CBCT-based predictability of attachment of the neurovascular bundle to the proximal segment of the mandible during sagittal split osteotomy

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

Objectives

To evaluate the positions of the mandibular foramen (MF) and mandibular canal (MC) between different skeletal classes to highlight the implications for bilateral sagittal split osteotomy (BSSO).

Methods

A cross-sectional study was performed using cone-beam computed tomography on 90 patients classified into classes I, II and III. Linear measurements were performed on multiplanar reconstructions as follows: from the MF to the edge of the mandibular ramus (1), to the mandibular notch (2), to the ramus width (3) and to the occlusal plane (4); and from the MC to the alveolar crest (A), to the lower border of the mandible (B) and to the mandibular buccal cortical bone (C). Mandibular thickness (D), width (E) and height (F) of the MC were measured. Intra-class correlation coefficient (ICC) checked the reliability. Two-way ANOVA and Tukey's test were used to compare measurements and classes.

Results

Linear measurements 2 presented a statistically significant difference between classes I and II. There was no statistically significant difference between the classes and measurements B, C, D, E and F. Linear measurements A were shorter in class III than in class II.

Conclusions

Although most measurements suggest that the BSSO technique does not need to be modified for each skeletal class, measurements from the MF to the mandibular notch in class II and from the MC to the alveolar crest on distal of the second molars in class III could help surgeons to recognize critical regions.

Do positional changes of the inferior alveolar canal after sagittal split mandibular osteotomy affect neurosensory recovery?

The purpose of this study was to assess the pre- and postoperative position and dimensions of the inferior alveolar canal (IAC) following sagittal split osteotomy (SSO) and identify any association with postoperative neurosensory deficit (NSD) at 1 year. This retrospective cohort study enrolled consecutive patients who had SSO performed to correct skeletal malocclusion. The pre- and postoperative cone beam computed tomography data were superimposed to visualize differences in IAC position and dimensions. Subjective and objective neurosensory tests were used to determine NSD in the inferior alveolar nerve distribution. A total of 20 subjects were included. The preoperative distance from the lateral cortex of the IAC to the inner aspect of the lateral cortex of the mandible was significantly greater in sides with NSD when compared to sides without NSD (P =  0.01). A significantly greater reduction in the postoperative distance measurement was seen in sides with NSD when compared to sides without NSD (P =  0.01). The magnitude of mandibular movement was significantly increased in sides with NSD (P = 0.02). The preoperative location of the IAC, as well as certain changes in the mediolateral and vertical positions as a result of SSO, are risk factors for postoperative NSD.

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

PURPOSE

This 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 METHODS

This 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).

RESULTS

The 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).

CONCLUSION

It 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.

Surgical implications of the anatomic situation of the mandibular canal for mandibular osteotomies: a cone beam computed tomographic study

PURPOSE

In bilateral sagittal split osteotomy (BSSO), the risk of lesion of the inferior alveolar nerve (IAN) is important. The aim of this study was to investigate the situation of the IAN in the area of the BSSO in preoperative 158 CBCT.

METHODS

The situation of the mandibular canal (MC) has been studied in six coronal sections (one section each 4 mm) from the proximal root of the second mandibular molar. The height of the MC related to the height of the mandible, and the horizontal distance between the MC and the lateral cortical plate related to the mandibular width have been determined in each section. The cancellous bone width has been measured allowing to determine a cancellous bone ratio.

RESULTS

The variability of the MC was high, depending mainly on the cancellous bone ratio which was higher when the IAN was deep. When a third molar was present, the MC was lower in the area of the third molar.

CONCLUSIONS

To decrease the risk of injuring the IAN in BSSO, the evaluation of the cancellous bone ratio by a preoperative CBCT may be proposed to adapt the surgical technique to the anatomy.

Radiographic Evaluation of Anterior Loop of Inferior Alveolar Nerve: A Cone-Beam Computer Tomography Study

Background:

A well awareness of the variation of inferior alveolar canal is mandatory to avoid iatrogenic complication. This study was conducted among 90 patients to determine variation in inferior alveolar nerve (IAN) loop through cone-beam computed tomography (CBCT) images.

Materials and Methods:

CBCT images of 90 patients were involved in this study. All images were studied by the expert radiologist to see Type I, Type II, and Type III pattern of IAN canal (IANC). Results were subjected to statistical analysis for correct inferences.

Results:

Forty males and 50 females were included in the study. The difference was statistically nonsignificant (P = 0.5). Type I pattern was seen in 26 patients, Type II in 19, and Type III in 45 patients. The difference was statistically significant (P < 0.05). The most prevalent pattern was Type III (males - 15 and females - 30), followed by Type I (males - 14 and females - 12) and Type II (males - 11 and females - 8). There was statistical significance difference between males and females in Type II (P < 0.05).

Conclusion:

The anterior loop of IAC is quite common and IANC may show variation in structure. The most common pattern recorded was Type III. CBCT is very useful in the detection of IANC.

Assessment of the anterior loop of the inferior alveolar nerve via cone-beam computed tomography

Objectives

The aim of this study was to evaluate different anatomical variants of the anterior loop of the inferior alveolar nerve (IAN) via cone-beam computed tomography (CBCT).

Materials and Methods

CBCT images of 71 patients (36 males and 35 females) were evaluated. We used the classification described by Solar for IAN evaluation. In this classification, three different types of IAN loops were introduced prior to emerging from the mental foramen. We classified patients according to this system and introduced a new, fourth type.

Results

Type I was seen in 15 sites (10.6%), type II in 39 sites (27.5%), and type III in 50 sites (35.2%). We found a new type in 38 sites (26.8%) that constituted a fourth type.

Conclusion

We found that type III was the most common variant. In the fourth type, the IAN was not detectable because the main nerve was adjacent to the cortical plate and the incisive branch was thinner than the main branch and alongside it. In this type, more care is needed for surgeries including inferior alveolar and mental nerve transposition.

Laser Therapy in the Treatment of Paresthesia: A Retrospective Study of 125 Clinical Cases

OBJECTIVE

The aim of this retrospective study was to evaluate the effectiveness of laser therapy for acceleration and recovery of nerve sensitivity after orthognathic or minor oral surgeries, by analysis of clinical records of patients treated at the Special Laboratory of Lasers in Dentistry (LELO, School of Dentistry, University of São Paulo), throughout the period 2007-2013.

BACKGROUND DATA

Nerve tissue lesions may occur during various dental and routine surgical procedures, resulting in paresthesia. Laser therapy has been shown to be able to accelerate and enhance the regeneration of the affected nerve tissue; however, there are few studies in the literature that evaluate the effects of treatment with low-power laser on neural changes after orthognathic or minor oral surgeries.

METHODS

A total of 125 clinical records were included, and the data on gender, age, origin of the lesion, nerve, interval between surgery and onset of laser therapy, frequency of laser irradiation (one or two times per week), final evolution, and if there was a need to change the irradiation protocol, were all recorded. These data were related to the recovery of sensitivity in the affected nerve area. Descriptive analyses and modeling for analysis of categorical data (α=5%) were performed.

RESULTS

The results from both analyses showed that the recovery of sensitivity was correlated with patient age (p=0.015) and interval between surgery and onset of laser therapy (p=0.002).

CONCLUSIONS

Within the limits of this retrospective study, it was found that low- power laser therapy with beam emission band in the infrared spectrum (808 nm) can positively affect the recovery of sensitivity after orthognathic or minor oral surgeries.

Intraoperative Computed Tomography in Bilateral Sagittal Split Osteotomy

OBJECTIVES

The objective of the study was to show the importance of intraoperative computed tomography as an aid for ensuring inferior alveolar nerve safety during bilateral sagittal split osteotomy.

MATERIALS AND METHODS

This study included ten patients who underwent bilateral sagittal split osteotomy procedure. All patients were treated for orthognathic reasons. The unerupted lower third molars, if present, were removed at least 6 months prior to Sagittal Split Osteotomy. The Sagittal Split Osteotomy surgical technique was previously described in detail. Each patient underwent computed tomography with an Artis Zeego multi-axis system (Siemens AG, Healthcare Sector, Henkestrasse 127 D-91052 Erlangen, Germany) at the beginning of the operation and immediately after placement of the osteosynthesis plates and screws. The neurosensory tests consisted of a light touch test using the 5.07/10-g Semmes Weinstein monofilament (Stoelting Co, Wood Dale, IL), and patient self-reporting.

RESULTS

Eight (80 %) patients presented with hypoesthesia of lower lip at 6 weeks follow up. At 6 month follow up only two patients (20 %) presented with diminished sensation in the lower lip. Labial sensibility was normal in all patients at the last follow-up visit.

CONCLUSION

Intraoperative computed tomography enables immediate assessment of treatment and the option to modify the treatment if necessary. Our results indicate that intra-operative computed tomography would be a helpful procedure during orthognathic surgery to improve the postoperative health of the inferior alveolar nerve.

Evaluation of the relationship between mandibular third molar and mandibular canal by different algorithms of cone-beam computed tomography

OBJECTIVES

Exact location of the inferior alveolar nerve (IAN) bundle is very important. The aim of this study is to evaluate the relationship between the mandibular third molar and the mandibular canal by cone-beam computed tomography.

STUDY DESIGN

This was a cross-sectional study with convenience sampling. 94 mandibular CBCTs performed with CSANEX 3D machine (Soredex, Finland) and 3D system chosen. Vertical and horizontal relationship between the mandibular canal and the third molar depicted by 3D, panoramic reformat view of CBCT and cross-sectional view. Cross-sectional view was our gold standard and other view evaluated by it.

RESULTS

There were significant differences between the vertical and horizontal relation of nerve and tooth in all views (p < 0.001).

CONCLUSION

The results showed differences in the position of the inferior alveolar nerve with different views of CBCT, so CBCT images are not quite reliable and have possibility of error.

Safe surgical access to the mandibular nerve at the infratemporal fossae

Some anatomic patterns formed by the anterior border of the ascending ramus relative to the mandibular canal can cause nerve complications during surgery. We determined the frequency of obstructive anatomy in patients undergoing jaw surgery, and we described a perioperative method for a bilateral sagittal split osteotomy that ensured inferior alveolar nerve (IAN) protection. The anatomy of the anterior border of the ascending ramus of the mandible was examined on axial and cross-sectional cone beam computed tomographic images of 114 consecutive patients undergoing bilateral sagittal split osteotomies. The thickness of the anterior border of the ascending ramus determined whether the mandibular foramen could be visualized (pattern A) or was obscured (pattern B). Patients with pattern B anatomy received a perioperative procedure. Direct visualization of the mandibular foramen was achieved in 100% of patients with pattern A anatomy. We examined 228 anterior borders of the ascending ramus of the mandible relative to the mandibular foramen in 114 patients. Pattern A was observed in 146 cases (64%); pattern B, in 82 (36%) cases. The use of the nerve hook resulted in no injuries to the IAN in all cases. The described procedure ensured direct visualization of the IAN, which prevented inadvertent damage to the IAN during instrumentation and surgical procedures at the mandibular foramen.

Quantitative evaluation of cortical bone thickness in mandibular prognathic patients with neurosensory disturbance after bilateral sagittal split osteotomy

PURPOSE

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.

PATIENTS AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

Self-reported hypoesthesia of the lower lip after sagittal split osteotomy

Sagittal split osteotomy may result in sensory impairment of the inferior alveolar nerve; altered sensation in the lower lip varies from patient to patient. We evaluated individual and intraoperative risk factors of sagittal split osteotomy and correlated these findings with self-reported postoperative changes in lower-lip sensation. Follow-up data for 163 consecutive patients who underwent a bilateral sagittal split osteotomy were assessed for self-reported sensibility disturbances in the lower lip at the last follow-up visit. These self-reports were categorized as normal, hypoesthesia, hyperesthesia, or slightly diminished sensation in the central area of the chin. The overall rate of self-reported changed sensibility was 15.1% (49/324; 13.0% on the right side and 17.3% on the left side). Of 16 patients (9.9%) who experienced hypoesthesia on the right side and 25 patients (15.4%) who experienced hypoesthesia on the left side, 10 experienced bilateral hypoesthesia (31 patients total, 19.1%). Genioplasty and age at surgery were significant predictors of hypoesthesia; a 1-year increase in age at surgery increased the odds of hyposensitivity by 5%, and the odds of hypoesthesia in patients with concurrent genioplasty were 4.5 times higher than in patients without genioplasty. Detachment of the nerve at the left side, but not at the right side, was significantly correlated with hypoesthesia.

Visibility of mandibular canal on panoramic radiograph after bilateral sagittal split osteotomy (BSSO)

PURPOSE

This study aimed to assess the visibility of the mandibular canal (MC) on panoramic radiographs after bilateral sagittal split osteotomy (BSSO), and to investigate what factors affect this MC visibility.

METHODS

We assessed MC visibility on panoramic radiographs of 200 BSSO patients. Images were acquired preoperatively (T0), immediately postoperatively (T1), 6 months postoperatively (T2), and 1 year postoperatively (T3), from three different predetermined regions of the mandible: the angle (Angle), distally to the second molar (M2), and mesially to the first molar (M1). All analyses were performed using SAS version 9.22.

RESULTS

The visibility of the MC was registered preoperatively in over 96 % (387/400) of the measurements at the angle of the mandible, 79 % (317/400) at M2, and <63 % (251/400) at M1. MC visibility decreased immediately after the operation and increased thereafter. Region of the mandible (P ≤ 0.0001), plate removal (P ≤ 0.0001), time of assessment (P ≤ 0.0001), and age (P = 0.0034) were the important predictors of whether MC would be radiographically visible.

CONCLUSIONS

The visibility of the MC decreased immediately after BSSO, especially at the operation site (M2 and M1), while maximum MC visibility was achieved at 12 months postoperatively in our series. Since MC was not visible at the operation site after BSSO for 50 % of the subjects, it may be necessary to use additional visualization modalities for postoperative patient assessment in this region.