Positions of the Mandibular Foramen and Canal in Different Skeletal Classes and Implications for Bilateral Sagittal Split Osteotomy

Kokuryo S., Habu M., Kita R., Katsuki T., Tominaga K., Yoshioka I.

According to the literature, ultrasonic surgery reduces the incidence of neurosensory disturbance (NSD) of the inferior alveolar nerve (IFAN) after bilateral sagittal split osteotomy (BSSO). The purpose of this study was to evaluate the effects of ultrasonic surgery and the anatomic position of the IFAN canal on NSD after BSSO.This retrospective cohort study included skeletal mandibular prognathism cases operated on with an ultrasonic bone scalpel or a reciprocating saw. The primary predictor variable was osteotomy technique (ultrasonic or conventional surgery). The primary outcome variable was NSD. Other variables included age, gender, operator, degree of setback, surgical duration, blood loss, and IFAN position. Comparisons of 2 variables were performed by use of the Student t test or Fisher exact test. A regression model was used to examine the relationship between the presence or absence of NSD and other variables. The level of significance was set at P < .05 for all statistical tests.The ultrasonic group was composed of 35 patients, whereas the conventional group was composed of 32. Three months after surgery, NSD was observed on 16 of 70 sides (22.9%) in the ultrasonic group and 28 of 64 sides (43.8%) in the conventional group; this difference was significant. Furthermore, recovery from NSD at 3 months after BSSO was significantly more common in the ultrasonic group than in the conventional group. In the ultrasonic group, even when the distance from the buccal aspect of the IFAN canal to the outer buccal cortical margin was shorter, NSD of the IFAN was less frequent.Ultrasonic surgery may be an effective technique to reduce the incidence of NSD after BSSO, and it contributed to recovery from NSD. The use of an ultrasonic device for BSSO is recommended when the distance from the buccal aspect of the IFAN canal to the outer buccal cortical margin is shorter on computed tomography.

Promma L., Sakulsak N., Putiwat P., Amarttayakong P., Iamsaard S., Trakulsuk H., Hirunyakorn K., Suarbua S., Wattanaraeungchai Y.

Preoperative delineation of the mandibular canal and surrounding cortical bone thickness is mandatory prior to bilateral sagittal split osteotomy (BSSO). The cortical bone thickness of 101 cadaveric mandibles was measured to define the mandibular canal. The mandibles were cut at the anterior ramus, at the third, second, and first molar, and at the premolar. The cortical bone thickness was measured between the mandibular canal and inferior border, buccal cortex, and lingual cortex at each cutting point. No difference was found between the right and left sides of the mandible, or between males and females, with one exception: males were found to have thicker inferior cortical bone at the premolar site than females. The implications for BSSO are: (1) for sagittal bone cutting, the maximum cutting depth of the buccal cortex at the ramus is 4.5mm, at the second and third molars is 6.5mm, and at the first molar is 5mm; (2) for vertical bone cutting at the first molar, the maximum cutting depth from the inferior border is 7.5mm. The measurement of cortical bone thickness from cadaveric mandibles provides useful preoperative information and confirms the results of computed tomography.

Freire-Maia B., Machado V.D., Valerio C.S., Custódio A.L., Manzi F.R., Junqueira J.L.

The aim of this study was to compare the accuracy of linear measurements of the distance between the mandibular cortical bone and the mandibular canal using 64-detector multi-slice computed tomography (MSCT) and cone beam computed tomography (CBCT). It was sought to evaluate the reliability of these examinations in detecting the mandibular canal for use in bilateral sagittal split osteotomy (BSSO) planning. Eight dry human mandibles were studied. Three sites, corresponding to the lingula, the angle, and the body of the mandible, were selected. After the CT scans had been obtained, the mandibles were sectioned and the bone segments measured to obtain the actual measurements. On analysis, no statistically significant difference was found between the measurements obtained through MSCT and CBCT, or when comparing the measurements from these scans with the actual measurements. It is concluded that the images obtained by CT scan, both 64-detector multi-slice and cone beam, can be used to obtain accurate linear measurements to locate the mandibular canal for preoperative planning of BSSO. The ability to correctly locate the mandibular canal during BSSO will reduce the occurrence of neurosensory disturbances in the postoperative period.

Huang C., Liao Y.

The purpose of this study was to determine the position of the mandibular canal in relation to the buccal cortical bone in Chinese patients with three dentofacial relationships: normal dentition, retrognathism, and prognathism.Cone-beam computed tomography and lateral cephalograms of patients with normal dentation, retrognathism, and prognathism (n = 32 each group) were reviewed. Measurements of the shortest distance from the outer/buccal edge of the mandibular canal to the inner surface of the buccal cortex, and the distance from the lingula of the ramus to the dorsal root of the first molar were recorded.No significant difference was observed between the three groups in the distribution of contact or fusion of the mandibular canal, or in the course of the mandibular canal on the right or left side. When the shortest distance at the lingula on the left side was >2.1 mm, no instances of contact or fusion were observed. On the right side, 100% of the patients had no contact or fusion when the shortest distance was >2.7 mm at the lingula.The shortest distance from the outer/buccal edge of the mandibular canal to the inner surface of the buccal cortex measured at the lingula can predict contact or fusion. During sagittal split ramus osteotomy, great care should be observed at the point halfway between the lingula and the anterior ramus border where the inferior alveolar nerve is the closest to the cortical bone.

Chrcanovic B.R., de Carvalho Machado V., Gjelvold B.

The aim of the present study was to morphometrically analyze the mandibular canal through the mandibular ramus by cone beam computed tomography (CBCT) and to relate the findings to performing sagittal split ramus osteotomy. CBCT of 200 patients were analyzed. Five parameters were measured at the axial scan, from the mandibular foramen to 21 mm below it (3-mm intervals). The canal was classified according to the position within the bone marrow space. Variations were evaluated according to age, sex, side, and number of mandibular teeth. The following measurements increased gradually towards the most inferior level of measurement: the total thickness of the mandibular ramus through the center of the mandibular canal, the width of the bone marrow space (both buccal and lingual), and the narrowest width from the mandibular canal inner cortical to the mandibular ramus external cortical. The inner diameter of the mandibular canal slightly decreased to the same direction. Concerning the mandibular canal position within the bone marrow space, the percentage of the separate type increased towards the most inferior level of measurement, and the contact and fusion types decreased. Age, number of teeth, and sex had no significant influence on the total thickness of the mandibular ramus and on the narrowest width from the mandibular canal inner cortical to the mandibular ramus external cortical.

Haas L.F., Dutra K., Porporatti A.L., Mezzomo L.A., De Luca Canto G., Flores-Mir C., Corrêa M.

To investigate the anatomical variations of the mandibular canal through assessment in situ, panoramic radiography, CT or CBCT and assess their frequency.Articles were selected from databases (Cochrane Library, LILACS, ProQuest, PubMed, Scopus, Web of Science and Google Scholar), articles without limitations of language, in which the main objective was to evaluate the frequency of bifurcation of the mandibular canal through assessment in situ, panoramic radiography, CT or CBCT were selected. A meta-analysis of prevalence using random effects was performed.Using a selection process in two phases, 15 articles were identified, and a meta-analysis was conducted. The results from these meta-analyses showed that the overall prevalence of anatomical variations for in situ studies was 6.46%, and through assessment of panoramic radiography and CT or CBCT the overall prevalence shown was 4.20% and 16.25%, respectively.There are two types of variations of the mandibular canal: the retromolar canal and bifid mandibular canal. The frequency variations through assessing in situ, panoramic radiography and CT or CBCT were 6.46%, 4.20% and 16.25%, respectively.

Miles M.S., Parks E.T., Eckert G.J., Blanchard S.B.

The purpose of this study was to determine the visibility of the mandibular canal (MC) in CBCT images and if the visibility of the MC is affected by gender, location and/or age.CBCT images were evaluated for the visibility of the MC by a board-certified oral and maxillofacial radiologist, a board-certified periodontist and a periodontics resident. Representative slices were examined for the first premolar (PM(1)), second premolar (PM(2)), first molar (M(1)) and second molar (M(2)) sites by all examiners. The visibility of the MC was registered as either present or absent.360 total CBCT cross-sectional images were examined, with the MC identified in 204 sites (56%). Age had a significant effect on MC visibility, but it differed by location: for PM(1), age 47-56 had lower visibility than age 65+ (p = 0.0377). Gender also had a significant effect on canal visibility, where females had lower visibility than males overall (p = 0.0178) and had the most pronounced difference for PM(1) (p = 0.0054). Location had a significant effect on visibility, but it differed by age and by gender: for age 65+, M(2) had lower visibility than PM(1) (p = 0.0411) and PM(2) (p = 0.0180), while for females, PM(1) had lower visibility than M(1) (p = 0.0123) and M(2) (p = 0.0419).The MC was visualized only in just over half of the CBCT images. Age, gender and location had significant effects on the visibility.

Verweij J.P., Mensink G., Fiocco M., van Merkesteyn J.P.

This retrospective study aimed to identify anatomical predictors of neurosensory disturbance (NSD) after bilateral sagittal split ramus osteotomy (BSSO) by evaluating the morphology of the mandible on lateral cephalograms (LCs) and orthopantomograms (OPTs). The LCs and OPTs of 142 patients who underwent BSSO were reviewed. The influence of the mandibular angle was assessed on LCs, while the following morphological landmarks and subsequent measurements were analysed on OPTs: vertical and horizontal positions of the lingula, ramus width, mandibular body height, mandibular canal position and mandibular angle length. Post-operative NSD (hypoaesthesia) was considered permanent when objective tests or subjective evaluations indicated altered sensation one year after BSSO. Generalised linear mixed models were used to take into account the repeated measurement design (left and right measurements within one patient). Hypoaesthesia was present in 10.6% of the patients (5.6% of sites). After adjusting for age, a small mandibular body height was found to significantly increase the risk of hypoaesthesia. The other measurements showed no significant association with hypoaesthesia. These findings show a relationship between mandibular morphology and hypoaesthesia after BSSO and can aid surgeons in pre-operative assessments of the risk of NSD. Further research is needed to identify risk factors for NSD based on mandibular morphology.

Park H., Lee J.

During the orthognathic surgery, it is important to know the exact anatomical location of the mandibular foramen to achieve successful anesthesia of inferior alveolar nerve and to prevent damage to the nerves and vessels supplying the mandible. Cone-beam computed tomography (CBCT) was used to determine the location of the mandibular foramen in 100 patients: 30 patients with normal occlusion (13 men, 17 women), 40 patients with skeletal class II malocclusion (15 men, 25 women), 30 patients with skeletal class III malocclusion (17 men, 13 women). The distance from the anterior border of the mandibular ramus to mandibular foramen did not differ significantly among the three groups, but in the group with skeletal class III malocclusion, this distance was an average of 1.43 ± 1.95 mm longer in the men than in the women (p < 0.05). In the skeletal class III malocclusion group, the mandibular foramen was higher than in the other two groups and was an average of 1.85 ± 3.23 mm higher in the men than in the women for all three groups combined (p < 0.05). The diameter of the ramus did not differ significantly among the three groups but was an average of 1.03 ± 2.58 mm wider in the men than in the women for all three groups combined (p < 0.05). In the skeletal class III malocclusion group, the ramus was longer than in the other groups and was an average of 7.9 ± 3.66 mm longer in the men than women. The location of the mandibular foramen was higher in the skeletal class III malocclusion group than in the other two groups, possibly because the ramus itself was longer in this group. This information should improve the success rate for inferior alveolar nerve anesthesia and decrease the complications that attend orthognathic surgery.

Agbaje J.O., Salem A.S., Lambrichts I., Jacobs R., Politis C.

Abstract Extreme variation in the reported incidence of inferior alveolar nerve (IAN) disturbances suggests that neurosensory disturbances after orthognathic surgery have not been evaluated adequately. Here we review the reported incidence of IAN injury after orthognathic surgery and assess recently reported methods for evaluating sensory disturbances. A search was conducted of the English-language scientific literature published between 1 January 1990 and 31 December 2013 using the Limo KU Leuven search platform. Information on various aspects of assessing IAN injury was extracted from 61 reports. In 16 reports (26%), the incidence of injury was not indicated. Preoperative IAN status was not assessed in 22 reports (36%). The IAN assessor was described in detail in 21 reports (34%), while information on the training of the assessors was mentioned in only two reports (3%). Subjective evaluation was the most common method for assessing neurosensory deficit. We conclude that the observed wide variation in the reported incidence of IAN injury is due to a lack of standardized assessment procedures and reporting. Thus, an international consensus meeting on this subject is needed in order to establish a standard-of-care method.

Aarabi M., Tabrizi R., Hekmat M., Shahidi S., Puzesh A.

Rich J., Golden B.A., Phillips C.

Abstract The purpose of this study was to review the current literature for the relationship between the preoperative position of the mandibular canal on three-dimensional (3D) radiographic imaging and postoperative neurosensory disturbance (NSD) following a sagittal split ramus osteotomy (SSRO). A literature search was conducted using PubMed, EMBASE, and the Cochrane Database for articles published from 1 January 2000 through 31 December 2013. Studies that included preoperative 3D imaging and assessment of NSD after surgery were reviewed. Study sample characteristics and results were extracted. Of the 69 articles identified, seven met the inclusion and exclusion criteria. There was no standardization for measuring the canal position or for evaluating NSD. General consensus was that the less space between the mandibular canal and the outer border of the buccal cortex the more frequent the occurrence of NSD. Increased bone density also appeared to contribute to a higher incidence of NSD. Utilization of 3D images to locate and measure the position of the mandibular canal is not standardized. Advances in 3D imaging and evaluation tools allow for new methodologies to be developed. Early attempts are informative, but additional studies are needed to verify the relationship between the location of the nerve and NSD following surgery.

Huang C.S., Jia-Syuan Syu J., Ko E.W., Chen Y.R.

The buccal cortical thickness (BCT) between the mandibular canal and the corresponding external cortical surface was compared in patients with and without neurosensory disturbance (NSD) after they underwent a bilateral sagittal split osteotomy (BSSO) to correct mandibular prognathism.This prospective cohort study was conducted in 146 patients (95 women, 65.1%; 51 men, 34.9%) 18 to 39 years old who underwent bimaxillary surgery (ie, Le Fort I osteotomy and BSSO) to correct mandibular prognathism. NSD was identified using a light touch test with a Semmes-Weinstein monofilament and a pricking pain test with a sharp dental explorer 1 week after surgery. Preoperative cone-beam computed tomographic (CBCT) imaging was used to visualize the bone contacts or fusion of the mandibular canal to the buccal cortical bone and to decrease injury to the mandibular nerve during surgical dissection. Preoperative CBCT imaging also was used to assess the BCT every 2 mm from the mandibular foramen to the furcation of the mandibular first molar in the NSD group and the sensory normal (N) group.The incidence of NSD was 32.5% at 1 week after surgery. There was no statistically significant difference between men and women, the side affected, or genioplasty at the time of undergoing BSSO. Of the total sample group, decreased BCT was identified throughout the observed length of the mandibular canal in the NSD group compared with the N group. Statistically significant decreased BCTs were 16 to 20 mm and 24 mm in the total sample, 6 to 8 mm in the female group, and 16 to 18 mm in the male group.Compared with the N group, BCTs in the NSD group were always decreased, especially those located at 16 to 20 mm and 24 mm in the total sample, 6 to 8 mm in the female group, and 16 to 18 mm in the male group.

Monson L.

The bilateral sagittal split osteotomy is an indispensable tool in the correction of dentofacial abnormalities. The technique has been in practice since the late 1800s, but did not reach widespread acceptance and use until several modifications were described in the 1960s and 1970s. Those modifications came from a desire to make the procedure safer, more reliable, and more predictable with less relapse. Those goals continue to stimulate innovation in the field today and have helped the procedure evolve to be a very dependable, consistent method of correction of many types of malocclusion. The operative surgeon should be well versed in the history, anatomy, technical aspects, and complications of the bilateral sagittal split osteotomy to fully understand the procedure and to counsel the patient.

Agbaje J.O., Sun Y., De Munter S., Schepers S., Vrielinck L., Lambrichts I., Politis C.

Injury to the inferior alveolar nerve (IAN) during surgery is an important complication of bilateral sagittal split osteotomy. With cone beam computed tomography, the course of the nerve and its relationship to the surrounding structures can be assessed in three dimensions. This study aims to determine whether tomography can predict attachment of the neurovascular bundle to the proximal segment of the mandible during sagittal split osteotomy (SSO). Bilateral linear measurements were taken on cross-sectional tomography images. During osteotomy, it was noted for each patient whether the neurovascular bundle was attached to the proximal segment during the split. If attached, a bone-cutting instrument or a blunt instrument was needed to free the nerve. The nerve was attached at more than one-third of operation sites (170 sites). Of these, over 65% of attached nerves (108 sites) required a bone-cutting intervention to free them from the mandible. After correcting for confounding factors, the linear distances from the buccal cortical margin of the IAN canal to the inner and outer buccal cortical margins of the mandible were important predictors of whether the IAN will be attached to the proximal segment of the mandible during SSO.

Sharma M., Bajjad A.A., Mendiratta A.K., Gupta S., Patil K.J., Saxena S.

Darawsheh H., Alsaegh A., Nikolenko V., Bakieva S., Smilyk I., Panin A., Kheygetyan A., Troitskiy V., Leonov D., Vasil’ev Y.

Background and Objectives: the mandibular foramen is an essential anatomic landmark in performing various dental and surgical procedures, including inferior alveolar nerve block (IANB). However, its position may vary based on the individual morpho-functional features of the skull and face. This study aims to conduct a personalized assessment of the location of the mandibular foramen in various shapes of skulls, faces, and mandibles. Materials and Methods: this anatomic morphometric cross-sectional study was performed using one hundred and six (n = 106) certified human cadaver heads of both sexes. The cranial index (CI) and Izard’s facial index (FI) were calculated, the linear anatomic parameters of the skull and mandible were measured, the location of the mandibular foramen was identified, and the shapes of the skulls and mandibles were determined. Quantitative statistical data were obtained based on the location of the mandibular foramen, considering different shapes of skulls and faces. Results: there is a significant correlation between the location of the mandibular foramen, the high lengthy index (HLI) of the mandible, and the longitudinal latitude index (LLI) of the mandibular process. Conclusions: personalized assessment of the mandibular foramen based on a comprehensive analysis of craniometric characteristics can contribute to preventing unwanted dental and surgical complications, such as inferior alveolar nerve damage.

Alali Y.S., Mohammed (Bin) W.A., Alotaibi S.M., Alshehri S., Alshayban M.

Background/Objectives: Locating the mandibular foramen (MF) through imaging is clinically important for inferior alveolar nerve (IAN) anesthesia and mandibular ramus osteotomies. Although cone-beam computed tomography (CBCT) is superior in imaging the mandible, an orthopantomogram (OPG) is preferred for its ease of use and availability. Therefore, the present study aimed to evaluate the accuracy of digital OPG in localizing the MF, in a subset of the Middle Eastern population. Methods: Radiographic images (OPG and CBCT) of selected patients (adults, dentulous and no mandibular abnormalities) were used to locate the MF through digital measurements (mm) of the anteroposterior distance from the anterior border of the ramus (MF-AP) and the superoinferior position from the mandibular occlusal plane (MF-SI). Measurements were statistically compared between OPG and CBCT for accuracy. Differences in measurements between OPG and CBCT were compared against the anatomic location (right/left), age and biological sex, assuming a p-value < 0.05 as significant. Results: A total of 204 radiographic records (males: 100/females: 104/mean age: 34.65 ± 11.55 years) were evaluated. The measurements for the MF were MF-AP-OPG (right: 13.53 ± 2.44/left: 13.19 ± 2.25), MF-AP-CBCT (right: 13.61 ± 2.39/left: 13.36 ± 2.19), MF-SI-OPG (right: 5.25 ± 1.71/left: 5.41 ± 1.65) and MF-SI-CBCT (right: 5.59 ± 1.66/left: 5.52 ± 1.61). Measurements between OPG and CBCT were not significantly different, except for MF-SI (right) (p = 0.042). While the overall difference between OPG and CBCT (MF-AP/MF-SI) measurements showed a significant association (p < 0.01) with the anatomic location (right/left), a significant association (p < 0.05) with biological sex was observed only for MF-AP. Conclusions: Based on this study’s outcomes, digital OPG is an accurate modality to locate the MF based on anteroposterior (MF-AP) and superoinferior (MF-SI) measurements. This would be clinically beneficial for dental and oral surgeons to achieve the optimum IAN block anesthesia based on preoperative panoramic radiographs. Similarly, it would assist maxillofacial surgeons in planning mandibular orthognathic surgeries and ramus osteotomies without complications.