Stress Distribution In Bone Research Articles

Effects of proximal fibular osteotomy on stress changes in mild knee osteoarthritis with varus deformity: a finite element analysis

BackgroundMany previous studies lack sufficient quantitative evidences about changes in biomechanical properties of the knee in response to proximal fibular osteotomy (PFO). Therefore, the aim of this study was to compare the preoperative and postoperative effects of PFO on mechanical stresses in the knee joint and provide with a biomechanical basis for PFO in the treatment of mild knee osteoarthritis (KOA) with varus deformity.MethodsA total of 10 patients suffering mild KOA with varus deformity were enrolled in this study. Their image data from computerized tomography (CT) and magnetic resonance imaging (MRI) were used for finite element models, and PFO models were established. Static structural analysis was carried out using ABAQUS to compare the von Mises stress distribution and values of the maximal von Mises stress of femoral cartilage, meniscuses, tibial cartilages, and tibial plateau before and after surgery.ResultsThe stress distribution in the cortical bone of the tibial plateau showed that stresses were transferred from the anterior medial area to the posterior medial area after PFO. Values of the maximal von Mises stress in femoral cartilage, medial meniscus, medial tibial cartilage, and tibial plateau after surgery were significantly lower than the preoperative values, with statistically significant differences (P < 0.05). Postoperative values of the maximal von Mises stress of lateral meniscus and lateral tibial cartilage were significantly higher than the preoperative ones, with statistically significant differences (P < 0.05).ConclusionPFO could reduce the stresses in the medial compartment of the knee joint with stress pathways transferring from the anterior medial area to the posterior medial area of the tibial plateau. Therefore, PFO is recommended for the treatment of mild KOA with varus deformity featuring favorably pain-relieving effects.Graphical abstract

Finite Element Analysis of a New Dental Implant Design Optimized for the Desirable Stress Distribution in the Surrounding Bone Region

Dental implant macro- and micro-shape should be designed to maximize the delivery of optimal favorable stresses in the surrounding bone region. The present study aimed to evaluate the stress distribution in cortical and cancellous bone surrounding two models of dental implants with the same diameter and length (4.0 × 11 mm) and different implant/neck design and thread patterns. Sample A was a standard cylindric implant with cylindric neck and V-shaped threads, and sample B was a new conical implant with reverse conical neck and with “nest shape” thread design, optimized for the favorable stress distribution in the peri-implant marginal bone region. Materials and methods: The three-dimensional model was composed of trabecular and cortical bone corresponding to the first premolar mandibular region. The response to static forces on the samples A and B were compared by finite element analysis (FEA) using an axial load of 100 N and an oblique load of 223.6 N (resulting from a vertical load of 100 N and a horizontal load of 200 N). Results: Both samples provided acceptable results under loadings, but the model B implant design showed lower strain values than the model A implant design, especially in cortical bone surrounding the neck region of the implant. Conclusions: Within the limitation of the present study, analyses suggest that the new dental implant design may minimize the transfer of stress to the peri-implant cortical bone.

Stress distribution in ceramic orthodontic bracket, tooth, bone and PDL contact assembly - A finite element study

Malocclusion (teeth irregularity) problems are increasing rapidly across the world in all age groups. Malocclusion is treated in orthodontics which is a specialty of dentistry. Orthodontic bracket is a component of fixed orthodontic appliance which is used to treat the malocclusion through archwire forces transferred to the tooth. In orthodontic treatment, the preadjusted orthodontic brackets are most widely used compared to the conventional brackets as there is an in-built torque by the angulated slot walls. This study aim to compare the stress distribution in the preadjusted ceramic brackets with and without Stainless steel (SS) metal slot insert along with tooth, alveolar bone and Periodontal Ligament (PDL) contact assembly using Finite Element Analysis (FEA). A preadjusted maxillary right central incisor ceramic orthodontic bracket (with and without metal insert in the slot) are modeled using CATIA software. The solid model of a maxillary right central incisor tooth is obtained from a Computer Tomography (CT) scan using image processing software. The PDL and alveolar bone are modelled using CATIA as per the dimensions. The assembled solid model consists of bracket with and without SS metal slot insert, adhesive layer, tooth, alveolar bone and PDL. The contact between the components and the mesh is created using hypermesh software. The archwire torque is applied as couple inside the bracket slot without using an archwire. The stress distribution in the assembly components are analysed for the applied couple (torque). The stresses induced in the assembly components are compared between ceramic bracket with and without metal slot insert. This in-silico study would help the clinicians to understand the behavior of commonly used ceramic bracket with and without metal slot insert and choose the appropriate bracket for successful treatment.

Finite element analysis of different diameter prosthesis ball head in artificial femoral head replacement

In order to select the proper size of prosthesis ball head, the biomechanical changes of hip joint using different diameter prosthesis ball head was studied by three-dimensional finite element analysis. The thin-layer CT data and related parameters of artificial femoral head prosthesis were used to establish the finite element model of hip joint after artificial femoral head replacement with different ball diameter of prosthesis(M0:preoperative model;M1:ball head diameter=original femoral head diameter;M2:ball head diameter=original femoral head diameter+1 mm;M3:Ball head diameter= Original femoral head diameter -1 mm;M4:ball head diameter =original femoral head diameter -2 mm). Loading the joint forces and related muscle loads were loaded, and the stress distribution and change of bone and cartilage around acetabulum were analyzed by simulating the standing state of one foot when walking slowly. (1) In M1 to M4, the stress concentration in pelvis was different. The peak value of Von Mises stress in the pelvis of M3 was 44.8 MPa, which was the closest to that before operation, with an increment of 13.4%. The displacement of the pelvis of M3 was the smallest in the four groups after operation, with an increment of 1.40 mm. The next was M1, with a peak value of 47.3 MPa, with an increment of 19.7%, and a pelvic displacement of 1.59 mm. (2) In acetabulum area, the peak value of Von Mises stress in M3 was 23.3 MPa, which was the closest to that before operation, with an increment of about 6.3%, followed by M1, with a peak value of 24.0 MPa and an increment of about 8.1%. (3) On the acetabulum cartilage, the stress distribution of M1 and M3 was similar to that before operation, and the peak value of Von Mises stress of M3 was 18.5 MPa, which was the closest to that before operation, followed by M1, which was 22.5 MPa. (4) M1 to M4 showed different degree of stress concentration in the outer upper quadrant of the artificial femoral head, but showed stress shielding under it;among them, the von Mises stress distribution of M3 was more uniform than that of other models, and its peak value (70.8 MPa) was the lowest in each group, followed by M1 (80.7 MPa). When femoral head replacement is performed, it is suggested that the prosthesis ball head with the diameter less than 1 mm and the prosthesis ball head with the same diameter as the original femoral head should be used first, so as to obtain the closest natural mechanical characteristics of the hip joint before the replacement and reduce the risk of complications caused by size differences.

Influence of Dental Implant Design on Stress Distribution and Micromotion of Mandibular Bone

This research was conducted to provide a feasible method for reconstructing the 3D model of mandibular bone to undergo finite element analysis to investigate von Mises stress, deformation and shear stress located at the cortical bone, cancellous one and neck implant of the proposed dental implant design. Dental implant has become a significant remedial approach but although the success rate is high, the fixture failure may happen when there are insufficient host tissues to initiate and sustain the osseointegration. Computerised Tomography scan was conducted to generate head images for bone reconstruction process. MIMICS software and 3-matic software were used to develop the 3D mandibular model. The reconstructed mandibular model was then assembled with five different 3D models of dental implants. Feasible boundary conditions and material properties were assigned to the developed muscle areas and joints. The highest performance design with the best responses was the design B with the value for the von Mises stress for the neck implant, cortical and cancellous bone were 7.53 MPa, 16.91 MPa and 1.34 MPa respectively. The values for the maximum of micromotion for the neck implant, cortical and cancellous bone of design B were 20.60 μm, 21.17 μm and 5.83 μm respectively. Shear stress for neck implant, cortical and cancellous bone for this design were 0.15 MPa, 4.74 MPa and 1.54 MPa respectively. The design with a cone shaped hole which is design B was the proper design when compared with other designs in terms of von Misses stress, deformations and shear stress.

Finite element analysis of narrow dental implants

Narrow-diameter implants (NDIs) traditionally have been associated to higher rates of failure in comparison with regular-diameter implants (RDIs) and wide-diameter implants (WDIs), since they generate a more unfavorable stress distribution in peri-implant bone. However, it is well known that the load sharing effect associated with prostheses supported by multiple implants (also called splinted prostheses) affords mechanical benefits. The present study involves finite element analysis (FEA) to determine whether the risks linked to NDIs could be mitigated by the mechanical advantages afforded by the splinting concept. For this purpose, a three-dimensional (3D) model of a real maxilla was reconstructed from computed tomography (CT) images, and different implants (NDIs, RDIs and WDIs) and prostheses were created using computer-aided design (CAD) tools. Biting forces were simulated on the prostheses corresponding to three different rehabilitation solutions: single-implant restoration, three-unit bridge and all-on-four treatment. Stress distribution around the implants was calculated, and overloading in bone was quantified within peri-implant volumes enclosed by cylinders with a diameter 0.1mm greater than that of each implant. The mechanical benefits of the splinting concept were confirmed: the peri-implant overloaded volume around NDIs splinted by means of the three-unit bridge was significantly reduced in comparison with the nonsplinted condition and, most importantly, proved even smaller than that around nonsplinted implants with a larger diameter (RDIs). However, splinted NDIs supporting the all-on-four prosthesis led to the highest risk of overloading found in the study, due to the increase in compressive stress generated around the tilted implant when loading the cantilevered molar.

Biomechanical Comparison of a New Triple Cylindrical Implant Design and a Conventional Cylindrical Implant Design on the Mandible by Three-Dimensional Finite Element Analysis.

The aim of this study was to evaluate the effect of implant designs with different lengths and diameters on the stress distribution in abutments, implants, and cortical and trabecular bone of the edentulous mandible via three-dimensional finite element analysis. Eight different finite models (cylindrical 3.5 × 6; cylindrical 3.5 × 10.5; cylindrical 4.5 × 6; cylindrical 4.5 × 10.5; triple cylindrical 3.5 × 6; triple cylindrical 3.5 × 10.5; triple cylindrical 4.5 × 6; and triple cylindrical 4.5 × 10.5) were created. Abutments, abutment screws, and metal-retained porcelain crowns were modeled on the implants. A 200-N oblique load was applied on the buccal cusp of the crown. The highest maximum principal (Pmax) and minimum principal (Pmin) stresses were calculated for trabecular and cortical bone, and von Mises stress values were calculated for the implant and abutment. The triple cylindrical implant abutments showed lower stress values than cylindrical implant abutments. The highest von Mises stress values were observed in the cervical third of the abutments. The stress values on implants were found at the neck of the implants, and cylindrical implants showed higher stress values than triple cylindrical implants. The peak Pmax and Pmin values in cortical bone were detected around the implant neck. For implants with a 3.5-mm diameter, the triple cylindrical implant design showed lower stresses in cortical bone than the cylindrical implant design; however, similar stresses were observed in 4.5-mm implants for both designs. Implant length did not affect the stresses in cortical bone. Implants with a 10.5-mm length showed lower Pmax values than implants with a 6-mm length in trabecular bone. For Pmin values in trabecular bone, the triple cylindrical implant design had lower values than did the cylindrical implant design. Within the limitations of this study, the triple cylindrical implants, with a new implant design, showed appropriate results in terms of abutment, implant, and bone tissue stress.

In silico evaluation of the stress fields on the cortical bone surrounding dental implants: Comparing root-analogue and screwed implants

Tooth loss is a problem that affects both old and young people. It may be caused by several conditions, such as poor oral hygiene, lifestyle choices or even diseases like periodontal disease, tooth grinding or diabetes. Nowadays, replacing a missing tooth by an implant is a very common process. However, many limitations regarding the actual strategies can be enumerated. Conventional screwed implants tend to induce high levels of stress in the peri-implant bone area, leading to bone loss, bacterial bio-film formation, and subsequent implant failure. In this sense, root-analogue dental implants are becoming promising solutions for immediate implantation due to their minimally invasive nature, improved bone stress distribution and because they do not require bone drilling, sinus lift, bone augmentation nor other traumatic procedures.The aim of this study was to analyse and compare, by means of FEA, the stress fields of peri-implant bone around root-analogue and screwed conventional zirconia implants. For that purpose, one root-analogue implant, one root-analogue implant with flaps, two conventional implants (with different threads) and a replica of a natural tooth were modelled. COMSOL was used to perform the analysis and implants were subjected to two simultaneous loads: 100 N axially and 100 N oblique (45°). Resultsrevealed that root-analogue implants, namely with flaps, should be considered as promising alternatives for dental implant solutions since they promote a better stress distribution in the cortical bone when compared with conventional implants.

Influence of Socket-shield technique on the biomechanical response of dental implant: three-dimensional finite element analysis

This study evaluated the bone microstrain, displacement, and stress distribution according to the surgical technique (conventional or Socket-shield) and evaluation period (immediately after implant installation or after healing). Each condition was modeled for the finite element analysis, totaling four groups, with a morse-taper implant and a cemented prosthesis. The maximum displacement, von Mises stress, and bone microstrain yielded higher values during the immediate stage, without a difference between Socket-shield and conventional treatments. The use of the Socket-shield technique does not negatively impact the biomechanical behavior of an implant-supported prosthesis immediately after healing from the implant installation.

Finite element analysis of stress distribution around short and long implants in mandibular overdenture treatment

Optimal stress distribution around implants plays an important role in the success of mandibular overdentures. This study sought to assess the pattern of stress distribution around short (6 mm) and long (10 mm) implants in mandibular two implant-supported overdentures using finite element analysis (FEA). In this descriptive and experimental study two implant-supported overdenture models with bar and clip attachment system on an edentulous mandible were used. Two vertical implants were connected by a bar. The implant length was 6 mm (short implant) in the first and 10 mm (long implant) in the second model. Vertical loads (35, 65, and 100 N) were applied bilaterally to the second molar area. In another analysis, vertical loads of 43.3 N and 21.6 N were applied to working and nonworking sides, respectively, at the second molar area. Furthermore, the lateral force (17.5 N) was applied to the canine area of overdenture. The stress distribution pattern around implants was analyzed using FEA. The maximum von Mises stress was 57, 106, and 164 MPa around short implants and 64, 118, and 172 MPa around long implants following the application of 35, 65, and 100 N bilateral forces, respectively. Application of bilateral loads created 87 and 65 MPa stress around working and nonworking short implants, respectively; while these values were reported to be 92 and 76 MPa for long implants at the working and nonworking sides, respectively. Increasing the vertical loads increased the level of stress distributed around the implants; however, no considerable differences were noted between long and short implants for similar forces. Following unequal load application, the stress in the working side bone was more than that in the nonworking side, but no major differences were noted in similar areas around long and short implants. Following lateral load application, the stress distributed in the peri-implant bone at the force side was more than that in the opposite side. In similar areas, no notable differences were observed between long and short implants regarding the maximum stress values. Using implants with different lengths in mandibular overdenture caused no major changes in stress distribution in peri-implant bone; short implants were somehow comparable to long implants.

The effect of implant neck microthread design on stress distribution of peri-implant bone with different level: A finite element analysis

Background/purposeSignificant research has proposed that the implant with microthread in the neck can significantly reduce marginal bone loss, but whether it is consistent in the condition of marginal bone loss is still unknown. The objective of this study is to investigate the effect of microthread on stress distribution in peri-implant bone with different bone level using finite element analysis. Materials and methodsA series of computational models of mandible segments with different bone resorption and implant models with or without microthread in the neck was installed by computer-aided design software. The simulated occlusal force of 150N was applied buccolingually on the top center point of implant. The FEA was performed, and the von Mises stress, principal stress and shear stress in peri-implant bone were recorded and analyzed. ResultsIn all models, the T-neck group exhibits higher von Mises stress and principal stress, as well as lower shear stress than S-neck group. Three types of stresses increase with the depth of bone resorption developed, but the differences of shear stress between two groups of implants were gradually decreased. ConclusionThe micro-thread design in implant neck can reduce marginal bone loss by decreasing shear stress in peri-implant bone, but this effect is gradually weakened with the decline of the marginal bone level.

Influence of thread shapes of custommade root-analogue implants on stress distribution of peri-implant bone: A three-dimensional finite element analysis

To explore the effects from the thread shapes of custom-made root-analogue implant (RAI) on distributions of von Mises stress around the peri-implant bone. Five one-stage RAI three-dimensional finite element (FE) models with different thread shapes (V-shaped design, square design, buttress design, reverse buttress design and none thread design) and congruent bone were created through reverse engineering technology. The data of the five models were imported into the FE analysis software to calculate. A force of 100 N was applied parallelly and of 45° to the implant axis respectively. Analysis was performed to evaluate the von Mises stress distributions at the peri-implant regions with the help of the Ansys 16 software. The von Mises stresses distributed mostly at the implant cervical regions and the tip ends of the threads on the cortical bone under oblique loading, while on the cancellous bone, the stresses concentrated mostly on the implant lateral cervical regions, the tip ends of the threads and the apical regions. When under vertical loading, the von Mises stresses distributed mostly at the implant cervical regions on the cortical bone while at the tip ends of the threads and the lateral apical regions on the cancellous bone. The von Mises stresses were better distributed on the thread groups under both kinds of loadings compared with no thread design. But there was no obvious difference among the different thread groups. The concentrations of the von Mises stresses on the cancellous bone in the thread groups were mostly at the tip ends of the threads while less in the apical area. The von Mises stresses were better distributed on the cancellous bone on the other three thread designs than on square design. Thread designs are advocated for the reason that adding thread designs to the RAI standard design will have a positive effect on stress distributions at the peri-implant regions and it will reduce the concentrations of von Mises stresses on the cortical bone. From the standpoint of the stress distribution, V-shaped design, buttress design and reverse buttress design are more suitable for RAI than square design. There is no difference of the distributions of the von Mises stresses in the RAI between different thread designs.

Study on the biomechanical responses of the loaded bone in macroscale and mesoscale by multiscale poroelastic FE analysis

BackgroundBone is a hierarchically structured composite material, and different hierarchical levels exhibit diverse material properties and functions. The stress and strain distribution and fluid flow in bone play an important role in the realization of mechanotransduction and bone remodeling.MethodsTo investigate the mechanotransduction and fluid behaviors in loaded bone, a multiscale method was developed. Based on poroelastic theory, we established the theoretical and FE model of a segment bone to provide basis for researching more complex bone model. The COMSOL Multiphysics software was used to establish different scales of bone models, and the properties of mechanical and fluid behaviors in each scale were investigated.ResultsFE results correlated very well with analytical in macroscopic scale, and the results for the mesoscopic models were about less than 2% different compared to that in the macro–mesoscale models, verifying the correctness of the modeling. In macro–mesoscale, results demonstrated that variations in fluid pressure (FP), fluid velocity (FV), von Mises stress (VMS), and maximum principal strain (MPS) in the position of endosteum, periosteum, osteon, and interstitial bone and these variations can be considerable (up to 10, 8, 4 and 3.5 times difference in maximum FP, FV, VMS, and MPS between the highest and the lowest regions, respectively). With the changing of Young’s modulus (E) in each osteon lamella, the strain and stress concentration occurred in different positions and given rise to microscale spatial variations in the fluid pressure field. The heterogeneous distribution of lacunar–canalicular permeability (klcp) in each osteon lamella had various influence on the FP and FV, but had little effect on VMS and MPS.ConclusionBased on the idealized model presented in this article, the presence of endosteum and periosteum has an important influence on the fluid flow in bone. With the hypothetical parameter values in osteon lamellae, the bone material parameters have effect on the propagation of stress and fluid flow in bone. The model can also incorporate alternative material parameters obtained from different individuals. The suggested method is expected to provide dependable biological information for better understanding the bone mechanotransduction and signal transduction.

Designing a mandibular advancement device with topology optimization for a partially edentulous patient

Statement of problemPatients with partial tooth loss treated with implant-supported fixed partial dentures (FPDs) have difficulty using conventional mandibular advancement devices (MADs) because of the risk of side effects. Also, which design factors affect biomechanical stability when designing MADs with better stability is unclear. PurposeThe purpose of this finite element (FE) analysis study was to analyze the effect of the MAD design on biomechanical behavior and to propose a new design process for improving the stability of MADs. Material and methodsEach 3D model consisted of the maxillofacial bones, teeth, and implant-supported FPDs located in the left tooth loss area from the first premolar to the second molar and a MAD. Three types of custom-made MADs were considered: a complete-coverage MAD covering natural tooth-like conventional MADs, a shortened MAD excluding the coverage on the implant-supported FPD, and a newly designed MAD without anterior coverage. For the new MAD design, topology optimization was conducted to reduce the stress exerted on the teeth and to improve retention of the MAD. The new MAD design was finished by excluding the coverage of the maxillary and mandibular central incisors based on the results of the topology optimization. A mandibular posterior restorative force for a protrusion amount of 40% was used as the loading condition. The principal stress and pressure of the cancellous bone and periodontal ligaments (PDLs) were identified. ResultsConsidering the load concentration induced by the complete-coverage MAD, bone resorption risk and root resorption risk were observed at both ends of the mandibular teeth. The shortened MAD resulted in the highest stress concentration and pressure with the worst stability. However, in the case of the complete-coverage MAD, the pressure in the PDLs was reduced to the normal range, and the risk of root resorption was reduced. ConclusionsFor patients with implant-supported FPDs, MAD designs with different extents of coverage had an influence on biomechanical behavior in terms of stress distribution in cancellous bone and PDLs. A MAD design without anterior coverage provided improved stability compared with complete-coverage or shortened designs. The presented method for MAD design, which combined FE analysis and topology optimization, could be effectively applied in the design of such improved MADs.

Evaluation of Stress Distribution on Mandibular Implant-Supported Overdentures With Different Bone Heights and Attachment Types: A 3D Finite Element Analysis.

The biomechanical behavior of the edentulous mandible with bone irregularities that has been rehabilitated with implant-supported overdentures has become an important factor for treatment planning. Restorative options, including dental implants with various attachments, affect the stress distribution. The purpose of this study was to evaluate the stress distribution of cortical bone around the implant neck and implant structures in overdentures with two different attachment types at the edentulous mandible and with different bone heights using three-dimensional finite element analysis. Five three-dimensional models of an edentulous mandible were designed and implemented. Ten models were constructed with ball and locator attachments. Static bilateral and unilateral vertical and oblique occlusal loads with magnitudes of 100 N were applied to the overdentures. The principal stresses were higher in the presence of oblique loads compared to vertical loads in all the analyzed models. Maximum principal stresses were observed around the mesial side of the contralateral implant, and the minimum principal stresses were noted around the distal side of ipsilateral implant during unilateral vertical loading. These patterns were reversed during oblique loadings. The ball attachment models yielded lower von Mises stress values than the locator models at all the loading conditions, while the stress distributions were similar in the models with the same and different bone levels. Correspondingly, bone corrections due to irregularities may not be necessary in terms of biomechanics. The results of this study may provide clinicians a better understanding for the mandibular overdenture design in the cases at which different bone heights exist.

The influence of implant angulation on stress distribution in maxillary central incisor – 3D finite element analysis

Background Implant -supported prostheses in the anterior maxilla have been considered a prosthetic and surgical challenge due to the small quantity of bone. Guided bone regeneration technology solves the problem of insufficient bone volume to some extent. Alternatively, the implant may be placed with an angulation, which is simple, cost-effective, less invasive and reduces treatment time. However, implant angulation may increase the likelihood of overloading, leading to implant failure. Aim/Hypothesis The influence of implant angulation on stress distribution is still a matter of debate. The aim of this study was to investigate the stress distribution on the bone around tilted implants in maxillary central incisor by means of finite element analysis. Material and Methods FEA models of a single-unit crown supported by the implant (diameter: 3.5 mm, length: 11.5 mm) and angulated screw channel abutment (NobelProcera ASC) or straight abutment were used. According to the different angulation of the implant placed in bone, solid models were assembled, and divided into 3 groups, totally 9 models. In control group, the implant was placed in an ideal direction, recorded as 0°. In group A(palatal inclination), implants were palatal placed at -10°, -5°. In group B(inclination), the implant was labially placed at 5°, 10°, 15°, 20°, 25°, 20°. Then all the models were meshed in ANSYS 15.0 software. A palatal bite force of 140 N was applied to a point 2 mm below the incisal edge, with an approximately 50° to the long axis of the crown. The von Mises stress distribution in bone around implants were analyzed. Results The general patterns for stress distribution were similar in all models. Stress was mainly concentrated in the crestal bone around the neck of implants, the stress values in cortical bone were higher than that in cancellous bone. With the increase of implant labial inclination, the stress was gradually concentrated in the labial crestal bone. Comparing with the control group, when the implant was labially placed at the angle of 20°, 25°, 30°, the maximum von Mises stress in bone increased significantly. The stress of cortical bone increased by 127.33%, 189.91% and 117.11%, meanwhile increased by 155.26%, 156.76% and 89.19% in cancellous bone. There was no significant correlation between the maximum von Mises stress and the angle of implant tilted. Conclusion and Clinical Implications In the anterior maxilla, the angles ranging from 0 degree to 15 degree are optimal choice for the anterior implants.When the implant tilted labially reached 20 degree, the stress values in bone increased significantly, which may increase the chance of implant failure.

295. Comparison of the biomechanical performances among PLF, TLIF, OLIF and XLIF: a finite element analysis

BACKGROUND CONTEXT Posterolateral fusion (PLF) and lumbar interbody fusion (LIF) are the commonly used techniques for the treatment of lumbar degenerative diseases. Although the superiority of PLF or LIF remains controversial, LIF technique provides the potential advantages of anterior column supports and 360° arthrodesis. The most commonly used LIF technique is transforaminal LIF (TLIF). Lateral approaches including extreme LIF (XLIF) and the subsequent oblique LIF (OLIF), have been accepted by an increasing number of spine surgeons due to their unique advantages. Previous studies revealed that radiological outcomes significantly varied among PLF, TLIF, XLIF and OLIF, suggesting their different biomechanical properties. PURPOSE To compare the biomechanical differences among PLF, TLIF, XLIF and OLIF construct and determine which surgical construct was most beneficialto the segmental stability and cage subsidence resistance. STUDY DESIGN/SETTING a finite element (FE) analysis. OUTCOME MEASURES The ranges of motion (ROMs) and stress peaks in the cortical endplate, cancellous bone and posterior instrumentations were compared among the five constructs. METHODS An intact FE model of the L3-L5 lumbar spine was constructed. After validation, the PLF, TLIF with a banana-shaped cage, TLIF with a straight cage, XLIF and OLIF procedures were simulated at the L4/5 level. A bilateral pedicle screw fixation was added in each construct. The TLIF banana-shaped cage was placed on the anterior one-third portion of the endplate. The TLIF straight cage was placed around the midpoint of the endplate and was diagonally positioned at an angle of 45° . The XLIF cage was placed at the mid-endplate and the OLIF cage was placed more anteriorly. An axial preload of 400 N was imposed on the superior surface of L3 to simulate the corresponding physiologic compression. Another 8 Nm was applied on L3 to simulate flexion, extension, bending and axial rotation. RESULTS The PLF construct has much higher ROMs than the LIF constructs (0.44° to -1.05° vs 0.29° to -0.72°). TLIF with a straight cage induces the highest stress peak in the endplate and cancellous bone (23.2-63.7 MPa and 0.69-2.03 MPa, respectively), followedby TLIF with a banana-shaped cage (23.7-44.8 MPa and 0.6-1.36 MPa, respectively). OLIF (16.76-32.41 MPa and 0.54-1.07 MPa, respectively) and XLIF (17.01-35.34 MPa and 0.56-1.12 MPa, respectively) constructs induces much lower stress peaks in the endplate and cancellous bone. In the PLF construct, the stress peaks in the posterior instrument range from 244.6 MPa to 377.4 MPa, which are significantly higher than those in the LIF constructs (123.9-237.4 MPa). CONCLUSIONS The PLF construct had\s less stability than the LIF construct due to the higher ROMs and stress peaks in the posterior instrument. TLIF with a banana-shaped cage outperforms TLIF with a straight cage in decreasing the stress peaks in the endplate and cancellous bone, as the banana-shaped cage is ideally located more anteriorly and placed on the strong cortical rim of the endplate. Compared with TLIF constructs, the much larger cages used in the OLIF and XLIF constructs induce significantly fewer stress peaks and increase homogeneous stress distributions in the endplate cancellous bone, which was beneficial to the subsidence resistance and maintenance of disc height and segmental angle. FDA DEVICE/DRUG STATUS XLIF (Approved for this indication), OLIF (Approved for this indication)

Analysis of Biomechanical Differences Between Condylar Constrained Knee and Rotating Hinged Implants: A Numerical Study

BackgroundDifferent levels of constraint for total knee arthroplasty can be considered for revision surgeries. While prior studies have assessed the clinical impact and patient outcomes of condylar constrained knee (CCK) and rotating hinged (RTH) implants, nowadays little is known about the biomechanical effects induced by different levels of constraint on bone stress and implant micromotions. MethodsCCK and RTH implant models were analyzed using a previously validated numerical model. Each system was investigated during a squat and a lunge motor task. The force in the joint, the bone and implant stresses, and micromotions in this latter were analyzed and compared among designs. ResultsDifferent activities induced similar bone stress distributions in both implants. The RTH implant induces mostly high stress compared to the CCK implant, especially in the region close to tip of the stem. However, in the proximal tibia, the stresses achieved with the CCK implant is higher than the one calculated for the RTH design, due to the presence of the post-cam system. Accordingly, the condylar constrained design shows higher implant micromotions due to the greater torsional constraint. ConclusionDifferent levels of constraint in revision arthroplasty were always associated with different biomechanical outputs. RTH implants are characterized by higher tibial stress especially in the region close to the stem tip; condylar implants, instead, increase the proximal tibial stress and therefore implant micromotions, as a result of the presence of the post-cam mechanism. Surgeons will have to consider these findings to guarantee the best outcome for the patient and the related change in the bone stress and implant fixation induced by different levels of constrain in a total knee arthroplasty.

Finite Element Analysis of Human Tibia Modeled as a Functionally Graded Material

Human tibia, the second largest bone in human body, is made of complex biological material having inhomogeneity and anisotropy in such a manner that makes it a functionally graded material. While analyses of human tibia assuming it to be made of different material regions have been attempted in past, functionally graded nature of the bone in the mechanical analysis has not been considered. This study highlights the importance of functional grading of material properties in capturing the correct stress distribution from the finite element analysis (FEA) of human tibia under static loading. Isotropic and orthotropic material properties of different regions of human tibia have been graded functionally in three different manners and assigned to the tibia model. The nonfunctionally graded and functionally graded models of tibia have been compared with each other. It was observed that the model in which functional grading was not performed, uneven distribution and unrealistic spikes of stresses occurred at the interfaces of different material regions. On the contrary, the models with functional grading were free from this potential artifact. Hence, our analysis suggests that functional grading is essential for predicting the actual distribution of stresses in the entire bone, which is important for biomechanical analysis. We find that orthotropic nature of the bone tends to increase the maximum von Mises stress in the entire tibia, while inclusion of cross-sectional inhomogeneity typically increases the stresses across normal cross section. Accordingly, our analysis suggests that both orthotropy as well as cross-sectional inhomogeneity should be included to correctly capture the stress distribution in the bone.

Prosthetic Correction of Proclined Maxillary Incisors: A Biomechanical Analysis.

In some cases of proclined maxillary incisors, the proclination can be corrected by a fixed prosthesis. The aim of this study was to investigate the magnitude and distribution of (i) principal stresses in the adjacent alveolar bone and (ii) direct and shear stresses that are normal and parallel, respectively, to the bone-tooth interface of a normal angulated maxillary incisor, a proclined one, and a proclined one corrected with an angled prosthetic crown. 2D finite-element models were constructed, and a static load of 200 N on the palatal surface of the maxillary incisor at different load angles was applied. Load angles (complementary angle to interincisal angle) ranging from 20° to 90° were applied. The results indicate that the load angle could have a more significant impact on the overall stress distributions in the surrounding alveolar bone and along the bone-tooth interface than the proclination of the maxillary incisor. Provided that the resulting interincisal angle is 150° or smaller, the stresses in the surrounding bone and at the bone-tooth interface are similar between a proclined maxillary incisor and the one with prosthodontic correction. Hence, such a correction, when deemed appropriate clinically, can be undertaken with confidence that there is little risk of incurring additional stresses over that already in existence, in the supporting bone and at the tooth-bone interface.