Introduction

Like other synovial joints, the TMJ is vulnerable to injuries and pathologies inherent in synovial joints. Despite advances the TMJ is a complex joint, making it difficult to reestablish the ideals of form and function, generating controversy regarding the most appropriate technique to carry out this task. With the technological advancement of materials, the development of prototypes that biomechanically resemble normal articulation, a new prosthesis for TMJs was developed. Since the early days, surgeons have tried to recover the loss of function in patients who have diseases or intra-articular injuries in the TMJ, limiting the physiological movements of the jaw affecting its function, not allowing adequate masticatory movement. In 1934, Risdon used laminated sheets of gold in the articular fossa in an attempt to prevent relapse in patients with ankylosis in the joint region of the skull base (labrum). Previously, Eggers [1] used sheets of tantalum on the condylar surface. From these early attempts to prevent or avoid relapse in patients with ankylosis and allow proper physiological function, researchers have studied new materials and surgical techniques to restore jaw function, providing these patients a healthier life. Developing a prosthesis for TMJ has benefited patients with bony ankylosis, fibrous ankylosis, degenerative arthritis, psoriatic arthritis, Sjögren’s syndrome, patients undergoing multiple TMJ surgeries, sequelae of trauma and tumors in the region and other conditions that may affect synovial joints. Mercuri [2,3] reports of the development of a number of prostheses aimed at reconstructing and replacing temporomandibular joints with different materials and patterning, (Christensen TMJ prosthesis system, Endotec Hoffmann Pappas TMJ prosthesis system, Lorenz prosthesis and TMJ Concept/Stryker) [2].

The total or partial reconstruction of the TMJ has its issues; some studies (Leibenger research) show thati t is not possible to use a condylar prosthesis without lining the skull base (Glenoid fossa prosthesis), for a period no longer than 20 months, since it may imply a process of reabsorption of the skull base with or without fistula formation, metallosis and new bone formation (ectopic bone). Many materials have been used to create an ideal prosthesis, but most have had a short shelf life or characteristics that have prevented its use [4]. PEEK is a polymer (Polyetheretherketone), derived from petroleum, developed by Invibio/ UK, subdivision from Victrex Co. Marketed in the 1980s, it is a thermoplastic polymer, interconnected to a ketone and other functional groups attached to an aromatic molecular structure, and is semicrystalline [5]. It was previously used for orthopedic and spinal implants. Its molecular structure confers resistance to high temperatures, providing stability, with an inert compound. It is compatible with fillers such as glass and carbon fibers that have greater strength than many metals. In the 1990s, many researchers evaluated the biocompatibility and in vivo stability of PEEK, classifying it as a high-performance material. Early use of synthetic polymers as a framework for developing biomaterials and producing polymethyl methacrylate bone cement was used in 1943; these polymers continue to successfully compete with the metal and ceramic applications for craniomaxillofacial and orthopedic implants [611].

In recent decades, biomedical engineering has emerged as a single discipline, crossing the traditional boundaries between physical and biological sciences. Engineering has expanded the clinical application of polymers as biomaterials, with great benefit and reaching a position of undeniable relevance [11-16]. Since the 1980s, the polyaryletherketone (PEEK) have been increasingly used as a biomaterial of choice for trauma, orthopedic, and spinal implants. And there is an extensive literature from Kurtz [9] on polymer science, with respect to the structure, mechanical properties and chemical resistance of PEEK as a synthesized biomaterial. Based on this research, it can be understood why this polymer family is inherently strong, inert and biocompatible. Due to its relative inertia, PEEK Lt1 20% Ba is already commonly used in developing new bioactive materials. PEEK Lt1 20% Ba has had the greatest clinical impact in the design field of spinal implants (cage, knee prosthesis), being widely accepted due to its radiopacity. It has been used as the material of choice for replacing synovial joints, such as knee prostheses and recently for TMJ (Genovesi.W). Our studies began in 2006, and recently, after extensive laboratory tests (Labmat and CENIC laboratories, Brasil) a TMJ prosthesis system in PEEK Lt1 20% Ba was developed [17]. Numerous studies document the clinical success in developing new products with PEEK Lt1 20% Ba and or CFR PEEK polymers in orthopedic and craniomaxillofacial surgery. A recent survey conducted by the School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA;[11] studies in bio tribology have also investigated PEEK composites of high strength material for friction, impact, and biocompatibility, as well as for use in arthroplasty implants. Due to the interest in further improving implant fixation, biomaterials in PEEK research[9-10] also focused on the compatibility of the polymer with bioactive materials, including hydroxyapatite (HA) as the composite filler or as a surface coating material. As a result of research into biomaterials, PEEK and related compounds can now be manipulated with a wide range of physical, mechanical, and surface properties depending on the application of the implant. PEEK Lt1 20%Ba, in turn, is a light, sturdy and completely biocompatible, even when using Peek on PEEK in a TMJ or knee prosthesis. If a little fragmentation occurs, it will not cause a bodily reaction, as a function of its biocompatibility. Regarding its micro-particles, a histological study shows microparticles being phagocytized, and new vessel formation around them (not giant cell formation). This new material can be indicated for a new products development, it can be a new alternative for medical devices (Figure 1, Figure 2). Furthermore, PEEK particles were incorporated by macrophages, but no giant-cell reactions could be seen. This applies to all sizes of the PEEK Lt1 20%Ba particles.

Figure 1: Glenoid component.

Materials and Methods

After conducting studies on CT scans of 50 TMJs, which measured the size of the mandibular ramus, from the Sigmoid notch to the angle of the jaw, was determined the average length to be 470 mm (Figure 3a). In the glenoid cavity, an average of 0.8 mm concave radius and length of lateral / medial (19 mm), was obtained. (Figure 3b, Figure 3c). A system for customized TMJ prostheses (temporomandibular joint) was developed in PEEK Lt1 20%Ba with 2/3 of the ramus length, understanding that, it is not necessary to cover all the ramus surface for good fixation and preserve all mandible movement. This prosthesis system has been developed by the author since 2012, with PEEK Lt1 20%Ba material, making it possible now to market the product. The Laros Corporation sponsored all projects of developing PEEK LtI 20%Ba, in a customized prosthesis system, by injection molding. In the near future, it will be marketed in three sizes – (small, medium, large). Unlike the existing models on the market, this prosthesis system presents an anatomical / functional design, as shown in the Figures 4a, Figure 4b.

Prototype Prepared for Laboratory Tests

The osteotomy was done at the neck of the condyle, with 15mm under condyle articular surface, maintain horizontal plane at the sigmoid norch, physically it´s not necessary cover all the ramus, 2/3 of the length is enough to fixed it. The ramus component is situated at a 90º angle with the condyle, which must be adapted on the mandibular osteotomy preserving the gravity center with the base of skull. The glenoid cavity was shaped into a flattened plane, with removal of the articular eminence of the temporal bone, at an angle of 90° with the base of the skull, avoiding recurrent subluxation. Thereby, allowing a free (syncopated) joint, avoiding the possibility of dislocation of the prosthesis. (Figure 5a, Figure 5b, Figure 5c, Figure 5d, Figure 6). The tests were carried out in dry medium and at room temperature in an electromechanical machine of the Model E1000 of the brand INSTRON^®. The total PEEK Lt1 20%Ba Prosthesis system mounted in a model Poliurethene Skull/ Mandibular, with density 30D (similar human bone density). It was submitted to cyclic loading with a frequency of 3HZ, with a ratio between loading (R=0.1). The number of cycles was recorded until the failure of the test body or until the limit of cycles for interruption of the assay has been achieved.

Figure 5: A: Mandibular osteotomy with15mm from the glenoid fossa. B: Horizontal plane at the sigmoid norch and 2/3 of the length cover of the ramus. C: The Ramus component is situated at a 90º angle with the condyle. D: The condile is in the center of mandibular gravity.

Figure 6: Eminectomy to maintain flatted with 90° with base skull.

After the fatigue test, the system was subjected to a static compression (Figure 7). The PEEK Lt1 20%Ba screws diameters 2.0mm for (Glenoid fossa component) and 2.4mm for (Mandibular component) were submitted a test of Twisting (torsion) insertion/pullout (Figure 8). For analysis of the roughness parameters was using a measuring machine, the glenoid component was evaluated in six (6) tracks, as identified Figure 9 and the mandibular component was evaluated in fourteen (14) tracks as identified in Figure 10. The reported expanded measurement uncertainty U is stated as the standard measurement uncertainty multiplied by the coverage factor k, which for a T distribution with Veff effective degrees of freedom. It was evaluated under Calibration Laboratory conditions according to ABNT NBR ISO/IEC 17025.

Figure 7: Laboratory experiment with cranio-mandibular model in polyacrylic resin of TMJ Prothesis in PEEK Lt1 20%Ba.

Figure 8

Figure 9

Figure 10

Laboratory results

According to Table 1, was observed that the components of both the joint cavity and the mandibular branch of prosthesis in PEEK Lt1 20%Ba did not present any failure during and after the compression in dynamic and static tests on its surface, of the sample and experimental model. In relation to the resistance curve and maximum strength of PT in PEEK Lt1 20%Ba, was verified according to Figure that the material presents a high degree of resilience when subjected to compression and fatigue loads when compared to other prosthetic materials, reaching in Newtons the maximum resistance of 800N. (Figure 11). According to Figure 12 the TMJ system with 3.000.000 cycles with 350N in dynamic test, compression fatigue did not show any failure. Obs: The brown color of the system in these pictures means that occurred over heating during the injecting molding, but according Invibio Co, UK, it doesn´t alter the PEEK composition, it means that the product it’s in good conditions. Table 2 Shows test results of compression fatigue. The PEEK Lt1 20%Ba screws diameters 2.0mm were submitted a test the according to Figure the curves obtained in the torsion screws test with torque (Nm) axle “x” and Angular Displacement (o) axle “y”, it`s fracture around 351 Newtons (N). (Figure 13a, Figure 13b).

Table 1: Representation of the study variables and the results of the experimental model of TMJ Prothesis in PEEK submitted to compression  and fatigue cycles by compression in the laboratory.

Table 2: Shows test results of compression fatigue.

Figure 11: Graph representing the curve of the experimental laboratory test of maximum fatigue and compression of the TMJ PT model components in PEEK Lt1 20%Ba, Maximum force curves (N) x Number of cycles