Charles Savoldelli

Determination of Young's modulus of mandibular bone using inverse analysis.

Development of a numerical model applicable to clinical practice, and in particular oral implantology, requires knowledge of the mechanical properties of mandibular bone. The wide range of mechanical parameters found in the literature prompted us to develop an inverse analysis method that takes into account the exact geometry of each specimen tested, regardless of its shape. The Youngs modulus of 3000MPa we determined for mandibular bone using this approach is lower than the values reported in the literature. This difference can be explained by numerous experimental factors, related in particular to the bone specimens used. However, the main reason is that, unlike most previously published papers on the subject, the heterogeneity of bone led us to select a specimen size at the upper end of the scale, close to clinical reality.

Stress distribution in the temporo-mandibular joint discs during jaw closing: a high-resolution three-dimensional finite-element model analysis.

PurposeThis study aims at analysing the stresses distribution in the temporomandibular joint (TMJ) using a complete high-resolution finite element model (FE Model). This model is used here to analyse the stresses distribution in the discs during a closing jaw cycle. In the end, this model enables the prediction of the stress evolution in the TMJ disc submitted to various loadings induced by mandibular trauma, surgery or parafunction.Materials and methodsThe geometric data for the model were obtained from MRI and CT scans images of a healthy male patient. Surface and volume meshes were successively obtained using a 3D image segmentation software (AMIRA®). Bone components of skull and mandible, both of joint discs, temporomandibular capsules and ligaments and dental arches were meshed as separate bodies. The volume meshes were transferred to the FE analysis software (FORGE®). Material properties were assigned for each region. Boundary conditions for closing jaw simulations were represented by different load directions of jaws muscles. The von Mises stresses distribution in both joint discs during closing conditions was analyzed.ResultsThe pattern of von Mises stresses in the TMJ discs is non-symmetric and changed continuously during jaw movement. Maximal stress is reached on the surface disc in areas in contact with others bodies.ConclusionsThe three-dimension finite element model of masticatory system will make it possible to simulate different conditions that appear to be important in the cascade of events leading to joint damage.

Immediate Functional Loading of an Implant-Supported Fixed Prosthesis at the Time of Ablative Surgery and Mandibular Reconstruction for Squamous Cell Carcinoma

The authors describe a case of squamous cell carcinoma of the oral cavity managed by ablative surgery, mandibular reconstruction with a fibula free flap, and implant placement during the same session. Immediate functional implant loading, respecting the principles of basal implantology, was performed 48 hours later using a highly rigid, screw-secured fixed prosthesis that served as an external fixator for the implants and grafted bone. Implant loading before external beam radiotherapy improves flap stability, bone consolidation, and quality of life. Functional and esthetic outcomes were evaluated 2 years after radiotherapy was completed.

La distraction symphysaire : protocole simplifié

INTRODUCTION Severe mandibular incisor crowding with bone insufficiency is usually treated by dental extractions and orthodontic management. Symphyseal distraction was proposed to avoid tooth extraction. This technique is still considered as invasive, complex and unsafe. We evaluated symphyseal distraction to clarify its indications, and to suggest a simplified surgical protocol. PATIENTS AND METHODS Six patients were treated by symphyseal distraction: three with a bone-anchored device and three with a dental anchored one. Pre and postoperative inter-canine measurements and occlusal stability were analyzed. RESULTS Postoperative inter-canine measurements increased from 3.4 to 6.8mm (mean 5.2mm). All patients were in Angle class I occlusion without complications. Dental anchored device simplified the surgical procedure. DISCUSSION Symphyseal distraction with dental anchored device is a simple, efficient and reliable to treat severe transverse mandibular deficiency. The orthodontist can manage the procedure by himself and controls the whole expansion process according to specific requirements.

Article originalLa distraction symphysaire : protocole simplifiéSymphyseal distraction: A simplified procedure

INTRODUCTION Severe mandibular incisor crowding with bone insufficiency is usually treated by dental extractions and orthodontic management. Symphyseal distraction was proposed to avoid tooth extraction. This technique is still considered as invasive, complex and unsafe. We evaluated symphyseal distraction to clarify its indications, and to suggest a simplified surgical protocol. PATIENTS AND METHODS Six patients were treated by symphyseal distraction: three with a bone-anchored device and three with a dental anchored one. Pre and postoperative inter-canine measurements and occlusal stability were analyzed. RESULTS Postoperative inter-canine measurements increased from 3.4 to 6.8mm (mean 5.2mm). All patients were in Angle class I occlusion without complications. Dental anchored device simplified the surgical procedure. DISCUSSION Symphyseal distraction with dental anchored device is a simple, efficient and reliable to treat severe transverse mandibular deficiency. The orthodontist can manage the procedure by himself and controls the whole expansion process according to specific requirements.

Comparison of stress distribution in the temporomandibular joint during jaw closing before and after symphyseal distraction: a finite element study

The aim of this study was to predict stress modification in the temporomandibular joint (TMJ) after symphyseal distraction (SD). The study was performed using three-dimensional finite element analysis using a complete mastication model. Geometric data were obtained from MRI and CT scans of a healthy male patient and each component was meshed as various regions. The distraction was performed with a 10mm expansion after simulation of a surgical vertical osteotomy line on the model in the mandibular midline region. The geometry and mesh of the bone callus were constructed. The bone callus was modelled as a strengthened region characterized by a Youngs modulus corresponding to consolidated bone to predict the long-term biomechanical effect of SD. Boundary conditions for jaw closing simulations were represented by different jaw muscle load directions. The von Mises stress distributions in both joint discs and condyles during closing conditions were analysed and compared before and after SD. Stress distribution was similar in discs and on condylar surfaces in the pre- and post-distraction models. The outcomes of this study suggest that anatomical changes in TMJ structures should not predispose to long-term tissue fatigue and demonstrate the absence of clinical permanent TMJ symptoms after SD.

Mise au pointApport de la méthode des éléments finis en chirurgie maxillofacialeContribution of the finite element method in maxillofacial surgery

The finite element method is a numerical modeling tool used in various fields in medicine and surgery such as orthopedics, traumatology, and cardiovascular surgery. But this tool also has several applications in maxillofacial surgery. We present the advantages of this method by describing its principles as well as the various fields of application in maxillofacial surgery. This article was intended to help novices understand the results of various studies using this method.

Apport de la méthode des éléments finis en chirurgie maxillofaciale

The finite element method is a numerical modeling tool used in various fields in medicine and surgery such as orthopedics, traumatology, and cardiovascular surgery. But this tool also has several applications in maxillofacial surgery. We present the advantages of this method by describing its principles as well as the various fields of application in maxillofacial surgery. This article was intended to help novices understand the results of various studies using this method.

Computer-assisted teaching of bilateral sagittal split osteotomy: Learning curve for condylar positioning

Bilateral sagittal split osteotomy (BSSO) is a widely-performed procedure in orthognathic surgery for the correction of dentofacial deformity. Condylar positioning is a critical step during BSSO to maximize functional and morphological results. The unsuitable positioning of condyles represents one of the causative mechanisms that may induce temporomandibular joint noxious effects after BSSO. Repositioning devices can assist surgeons in maintaining the preoperative condylar position; however, empirical repositioning methods based on experience gained are still commonly used. Trainee learning curves are difficult to assess. The aim of this study was to evaluate the relevance of computer-assisted surgery in the acquisition of condylar positioning skills. Forty-eight patients underwent BSSO performed by six maxillofacial trainees (four junior residents and two senior experienced residents). A condyle positioning system (CPS) was used by a senior surgeon to record a condylar position score during the procedure. Firstly, scores were recorded when the trainee manually positioned the condyle without access to the CPS score (phase 1) and then when the trainee positioned the condyle and performed osteosynthesis with visual access to the CPS score (phase 2). Six parameters describing condylar three-dimensional motions were assessed: translational motion from top to bottom (TB), back to front (BF), and left to right (LR), axial rotation (AR), sagittal rotation (SR), frontal rotation (FR), and a total score (TS). There were no significant differences between junior and senior residents in condyle positioning without access to the CPS. Condyles were significantly better positioned during phase 2 with access to the CPS (p<0.001). Over time, use of the CPS (phase 2) produced significantly quicker improvements in scores (p = 0.042). For those teaching surgeries to trainees, computer-assisted devices can potentially result in more rapid learning curves than traditional “observations-imitation” models. Use of a CPS by trainees facilitated condylar repositioning that resulted in an accurate occlusal result and avoidance of adverse effects on the temporomandibular joint.

Model to assess duration of distraction compared with degree of incisal crowding in symphyseal distraction osteogenesis

Our aim was to evaluate symphyseal distraction in relation to duration of expansion, and to propose an optimised procedure. Eighteen patients (mean (SD) age 19 (7) years) with transverse mandibular deficiency were treated by symphyseal distraction osteogenesis. The mean (SD) anterior dental crowding measured was 6.8 (4.2) mm. We retrospectively compared the width of expansion between the canines (ICE) and expansion between the first molars (IFME) after symphyseal distraction according to the distraction time. The median (range) duration of expansion was 13.6 (7-21) days. The median (range) ICE distraction width was 5.5 (3.4-8) mm and IFME width 3.3 (1-7.9) mm (p<0.001). There was a significant correlation between expansion width and distraction time (p<0.001). The transverse anterior and posterior expansion widths differed significantly until 14 days after expansion. The expansion ratio (ICE:IFME) decreased as expansion time increased. The results suggest that the duration of activated expansion can be predicted from the degree of incisal crowding using the formula: distraction time (days)=0.84+3.4×[IC (mm)]-0.2×[IC (mm)](2).