Construction of a 3D finite element model of temporomandibular joints including the musculoskeletal system / 医用生物力学

Objective To discuss the feasibility of constructing a 3D finite element model of the temporomandibular joint (TMJ) including the musculoskeletal system based on imaging and anatomy, and to provide new ideas of modeling for TMJ biomechanical researches. Methods CT images of the skull, MRI images of masticatory muscles and bilateral TMJ from No.23 Chinese virtual human in the second generation were collected and imported in batches into Mimics in format of DICOM for 3D reconstruction. Then the model was integrated and optimized by Geomagic Studio, and the TMJ capsule and articular cartilage were also constructed. After the material properties of TMJ tissues were defined, a 3D finite element model of TMJ including the musculoskeletal system was finally constructed by ANSYS. Results The 3D finite element model of TMJ with the musculoskeletal system was constructed, including TMJ disc, articular cartilage, TMJ capsule, maxilla (including zygoma and nasal), mandible, sphenoid, temporal bones (including part of parietal), maxillary teeth, mandibular teeth, temporalis muscles, masseter muscles, medial/lateral pterygoid muscles, temporomandibular ligaments, sphenomandibular ligaments and sylomandibular ligaments. Conclusions Based on CT and MRI images and anatomy, the 3D finite element model of TMJ including the musculoskeletal system can be precisely and feasibly constructed by Mimics, Geomagic Studio and ANSYS. This model can restore the biomechanical environment of the TMJ, provide new ideas of modeling for biomechanical researches on the TMJ, and offer the simulation platform for visualization treatment of TMJ disease in clinic.

Influence of insertion torque on biomechanical characteristics at implant-bone interface / 医用生物力学

Objective To evaluate the influence of different insertion torque values on stress and strain distributions at implant-bone interface. Methods The three-dimensional finite element model of the whole mandible with dental implants for immediate loading was created by CT scanning and self-developed USIS (universal surgical integration system) software. The insertion torque values of dental implants were supposed to be 0、15、25 N•cm3, respectively. The values of Von Mises stress and strain at implant-bone interface were calculated with ANSYS software, when the dental implants were loaded with vertical and buccolingual force at a 45°oblique angle of 150 N. Results When the dental implants under the three insertion torques were loaded with the vertical force, the maximum Von Mises stress was 33.6, 56.4, 69.6 MPa and the maximum strain was 5 157, 8 645, 15 630 με, respectively, while loaded with the buccolingual force, the maximum Von Mises stress was 95.3, 100.6, 108.3 MPa and the maximum strain was 17 110, 18 690, 21 380 με, respectively. Conclusions With the increased torque value of dental implants, the stress and strain at the implant-bone interface were both increased, but the increase was much slower under buccolingual loading than that under vertical loading.

Clinical application of a self-developed bone collector in dental implantation / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To introduce a self-developed bone collector designed by the authors and evaluate its effect in clinical application.</p><p><b>METHODS</b>A self-developed bone collector was used in 38 patients who underwent the dental implant operation from May 2008 to October 2009. During the operation the bone particles were harvested, which was used for the reconstruction of the bone defects around the implant simultaneously. The defects were fenestrate in 29 regions and triangle in 23 regions on buccal or lingual side of the dental implants.</p><p><b>RESULTS</b>All cases had no surgical wound infection and dehiscence 7 - 10 days after operation. Three to six months after implantation, the X-ray showed that all the dental implants had perfect osseointergration and the alveolar bone were successfully augmented.</p><p><b>CONCLUSIONS</b>Bone debris harvested by self-developed bone collector could repair small peri-implant bone defects, which is simple to use in clinic.</p>

Finite element modeling of individual maxillofacial hexahedron based on mapping method / 医用生物力学

Objective To establish patient-specific hexahedral finite element mesh model for the maxillofacial surgery. Methods A standard and common hexahedral finite element mesh model for the face soft tissue was first built by semi-automatic procedure, and the an individual facial hexahedral mesh was then generated by an example learning method based on volumetric mapping. Results It was convenient to generate a high quality patient-specific hexahedral mesh with geometric shape feature and mesh element quality preserved as much as possible with this method. Conclusions The new hexahedral mesh modeling method can provide high quality hexahedral mesh input for biomechanics analysis with good application prospect in many fields such as oral and maxillofacial surgery.

Infections of the head and neck leading to descending necrotizing mediastinitis: management of 9 cases / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To report nine cases of descending necrotizing mediastinitis (DNM) and to summarize the management experience.</p><p><b>METHODS</b>Between December 2005 and December 2008, nine patients (mean age, 55.7 years; age range, 38 to 78 years) with DNM were treated. Eight patients underwent surgical drainage of the involved cervical region and mediastinum (4 with cervical drainage alone; 4 with cervical drainage and right thoracotomy).</p><p><b>RESULTS</b>Two patients died, one of them refused surgical therapy and the other one died of multiorgan failure related to postoperative septic shock. Seven patients recovered. The mortality rate was 22%.</p><p><b>CONCLUSIONS</b>Delayed diagnosis and inadequate drainage are the main causes of high mortality rate of DNM. Aggressive surgical drainage and debridement of the neck and mediastinum by a multidisciplinary team of surgeons are very important in the treatment of DNM.</p>

Three dimension finite element analysis of anisotropic mandible with dental implants effect on implant-bone interface / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To establish anisotropic mandible model with dental implants and to investigate the effect of anisotropy material on stress and strain distribution of implant-bone interface.</p><p><b>METHODS</b>Three-dimensional finite element models of whole mandible with anisotropic and equivalent isotropic material were created by CT scanning and universal surgical integration system (USIS) software developed by the authors. Two ITI threaded implants were implanted in the posterior teeth area. The values of principal stress and principal strain on the bone around dental implants were calculated in two different finite element models with buccolingual load.</p><p><b>RESULTS</b>In the anisotropic mandible model, nearly all values of the principal stress and principal strain on cortical and cancellous bone increased compared with the equivalent isotropy model, 2.1%-74.1% for principal stress and 4.7%-57.3% for principal strain, but 10. 3%-71.4% for principal stress and 19.5%-63.4% for principal strain on cancellous bone.</p><p><b>CONCLUSIONS</b>In the three-dimensional finite element analysis, anisotropic mandible model with dental implants has an apparent effect on the stress and strains of the implant-bone interface. Anisotropic mechanical properties of mandible should be emphasized in biomechanical study.</p>

Experimental study on the reconstruction of mandibular symphyseal defects by internal tri-focal distractor / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To introduce the internal tri-focal distractor developed by the authors and evaluate its primary application and feasibility in animal experiment.</p><p><b>METHODS</b>Four hybrid dogs were selected and segmental resection at the mandibular symphysis was performed. Two transfer disks, 10 mm in width, were respectively fixed at the two ends of bone defect and the internal tri-focal distractor was installed. The force was applied one week after the operation, with a tractive speed of 0.5 mm/12 h. After 13 - 16 days, the traction was completed when the two transfer disks were combined. The occlusal films were taken at the 1st day, 4th, 8th and 12th week after traction. The animals were killed at the 12th week, samples of the traction area taken and histological examination performed. Finally, the new bone formation was observed.</p><p><b>RESULTS</b>All the animals survived in the experiment, abruption and rust-eaten was not found in distractor. In the 12th week after installation, new bones in traction gap were mature and bony union between the two transfer dishes was accomplished.</p><p><b>CONCLUSIONS</b>The internal tri-focal distractor used in this study may become a potential device in reconstruction of mandibular symphyseal defects.</p>

A finite element analysis system for two-demension morphological analysis of the soft tissue in orthognathic surgery / 中华整形外科杂志

<p><b>OBJECTIVE</b>To evaluate a finite element method (FEM) for analysis of the cranial-facial morphology.</p><p><b>METHODS</b>The two-dimensional finite element analysis system was established and used to analysis the lateral side morphology of the soft tissue by the change of each finite unit of the soft tissue in a X-ray cranial-facial lateral cepholometrics film.</p><p><b>RESULTS</b>The finite element analysis system was showing very well in the figures and data made by the system.</p><p><b>CONCLUSION</b>Finite element analysis system may be a good supplement of the traditional X-ray cephalometrics to the soft tissue of orthognatics.</p>