the extended duration of the split stage may increase the risk of IAN injury, and lower border osteotomy has been beneficial in preventing this problem in BSSO procedures. The lower border osteotomy is believed to weaken the lower region of the jaw, resulting in a more controlled split with less force. In this way, it is predicted that the risk of bad splits and IAN damage will decrease (15).

In the literature, there are a limited number of ex vivo and in vivo studies examining the advantages and disadvantages of lower border osteotomies (9, 15, 16). The first hypothesis for the study was that patients who underwent lower border osteotomy of the mandible would be more prone to type 1 fracture patterns after splitting. The second prediction was that, in the postoperative period following a lower border osteotomy, there would be less numbness in the lower lip and jaw regions. Finally, we postulated that the mandible would be more easily separated in patients who underwent lower border osteotomies. The study aimed to investigate the effect of lower border osteotomy on the lingual split pattern and IAN in BSSO procedures.

Study Design

The study was designed and conducted retrospectively. The procedures were performed between April 2021 and April 2022 at Erciyes University Faculty of Dentistry, Oral, Dental and Maxillofacial Surgery Hospital in Kayseri, Turkey. The study comprised patients who underwent orthognathic surgery (BSSO surgery with Le Fort 1 osteotomy or BSSO surgery alone) for the treatment of jaw and facial deformities. Informed consent forms were approved and signed by each patient. The study involved patients who have had their wisdom teeth removed at least six months before surgery, who have normal preoperative IAN function, and who have complete radiographic and clinical records. Patients who underwent simultaneous genioplasty surgery with BSSO, who have cleft palate-lip or craniofacial syndromes, and who have a history of maxillofacial trauma or undergone any operation in the maxillofacial region were excluded from the study. The study was approved by the Erciyes University Faculty of Medicine Clinical Research Ethics Committee (decision no. 2022/794).

Study variables

The primary predictor variable was the absence or presence of the mandibular lower border osteotomy in BSSO surgery. The primary outcome variable was determined as the lingual fracture pattern of the mandible in BSSO surgery. The secondary outcome variable was designed as neurosensory recovery of the IAN one year after the BSSO surgery. The tertiary outcome variable was defined as the split difficulty of the mandible at the split stage in BSSO surgery.

Surgical technique

The Hunsuck-Epker approach of the conventional Obwegeser/Dal Pont process was used for all BSSO operations. In addition to this surgical procedure, a mandibular lower border osteotomy was performed in some patients. Patients who operated solely using the traditional BSSO procedure were included in the conventional group. On the other hand, patients in the modified group also had lower border osteotomy in addition to the standard BSSO procedure. All operations were performed under general anesthesia with nasotracheal intubation. 4 mL of local anesthetic (Ultracain Ds Fort 2 mL ampoule) was infiltrated into the surgery area for local anesthesia. After the Ellis incision in the mandible, the mucoperiosteal flap was lifted and the bony areas of the mandible planned to be cut were exposed. Piezosurgery was used for all osteotomy procedures (Mectron Medical Technology, Carasco, Genova, Italy). Lingual osteotomy was performed horizontally along the cortical bone just above and behind the mandibular foramen. Buccal vertical osteotomy was performed in the cortical bone area between the first and second molar. Both osteotomies were combined with a third osteotomy along the oblique line. The patients in the modified group underwent mandibular lower border osteotomy following standard BSSO procedure. The tip of the piezosurgery was gently positioned towards the lower border of the mandible to divide the mandible into buccal and lingual. An osteotomy of approximately 10 mm in length was performed in the bone without advancing the tip of the instrument too far toward the lingual region with the help of a piezosurgery (Fig. 1). The osteotomy was then completed using a chisel, mallet, and Smith’s spreader. After the mandibular split process, the IAN was carefully released and transferred to the distal segment if it remained tethered in the proximal segment. Bilateral condyle locations were confirmed at the end of the osteotomy, and two 4-hole flat mini plates were used to fix the proximal and distal segments. Incision sites were sutured with absorbable 3 − 0 Vicryl and the procedure was completed.

The same surgeon performed all operations, and surgical epicrises were routinely documented. Patients were called for regular post-discharge follow-up appointments for routine clinical and radiographic examinations. The clinical and radiological examination findings of the patients were recorded in the physician observation file.

Collected data

The cone beam computed tomography (CBCT) images were taken one day after orthognathic surgery. The lingual split scale (LSS) introduced by Plooij et al. was used to assess the lingual fracture pattern in the study (8). An independent investigator determined the lingual fracture pattern of all patients according to the LSS by analyzing these CBCT images. According to the classification, a Type 1 fracture (LSS1) is defined as a vertical fracture line extending to the lower border of the mandible. The line of type 2 fracture (LSS2) reaches the boundary of the posterior ramus horizontally. Fractures extending from the inferior alveolar canal to the lower border of the mandible represent type 3 fractures (LSS3). Other unfavorable fracture patterns are referred to as type 4 fracture (LSS4) (Fig. 2).

A scale of 1 to 3 was used to determine how difficult it was to separate the mandible during the mandibular split stage; the data were recorded as follows: 1 for easy, 2 for moderate difficulty, and 3 for extremely difficult. These numerical values between 1 and 3, which the surgeon noted in the operative epicrisis about the difficulty of splitting the mandible immediately after the surgery, were obtained from the surgical epicrises.

The neurosensory recovery status of the IAN was evaluated in follow-up visits with the patients one year after the surgery. The neurosensory recovery status of the IAN was evaluated at the patient follow-up visits one year after the operation. For this purpose, patients were asked to evaluate the degree of numbness in the lower lip or mental region by comparing the contralateral side. The degree of numbness was measured using a visual analog scale (VAS), with 0 representing no numbness and 100 representing total numbness. The data regarding the VAS values of the patients were obtained from the physician observation file. Additionally, data regarding the position of the IAN (proximal or distal segment) after the mandibular split procedure was obtained from the surgical epicrisis.

Statical analyses

Data were analyzed using the SPSS 22.0 package program (SPSS 22, IBM Corp., Armonk, New York, USA). Descriptive statistical data are given as numbers (and), percentages (%), means (x̄), and standard deviations (SD). The conformity of the data to a normal distribution was evaluated by the Shapiro-Wilk test. The Pearson Chi-Square Test was used to compare categorical data, and the odds ratio value was used to calculate the risk. The comparison of dependent paired groups that follow the normal distribution was performed using a dependent sample t-test.

The study comprised 32 patients in total, 14 female and 18 male. For these 32 patients, a total of 64 bilateral (right and left side) BSSO operations were performed. Of these 64 sides, 32 had conventional BSSO surgery alone, and the remaining 32 had lower border osteotomies in addition to conventional BSSO surgery. The mean age of the patients was 22.62 ± 4.61 years, and the age range was between 18 and 37 years. The patients ranged in age from 18 to 37 years old, with a mean age of 22.62 ± 4.61 years. Three patients underwent BSSO alone, and 29 patients underwent BSSO and a Le Fort 1 osteotomy at the same time.

Patients in the conventional and modified groups were compared for mandibular split difficulty, and a statistically significant difference was observed (p = 0.032). Mandibular splitting was determined to be easy on 3 (9.4%) sides, moderately difficult on 26 (81.3%) sides, and extremely difficult on 3 (9.4%) sides in the conventional group. The mandibular split procedure was performed with moderate difficulty on 12 (37.5%) sides and easily on 20 (62.5%) sides in the modified group. The modified group was determined to be 85% simpler to split when the mandibular split difficulty levels were compared with the conventional group (Table 1).

Table 1

Comparison of split difficulty percentages of the groups (n = 32)
	Combined group		Conventional group		x²	p	OR [%95CI]
	n	%	n	%	x²	p	OR [%95CI]
Split difficulty Easy Moderate difficult Extremely difficult	20 12 -	62.5 37.5 -	3 26 3	9.4 81.3 9.4	6.892	0.032	0.850 [0.707–1.022]

In the conventional group, it was found that IAN remained in the proximal segment on 12 (37.5%) sides and in the distal segment on 20 (62.5%) sides following the mandibular split process in BSSO surgery. In the modified group, IAN remained in the proximal segment on 3 (9.4%) sides and in the distal segment on 29 (90.6%) sides. Following the mandibular split process, there was no statistically significant difference in nerve position between the modified group and the conventional group (p = 0.069) (Table 2). One year following surgery, the mean numbness levels for patients in the modified group and the conventional group were 5.93 ± 12.60% and 11.56 ± 18.46%, respectively. The mean numbness level of the modified group one year after surgery was statistically significantly lower than that of the conventional group (p = 0.019) (Table 3).

Table 2

Comparison of the percentages of nerve positions of the groups (n = 32)
	Modified group		Conventional group		x²	p
	n	%	n	%	x²	p
Nerve position Proximal Distal	3 29	9.4 90.6	12 20	37.5 62.5	3.517	0.069

Table 3

Comparison of the mean numbness levels of the groups one year after the surgery (n = 32)
	Modified Group	Conventional Group	TEST
	x̄±SD	x̄±SD	TEST
Level of numbness	5.93 ± 12.60	11.56 ± 18.46	t: -3.885 p = 0.019
t: Dependent Sample t-Test

In the conventional group after BSSO surgery, the lingual split pattern was seen as type 1 fracture on 22 sides (68.8%), type 2 fracture on four sides (12.5%), and type 3 fracture on six sides (18.8%). The lingual fracture pattern in the modified group was type 1 on 28 sides (87.5%), type 2 on one side (3.1%), and type 3 on three sides (9.4%). Type 4 fracture formation was not observed in any group. There was no statistically significant difference between the conventional group and modified group patients regarding lingual fracture pattern (p = 0.089) (Table 4).

Table 4

Comparison of lingual split pattern percentages of the groups (n = 32)
	Modified Group		Conventional Group		x²	p
	n	%	n	%	x²	p
Lingual split pattern Type 1 Type 2 Type 3 Type 4	28 1 3 -	87.5 3.1 9.4 -	22 4 6 -	68.8 12.5 18.8 -	1.429	0.089

In the study, we evaluated the effects of inferior border osteotomy on the lingual split pattern and the recovery status of the IAN in addition to the conventional BSSO procedure. The result of the study revealed that the lingual fracture pattern in the modified group was realized as type 1 at a high rate, although not statistically significant. It was observed that the mandibular split procedure was easier for the additional osteotomy group. One year following surgery, the additional osteotomy group patients experienced less numbness in the lower lip and jaw area.

The BSSO procedure, which is regrarded as one of the most established technique of orthognathic surgery, has been used for many years for the correction of skeletal deformities in the lower jaw. Several modifications have been made to the original approach since it was published in the literature to reduce the risk of perioperative complications, avoid recurrence, hasten bone healing, and better control the split procedure (9, 15). The inferior border osteotomy, which Wolford et al. first reported in the literature, is one of these modifications. The inferior border osteotomy, according to the authors, allowed for a more controlled and predictable mandibular split (6). Böckmann et al. investigated the benefits of a lower border osteotomy in addition to the Obwegeser Dal Pont technique in a study designed on the pig mandible. The fracture line following the mandibular split was nearly optimal on the additional osteotomy sides, according to the authors, who also noted that a lesser amount of force was required during the split on these sides. The researchers concluded that lower border osteotomies reduced the risk of bad splits and IAN injuries (16). Böckmann et al. used human mandibles in another study designed in vitro and as a split mouth. The researchers performed BSSO surgery on one side of the lower jaw with the traditional Obwegeser-Dal Pont technique and on the opposite side with the lower border osteotomy in addition to the traditional Obwegeser-Dal Pont technique. The authors noted that less force should be applied for mandibular splitting on the side with a lower border osteotomy. They emphasized that there would be less damage to the IAN since the mandibular fracture line was more predictable on the side of the lower border osteotomy (15). In line with previous studies, the mandibular splitting process was easier in the lower border osteotomy group compared to the conventional group. This may be due to the additional osteotomy of the lower border of the mandible, which weakens this area. Moreover, the additional osteotomy line may have acted as a guide for the mandibular split procedure, reducing the difficulty of the split.

Schoen et al. designed an experimental study to investigate the efficacy of mandibular caudal border osteotomy in addition to the Obwegeser-Dal Pont technique. The researchers performed the original Obwegeser-Dal Pont technique and its modification to the pig mandible to evaluate the split difficulty and split pattern of the mandible. The results of their study revealed that the modified approach used in the split stage of BSSO resulted in 30% less force being applied to the jaws than the original technique. Furthermore, it was determined that when the original technique was used, the mandible was separated 100% in the direction of the mandibular canal, while when the modified technique was used, the mandible was separated 25% in the direction of the mandibular canal and 75% in the direction of the lower caudal border. The authors concluded that they expected a better neuro-sensitive result with the modified Obwegeser-Dal Pont technique due to a split pattern away from the IAN (13). When the split difficulty of the modified technique group and the conventional technique group were compared in this study, it was found that the modified technique group's split procedure was 85% easier. The results of present study are similar to those of Schoen et al. in this regard (13). Additionally, in our study, the mean level of numbness in the modified group one year after the surgery was lower than the mean level of the other group. Although not statistically significant, it was noted that upon mandibular split, IAN in the conventional group remained in the proximal segment at a greater rate and consequently transferred to the distal segment at a higher rate. In BSSO surgery, even if the release of the split nerve from the proximal segment and transfer to the distal segment is performed carefully and gently, the nerve may be damaged (17). This may explain the higher mean level of numbness in the conventional group compared to the modified group.

In a study by Möhlhenrich et al., BSSO surgery was performed on the mandibles of fresh human cadavers using the standard Hunsuck/Epker method or with an additional lower border osteotomy. The investigators compared the lingual fracture patterns of the lower jaw and the duration of surgery between the groups. The modified lower border osteotomy, according to the authors, increased the probability of an unfavorable split, prolonged the total time of the procedure, and did not allow for a controlled split (18). In present study, there was no increase in the incidence of bad splits on the sides that underwent lower border osteotomy, contrary to the findings of Möhlhenrich et al. (18). Al-Dawoody et al. conducted a randomized controlled clinical trial to evaluate the effects of adding a fourth osteotomy to the lower border of the mandible in standard BSSO surgery (Obwegeser/Dal Pont) on the lingual cortical fracture pattern. The researchers conducted the study as a split-mouth design on a total of 20 patients and radiographically examined the lingual fracture pattern after surgery. In the research, the distribution of type 1, type 2, type 3, and type 4 fracture types in terms of lingual fracture pattern was determined as 6 (15%), 8 (20%), 13 (32.5%), and 3 (7.5%), respectively. The distribution of type 1, type 2, type 3, and type 4 fracture types in the regions where an additional fourth osteotomy was performed on the mandibular border after BSSO was 10 (25%), 6 (15%), 4 (10%), and 0 (0%), respectively. The authors noted that lower border osteotomy tends to direct the lingual fracture line towards the inferior and posterior margins of the mandible and minimizes the risk of bad splits (9). The conventional BSSO group in this study had the greatest percentage of type 1 fractures (68.8%), followed by type 3 fractures (18.8%) and type 2 fractures (12.5%) in term of lingual fracture pattern. The lower jaw was split as type 1 (87.5%) at a higher rate, type 2 (3.1%) at a lower rate, and type 3 (9.4%) at a lower rate in the modified group. Although there was no statistically significant difference between the two groups, it was determined that the additional osteotomy group had more type 1 fracture patern in the lower jaw than the other group. Moreover, one reason for the lower mean level of numbness in the modified group one year after surgery may be the higher incidence of type 1 and type 2 fractures compared to the other group. This could result from the fracture line being further from the IAN border, which lowers the possibility of nerve injury. In this respect, the results of our study are consistent with the literature (9, 15).

This study has some limitations. Firstly, the surgeon's subjective scoring was used to determine the difficulty of the mandibular split. To rule this out, all BSSO operations and split difficulty scoring were performed by the same surgeon. Second, the degree of numbness experienced by the patients throughout the recovery phase was assessed using a subjective method. Nonetheless, studies in the literature have compared subjective assessment methods with objective assessment methods and found a positive correlation between them (19, 20). Within the scope of this study, we believed that a subjective assessment of the patients would be sufficient.

The lower border osteotomy performed in addition to the conventional BSSO surgery allows the split procedure easier. This modification resulted in an increased incidence of type 1 lingual fracture pattern in the mandible. Additionally, the IAN tended to remain in the distal segment after splitting with the lower border osteotomy. The neurosensory recovery capacity of the IAN in the postoperative period is higher in areas where lower-border osteotomies are performed. Further large-scale randomized controlled split-mouth clinical trials are required to confirm the study's results.

IAN Inferior alveolar nerve

BSSO Bilateral sagittal split osteotomy

CBCT Cone beam computed tomography

LSS Lingual split scale

Ethics approval and consent to participate

The study was approved by the Erciyes University Faculty of Medicine Clinical Research Ethics Committee (decision no. 2022/794). All methods in the study were performed in accordance with the ethical guidelines outlined in the 1964 Helsinki Declaration. Informed consent forms were approved and signed by each patient.

Consent for publication

Not applicable.

Availability of data and materials

All data are available from the corresponding author upon reasonable request.

Competing interests

The authors declare that they have no competing interests

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions

Demirbas AE and Bilge S conceived and planned the experiments. Topan C and Bilge S carried out the experiments. Demirbas AE contributed to the interpretation of the results. Topan C took the lead in writing the manuscript. All authors provided critical feedback and helped shape the research, analysis, and manuscript.

Acknowledgements

Not applicable.

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No competing interests reported.

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Is inferior border osteotomy beneficial in bilateral sagittal split osteotomy? A retrospective clinical study

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Abstract

Background

Materials and Methods

Results

Conclusion

Figures

Introduction

Materials and Methods

Study Design

Study variables

Surgical technique

Collected data

Statical analyses

Results

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

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