Mandibular implant
TECHNICAL FIELD
The present disclosure relates to alloplastic implants, in particular patient-specific alloplastic implants and more in particular, mandible reconstruction implants.
BACKGROUND
Due to affliction and/or trauma, defects in bones and/or joints may occur in patients which may benefit from implants for repair, reconstruction or even replacement of the original bone part(s) . Such implants may comprise autoplastic implants, wherein a graft is taken from another portion of the body of the patient and/or alloplastic implants wherein body foreign objects are implanted.
Any implant requires good acceptance by the receiving body (portion) . Further, bone structures may have significant aesthetic effects, in particular facial and or cranial bone structures. Thus, there is ongoing research towards implants fitting the (remaining) anatomy of the patient and providing desired aesthetic features. This is particularly important where the implant is to form part of an otherwise unaffected joint.
The mandible or lower jaw bone is important for eating and as such it is subject to significant forces in normal use. It is further a major aesthetic determinant, hence
reconstruction of the mandible must address these different aspects. Mandibular implants are known. Traditionally,
mandibular implants were based on fortifications of existing bone fragments, e.g. as described in US 6,129,728, US
2007/0293859 and WO 2007/060507. However such structures are known to break due to various causes as described in e.g. "A three dimensional analysis of reconstruction plates used in different mandibular defects" by S. Atilgan et al., Biotechnol. & Biotechnol. Eq. 24 (2 ): 1893-1896 (2010), DOI : 10.2478/V10133- 010-0048-9. Reconstructions of larger mandible defects are
generally based on autoplastic grafts, e.g. rib portions, possibly fortified with metallic structures. Devices and methods for such techniques are e.g. described in WO 97/43978, US, 3,849,805, US 4,636,215 and US 5,580,247. Use of alloplastic implants to reconstruct missing bone fragments has been
described in WO 2007/061382 and WO 2005/086920.
Further, different studies have concentrated on implants for or including the temporomandibular joint, e.g. WO 2007/061382, US 5,445,650, US 4,917,701, "Total condylar
prosthesis for alloplastic jaw articulation replacement" by I. Sonnenburg and M. Sonnenburg, J.Max. -Frac. Surg. 13:131-135 (1985), "Total mandibular replacement with a titanium plate after mandibulectomy for osteosarcoma" by A. Garcia et al., J. Oral Maxillofac. Surg. 52:863-867 (1994) and "Total prosthetic replacement of the TMJ: experience with two system 1988-1997" by B. Speculand et al . , British J. Oral Maxillofac. Surg. 38:360- 369 (2000) .
More recent developments are presented in the paper "The use of TMJ Concepts prostheses to reconstruct patients with major temporomandibular joint and mandibular defects" by A.
Westermark et al . , Int. J. Oral Maxillofac. Surg. 40:487-496 (2011). This paper describes computer-assisted designed and manufactured prostheses constructed on a stereolithic 3- dimensional model fabricated from the patient's computed
tomography scan data. The described mandibular components are made of machined alloyed titanium with a condylar head of chrome-cobalt-molybdenum alloy. In "case 4" of this paper, an implant is described which replaces a mandible as a complete unit extending from one condyle to another and supporting a remaining portion of the mandibleattached to the implant.
SUMMARY
Although the above-cited publications generally describe successful treatment, improvements are still desired with respect to treatment efficiency, accuracy of the implant (s and reduction of complications. Further, cost reductions and flexibility in manufacturing of the implant are desired.
In view of these demands, a mandibular implant is herewith provided, comprising at least one portion manufactured by additive manufacturing technology.
Additive manufacturing technology, such as
stereolithography, fused deposition modelling, (direct metal) laser sintering, selective laser melting or electron beam
melting, laser or electron beam cladding etc., allows
manufacturing of very diverse shapes with very high precision to a predetermined model. Production by additive manufacturing technology is currently broadly used in the aerospace industry. It has been found that the techniques are suitable to provide medical grade implantable objects. E.g., in 2006 this technology has been applied for manufacturing of patient specific cranial implants by the present inventors.
It has now been found that additive manufacturing technology allows to meet the requirements for strength and weight of a mandible, not only for aesthetical reconstructive aspects, but also the functional aspects of maintaining airway, allowing speech and swallowing, and most important, the dental and mastication functionalities. In particular, a mandibular implant manufactured by additive manufacturing technology may have a symmetric or asymmetric shape that can be implanted in the original cavity and that can withstand the forces of normal use of the person. The implant may provide only a fragment of the mandible, and may closely follow an edge of a defect in an existing mandible (fragment), which defect may be the result of trauma or surgery, etc.
The risk of ruining an object during manufacturing e.g. by taking away too much material, which is possible with
machining, is virtually absent. Thus, the mandibular implant may be a patient specific mandibular implant and may conform to the particular anatomy of the patient.
Further, additive manufacturing technology allows faithful ( re- ) creation of an object according to digital
instructions. Hence, an implant may be designed and reliably manufactured by one or more automated processes. This allows remote manufacturing of an ordered implant, which may be a fast procedure, possibly overnight. Typical manufacturing volumes for additive manufacturing technology are about 250 x 250 x 450 millimeters, which is generally sufficient for manufacturing implants. In the manufacturing volume the implant is formed layer by layer wherein layer thicknesses may be selected and/or may be material-specific. A thus manufactured implant may adhere to tolerances on the order of about 50-200 micrometers, mainly depending on the thickness of the deposited layer. Suitable materials comprise metals, e.g. titanium, tantalum etc., polymeric materials, e.g. polymethyl methacrylate (PMMA), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), etc., and/or ceramic materials, e.g. zirconium oxide or
aluminium oxide.
In particular, the implant may comprise a condylar portion, which can be made in one piece with a ramus, angle, and/or other mandible body portions of the implant, depending on the extent of the implant. Thus, an integral implant may be manufactured, which prevents weak spots e.g. at the transition from (an portion of) one material to another (portion) and which increases overall strength of the implant. In a particular case, an implant manufactured as a single object and successfully replacing an entire mandible has been provided, as will be detailed below.
It has been found that the condylar portion may be formed accurately enough to fit the original fossa mandibularis, obviating a further implant component and reducing complexity of the implantation surgery and associated healing processes.
However, a fossa component may be provided, in particular formed to fit the condyle (s) of the mandible portion. The fossa component may be manufactured also by additive
manufacturing technology, possible in one process with
manufacturing the mandible portion. The fossa component may comprise a relatively soft or resilient portion, e.g. of a polymer or other alloplastic material, for absorption of
displacement and/or smoothened articulation, like cartilage. The mandibular implant may be manufactured largely or substantially completely from metal, e.g. from titanium and/or titanium alloys, which are biocompatible and combine strength with relatively low weight. Combinations of different materials are also conceivable. One or more surface portions may be covered with other materials, in particular a biocompatible layer, e.g. hydroxyapatite , to increase biocompatibility and facilitates adhesion of tissue such as muscles, periost and other soft tissue.
Also, one or more provisions, e.g. recesses and/or through holes, for attachment of sutures and/or tissue to the implant may be provided. Recesses or dimples reduce weight of the implant, preventing muscular fatigue and possible wear of joints, and they provide increased surface area and structural features for tissue adhesion to the implant. Through holes and/or hook-like portions may further provide holds for sutures etc. Also, one or more surface portions may have relatively rough surface portions, e.g. having millimetre or sub-millimetre sized structures like protrusions and/or pores. Pores may facilitate tissue ingrowth. Such structures may be designed and/or result from the additive manufacturing process, e.g.
step-edges between different sintering layers.
Further, at least one portion of the implant, in particular a condylar portion, a recess and/or a through hole may have a surface portion with a smooth finish, e.g. being polished. Such portions rather prevent tissue adhesion and prevent damage of tissue in contact with such portions. E.g., a smooth condyle facilitates jaw movement. Polishing may comprise mechanical polishing and/or (electro-) chemical polishing.
Additive manufacturing technology facilitates provision of predetermined portions of the implant with a particular roughness, substantially massive portions, substantially hollow portions fortifications and/or spongiform portions may be manufactured in particular areas. Thus, implants with largely predetermined strength, weight and/or particular attachment structures may be provided. E.g. a condylar portion may be provided substantially massive, so that it may be provided with an accurately determined shape. Also, a predetermined volume to be removed in a finishing process may be provided.
The implant may comprise one or more tooth prosthetics provisions, which may in particular be formed by threaded holes. This facilitates future provision of tooth implants supporting dentures or fixed dental structures that provide a natural appearance and function.
The implant may comprise a hole for attachment of a future implant, e.g. one or more tooth implants, which may be an implant to be implanted in a subsequent surgical implantation session, and it may then comprise a removable closure arranged to maintain the hole closed, when implanted, between
implantation of the mandibular implant and implantation of the future implant. The hole may be a blind hole or a through hole, in which latter case the hole may be closed from both ends.
The closure (s) prevent (s) tissue ingrowth into the hole and/or collection of debris into it. This improves hygiene and it facilitates subsequent implantation of the future implant. It further allows using blind holes, thus allowing a stronger implant than when only through holes may be used.
In an advantageous embodiment, the (blind) hole and the closure comprise matching screw threads and/or bayonet features, although a tight fit may also be provided and/or some adhesive may also be provided.
The implant may comprise at least one channel, which may be partly open, configured to guide and/or support one or more nerves, in particular a nervus mandibularis , e.g. an
inferior alveolar nerve and/or a mental nerve. Such delicate tissue may benefit from the channel having a smooth surface finish. One or more such nerves or nerve fragments that have been spared in surgery may be arranged in such channel an
possibly be fixed there, e.g. with a further implant and/or some kind of adhesive material, like a cement.
Such nerve channel may also be provided in mandibular implants manufactured by other techniques than additive
manufacturing technology. Any recesses, holes and/or channels may be formed in the additive manufacturing process and/or be formed
traditionally with drilling, reaming and/or cutting thread.
In conventional mandibular implantation surgery, an existing mandible (fragment) is removed by cutting the bone and removing the cut fragments, preferably by delivery through relatively small submental incisions, wherein the mandible is cut substantially perpendicular to the bone structure. In such procedure, the nervi mandibulari are severed as a matter of course. The patient then suffers significant sensory loss, which may be temporary but generally is permanent. The present
inventors have considered such loss generally unnecessary and inacceptable , and therefore provide hereby a mandibular implant comprising at least one channel configured to guide a facial nerve, in particular a nervus mandibularis , e.g. an inferior alveolar nerve and/or a mental nerve. Further, in an aspect a novel method of implanting a mandibular implant is provided , which comprises identifying a position of a nervus mandibularis in an original mandible fragment, cutting the fragment along at least a portion of the nervus mandibularis and removing the fragment portions without substantially damaging the nervus mandibularis, and implanting the mandibular implant without substantially damaging the nervus mandibularis. The method may comprise splitting the mandible, e.g. with one or more chisels, along a nerve duct. E.g. the method may comprise cutting in a direction along the nerve duct between the mandibular foramen and the mental foramen at both outer and inner sides of the mandible. The exact shape of such duct may be visualised from one or more X-ray, C (A) T (comput (eriz) ed (axial) tomography) and/or MRI (magnetic resonance imaging) and/or ultrasound scans. Further, a cut may be started from the respective foramen and the shape of the cut may be determined by following the duct with a probing tool, which may be attached to the cutting tool such as an oscillating saw. The method may further comprise arranging the nervus mandibularis in a conduit in the mandibular implant . Conventional implants do not have a provision for guiding and/or supporting nerves and thus, even if a nerve were spared, it would be substantially unprotected and might provide painful spots, which is prevented by an implant comprising at least one channel configured to guide a facial nerve, in particular a nervus mandibularis , e.g. an inferior alveolar nerve and/or a mental nerve. Such implant may be manufactured with any suitable technique, including an autograft of which a portion is suitably adapted and it need not be manufactured by additive manufacturing technology, although that provides the benefits presented elsewhere in this disclosure.
In correspondence with the above, a method of manufacturing a mandibular implant is provided hereby,
comprising manufacturing at least a portion of the implant by additive manufacturing technology.
It is considered advantageous if the method comprises imaging one or more portions of the maxillo-mandibular portion of the patients head, possibly including significant fractions of the skull via suitable techniques such as X-ray imaging, C (A) T scanning, MRI scanning or ultrasound and it may comprise modelling one or more of the detected bone structures. Modelling may be virtual, e.g. digital rendering of the structures in two or three dimensions, the latter being preferred. Modelling may also include realising a tangible model via one or more
manufacturing techniques such as machining and/or additive manufacturing the latter being preferred. Realisation of a model may include manufacturing the implant itself, possibly in combination with other portions such as remaining bone
structures and/or skull portions, such as a fossa, e.g. to test operation of the mandible implant.
The method may comprise coating at least one surface portion of the implant with a biocompatible coating, e.g.
hydroxyapatite, and it may comprise providing at least one portion of the implant with a rough finish or rather with a smooth finish, e.g. by polishing.
In particular in case of a treatment with a previewed succession of implantation steps, the method may comprise providing the implant with a hole, which may be a blind hole, for attachment of a future implant, in particular a future implant to be implanted in a subsequent surgical implantation session, and closing the hole with a removable closure to close the hole and to maintain the hole closed, when implanted, between implantation of the mandibular implant and implantation of the future implant.
Also, another aspect of the present disclosure is a kit of parts comprising an implant as described herein and one of one or more fossa components, closures, fasteners and/or
cements, e.g. for closing a hole and/or a nerve channel.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-described aspects will hereafter be more explained with further details and benefits with reference to the drawings showing an embodiment of the invention by way of example .
Fig. 1 is a perspective view of a mandible remnant of a patient and a first design of a mandibular implant;
Figs. 2-6 are perspective, front, top, rear and
perspective views, respectively, of a patient specific
mandibular implant .
DETAILED DESCRIPTION OF EMBODIMENTS
It is noted that the drawings are schematic, not necessarily to scale and that details that are not required for understanding the present invention may have been omitted. The terms "upward", "downward", "below", "above", and the like relate to the embodiments as oriented in the drawings, unless otherwise specified. Further, elements that are at least
substantially identical or that perform an at least
substantially identical function are denoted by the same
numeral .
In an outpatient clinic recently a patient was received suffering from progressive osteomyelitis of almost the entire mandible. The classic treatment for this patient would be
decortication; removing the damaged part of the mandible. This would leave the patient, at best, with a small mandible fragment significantly without support and function. Considering the age of the patient, 83 years old, a complicated complex
microsurgical reconstruction such as decortication was found unsuitable or at least not preferred. Instead, a total
reconstruction of the mandible with a patient specific implant was performed.
In this patient, the natural fossae were found unaffected and the implant was made to fit these, promoting healing and preventing burden on the patient.
The mandibular implantation of a monolithic patient specific implant that replaces a total mandible including the mandibular condyles, as well as the replacement of a total mandible using the natural fossae are, to the knowledge of the inventors, unique procedures.
Prior to the implantation the remaining bone structures were imaged and a virtual model was made of the lower skull portions and the mandible. The patient specific mandibular implant was custom-designed to a shape to replace the original mandible and to be implanted within the original cavity.
Fig. 1 is a perspective view of a first designed mandibular implant 1 (smooth heavy lines) compared with the mandible remnant R, Rc of the patient (ragged light lines) . As may be seen, the implant 1 was designed in such way that the sharp edges that occur in the original bone structure R were smoothed. As an option, the coronoid processus Rc were left out completely in the design, since these were considered not
required for successful muscle attachment to the implant 1 and further to spare soft tissue surrounding the implant 1 due to any possible scissor-like action of the implant 1 against the surrounding bone structures such as the temporal bone and the zygomatic arch. Also the processus alveolaris is significantly reduced in size and rounded off, as is any other edge or corner. The design of the implant 1 was otherwise made in consideration with the original dimensions.
Figs 2-6 show a further developed design of an implant 1 for a total mandible replacement for the aforementioned patient. An implant 1 according to this design was manufactured by additive manufacturing technology by selective laser melting from medical grade titanium alloy, which was then partly covered with hydroxyapatite . The implant was successfully implanted in the patient.
The implant 1 is a total mandible 1, comprising (see Fig. 2) on each side a condylar portion 3, a ramus portion 5, a lateral body portion 7, an alveolar ridge portion 9 and a coronoidal portion 11, the coronoidal process being absent as discussed above. The implant further comprises a mental (chin) portion 13. As indicated in Fig. 3, in the lateral body portions 7 through holes in the form of windows 15 and recesses 17 are provided. The mental portion 13 comprises windows 19 and tooth prosthetics provisions, here in the form of threaded holes 21. Between the lateral body portions 7 and the mental portion 13, channels 23 are provided, each configured to guide and support a nervus mandibularis . The implant 1 further comprises two
condyles 25, formed to correspond to the shape of the natural fossae mandibular! generally indicated with curves 27.
In the manufactured implant 1, the condyles 25 have been designed and formed slightly smaller than the natural condyles (cf. Fig. 2), here being reduced by 1 mm at both sides in mesio-lateral direction, to assure proper fitting and to enable placement without unnecessary soft-tissue strain and/or cartilage wear etc. Optionally other portions, e.g. the colli mandibulae may be sized slightly larger than the original if additional strength is desired.
The windows 15, 19 are generally radially arranged and, besides reducing weight, facilitate attaching tissue and/or sutures to the implant. The windows 15 are provided in
particular for attachment of the muscles temporalis and the muscles masseter, the windows 19 for attachment of the muscles diagastric. The recesses 17 also reduce weight and increase surface area for natural tissue adhesion.
Best seen in the shading in Fig. 6, most surface portions, including the windows 15, 19 and the recesses 17 are covered with hydroxyapatite and comprise a generally rough finish, to promote soft tissue adhesion and ingrowth so as to promote acceptance of the implant by the patient body.
In contrast, the articulating surfaces of the condyles 25 are polished to a smooth, shiny finish so as provide smooth joint movement in the fossa mandibulares . The condyles 25 may be formed differently and may be made to fit an artificial, possibly custom made, joint extension.
The channels 23 are also polished to a smooth, shiny finish to spare the nerves received therein. A suitable size for the channel is found with a diameter of about 3-6 mm, in
particular about 4-5 mm, here about 4.5 mm. The entrance opening may be wider, of equal width or smaller, e.g. here being about 2.5 mm wide, and may be closable to keep the nerves in place. The nerves may be freely movable, movably attached or fixed to the channels 23. Further ridges and/or channels may be provided.
The interior sides of the threaded holes 21 for teeth prostheses are also smooth and not covered by a surface coating to facilitate screwing a screw in them. One or more closures, in particular screws, e.g. of titanium, may also close the holes 21 during or after implantation, e.g. until the patient has healed sufficiently for allowing implantation of a tooth prosthesis into the holes. Such tooth prosthesis may comprise a single tooth or a set of dentures comprising plural teeth.
One or more portions of the implant may be used for marking, e.g. with serial numbers, but also comprising
instructions to the surgeon, e.g. markings noting a particular suture, insert screw or other fastener, or other reference indications. A marker may also form a scanning beacon for future reference .
For implantation, the teeth of the patient may be pulled and the gums be left to close the teeth holes. In that case contamination of the implant from the oral cavity may be prevented and the implantation process simplified. This
procedure was followed with the aforementioned patient.
The natural mandible was cut in several fragments and removed through an incision. Most notable, the jaw was also split lengthwise along the nerve channel in the lateral body portion so that the nerves were left substantially unharmed.
In particular, the mandible was sliced in several parts with an oscillating saw. The first piece that was removed was the anterior middle part of the mandible by cutting the mandible at two sides in between the two nerve exits. Subsequently, a large portion of the remaining mandible was mobilized by a more distant cut. This large part was divided into plural parts, here a superior part and a inferior part, by slicing the superficial cortical bone at the anterior and posterior side in order to weaken the strength of the remaining bone. After using a chisel and hammer, both bony parts could be divided without harm to the nerve contained within the bone. Finally the remaining part of the mandible containing the joint part was removed by using an extra-oral incision.
The nerve bundles were later gently inserted into the channels 23 of the implant 1. Indeed, after operation the
implant reported no noticeable loss of sensation. The implant fitted immediately and the patient was speaking the next day. Presently, the implant has been accepted by the surrounding tissue and has remained successfully in place without
complications for several months.
The invention is not restricted to the above described embodiments which can be varied in a number of ways within the scope of the claims. For instance, the implant may comprise at least one fastener that may be movably attached to the at least one mounting portion.
Alternative materials include, but are not limited to, polymers, e.g. polymethyl methacrylate (PMMA), polyether ether ketone (PEEK), or polyether ketone ketone (PEKK), and ceramic materials, e.g. zirconium oxide or aluminium oxide. Possibly, the implant comprises a core of one material, e.g. a polymer material, with a general shape lacking detail which is provided with one or more outer layers and/or surface layers, e.g.
titanium or tantalum, to produce the desired size, structures and/or details and which may provide biocompatibility to the implant. Possibly the core provides a general low-cost filler material for a generally high-cost outer structure. The core may be stronger or weaker than the outer layer (s) .
Elements and aspects discussed for or in relation with a particular embodiment may be suitably combined with elements and aspects of other embodiments, unless explicitly stated otherwise .