IMPLANT DEVICE FOR DENTAL PROSTHESES

Abstract: The implant device, for installation in an edentulous area of a maxillary bone of a patient for supporting a dental prosthesis, comprises a laminar mantle of perforated titanium (10), shaped as a plane convex saddle (10) to accurately match the bone, and having one or two integral stumps (14) for dental prosthesis; and an endosteal fastening rib (12), also of perforated titanium, integral with the saddle-shaped mantle, perpendicularly projecting from its underside along its ridge, and adapted to be inserted in at least one corresponding recess made in the maxillary bone.

Description: "Implant device for dental prostheses" Disclosure This invention is concerned with an implant device which is applicable to the maxillary bone for supporting a dental prosthesis. Modern osteo-integrated implantology has brought a useful revolution in dental practice, thus allowing a greater number of patients than in the past to benefit from a formerly unimaginable fixed prosthesis, with a rate of operation successes near to 98%. However, a large part of the population cannot benefit from these operative methods because they do not possess the ideal anatomical prerequisites for receiving modern osteo-integrated implants. Among the impediments are, for instance, bone atrophies, not necessarily serious or severe, or voluminous maxillary sinuses, causing a decrease of the bone thickness necessary for implant surgery, or, in the case of the lower maxillary bone, an alveolar nerve running too close to the surface, with similar consequences as for the upper maxilla. In all these cases, titanium implants can be effectively accomplished by applying complex and expensive bone regeneration techniques, with attendant grafts of autologous bone taken from anatomical districts which may be remote from the implant target site (such as the iliac crest or fibula, etc.). Such impediments of anatomical nature are compounded by the high costs of the conventional implant, which in fact deny large sections of the population the benefit of dental implantology. The number and importance of the surgical steps necessary , to achieve the fixed prosthesis, as well as the high costs and long therapeutic intervals, discourage many potential patients from the implant option. The main object of the invention is therefore to provide an implant device which solves the above critical cases in a single surgical step, at a limited cost, by allowing a suitable fixed prosthesis to be installed without having recourse to complex surgical maneuvers of osteoregeneration. More specifically, this invention aims to provide an implant device that can be implanted even in situations where, due to insufficiency of bone tissue or to proximity of vulnerable organs or to other reasons, it is not possible to incise the patient's bone to the depth required for conventional implants, such as Linkow blades or titanium screws. A further aim of the invention is to provide an implant device that can be implanted by surgical procedures less critical than conventional procedures and that, for equal ability of the surgeon, are less liable to error or flawed surgical performance. Still another object is to provide an implant device which can be implanted more rapidly than conventional devices, and which more specifically allows the surgeon to carry out, in a single stage, the entire operative procedure including opening the mucoperiosteal flap, baring the bone, incising the bone, inserting the device, suturing the flap, and possibly setting up a temporary prosthesis. A further object of the invention is to provide an implant device allowing implantation to be performed at a lower cost than prior devices. . The invention achieves the above and other objects and advantages, such as will appear from the following disclosure, with an implant device for dental prostheses having the features recited in claim 1. The subordinate claims recite other advantageous features of the invention. The features, aims and advantages of the invention will appear more clearly from the following detailed disclosure, with reference to the attached drawings, given by way of nonlimiting example, and wherein: Fig. 1 is a side view, to an enlarged scale, of an implant device according to a preferred embodiment of the invention; Fig. 2 is a front view of the implant device of Fig. 1; Fig. 3 is a lateral view taken obliquely from beneath, of the implant device of Fig. 1; , Fig. 4 is a perspective view of a bite-mapping jig, used during the procedure for implanting the implant device of the invention; Fig. 5 is a diagrammatical view of a radiographic mapping performed on a patient by means of the jig of Fig. 4; Fig. 6 is a perspective view of a surgical jig used during the procedure for implanting the implant device of the invention; Fig. 7 is a perspective view of a jawbone on which the surgical jig of Fig. 6 has been applied; Fig. 8 is a view in transverse cross-section of the jawbone of Fig. 7 during the step of incision of a sulcus for the application of the implant device according to the invention; Fig. 9 is a view in transverse cross-section of the jawbone of Fig. 7, on which the implant device of Figs. 1 to 3 has been applied in the final position; and Fig. 10 is a view in transverse cross-section of a jawbone with implant device and prosthesis. The invention consists in using a titanium implant device, shown on Figs. 1 to 3, and comprising a saddle-shaped laminar mantle 10, a laminar rib 12 which is integral with the underside of mantle 10, perpendicularly along its ridge, and a couple of cylindrical stumps 14 rising from the topside of mantle 10, in alignment with rib 12. Both mantle 10 and rib 12 are thickly perforated with a honeycomb arrangement of small, round holes such as 16. The average thickness of both mantle 10 and rib 12 is preferably 0.6 mm, and holes 16 have a preferred diameter of 2 mm. Rib 12 preferably extends for the entire length of mantle 10, with a preferred average height of 4 mm, although its height is not necessarily uniform, but rather is liable to variations, possibly vanishing locally, as will be explained in more detail below. The above described device is custom-designed for the specific patient and for the specific area of maxillary bone requiring a prosthesis, to have a shape and size such that the underside of mantle 10 perfectly matches the bone surface and that rib 12 is tailored to be inserted with a precise coupling in a groove or sulcus carved in the bone by the dentist. The best procedure found by the inventor for building the device of Figs. 1 to 3, as well as for using it, is described below. In order to perform the implantation with maximum advantage in the cost of the operation and the safety and comfort of the patient, according to the invention the patient is first submitted to a dental panoramic radiograph and to a TAC by a spiral TC apparatus, in order to obtain geometric data on the patient's maxilla, from which, by appropriate digital data processing, a stereolithographic model of the maxillary bone is made in transparent resin. The model shall be an exact tridimen- sional replica of the patient's upper and/or lower maxillary bone, on which tests and measures can be carried out which are equivalent to tests and measures made directly on the patient's maxillary bone. Nowadays, a stereolithographic model can be built from the initial geometric data in a largely automated process by selective sintering of a thermoplastic powder, as known, for instance, from EP 0 287 657. The stereolithographic model gives a complete representation only of the geometry of the maxillary bone. Therefore, in order to have adequate geometric data also for the mucous membrane and for the patient's occlusal registration, prior to the surgical operation, the patient should perform, according to the invention, a test on a wax registration bite, in which suitable radio-opaque profiles are incorporated. To such an end, and with reference to Fig. 4, a transparent measurement jig of an acrilic resin is prepared on a conventional chalk cast (not shown) of the patient's maxilla. The jig should be adapted to rest in a predetermined position on the maxilla, and should comprise a bridge 20 crossing the lingual area behind the incisors and integrally connecting two saddles 22, 24, resting on the edentulous areas, the saddles supporting respective, conventional wax bites 26 and 28. On the floor of the measurement jig, beneath each of bites 26 and 28, and therefore in virtual contact with the crestal mucosa of the edentulous area, lies a first thin wire 30 of a ductile, plastic metal, and a second, identical wire 32 lies on the occlusal surface of the bite, both wires acting as radio-opaque profiles. Jig 20-22-24 is inserted in place in the patient's mouth. The patient then closes his/her mouth to effect the occlusal registration. Once the registration is completed, a small intra-o al radiograph is taken, the film being mounted on a holder (not shown) so that an image similar to Fig. 5 is obtained, where wires 30 and 32 represent the profile and the uniform mapping of the soft tissues with respect to bone 34 and to the antagonistic occlusal surface, respectively. Consequently, the vertical dimension of stumps 14 can be determined in advance, and, by means of the bite impression, also their optimal placement and lie in view of setting up a prosthesis, as will be apparent to persons skilled in the art. A wax model of the implant structure is now built. The trace of the surgical sulcus which shall accommodate the vertical rib is marked on the stereolithographic model by an indelible marker, such as a pen. A crestal incision is made in the resin, under water cooling, by a suitable circular, saw of a 10 mm diameter, 0.5 mm thickness, and a cutting depth of 4 mm, the saw being mounted on a drill. After the cut has been spread with an isolating liquid, a gauged, honeycomb wax strip (as commonly used in odontotechnics and commercially available) of 0.6 mm thickness is inserted in the cut, and the strip is then delicately carved with a thin blade along its crestal outcrop. The peripheral outline of the saddle is now drawn with a pen or other marker: its extension should be as large as possible, though limited by the anatomical constraints imposed by the extension of the flap and by possible obstacles such as the emergence of the lower maxillary alveolar nerve. After the area has been spread with an isolating agent, a rectangular piece of gauged honeycomb wax, of 0.6 mm thickness, is laid and shaped on the area and is welded with the underlying rib, whereby the holes near the rib are plugged, for reasons explained below. The peripheral outline is then cut off with a thin blade. Suitably molded, vertical wax stumps are then placed at the predefined sites and axes and are then welded to the saddle. A wax model of the inventive implant device is thereby obtained, which is ready for making a titanium single casting corresponding to the implant device as shown on Figs. 1 to 3, and accurately matching the geometry and the specific conditions of the edentulous area of the patient's maxillary bone. For an easier and more accurate surgical operation on the maxillary bone, the inven- tion provides that a titanium template is used, allowing the crestal cut made on the resin model to be exactly replicated in the patient's mouth. To this purpose, a wax model of the template is made by laying and shaping a sheet of 0.6 mm gauged, solid wax onto the model which has been previously marked with a pen. As explained below in more detail, the function of the template is to accurately steer the cutting tool, so that its overall surface in breadth can be obtaining by cutting its edges well within the area bounded by the pen for the implant device: on the other hand, it is necessary to hot-carve the template model with a wax knife along the crestal cut, and fully clear the sulcus of any wax. As shown on Fig. 6, a laminar, saddle-shaped titanium template 36 is cast from the wax model so molded, which template will perfectly match the stereolithographic model (not shown) in the edentulous area (and therefore, later, the maxillary bone itself) and having a slot 38 corresponding to the sawed cut described above. On the basis of the implant device that has been built and of the data obtainable from the radiographic survey of Fig. 5, both a temporary fixed, titanium-reinforced resin bridge, and a final prosthesis, say of porcelain, are produced by techniques well known and therefore not described here. After the implant device, the surgical template and the temporary prosthesis have been custom-made on the basis of the stereolithographic model, the surgical stage is initiated. By way of example, and with reference to Fig. 7, it is assumed that an implant is to be performed on a lower maxillary bone 40, shown schematically, in which the associated alveolar nerve 42, as well as its emergence point 44, are shown in dotted lines. The dentist performs the operation under local anesthesia and, as shown on Fig. 7, begins by opening the mucoperiosteal flap 45 in the edentulous area. The flap should be full-thickness and as large as possible, so as to free an area allowing template 36 to be properly and easily adjusted on the edentulous area of the maxillary bone. Preferably, the stability of the template is insured by fastening it to the cortical bone by means of one or two screws of appropriate length for osteo- synthesis. With reference to Fig. 8, a circular saw 46, of 0.5 mm thickness and as used for the stereolithographic model, is applied to maxillary bone 40 through slot 38 in template 36, at a speed of about 1000 RPM and under constant physiological cooling. The bone is incised delicately without strain, with slow to-and-fro movements along the template slot, allowing the saw to cut both downwards and length- wise. After removing template 36, the above described manoeuver is then repeated with a 0.6 mm saw, in order to finish the sulcus. The saddle-shaped implant device is now carefully laid onto the bone and its adaptability is checked, by placing its rib within the open sulcus in the bone ridge. The rib should not fit the sulcus loosely, but rather closely or tightly, and, if necessary, it should be hammered home by lightly hitting the stumps. Should the primary stability of the saddle on its seat be in doubt, then the saddle should be fastened by means of two screws for osteosynthesis, one being placed on the vestibular side and the other on the lingual or palatal side. Fig. 9 is a perspective view of the maxillary bone equipped with an implant device according to the invention, and Fig. 10 shows the same bone in a transverse cross-section, with a prosthesis 48 mounted on the stump. Once the implant device is installed, the surgical flap is sutured, while taking care to make suitable relief dents at the emergence sites of the vertical stumps, in order to allow the mucosa to properly wrap around the stumps without stresses. A temporary fixed bridge may be mounted in situ immediately after completing the suture, provided there are no evident contrary indications such as oedema, bleeding, gross occlusal interferences that cannot be corrected at once, or poor initial stability of the implant. After a suitable waiting period, during which the bone will integrate with the implant device and grow through the holes of rib 12 and possibly also filling the holes in mantle 10, the final fixed prosthesis can be mounted on the stumps. Plugging the holes above the ribs prevents the connective tissue from growing into the holes and hinder ossification. The waiting period may vary from one case to the other, depending on the operator's assessment. As the person skilled in the art will appreciate, the rib of the above described implant is progressively integrated and anchored in the bone, but the forces acting on the implant during mastication are transferred to the maxilla mainly through the saddle-shaped mantle: for this reason, a small penetration of the rib into the bone is sufficient, in contrast to a penetration of over 1 cm as required with conventional implants. At the same time, due to the reticular structure of the saddle-shaped mantle, the periosteum will satisfactorily seal after surgery. It will also be appreciated that, once the radiographic and tomographic survey has been completed, the dentist will operate on the patient in only a single surgical session, the execution of the surgery being straightforward and substantially free from the need for assessments or decisions to be made on the spot: this circumstance will drastically decrease all risks of mistakes or incidents. The procedure also turns out to be less burdensome for the patient. A preferred embodiment of the invention and of the best manner of carrying it out as envisaged at this time has been described above, but many changes are possible within the idea of the invention. It should obviously be contemplated that the dimensions of the parts may be varied, as well as the diameters and the shapes of the holes in the mantle and the rib (which might be, for instance, elliptical or hexagonal), and the rib itself might be discontinuous and of variable height, depending on the limits placed by local anatomy, or it could even be replaced with a number of pegs or tabs. The stumps might also be replaced with other types of supports, e.g. threaded seats for subsequent installation of threaded pillars, as the person skilled in the art will readily appreciate. Furthermore, the procedural modes described above for the installation of the device could be changed, both in respect of the manufacture of the stereolithographic model, which might be obtained by other techniques, and in respect of the use of accessory tools such as the template or the wax bite, which could be made differently or replaced by other techniques. It can also be envisaged that the implant device, as well as the template, may be built by the sinterizing techniques described above or by other technologies, directly starting from the geometrical data delivered by the tomographical survey, without having to actually build an intermediate stereolithographic model.

Claims: CLAIMS 1. An implant device for installation in an edentulous area of a maxillary bone of a patient for supporting a fixed dental prosthesis, characterized in that it comprises: a laminar, saddle-shaped mantle of titanium (10), shaped to accurately match said edentulous area of the maxillary bone; at least one projection for endosteal anchoring (12), also of titanium, integral with the saddle-shaped mantle, perpendicularly projecting from its underside along its ridge, and adapted to be inserted in at least one corresponding recess made in the maxillary bone; and at least one titanium support (14) for a dental prosthesis, integral with the mantle along its ridge. 2. The implant device of claim 1, characterized in that said mantle (10) has an average thickness of about 0.6 mm. 3. The implant device of claim 1 or 2, characterized in that said mantle (10) is thickly perforated in a honeycomb arrangement. 4. The implant device of claim 3, characterized in that said mantle (10) is perforated with round holes. 5. The implant device of claim 4, characterized in that said round holes have a diameter of about 2 mm. 6. The implant device of any one of claims 1 to 5, characterized in that said projection is a thin rib (12), substantially extending along the entire ridge of the mantle (10). 7. The implant device of claim 6, characterized in that said rib (12) has an average height of about 4 mm. 8. The implant device of claim 6 or 7, characterized in that said rib (12) is thickly perforated transversely. 9. The implant device of any one of claims 1 to 8, characterized in that said prosthesis support consists of at least one stump (14) projecting upwards from the mantle ridge, in the shape of a column. 10. The implant device of claim 9, characterized in that it comprises at least two of said stumps (14). 11. The implant device of any one of claims 1 to 10, characterized in that the entire device is made by single casting. 12. The implant device of claim 11, characterized in that the device is made by single casting from a wax model.

Inventors: CORTESE GIANCARLO, CORTESE, GIANCARLO
Applicants: CORTESE GIANCARLO, CORTESE, GIANCARLO
Application year: 2001
Main classification: A61C8
IPC codes: A61C8