A 3D dynamic finite element analysis of biomechanical behaviour of maxilla and fixative appliances following advancement Le Fort I surgery applied in different lengths.

OBJECTIVES: Dynamic analysis of chewing impact on the stability of rigid fixation techniques following Le Fort I osteotomy has not been investigated in the previous literature. The aim of the present study was to evaluate segmental displacement and von Mises (VM) stress values on the fixation devices following different amounts of Le Fort I advancements under dynamic loading conditions. MATERIALS AND METHODS: The 3D finite element models simulating 3, 5 and 8 mm advancement of maxilla at the Le Fort I level were generated using CBCT scan data. The models included two anterior L plates and two posterior I plates fixations bilaterally. Dynamic finite element analysis was performed to evaluate their biomechanical behavior against chewing cornflakes bio. Von Mises stresses and displacement values on three points were calculated. RESULTS: Calculations were made in a time of 38, 40 and 40.5 ms for 3, 5 and 8 mm advancement models, respectively. As the advancement increased, stress values on the plates and displacement values in the D1 (intersection of the apex of the canine tooth with the osteotomy line), D2 (the most prominent point of zygomatic buttress on the osteotomy line), and D3 (intersection of the midline of the second molar tooth with the osteotomy line) points increased. The lowest stress and displacement values were found in the 3 mm advancement model. As advancement increased, the highest values were found in the I plates. The stress levels on the plates and screws remained within safe limits. CONCLUSIONS: The von Mises stresses and displacement values tend to increase in according with the amount of advancement. More stress is transferred to posterior I plates and screws under dynamic forces.

How do implant threads and diameters affect the all-on-four success? A 3D finite element analysis study.

BACKGROUND: The effect of different thread designs and diameters on the all-on-four concept is unclear. OBJECTIVE: The aim of the study was to clarify the differences in stress distribution of dental implants with various thread designs and diameters based on the all-on-four concept with three dimensional (3D) finite element analysis (FEA). METHODS: A 3D model of a totally edentulous mandible was used to perform the FEA. Four different models (M1, M2, M3, and M4) including 3.5 and 4.3 mm diameter dental implants with active and passive threaded designs were generated. The dental implants were positioned according to the all-on-four concept. The Von Mises stresses on dental implants and maximum and minimum principal stresses (Pmax and Pmin) on bony structures were calculated under vertical, oblique and horizontal loads. RESULTS: For Von Mises stresses, the highest stress values were detected on the distal implants for all models. Distal implants had also the highest stress values for vertical loading. The Von Mises stresses were found to be concentrated around the implant's neck. In all models the highest Pmax and Pmin stresses occurred in the bone surrounding the distal implant. It was noted that the active threaded implants showed the highest Pmax and Pmin stress values. CONCLUSION: The implant thread design and diameter might have a strong influence on the stress values in the all-on-four concept.

An Effective Phytoconstituent Aconitine: A Realistic Approach for the Treatment of Trigeminal Neuralgia.

Trigeminal neuralgia pain remains a challenge to treat. Natural compounds may be promising options for relieving pain. This study was aimed at investigating the effects of aconitine in a rat model of trigeminal neuralgia pain. Infraorbital nerve chronic constriction injury was performed in adult Wistar Albino rats. After the neuropathic pain developed, the rats were assigned to one of the treatment groups: carbamazepine 40 or 80 mg/kg; aconitine 0.25, 0.50, or 0.75 mg/kg; or saline injection (control group). Behavioral testing with von Frey filaments and the rotarod test were carried out before the surgical procedure and on the 24th to 29th postoperative days. Following the completion of tests, ipsilateral and contralateral spinal cords were harvested for Western blot analyses to assess NR-1 protein expression. ANOVA followed by Mann-Whitney U test was performed for the statistical analyses. P values of <0.05 were considered significant. Aconitine significantly reduced mechanical sensitivity in a dose-dependent manner. A significant reduction in motor coordination was noted for the higher doses of aconitine which was similar with the 40 and 80 mg/kg doses of carbamazepine. NR-1 expression was reduced in the ipsilateral spinal cord, whereas no significant difference was noted between the groups in the expression of NR-1 in the contralateral spinal cord. Aconitine had a significant pain relieving effect, which was similar to carbamazepine, in a dose-dependent manner. Aconitine may be an alternative pharmacological agent for the control of trigeminal neuralgia pain.

Does the angulation of the mandibular third molar influence the fragility of the mandibular angle after trauma to the mandibular body? A three-dimensional finite-element study.

The relationship between mandibular third molar (M3) angulation and mandibular angle fragility is not well established. The aim of this study was to evaluate the impact of M3 angulation on the mandibular angle fragility when submitted to a trauma to the mandibular body region. A three-dimensional (3D) mandibular model without M3 (Model 0) was obtained by means of finite-element analysis (FEA). Four models were generated from the initial model, representing distoangular (Model D), horizontal (Model H), mesioangular (Model M) and vertical (Model V) angulations. A blunt trauma with a magnitude of 2000 N was applied perpendicularly to the sagittal plane in the mandibular body. Maximum principal stress (Pmax) (tensile stress) values were calculated in the bone. The lowest Pmax stress values were noted in Model 0. When the M3 was present extra stress fields were found around marginal bone of second molar and M3. Comparative analysis of the models with M3 revealed that the highest level of stress was found in Model V, whereas Model D showed the lowest stress values. The angulation of M3 affects the stress levels in the mandibular angle and has an impact on mandibular fragility. The mandibular angle becomes more fragile in case of vertical impaction when submitted to a trauma to the mandibular body region.

Coronal Split Corpus Osteotomy of the Mandible: A Modified Visor Osteotomy Technique for Bone Volume Enhancement.

The bony augmentation of severely atrophied mandible is generally required for the purposes of prosthetic rehabilitations. The treatment strategies have been well defined in the literature ranging from osteotomy techniques to distraction osteogenesis. Visor osteotomy is the milestone of the reconstructive surgery for the atrophied mandible which has received some modifications. In the present study, the authors describe a new modification of visor osteotomy in which a complete coronal split osteotomy down to the inferior border at the mental region has been performed. The main advantage of this modification is to preserve the lingual cortex from the inferior border of the mandible up to the alveolar region without disturbance of the suprahyoid muscle attachments. The procedure is thought to be a "highly sensitive" one and undesired fractures may occur during splitting of the bony segments.

Biomechanical Evaluation of Different Fixation Methods for Mandibular Anterior Segmental Osteotomy Using Finite Element Analysis, Part One: Superior Repositioning Surgery.

The aim of the current study was to comparatively evaluate the mechanical behavior of 3 different fixation methods following various amounts of superior repositioning of mandibular anterior segment. In this study, 3 different rigid fixation configurations comprising double right L, double left L, or double I miniplates with monocortical screws were compared under vertical, horizontal, and oblique load conditions by means of finite element analysis. A three-dimensional finite element model of a fully dentate mandible was generated. A 3 and 5 mm superior repositioning of mandibular anterior segmental osteotomy were simulated. Three different finite element models corresponding to different fixation configurations were created for each superior repositioning. The von Mises stress values on fixation appliances and principal maximum stresses (Pmax) on bony structures were predicted by finite element analysis. The results have demonstrated that double right L configuration provides better stability with less stress fields in comparison with other fixation configurations used in this study.

Biomechanical Evaluation of Different Fixation Methods for Mandibular Anterior Segmental Osteotomy Using Finite Element Analysis, Part Two: Superior Repositioning Surgery With Bone Allograft.

In this study, the biomechanical behavior of different fixation methods used to fix the mandibular anterior segment following various amounts of superior repositioning was evaluated by using Finite Element Analysis (FEA). The three-dimensional finite element models representing 3 and 5 mm superior repositioning were generated. The gap in between segments was assumed to be filled by block bone allograft and resignated to be in perfect contact with the mandible and segmented bone. Six different finite element models with 2 distinct mobilization rate including 3 different fixation configurations, double right L (DRL), double left L (DLL), or double I (DI) miniplates with monocortical screws, correspondingly were created. A comparative evaluation has been made under vertical, horizontal and oblique loads. The von Mises and principal maximum stress (Pmax) values were calculated by finite element solver programme. The first part of our ongoing Finite Element Analysis research has been addressed to the mechanical behavior of the same fixation configurations in nongrafted models. In comparison with the findings of the first part of the study, it was concluded that bone graft offers superior mechanical stability without any limitation of mobilization and less stress on the fixative appliances as well as in the bone.

Hounsfield unit comparison of grafted versus non-grafted extraction sockets.

Volumetric changes of the alveolar ridge after socket preservation with various techniques have been investigated frequently. However, changes in bone density and quality of bone within the extraction sockets have seldom been studied. The purpose of this study was to evaluate the bone quality of grafted versus non-grafted socket sites prior to dental implant placement using Hounsfield unit (HU) values derived from cone-beam computed tomography (CBCT) imaging. The data was collected from 39 healed extraction sites reviewed over a one-year period. Subjects eligible for the study had a bone replacement graft and barrier membrane. Both study and control groups had CBCT scans performed immediately after extraction and four to five months after extraction for planning implant placement. HU values were measured from the CBCT scans and compared between groups. Intragroup variability was assessed utilizing standard deviation and standard error of the mean. Intergroup differences were evaluated using unpaired t-test. A generalized lack of significant difference in bone quality was observed between groups with the only statistically significant difference observed in the posterior maxilla. Future radiographic and histologic assessments of bone quality after socket preservation are required to determine the 'ideal' approach to preserve an extraction socket prior to implant placement.

J-bone graft for the reconstruction of the jaws.

The J-bone graft technique has been used for the reconstruction of glenoid surfaces with significant bone loss in orthopedic surgery in which the J-shaped bicortical bone graft is harvested from the iliac crest. Because of the osteotomy design, the press-fit fixation into the defect is obtained. In this technical note, the authors adopted this technique to oral and maxillofacial surgery and described the technique for the reconstruction of the jaws.

Evaluation of bone graft harvesting techniques from anterior ilium.

Autogenous bone harvest from the anterior ilium is a common procedure in the surgical field. In the current study, a retrospective analysis was performed regarding the bone graft harvesting techniques from the anterior ilium. The retrospective analysis with a 1-year period included 16 patients who had undergone iliac bone grafting for oral and maxillofacial reconstruction. Medial and lateral approaches were assessed. No major complications were observed. One patient undergoing medial approach and 2 patients undergoing lateral approach experienced gait disturbances at the postoperative period. Harvesting bone from the anterior ilium did not result in greater donor site morbidity or complications in the early term. The medial approach revealed an earlier recovery time than the lateral one. Anterior ilium is a good choice for the reconstruction of jaws, but donor site morbidity remains a problem and should be considered in the treatment plan.

Dental treatment of a patient with central sleep apnea and phobic anxiety under sedation: report of a case and clinical considerations.

Central sleep apnea (CSA) results from a reduction in lack of output from the central respiratory generator in the brainstem, manifesting as apneas and hypopneas without discernible efforts. CSA can lead to hypercarbia, arrhythmias, pulmonary hypertension, and heart failure. Indeed, the patient may develop a disturbed breathing during sedation procedures. We report a patient who was diagnosed with CSA and had been on continuous positive airway pressure (CPAP) therapy for 5 years. He was referred for multiple tooth extractions under sedation owing to severe gag reflex and phobic anxiety disorder. The treatment was completed uneventfully under N(2)O and sevoflurane inhalation accompanied by midazolam and ketamine induction. The role of sedative, analgesic, and anesthetic agents as a precipitating factor for CSA is of particular concern. The combined administration of midazolam, ketamine, sevoflurane, and N(2)O/O(2) is a useful and safe option for patients requiring sedation.

Unusually severe limitation of the jaw attributable to fibrodysplasia ossificans progressiva: a case report with cone-beam computed tomography findings.

Fibrodysplasia ossificans progressiva (FOP) is a rare hereditary connective tissue disease characterized by the progressive ectopic ossification of ligaments, tendons, and facial and skeletal muscles throughout life. Symptoms begin in childhood as localized soft tissue swellings. Immobility and articular dysfunction appear with involvement of the spine and proximal extremities. The temporomandibular joint (TMJ) is a critical component involved in the maxillofacial region, resulting in severe limitation of masticatory function, although TMJ involvement is rare. We report a case of FOP presenting as severely limited TMJ movements owing to ectopic calcification of the left coronoid process. In addition to the clinical examination, panoramic radiography and cone-beam computed tomography images were obtained. The case is presented and the clinical and imaging findings, differential diagnosis, and treatment modalities are discussed.