ARTHROPLASTY OF THE TEMPOROMANDIBULAR JOINT AND MANUFACTURING PROCESS FOR SUCH PROSTHESIS

FIELD OF INVENTION

[001]. The present invention pertains to the technological sector of dentistry (medical products) and refers to a prosthesis for hybrid temporomandibular joint arthroplasty made of metal alloy and polyethylene with carbon nanostructures treatment.

[002]. Furthermore, the present invention relates to an additive manufacturing process by 3D printing for said prosthesis.

FUNDAMENTALS OF THE INVENTION

[003]. The temporomandibular joint (TMJ) is the connection between the condylar process of the mandible and the glenoid cavity (articular fossa). Problems such as severe trauma and fractures in the bone tissue of the jaw, fibrous ankylosis and other types of complications and injuries can cause a permanent problem in the temporomandibular joint, requiring the installation of an appropriate prosthesis.

[004]. It is a prosthesis for a complex type of joint, in which a condylar joint surface is received in an elliptical cavity in order to allow flexion and extension, adduction and abduction and circumduction movements, that is, all joint movements, less axial rotation.

[005]. There are, in the state of the art, TMJ prostheses that use techniques to restore the total or partial functionality of the TMJ, with different designs and sizes.

[006]. Document BR 20 2019 001420-8 refers to a prosthesis for the temporomandibular joint with a polymer and metal glenoid portion and a condylar portion. However, the glenoid portion occurs through a direct fit between the metallic part and the polymeric part, the fitting point being a region of tension accumulation, prone to injuries and disengagement of the part after being installed in a patient, compromising the construction of the long-term play. Additionally, the condylar portion is welded together, being a fragile region.

[007]. Document BR 11 2019 017141-0 describes a prosthesis for temporomandibular joint with a polymer cranial fossa portion and a metal portion connected by direct fitting, one piece sliding into the other's socket, with the condylar plate being the union of two parts previously separated, being the plate and the head. Again, these types of connections are vulnerable to stresses in the direction of the joint, so the prosthesis can be damaged over time after placement in the patient.

[008]. Documents CN 104546225 and US 6,132,466 disclose temporomandibular joint prostheses with a glenoid portion of polymer and metal connected by fitting, subject to the same problems described above. [009]. As can be seen, most of the existing prostheses in the state of the art have their portion of the articular fossa (glenoid cavity) in two parts and maintained as two parts, being fixed only by a simple fitting. Whereas the prostheses that use polyethylene melting techniques have a smooth metal-polymer interface, which leads to possible disruptions of the metal- polymer interface. Additionally, the prostheses have a condylar part made of two metallic pieces fixed via welding or fitting, which again creates a point of weakness in the condylar part.

[0010]. Another important factor is the feasibility of implementing an automated and flexible manufacture for the production of these prostheses, which reduces production costs and makes possible a decentralized manufacturing process, in which the diagnosis and radiography examination can be given in a clinic and the prostheses can be custom- made according to the patient's clinical data. [0011]. To solve these problems, the present invention designs a prosthesis for temporomandibular joint arthroplasty, an innovative hybrid of metallic alloy and polyethylene with a condylar piece, manufactured in a single piece by additive manufacturing, with no connections, fittings or welds - 3D printing process (Selective Laser Melting (SLM) or Direct Metal Laser Sintering (DMLS)) and with the metallic portion of the articular fossa (glenoid cavity) made with 3D printing technology and polyethylene injection on the metallic part in order to form an 'impossible anchorage, that is, a fitting that can only happen by injecting material in a liquid phase, but which, after solidification, has no means of separating.

[0012]. Therefore, in the state of the art, there is no solution equivalent to the one presented here in the present invention that combines, with an inventive construction, technical differentials, practicality and quality. OBJECTIVES OF THE INVENTION

[0013]. Thus, it is an object of the present invention to provide a solution to the above-listed challenges and limitations by presenting a hybrid metallic and polymeric alloy temporomandibular joint arthroplasty prosthesis.

[0014]. It is an objective of the present invention to provide a prosthesis with degrees of freedom that allow flexion and extension, adduction and abduction and circumduction movements of the jaw bone.

[0015]. It is a further object of the present invention to provide a strong articular fossa (glenoid cavity) component, where the metal-polymer interface has high anchorage, and cannot be detached.

[0016]. It is still an objective of the present invention to provide a condylar component manufactured in a single piece made possible by additive manufacturing, without connections, fittings or welds, making the piece extremely resistant.

[0017]. It is also an objective of the present invention to provide a prosthesis with an external surface covering with carbon nanostructures, which further improve the sliding of the condylar head by reducing the friction caused by the covering itself, reducing the chances of failure and rejection of the prosthesis.

[0018]. It is still an objective of the present invention to reconcile the ambitions of the present invention to contemporary manufacturing processes, with high automation, precision and flexibility via additive manufacturing.

[0019]. It is also an objective of the present invention to provide a prosthesis for the temporomandibular joint that can be produced in different sizes and can also include different details in its construction, meeting the needs of each user.

[0020]. It is still an objective of the present invention to provide a prosthesis for the temporomandibular joint that has a longer useful life than those known today because it does not present problems arising from wear, eventual disengagement or breakage.

SUMMARY OF THE INVENTION

[0021]. The present invention achieves these and other objectives by means of a prosthesis for arthroplasty of the temporomandibular joint comprising:

- a condylar portion and an articular fossa (glenoid cavity)

- the condylar portion comprising a condylar head and a condylar plate, a single piece composed of the same raw material and without connections between the integral parts;

- said condylar head comprising a curved polished surface with circular transverse profile and oval longitudinal profile;

- condylar plate being a thin portion comprising juxtaposed fixing holes for fixing the condylar portion to the ramus of the patient's mandible;

- the articular fossa comprising a metallic structure and a polymeric structure;

- the metallic structure comprising a row of holes, a central portion with anchor pins at the bottom and a chamfered portion at the edge.

- the polymeric structure comprising a lower concave surface, which forms a cavity;

- said polymeric structure further comprising a side chamfered surface, aligned with the chamfered portion of the metallic structure; where the condylar portion is fixed to the right or left ramus of the patient's mandible with appropriate screws that pass through the fixation holes while the articular fossa is fixed to the zygomatic bone of the patient's skull with appropriate screws that pass through the fixation holes and the joint of the temporomandibular prosthesis occurs by fitting the condylar head, the condylar portion, into the cavity of the articular fossa, so that the polished condylar head slides with little friction in the cavity, allowing movements of flexion and extension, adduction and abduction and circumduction of the mandible of the patient.

[0022]. Furthermore, the present invention achieves these and other objectives by means of a process for manufacturing a prosthesis for arthroplasty of the temporomandibular joint that comprises the following steps:

- draw a 3D virtual model of a condylar portion and a metallic structure;

- receive data from the representation of the condylar portion (metallic part) in a selective laser sintering machine, which, by means of a light beam projection (LASER) directed under metallic powder, where said light falls exactly on the cross-sectional design of the model of the of the respective part to be produced;

- laser sintering of the condylar portion, by stacking layers of metallic material to compose said condylar portion, by at least one method among: selective laser sintering (SLS) and Direct Metal Laser Sintering (DMLS);

- removal of support structures from the sintering method;

- carbon nanostructure coating on the outer surface of the condylar plate and on the condylar head;

- injection of molten polymeric material at controlled temperature under the lower part of the metallic structure, so that a polymeric structure is formed with a cavity coupled to the anchor pins of said metallic structure;

- fitting the condylar head to the cavity; being that the sintering is controlled by a software and replicates the said CAD model previously built and after the polymeric material hardens, the polymeric structure is formed around the anchor pins, fixing the said polymeric structure to the metallic structure and forming a metal-polymer interface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]. The present invention will be described on the basis of the drawings appended hereto, which illustrate:

- Figure 1 illustrates the perspective view of the complete denture in a preferred embodiment of the present invention.

- Figure 2 illustrates the front view of the metallic structure comprised in the prosthesis of the present invention showing the standard parts for all embodiments of the present invention.

- Figure 3 illustrates the side view of said metallic structure showing the standard parts for all embodiments of the present invention.

- Figure 4 illustrates the view of said metallic structure showing the detail of the construction of the anchor pins.

- Figure 5 illustrates the bottom view of said metallic structure showing the detail of the construction of the anchor pins.

- Figure 6 illustrates the perspective view of the cranial fossa in a large embodiment of the present invention.

- Figure 7 illustrates the sectional view of the cranial fossa in a large embodiment of the present invention.

- Figure 8 illustrates the perspective view of the cranial fossa in a medium embodiment (b) of the present invention.

- Figure 9 illustrates the sectional view of the cranial fossa in an average embodiment (b) of the present invention.

- Figure 10 illustrates the perspective view of the cranial fossa in a small embodiment (c).

- Figure 11 illustrates the sectional view of the cranial fossa in a small embodiment (c) of the present invention.

- Figure 12 illustrates the perspective view of the cranial fossa in an extra-small embodiment (d) of the present invention.

- Figure 13 illustrates the sectional view of the cranial fossa in an extra small embodiment (d) of the present invention.

- Figure 14 illustrates the side view of the condylar portion in a large embodiment of the present invention.

- Figure 15 illustrates the side view of the condylar portion in an average embodiment (b) of the present invention.

- Figure 16 illustrates the side view of the condylar portion in a small embodiment (c) of the present invention.

- Figure 17 illustrates the side view of the condylar portion in a slim- medium embodiment (d) of the present invention.

- Figure 18 illustrates the side view of the condylar portion in a slim- small embodiment(e) of the present invention.

- Figure 19 represents the exemplified view of the detail of the condylar structure in a trabeculated form, for any size embodiments described. - Figure 20 represents the exemplified view of the detail of the condylar structure in a trabeculated shape with varying density, for any embodiments of described sizes.

- Figure 21 represents the condylar part submitted to a mechanical test in a virtual environment.

- Figure 22 represents the result of maximum deformation of the condylar part after the application of a compression force on the condylar head of the piece.

- Figure 23 represents the SN curve of the condylar part after a fatigue test.

DETAILED DESCRIPTION OF THE INVENTION [0024]. The present invention relates to a prosthesis for arthroplasty of the temporomandibular joint. The present invention uses innovative constructions in its two main parts: the condylar part and the articular fossa part, to achieve a high quality, resistance, safety and longevity of the prosthesis, while keeping its structure ready to be applied in different processes of manufacture.

[0025]. The present invention presents numerous technical and economic advantages when compared to the state of the art, some of which are listed below:

• The present invention presents an inventive condylar construction, being manufactured in a single piece, without fittings and welds that create stress and breakage points, being made possible by an additive manufacturing process and coating by carbon nanostructures;

• The present invention constitutes an inventive articular fossa construction, which uses toothed surfaces added to the injection of molten polymer, which provide a complex metal-polymer interface, without fitting and disengagement directions;

• The present invention is able to incorporate improvements in the state of the art, solving manufacturing problems associated with the increase in the complexity of the prosthesis, compared to other state of the art alternatives;

• The present invention presents a prosthesis with properties derived from the coating of its surface with carbon nanostructures (graphene, carbon nanotube (NTC), nanographite, graphene oxide, graphite oxide, etc.);

• The present invention presents a prosthesis made by additive manufacturing (condylar portion and metallic part of the glenoid fossa) and polymeric injection (polymeric part of the glenoid fossa) which reduces production costs in addition to offering products with high quality and made uniformly.

[0026]. The present invention comprises a temporomandibular joint prosthesis 01 . Referring to Fig. 1 , the prosthesis 01 is formed by a condylar portion 03 and an articular fossa portion 08. In a preferred embodiment of the present invention, the condylar portion 03 comprises a head condylar 04 and a condylar plate 05.

[0027]. The condylar portion 03, shown in Figs. 14-18, is a single metallic piece, without connections or fittings, where the condylar head 04 located in the upper part of the condylar portion comprises a curved polished surface 07 with a circular cross-sectional profile, and a oval longitudinal profile.

[0028]. As it is a round and polished surface, the condylar head 04 has a low coefficient of friction with the articular fossa.

[0029]. The condylar plate 05 is a thin portion that comprises fixing holes 06 juxtaposed for fixing the condylar portion 03 to the ramus of the patient's mandible. The region of the condylar plate 05 makes direct contact with the patient's bone, and is fixed with the help of appropriate screws.

[0030]. The condylar plate 05 can be endorsed with numerous holes for its fixation, preferably from 7 to 17 holes. Such holes may not be fully used in a surgical procedure, but they allow an alternative if the professional notices the impossibility of not using any screw.

[0031]. In a preferred embodiment, less than 05 screws are used.

[0032]. Additionally, the condylar portion 03 has a carbon nanostructure treatment in the region of the condylar head 04 and on the external surface of the condylar plate (contact region in the soft tissues), and the internal surface does not have a carbon nanostructure cover (region in contact with bone) in order for osseintegration to occur. This technology is crucial for covering the prosthesis, which minimizes the friction between the pieces, improving the sliding between the condyle and articular fossa connecting parts. Furthermore, this treatment on the surface of the newly sintered condylar head 04 results in the polished surface 07 with a low coefficient of friction.

[0033]. Additionally, the condylar portion 03 is preferably made of titanium alloy (ASTM F3001) by additive manufacturing, such as via 3D printing, selective laser sintering (SLS) or Direct Metal Laser Sintering (DMLS).

[0034]. In addition, the condylar part 03 can comprise a trabeculated surface, as referenced in Fig. 19. This characteristic is achieved via additive manufacturing, which allows a manufacturing where a structure is made, containing "empty" parts and other "filled" parts, being possible to perform the combination of biological gain with the mechanical properties desired to the product, reducing the consumption of the raw material and thus optimizing the entire process. As a result, it is ideal for osteoblasts that are young cells with intense metabolic activity and responsible for the production of the organic part of the bone matrix, composed of type I collagen, glycoproteins and proteoglycans.

[0035]. Additionally, the condylar part 03 can comprise calcium phosphate in its composition, participating in the mineralization of the matrix. Thus, the osseointegration of the temporomandibular articulation prosthesis will occur in a shorter term.

[0036]. The condylar portion 03 can be adapted to different sizes, as shown in Fig. 14-18, depending on the patient's clinical condition. A medical professional must choose the optimal embodiment for each case, taking into account the region of bone tissue available for fixation of the piece, and the invasiveness of each piece, which increases according to the size of the condylar plate. Therefore, it is necessary to use the smallest embodiment that is capable of being fixed to the bone region of the patient.

[0037]. In a large embodiment of the condylar portion 03a, as shown in Fig. 14, the condylar plate 05 has a curved shape with 17 fixing holes 06, so that the fixing holes 06 cover a large lateral region of the mandibular bone. In cases where there is serious injury to the bone tissue and part of the patient's mandibular bone is lost, the additional rows of fixing holes 06 reach the remaining bone region, so that it is possible to fix said condylar plate 05 to the bone tissue of the patient.

[0038]. In a large embodiment of the condylar portion 03b, as shown in Fig.15, the condylar plate 05 has a curved shape, similar to the medium condylar plate 03a, but with smaller dimensions and with 14 fixing holes 06. This embodiment is also recommended for cases of large lesions in the mandibular bone, but in situations where the patient has a smaller bone structure, or where the remaining region of the mandibular bone for fixation is larger.

[0039]. In a small embodiment of the condylar portion 03c, as shown in Fig. 16, the condylar plate 05 has a triangular shape, with less invasiveness compared to the plates 03a and 03b and with 9 fixing holes 06, being suitable in cases where there is a larger remaining bone region for adequate fixation.

[0040]. The slim-medium 03d slim-small embodiments 03e of the condylar portion, according to Fig.17 and Fig.18, respectively, comprise the condylar plates 05 being vertical, with only two rows of fixing holes 06, the slim- medium 03d having 9 fixing holes 06 and the slim-medium plate 03d having 7 fixing holes 06. Therefore, these embodiments are less invasive, whereas they are limited to cases of minor injuries.

[0041]. Further, it is possible that the condylar portion 05 is custom- made for the patient's bone structure, being a unique piece for each case.

[0042]. Being composed of a single part, manufactured in additive manufacturing, creates the ideal condition for vascularization, it is possible to create complex forms of structures, without the need for connections or fittings, offering a format that optimizes the vascularization of tissues and, consequently, osseointegration, while the invention still has a better mechanical performance when compared to the state of the art.

[0043]. After performing a virtual mechanical test, through analysis by finite elements, it is possible to observe mechanical performance of the condylar part 03 represents an improvement in the state of the art.

[0044]. In a compression test, the condylar part 03 is fixed through the holes of the condylar plate to a firm block. The plate is fixed in such a way as to leave the last top hole free, according to Figs 21 and 22. This procedure is used to stress the condylar part, creating a stress concentration point.

[0045]. A force application on the condylar head 04 is simulated with a load of 43N. State-of-the-art studies show that stress in the condulum region during chewing is in the range of 43N (AG. Hannam Et al. A dynamic model of jaw and hyoid biomechanics during chewing. Journal of Biomechanics 41,2008 ).

[0046]. Furthermore, the fatigue test on the condylar 03 part provides the stress results by number of cycles.

[0047]. Fig. 23 represents the SN curve of the condylar part 03, based on the data obtained in the test. The assay also shows that the number of stress cycles that the condylar 03 can take is in the order of 8.6x10 ¹⁵ , being therefore durable for the entire duration of the patient's life.

[0048]. The articular fossa component 08, shown in Fig. 4-11 , comprises a metallic structure 09 and a polymeric structure 14.

[0049]. Referring to Fig. 2 and 3, the metallic structure 09 comprises a row of holes 10, the number of holes 10 being adapted for different cases, a central portion 11 with anchor pins 12 at the bottom and a chamfered portion 13 at the edge.

[0050]. The polymeric structure 14, as shown in Figs. 6-13, comprises a lower concave surface 15, which forms a cavity 16, and an upper interface surface. The polymeric structure 14 further comprises a side chamfered surface 16, aligned with the chamfered portion 13 of the metallic structure 09.

[0051]. The articular fossa 08 is the union of two items, the metallic structure 09 made of titanium alloy Ti6AI4V through the manufacturing process by 3D printing (additive manufacturing), by at least one method among: selective laser sintering (SLS) or Direct Metal Laser Sintering (DMLS).

[0052]. Additionally, the metal structure 09 can comprise trabecular structure. Preferably the metal structure 09 trabecular has a giroid pattern, with variable fill density, as illustrated in Figure 20. Through additive manufacturing, it is possible to control the filling of the metal part, leaving less dense near the part there is blood circulation and denser to the part where a greater mechanical resistance is required.

[0053]. Subsequently, liquid polymeric material, such as polyethylene type UFIMWPE, is injected into a mold coupled to a metallic part in order to compose the polymeric structure and become a single part. Additionally, in the metallic regions, carbon nanostructures are applied. The injection takes place automatically through an injection nozzle.

[0054]. The polymeric material of the polymeric structure 14 is injected under the metallic structure 09, so that said polymeric structure 14 is formed around the anchor pins 12, fixing said polymeric structure 14 to the metallic structure 09 and forming a metal-polymer interface 02.

[0055]. The anchor pins 12 are arranged in rows and columns and have a spiral shape, according to Fig.4 and Fig.5, with a longitudinal cone section. In this way, it is not possible to fit in and out of the metallic parts 09 and polymeric 14, and the injection of liquid polyethylene is the only way to join these interfaces.

[0056]. Additionally, the glenoid fossa 08 can be adapted to different sizes, as shown in Fig. 6-13, depending on the patient's clinical condition, in particular, the metallic structure 09 can undergo adaptations in its arrangement of holes 10, and remain compatible with the polymeric structure 14. In this way, the cavity 16 of the articular fossa 08 has the same size, regardless of the embodiment of the piece. A medical professional must choose the optimal implementation for each case, taking into account the region of bone tissue available for fixation of the piece, and the invasiveness of each piece.

[0057]. In a large embodiment of the glenoid fossa 08a, referring to Figs. 6 and 7, the row of holes 10 of the metallic structure 09 is elongated in relation to the polymeric structure 14 and follows the curvature of the bone region that is inserted. In cases where there is serious injury to the bone tissue and/or part of the patient's zygomatic bone is lost, the two additional holes 10 reach the remaining bone region, so that it is possible to fix said articular fossa 08a to the remaining bone tissue of the patient. [0058]. In an average embodiment of the glenoid fossa 08a, referring to Figs. 8 and 9, the row of holes 10 of the metallic structure 09 is elongated in relation to the polymeric structure 14 and follows the curvature of the bone region that is inserted. The additional hole 10 reaches the remaining bone region, so that it is possible to fix said articular fossa 08a to the patient's remaining bone tissue.

[0059]. In a small embodiment of the articular fossa 08c, referring to Figs. 10 and 11 , the row of holes 10 of the metallic structure 09 has approximately the same length as the polymeric structure 14. In cases where there is a moderate size lesion in the bone tissue and / or part of the patient's zygomatic bone is lost, the four holes 10 are sufficient to place the articular fossa 08 to the patient's zygomatic bone, being less invasive than larger prostheses.

[0060]. In an extra-small embodiment of the glenoid fossa 08d, referring to Figs. 12 and 13, the row of holes 10 of the metallic structure 09 is approximately the same length as the polymeric structure 14. Additionally, the polymeric structure 14 for this embodiment is rounded and symmetrical, and can be used in cases of small lesions on the right or left side.

[0061]. Further, it is possible that the glenoid fossa 08 is custom-made for the patient's bone structure, being a unique piece for each case.

Device Operation

[0062]. The condylar portion 03 is fixed on the patient's mandible branch with appropriate screws that pass through the fixing holes 06; while the articular fossa 08 is fixed to the zygomatic bone of the patient's skull with appropriate screws that pass through the fixation holes 10. [0063]. The joint of the temporomandibular prosthesis 01 is made by the arrangement of the condylar head 04, the condylar portion 03, in the cavity 16 of the articular fossa 08, so that the polished condylar head 04 slides with little friction in the cavity 16, allowing flexion and extension movements, adduction and abduction and circumduction of the patient's mandible.

[0064]. Both the condylar portion 03 and the articular fossa 08 can have different dimensions, according to the embodiments 03a, 03b, 03c, 03d, 03e 08a, 08b, 08c, 08d respectively, adapted for different sizes of bone structures and patient injuries.

[0065]. Because the condylar head 04 and the cavity 16 have a standard size for all embodiments, it is possible to use different sizes of the condylar portion 03 and articular fossa 08, so that the configuration with an optimal anchorage/invasiveness ratio for each clinical condition is obtained.

[0066]. The prostheses described and illustrated represent embodiments of the prosthesis for the right temporomandibular joint, so the descriptions described herein are true of the left joint embodiments, these being mirrored in relation to the drawings and figures shown.

[0067]. Having described some examples of preferred embodiments of the present invention, it should be understood that the scope of the present invention encompasses other possible variations of the inventive concept described, being limited solely by the content of the claims only, including possible equivalents therein.