Comparative analysis of the biomechanical behavior of the maxillary central incisors restored with glass fiber post and cast metal post and core submitted to orthodontic forces: A study with finite elements.

INTRODUCTION: Different types of intraradicular restorations and their insertion have an impact on teeth biomechanics. This study aimed to analyze the biomechanical behavior of maxillary central incisors restored with glass fiber post (GFP) and cast metal post and core (CMP) subjected to buccolingual and mesiodistal orthodontic forces using the finite element method. METHODS: Two models of the maxillary central incisor with periodontal ligament, cortical bone, and trabecular bone were made. One of the models included intraradicular restoration with GFP, whereas, in the other, the incisor was restored with CMP. After creating the tridimensional mesh of finite elements, applying 2 orthodontic forces were simulated: 65 g of buccolingual force and 70 g of mesiodistal force. The forces were applied parallel to the palatal plane in the region of the bracket slot, located 4 mm to the incisal edge. RESULTS: The maximum stresses generated in the GFP-restored root were 3.642 × 10-1 MPa and 4.755 × 10-1 MPa from the buccolingual and mesiodistal forces, respectively. Likewise, the stresses in the CMP restored root were 2.777 × 10-1MPa and 3.826 × 10-1MPa. The radicular area with higher stress on both models was located in the cervical third: on the buccal surface when the buccolingual force was applied and on the mesial surface when the mesiodistal force was applied. The highest stress levels were found on the CMP structure. CONCLUSIONS: The incisor restored with cast metal post revealed lower stress values transferred to the root than the one restored with GFP. The stresses on the structure of the GFP were lower and more homogeneous than the ones found on the cast metal post. The difference among the stress values in the materials is within a safe margin for using both materials in relation to orthodontic forces.

Mechanical stress distribution over the palate by different pacifiers assessed by finite element analysis and clinical data.

The mechanical behavior of each type of pacifier on rigid structures and their various impacts on orofacial growth have yet to be discovered. The study aimed to evaluate the stress distribution over a child's palate by three types of pacifiers using finite element analysis and clinical and laboratory data. Modulus of elasticity was obtained from 30 specimens comprising 10 of each conventional (A), orthodontic (B), and breast-shaped (C) pacifiers. Tongue strength was assessed in eight 3-year-old children (kPa). A hemi-maxilla model was obtained from 2- to 3-year-old skull tomography, and the images of pacifiers A, B, and C were captured using 3D scanning. The Hypermesh® program generated a mesh of 6-node tetrahedral elements for applying forces in the X, Y, and Z directions to enable a nonlinear analysis. Pacifier B exhibited the highest values for distributed stress on the palate, followed by pacifier A. Pacifier B stimulated the maxilla forward and sideways. In contrast, pacifier A promoted a forward and upward load, favoring a more atresic palate. Pacifiers A and B tended to rotate in the sagittal plane, generating tensions in the anterior incisors and favoring the open bite. Pacifier C exhibited lateral expansion by stress induction over the mid-palatal suture with less influence on incisor inclination. Pacifiers showed different detrimental stress distributions on the palate. This information can be helpful for improving recommendations given to parents.

In Silico Mechanical Effort Analysis of the All-On-4 Design Performed With Platform-Switching Distal Short Dental Implants.

Short dental implants with platform matching connection have been used for the rehabilitation of atrophic jaws whenever standard-length dental implants cannot be placed without prior bone augmentation. Yet, there remains a lack of data regarding the risk of technical failures when the all-on-4 configuration is performed in atrophic jaws with platform-switching distal short dental implants. Thus, the current study used the finite element method to evaluate the mechanical behavior at the level of the prosthetic components of the all-on-4 concept performed in atrophic mandible using short-length distal implants with platform switching (PSW) connection. Three models of the all-on-4 configuration were generated in human atrophic mandibles. The geometric models consisted of PSW connection tilted standard (AO4T; θ = 30 deg; 11 mm-length), straight standard (AO4S; θ = 0 deg; 11 mm-length) and straight short (AO4Sh; θ = 0 deg; 8 mm-length) distal implants. A resultant force of 300 N was performed obliquely in the left side and posterior region of the prosthetic bar. The von Mises equivalent stress (σvm) and maximum and minimum principal stresses (σmax and σmin) were performed at level of the prosthetic components/implants and peri-implant bone crest, respectively. The general displacement of the models was also evaluated. The stress analysis was performed on the side of load application. The AO4S configuration showed the lowest values of σvm in the mesial left (ML) and distal left (DL) abutments (37.53 MPa and 232.77 MPa, respectively) and dental implants (91.53 MPa and 231.21 MPa, respectively). The AO4Sh configuration showed the highest values of σvm in the bar screw (102.36 MPa), abutment (117.56 MPa), and dental implant (293.73 MPa) of the ML area. Among the models, the highest values of σmax and σmin were noticed in the peri-implant bone crest of the AO4T design (131.48 MPa and 195.31 MPa, respectively). All models showed similar values of general displacements, which were concentrated in the mandible symphysis. The all-on-4 configurations designed with PSW connection and tilted standard (AO4T; θ = 30 deg; 11 mm-length), straight standard (AO4S; θ = 0 deg; 11 mm-length) or straight short (AO4Sh; θ = 0 deg; 8 mm-length) distal implants were not associated with higher odds of technical failures. The AO4Sh design may be a promising option for the prosthetic rehabilitation of atrophic jaws.

Crown Material and Occlusal Thickness Affect the Load Stress Dissipation on 3D Molar Crowns: Finite Element Analysis

PURPOSE: To compare the mechanical behavior (stress load dissipation and/or concentration) of posterior crowns made from Lava Ultimate (LU; 3M ESPE) and IPS e.max CAD (LD; Ivoclar Vivadent) using finite element analysis (FEA). MATERIALS AND METHODS: A 3D model of a mandibular first molar was prepared by reducing the occlusal surface by 1 or 2 mm (according to group), the axial walls by 1.5 mm, and using a 0.8-mm-deep shoulder margin as a finish line. A convergence of 6 degrees between opposing walls was set. Subsequently, four 3D crown models were created according to two test groups with two different occlusal thicknesses: (1) LD with 1.0 mm (LD1); (2) LD with 2.0 mm (LD2); (3) LU with 1.0 mm (LU1); and (4) LU with 2.0 mm (LU2). FEA models were constructed using the software Femap (Siemens). A load of 200 N was applied in the axial and oblique (20 degrees) directions for each group, and stress dissipation was viewed using the NEi Nastran software. RESULTS: FEA results demonstrated that the LU crowns dissipated the occlusal load to the tooth structure, whereas the LD material concentrated the load inside the crowns. For the LU material, the lower the occlusal thickness, the higher the stress concentration inside the crown became, and the 2.0-mm occlusal thickness transferred lower stress to the tooth structure. The oblique, rather than the vertical, load caused an increase in the maximum stress concentration at the shoulder margin and axial walls. CONCLUSION: The higher the Young's Modulus mismatch between the crown material and substrate, the higher the load stress concentration inside the material became. The 2-mm occlusal thickness acted by decreasing the load stress to the tooth substrate. Finally, the axial load delivered more favorable stress transmission to the tooth substrate. The crown material and the occlusal thickness appear to be two factors that affect the mechanical behavior of stress dissipation to the tooth structure.

The Hyrax appliance with tooth anchorage variations in surgically assisted rapid maxillary expansion: a finite element analysis.

PURPOSE: It is known that a correct transverse maxillary dimension is a key factor for a stable occlusion, which brings functional and esthetic benefits for the patient. In patients presenting maxillary atresia and the completion of bone growth, a highly recommended option for correction is the surgically assisted rapid maxillary expansion (SARME) associated with the Hyrax appliance. The objective of this study was to evaluate the influence of tooth anchorage variations of the Hyrax appliance in SARME through finite element analysis, evaluating which anchorage option might be associated with more effective orthopedic results with less undesired side effects. METHODS: Five different dental anchoring conditions for the Hyrax appliance were simulated through FE analysis applying premolars and molars as anchorage, having the same force applied by the activation of the Hyrax screw (0.5 mm) in all groups. The maxillary displacement results (axes X, Y, and Z) and generated stresses for both teeth and maxillary bone were calculated and represented using a color scale. RESULTS: All groups presented significant bone displacement and stress concentration on anchoring teeth, with the group presenting anchorage in the 1st and 2nd molars showing the greatest maxillary horizontal displacement (axis X) and suggesting the lowest tendency of dental vestibular inclination. CONCLUSIONS: Variations in dental anchorage might substantially affect the maxillary bone and teeth displacement outcome. The protocol for the Hyrax apparatus in SARME applying the 1st and 2nd molars as anchorage might generate less tilting and inclination of the anchoring teeth.

Biomechanics of internal connection in mandibular implant-supported prosthesis under effect of loadings and number of implants: A 3D finite element analysis.

INTRODUCTION: The success of bone-implant prostheses depends on several factors, among them an adequate distribution and passive adaptation of occlusal loading. OBJECTIVE: this study evaluated the stress distribution in mandibular implant-supported prosthesis with internal connection morse taper interface, under effect of number of implants (4 or 5) and loadings (bilateral 100 N, bilateral 300 N). MATERIALS AND METHODS: the virtual models were subjected to analysis by 3D finite element method, across four experimental conditions. RESULTS: The stress values were evenly distributed to the peri-implant bone and implants in all simulated conditions. Stress values did not increase in the same proportion as the increase in the applied load (from 100 to 300 N). The stress value was 1.1 times higher on the implants and nearly doubled (1.5-2 times) on the peri-implant bone. CONCLUSION: For mandibular implant-supported prosthesis, the morse taper interface is strongly recommended, with similar mechanical demand for four and five implants in both loading conditions. Five implants offered no additional benefit over four implants. The commercial pure titanium frameworks presented stress values close to the yield strength of the metal, especially at the intersection with the cantilever.

A New Proposal for Calibrated Gauges for Removable Partial Dentures: A Finite Element Analysis.

AIM: The aim of this study was to evaluate the stress distribution of a planned removable partial denture (RPD) using new proposals for calibrated gauges of 0.3 mm and 0.35 mm undercuts through the three-dimensional (3D) finite element methodology, and compare them with 0.25 mm and 0.5 mm gauges that are already existing in clinical practice. MATERIALS AND METHODS: Kennedy class-I edentulous 3D models and their respective RPDs (InVesalius software; Rhinoceros and SolidWorks CAD) were created and exported to the finite element program HyperMesh 2019 for mesh configuration. In the following steps, axial loading (0º) of 40 N per point was performed, with 3 points on the molars and 2 points on the premolars, totaling 280 N unilaterally. The model was processed by the OptiStruct 2019 software and imported into the HyperView 2019 software to obtain the stress maps (MPa). RESULTS: The use of 0.30 and 0.35 mm calibrated gauges presented tensions similar to those with the 0.25 mm gauge (gold standard) and caused no significant damage to biological structures. The use of a 0.5 mm undercut caused greater traction force in the periodontal ligament of the abutments. CONCLUSIONS: The 0.35 mm undercut seems promising as it presented more favorable results in this simulation, on the other hand, a 0.5 mm undercut is greater than that necessary for retainers made of CoCr. CLINICAL SIGNIFICANCE: This study aims to measure a new undercut gauge (0.35 mm) to increase the retention area in abutment teeth of removable partial dentures.

Biomechanical Evaluation of Different Implant-Abutment Connections, Retention Systems, and Restorative Materials in the Implant-Supported Single Crowns Using 3D Finite Element Analysis.

This is an in silico study aimed to evaluate the biomechanical influence of different implant-abutment interfaces (external hexagon and Morse taper implants), retention systems (cement and screw retained), and restorative crowns (metal-ceramic and monolithic) using 3-dimensional finite element analysis (3D-FEA). Eight 3D models were simulated for the maxillary first molar area using InVesalius, Rhinoceros, and SolidWorks and processed using Femap and NEi Nastran software. Axial and oblique forces of 200 and 100 N, respectively, were applied on the occlusal surface of the prostheses. Microstrain and von Mises stress maps were used to evaluate the deformation (cortical bone tissue) and stress (implants/fixation screws/crowns), respectively, for each model. For both loadings, Morse taper implants had lower microstrain values than the external hexagon implants. The retention system did not affect microstrain on the cortical bone tissue under both loadings. However, the cemented prosthesis displayed higher stress with the fixation screw than the external hexagon implants. No difference was observed between the metal-ceramic and zirconia monolithic crowns in terms of microstrain and stress distribution on the cortical bone, implants, or components. Morse taper implants can be considered as a good alternative for dental implant rehabilitation because they demonstrated better biomechanical behavior for the bone and fixation screw as compared to external hexagon implants. Cement-retained prosthesis increased the stress on the fixation screw of the external hexagon implants, thereby increasing the risk of screw loosening/fracture in the posterior maxillary area. The use of metal-ceramic or monolithic crowns did not affect the biomechanical behavior of the evaluated structures.

New highlights on effects of rapid palatal expansion on the skull base: a finite element analysis study.

OBJECTIVE: The objective of this study was to evaluate the effect of the rapid palatal expansion (RPE) on the pterygoid process (PP), spheno-occipital synchondrosis (SOS) and sella turcica (ST) in the skull of a patient with transversal maxillary collapse, and identify the distribution of mechanical stresses and displacement, by finite element analysis (FEA). METHODS: Cone-beam computed tomography (CBCT) was employed to examine the skull of a patient in this study. The patient was a 13-year-old boy, with Class II skeletal relationship due to transverse atresia and maxillary protrusion. The computer-aided design (CAD) geometry of skull was imported into the SimLab v. 13.1 software, to build the finite element mesh. For the simulation, a displacement of 1 mm, 3 mm and 5 mm in a transverse direction was defined at the midpalatal suture, thereby representing the RPE. For the analysis of results, maximum principal stress (MPS) and displacements were evaluated by identifying different nodes, which were represented by the points as per the areas of interest in the study. RESULTS: In MPS, the maximum tensile stress was found at point 2 (366.50 MPa) and point 3 (271.50 Mpa). The maximum compressive stress was found at point 8 (-5.84 Mpa). The higher displacements in the transversal plane and the lateral segment were located at point 1 (2.212 mm), point 2 (0.903 mm) and point 3 (0.238 mm). CONCLUSIONS: RPE has a direct effect on PP, SOS and ST in the Class II model skeletal relationship with a transversal maxillary collapse. PP supported a higher tensile stress and displacement.

Influence of the hyrax expander screw position on displacement and stress distribution in teeth: A study with finite elements.

INTRODUCTION: This study aimed to simulate the different positions of the hyrax appliance expander screw and evaluate tooth displacement and the stress distribution standard on the periodontal ligament using the finite element method. METHODS: Part of the maxilla with anchorage teeth, periodontal ligament, midpalatal suture, and the hyrax appliance was modeled, and finite element method models were created to simulate 6 different screw positions. There were 2 vertical positions at distances of 20 mm and 15 mm from the occlusal plane. Another position was anteroposterior, the center of the screw placed between and equidistant from the mesial face of the first molar and the distal face of the first premolar, aligned to the center of the crown of the first molar, with the anterior edge of the screw aligned to the distal face of the first molar. A 1 mm activation of the expander screw was simulated. The displacement (total, vertical, and buccolingual) and the stress distribution on the periodontal ligament of supporting teeth in each model were registered. RESULTS: The model simulating the expander screw in a more occlusal and anterior position presented higher displacement values and higher stress concentration, followed by the model with the screw in a more posterior but same vertical position. With the exception of the first premolar, the teeth presented cervical-apical displacement in the vestibular face and apical-cervical displacement in palatal faces. This displacement is compatible with the vestibular inclination associated with the activation of the expander screw. The first premolar presented an atypical tendency for the mesial and lingual displacement of the vestibular surface and counterclockwise rotation. CONCLUSIONS: The supporting teeth presented a tendency for vestibular crown displacement and lingual root displacement associated with compression areas in the vestibular-cervical region and tensile strength in the linguoapical region. Placing the expander screw in a more occlusal and anterior position generated more mechanical stress transfer, resulting in greater dental displacement.

Advances in Bone tissue engineering: A fundamental review.

Bone is a dynamic tissue that can always rebuild itself by modeling and remodeling to maintain functionality. This tissue is responsible for several vital functions in the body, such as providing structural support for soft tissues and the body, being the central region of hematopoiesis in human adults, and contributing to mineral homeostasis. Besides, it has an innate ability of auto-regeneration when damaged. All of these processes involve several molecular cues related to biochemical and mechanical stimulus. However, when the lesion is complicated or too big, it is necessary to intervene surgically, which may not effectively solve the problem. Bone tissue engineering seeks to provide resources to resolve these clinical issues and has been advancing in recent years, presenting promising devices for bone tissue repair. The understanding of some important biofactors and bone stem-cells influence might be crucial for an effective regenerative medicine, since bone is one of the most transplanted tissues. So, the purpose of this article is to provide an overview of the bone tissue, including the role of stem cells and some of the bioactive molecules associated with these processes. Finally, we will suggest future directions for bone tissue engineering area that might be helpful in order to produce biomimetic bone substitutes that become a real alternative to translational medicine.

Effect of bone quality and bone loss level around internal and external connection implants: A finite element analysis study.

STATEMENT OF PROBLEM: A consensus regarding the biomechanical effects of vertical bone loss in normal and osteoporotic bone tissue according to different implant-abutment interfaces is lacking. PURPOSE: The purpose of this finite element analysis study was to evaluate the effect of vertical bone loss (without bone loss; with 1.5-mm bone loss; with 3-mm bone loss; and with 4.5-mm bone loss) in normal and osteoporotic bone that received a Ø4×10-mm implant with different implant-abutment connections (external connection [external hexagon] and internal connection [Morse taper]) by using 3D finite element analysis. MATERIAL AND METHODS: Sixteen 3D models were simulated. Axial and oblique forces of 200 N and 100 N, respectively, were applied on the occlusal surfaces of the prostheses. Maximum principal stress and microstrain were determined from the bone tissue of each model. von Mises stress analysis was used to evaluate the stress distribution in implants and prosthetic components (fixation screws, abutment, and crown). RESULTS: The results showed higher stress concentrations in models with bone loss as increased vertical bone loss contributed to higher stress and microstrain in the bone tissue, regardless of the quality of bone and implant-abutment connection. Osteoporotic bone contributed to increase in microstrain in the trabecular bone. The internal connection showed lower stress than the external connection implants only in models without marginal bone loss. Furthermore, higher stress concentrations were observed in the implants and fixation screws in models with increased bone loss and external connection implants, mainly under oblique loading. Osteoporotic bone did not affect stress distribution in the implants and prosthetic components. CONCLUSIONS: Progressive bone loss contributed to higher stress in the bone tissue, implants, and prosthetic components. The osteoporotic bone affects only the microstrain in the trabecular bone, but not the stress in the implants and prosthetic components. The internal connection implants showed lower stress in the cortical bone only in models without bone loss, while external connection implants exhibited higher stress in the implants and screws under oblique loading.

Influence of Different Implants on the Biomechanical Behavior of a Tooth-Implant Fixed Partial Dentures: A Three-Dimensional Finite Element Analysis.

This study analyzed the biomechanical behavior of rigid and nonrigid tooth-implant supported fixed partial dentures. Different implants were used to observe the load distribution over teeth, implants, and adjacent bone using three-dimensional finite element analysis. A simulation of tooth loss of the first and second right molars was created with an implant placed in the second right molar and a prepared tooth with simulated periodontal ligament (PDL) in the second right premolar. Configurations of two types of implants and their respective abutments-external hexagon (EX) and Morse taper (MT)-were transformed into a 3D format. Metal-ceramic fixed partial dentures were constructed with rigid and nonrigid connections. Mesh generation and data processing were performed on the 3D finite element analysis (FEA) results. Static loading of 50 N (premolar) and 100 N (implant) were applied. When an EX implant was used, with a rigid or nonrigid connection, there was intrusion of the tooth in the distal direction with flexion of the periodontal ligament. Tooth intrusion did not occur when the MT implant was used independent of a rigid or nonrigid connection. The rigid or nonrigid connection resulted in a higher incidence of compressive forces at the cortical bone as well as stress in the abutment/pontic area, regardless of whether EX or MT implants were used. MT implants have a superior biomechanical performance in tooth-implant supported fixed partial dentures. This prevents intrusion of the tooth independent of the connection. Both types of implants studied caused a greater tendency of compressive forces at the crestal area.

Effect of Different Framework Materials in Implant-Supported Fixed Mandibular Prostheses: A Finite Element Analysis.

PURPOSE: To evaluate the biomechanical behaviors of different framework materials in implant-supported fixed mandibular prostheses using three-dimensional (3D) finite element analysis. MATERIALS AND METHODS: A model of a severely resorbed edentulous mandible was obtained from a tomography database. Morse taper-connection implants and multi-unit abutments were cut with an electro-erosion machine and scanned using a 3D scanner. The implants were positioned on the model at the bone level and distributed equally to support a fixed complete prosthesis. The simulations were divided into six groups according to the framework material: titanium (Ti); cobalt-chromium (Co-Cr); zirconia (ZrO2); polyether ether ketone (PEEK); carbon fiber-reinforced polyether ether ketone (CFR-PEEK); and polymethyl methacrylate (PMMA). The resultant load applied was obtained from the masseter, temporal, lateral, and medial pterygoid muscles. The principal stresses and von Mises equivalent stresses were analyzed and compared among the framework materials, and the results were described both quantitatively and qualitatively. RESULTS: PEEK and PMMA frameworks showed the highest total deformation values, showing decreases of von Mises stresses in the frameworks, implants, and abutments, but with a high tensile stress in the trabecular bone that achieved critical values. CFR-PEEK frameworks achieved their failure limit, whereas the ZrO2, Co-Cr, and Ti frameworks exhibited principal stresses in the bone region within physiologic limits. CONCLUSION: From a biomechanical point of view, the Ti, Co-Cr, and ZrO2 frameworks demonstrated the most favorable outcomes.

Influence of the hyrax expander screw position on stress distribution in the maxilla: A study with finite elements.

INTRODUCTION: Our objective was to evaluate the stress and deformation distribution patterns on the maxillary bone structure using the finite element method by simulation of different vertical and anteroposterior positions of the expansion screw on the hyrax expander appliance. METHODS: Part of the maxilla with anchorage teeth, midpalatal suture, and the hyrax appliance were modeled, and 6 distinct finite element method models were created to simulate different positions of the expansion screw. There were 2 vertical positions at distances of 20 and 15 mm from the occlusal plane. Another 3 positions were anteroposterior, with the center of the screw placed between and equidistant from the mesial face of the first molar and the distal face of the first premolar, aligned to the center of the crown of the first molar, and the anterior edge of the screw aligned to the distal face of the first molar. The initial activations of the expanders were simulated, and the stress distributions on the maxilla in each model were registered. RESULTS: The stress was concentrated in the anterior region of the models, close to the incisive foramen, dissipating through the palate in the posterior and lateral orientations, in the direction of the pterygoid pillar, diverting from the midpalatal suture region. When the expander screw was simulated closer to the occlusal plane and in a more anterior position, more stress was located around the incisive foramen and distributed through the midpalatal suture to its posterior portion. More posterior positions resulted in concentrated stress around the pterygoid pillars. At all simulations, the midpalatal suture showed a V-shaped expansion, with the vertex superior in the coronal view and posterior in the axial view. CONCLUSIONS: Different positions of the expander screw interfered with stress intensity and distribution patterns. When the expansion screw was simulated in a more occlusal and anterior position, it was more efficient to transfer the mechanical effects from the appliance to the bone structures.

Splinted and Nonsplinted Crowns with Different Implant Lengths in the Posterior Maxilla by Three-Dimensional Finite Element Analysis.

The aim of this study was to evaluate stress distribution in the implants/components and bone tissue for splinted and nonsplinted prostheses with different lengths of implants using three-dimensional finite element analysis. Six models from the posterior maxillary area were used in simulations. Each model simulated three Morse taper implants of 4.0 mm diameter with different lengths, which supported metal-ceramic crowns. An axial load of 400 N and an oblique load of 200 N were used as loading conditions. Splinted prostheses exhibited better stress distribution for the implants/components, whereas nonsplinted prostheses exhibited higher stress in the first molar under axial/oblique loading. Implant length did not influence stress distribution in the implants/components. In cortical bone tissue, splinted prostheses decreased the tensile stress in the first molar, whereas nonsplinted prostheses were subjected to higher tensile stress in the first molar; implant length had no influence on stress distribution. Within the limitations of this study, we conclude that splinted prostheses contributed to better stress distribution in the implant/abutment and cortical bone tissue; however, the reduction in the implant length did not influence the stress distribution.

Numerical model proposed for a temporomandibular joint prosthesis based on the recovery of the healthy movement.

The temporomandibular joint (TMJ) is an anatomical set of the buco-maxillary system that allows the movement of the mandible in most varied ways. Several factors can influence the malfunctioning of the joint and lead to the use of a total prosthesis. However, current prostheses do not supply the maximum amplitude of movement during protrusion and opening, due to mainly the anatomical differences between patients. For this reason, this article aims to study the patient's kinematic characteristics for a better comprehension of the problem and, consequently, to develop a numerical model for TMJ prostheses able to recover the healthy movement. The numerical model is based on the development of a mechanical joint whose profile is able to reproduce the movement of the health system. The results obtained through the developed model showed a good agreement with the experimental results, representing, therefore, a promising alternative to approach the problems related to TMJ.

Does lag screw fixation of condylar fractures result in adequate stability? A finite element analysis.

The great incidence and controversies related to the diagnosis, treatment, surgical accesses, and type of osteosynthesis materials confer an outstanding role to condylar fractures among facial fractures. Plate configurations, with diverse formats and sizes, may be used to surgically resolve condylar fractures. With the purpose of improving the advantages and minimizing the disadvantages of fixation techniques, the neck screw was developed aiming at the needed stabilization to render a correct fixation through a system of dynamic compression. This is achieved by increasing the contact between the fractured bone stumps, as well as assisting at the time of fracture reduction. The present paper aims at comparing the fixation and stability of mandibular condylar fractures using the neck screw and an overlaid "L"-shaped-4-hole-2 mm plate on the one hand, with a system in which the neck screw and the "L"-shaped plate form a single structure, having been joined by a welded point, on the other hand. The results with the neck screw are satisfactory, and, thus, it is an alternative for the reduction and fixation of fractures of the mandibular condyle, whether or not a plate is joined to the structure, provided it is correctly prescribed and with adequate surgical sequence and technique.

Parafunctional loading and occlusal device on stress distribution around implants: A 3D finite element analysis.

STATEMENT OF PROBLEM: An occlusal device is frequently recommended for patients with bruxism to protect implant-supported restorations and prevent marginal bone loss. Scientific evidence to support this treatment is lacking. PURPOSE: The purpose of this 3-dimensional (3D) finite element study was to evaluate the influence of an acrylic resin occlusal device, implant length, and insertion depth on stress distribution with functional and parafunctional loadings. MATERIAL AND METHODS: Computer-aided design software was used to construct 8 models. The models were composed of a mandibular bone section including the second premolar and first and second molars. Insertion depths (bone level and 2 mm subcrestal) were simulated at the first molar. Three natural antagonist maxillary teeth and the placement or not of an occlusal device were simulated. Functional (200-N axial and 10-N oblique) and parafunctional (1000-N axial and 25-N oblique) forces were applied. Finite element analysis (FEA) was used to determine the maximum principal stress for the cortical and trabecular bone and von Mises for implant and prosthetic abutment. RESULTS: Stress concentration was observed at the abutment-implant and the implant-bone interfaces. Occlusal device placement changed the pattern of stress distribution and reduced stress levels from parafunctional loading in all structures, except in the trabecular bone. Implants with subcrestal insertion depths had reduced stress at the implant-abutment interface and cortical bone around the implant abutment, while the stress increased in the bone in contact with the implant. CONCLUSIONS: Parafunctional loading increased the stress levels in all structures when compared with functional loading. An occlusal device resulted in the lowest stress levels at the abutment and implant and the most favorable stress distribution between the cortical and trabecular bone. Under parafunctional loading, an occlusal device was more effective in reducing stress distribution for longer implants inserted at bone level. Subcrestally, implant insertion yielded the most favorable biomechanical conditions at the abutment-implant interface and at the coronal surface of the cortical bone, mainly when there was no occlusal device.

Retention System and Splinting on Morse Taper Implants in the Posterior Maxilla by 3D Finite Element Analysis

Abstract The purpose of this study was to evaluate different retention systems (cement- or screw-retained) and crown designs (non-splinted or splinted) of fixed implant-supported restorations, in terms of stress distributions in implants/components and bone tissue, by 3-dimensional (3D) finite element analysis. Four 3D models were simulated with the InVesalius, Rhinoceros 3D, and SolidWorks programs. Models were made of type III bone from the posterior maxillary area. Models included three 4.0-mm-diameter Morse taper (MT) implants with different lengths, which supported metal-ceramic crowns. Models were processed by the Femap and NeiNastran programs, using an axial force of 400 N and oblique force of 200 N. Results were visualized as the von Mises stress and maximum principal stress (σmax). Under axial loading, there was no difference in the distribution of stress in implants/components between retention systems and splinted crowns; however, in oblique loading, cemented prostheses showed better stress distribution than screwed prostheses, whereas splinted crowns tended to reduce stress in the implant of the first molar. In the bone tissue cemented prostheses showed better stress distribution in bone tissue than screwed prostheses under axial and oblique loading. The splinted design only had an effect in the screwed prosthesis, with no influence in the cemented prosthesis. Cemented prostheses on MT implants showed more favorable stress distributions in implants/components and bone tissue. Splinting was favorable for stress distribution only for screwed prostheses under oblique loading.

Resumo O objetivo deste estudo foi avaliar diferentes sistemas de retenção (cimentada x parafusada) e configuração da coroas (unitárias x esplintadas) de próteses fixas implantossuportadas em relação a distribuição de tensões nos implantes/componentes e tecido ósseo pela análise de elementos finitos 3D. Quatro modelos 3D foram simulados com auxílio dos programas Invesalius, e Rhinoceros 3D, e SolidWorks. Os modelos foram confeccionados simulando bloco ósseo de região posterior da maxila (tipo ósseo III), com 3 implantes cone Morse com 4,0 mm de diâmetro e diferentes comprimentos, suportando prótese metalocerâmica de 3 elementos. Os modelos foram processados pelos programas FEMAP e NEiNastran sob força axial de 400 N e oblíqua de 200N. Os resultados foram plotados através de mapas de tensão de von Mises (vM) (implantes e componentes) e tensão máxima principal (TMP) (tecido ósseo). Sobre o carregamento axial, não foi observada diferenças entre os diferentes sistemas de retenção e tipo de prótese na distribuição das tensões nos implantes/componentes, porém, sobre o carregamento oblíquo as próteses cimentadas apresentaram melhor distribuição de tensões em comparação com as próteses parafusadas, enquanto que as próteses esplintadas apresentou uma tendência de redução das tensões no implante do primeiro molar. No tecido ósseo as próteses cimentadas apresentaram melhor distribuição das tensões em comparação com as próteses parafusadas, independente do carregamento. A esplintagem foi favorável somente para as próteses parafusadas, não havendo influência sobre as próteses cimentadas. As próteses cimentadas sobre implantes cone Morse apresentam melhor comportamento biomecânico nos implantes/componentes e tecido ósseo. A esplintagem foi efetiva somente nas próteses parafusadas sob carregamento oblíquo.