Biomechanical analysis of fixation methods for bone flap repositioning after lateral orbitotomy approach: A finite element analysis.

OBJECTIVE: In ophthalmic surgery, different materials and fixation methods are employed for bone flap repositioning after lateral orbitotomy approach (LOA), yet there is no unified standard. This study aims to investigate the impact of different fixation strategies on orbital stability through Finite Element Analysis (FEA) simulations of the biomechanical environment for orbital rim fixation in LOA. METHODS: A Finite Element Model (FEM) was established and validated to simulate the mechanical responses under various loads in conventional lateral orbitotomy approach (CLOA) and deep lateral orbital decompression (DLOD) using single titanium plate, double titanium plates, and double absorbable plates fixation methods. The simulations were then validated against clinical cases. RESULTS: Under similar conditions, the maximum equivalent stress (MES) on titanium alloy fixations was greater than that on absorbable plate materials. Both under static and physiological conditions, all FEM groups ensured structural stability of the system, with material stresses remaining within safe ranges. Compared to CLOA, DLOD, which involves the removal of the lateral orbital wall, altered stress conduction, resulting in an increase of MES and maximum total deformation (MTD) by 1.96 and 2.62 times, respectively. Under a horizontal load of 50 N, the MES in FEM/DLOD exceeded the material's own strength, with an increase in MES and MTD by 3.18 and 6.64 times, respectively, compared to FEM/CLOA. Under a vertical force of 50 N, the MES sustained by each FEM was within safe limits. Bone flap rotation angles remained minimally varied across scenarios. During follow-up, the 12 patients validated in this study did not experience complications related to the internal fixation devices. CONCLUSION: Under static or physiological conditions, various fixation methods can effectively maintain stability at the orbitotomy site, and absorbable materials, with their smoother stress transmission properties, are more suited for application in CLOA. Among titanium plate fixations, single titanium plates can better withstand vertical stress, while double titanium plates are more capable of handling horizontal stress. Given the change in the orbital mechanical behavior due to DLOD, enhanced fixation strength should be considered for bone flap repositioning.

A comprehensive biomechanical evaluation of length and diameter of dental implants using finite element analyses: A systematic review.

Background: With a wide range of dental implants currently used in clinical scenarios, evidence is limited on selecting the type of dental implant best suited to endure the biting force of missing teeth. Finite Element Analysis (FEA) is a reliable technology which has been applied in dental implantology to study the distribution of biomechanical stress within the bone and dental implants. Purpose: This study aimed to perform a systematic review to evaluate the biomechanical properties of dental implants regarding their length and diameter using FEA. Material and methods: A comprehensive search was performed in PubMed/MEDLINE, Scopus, Embase, and Web of Science for peer-reviewed studies published in English from October 2003 to October 2023. Data were organized based on the following topics: area, bone layers, type of bone, design of implant, implant material, diameter of implant, length of implant, stress units, type of loading, experimental validation, convergence analysis, boundary conditions, parts of Finite Element Model, stability factor, study variables, and main findings. The present study is registered in PROSPERO under number CRD42022382211. Results: The query yielded 852 results, of which 40 studies met the inclusion criteria and were selected in this study. The diameter and length of the dental implants were found to significantly influence the stress distribution in cortical and cancellous bone, respectively. Implant diameter was identified as a key factor in minimizing peri-implant stress concentrations and avoiding crestal overloading. In terms of stress reduction, implant length becomes increasingly important as bone density decreases. Conclusions: The diameter of dental implants is more important than implant length in reducing bone stress distribution and improving implant stability under both static and immediate loading conditions. Short implants with a larger diameter were found to generate lower stresses than longer implants with a smaller diameter. Other potential influential design factors including implant system, cantilever length, thread features, and abutment collar height should also be considered in future implant design as they may also have an impact on implant performance.

Design and Characterization of Deformable Superstructures Based on Amine-Acrylate Liquid Crystal Elastomers.

Deformable superstructures are man-made materials with large deformation properties that surpass those of natural materials. However, traditional deformable superstructures generally use conventional materials as substrates, limiting their applications in multi-mode reconfigurable robots and space-expandable morphing structures. In this work, amine-acrylate-based liquid crystal elastomers (LCEs) are used as deformable superstructures substrate to provide high driving stress and strain. By changing the molar ratio of amine to acrylate, the thermal and mechanical properties of the LCEs are modified. The LCE with a ratio of 0.9 exhibited improved polymerization degree, elongation at break, and toughness. Besides an anisotropic finite deformation model based on hyperelastic theory is developed for the LCEs to capture the configuration variation under temperature activation. Built upon these findings, an LCE-based paper-cutting structure with negative Poisson's ratio and a 2D lattice superstructure model are combined, processed, and molded by laser cutting. The developed superstructure is pre-programmed to the configuration required for service conditions, and the deformation processes are analyzed using both experimental and finite element methods. This study is expected to advance the application of deformable superstructures and LCEs in the fields of defense and military, aerospace, and bionic robotics.

Stress Distribution in Peri-implant Bone in the Replacement of Molars with One or Two Implants: A Finite Element Analysis.

Statement of the Problem: In most cases, insertion of single implants with a standard diameter is used to replace a molar tooth but placing two implants with a narrow diameter seems to be a viable treatment modality to withstand functional and biomechanical forces. Purpose: This study aimed to evaluate and compare stress distribution in the bone surrounding a single molar area rehabilitated by a single implant versus two implants with a narrow diameter. Materials and Method: The study was conducted by computer-aided in vitro modeling. The initial model used a single implant, 4.8 mm wide in diameter, inserted with a 3.9-mm distance from both sides and 12.6-mm mesiodistal space. The second model used two 3.3-mm narrow-sized implants with a 3-mm distance from one another, 1.5 mm from both sides, and a 12.6-mm mesiodistal space. Following the completion of these models, a 100-N force was exerted obliquely, once in three locations and once in the mesial aspect of the implant-supported crown. Stress distribution was then measured using finite element analysis (FEA) with ANSYS Workbench software package in both models. Results: The maximum stress in the bone around the single implant was less than that around double implants. The maximum stress of cortical bone in three-point loading was lower than mesial loading either in one (146.7 vs. 126.72 MPa) or two implants model (186.8 vs. 139.24). Conclusion: According to the results, because of more cortical bone contact area, the stress of surrounding bone in wide implant was decreased.

Stress distribution of endodontically treated mandibular molars with varying amounts of tooth structure restored with direct composite resin with or without cuspal coverage: A 3D finite element analysis.

Background: Decision-making regarding whether cuspal coverage is required or not for the restoration of root canal-treated posterior teeth is still a matter of challenge for the dentist. Methodology: Four models of endodontically treated mandibular molars with mesio-occlusal (MO) cavity were designed and simulated with direct composite resin restorations. Group 1A - cavity width <½ the intercuspal distance restored without cuspal coverage, Group 1B - same as Group 1A but with cuspal coverage, Group 2A - MO cavity width >½ but <2/3rd the intercuspal distance restored without cuspal coverage, and Group 2B - same as Group 2A but with cuspal coverage. The models received occlusal load to simulate a mastication load. Static finite element analysis (FEA) was adopted for predicting the stress distribution generated in the restored tooth by the loading condition. Results: FEA of the models have shown that the variations in stress values were significant in bulk-fill material compared to enamel and other structures. Comparing the maximum and minimum principal stress values in the overall region demonstrated that 2A was safer, whereas 2B was found to be the worst case. Conclusions: The results indicate that restoration of endodontically treated mandibular molar with loss of one marginal ridge with composite resin without cuspal coverage revealed minimal internal stress values and showed the best performance overall.

Bovine pericardium leaflet damage during transcatheter aortic valve crimping: a study of the mechanisms.

Leaflet damage has been documented to occur while deploying a transcatheter aortic valve (TAV) due to mechanical loads during the crimping procedures. In this study, the impact of compressive stress on folded leaflets was measured to investigate the mechanism of traumatic leaflet tissue damage. Numerical simulation of TAV crimping procedure was adapted to calculate stress magnitude and distribution of leaflets. A 20 mm balloon expanding short stent TAV with 0.25 mm thickness leaflets was used in the simulation. Then the calculated stresses were applied on leaflet material (bovine pericardium) samples by loading experiments. Mechanical properties evaluation combined with histological and microscopy observation were used to investigate the tissue damage. The elastic modulus and the tensile strength of the tissue began to decrease significantly at 2 MPa stress and 2.5 MPa stress, respectively. No significant differences were observed at 0-1.5 MPa stress. When the TAV was crimped to 14 Fr and 12 Fr, the 2 MPa greater areas on leaflets increased from 18.17% to 76.96%. 2 MPa compressive stress might be the threshold value for leaflet damage. The TAV crimping size should be paid attention to avoid the compressive stress higher than 2 MPa.

Evaluation of the Effect of Anterior Teeth Torque Values on the Space Occupied by Six Anterior Teeth: a Finite Element Analysis.

Statement of the Problem: Various factors have been introduced to achieve normal occlusion. One of them is anterior teeth torque that has a significant effect on orthodontic treatment outcomes. Purpose: The aim of this study was to investigate the effect of changes in anterior teeth torque on changes in the space occupied by six anterior teeth by using computer-aided three-dimensional interactive application (CATIA). Materials and Method: In this experimental finite element study, acrylic teeth with pre-adjusted MBT braces were aligned and three-dimensional (3D) scans were made by 3Dscaner. In the CATIA software program, upper incisors' torque was changed to -2, -4, -6, +2, +4 and+6 degrees and in the lower incisors to -1, - 3, -5, +3 and+5 degrees; the space was measured at 3 heights of maxillary incisor crowns and at incisal edges of mandibular incisors. Then maxillary incisors were then tapered and the measurements were made again. To evaluate the effect of tooth size, these procedures were carried out on teeth with +17% and -17% magnifications. Results: The results showed that by increasing anterior torque from 14.7 to 20.7 degrees in maxillary incisors, the space occupied by anterior teeth increased. Maximum changes were at cingulum height with 1.421mm. Reduction in anterior torque from 14.7 to 8.7 degrees resulted in a decrease in this space and maximum changes were observed in the cingulum height with 1.824mm. In the mandibular arch, a 10-degree change in anterior torque resulted in an -.752mm change in the space. Changes in the space occupied by anterior teeth was not significant in tapered and normal teeth in +6 and -6-degree torque (p Value= 0.78 and p Value=0.83). Conclusion: By increasing or decreasing the incisors' torque, the space occupied by anterior teeth increased and decreased, respectively. These changes were less in tapered teeth. Size variations had no significant effect on the results.

Biomechanical tests and finite element analyses of pelvic stability using bilateral single iliac screws with different channels in lumbo-iliac fixation.

Background: In lumbo-iliac fixation, the iliac screw can be placed in several locations and directions. There is no uniform standard for the placement of a single iliac screw. Biomechanical tests and finite element analyses were used to compare the effect of bilateral single iliac screws with three channels on pelvic stability to determine the best channel. Methods: Five embalmed adult cadaver pelvic specimens were selected. An unstable Tile C1 pelvic injury model was established. Lumbo-iliac fixation for the treatment of left sacral Denis II fracture includes the following: three channels of bilateral, single iliac screws (channel A from posterior superior iliac spine (PSIS) to anterior inferior iliac spine (AIIS), channel B from 1 cm medial and 1 cm caudal of PSIS to AIIS, and channel C from 2 cm below PSIS to AIIS). Biomechanical testing was performed for stiffness evaluations. A finite element model was established to study the stress distribution of the model and the maximum von Mises stress of internal fixation. Results: Biomechanical tests revealed that under vertical compression loading. The compressive stiffness fixed by channel B (246.15 ± 27.85 N/mm) was better than that fixed by channel A and channel C. Under torsional load, the torsional stiffness fixed by channel B (2.234 ± 0.223 N·m/°) was stronger than that fixed by channel A and channel C. However, there was no significant difference in terms of compressive and torsional stiffness between channel B and channel A (P > 0.05). Finite element analyses conformed that the maximum von Mises stress of the internal fixator fixed in channel B under the conditions of vertical, forwards bending, backwards extension, left bending, left rotating, and right bending (213.98 MPa, 338.96 MPa, 100.63 MPa, 297.06 MPa, 200.95 MPa and 284.75 MPa, respectively) was significantly lower than those fixed in channel A and channel C. Conclusions: The construct stiffness of the channel from 1 cm medial and 1 cm caudal of PSIS to AIIS is better than that of the other two channels. This channel has the advantages of good biomechanical stability, small maximum von Mises stress of internal fixation.

Finite element analyses of lateral condyle fracture fixation in paediatrics regarding configuration of Kirschner-wire.

BACKGROUND: This study aimed to discover the most stable outcome among different Kirschner-wire (K-wire) configurations for fixation of a lateral condyle fracture (Milch type II) in different loads of stress by using finite element analyses (FEA). METHODS: The right humerus of a 6-year-old boy with a lateral condyle fracture (Milch type II), was modelled with a computer aided engineering. Using FEA, peak von Mises stress and stiffness were evaluated first for a single K-wire fixation by varying the angle (0, 5, 10, 15, 20, 25, 30 degrees). Then, based on the single K-wire result, assessment of peak von Mises stress and stiffness were evaluated via FEA for two- or three-wire fixation under various configurations (two convergent, two parallel, three divergent). RESULTS: Single K-wire fixation by 5 and 25 degrees had the lowest peak von Mises stress. The fracture site showed higher stiffness at 0, 5 and 15 degrees. Considering the collected results and clinical situation, 5 degree K-wire was selected for the FEA of multiple K-wire fixation. For multiple K-wire fixation, three divergent (5-20-35 degrees) K-wires showed better stability, both in peak von Mises stress and stiffness, than any two-K-wire configurations. Among two K-wire fixations, two divergent (5-50 degrees) K-wires provided the lowest von Mises stress in varus and valgus while two divergent (5-65 degrees) K-wires showed better results in flexion, extension, internal and external rotation, and both configurations showed similar results in stiffness. CONCLUSIONS: We successfully created a paediatric lateral condyle fracture (Milch type II) model which was used to conduct FEA on different K-wire configurations to achieve stability of the fracture. Our results show that an initial K-wire inserted at 5 degrees, followed by the insertion of a second divergent wire at either 45 or 60 degrees provides the most stability in two K-wire fixations in this type of fracture repair.

Seismic Retrofitting of Existing Industrial Steel Buildings: A Case-Study.

Industrial single-storey buildings are the most diffuse typology of steel construction located in Italy. Most of these existing buildings were erected prior to the enforcement of adequate seismic provisions; hence, crucial attention is paid nowadays to the design of low-impact retrofit interventions which can restore a proper structural performance without interrupting productive activities. Within this framework, an existing industrial single-storey steel building located in Nusco (Italy) is selected in this paper as a case-study. The structure, which features moment resisting (MR) truss frames in both directions, is highly deformable and presents undersized MR bolted connections. Structural performance of the case-study was assessed by means of both global and local refined numerical analyses. As expected, the inadequate performance of connections, which fail due to brittle mechanisms, detrimentally affects the global response of the structure both in terms of lateral stiffness and resistance. This effect was accounted for in global analyses by means of properly calibrated non-linear links. Thus, both local and global retrofit interventions were designed and numerically investigated. Namely, lower chord connections were strengthened by means of rib stiffeners and additional rows of M20 10.9 bolts, whereas concentrically braced frames (CBFs) were placed on both directions' facades. Designed interventions proved to be effective for the full structural retrofitting against both seismic and wind actions without limiting building accessibility.

Controlling Mesenchyme Tissue Remodeling via Spatial Arrangement of Mechanical Constraints.

Tissue morphogenetic remodeling plays an important role in tissue repair and homeostasis and is often governed by mechanical stresses. In this study, we integrated an in vitro mesenchymal tissue experimental model with a volumetric contraction-based computational model to investigate how geometrical designs of tissue mechanical constraints affect the tissue remodeling processes. Both experimental data and simulation results verified that the standing posts resisted the bulk contraction of the tissues, leading to tissue thinning around the posts as gap extension and inward remodeling at the edges as tissue compaction. We changed the geometrical designs for the engineered mesenchymal tissues with different shapes of posts arrangements (triangle vs. square), different side lengths (6 mm vs. 8 mm), and insertion of a center post. Both experimental data and simulation results showed similar trends of tissue morphological changes of significant increase of gap extension and deflection compaction with larger tissues. Additionally, insertion of center post changed the mechanical stress distribution within the tissues and stabilized the tissue remodeling. This experimental-computational integrated model can be considered as a promising initiative for future mechanistic understanding of the relationship between mechanical design and tissue remodeling, which could possibly provide design rationale for tissue stability and manufacturing.

Finite Element Analysis of Silver Nanorods, Spheres, Ellipsoids and Core-Shell Structures for Hyperthermia Treatment of Cancer.

The finite element analysis technique was used to investigate the suitability of silver nanorods, spheres, ellipsoids and core−shell structures for the hyperthermia treatment of cancer. The temperature of the silver nanostructures was raised from 42 to 46 °C, in order to kill the cancerous cells. The time taken by the nanostructures to attain this temperature, with external source heating, was also estimated. The heat transfer module in COMSOL Multiphysics was used for the finite element analysis of hyperthermia, based on silver nanostructures. The thermal response of different shapes of silver nanostructures was evaluated by placing them inside the spherical domain of the tumor tissue. The proposed geometries were heated at different time intervals. Optimization of the geometries was performed to achieve the best treatment temperature. It was observed that silver nanorods quickly attain the desired temperature, as compared to other shapes. The silver nanorods achieved the highest temperature of 44.3 °C among all the analyzed geometries. Moreover, the central volume, used to identify the thermal response, was the maximum for the silver nano-ellipsoids. Thermal equilibrium in the treatment region was attained after 0.5 µs of heating, which made these structures suitable for hyperthermia treatment.

[Finite element analyses of retention of removable partial denture circumferential clasps manufactured by selective laser melting].

OBJECTIVE: To compare the retentions of different designs of cobalt-chromium (Co-Cr), pure titanium (CP Ti), and titanium alloy (Ti-6Al-4V) removable partial denture (RPD) circumferential clasps manufactured by selective laser melting (SLM) and to analyze the stress distribution of these clasps during the removal from abutment teeth. METHODS: Clasps with clasp arm size A (1.9 mm width/1.1 mm thickness at the body and 0.8-taper) or B (1.2 times A) and 0.25 mm or 0.50 mm undercut engagement were modeled on a prepared first premolar die, named as designs A1, A2, A3, and A4, respectively. The density and elastic modulus of SLM-built Co-Cr, CP Ti, and Ti-6Al-4V were measured and given to different groups of clasps. The density, elastic modulus, and Poisson ' s ratio of enamel were given to the die. The control group was the cast Co-Cr clasp with design A1, to which the density and elastic modulus of cast Co-Cr alloy were given. The Poisson's ratio of all metals was 0.33. The initial 5 N dislodging force was applied, and the maximum displacement of the clasp along the insertion path was computed. The load was reapplied with an increment of 5 N than in the last simulation until the clasp was completely dislodged. The retentive force range of different groups of clasps was obtained. The retentive forces of the SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with equivalent computed retentive force range to the control group were validated through the insertion/removal experiment. The von Mises stress distributions of these three groups of SLM-built clasps under 15 N loads were analyzed. RESULTS: SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with designs B1 or B2, and Co-Cr clasps with design A2 had higher retentive forces than those of the control group. SLM-built CP Ti and Ti-6Al-4V clasps with design A1 had lower retentive forces than those of the control group. SLM-built Co-Cr clasp with design A1 and SLM-built CP Ti and Ti-6Al-4V clasps with design A2 had equivalent retentive forces to those of the control group. The insertion/removal experiment showed that the measured retentive forces of these three groups of SLM-built clasps were (21.57±5.41) N, (19.75±4.47) N, and (19.32±2.04) N, respectively. No statistically significant measured retentive force difference was found among these three groups of SLM-built clasps (P>0.05). The maximum von Mises stress of these three groups of SLM-built clasps exceeded their responding yield strength except for the Ti-6Al-4V one. CONCLUSION: SLM-built Co-Cr circumferential clasps had higher retention than CP Ti and Ti-6Al-4V ones with the same clasp arm size and undercut engagement. The retention of SLM-built circumferential clasps could be adjusted by changing the undercut engagement and clasp arm size. If SLM-built circumferential clasps are used in clinical practice, the Ti-6Al-4V clasp with clasp arm size A and 0.50 mm undercut engagement is recommended considering the long-term use of RPD in the patient's mouth.

Validation of a numerical model for the mechanical behavior of a continuous positive airway pressure mask.

Finite Element models (FEM) are developed for the analysis of the contact pressures exerted by a Continuous Positive Airway Pressure (CPAP) mask applied to a dummy head. This is seen as a preliminary step in the analysis of the mechanical effects of CPAP masks applied to human faces, such as recently employed for the care of COVID-19 patients, or other purposes. These mechanical effects can range from negligible, in the case of correct positioning, sufficiently light tension in the headgear, correct mask design, etc., to the possible development of device-related pressure ulcers and/or dentofacial deformations, especially in children. The results of Finite Element analyses are compared, for their validation, with experimental ones. The numerical analysis tool appears able to predict, at an acceptable cost, both the intensity and the area distribution of the contact pressures, as well as the force-displacement relationship occurring in the headgear. This might help the design and the production of more effective and tolerable CPAP masks.

Stress Analysis in AAA does not Predict Rupture Location Correctly in Patients with Intraluminal Thrombus.

BACKGROUND: A biomechanical approach to the rupture risk of an abdominal aortic aneurysm could be a solution to ensure a personalized estimate of this risk. It is still difficult to know in what conditions, the assumptions made by biomechanics, are valid. The objective of this work was to determine the individual biomechanical rupture threshold and to assess the correlation between their rupture sites and the locations of their maximum stress comparing two computed tomography scan (CT) before and at time of rupture. METHODS: We included 5 patients who had undergone two CT; one within the last 6 months period before rupture and a second CT scan just before the surgical procedure for the rupture. All DICOM data, both pre- and rupture, were processed following the same following steps: generation of a 3D geometry of the abdominal aortic aneurysm, meshing and computational stress analysis using the finite element method. We used two different modelling scenarios to study the distribution of the stresses, a "wall" model without intraluminal thrombus (ILT) and a "thrombus" model with ILT. RESULTS: The average time between the pre-rupture and rupture CT scans was 44 days (22-97). The median of the maximum stresses applied to the wall between the pre-rupture and rupture states were 0.817 MPa (0.555-1.295) and 1.160 MPa (0.633-1.625) for the "wall" model; and 0.365 MPa (0.291-0.753) and 0.390 MPa (0.343-0.819) for the "thrombus" model. There was an agreement between the site of rupture and the location of maximum stress for only 1 patient, who was the only patient without ILT. CONCLUSIONS: We observed a large variability of stress values at rupture sites between patients. The rupture threshold strongly varied between individuals depending on the intraluminal thrombus. The site of rupture did not correlate with the maximum stress except for 1 patient.

Finite element analyses of retention of removable partial denture circumferential clasps manufactured by selective laser melting / 北京大学学报(医学版)

OBJECTIVE@#To compare the retentions of different designs of cobalt-chromium (Co-Cr), pure titanium (CP Ti), and titanium alloy (Ti-6Al-4V) removable partial denture (RPD) circumferential clasps manufactured by selective laser melting (SLM) and to analyze the stress distribution of these clasps during the removal from abutment teeth.@*METHODS@#Clasps with clasp arm size A (1.9 mm width/1.1 mm thickness at the body and 0.8-taper) or B (1.2 times A) and 0.25 mm or 0.50 mm undercut engagement were modeled on a prepared first premolar die, named as designs A1, A2, A3, and A4, respectively. The density and elastic modulus of SLM-built Co-Cr, CP Ti, and Ti-6Al-4V were measured and given to different groups of clasps. The density, elastic modulus, and Poisson ' s ratio of enamel were given to the die. The control group was the cast Co-Cr clasp with design A1, to which the density and elastic modulus of cast Co-Cr alloy were given. The Poisson's ratio of all metals was 0.33. The initial 5 N dislodging force was applied, and the maximum displacement of the clasp along the insertion path was computed. The load was reapplied with an increment of 5 N than in the last simulation until the clasp was completely dislodged. The retentive force range of different groups of clasps was obtained. The retentive forces of the SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with equivalent computed retentive force range to the control group were validated through the insertion/removal experiment. The von Mises stress distributions of these three groups of SLM-built clasps under 15 N loads were analyzed.@*RESULTS@#SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with designs B1 or B2, and Co-Cr clasps with design A2 had higher retentive forces than those of the control group. SLM-built CP Ti and Ti-6Al-4V clasps with design A1 had lower retentive forces than those of the control group. SLM-built Co-Cr clasp with design A1 and SLM-built CP Ti and Ti-6Al-4V clasps with design A2 had equivalent retentive forces to those of the control group. The insertion/removal experiment showed that the measured retentive forces of these three groups of SLM-built clasps were (21.57±5.41) N, (19.75±4.47) N, and (19.32±2.04) N, respectively. No statistically significant measured retentive force difference was found among these three groups of SLM-built clasps (P>0.05). The maximum von Mises stress of these three groups of SLM-built clasps exceeded their responding yield strength except for the Ti-6Al-4V one.@*CONCLUSION@#SLM-built Co-Cr circumferential clasps had higher retention than CP Ti and Ti-6Al-4V ones with the same clasp arm size and undercut engagement. The retention of SLM-built circumferential clasps could be adjusted by changing the undercut engagement and clasp arm size. If SLM-built circumferential clasps are used in clinical practice, the Ti-6Al-4V clasp with clasp arm size A and 0.50 mm undercut engagement is recommended considering the long-term use of RPD in the patient's mouth.

A new protocol to accurately track long-term orthodontic tooth movement and support patient-specific numerical modeling.

Numerical simulation of long-term orthodontic tooth movement based on Finite Element Analysis (FEA) could help clinicians to plan more efficient and mechanically sound treatments. However, most of FEA studies assume idealized loading conditions and lack experimental calibration or validation. The goal of this paper is to propose a novel clinical protocol to accurately track orthodontic tooth displacement in three-dimensions (3D) and provide 3D models that may support FEA. Our protocol uses an initial cone beam computed tomography (CBCT) scan and several intra-oral scans (IOS) to generate 3D models of the maxillary bone and teeth ready for use in FEA. The protocol was applied to monitor the canine retraction of a patient during seven months. A second CBCT scan was performed at the end of the study for validation purposes. In order to ease FEA, a frictionless and statically determinate lingual device for maxillary canine retraction was designed. Numerical simulations were set up using the 3D models provided by our protocol to show the relevance of our proposal. Comparison of numerical and clinical results highlights the suitability of this protocol to support patient-specific FEA.

Numerical Simulations of Components Produced by Fused Deposition 3D Printing.

Three-dimensional printing technology using fused deposition modeling processes is becoming more and more widespread thanks to the improvements in the mechanical properties of materials with the addition of short fibers into the polymeric filaments. The final mechanical properties of the printed components depend, not only on the properties of the filament, but also on several printing parameters. The main purpose of this study was the development of a tool for designers to predict the real mechanical properties of printed components by performing finite element analyses. Two different materials (nylon reinforced with glass or carbon fibers) were investigated. The experimental identification of the elastic material model parameters was performed by testing printed fully filled dog bone specimens in two different directions. The obtained parameters were used in numerical analyses to predict the mechanical response of simple structures. Blocks of 20 mm × 20 mm × 160 mm were printed in four different percentages of a triangular infill pattern. Experimental and numerical four-point bending tests were performed, and the results were compared in terms of load versus curvature. The analysis of the results demonstrated that the purely elastic transversely isotropic material model is adequate for predicting behavior, at least before nonlinearities occur.

Stress distribution of esthetic posts in the restored maxillary central incisor: Three-dimensional finite-element analysis.

BACKGROUND: Glass fiber posts, along with their esthetic properties, may have a better stress distribution than cast posts, Therefore, the aim of the present study was to investigate the effect of glass fiber, casting, titanium, and zirconia posts on stress distribution in maxillary central tooth treated with different amounts of ferrule using finite-element analysis. MATERIALS AND METHODS: In this experimental study, three-dimensional models of maxillary central incisors that have undergone root canal treatment were designed. Then, the models were divided into four groups according to the type of post (Ni-Cr casting, glass fiber, titanium, and zirconia) used. Zirconia monolithic crowns were used in all the four groups. Ferrule heights were repeated at 0 and 2 mm in all models. Models were entered into COMSOL Metaphysics software. Then, the force of 100 N with the angle of 135° on the palatal surface was applied to the longitudinal axis of the tooth, and the stress distribution in the models was investigated. RESULTS: Maximum stress was observed in the middle third of posts. Stress distribution in glass fiber post was better than zirconia and casting posts. Stress accumulation in models with zirconia, titanium, and casting posts was also found in the site between the middle third and coronal third, whereas in models with glass fiber post, stress accumulation was found between the crown and the cemento-enamel junction. In models without ferrule, stress accumulation was observed in one-third of the coronal, especially in glass fiber posts. CONCLUSION: The post material and ferrule height affected stress concentration. The stress in the cervical area of the dentin was more for glass fiber post when compared to other posts. The use of glass fiber post in teeth with no ferrule results in lower stress along the post, but greater stress in the simulated tooth region.

Ultra-high-molecular-weight Polyethylene (UHMWPE) Wing Method for Strong Cranioplasty.

We developed a new cranioplasty method that utilizes artificial bone made of ultra-high-molecular-weight polyethylene, with a wedge-shaped edge (UHMWPE Wing). This study shows the methods and data of case series and finite element analyses with the UHMWPE Wing. A circumferential wing was preoperatively designed for a custom-made artificial bone made of UHMWPE to achieve high fixed power and to minimize the usage of cranial implants. Here, we present 4 years of follow-up data and finite element analyses for patients treated with the UHMWPE Wing between February 2015 and February 2019. Eighteen consecutive patients underwent cranioplasty using our UHMWPE Wing design. There were no postoperative adverse events in 17 of the patients for at least 18 months. One case of hydrocephalus experienced screw loosening and graft uplift due to shunt malfunction. Placement of a ventriculo-peritoneal shunt immediately returned the artificial bone to normal position. Finite element analyses revealed that a model using the UHMWPE Wing had the highest withstand load and lowest deformation. This is the first report on the UHMWPE Wing method. This method may enable clinicians to minimize dead space and achieve high strength in cranioplasty.