By three-dimensional finite element analysis,the present research inquired about the stress on the surface of alveolar bone of mandibular incisor with different level of bone loss under different loadings. For the mandibular incisor without bone loss, the maximums of the von Mises stress under vertical and 15 degree oblique loading were 13.171 and 14.315 MPa respectively, both located in the apical region, and the lingual displacement of the tooth were 0.056 and 0.197mm respectively; under 30 degree oblique loading, the maximum of the von Mises stress was 15.262 MPa, located not only in the apical region but also on the crest, and the lingual displacement of the tooth was 0.324 mm. However, when vertical loading was applied on the mandibular incisor with half of the alveolar bone loss, the maximum of the stress increased significantly, located in the apical regions. And under oblique loadings, the value of the stress of this model increased dramatically,being three to five times over that of mandibular incisor without bone loss. Both of them concentrated on the crest. The scope of its distribution decreased from area to point. The significant lingual displacement happened, amounting to 2.850 mm. So when the loss of alveolar bone is not less than half,occlusal adjustment and splinting should be considered during the initial treatment of periodontal disease in order to avoid the significant change of the stress and alleviate the damage to the periodontal tissues.
Alveolar Bone Loss ; physiopathology ; Finite Element Analysis ; Humans ; Imaging, Three-Dimensional ; Incisor ; Mandible ; physiopathology ; Mandibular Diseases ; physiopathology ; Stress, Mechanical

OBJECTIVETo study the natural head posture (NHP) of edentulous patients compared with dentate people and to understand NHP shift immediately inserting complete dentures and three months after denture wearing.

METHODSThe NHPs of twenty edentulous patients and twenty-two dentate subjects were recorded with cephalometric technique. The NTPs of edentulous patients were exposed three times, before inserting, right after inserting and three months after inserting dentures. The NHPs of dentate subjects were recorded once as a controlled group. Six angles measured from the radiographs were evaluated for the NHP and three angles and two linear measures for the mandibular position.

RESULTSCompared with dentate subjects, the craniomandibular angles of the edentulous patients increased and the camber of the cervical columns decreased, but changes of the NHP were not significant. The mandible showed a significant upward moving (P < 0.05) and an insignificant forward moving. At the time of denture insertion, the camber of the cervical columns significantly increased (P < 0.05). Three months after using the dentures, the craniomandibular angles of the patients obviously decreased. (P < 0.05).

CONCLUSIONThe shift of NHP after denture inserting does exist. The shifted NHP of the patients with dentures is a new balanced posture and closer to the normal position than the NHP of them without dentures.

Adult ; Aged ; Aged, 80 and over ; Cephalometry ; methods ; Denture, Complete ; Female ; Head ; physiopathology ; Humans ; Male ; Mandible ; physiopathology ; Middle Aged ; Mouth Rehabilitation ; methods ; Mouth, Edentulous ; physiopathology ; rehabilitation ; Neck ; physiopathology ; Posture

OBJECTIVEThe purpose of this study is to evaluate the effect of therapeutic complete denture in rectifying malmaxillomandibular relation of complete.

METHODS11 patients were treated with therapeutic complete denture, of which the maxillary premolars and molars were artificial ceramic teeth and mandibular premolar and molar region was just like a splint. The changes before and after the treatment were recorded by mandibular kinesiograph(MKG). The effect was evaluated by self-control comparison.

RESULTSAfter rectifying, the concentration of the closing locus end position evidently increased, the symmetry of mandible motion significantly improved, CRO-ICO three-dimensional slide range decreased and moreover, the teeth had even and stable contact during sliding.

CONCLUSIONThe temporary therapeutic complete denture had a fair effect in rectifying malmaxil-lomandibular relation of edentulous patients.

Aged ; Centric Relation ; Dental Occlusion ; Denture, Complete ; Female ; Humans ; Male ; Malocclusion ; therapy ; Mandible ; physiopathology ; Mandibular Condyle ; physiopathology ; Maxilla ; physiopathology ; Middle Aged ; Mouth, Edentulous ; physiopathology ; Orthodontics, Corrective ; methods

OBJECTIVETo introduce the internal tri-focal distractor developed by the authors and evaluate its primary application and feasibility in animal experiment.

METHODSFour 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.

RESULTSAll 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.

CONCLUSIONSThe internal tri-focal distractor used in this study may become a potential device in reconstruction of mandibular symphyseal defects.

Animals ; Bone Remodeling ; Disease Models, Animal ; Dogs ; Female ; Male ; Mandible ; physiopathology ; surgery ; Mandibular Injuries ; physiopathology ; surgery ; Osteogenesis, Distraction ; instrumentation

OBJECTIVETo explore the biomechanical mechanism of impact force-induced mandibular fractures and its finite element analysis.

METHODSThree mandibular impact fracture models were prepared using intact human mandibular specimens and simulated maxillary models according to the Hanau principle of articulator and a MTS-858 biological material testing machine. Mandibular impact was delivered in the direction of the chin level at the mandibular postural position (MPP) on MTS. The computerized mandibular model was then established from 3-dimensional laser scanning images for finite element analysis using ANSYS7.0.

RESULTSThe 3 mandibular specimens were fractured at the chin, where the maximum force was 2151.10-/+ 125.18 N with response time of 17.3-/+2.3 ms. Impact simulation with ANSYS mimicking stress changes in the internal jaw suggested the chin as place where maximum stress occurred. According to the stress curve, the maximum stress of 3201.35 kPa occurred at the point 1.92 cm from the upper edge of the chin.

CONCLUSIONThe combination of mandibular impact experiments and finite element analysis allows quantification of several parameters of the jaw and provides clues for understanding the biomechanical mechanism of mandibular impact fractures.

Biomechanical Phenomena ; Finite Element Analysis ; Humans ; Mandible ; pathology ; physiopathology ; Mandibular Fractures ; physiopathology ; Models, Anatomic ; Stress, Mechanical ; Tensile Strength

OBJECTIVETo investigate the changes of mandibular vitodynamics in powerful bite working condition and impact working condition after mandibular angle osteotomy through 3-dimensional finit element analysis.

METHODSA patient of prominent mandibualr angle without malocclusion was selected and underwent 3-dimensional CT before and after operation. The DICOM data of 3-dimensional CT were read by Mimics software and 3-dimensional images were reconstructed. Then the 3-dimensional images were changed into IGES format and imported into ANSYS10.0. The boundary constrained condition and pre-processing condition was setting in ANSYS10.0 software. The 3-dimensional finite element models were generated in ANSYS10.0. Solution process was running and most powerful bite working condition and impact working condition were simulated and calculated.

RESULTSIn static stress analysis, the stress peak and stress maximal value point of mandible were basically at equal pace in preoperative and postoperative models. In transience dynamic stress analysis, although stress discrepancies were found in part time point and some region of mandible between preoperative model and postoperative model, the direction and topography of main stress were basically at equal pace. Main stress distributed beside external oblique line and concentrates at the neck of condyle. There was no significant difference of stress conduction and distribution between preoperative and postoperative models.

CONCLUSIONSCompared with preoperative model, postoperative model has different transduction phases of stress, but has almost the same tolerance extents of main stress.

Female ; Finite Element Analysis ; Humans ; Imaging, Three-Dimensional ; methods ; Mandible ; physiopathology ; surgery ; Osteotomy ; Stress, Mechanical

OBJECTIVETo study the changes of masseter muscle after reducing the mandibular by measuring some relative index after ostectomy of the mandibular angle along arch line.

METHODSLeft mandibular angle ostectomy was performed on New Zealand female rabbits aged three months. The right was not operated as control groups. Five rabbits were examined at the following intervals: 2, 4, 8, 12 and 24 weeks.

RESULTSThere were remarkable decreases in the experimented masseter muscle masses and the same type muscle fiber areas compared with the control group (P < 0.05). As for the fiber types, a decrease in type I fibers and an increase in type II fibers were noticed on operative side masseters (P <0.05). Sarcomere lengths in the operative side muscles were significantly reduced and showed statistical significance during first 4 weeks (P < 0.05), but there was no difference between the operative group and the control group after 8 weeks (P > 0.05).

CONCLUSIONSThe changes of masseter fibres show reconstruction of masseter muscle after mandibular angle ostectomy.

Animals ; Female ; Mandible ; physiopathology ; surgery ; Masseter Muscle ; physiology ; Oral Surgical Procedures ; Postoperative Period ; Rabbits

Anterior disc displacement is a common subtype seen in temporomandibular disorders (TMD) patients. It may cause mandibular movement disorders, such as clicking of joint, intermittent closed lock, limitation of mouth opening, etc. These disorders may affect the life qualities of patients. Anterior disc displacement may also cause mandibular malformations, especially among adolescents, which may affect the growth of condyle, therefore may have a correlation with mandibular retrusion or mandibular deviation when grown up. This paper going to review the influences of anterior disc displacement on oral mandibular function and morphology and their biological mechanisms.
Adolescent ; Humans ; Mandible ; abnormalities ; pathology ; Mandibular Condyle ; growth & development ; Mandibular Diseases ; etiology ; Movement ; Retrognathia ; etiology ; Temporomandibular Joint Disorders ; etiology ; physiopathology

Biodynamics of mandibular angle fractures has been extensively discussed in the literature in search for the best way to fixate and expedite recovery of trauma patients. Pioneers like Michelet and Champy had the greatest impact on evolving of osteosynthesis in maxillofacial traumatology; they introduced their basic principles frequently used to describe the biomechanics of mandibular fixation. Their concept states when a physiologic load is applied on mandibular teeth a negative tension will be created at superior border and a positive pressure will appear at inferior border. These simple definitions are the basis for the advent of fixation modalities in mandibular angle fracture. This article sought to reassess these principals based on load location via finite elements method.
Biomechanical Phenomena ; Dental Stress Analysis ; Finite Element Analysis ; Fracture Fixation, Internal ; methods ; Humans ; Mandible ; physiopathology ; Mandibular Fractures ; physiopathology ; surgery ; Tooth ; physiology

OBJECTIVE: To investigate the stress distribution to the mandible, with and without impacted third molars (IM3s) at various orientations, resulting from a 2000-Newton impact force either from the anterior midline or from the body of the mandible. MATERIALS AND METHODS: A 3D mandibular virtual model from a healthy dentate patient was created and the mechanical properties of the mandible were categorized to 9 levels based on the Hounsfield unit measured from computed tomography (CT) images. Von Mises stress distributions to the mandibular angle and condylar areas from static impact forces (Load I-front blow and Load II left blow) were evaluated using finite element analysis (FEA). Six groups with IM3 were included: full horizontal bony, full vertical bony, full 450 mesioangular bony, partial horizontal bony, partial vertical, and partial 450 mesioangular bony impaction, and a baseline group with no third molars. RESULTS: Von Mises stresses in the condyle and angle areas were higher for partially than for fully impacted third molars under both loading conditions, with partial horizontal IM3 showing the highest fracture risk. Stresses were higher on the contralateral than on the ipsilateral side. Under Load II, the angle area had the highest stress for various orientations of IM3s. The condylar region had the highest stress when IM3s were absent. CONCLUSIONS High-impact forces are more likely to cause condylar rather than angular fracture when IM3s are missing. The risk of mandibular fracture is higher for partially than fully impacted third molars, with the angulation of impaction having little effect on facture risk.
Adult ; Algorithms ; Biomechanical Phenomena ; Computer Simulation ; Dental Stress Analysis ; Elastic Modulus ; Female ; Finite Element Analysis ; Humans ; Imaging, Three-Dimensional ; Mandible/physiopathology* ; Mandibular Fractures/physiopathology* ; Models, Biological ; Molar, Third/physiopathology* ; Stress, Mechanical ; Tomography, X-Ray Computed