The invention in question relates to the sector of dental implantology, namely to that branch of medicine which involves the surgical placing of a specially designed device referred to below by the term"dental implant"or"dental prosthesis"inside the mandibular or jaw bone.

The object of the dental prosthesis is obviously that of restoring the capacity to chew which is hindered by the loss of one or more teeth.

As is known, during the last few years, increasingly in-depth studies in the area of biomechanics (and in particular the properties of certain materials such as titanium), osteointegration and more generally the anatomical and physiological characteristics of the tissue surrounding implants have resulted in the development of increasingly efficient dental prostheses and prosthesis implantation techniques, reducing the

waiting time for prosthesis preparation, expanding the surgical possibilities and improving the functional response of the fitted implants.

At present numerous implant systems are known, such as for example: endosseous implants (screw or blade type), subperiosteal implants, transosseous implants (clip, pin or other type), intramucous implants; endodontic implants, bone substitutes or other systems such as, for example, juxtaosseous systems which have now been abandoned.

Screw implants of various forms have, over time, become established because of their versatility and easy use, replacing, except in a few cases, all the other pre- existing implant systems.

A major contribution to dental implantology techniques was provided by the further research into osteointegration conducted by Professor Bränemark in the 1960s. Osteointegration is understood as meaning a process by means of which a rigid and clinically asymptomatic fixation of the alloplastic material within the bone is obtained and maintained during functional loading.

In other words generally it may be stated that, after the initial inflammatory stage, mechanical adhesion and chemical bonding occurs, also by means of ion

exchange processes, between the dental implant material and the vital bone tissue surrounding the implant, without the presence of soft tissue. The solidity of the bond increases with the increased maturation of the bone tissue.

As is known, the material from which an implant is made may behave, in terms of osteointegration, in an entirely different manner from the bone tissue depending on the type of implant, the superficial conditions of the implant, the types of load which are subsequently applied, the state of the implant site, the operating technique used and many other factors.

As is known, among the different types of implants mentioned above, endosseous implants are currently those which are by far most used in modern prosthesis implantation techniques.

For the purposes in particular of presentation of the present invention, however, when considering these implants it is still necessary to clearly distinguish screw implants from blade implants (also called leaf implant$).

The latter in fact have now been completely abandoned and replaced by screw implants which are suitable for more versatile use and allow much more satisfactory performance levels to be achieved. For

example, recent developments in the dental implantology of screw implants have, in an increasing number of cases, resulted in the possibility of achieving premature loading when using temporary prostheses, with obvious benefits for the patients.

Blade implants and screw implants constitute in each case two techniques of dental implantology which are completely distinct from each other and can in no way be compared, in particular since they are based on different principles of biomechanics and require surgical techniques which are quite different from each other.

For example, as explained above, the response during osteointegration is greatly influenced by factors such as the form, the surface conditions of the implant (in accordance with surface engineering technology), the type of load and the operating technique which varies considerably in screw implants compared to blade implants.

The geometry of the implant system must be such as to favour the primary stability of the implant during the healing phase. For example, the ideal distance at which the bone tissue retains a high osteoblastic activity is 200 microns.

The surgical technique of preparation of the implant site always play a fundamental role in the

osteointegrative process.

It is therefore entirely obvious that the two types of endosseous implants mentioned above represent, for a person skilled in the art, prosthesis implantation techniques which are quite different.

However, for reasons of convenience, associated for example with the form of the jaw bone or mandibular bone, it may still be decided to choose a blade implant, even though practically obsolete, in place of a screw implant.

Surgical techniques able to recreate the bone both heightwise and widthwise have been developed so that in most cases it is possible carry out fitting of an implant if necessary with surgical preparation beforehand.

It is also known to use blade implants which are of the multiple type or composed of a single endosseous-or root-element having, protruding from the top, several connection stumps for connecting a dental element-or an upper prosthesis part-with several teeth connected or separate from each other.

Figures A and B show two known examples of blade implants with their respective endosseous element, the first one being of the type with three mounts and a closed blade at the base and the second one being of the type with two mounts and an open blade at the base.

Traditionally, the endosseous element of a blade

implant comprises a metal plate made of titanium or only lined with titanium powder or also made of an alloy comprising several metals for example chromium, cobalt, molybdenum, aluminium, and if necessary lined with titanium. The plate is connected as a single body to the upper stump by means of a connecting collar.

The plate of the blade implant has a flattened form with different openings inside it having a shape able to allow the osteointegration process to become established once the plate has been implanted using the prosthesis implantation technique envisaged for this type of implant.

The dimensions of the blade body require a somewhat invasive operation in the patient's mouth and generally do not allow easy extraction of the implant in the event of unsuccessful integration.

At present, as mentioned above, the techniques most used for the fitting of both single and multiple endosseous implants envisage the use of individual screw implants which are placed using prosthesis implantation methods of a type known per se and described here briefly only with reference to an overall general procedure for the purposes of the present invention.

Once all the necessary checks have been completed, the gingival flap in the region of the free saddles is

opened and the cavities are formed for insertion of the endosseous elements (roots or screws) of the screw implant using surgical techniques which are well-known.

Once the screw has been inserted in the bone cavity it is possible to perform, depending on the circumstances, screwing of a covering cap onto its head or it is possible to fit beforehand a healing abutment.

In some cases, where there is high primary stability, it is possible to proceed directly with fitting of a provisional abutment or a provisional resin crown for immediate loading.

At this point the traditional technique envisages the formation of a plaster model able to reproduce accurately the arrangement of the teeth and the screws inside the mouth.

This model, as is well-known, is obtained by taking an impression of the patient's mouth which is able to reproduce the precise spatial location of the implant with respect to the jaw and the mandible and also with respect to the teeth and the gums.

For this purpose, before taking the impression, as is known, suitable impression copings, impression stumps or transfer devices are arranged on the heads of the screws, depending on the techniques used.

The impression is generally taken using an

impression holder. The latter may be of the standard type which can be adapted to the edentulous condition of the patient, creating openings in the region of the individual implants, or may consist of a personalised individual infrastructure. In this latter case, it is therefore necessary to provide a preliminary impression using alginate so as to allow the preparation of a spoon of self-polymerizing material adapted to the residual crest after the measuring components have been isolated using wax in order to create the space for the impression material.

Once the impression material, consisting of an elastomer, has hardened, the retaining screws which keep the copings on the implanted screws are unscrewed and it is possible to remove the impression from the mouth. At this point, the laboratory analogs are mounted on the coping and the positive impression consisting usually of a plaster model is prepared.

The upper part of the implant or dental element or overstructure is then formed on this model, which should accurately represent the patient's mouth, by means of various methods of the type known per se.

The dental element of a screw implant consists of a body generally made of metal such as titanium, gold or zirconium on which a capsule made of gold alloy, or other

material, lined with ceramic is mounted.

The abovementioned body of the tooth is generally obtained by means of preliminary application, to the corresponding laboratory analog, of an abutment which, depending on the different applications and the different manufacturing companies, may have a varying form and be made of various materials.

Connection of the abutment to the screw head is generally performed by means of a retaining screw mechanically associated with an anti-rotational connecting system having an internal or external hexagonal shape or by means of numerous other retaining shapes.

An abutment of the known type, which is currently used in prosthesis implants, is the stump known as "UKLA". This is made of calcinable plastic material on which a metal base is mounted and allows, either through addition, by means of the lost-wax overcasting technique or by means of cutting using milling cutters, the restoration of the parallel condition between implants which are greatly out of alignment and formation, according to requirements, of the abutment base on the screw head.

Obviously, once the abutment has been prepared on the plaster model, for example by means of milling and

shearing at the useful height, it is required to test the abutment directly inside the patient's mouth, in order to verify the perfect correspondence with the plaster model.

As is known, it is in fact possible-if not even probable-that there are small errors in the transfer of the spatial information from the mouth to the model via the impression.

For greater safety, it is possible to use the reassembly technique which envisages transferring, by means of a new impression, the position of the abutments inside the mouth to a new model generally called a master model.

Once modelled, the abutment generally undergoes in the laboratory an overcasting process using the lost wax technique, which results in the formation of an intermediate structure made of precious metal, such as gold or titanium, or an alloy of precious metals such as, for example, a gold alloy.

The above is generally applicable to UKLA abutments, while other types of abutments are usually given their specific form by means of cutting with a milling cutter.

The caps thus formed must obviously tested again on the endosseous implant placed inside the patient's mouth.

The preparation of the ceramic cover (biscuit) and the definition of the colour by means of testing on the

patient conclude the prosthetic procedure for fitting of the implant.

As is well known, a good prosthesis implantation technique requires numerous tests-to be carried out during the various steps for preparation of the abutment, the intermediate structure and the cover-aimed at checking the perfect correspondence as regards spatial arrangement of the dental element constructed in the laboratory on the model (called master model) once the said dental element is transferred into the patient's mouth above the endosseous implant.

It is entirely obvious that, in most cases, the surgeon is required with his skill to compensate for any imprecision which may arise in transfer of the information from the mouth to the master model by means of the impression.

The reasons for this non-perfect correspondence may be many and in particular may consist in a lack of precision during taking of the impression or preparation of the plaster model and in the fact that the characteristics of the materials which form the impression may undergo variations over time. For example, during taking of the impression it is necessary to exert a correct and uniform pressure by means of the impression-holder spoon and, in particular, the

extraction step, i. e. when the material has hardened, must be performed with a perfectly axial movement in order to avoid torsional or oscillating movements which could cause displacement of the transfers or pick-ups inside the impression.

As is known, moreover, the impression materials must have characteristics such as to ensure a stable and precise impression and are chosen by the surgeon on the basis of his customary practice and experience.

The impression materials used in dentistry are, as known, elastomers or synthetic rubbers (polysulphide rubbers, silicone rubbers with polymerization by means of addition or as a result polycondensation, polyether rubbers). For further information, see the text "Tecnologie dei materiali dentali" [Dental material technology], Piccin, 1985 by F. Simionato, which is included by way of reference in the present description.

These materials are usually provided in the form of two components which are mixed together before use in a manual and/or mechanical manner. In the patient's mouth the material which is in a paste-like state is converted into an elastomer by means of suitable polymerization chemical reactions and is then extracted after it has acquired suitable elastic characteristics.

Only a correct choice of materials, which duly takes

into account their viscous properties and a correct handling of the paste-like material obtained (working time, setting time, etc. ), allows very precise impressions to be provided.

In particular, since the polymerization may continue for a long period of time, a dimensional change in the impression may occur and result in the production of a model which does not correspond perfectly to the actual form of the mouth.

The abovementioned impression-forming problems with the consequent effects on the model are exacerbated in the case of multiple implants where the distances involved are greater and where in particular perfect correspondence is required not only between the implantation prosthesis and the dental and gingival formation, but also between the individual implants or the individual parts of the various implants. In particular, with reference to the most common example of multiple endosseous implants obtained by means of several independent screw implants, it is required to ensure correct orientation of the individual implants, which generally also results in their perfect mutual parallel alignment.

Owing to the prosthesis implantation technique used hitherto and in particular because of the possible

imprecisions which may arise in the master model, as mentioned, it is required to perform numerous checks in the patient's mouth in order to ensure the correct relative arrangement of the individual implants and the prosthetic articles which are to be prepared.

This fact usually results in a considerable increase in costs, in particular of multiple implants, longer waiting times, as well as a certain inconvenience for the patient who is obliged to attend a large number of sessions in order to check step by step the correct formation of the prosthesis part prepared on the master model in a laboratory.

Moreover, the quality of fitting of the implant depends mainly on the experience and ability of the surgeon, during implantation, and the laboratory technician, during preparation of the prosthesis, since they are required to compensate, with their skill, for any errors in position and parallel alignment which are transferred to the master model.

Basically, therefore, if on the one hand the use of endosseous screw implants must be regarded as an excellent result achieved by modern prosthesis implantation technology-said implants offering among other things a high degree of standardisation of their components while ensuring a wide and varied range of

solutions for all applicational requirements-on the other hand it is entirely obvious that the same individual screw implants, where more than one is used for restoration of a multiple edentulous condition, give rise to a whole serious of operational problems.

These same problems have an adverse effect on the costs and implant fitting times and certainly are less likely to result in optimum prosthesis implantation.

Since the quality of fitting of several individual implants is dependent to a large extent on the ability of the surgeon, a uniform qualitative standard is unlikely.

The main object of the present invention is therefore that of overcoming the drawbacks associated with the solutions of the known type mentioned above, by providing a multiple dental implant which allows rapid and safe placement, while ensuring the performance levels achieved by screw-type implants.

A further object of the present invention is that of providing a multiple dental implant which is constructionally inexpensive to manufacture, easy to fit and operationally entirely reliable.

A further object of the present invention is that of providing a prosthesis implantation method which allows the placement of said multiple dental implant without requiring numerous tests during the construction thereof,

aimed at determining any imprecision in the laboratory model.

A further object of the present invention is that of providing a prosthesis implantation method which reduces the waiting times hitherto required for the fitting of multiple dental implants.

A further object of the present invention is that of providing a prosthesis implantation method which allows the more frequent recourse to the possibility of effecting immediate loading.

A further object of the present invention is that of providing apparatus for allowing rapid and efficient implementation of said method.

These and other objects are all achieved by a multiple dental implant of the type formed by at least one biocompatible endosseous element able to be inserted in a specially provided bone cavity and by at least one multiple dental implant intended to be fixed onto the endosseous element.

According to the invention, the multiple dental implant is characterized in that the endosseous element comprises : at least two fixture portions, each of which is provided with a head, which can be joined to the dental element by means of fixing means, and with a shank supporting the head at the top and having a substantially

tubular elongated form with, associated on its surface, retaining means for exerting a mechanical sealing and osteointegrative action on the bone formation; at least one beam portion forming a single body with the fixture portions and extending by way of rigid connection of their bottom ends substantially in a direction perpendicular to the direction of extension of the individual fixture portions.

The technical features of the invention, in accordance with the abovementioned objects, may be determined from the contents of the claims indicated below and the advantages thereof will emerge more clearly from the following detailed description with reference to the accompanying drawings, which show some purely exemplary and non-limiting embodiments thereof and in which: - Figures 1a, 1b and lc show in schematic form a front view of some examples of embodiment of the multiple dental implant according to the invention for two, three and four teeth, respectively ; - Figures 2a, 2b and 2c show in schematic form a plan view of the implants according to Figures la, 1b and Ic ; - Figures 3a, 3b and 3c show in schematic form a bottom view of the implants according to Figures la, 1b

and lc ; - Figure 1d shows a front view of the multiple dental implant according to Figure 1c for four teeth, complete also with the dental element illustrated in very schematic form; - Figure 4 shows in schematic form a side view of the implants according to Figures la, lb and 1c ; - Figure 5 shows in schematic form a sectioned side view of the implants according to Figures la, lb and lc ; Figures 6a, 6b, 6c, 6d, 6e and 6f show in schematic form a front view of some further examples of embodiment of the multiple dental implant according to the invention, envisaged for different positions or dental situations. In particular, fixture portions with a different number of engaging seats and heads of different breadth, depending on the dental position involved, are illustrated; - Figures 7a, 7b, 7c, 7d and 8a, 8b, 8c, 8d show schematically a front view and a side view of a first example of embodiment of pick-up apparatus according to the present invention, with some parts sectioned so that other parts may be more clearly seen, respectively intended for the implants according to Figures la, Ib, Ic and 6e. In greater detail, the apparatus design proposed in this embodiment acts both as a transfer and impression

pick-up device, in this latter case able to contain the total height of the implant and avoid problems of insertion in the mouth; - Figures 9a, 9b, 9c, 9d and 10a, 10b, 10c, 10d show schematically a front view and a side view of a second example of embodiment of a pick-up apparatus according to the present invention, with some parts sectioned so that other parts may be more clearly seen, respectively intended for the implants of Figures la, lb, Ic and 6e; - Figures lla, lib, lie, lid and 12a, 12b, 12c, 12d show in schematic form a front view and a side view of an apparatus according to the invention consisting of templates respectively intended for the implants according to Figures la, lb, lc and 6e; - Figure 12e shows in schematic form a side view of a template inserted inside a resinous matrix for connection to the teeth of a patient; - Figures 13a, 13b and 13c show in schematic form respectively a first side view, a plan view and a second side view of an example of a spacer intended to be engaged in the templates of Figures lla, lib, lie, lid and 12a, 12b, 12c and 12d; -Figures 14a, 14b and 14c show three examples of spacers of varying heights; - Figures 15a, 15b, 15c and 15d show in schematic

form a front view of an example of embodiment of laboratory analogs, respectively intended for the implants according to Figures la, lb, lc and 6e with abutments and an intermediate structure arranged above; - Figures 16a, 16b, 16c and 16d show in schematic form a front view of the laboratory analogs according to Figures 16a, 16b, 16c and 16d with an intermediate structure arranged above and incorporating the abutments; - Figure 17 shows in schematic form a plan view of an apparatus according to the invention consisting of a guide for performing an incision in the multiple dental implant according to the present invention; -Figure 18 shows in schematic form a side view of the guide according to Figure 17 mounted on the multiple dental implant according to the present invention; - Figure 19 shows in schematic form a further example of a multiple dental implant according to the invention with a different design of the fixing means; - Figures 20a, 20b and 21a, 21b show respectively two different designs of impression pick-up devices and two different intermediate structures suitable for engagement with the fixing means shown in Figure 19; - Figure 22 shows in schematic form a further example of a multiple dental implant according to the invention with a different design of the fixing means;

- Figures 23a, 23b and 24a, 24b show respectively two different designs of impression pick-up devices and two different intermediate structures suitable for engagement with the fixing means shown in Figure 22.

In accordance with the figures of the accompanying drawings, 1 denotes in its entirety the multiple dental implant according to the present invention.

The implant 1 in question is intended to be placed inside a mandibular or jaw bone cavity of the mouth of a patient in particular, but not exclusively, by means of apparatus and by means of a prosthesis implantation method which also form the subject of the present invention.

The terms"screw implant"or"fixture portion"used below must be understood as referring to all the endosseous implants known on the market comprising a portion intended to be located inside a bone cavity and having a cylindrical or essentially cylindrical, conical or frustoconical form which may or may not be provided with threads, grooves, fins, knurls or holes or which may or may not be lined, wholly or partly, with powders consisting of materials with a high biocompatibility, with or without surfaces treated by means of sandblasting, mordanting or the like, and/or capable of inducing an effective osteointegrative effect. Basically

the"fixture portion"described below is entirely comparable to a screw portion of the known type, except for the connection to other parts as will be clearly explained further below.

The range of screws available is very wide. There exist, for example, threaded screws, smooth screws with the implant surface treated to a greater or lesser degree or modified by the presence of holes having systems for connection to the upper abutment of the anti-rotational type, with an external or internal hexagonal form, or with a connection of the conical or other type.

Particular reference must be made to implants with two- phase screws having a smooth collar for reducing the risk of bacterial colonisation.

It is also necessary to mention the expansion screws comprising an expandable fixture in the apex portion able to allow immediate and premature loading.

The multiple dental implant 1 according to the present invention is formed by a biocompatible endosseous element 2 and a dental element 3 intended to be fixed above the endosseous element 2, as will be fully clarified below.

The inventive idea lies in particular in the fact that the endosseous element 2 is composed of two or more fixture portions 4 and a beam portion 5 forming a single

body with the fixture portions 4.

As mentioned, each fixture portion 4 essentially consists of a known screw implant, of the type belonging to those mentioned above, intended to be generally inserted in a sealing manner inside a specially prepared bone cavity which can be obtained by means of surgical milling procedures of the type known per se.

In greater detail, each fixture portion 4 is provided with a head 6, with which fixing means 7 may be associated so as to allow it to be joined to a dental element 3, and a shank 8 which supports the head 6 at the top and has a substantially tubular elongated form, such as precisely the well-known form of the current screw implants.

In particular, the shank 8 may have a substantially conical, frustoconical or cylindrical form or may envisage a top part 8'which is substantially cylindrical and smooth and a bottom part 8"which is substantially conical (see Figure 4) and has, associated on its surface, retaining means 9 for exerting a mechanical sealing and osteointegrative action on the bone formation.

The beam portion 5 extends, according to the invention, in a direction Y perpendicular to the direction of extension X of the individual fixture

portions 4 and rigidly connects together the bottom ends 8'*'of the shanks 8. For this purpose, an internal lateral part 10 of the lateral shanks and both the lateral parts 10 of the central shanks are shaped so as to form a continuous connection with the beam portion 5, as is clearly illustrated in the example of the accompanying Figure 1.

The said continuous connection is formed by means of connecting portion 11 which has a shape rounded in the form of a saddle with the concavity 12 directed upwards.

Advantageously, in order to ensure greater adhesion between the implant 1 and the internal surface of the cavity surgically obtained in the bone formation, it is possible to envisage that the retaining means 9 extend at least partially over the surface of the beam portion 5.

The abovementioned retaining means 9 may, for example, be entirely similar to those envisaged in screw implants or may for example consist of fins, teeth or threads. obviously, since the multiple implant 1 according to the invention is not suitable for insertion inside the bone cavity by means of screwing, any threads will not be initially used to force-fit by means of screwing the implant 1 itself into the cavity.

In accordance with the surgical method for placing the implant 1 according to the invention it is in fact

envisaged performing vertical forced insertion of the endosseous element 2 into the bone cavity in particular by means of beating.

The fins, teeth or threads will preferably have a profile with a cavity 13 directed towards the apex.

In accordance with the preferred embodiment of the present invention which is clearly visible in Figure 4, the conical bottom part 8''of the shank 8 continues in a continuous manner, after its end 8''', with the beam portion 5 which has a maximum width D preferably in the range of between 0.5 mm and 2. 5 mm and a substantially rounded terminal base 14 with a radius of curvature R preferably in the range of between 0.75 mm and 1.75 mm.

A hole 40 with an internal thread 41 is provided coaxially on the head 6 of each fixture portion 4, so as to allow the engagement in particular of the dental element 5.

The present invention also relates to a specially designed surgical method for allowing optimum siting of the multiple implant 1 described above, with reference to which the method is illustrated hereinbelow.

Once all the checks required in each case have been completed, firstly the gingival flap opposite the free saddle where the implant 1 is to be placed is opened and then the cavity is formed for insertion of the endosseous

element 2.

Traditionally, when ordinary implants were fitted, once the position of the implant site had been established, the surgical procedure was started by firstly marking the site with a round drill and then continuing milling with a 2-mm twist drill in order to penetrate the marked site, carrying out several checks as to the direction, the position and the parallel alignment of the individual implants by inserting a director indicator several times and/or by means of X-rays. The crown part of the site was then widened using a pilot milling cutter and the cavity created widened according to the prechosen implant, using milling cutters of different diameter and height. At this point, the cavity could still be machined using a shoulder trimmer so as to allow the screws to be flush with the bone crest and/or using a tapping device for machining the internal surface of the cavity.

Finally, by means of a mounting engaged with a drill driver or spanner, the screw was inserted inside the cavity.

Once the screw has been inserted into the bone cavity and the mounting disengaged, it was possible to perform screwing, onto the screw head, of a covering cap or a healing abutment (i. e. a transmucous connector able

to promote healing of the surrounding mucus) or also perform directly, in infrequent cases of high primary stability, fitting of a temporary resin crown for immediate loading.

According to the prosthesis implantation method according to the present invention, the placing of a multiple dental implant is performed in accordance with the following main steps: Preparation, on a mandibular or jaw bone portion, of two or more contiguous cavities, depending on the size of the implant, able to receive the fixture portions 4 of the implant 1.

For example, a fixture with a 3.75 mm diameter and 4.1 mm base or engaging seat is advantageously arranged in a cavity of 3.45 mm width.

At this point, the abovementioned contiguous cavities are connected along the section situated between them by means of connecting grooves which have a width less than the diameter of the said cavities (approximately 1 mm).

This is then followed by forced insertion of the endosseous element 2 of the implant 1 inside the bone opening obtained by means of joining together of the cavities via the grooves. Obviously, the fixture portions 4 will be forced into the cavities, with the

beam portion 5 extending so as to also fill internally the grooves.

In this way, finally it will be possible to arrange a dental element in a retaining manner on the heads 6 of the inserted fixture portions 4.

In greater detail, the step of forming of the bone opening is performed by stably mounting beforehand, on the mandibular or jaw bone formation of the open gingival flap, a special template 15 which also forms the subject of the present invention.

It comprises a support rim 16 with a shaped incision 17 formed internally and composed of two or more circular holes 18 connected together by substantially straight sections 19.

A portion of solidified resinous material is connected to at least one end of the template 15, being correspondingly shaped with respect to one or more teeth in the patient's mouth which are arranged alongside the open bone formation so as to allow firmer anchoring of the template 15 (see Figure 12e).

The latter must in fact be fixed above the bone formation so as to allow the formation of the bone cavities with a high degree of precision.

Advantageously, therefore, the portion 20 adheres in a sealing manner to the teeth, thereby providing an

effective anchoring system for the template 15.

The template 15 is initially obtained by incorporating the rim 16 in a portion 20 of resinous material which is shaped and moulded so as to make contact with the teeth arranged laterally with respect to the bone formation.

The rim part 16 of the template 15 which has the incision internally may be substantially of the standard type and therefore envisage a pre-set distance between two teeth or between two fixtures, so as to allow, for example, the initiation of an optimum osteointegrative process in accordance with known parameters which also take into account the distances between the individual implants.

Obviously, both the shape and the dimensions of the template 15 may vary in particular to take account of the number and the arrangement of the teeth without thereby departing from the protective scope of the present invention.

For greater stability during mounting, the template 15 may also provided with one or more holes 21 able to receive one or more screws for effecting fixing onto the bone formation.

In greater detail, the shaped incision 17 has a peripheral upper edge 22 which is shaped to receive, if

necessary, in an engaging manner a corresponding locating element 23 of a spacer 24 (see Figures 13a, 13b, 13c).

The template 15 shown in the Figures lid and 12d has a hole 21'able to receive in engagement a pin provided in the bottom part of a similar template 15 in order to allow the arrangement of several multiple implants alongside each other along the arch of the mouth and preferably in a symmetrical position with respect to a plane which separates the front incisors of the mouth.

Removable fastening means for mounting the spacer 24 on the template 15 are also envisaged, said means consisting, according to a possible embodiment, of a pair of flanges 25 which extend radially from the spacer 24 and are shaped so as to engage in a retaining manner in corresponding seats 26 formed on the template 15 itself.

Therefore, in order to form the bone opening able to receive the multiple implant 1 in question, an entirely traditional approach will be adopted, namely with the sequence of required milling cutters inserted into the circular holes 18 of the template 15. At the end of the milling operations intended to create the cavities for the fixture portions 4, a small-size milling cutter will be used to join the two abovementioned cavities by forming grooves for the beam portion 5. This milling cutter will move in a guided manner along the straight

sections 19 so as to form the required grooves. The spacers 24 may vary heightwise, as shown in Figures 14a, 14b, 14c, in order to guide the drilling mills to the required depth inside the bone formation.

The distances and the arrangements of the axes X of the different fixture portions 4 will be defined beforehand by virtue of the mechanical connection represented by the beam portion 5.

As a result, when preparing the abutments, or the elements which form the dental element 3 intended to be positioned on top of the endosseous element 2, the surgeon will not have to make any particular relative adjustments to the model and the actual conditions in order for the head 6 of the fixtures to fit perfectly with the base of the abutments or the dental element 3 as a whole.

Owing to the possibility of forming the endosseous element 2 as one piece with the positions of the heads 6 of the fixtures 4 fixed, it is possible to provide a pick-up device 50 which is pre-formed as one piece and able to be anchored perfectly on top of the endosseous element 2 by means of retaining screws 51. It will advantageously consist of one or more transfer stumps 52 rigidly connected together as one piece by a connecting bar 53.

According to the embodiment proposed in Figures 7 and 8 (where different possibilities of engagement are envisaged), the apparatus 50 may act both as a transfer and an impression pick-up device able to contain the total height of the implant and avoid problems of insertion inside the mouth. Alternatively, the apparatus 50 may assume the form shown, for example, in Figures 9 and 10 where the presence of an additional anchoring element 90 is envisaged.

The precision of the connection is no longer left to the surgeon's skill, but is instead ensured by modern industrial techniques involving precision mechanics.

In this way, the risks of imprecision during taking of the impression or misalignment or lack of parallelism between the individual fixtures 4 is avoided.

The method according to the invention therefore envisages the use of a pick-up device as described above for preparation of the master model on which the dental element 3 can be formed in the laboratory.

Obviously, in view of the perfect correspondence between the plaster master model and the spatial configuration present in the patient's mouth, it is possible to dispense with numerous checks traditionally required in order to verify the spatial correspondence of the elements produced in the laboratory during the

various stages of construction of the dental element 3.

Once the master model has been created, the invention therefore envisages a first step involving mounting of the preformed abutments 26 together with the bases 27 shaped so as to fit precisely with the heads 6 of the fixture portions 4.

Laboratory analogs of the type shown in Figures 15 and 16 will be used in the construction of the master model and will have substantially the same form as the endosseous implant 2 intended to be implanted in the patient's mouth, but will be of the type having a non- machined surface and a traditionally lower cost. In Figures 15 and 16 the reference numbers of the laboratory analogs have been left unchanged with respect to those of the endosseous element 2.

Subsequently, during a second assembly stage, an intermediate structure 28 also of a pre-formed type may be arranged on top of the abutments 26.

Said structure, in accordance with the example of embodiment shown in Figures 15a, 15b, 15c and 15d, may advantageously be formed by a unitary assembly composed of two or more shaped capsules 29 which are rigidly connected by cross-members 30.

The intermediate structure 28 according to the present invention may also be engaged with precision on

top of the abutments 26.

In this way, most of the dental element 3 may be made in an entirely standardised manner using extremely precise production techniques.

In accordance with a further constructional solution illustrated in Figures 16a, 16b, 16c and 16d, the intermediate structure 28 incorporates within it, as one piece, also the abutments 26 which are joined together again by cross-members 30.

The difference between the two designs proposed in Figures 15 and 16 lies in the different type of endosseous element 2 which is to be fitted. The cemented prosthesis shown in Figure 15 offer advantages in terms of strength and aesthetics compared to the screw prostheses shown in Figure 16.

The shaped capsules 29 of the cemented prostheses are connected to the abutments directly by means of a layer of cement and may contribute to the formation of the dental element 3 which is closed above, while the capsules 29 of the screwed prostheses always allow access above for unscrewing of the intermediate structure, by means of a metal island with a hole in the centre.

In the case of screw-type prostheses, the intermediate structure 28 may be used directly to perform overcasting for support of the ceramic part, while still

leaving a small channel for access to the screw. In this case there is a greater thickness of metal and the intermediate structure becomes more rigid and is less likely to be distorted during overcasting.

The remaining part of the process for forming the dental element 3 does not involve particular problems and may be realised in a fairly traditional manner, in particular by using a lost-wax overcasting method, resulting in the formation of a metal and ceramic capsule able to be rigidly joined to the intermediate structure 28.

An important advantage achieved by the implant and the method according to the invention consists in the fact that, with the multiple implants 1 thus formed, it is possible to achieve a very high primary stability which allows the fitting of a temporary dental element for immediate loading, having a shaped so to fit with precision onto the heads 6 of the fixture portions 4.

In accordance with a further characteristic feature of the present invention, should a part of the multiple implant not bond properly inside the bone cavity such that removal of the implant is required, the surgical method in question will also allow this latter operation to be performed in a very simple manner using a special

guide 32 shown in detail in Figures 17 and 18. This guide comprises a main body 33 provided with a connecting hole 34 able to receive a retaining screw 35 intended to removably fix the guide 32 inside the head 6 of the fixture portion 4 to be removed. The guide 32 also has a second guide hole 36 which has an axis S inclined with respect to the axis R of the connecting hole 34 and forming with the latter an angle a of about 6 degrees. A milling cutter can be inserted easily and in a guided manner inside the guide hole 36 such that it can reach the lateral part 10 of the beam portion 5 in order to cut and separate it from the remainder of the endosseous element 2 of the implant 1.

Obviously, in the case where a central fixture portion 5 of the implant 1 must be extracted, it is necessary to perform two separate cuts in the lateral parts 10 thereof.

The second guide hole 36 has a cross-section widened in the form of an eyelet so as to allow movement of the milling cutter into several positions arranged alongside each other so as to allow complete cutting of the beam portion 5.

The invention thus conceived therefore achieves the predefined objects.

Obviously, it may also assume, in its practical

embodiment, different forms and configurations from that illustrated above without thereby departing from the present scope of protection. Moreover all the details may be replaced by technically equivalent elements and the forms, dimensions and materials used may be of any nature according to requirements.