Influence of PEEK Coating on Hip Implant Stress Shielding: A Finite Element Analysis

State-of-the-art polyetheretherketone three-dimensional printing and multifunctional modification for dental implants

Polyetheretherketone (PEEK) is a high-performance thermoplastic polymer with an elastic modulus close to that of the jawbone. PEEK has the potential to become a new dental implant material for special patients due to its radiolucency, chemical stability, color similarity to teeth, and low allergy rate. However, the aromatic main chain and lack of surface charge and chemical functional groups make PEEK hydrophobic and biologically inert, which hinders subsequent protein adsorption and osteoblast adhesion and differentiation. This will be detrimental to the deposition and mineralization of apatite on the surface of PEEK and limit its clinical application. Researchers have explored different modification methods to effectively improve the biomechanical, antibacterial, immunomodulatory, angiogenic, antioxidative, osteogenic and anti-osteoclastogenic, and soft tissue adhesion properties. This review comprehensively summarizes the latest research progress in material property advantages, three-dimensional printing synthesis, and functional modification of PEEK in the fields of implant dentistry and provides solutions for existing difficulties. We confirm the broad prospects of PEEK as a dental implant material to promote the clinical conversion of PEEK-based dental implants.

Structural optimization of orthopedic hip implant using parametric and non-parametric optimization techniques

This research investigates the reduction in weight of hip implant by the application of parametric and non-parametric optimization techniques. Orthopaedic hip implants can be made from metals, ceramics, composites, or metallic alloys and are generally solid structures. The stiffness of orthopaedic hip implant is a pertaining problem when implanted in the human body as Hip implant are stiffer than bone material and causes stress shielding. This results in bone weakening which causes osteoporosis. Reduction in mass of femur stem results in stiffness reduction of femur stem. Non-Parametric topology optimization results in 34.9% mass reduction and parametric optimization based on Central Composite Design technique in Design of Experiments (DoE) uses hole diameters as parameters and performs structural optimization that results in 22% mass reduction.

Optimization of stress distribution of bone-implant interface (BII)

Many studies have found that the threshold of occlusal force tolerated by titanium-based implants is significantly lower than that of natural teeth due to differences in biomechanical mechanisms. Therefore, implants are considered to be susceptible to occlusal trauma. In clinical practice, many implants have shown satisfactory biocompatibility, but the balance between biomechanics and biofunction remains a huge clinical challenge. This paper comprehensively analyzes and summarizes various stress distribution optimization methods to explore strategies for improving the resistance of the implants to adverse stress. Improving stress resistance reduces occlusal trauma and shortens the gap between implants and natural teeth in occlusal function. The study found that: 1) specific implant-abutment connection design can change the force transfer efficiency and force conduction direction of the load at the BII; 2) reasonable implant surface structure and morphological character design can promote osseointegration, maintain alveolar bone height, and reduce the maximum effective stress at the BII; and 3) the elastic modulus of implants matched to surrounding bone tissue can reduce the stress shielding, resulting in a more uniform stress distribution at the BII. This study concluded that the core BII stress distribution optimization lies in increasing the stress distribution area and reducing the local stress peak value at the BII. This improves the biomechanical adaptability of the implants, increasing their long-term survival rate.

Stress Shielding and Bone Resorption of Press-Fit Polyether-Ether-Ketone (PEEK) Hip Prosthesis: A Sawbone Model Study

Stress shielding secondary to bone resorption is one of the main causes of aseptic loosening, which limits the lifespan of the hip prostheses and increases the rates of revision surgery. This study proposes a low stiffness polyether-ether-ketone (PEEK) hip prostheses, produced by fused deposition modelling to minimize the stress difference after the hip replacement. The stress shielding effect and the potential bone resorption of the PEEK implant was investigated through both experimental tests and FE simulation. A generic Ti6Al4V implant was incorporated in this study to allow fair comparison as control group. Attributed to the low stiffness, the proposed PEEK implant showed a more natural stress distribution, less stress shielding (by 104%), and loss in bone mass (by 72%) compared with the Ti6Al4V implant. The stiffness of the Ti6Al4V and the PEEK implant were measured through compression tests to be 2.76 kN/mm and 0.276 kN/mm. The factor of safety for the PEEK implant in both static and dynamic loading scenarios were obtained through simulation. Most of the regions in the PEEK implant were tested to be safe (FoS larger than 1) in terms of representing daily activities (2300 N), while the medial neck and distal restriction point of the implant attracts large von Mises stress 82 MPa and 76 MPa, respectively, and, thus, may possibly fail during intensive activities by yield and fatigue. Overall, considering the reduction in stress shielding and bone resorption in cortical bone, PEEK could be a promising material for the patient-specific femoral implants.

A Review of Biomaterials and Associated Performance Metrics Analysis in Pre-Clinical Finite Element Model and in Implementation Stages for Total Hip Implant System

Total hip replacement (THR) is a common orthopedic surgery technique that helps thousands of individuals to live normal lives each year. A hip replacement replaces the shattered cartilage and bone with an implant. Most hip implants fail after 10–15 years. The material selection for the total hip implant systems is a major research field since it affects the mechanical and clinical performance of it. Stress shielding due to excessive contact stress, implant dislocation due to a large deformation, aseptic implant loosening due to the particle propagation of wear debris, decreased bone remodeling density due to the stress shielding, and adverse tissue responses due to material wear debris all contribute to the failure of hip implants. Recent research shows that pre-clinical computational finite element analysis (FEA) can be used to estimate four mechanical performance parameters of hip implants which are connected with distinct biomaterials: von Mises stress and deformation, micromotion, wear estimates, and implant fatigue. In vitro, in vivo, and clinical stages are utilized to determine the hip implant biocompatibility and the unfavorable local tissue reactions to different biomaterials during the implementation phase. This research summarizes and analyses the performance of the different biomaterials that are employed in total hip implant systems in the pre-clinical stage using FEA, as well as their performances in in vitro, in vivo, and in clinical studies, which will help researchers in gaining a better understanding of the prospects and challenges in this field.

An Experimental and Virtual Approach to Hip Revision Prostheses

(1) Introduction: The changes in the joint morphology inevitably lead to prosthesis, but the hip pathology is complex. The hip arthroplasty is a therapeutic solution and can be caused, most frequently, by primary and secondary coxarthrosis due to or followed by traumatic conditions. The main aim of this study was to find the method of revision hip prosthesis that preserves as much bone material as possible and has sufficiently good mechanical strength. (2) Materials and Methods: In this study, in a first step, the two revision prostheses were performed on bone components taken from an animal (cow), and then, they were tested on a mechanical testing machine until the prostheses physically failed, and the force causing their failure was determined. (3) Results: These prostheses were then modelled in a virtual environment and tested using the finite element method (FEM) in order to determine their behaviour under loading from normal human gait. Displacement, strain, and stress maps were obtained. (4) Discussion: Discussions on hip revision prostheses, method, and theory analysis are presented at the end of the paper. (5) Conclusions: Important conclusions are drawn based on comparative analyses. The main conclusion shows that the both orthopaedic prostheses provide a very good resistance.

Impact of rGO-coated PEEK and lattice on bone implant

The composite coating can effectively inhibit bacterial proliferation and promote the expression of bone-building genes in-vitro. Therefore, a novel production was used to produce poly-ether-ether-ketone, and reduced graphene oxide (PEEK-rGO) scaffolds with ratios of 1-3%, combining a different lattice for a bone implant. An inexpensive method was developed to prepare the new coatings on the PEEK scaffold with reduced graphene oxide (rGO). Mechanical testing, data analysis and cell culture tests for in-vitro biocompatibility scaffold characterisation for the PEEK composite were conducted. Novel computation microanalysis of four-dimensional (4D) printing of microstructure of PEEK-rGO concerning the grain size and three dimensional (3D) morphology was influenced by furrow segmentation of grains cell growth on the composite, which was reduced from an average of 216-155 grains and increased to 253 grains on the last day. The proposed spherical nanoparticles cell grew with time after dispersed PEEK nanoparticles in calcium hydroxyapatite (cHAp) grains. Also, the mechanical tests were carried out to validate the strength of the new composites and compare them to that of a natural bone. The established 3D-printed PEEK composite scaffolds significantly exhibited the potential of bone implants for biomimetic heterogeneous bone repair.

Antibacterial Activity Studies of 3D-Printing Polyetheretherketone Substrates with Surface Growth of 2D TiO2/ZnO Rodlike Arrays

Heterogeneous metal implants have been applied in clinical treatments of skeletal wounds, but their low antibacterial properties and the possibility of a release of metal ions may have harmful influences on the human body. Therefore, a polymer implant with low cost, high safety, an elastic modulus similar to that of human bone, and a good antibacterial property must be produced for orthopedic treatments. In this study, the surface of a 3D-printed polyetheretherketone (PEEK) disk was grown with ZnO/TiO₂ rodlike arrays using a chemical bath deposition. X-ray diffraction patterns and transmission electron microscopy images showed that TiO₂/ZnO rodlike arrays were deposited onto the PEEK substrate. With the direct absorption of antibiotic agents onto the surface of TiO₂/ZnO/PEEK samples, their antibacterial performances greater than the values of minimum inhibitory concentration required to inhibit the growth of 90% of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) remained for around 10 days. The concentration of Zn²⁺ ions in a buffer solution is reduced with the coating of a TiO₂ layer on a ZnO rodlike array. The sample with absorption from a mixture containing ampicillin and vancomycin salts with a weight ratio of 1:1 had the best inhibitory effect on the growth of E. coli and S. aureus.

When the Total Hip Replacement Fails: A Review on the Stress-Shielding Effect

Total hip arthroplasty is one of the most common and successful orthopedic surgeries. Sometimes, periprosthetic osteolysis occurs associated with the stress-shielding effect: it results in the reduction of bone density, where the femur is not correctly loaded, and in the formation of denser bone, where stresses are confined. This paper illustrates the stress shielding effect as a cause of the failing replacement of the hip joint. An extensive literature survey has been accomplished to describe the phenomenon and identify solutions. The latter refer to the design criteria and the choice of innovative materials/treatments for prosthetic device production. Experimental studies and numerical simulations have been reviewed. The paper includes an introduction to explain the scope; a section illustrating the causes of the stress shielding effect; a section focusing on recent attempts to redefine prosthetic device design criteria, current strategies to improve the osteointegration process, and a number of innovative biomaterials; functionally graded materials are presented in a dedicated section: they allow customizing prosthesis features with respect to the host bone. Conclusions recommend an integrated approach for the production of new prosthetic devices: the “engineering community” has to support the “medical community” to assure an effective translation of research results into clinical practice.

Static, fatigue and stress-shielding analysis of the use of different PEEK based materials as hip stem implants

There is a possibility that hip joints may become dysfunctional due to age, wear or some accidents, and in this case they need to be replaced with hip implants. However, after conventional hip stem implantation, the load transferred to the bone usually decreases due to the high stiffness of the metallic (most commonly Ti6Al4V, CoCr or stainless steel) hip stem implant, and as a result, mineral loss occurs in the bone which weakens. On the other hand, PEEK is an advantageous material with its low cost, ease of production, corrosion resistance and biocompatibility. More importantly, it has the potential to be a good alternative to metallic materials in load-bearing bone replacements, thanks to its mechanical properties and density close to that of the bone. In this study, hip stem implants having three different commercial PEEK materials and four different metallic main spar designs were modeled. Their behavior under static and dynamic loading conditions was analyzed according to ASTM-F2996-20 and ISO-7206-4:2010 standard test methods, and the stress-shielding effect of hip stems modeled as implanted into the femur was simulated using ANSYS commercial finite element analysis software. According to the results, it was observed that CFP based hip stem models meet the five million life time criteria and increase the stress on the femur bone by up to 57%.

Influence of margin design and restorative material on the stress distribution of endocrowns: a 3D finite element analysis

Background

This study aimed to evaluate the stress distributions in endocrown restorations as applied to endodontically treated teeth (ETT), according to the factors of “margin design” (four levels) and “restorative material” (six levels).

Methods

Four 3D-finite elements models were constructed for endocrown restored molars considering different margin designs. Model A was prepared with a flat butt joint margin and received an endocrown with a 2.0-mm occlusal thickness. Model B was prepared with a 20° bevel margin and received an endocrown with a 2.0-mm occlusal thickness. Model C was prepared with an axial reduction and 1-mm shoulder margin and received an endocrown with a 2.0-mm occlusal thickness. Model D was prepared with an anatomic margin and received an endocrown with a 2.0-mm occlusal thickness. The following endocrown materials were used: In-Ceram Zirconia (Zr), Vita Suprinity (VS), IPS Empress (IE), Grandio blocs (GR), VisCalor bulk (VS), and CopraPeek Light (CP). The Load application (600 N) was performed at the food bolus and tooth surface during the closing phase of the chewing cycle. The results for the endocrown and tooth remnants were determined according to the von Mises stress. The failure risk of the cement layer was also calculated based on the normal stress criterion.

Results

Model D (with an anatomic margin) showed the greatest stress concentrations, especially in the irregular and sharp angles of the restoration and tooth remnants. The stress concentrated on the dentin was significantly lower in Model B with a 20° bevel margin (20.86 MPa), i.e., 1.3 times lower than the other three margin designs (27.80 MPa). Restorative materials with higher elastic moduli present higher stress concentrations inside the endocrown and transmit less stress to the cement layer, resulting in lower bonding failure risks. In contrast, materials with an elastic modulus similar to that of dentin presented with a more homogeneous stress distribution on the whole structure.

Conclusions

An endocrown with a 20° bevel margin design could be a favorable preparation option for ETT. Composite resins (GR and VC) exhibit a more even stress distribution, and seem to be more promising materials for endocrown molars.

An Amorphous Peri-Implant Ligament with Combined Osteointegration and Energy-Dissipation

Progress toward developing metal implants as permanent hard-tissue substitutes requires both osteointegration to achieve load-bearing support, and energy-dissipation to prevent overload-induced bone resorption. However, in existing implants these two properties can only be achieved separately. Optimized by natural evolution, tooth-periodontal-ligaments with fiber-bundle structures can efficiently orchestrate load-bearing and energy dissipation, which make tooth-bone complexes survive extremely high occlusion loads (>300 N) for prolonged lifetimes. Here, a bioinspired peri-implant ligament with simultaneously enhanced osteointegration and energy-dissipation is presented, which is based on the periodontium-mimetic architecture of a polymer-infiltrated, amorphous, titania nanotube array. The artificial ligament not only provides exceptional osteoinductivity owing to its nanotopography and beneficial ingredients, but also produces periodontium-similar energy dissipation due to the complexity of the force transmission modes and interface sliding. The ligament increases bone-implant contact by more than 18% and simultaneously reduces the effective stress transfer from implant to peri-implant bone by ≈30% as compared to titanium implants, which as far as is known has not previously been achieved. It is anticipated that the concept of an artificial ligament will open new possibilities for developing high-performance implanted materials with increased lifespans.

Biomechanical analyses of one-piece dental implants composed of titanium, zirconia, PEEK, CFR-PEEK, or GFR-PEEK: Stresses, strains, and bone remodeling prediction by the finite element method

This work aimed to assess the biomechanics, using the finite element method (FEM), of traditional titanium Morse taper (MT) dental implants compared to one-piece implants composed of zirconia, polyetheretherketone (PEEK), carbon fiber-reinforced PEEK (CFR-PEEK), or glass fiber-reinforced PEEK (GFR-PEEK). MT and one-piece dental implants were modeled within a mandibular bone section and loaded on an oblique force using FEM. A MT implant system involving a Ti6Al4V abutment and a cp-Ti grade IV implant was compared to one-piece implants composed of cp-Ti grade IV, zirconia (3Y-TZP), PEEK, CFR-PEEK, or GFR-PEEK. Stress on bone and implants was computed and analyzed while bone remodeling prediction was evaluated considering equivalent strain. In comparison to one-piece implants, the traditional MT implant revealed higher stress peak (112 MPa). The maximum stresses on the one-piece implants reached ~80 MPa, regardless their chemical composition. MT implant induced lower bone stimulus, although excessive bone strain was recorded for PEEK implants. Balanced strain levels were noticed for reinforced PEEK implants of which CFR-PEEK one-piece implants showed proper biomechanical behavior. Balanced strain levels might induce bone remodeling at the peri-implant region while maintaining low risks of mechanical failures. However, the strength of the PEEK-based composite materials is still low for long-term clinical performance.

Biofilm Formation on the Surface of (Poly)Ether-Ether-Ketone and In Vitro Antimicrobial Efficacy of Photodynamic Therapy on Peri-Implant Mucositis

Poly-ether-ether-ketone (PEEK) is an aesthetically pleasing natural material with good biocompatibility and shock absorption characteristics. The application of PEEK as a dental implant or abutment is expected to reduce the risk of failure and enhance aesthetics. Given that approximately one in 15 patients have allergic reactions to antibiotics, photodynamic therapy (PDT) has been gaining attention as an alternative treatment. Herein, the applicability of PEEK dental implants or abutments was investigated using material analyses, biofilm formation assay, and cell viability tests. The possible use of PDT for peri-implant mucositis was evaluated with the biofilm removal assay. The obtained data were analyzed based on the multivariate analysis of variance, paired t-tests, and the Pearson correlation coefficient (α = 0.05). The results revealed that PEEK was significantly less conducive to the formation of biofilms with S. mutans and A. actinomycetemcomitan (p < 0.001) but exhibited comparable MG-63 (human osteoblast-like) osteoblast cell viability (p > 0.05) to the other materials. PDT had similar antimicrobial efficacy and yielded similar biofilm removal effects to antibiotics. Altogether, these findings suggest that PEEK has attractive features and can serve as an alternative material for dental implants or abutments. In cases where peri-implant mucositis occurs, PDT can be used as an accessible therapeutic approach.

Review on Development and Dental Applications of Polyetheretherketone-Based Biomaterials and Restorations

Polyetheretherketone (PEEK) is an important high-performance thermoplastic. Its excellent strength, stiffness, toughness, fatigue resistance, biocompatibility, chemical stability and radiolucency have made PEEK attractive in dental and orthopedic applications. However, PEEK has an inherently hydrophobic and chemically inert surface, which has restricted its widespread use in clinical applications, especially in bonding with dental resin composites. Cutting edge research on novel methods to improve PEEK applications in dentistry, including oral implant, prosthodontics and orthodontics, is reviewed in this article. In addition, this article also discusses innovative surface modifications of PEEK, which are a focus area of active investigations. Furthermore, this article also discusses the necessary future studies and clinical trials for the use of PEEK in the human oral environment to investigate its feasibility and long-term performance.

Does the prosthesis weight matter? 3D finite element analysis of a fixed implant-supported prosthesis at different weights and implant numbers

PURPOSE

This study evaluated the influence of prosthesis weight and number of implants on the bone tissue microstrain.

MATERIALS AND METHODS

Fifteen (15) fixed full-arch implant-supported prosthesis designs were created using a modeling software with different numbers of implants (4, 6, or 8) and prosthesis weights (10, 15, 20, 40, or 60 g). Each solid was imported to the computer aided engineering software and tetrahedral elements formed the mesh. The material properties were assigned to each solid with isotropic and homogeneous behavior. The friction coefficient was set as 0.3 between all the metallic interfaces, 0.65 for the cortical bone-implant interface, and 0.77 for the cancellous bone-implant interface. The standard earth gravity was defined along the Z-axis and the bone was fixed. The resulting equivalent strain was assumed as failure criteria.

RESULTS

The prosthesis weight was related to the bone strain. The more implants installed, the less the amount of strain generated in the bone. The most critical situation was the use of a 60 g prosthesis supported by 4 implants with the largest calculated magnitude of 39.9 mm/mm, thereby suggesting that there was no group able to induce bone remodeling simply due to the prosthesis weight.

CONCLUSION

Heavier prostheses under the effect of gravity force are related to more strain being generated around the implants. Installing more implants to support the prosthesis enables attenuating the effects observed in the bone. The simulated prostheses were not able to generate harmful values of peri-implant bone strain.

Surface Characterization of Electro-Assisted Titanium Implants: A Multi-Technique Approach

The understanding of chemical-physical, morphological, and mechanical properties of polymer coatings is a crucial preliminary step for further biological evaluation of the processes occurring on the coatings' surface. Several studies have demonstrated how surface properties play a key role in the interactions between biomolecules (e.g., proteins, cells, extracellular matrix, and biological fluids) and titanium, such as chemical composition (investigated by means of XPS, TOF-SIMS, and ATR-FTIR), morphology (SEM-EDX), roughness (AFM), thickness (Ellipsometry), wettability (CA), solution-surface interactions (QCM-D), and mechanical features (hardness, elastic modulus, adhesion, and fatigue strength). In this review, we report an overview of the main analytical and mechanical methods commonly used to characterize polymer-based coatings deposited on titanium implants by electro-assisted techniques. A description of the relevance and shortcomings of each technique is described, in order to provide suitable information for the design and characterization of advanced coatings or for the optimization of the existing ones.

Effect of different materials and undercut on the removal force and stress distribution in circumferential clasps during direct retainer action in removable partial dentures

OBJECTIVES

This study aimed to evaluate the effect of different materials and undercut on the removal force and stress distribution in the supporting tooth and in the circumferential clasp used in removable partial prosthesis.

METHODS

Upper molars prepared for Akers circumferential clasp with retention and opposing arm were modeled, scanned, elaborated with CAD software and the geometries imported in FEA and analyzed. Six different materials were selected for the clasp (Polyamide, Polyoxymethylene, Polyetheretherketone - PEEK, Gold alloy, Titanium and CoCr) and 3 different undercuts (0.25, 0.50 and 0.75mm), totaling 18 groups.

RESULTS

The clasps presented greater stress in their structure and potentially greater damage to the dental enamel when made with rigid materials and with more undercut; however, they presented greater ability to remain in position.

SIGNIFICANCE

Polyamide with a higher undercut is an esthetic alternative to rigid metallic clasps. It showed promising behavior because it strongly reduces the damage to the enamel, and even with an undercut of 0.75, the retention is lower than for CoCr with a 0.25 undercut, and this retention might still be sufficient. Polyoxymethylene and Polyetheretherketone (PEEK) are not suitable materials for the clasps, because the maximum stress occurring during removal with higher undercuts is higher than the material strength.

Materials for Hip Prostheses: A Review of Wear and Loading Considerations

Replacement surgery of hip joint consists of the substitution of the joint with an implant able to recreate the articulation functionality. This article aims to review the current state of the art of the biomaterials used for hip implants. Hip implants can be realized with different combination of materials, such as metals, ceramics and polymers. In this review, we analyze, from international literature, the specific characteristics required for biomaterials used in hip joint arthroplasty, i.e., being biocompatible, resisting heavy stress, opposing low frictional forces to sliding and having a low wear rate. A commentary on the evolution and actual existing hip prostheses is proposed. We analyzed the scientific literature, collecting information on the material behavior and the human-body response to it. Particular attention has been given to the tribological behavior of the biomaterials, as friction and wear have been key aspects to improve as hip implants evolve. After more than 50 years of evolution, in term of designs and materials, the actual wear rate of the most common implants is low, allowing us to sensibly reduce the risk related to the widespread debris distribution in the human body.

Development and in vitro validation of a simplified numerical model for the design of a biomimetic femoral stem

BACKGROUND

Dense and stiff metallic femoral stems implanted into femurs for total hip arthroplasties produce a stress shielding effect since they modify the original load sharing path in the bony structure. Consequently, in the long term, the strain adaptive nature of bones leads to bone resorption, implant loosening, and the need for arthroplasty revision. The design of new cementless femoral stems integrating open porous structures can reduce the global stiffness of the stems, allowing them a better match with that of bones and provide their firm fixation via bone ingrowth, and, thus reduce the risk of implantation failure.

METHODS

This paper aims to develop and validate a simplified numerical model of stress shielding, which calculates the levels of bone resorption or formation by comparing strain distributions on the surface of the intact and the implanted femurs subjected to a simulated biological loading. Two femoral stems produced by laser powder-bed fusion using Ti-6Al-4V alloy are employed: the first is fully dense, while the second features a diamond cubic lattice structure in its core. The validation consists of a comparison of the numerically calculated force-displacement diagrams, and displacement and strain fields with their experimental equivalents obtained using the digital image correlation technique.

RESULTS AND CONCLUSIONS

The numerical models showed reasonable agreement between the force-displacement diagrams. Also, satisfactory results for the correlation analyses of the total displacement and equivalent strain fields were obtained. The stress shielding effect of the implant was assessed by comparing the equivalent strain fields of the implanted and intact femurs. The results obtained predicted less bone resorption in the femur implanted with the porous stem than with its dense counterpart.