What factors affect the attachment of the inferior alveolar nerve to the buccal plate following sagittal split osteotomy?

PurposeThis study aimed to assess the factors that can possibly affect the positioning of the inferior alveolar nerve (IAN) in the proximal or distal segment following sagittal split osteotomy (SSO).Materials and methodsThis was a prospective cohort study. The patients were assigned according to the position of the IAN: the IAN was attached to the buccal plate in group 1 (27 SSOs), while it was in the distal segment in group 2 (83 SSOs).ResultsThe mean of the buccolingual thickness of the proximal segment at the vertical cut of the osteotomy (BLTP) was 5.0 ± 0.62 mm in group 1 and 4.16 ± 0.72 mm in group 2. The mean of the distance between the IAN and the external cortical bone at the distal of the second molar before the osteotomy (IANB) was 0.5 ± 0.24 mm in group 1 and 1.24 ± 0.45 mm in group 2. There were significant differences for the mean BLTP and IANB between the two groups (P = 0.001).ConclusionIt seems that the thickness of the buccal plate of the proximal segment, the distance from the IAN to the external cortical bone, the osteotomy technique, and the presence or absence of impacted third molars may be associated with the positioning of the IAN following SSO.     

Age as a factor in the complication rate after removal of unerupted/impacted third molars at the time of mandibular sagittal split osteotomy.

PURPOSE: This study was designed to investigate the effect that the presence of an unerupted third molar has on the mandibular sagittal split osteotomy (SSO). PATIENTS AND METHODS: One operator performed 139 SSOs (70 right side and 69 left side) in 70 patients during a period of 6 months. Data related to gender, age, presence or absence of unerupted third molar teeth, split difficulty during SSO, fracture complications of the segment, neurovascular bundle involvement at surgery, removal of unerupted third molar teeth, and the postoperative recovery of nerve function were recorded. RESULTS: The SSOs evaluated as technically difficult were significantly more prevalent in mandibles with unerupted third molar teeth. All fractures (4) occurred in the younger age group (<20 years) with unerupted third molars present at the time of surgery. Although inferior alveolar nerve recovery was slower in the patients in whom the unerupted third molar teeth were present at the time of surgery due to increased frequency of neurovascular bundle manipulation, the recovery rates at 1 year were equal. CONCLUSIONS: The presence of unerupted third molar teeth increases the degree of difficulty of the SSO. Fracture of proximal and/or distal segments during SSO tend to occur more frequently in the younger age group (<20 years) with an unerupted third molar present.     

The Unfavourable Split: a novel classification and an 11-year retrospective study looking at alternative methods for management of this well-known complication

An unfavourable split is a well-known complication following a sagittal split osteotomy (SSO) of the mandible. Our aim was to analyse all unfavourable mandibular splits that had occurred when carrying out a SSO with the aim to design a classification which can facilitate management. We carried out a retrospective study analysing all orthognathic surgery from January 2010 until April 2021. Data surrounding unfavourable splits during this period were specifically analysed. Orthognathic surgery during this period was performed by a single OMFS unit with osteotomies performed by a single surgeon and their trainee. The dataset included 311 patients who underwent either a bilateral sagittal split osteotomy (BSSO) or a bimaxillary osteotomy. There were 225 bimaxillary osteotomies and 86 BSSOs. Twenty-one patients had unfavourable splits following their BSSO with a total of 22 out of 622 sagittal split osteotomies over this 11-year period. Bilateral unfavourable splits occurred in one patient. These results correlate to an incidence rate of 6.8% of unfavourable splits following SSO's in an 11-year period. The results reveal common patterns of unfavourable splits to suggest a simple classification based on our results. This can be applied to any unfavourable splits in SSO which then allows the clinician to proceed with surgery and prevent abandonment of the procedure. It is classified as follows: Type 1 fractures where the mandibular condyle is attached to the proximal fragment; Type 2 fractures whereby the mandibular condyle is attached to the tooth-bearing segment; Type 3 fractures are lingual cortex fractures. Each of these fracture types has a specific management protocol, which we recommend is used in all unfavourable splits.     

Pre-operative Assessment of Anatomical Position of Inferior Alveolar Nerve and Its Significance in Bilateral Sagittal Split Osteotomy

The aim of this study is to investigate the position and course of the mandibular canal through the ramus, angle and body of mandible using computed tomographic (CT) imaging pre-operatively and to relate these predetermined values intra-operatively to perform sagittal split ramus osteotomies. Pre-operative CT scans were taken and four points were marked at mandibular foramen, mandibular angle, mandibular body and midpoint and different dimensions of IAN were measured to localize the inferior alveolar nerve. With the obtained values, precise osteotomy cuts were made intra-operatively and intra-operative measurements for position of IAN were noted. Based on the preoperative CT measurements, the chance to encounter IAN bundle, during surgery was evaluated. The present study proved that pre-operative CT imaging prior to BSSO surgical procedure is an effective way to investigate the position and course of the IAN canal through the framework of the mandible and by interpolating these dimensions intra operatively, reduces the risk of direct injury to the IAN bundle.     

The spatial location of the mandibular canal in Chinese: a CT study

The inferior alveolar nerve (IAN) is vulnerable to injury from mandible fractures and surgical procedures so anatomical variations of IAN are important. Postoperative sensory alteration of the lip and chin region is high after mandibular orthognathic surgery. The incidence of IAN paresthesia following sagittal split ramus osteotomy (SSRO) ranges from 54% to 86% at 4–8 days, 41 to 75% at 1 month, 33 to 66% at 3 months, 17 to 58% at 6 months and 15 to 33% at 1 year postoperatively. This study determined the anatomical position of the mandibular canal in relation to cortical bone and molar teeth in Chinese using archived CT records. The mandibular canal was the farthest from the buccal cortex at the second molar region (mean 6.79 mm; minimum distance 4.80 mm). The anatomical location of the mandibular canal in local Chinese compares with studies on Asian cadavers. The mandible body was thickest in the region of the second molar (11.9 mm). The vertical buccal cut for SSRO should be in the region of the mandibular second molar where the bone is thickest and the mandibular canal is furthest from the buccal cortex. The safe depth for the vertical buccal cut is 4.8 mm (minimum horizontal distance).     

Do lower third molars increase the risk of complications during mandibular sagittal split osteotomy? Systematic review and meta-analysis

The aim of this systematic review was to investigate whether the presence of third molars (3Ms) during sagittal split osteotomy of the mandible increases the risk of complications. Searches were conducted using MEDLINE via PubMed, LILACS, Cochrane Central, Scopus, DOSS, and SIGLE via OpenGrey up to December 2020. Fifteen articles were included for evaluation and 14 in the meta-analysis, with a total of 3909 patients and 7651 sagittal split osteotomies (670 complications). Inferior alveolar nerve (IAN) exposure in the proximal segment was the most frequent complication (n = 409), followed by bad splits (n = 151). Meta-analysis revealed no significant increase in the incidence of 3M-related IAN exposure (P = 0.45), post-surgical infections (P = 0.15), osteosynthesis material removal (P = 0.37), or bad splits (P = 0.23). The presence of 3Ms was associated with a reduced risk of nerve disorder (P = 0.05) and favoured bad splits in the lingual plate (P = 0.005). The quality of evidence was very low, mainly due to non-randomized study designs, high risk of bias, inconsistency, and imprecision. This systematic review suggests that the removal of 3Ms before sagittal mandibular osteotomy does not reduce the incidence of complications. Thus, we recommend future better-designed studies with rigorous methodologies and adjustments for confounding factors.     

Ultrasonic surgery--an alternative way in orthognathic surgery of the mandible. A pilot study

The aim of this report is to present preliminary results and experiences using an ultrasonic bone-cutting device in bilateral sagittal split osteotomies of the mandible (BSSRO) with particular attention to possible damages to the inferior alveolar nerve (IAN). Seven patients with class II or class III malocclusion were treated by BSSRO with a conventional combined orthognathic and surgical approach. The osteotomy was carried out using an ultrasonic bone-cutting device. Subjective neurosensory deficits of the inferior alveolar nerve were assessed on 14 sides. Compared to the conventional techniques using saws, chisels and burs, the use of the ultrasonic device was more time-consuming, but the osteotomies were carried out at a high level of precision. In addition, this procedure offered the advantage of a blood-free surgical field and thus provided good control of the surgical procedure. Subjective neurosensory disturbances of the IAN showed a continuous decrease from 57.1% (eight sides) 2 months after the surgical procedure to 14.3% (2 sides) after 5 months and to 7.1% 7 months after BSSRO. Within the seven patients of this pilot study associated neurosensory disturbances were low. A possible advantage in terms of nerve protection is subject to a prospective study.     

Use of an 'osteocompressor' to avoid damage to the inferior alveolar nerve in the mandibular setback procedure: can the positive effects of osteodistraction be used in reverse? An experimental study in dogs

We have designed an osteocompressor to try and avoid damage to the inferior alveolar nerve during sagittal split setback osteotomy of the mandibular ramus, and tested it on the mandibles of 10 dogs. The osteocompressor bears a superficial resemblance to an osteodistractor, but has a different internal structure that allows it to compress rather than distract. We were able to compress the neurovascular canal, the neurovascular bundle, the cancellous bone, and the mandible in dogs at a rate of 1 mm/day by rotating the screw of the compressor 1.5 times. We conclude that in dogs the neurovascular canal and neurovascular bundle can be compressed with this device without loss of sensation. We believe that this is the first publication on nerve canal compression and osteocompression.     

Risk factors and prevention of bad splits during sagittal split osteotomy

Purpose

One of the operative complications of the sagittal split osteotomy of the mandible is a bad split, which describes an unfavorable or irregular fracture of the mandible in the course of the osteotomy. The purpose of this study is to identify previous studies which reported incidences of bad split occurrence during sagittal split osteotomy and to discuss its mechanisms and risk factors, based on a literature review, in order to minimize their occurrence. A few illustrative cases are also presented.

Methods

An electronic search was undertaken in January 2011. The titles and abstracts from these results (n?=?363) were read for identifying studies which reported incidences of bad split occurrence during sagittal split osteotomy procedures.

Results

Twenty-one studies were identified and assessed. The incidence of bad splits from these studies varied between 0.21% and 22.72%. The buccal plate of the proximal segment and the posterior aspect of the distal segment were the most affected areas.

Discussion

The surgical patient should be evaluated according to age and the presence of unerupted/impacted third molars. Prevention is focused on adequate osteotomy design, eliminating sharp angle where abnormal stress occurs on bony segments, completion of adequate cuts into the retrolingular depression and through the inferior border, and careful separation of the segments. The SSO is an extremely technical and sensitive procedure, and careful attention will probably prevent most unfavorable splits. If a fracture occurs, the fractured segments should be incorporated into the fixation scheme if possible. The occurrence of bad splits cannot always be avoided. When adequately treated the chances of functional success are good.     

Reverse sagittal split of the mandibular ramus for an unusual deformity

A reverse sagittal split osteotomy of the mandible for advancement or retraction of the mandible is described to be used in selected instances when the transoral modified sagittal ramus osteotomy would probably result in a pathologic fracture or an inadequate proximal segment. This procedure provides the same benefits as does the modified sagittal split osteotomy. A disadvantage of the procedure is that it requires both intraoral and extraoral incisions.     

Cortical thickness in human mandibles: clinical relevance to the sagittal split ramus osteotomy.

Human cadaver hemimandibles were subjected to sagittal split ramus osteotomy, and the cortical thickness of each mandible was then measured in several areas. A measurable difference in morphology was found in the proximal segment of the mandible. Because cortical bone thickness is directly related to bone-screw holding strength, these results have important implications for the use of rigid internal fixation. The results suggested that the areas that coincide with the most anterior and superior extent of the osteotomy would be the ideal locations for screw placement.     

下颌前突患者下颌支部下颌管的定位和走行

目的：应用CT观测下颌前突患者下颌管的定位和走行,以给临床医师提供有意义的信息,减少对下牙槽神经的损伤。方法：38例实施下颌支矢状劈开术的骨性Ⅲ类下颌前突患者,术前进行颌骨CT扫描。以下颌管最先形成的平面作为0平面,向下每5mm作为一个测量平面,测量下颌管内径、下颌骨的厚度、颊舌侧骨皮质的厚度和下颌管外侧壁到颊舌侧骨皮质之间的距离。测量结果采用SPSS13.0软件包进行统计学分析。结果：从下颌小舌到下颌骨下缘,下颌骨厚度增加,颊舌侧骨皮质也逐渐增厚,下颌管内径变化不大。舌侧骨髓腔的宽度是从无到有的逐渐递增趋势,而在每一层测量值中,颊侧骨髓腔的宽度均大于舌侧。根据下颌管在下颌骨内的位置分类,绝大多数为分开类型（n=391）,占总测量平面456的85.75%,接触和融合型分别占12.71%和1.54%。各测量值左右两侧无显著性差异,下颌管内径（ID）值和下颌管外侧壁到颊骨皮质的距离（BP）值的性别差异有显著性（P〈0.01;P〈0.001）。结论：下颌管形成后,渐渐远离舌侧而向颊侧靠近,然后又渐远离,但其总体走行还是靠近舌侧。对颊侧骨髓腔缺失的病例,尤其是融合型患者,建议选用其他术式,以免造成下牙槽神经损伤。     

Modification of the bilateral sagittal split osteotomy (BSSO) in a study using pig mandibles

In a bilateral sagittal split osteotomy (BSSO) mechanical irritation of the inferior alveolar nerve (IAN) (e.g. by chiselling) should be avoided to prevent neural damage. A modification of the Obwegeser-Dal Pont operation technique was studied by splitting 100 pig mandibles ex vivo. An additional osteotomy at the caudal border of the mandible was used to facilitate the sagittal split by means of a locus of minor resistance. The chisel was inserted distal to the second molar and far away from the IAN. The mandible was split by torque. The modified technique reduced the required torque to split the mandible about 30% compared with the original technique (paired t-test, t(69) = −12.89; p < 0.05). 75% of all mandibles split by the modified technique were classified as bad splits compared with 100% using the original technique using the same protocol without the additional osteotomy.     

Modified sagittal split ramus osteotomy with a reciprocating saw and new retractors

Modified sagittal split ramus osteotomy with new instruments and a reciprocating saw is reported. With this modification, the sagittal separation of the ramus is performed by the reciprocating saw with an original wide-blade buccal retractor and a new lingual retractor, instead of the traditional channeled retractor. The wide-blade retractor is inserted to the buccal aspect of the mandibular ramus, which ensures protection from instrumental injury to the adjacent soft tissues and vessels, and the new lingual retractor, instead of the channeled retractor, is inserted to the lingual aspect of the ramus. The osteotomy line follows that of Dal Pont's modification. Close attention must be paid to the direction of the saw blade. The separated bone plane should be located in the external cortical bone layer of the ramus, so as to avoid injury of the inferior alveolar neurovascular bundle. The osteotomy is completed with the smooth osteotomized interface, which facilitates positioning of the bone segments by the surgeon. The new instruments and the reciprocating saw may provide safe and rapid sagittal split ramus osteotomy.     

Inferior alveolar nerve transposition with involvement of the mental foramen for implant placement

Inferior Alveolar Nerve (IAN) transposition is an option for prosthetic rehabilitation in cases of moderate or even severe bone reabsorption for patients that do not tolerate removable dentures. The aim of the present report is to describe an inferior alveolar nerve transposition with involvement of the mental foramen for implant placement. The surgical procedure was performed under local anesthesia, by the inferior alveolar, lingual and buccal nerve blocking technique. Centripetal osteotomy was performed, and bone tissue was removed, leaving the nerve tissue free in the foramen area. After that, transsection of the incisor nerve was performed, and lateral osteotomy was started from the buccal direction, toward the trajectory of the IAN. The procedure was concluded, by making use of a delicate resin spatula to manipulate the vascular-nervous bundle. The drilling sequence for placing the dental implants was performed, and autogenous bone was harvested using a bone collector attached to the surgical suction appliance. After the implants were placed, the bone tissue previously collected during the osteotomies and drilling processes was placed in order to protect the IAN from contact with the implants. The surgical protocol for inferior alveolar nerve transposition, followed by implant placement presented excellent results, with complete recovery of the sensitivity, seven months after the surgical procedure.     

Control of the condylar-proximal mandibular segments after sagittal split osteotomies to advance the mandible

Maintenance of the normal or presurgical anatomic position of the mandibular condyles and contiguous proximal mandibular ramus segments after sagittal split ramus osteotomies is important, not only to enhance the stability of results but also to avoid iatrogenic temporomandibular joint complications. Accordingly, during the past few years, we have attempted to improve the surgical control of condyle and proximal segment position while using the sagittal split ramus osteotomy to advance the mandible. After several modifications, the device reported herein was used and the results evaluated in ten consecutive patients who underwent bilateral sagittal split ramus osteotomies with symmetric advancement of the mandible. This device enables the surgeon to obtain very precise reproduction of the "normal" proximal segment and condyle position at the time of surgery. The use of the device and documentation of its efficiency are presented.     

Radiographic stereophotogrammetric evaluation of intersegmental stability after mandibular sagittal split osteotomy and rigid fixation

PURPOSE: The purpose of this study was to determine if rigid fixation with bicortical screws and/or miniplates with monocortical screws prevent mobility at the osteotomy site after bilateral mandibular sagittal split osteotomy. PATIENTS AND METHODS: Three metal bone markers were inserted in the proximal and the distal segments of the mandible during the sagittal split operation in 10 patients. These served as measurement points in postoperative follow-up by radiographic stereophotogrammetry. The patients were examined at intervals during the first postoperative year. At each examination, 2 sets of radiographic stereograms were obtained: 1 in rest position and 1 with stress applied to the osteotomy sites. The difference in the position of the proximal segment in relation to the distal segment between the 2 sets of stereograms was recorded. Findings greater than 0.4 degrees and 0.2 mm change indicated true displacement of the bone segments. RESULTS: Immediately after surgery, mobility at of the osteotomy site(s) was found in 8 of 10 patients, and after 1 year it was still present in 4 patients. CONCLUSIONS: Fixation with bicortical screws or miniplates and monocortical screws does not prevent mobility at the osteotomy site after sagittal split osteotomies. This mobility may remain as long as 1 year after surgery. The term "rigid fixation" is thus not a proper term for this kind of fixation.     

Histological evaluation of inferior alveolar nerve injury after osteotomy of mandibular buccal cortex using piezoelectric versus conventional rotary devices: a split-mouth randomised study in rabbits

Up until now, only a limited number of evidence-based studies with different results has evaluated traumatic nerve injury after maxillofacial surgery using piezoelectric devices versus rotary instruments. The present experiment was performed to evaluate damage to the inferior alveolar nerve (IAN), histologically, after osteotomy of the buccal cortex of the mandible using piezoelectric devices versus surgical handpieces. Forty rabbits underwent bilateral osteotomy of the mandibular buccal cortex. For the osteotomy of one side, piezoelectric devices were used, and for the other, conventional rotary handpieces. After cleavage of the osteotomised cortical bone segments, the exposed part of the IAN was excised and examined histologically for nerve injury. IAN damage was scored histologically from Grade 0 (no nerve damage) to Grade 4 (complete nerve transection). It was found that 25% and 17.5% of nerves had Grade 0; 17.5% and 10% had Grade 1; 25% and 20% had Grade 2; 17.5% and 27.5% had Grade 3; and 15% and 25% had Grade 4 injury in piezosurgery and rotary groups, respectively. Statistical analyses revealed no significant difference between groups in damage to the IAN. The present study showed that piezosurgery devices, similar to conventional rotary instruments, have the potential to cause severe nerve damage during surgery and should therefore be used with care.     

Risk factors of nerve injury during mandibular sagittal split osteotomy

There is little objective data about whether surgical technique or mandibular anatomy are a risk for inferior alveolar nerve (IAN) injury during bilateral sagittal split osteotomy (BSSO). Orthodromic sensory nerve action potentials (SNAPs) of the IAN were continuously recorded on both sides in 20 patients with mandibular retrognathia during BSSO operation. Changes in latency, amplitude, and sensory nerve conduction velocity (SNCV) at baseline and at different stages of the operation were analyzed. The SNAP latencies prolonged, the amplitudes diminished, and the SNCVs slowed down during BSSO (P = 0.0000 for all parameters). The most obvious changes occurred during surgical procedures on the medial side of the mandibular ramus. There was a clear tendency towards more disturbed IAN conduction with longer duration of these procedures (right side R = -0.529. P = 0.02; left side R = -0.605, P = 0.006). Exposure or manipulation of the IAN usually had no effect on nerve function, but the IAN conduction tended to be more disturbed in cases with nerve laceration. Low corpus height (R = 0.802, P = 0.001) and the location of the mandibular canal near the inferior border of the mandible (R = 0.52, P = 0.02) may increase the risk of IAN injury. There was no correlation between the age of the patients and the electrophysiological grade of nerve damage.     

口内路径下颌骨升枝矢状劈开截骨术治疗下颌前突畸形

下颌骨升枝矢状劈开术是目前世界上使用最普遍的矫正下颌骨畸形的手术方法之一。作者采用口内入路下颌骨畸形的手术方法之一。作者采用口内入路下颌骨升枝矢状劈开截骨术治疗下颌骨前突１８２例，其中真性下颌前突１４３例，假性下颌前突３９例。年龄在１５～５８岁之间，平均２４岁。随访６个月～９年。除９例术后畸形复发需再次矫正以外均获满意效果。本文介绍了口内入路下颌骨升枝矢状截骨术的手术过程及注意事项，并着重讨论了其优缺点，可能出现的并发症及处理方法