Morphological characteristics of coronoid process and revisiting definition of coronoid hyperplasia.

The aim of this study was to assess the morphological characteristics of the coronoid process (CP) and define coronoid hyperplasia (CH) using cadaveric mandibles of a Caucasian population. A sample of 151 adult dry cadaveric mandibles (302 CPs) was acquired. Three distances were measured, which included the width, height, and length of CP. The surface area measurements involved area A: above the width distance line; area B: between incisura mandibulae-Alveolar ridge line and width distance line; area C: between distance lines of width and height. Finally, angulations of the CP and gonial angles were identified. Both length and surface area A + B acted as hyperplastic indicators. Based on the selection criteria, a sample of 197 CPs was included. The hooked shape (59%) was most commonly observed. No significant difference existed between left and right sides (p > 0.05). The mean values of length and surface area A + B were 2.2 ± 0.3 cm and 3.3 ± 0.8 cm2, and any values above 2.7 cm (n = 5 CPs- 2.5%) and 5.0 cm2 (n = 9 CPs- 4.6%) were described as hyperplastic, respectively. The presented data could act as quantitative reference for differentiating between normal and hyperplastic conditions.

The impact of CBCT-head tilting on 3D condylar segmentation reproducibility.

OBJECTIVES: To investigate whether variations in head positioning may influence the reproducibility of cone-beam CT (CBCT) three-dimensional (3D) segmented models of the mandibular condyle. METHODS: Five fresh frozen cadaver heads were scanned in four different positions: reference position (RP) and a set of three tilted alternative head positions (AP) in anteroposterior direction (AP1: 2 cm anterior translation, AP2: 5° pitch rotation, AP3: 10° pitch rotation). Surface models of mandibular condyles were constructed and compared with the condylar reference position using voxel-based registration. Descriptive statistics and a linear mixed-effects model were performed to compare condylar volumetric differences and root mean square (RMS) distance between surfaces of AP vs RP. RESULTS: The mean differences in condylar volumes of AP vs RP were 14.1 mm³ (95% CI [-79.3, 107.4]) for AP1, 1.0 mm³ (95% CI [-87.2, 89.2]) for AP2 and 0.1 mm³ (95% CI [-88.3, 88.4]) for AP3. Mean and absolute volumetric differences did not exceed earlier reported intraoperator differences of 30 mm³. The RMS distance values obtained per group were 0.12 mm (95% CI [0.05,0.20]) for AP1, 0.17 mm (95% CI [0.10, 0.22]) for AP2 and 0.17 mm for AP3 (95% CI [0.10,0.22]). The confidence intervals (CI) for RMS distance remained far below the threshold for clinical acceptability (0.5 mm). CONCLUSIONS: Within the limits of the present study, it is suggested that tilted head positions may affect the reproducibility of 3D condylar segmentation, thereby influencing outcome in repeated CBCT scanning. Nevertheless, observed differences are unlikely to have a meaningful impact on clinical patient diagnosis and management.

Correlation of MRI and arthroscopic findings with clinical outcome in temporomandibular joint disorders: a retrospective cohort study.

BACKGROUND: Arthroscopy is a minimally invasive diagnostic tool and treatment strategy in patients suffering from temporomandibular disorders (TMD) when conservative treatment fails. This study aimed to find specific variables on pre-operative MRI or during arthroscopy that could predict success of arthroscopic lysis and lavage. METHODS: This retrospective analysis compared pre-operative maximum interincisal opening (MIO), pain and main complaint (pain, limited MIO or joint sounds) with results at short-term and medium-term follow-up (ST and MT respectively). Different variables scored on MRI or arthroscopy were used to make a stepwise regression model, subsequently a combined analysis was conducted using variables from both MRI and arthroscopy. RESULTS: A total of 47 patients (50 joints) met the inclusion criteria. The main complaint improved by 62 and 53% at ST and MT respectively. The absolute or probable absence of a crumpled disc scored on MRI predicted success at ST and MT (p = 0.0112 and p = 0.0054), and remained significant at MT in the combined analysis (p = 0.0078). Arthroscopic findings of degenerative joint disease predicted success at ST (p = 0.0178), absolute or probable absence of discal reduction scored during arthroscopy significantly predicted success in the combined analysis at ST (p = 0.0474). CONCLUSION: To improve selection criteria for patients undergoing an arthroscopic lysis and lavage of the TMJ, future research might focus on variables visualized on MRI. Although more research is needed, disc shape and in particular the absolute or probable absence of a crumpled disc might be used as predictive variable for success.

Layered deep learning for automatic mandibular segmentation in cone-beam computed tomography.

OBJECTIVE: To develop and validate a layered deep learning algorithm which automatically creates three-dimensional (3D) surface models of the human mandible out of cone-beam computed tomography (CBCT) imaging. MATERIALS & METHODS: Two convolutional networks using a 3D U-Net architecture were combined and deployed in a cloud-based artificial intelligence (AI) model. The AI model was trained in two phases and iteratively improved to optimize the segmentation result using 160 anonymized full skull CBCT scans of orthognathic surgery patients (70 preoperative scans and 90 postoperative scans). Finally, the final AI model was tested by assessing timing, consistency, and accuracy on a separate testing dataset of 15 pre- and 15 postoperative full skull CBCT scans. The AI model was compared to user refined AI segmentations (RAI) and to semi-automatic segmentation (SA), which is the current clinical standard. The time needed for segmentation was measured in seconds. Intra- and inter-operator consistency were assessed to check if the segmentation protocols delivered reproducible results. The following consistency metrics were used: intersection over union (IoU), dice similarity coefficient (DSC), Hausdorff distance (HD), absolute volume difference and root mean square (RMS) distance. To evaluate the match of the AI and RAI results to those of the SA method, their accuracy was measured using IoU, DSC, HD, absolute volume difference and RMS distance. RESULTS: On average, SA took 1218.4s. RAI showed a significant drop (p<0.0001) in timing to 456.5s (2.7-fold decrease). The AI method only took 17s (71.3-fold decrease). The average intra-operator IoU for RAI was 99.5% compared to 96.9% for SA. For inter-operator consistency, RAI scored an IoU of 99.6% compared to 94.6% for SA. The AI method was always consistent by default. In both the intra- and inter-operator consistency assessments, RAI outperformed SA on all metrics indicative of better consistency. With SA as the ground truth, AI and RAI scored an IoU of 94.6% and 94.4%, respectively. All accuracy metrics were similar for AI and RAI, meaning that both methods produce 3D models that closely match those produced by SA. CONCLUSION: A layered 3D U-Net architecture deep learning algorithm, with and without additional user refinements, improves time-efficiency, reduces operator error, and provides excellent accuracy when benchmarked against the clinical standard. CLINICAL SIGNIFICANCE: Semi-automatic segmentation in CBCT imaging is time-consuming and allows user-induced errors. Layered convolutional neural networks using a 3D U-Net architecture allow direct segmentation of high-resolution CBCT images. This approach creates 3D mandibular models in a more time-efficient and consistent way. It is accurate when benchmarked to semi-automatic segmentation.

Impaired Callus Formation in Pathological Mandibular Fractures in Medication-Related Osteonecrosis of the Jaw and Osteoradionecrosis.

PURPOSE: Nonsurgical treatment of mandibular fractures secondary to medication-related osteonecrosis of the jaw (MRONJ) or osteoradionecrosis (ORN) mostly results in nonunion, whereas nonsurgical fracture treatment of atrophic fractures can achieve favorable results in selected cases. The aim of this study was to compare callus formation in pathological mandibular fractures due to MRONJ, ORN, or extreme mandibular atrophy. METHODS: A retrospective cohort study reviewing the medical records of all MRONJ-, ORN-, or atrophy-related fractures treated at the departments of maxillofacial surgery in the Leuven or Lille university hospitals between 2010 and 2019 was undertaken. The primary predictor variable in this study was disease state (MRONJ, ORN, or extreme mandibular atrophy). The primary outcome variable was callus formation after 1 month of follow-up (present, absent). Additional study variables measured included patient age and gender. T-tests, Fisher exact tests, and multiple logistic regression were used for statistical analysis. The significance level was set at P < .05. RESULTS: Seventy patients were analyzed (12 MRONJ cases, 54 ORN fractures, 4 atrophic fractures). The callus formation prevalence in nonsurgically approached fractures secondary to ORN and MRONJ after 1 month of follow-up was 3.03% (2/66 cases). In contrast, callus was detected in all patients in the mandibular atrophy-related fracture group. Osteonecrosis was statistically correlated with impaired callus formation (P = .0121). CONCLUSION: Whereas one would expect indirect fracture healing and thus callus formation to occur in all non-surgically treated fractures, our data demonstrate its absence in the majority of MRONJ- and ORN-related fractures. Multiple plausible explanations for this phenomenon were identified: periosteal damage with loss of callus-forming cells, compromised vasculature, and bacterial colonization.

Automatic 3D dense phenotyping provides reliable and accurate shape quantification of the human mandible.

Automatic craniomaxillofacial (CMF) three dimensional (3D) dense phenotyping promises quantification of the complete CMF shape compared to the limiting use of sparse landmarks in classical phenotyping. This study assesses the accuracy and reliability of this new approach on the human mandible. Classic and automatic phenotyping techniques were applied on 30 unaltered and 20 operated human mandibles. Seven observers indicated 26 anatomical landmarks on each mandible three times. All mandibles were subjected to three rounds of automatic phenotyping using Meshmonk. The toolbox performed non-rigid surface registration of a template mandibular mesh consisting of 17,415 quasi landmarks on each target mandible and the quasi landmarks corresponding to the 26 anatomical locations of interest were identified. Repeated-measures reliability was assessed using root mean square (RMS) distances of repeated landmark indications to their centroid. Automatic phenotyping showed very low RMS distances confirming excellent repeated-measures reliability. The average Euclidean distance between manual and corresponding automatic landmarks was 1.40 mm for the unaltered and 1.76 mm for the operated sample. Centroid sizes from the automatic and manual shape configurations were highly similar with intraclass correlation coefficients (ICC) of > 0.99. Reproducibility coefficients for centroid size were < 2 mm, accounting for < 1% of the total variability of the centroid size of the mandibles in this sample. ICC's for the multivariate set of 325 interlandmark distances were all > 0.90 indicating again high similarity between shapes quantified by classic or automatic phenotyping. Combined, these findings established high accuracy and repeated-measures reliability of the automatic approach. 3D dense CMF phenotyping of the human mandible using the Meshmonk toolbox introduces a novel improvement in quantifying CMF shape.

Pitfalls and Promise of 3-dimensional Image Comparison for Craniofacial Surgical Assessment.

Three-dimensional (3D) photography is becoming widely used in plastic surgery. It provides an accurate and reproducible record of the facial surface anatomy and could be a versatile tool for treatment planning and assessment. However, the existing software tools available for the assessment of 3D facial imaging often give highly misleading results. The goal of this special topic article is to give clinicians an insight into methods of 3D image assessment and explain the reasons why results may be misleading. We point toward the advantages of an alternative approach using "nonrigid surface registration" for the comparison of pre- and postsurgical images. This approach is compared with the regular rigid surface registration, and this is illustrated by the assessment of a child with Crouzon syndrome before and after LeFort III osteotomy and distraction. Findings of the standard method imply that changes have occurred that are anatomically not possible, whereas the alternative approach indicates realistic changes. Furthermore, we demonstrate an exciting capacity of 3D image analysis to construct reference populations of normal head size and shape. These can be used to assess the parts of the head that are normal and abnormal pre- and posttreatment of the same child. We conclude that, while 3D image analysis has great potential in surgical assessment, existing software does not always give an adequate assessment. Collaboration among surgeons and engineering and computer science specialists should be encouraged. This way, more comprehensive and accurate techniques in patient assessment and surgical planning can be developed and applied in clinical practice.

Validation of a 3D CBCT-based protocol for the follow-up of mandibular condyle remodeling.

OBJECTIVES: Three-dimensional models of mandibular condyles provide a way for condylar remodeling follow-up. The overall aim was to develop and validate a user-friendly workflow for cone beam CT (CBCT)-based semi-automatic condylar registration and segmentation. METHODS: A rigid voxel-based registration (VBR) technique for registration of two post-operative CBCT-scans was tested. Two modified mandibular rami, with or without gonial angle, were investigated as the volume of interest for registration. Inter- and intraoperator reproducibility of this technique was tested on 10 mandibular rami of orthognathic patients by means of intraclass correlation coefficients (ICC's) and descriptive statistics of the transformation values from the VBR. The difference in reproducibility between the two modified rami was evaluated using a paired t-test (p < 0.05). For the segmentation, eight fresh frozen cadaver heads were scanned with CBCT and micro-CT. These data were used to test the inter- and intraoperator reproducibility (ICC's) and accuracy (Bland-Altman plot) of a newly designed workflow based on semi-automated contour enhancement. RESULTS: Excellent ICC's (0.94-0.99) were obtained for the voxel-based registration technique using both modified rami. If the gonial angle was not included in the volume of interest, there was a trend of increased operator error suggested by significant higher interoperator differences in translation values (p = 0,0036). The segmentation workflow proved to be highly reproducible with excellent ICC's (0.99), low absolute mean volume differences between operators (23.19 mm3), within operators (28.93 mm3) and low surface distances between models of different operators (<0.20 mm). Regarding the accuracy, CBCT-models slightly overestimate the condylar volume compared to micro-CT. CONCLUSIONS: This study provides a validated user-friendly and reproducible method of creating three-dimensional-surface models of mandibular condyles out of longitudinal CBCT-scans.

Metal debris after dental implant placement: A proof-of-concept study in fresh frozen cadavers using MRI and histological analysis.

PURPOSE: This report originated from the finding of metal artefacts on magnetic resonance images (MRI) which were not detected on panoramic radiography or cone beam computed tomography (CBCT) imaging. It was hypothesised that drills or implants might release metal particles during surgical procedures in the jawbones. Therefore, the aim was to assess whether dental implants or surgical drills might cause metal debris in the surrounding tissues. MATERIALS AND METHODS: The experiment consisted of a postmortem and an antemortem model. A split-mouth design was carried out in a postmortem fresh frozen cadaver head. In the left mandible only the drill preparation sequence was performed, whereas in the right mandible, the drill sequence was followed by implant placement. Before surgery, the postmortem model underwent a baseline MRI acquisition. A second MRI (MRI2) was acquired after performing the osteotomies on both sides and implant placement on the right side. Finally, the implants were carefully removed, and a final MRI (MRI3) was acquired. Bone blocks containing the implant and osteotomy sites were isolated. For the antemortem model, a fresh frozen cadaver head was selected that already had implants in place. An implant in the anterior maxilla was removed and the surrounding bone block was isolated as well. A histological analysis was prepared for both models. RESULTS: In the antemortem model, histological analysis showed irregular-shaped dark particles near the bone-implant interface consistent with metal debris. Additionally, in the postmortem model, both sites showed metal artefacts on MRI2 and MRI3, and by using a balanced fast field echo sequence, and histological analysis, the suspected particles of metal debris were confirmed on both sides of the mandible. CONCLUSIONS: Further studies should investigate the origin and extent of the metal debris following implant placement, as well as its clinical significance, possible risk factors and preventive measures.

Fibula Free Flap in Head and Neck Reconstruction: Identifying Risk Factors for Flap Failure and Analysis of Postoperative Complications in a Low Volume Setting.

The fibula free flap (FFF) has been a workhorse in maxillofacial reconstruction. High success rates of this technique are reported. However, identifying risk factors for flap failure and analyzing complications can open the way to better patient care. A retrospective analysis was conducted of all FFFs performed over a 20-year period at a low-volume single tertiary center to identify risk factors and postoperative complications. A total of 129 FFFs were included (122 mandible, 7 maxilla). Complete flap failure occurred in 12.4% and partial flap failure in 7.8% of patients. A significant relation was found between younger age and flap failure, and most failures were associated with venous thrombosis. In-hospital surgical complications occurred in 60.5%, in-hospital medical complications in 49.6%, and out-of-hospital complications in 77.5% of patients. The in-hospital reintervention rate was 27.1%, and including salvaged flaps, flap survival rate was 87.6%. Osteomyocutaneous FFF failure (complete 12.4%; partial 7.8%) is an important clinical reality in a low-volume head and neck reconstruction center resulting in an in-hospital reintervention rate of 27.1%. Postoperative complications are frequent, both surgical and out-hospital complications. These results provide a better understanding of the limitations of the FFF in a low-volume center and can be used to optimize care in this kind of setting.

The Biomechanical Effect of the Sagittal Split Ramus Osteotomy on the Temporomandibular Joint: Current Perspectives on the Remodeling Spectrum.

The sagittal split ramus osteotomy is a key approach for treating dentofacial deformities. Although it delivers excellent results, the sagittal split ramus osteotomy is believed to induce stress to the temporomandibular joint. Potential stress inducers could be classified as intra- and postoperative factors resulting in an inflammatory response and molecular cascades, which initiate physiological remodeling. Occasionally, this process exceeds its capacity and causes pathological remodeling, through either degenerative joint disease or condylar resorption. Hard evidence on how orthognathic surgery causes inflammation and how this inflammation is linked to the spectrum of remodeling remains scarce. Current concepts on this matter are mainly based on clinical observations and molecular mechanisms are extrapolated from fundamental research in other body parts or joints. This perspective study provides an overview of current knowledge on molecular pathways and biomechanical effects in temporomandibular joint remodeling. It provides research directions that could lead to acquiring fundamental evidence of the relation of orthognathic surgery and inflammation and its role in remodeling. Performing osteotomies in animal models and identifying inflammatory mediators as well as their effect on the joint seem promising. Patients affected by pathological remodeling can also provide samples for histological as well as molecular analysis. Individual susceptibility analysis by linking certain suspect phenotypes to genetic variation could identify the cause and molecular pathway responsible for degenerative joint disease and condylar resorption, ultimately leading to clinically applicable treatment and prevention strategies.

Surgical Management of an Aggressive Multifocal Squamous Odontogenic Tumor.

Squamous odontogenic tumor is a rare benign epithelial odontogenic tumor of the jaw. Most are solitary lesions, although rare multifocal lesions have been described. Maxillary lesions have more aggressive behavior. Because of their benign character, these lesions are usually treated using a conservative surgical approach with curettage and surgical enucleation. This report describes the case of a 29-year-old woman with multifocal lesions who was initially treated with conservative surgical therapy. Early recurrence 6 months after surgery prompted more aggressive resection. This case is discussed in the context of current evidence related to the epidemiology, etiology, diagnosis, and therapy of squamous odontogenic tumors.

Surgical treatment of the Anterior Cruciate Ligament Rupture : where do we stand today?

The rupture of the anterior cruciate ligament is one of the most common orthopaedic injuries. This review gives an overview of the surgical treatment of the ACL rupture. A correct knowledge of the anatomy of the ACL is crucial in treating this injury. Recent studies describe the ACl as flat rather than divided in distinct structural bundles. Reconstructive and primary repair techniques can be used to approach this native anatomy. Reconstructive surgery of the ACL still is the golden standard in ACL surgery. An individualized approach is key and should be used. However, ACL reconstruction is not always a success. Return to preinjury of sports only reaches 65% and ACL-reconstructed knees are prone to osteoarthritis. Previous attempts at the primary repair of the ACL were archaic and had disappointing results. Modern diagnostics, operative and biological techniques and strict patient selection could initiate a revival of this technique.