ITRM20110084A1 - NAVIGATION SYSTEM FOR DENTAL AND MAXILLOFACIAL INTERVENTIONS - Google Patents

Description

DESCRIPTION

â € œ NAVIGATION SYSTEM FOR DENTAL AND MAXILLOFACIAL INTERVENTIONSâ €

In general, the present invention relates to a navigation system for dental and maxillofacial operations.

In particular, the present invention relates to a navigation system configured to guide and assist:

â € ¢ dentists during dental treatments and dental surgery; And

â € ¢ maxillofacial surgeons during oral maxillofacial surgery.

As is known, current medical imaging techniques, such as Computed Axial Tomography (CT), Tomographic Magnetic Resonance (RMT) and Positron Emission Tomography (`` Positron Emission Tomography '' - PET ), are exploited not only for diagnostic purposes, but also to provide assistance during surgical interventions. Pre-recorded medical images of the body of a patient who must undergo a medical intervention or a surgical operation can, in fact, be viewed during the medical intervention or surgery in order to provide the doctor with a visual reference of the parts of the patient's body affected by said medical intervention or said surgical operation.

In addition, surgical navigation systems have also been developed in the recent past. These surgical navigation systems are able to trace the movements and positions, with respect to the body of a patient undergoing surgery, of medical-surgical instruments used by a surgeon during said operation and to reproduce them dynamically on one or more screens on which also shows the patient's body or the parts of the patient's body affected by said surgery. In this way, said surgical navigation systems assist and guide the surgeon during the surgery and, therefore, help him to perform the surgery correctly.

An example of a surgical navigation system is provided by US patent US 6,687,531. In particular, the United States patent US 6,687,531 describes a system for monitoring the position of a medical instrument with respect to the body of a patient and for displaying, among a plurality of pre-recorded images of the patient's body, at least one which corresponds to the position of the instrument. doctor.

In detail, the system described in US patent US 6,687,531 includes a reference unit, a remote unit, a magnetic field emitter, a magnetic field sensor and a position calculation device. Specifically, in use,

â € ¢ the reference unit is secured to a patient's body in such a way that it is immobile with respect to the part of the patient's body involved in medical treatment or surgery;

â € ¢ the remote unit is coupled to a medical-surgical instrument used during said medical treatment or surgery;

â € ¢ the magnetic field emitter is coupled either to the reference unit or to the remote unit and emits a magnetic field in an area that includes the part of the patient's body affected by medical treatment or by € ™ surgery;

â € ¢ the magnetic field sensor is coupled to the other unit, detects the magnetic field emitted by the magnetic field emitter and produces an output signal representative of the magnetic field detected; and â € ¢ the position calculation device receives the output signal produced by the magnetic field sensor and, on the basis of said output signal received, generates position data representative of the position of the remote unit with respect to the reference.

Furthermore, the system disclosed in US 6,687,531 also includes a mutually coupled storage unit and recording unit. In particular, in use,

â € ¢ the storage unit stores a plurality of pre-recorded images of the patient's body each of which represents a respective part of the patient's body, and

â € ¢ the recording unit receives the position data from the position calculation device, correlates said position data with the plurality of pre-recorded images stored in the storage unit and identifies at least one associated pre-recorded image the position of the remote unit with respect to the patient's body.

Finally, the system described in US patent US 6,687,531 also includes a screen for displaying the image identified, or images identified, by the recording unit, as well as, preferably, also the position of the medical-surgical instrument at the inside such image (s) displayed. Therefore, the system just described allows the doctor to always have available on the screen the images of the patient's body which correspond to the position of the medical-surgical instrument used. Moreover, the United States patent US 6,687,531 also describes the possibility of displaying on the screen a three-dimensional composite image generated on the basis of the images identified by the recording unit.

The Applicants have however noted that the known surgical navigation systems based on magnetic tracking, such as the system described in US patent US 6,687,531, cannot be exploited during dental treatments, dental surgery and maxillofacial surgery involving the area. of a patient. In fact, the tracking of the position of a medical instrument based on the use of a magnetic field emitter and a magnetic field sensor, in order to be reliable, necessarily requires that one of these devices be secured to the patient's body in such a way that is immobile with respect to the part of the patient's body affected by the medical-surgical intervention, for example the jaw. However, since the patient's jaw could move during dental or maxillofacial surgery, the tracking of the position of medical instruments provided by known surgical navigation systems would not be reliable since said systems do not allow a suitable coupling of the field generator magnetic field sensor or magnetic field sensor to the patient's body, or a coupling such as to ensure that the magnetic field generator or the magnetic field sensor is integral with the patient's jaw.

Furthermore, as is well known, in dentistry and maxillofacial surgery, medical and surgical instruments are often used, such as drills, burs, etc., which emit magnetic fields that can have very high intensities. Therefore, the known surgical navigation systems based on magnetic tracking, if they were used to track the position of a medical-surgical instrument that emits magnetic fields, such as a dentist's drill, would not provide reliable tracking of said medical surgical instrument due to the € ™ high interference created by the medical-surgical instrument itself.

The aim of the present invention, therefore, is to provide a system which allows to solve, at least in part, the aforementioned technical problems of known surgical navigation systems.

The aforesaid object is achieved by the present invention as it relates to a navigation system for dental and maxillofacial operations, as defined in the attached claims.

For a better understanding of the present invention, some preferred embodiments, provided purely by way of non-limiting explanatory example, will now be illustrated with reference to the annexed drawings (not to scale), in which:

- Figure 1 is an overall view of the system object of the present invention;

Figure 2 is a side and plan view respectively of two elements of a fixing assembly of the system of Figure 1; And

- Figure 3 is an exploded view showing two elements of Figure 2.

The present invention will now be described in detail with reference to the attached figures to allow a skilled person to make it.

In Figure 1, the numeral 1 indicates as a whole a navigation system for dental and maxillofacial operations according to the present invention.

In particular, with reference to Figure 1, the system 1 comprises:

â € ¢ a central processing and control unit 2; â € ¢ a first magnetic tracking device (not illustrated for simplicity) which is connected, in â € œwirelessâ € or â € œwiredâ € mode, with the central processing and control unit 2 and is fixed on an instrument medical surgery 3 used in a dental and / or maxillofacial operation to which a patient is subjected;

â € ¢ a fixing unit 4 useful for connecting a second magnetic tracking device to the patient's jaw in an integrally rigid manner and illustrated in more detail in Figure 2; and

â € ¢ a screen 5 for viewing, during the operation, the position of the surgical instrument 3 with respect to the patient's jaw.

As illustrated in figure 2, the fixing group 4 comprises an endosseous screw implant 6 made of pure titanium and / or pre-sterile steel and comprising, in turn, a threaded stem 7 arranged, in use, inside the The mandibular bone, and a coupling head 8 made of one piece with the threaded shank 7. The coupling head 8 has an octagonal shape on the side wall 8a of which a circumferential groove 9 is obtained.

Differently from what has just been described, the coupling head 8 can be made in a separate form from the threaded shank 7, to which it is coupled by means of a connection screw for the realization of the endosseous implant as a whole.

As illustrated in Figure 2, the fixing assembly 4 also comprises a rigid connection arm 10 adapted to rigidly connect the second magnetic tracking device to the endosseous screw implant 6. The rigid connection arm 10 comprises for example a first end 10a of it a hooking portion 11, in use, connected to the hooking head 8, and to a second end 10b of it a bayonet attachment element 12 useful for connecting the second magnetic tracking device. The attachment element 12, similarly to the attachment head 8 of the endosseous implant 6, has a polygonal plan conformation on the side wall of which a circumferential groove is obtained.

The coupling portion 11 has an octagonal opening 13 suitable for housing the coupling head 8 and a plurality of spring bearings 14 suitable for snap-engaging the circumferential groove 9. The coupling between the octagonal head 8 and the opening octagonal 13 and the engagement of the circumferential groove 9 by the spring bearings 14 ensure both axial and radial locking of the coupling portion 11 to the coupling head 8. Furthermore, if deemed necessary, it is possible to further stabilize the locking by using a safety micro-screw.

The connection arm 10 must be made of a material such as to confer an extremely high degree of rigidity in order to minimize vibrations and micro-movements during the intervention. The particular conformation of the connection arm 10 in figure 2 is just one example among many and strictly depends on the part of the mandible to which the endosseous screw implant 6 is to be fixed.

In figure 2, the second magnetic tracking device is schematically illustrated with 15, which is integrated in a casing 16, that is a support, made of plastic or metal, sterilizable and sealed, which comprises an attachment portion 16a adapted to cooperate with bayonet coupling 12. In particular, the coupling portion 16a, similarly to the coupling portion 11, has an octagonal opening suitable for housing the coupling element 12, and a plurality of spring bearings suitable for engaging snap the circumferential groove obtained in the attachment element 12 itself.

In this way, the casing 16, as well as being fixed to the end 10b of the rigid connection arm 10, can be fixed directly to the coupling head 8 of the endosseous implant 6.

The particular connection of the rigid connection arm 10 to the coupling head 8 as well as that to the casing 16 are only possible examples and can be replaced by different solutions as long as they are always able to ensure a high connection rigidity of the second connection device. magnetic tracking 15 to the mandible.

Conveniently, during instrumental diagnostic tests, for example radiographs, to which the patient is subjected before the operation, to the bayonet attachment 12, instead of the second magnetic tracking device 15, a radiographic grid can be attached. In this way the radiographic grid, known and not illustrated for simplicity, is connected in an integral way to the rigid connection arm 10 and, therefore, to the endosseous screw implant 6. The radiographic grid has a geometric structure known to the navigation 1 and is made with metals of different radiopacities, each of which is specific for the instrumental examination to be performed and compatible with the different settings that the diagnostic system requires. Basically, the radiographic grid has a prismatic shape recognizable by dedicated software, and it is possible to identify its geometry with a digitization system, or point digitizer, known and not illustrated for simplicity, whose operation will be described in detail below.

The fixing assembly 4 described above could also not include the rigid connection arm 10, if it is possible to position the second magnetic tracking device 15 or the radiographic grid directly on the endosseous screw implant 6. In this particular embodiment, the Endosseous screw implant may have a specific conformation, for example it may include a notch obtained on one of its upper portion, such as to provide a spatial reference useful for determining the spatial orientation of said endosseous screw implant during diagnostic examinations instruments to which the patient is subjected before surgery in order to uniquely orient the radiographic grid and / or the magnetic tracking device 15.

Going even more into the detail of the present invention, the navigation system 1 preferably comprises:

â € ¢ the previously introduced point digitizer which allows you to associate the shapes and position of the patient's anatomical structures and / or the previously described radiographic grid with the three-dimensional data collected from the instrumental diagnostic tests the patient was subjected to before of the intervention, such as x-rays, CT, MRI, PET, etc .;

â € ¢ a magnetic tracking system to track the position and movements of the medical surgical instrument 3 and, conveniently, also the position and movements of the point digitizer, said magnetic tracking system comprising the first magnetic tracking device and the second device magnetic tracking device 15 previously introduced and, conveniently, also a third magnetic tracking device mounted on the point digitizer;

â € ¢ the central processing and control unit 2, created for example through an electronic processor, or a computer, which stores a computer program, or management software which, when executed, causes the central processing unit processing and control 2 manage in real time

- data according to the DICOM standard (â € œDigital Imaging and COmmunications in Medicineâ €) deriving from instrumental diagnostic tests,

- a schedule of surgical interventions,

- information coming out of the point digitizer,

- information coming out of the magnetic tracking system, ed

- a coupling of the information coming out of the point digitizer and the magnetic tracking system with the DICOM data; and

â € ¢ the fixing group 4 previously described. The medical-surgical instrument 3 can be an electrically powered device that includes a motor that generates motion and a handpiece that transfers the motion generated by the motor to an intervention portion, for example to a surgical bur, possibly multiplying or reducing its speed. . In particular, the motor can generate a rotation or an oscillation. The motors mainly used in current medical-surgical instruments to generate rotation are electromagnetic induction motors and brush motors, while the motors to generate oscillations are piezoelectric motors.

In detail, the electromagnetic induction motors generate a rotation of the internal gears which is then transmitted, through the handpiece, to a cutting instrument called the â € œmillâ €. By virtue of their principle of operation based on magnetic induction, these motors emit a magnetic field that can interfere with the magnetic tracking system. For this reason, the current navigation systems used in dentistry and oro-maxillofacial surgery exploit optical and non-magnetic tracking subsystems. On the contrary, the present invention provides for the use of motors equipped with a coating capable of shielding the magnetic field produced by the motor itself. In particular, for motors currently on the market it is envisaged to apply external shielding coatings. Therefore, according to the present invention, it is possible to use both motors already designed to shield their own magnetic radiations, and traditional motors coated with materials capable of shielding the radiations emitted by said traditional motors.

Unlike the magnetic induction motor, the piezoelectric motor, exploiting the physical phenomenon described as the “piezoelectric effect”, generates an oscillating movement with cutting capacity at the tip. In particular, the piezoelectric motor makes it possible to make cuts thanks to special handpieces that transmit the oscillations generated by the motor to non-rotating, but oscillating, tips.

Examples of medical-surgical instruments with which the present invention can be exploited are: surgical handpieces, surgical instruments, rotary burs, endoscopic trocars and every possible type of instrument that must be inserted in the context of the operating field.

The present invention can be advantageously exploited with medical-surgical instruments which include magnetic induction motors, brush motors and piezoelectric motors.

According to a first preferred embodiment of the magnetic tracking system, the second magnetic tracking device 15 in use is fixed, as previously described, to the part of the patient's body involved in the dental or maxillofacial intervention, for example the mandible, by means of the fixing assembly 4 and comprises a magnetic field emitter configured to emit a predefined magnetic field. Still according to said first preferred embodiment of the magnetic tracking system, the first magnetic tracking device in use is fixed, as described above, to the medical-surgical instrument 3, preferably to the motor of the medical-surgical instrument 3, and comprises a first position sensor configured to detect the magnetic field emitted by the magnetic field emitter and to determine, on the basis of the magnetic field detected, its position with respect to the magnetic field emitter.

The reciprocal position between the position sensor and the magnetic field emitter determined by the position sensor corresponds to the reciprocal position between the part of the patient's body affected by the dental or maxillofacial intervention, for example the jaw, and the motor of the medical-surgical instrument.

Alternatively, in particular according to a second preferred embodiment of the magnetic tracking system, the magnetic field emitter is not integrated in the second magnetic tracking device, but is positioned inside the environment where the patient is subjected to this operation, for example it can be fixed to the operating table. In said second preferred embodiment of the magnetic tracking system, the first magnetic tracking device does not change with respect to the first preferred embodiment of the magnetic tracking system, while the second magnetic tracking device 15 comprises, instead of the emitter of magnetic field, a second position sensor configured to detect the magnetic field emitted by the magnetic field emitter and to determine, on the basis of the magnetic field detected, its position with respect to the magnetic field emitter.

In this alternative embodiment of the magnetic tracking system, since at a given moment the positions of the two position sensors with respect to the magnetic field emitter are known, it is also possible to know the reciprocal position between the two sensors and, therefore , the reciprocal position between the part of the patient's body affected by the dental or maxillofacial intervention, for example the mandible, and the motor of the medical-surgical instrument.

The magnetic tracking system can be conveniently made using one of the magnetic tracking systems currently on the market.

In addition, the magnetic tracking system is conveniently configured to detect position changes of less than 0.5mm. Experimental tests conducted by the Applicants have shown that it is possible to obtain such precision by exploiting one of the magnetic tracking systems currently on the market.

As previously described, a position sensor is fixed integrally to the motor of the medical-surgical instrument 3. This is not sufficient to know the position of the extremity of the medical-surgical instrument 3 because said position also depends on the type of handpiece mounted on the motor (shape and size) and the type of cutter used (shape and size). However, once the handpiece and the bur, once they have been coupled to the motor, always maintain the same position with respect to the motor and, therefore, with respect to the position sensor coupled to said motor. Therefore, it is possible to know the position of the end of the bur through a simple calibration operation of the magnetic tracking system which includes recording, by digitization, the position of the end of the medical-surgical instrument 3 while it is being placed in contact with a known landmark integral with the second magnetic tracking device 15 fixed on the patient.

As regards, instead, the problem of the interference created by the motor of the medical surgical instrument 3 to the magnetic tracking system, the present invention provides for the simultaneous or alternative use of two specific countermeasures. In particular, a first countermeasure, already described above, provides for shielding the motor of the medical-surgical instrument 3 by means of special insulating sheaths, while a second countermeasure involves calibrating the magnetic tracking system by moving the handpiece of the medical-surgical instrument 3 at a given speed. Taking into consideration, for example, a medical-surgical instrument including a motor that generates rotation, if the rotation speed is constant during dental or maxillofacial surgery, the interference generated by the motor is in turn constant and, therefore, it is included in the initial calibration of the magnetic tracking system. Therefore, in the event of constant motor speed during dental or maxillofacial surgery, the accuracy of the magnetic tracking system is maintained. If, on the other hand, the rotation speed of the handpiece is changed, voluntarily or accidentally, during dental or maxillofacial surgery, the accuracy of the magnetic tracking system is lost and it is therefore necessary to repeat the calibration of the magnetic tracking system. .

Future developments of the present invention may conveniently include in the computer management program a real-time update of the disturbing magnetic field generated by the engine of the medical-surgical instrument 3, so as to be able to use motors controlled by rheostats so as to be able to change them instantaneously. speed, for example by means of a pedal.

As previously described, the magnetic tracking system provides the position of the tip of the medical-surgical instrument 3 with respect to the part of the patient's body affected by the dental or maxillofacial intervention, for example the mandible, while the inclination of the medical instrument - surgical 3 is determined by at least two high-precision miniaturized inclinometers and / or two high-precision miniaturized accelerometers, each of which is integrated into a respective magnetic tracking device.

Furthermore, as previously mentioned, the magnetic tracking system preferably also comprises a third magnetic tracking device which, in use, is attached to the point digitizer and comprises:

â € ¢ a third position sensor configured to detect the magnetic field emitted by the magnetic field emitter and to determine, on the basis of the magnetic field detected, its position with respect to the magnetic field emitter; and

â € ¢ a miniaturized high precision inclinometer and / or a miniaturized high precision accelerometer to determine the inclination of the point digitizer.

Conveniently, each magnetic tracking device is suitably miniaturized for medical use.

In use, the data collected by the magnetic tracking system are transmitted to the central processing and control unit 2 in â € œwirelessâ € and / or â € œwiredâ € mode.

Furthermore, as previously mentioned, the point digitizer is used to associate the information obtained from the magnetic tracking system with the three-dimensional data obtained from the instrumental diagnostic tests the patient underwent before the surgery. In particular, this association (â € œmatchingâ €) can be conveniently achieved by positioning the digitizer of points on anatomical reference structures of the patient's body which are then also identified on the images obtained from the instrumental diagnostic tests. Therefore, the association of the digitized points with the three-dimensional data obtained from the instrumental diagnostic tests allows the anatomical structures of the patient affected by the dental or maxillofacial intervention to be viewed at any time on the screen 5.

In detail, the point digitizer is a surface reader, mechanical, laser or electromagnetic, configured to recognize the surfaces of the patient's anatomical structures. Said point digitizer, since it is coupled to the third magnetic tracking device, allows to associate the shapes and position of the patient's anatomical structures with the three-dimensional data obtained from instrumental diagnostic tests.

The data received from the central processing and control unit 2 make it possible to relate the anatomical structures of the patient involved in the dental or maxillofacial intervention with the medical device 3, thus allowing a three-dimensional navigation within these anatomical structures.

In particular, once the central processing and control unit 2 has associated, on the basis of the data received from the point digitizer and the magnetic tracking system, specifically from the third magnetic tracking device, the anatomical structures of the patient with the three-dimensional data obtained from instrumental diagnostic tests, said central processing and control unit 2 displays in real time on screen 5:

â € ¢ three-dimensional reproductions of the patientâ € ™ s anatomical structures involved in the dental or maxillofacial intervention; and

â € ¢ a three-dimensional reproduction of the medical-surgical device 3 referenced, on the basis of the position data provided by the magnetic tracking system, specifically by the first magnetic tracking device and by the second magnetic tracking device 15, with respect to the anatomical structures displayed.

In this way, in use, the navigation system 1 guides, with three-dimensional navigation, the dentist or maxillofacial surgeon during the operation.

In detail, the management computer program stored in the central processing and control unit 2 allows you to:

â € ¢ three-dimensional reconstruction and visualization of the patient's anatomical structures on screen 5;

â € ¢ plan surgical interventions; in detail, the management computer program allows you to identify and design the particularly sensitive anatomical structures from which you need to keep a distance, set an audible and / or visual alarm signal in the event that the medical-surgical instrument 3 approaches beyond a given datum limit to these sensitive anatomical structures, program the surgery by identifying, for example, the cutting lines on hard tissues or drawing the osseointegrated implants to be performed, and set an additional audible and / or visual alarm signal in case where the medical-surgical instrument 3 departs beyond a given limit from the previously performed programming;

â € ¢ manage the output data from the point digitizer; in detail, the computer management program makes it possible to associate the three-dimensional reconstruction performed starting from the instrumental diagnostic tests with the real anatomy of the patient, digitizing recognizable landmarks on the three-dimensional reconstruction;

â € ¢ automatically or manually associate the reference points identified through the point digitizer with the corresponding points of the three-dimensional reconstruction;

â € ¢ manage the output data from the magnetic tracking system in such a way as to display at any time on the screen at least the tip of the cutter and the cutting direction; in detail, the management computer program allows to have a visualization in each of the planes of the space through two-dimensional images, or a three-dimensional visualization; and

â € ¢ to emit sound signals, through signaling devices coupled to the central processing and control unit 2, in the event of an error or proximity to the patientâ € ™ s anatomical structures that must not be touched; in detail, the management computer program is able to emit, through the signaling devices, different sound signals that can be set by the dentist or by the surgeon according to one's preferences.

Going even more in detail, the computer management program, when executed, processes the data coming from the magnetic tracking system and also allows you to perform a calibration of the magnetic tracking system for each medical surgical instrument that must be used. Conveniently, the management computer program can be expandable and programmable for any type of medical surgical instrument by means of a database that stores its respective three-dimensional structure. Furthermore, the computer management program can conveniently allow navigation based on the â € œtip & axisâ € system in which only the tip and inclination of the medical-surgical instrument is calibrated 3, but there is no possibility of a global three-dimensional recognition. As previously described, the management computer program, preferably, also allows you to perform a surgical design that can be adapted, through the previously described database, to any implant system and / or other surgical purposes, such as tools for carrying out interventions resective surgery, endodontic surgery, exodontic surgery, etc. In addition, the management computer program can provide for the possibility of alerting the dentist or surgeon when the parameters established during planning are not respected, allows you to adjust the speed of handpieces for implant purposes so that the speed can be reduced until it stops in the event that the parameters established during the planning are not respected and allows to establish a degree of tolerance and a reduction coefficient based on the needs of the ™ dentist or surgeon.

In addition to what has been previously described, the navigation system 1 can also include:

â € ¢ an ergonomic surgical trolley;

â € ¢ touchscreen panels;

â € ¢ receptors for voice commands;

â € ¢ connection hardware interfaces with cables and / or wireless;

â € ¢ â € œvirtual touchâ € hologram display panels; and

â € ¢ a calibration system to determine the error that can affect the magnetic tracking system and to identify any artifacts or errors due to diagnostic devices.

From the foregoing description the advantages of the present invention can be immediately understood.

In particular, the system object of the present invention is able to trace in a safe and precise way dental / surgical instruments used during interventions in the oral field.

Claims (18)

CLAIMS 1. Navigation system (1) for dental and oro-maxillofacial operations comprising: â € ¢ a magnetic tracking system which includes a first magnetic tracking device intended to be fixed on a medical-surgical instrument (3) used in a dental / oromaxillofacial intervention and a second magnetic tracking device (15) intended to be connected to a specific portion of the body of a patient affected by the dental / oro-maxillofacial intervention, said magnetic tracking system being configured to determine in real time during the dental procedure / oro-maxillofacial, through the first and second ( 15) magnetic tracking device, a position of the medical-surgical instrument (3) with respect to the specific portion of interest; â € ¢ a fixing group (4) adapted to connect the second magnetic tracking device (15) integrally to the specific portion of interest; and â € ¢ a central processing and control unit (2) connected to a screen (5) and to the magnetic tracking system to acquire from this the position of the medical-surgical instrument (3) with respect to the specific portion of interest and configured to display on a screen (5) in real time during the dental / oro-maxillofacial procedure the position of the medical-surgical instrument (3) with respect to the specific portion of interest. Navigation system (1) according to claim 1, characterized in that the fixing assembly (4) comprises an endosseous screw implant (6) comprising a threaded stem (7) and a coupling head (8). Navigation system (1) according to claim 2, characterized in that the coupling head (8) has a polygonal plan conformation on the side wall (8a) of which a circumferential groove (9) is obtained. 4. Navigation system (1) according to claim 3, characterized in that the fixing assembly (4) comprises a rigid connection arm (10) adapted to rigidly connect the second magnetic tracking device (15) to the ™ endosseous screw implant (6). 5. Navigation system (1) according to claim 4, characterized in that the rigid connection arm (10) comprises at one of its first end (10a) a coupling portion (11) suitable for being connected to the coupling head ( 8), and at a second end thereof (10b) an attachment element (12) adapted to connect the second magnetic tracking device (15). 6. Navigation system (1) according to claim 5, characterized in that the coupling portion (11) has a polygonal opening (13) suitable for housing the coupling head (8) and a plurality of spring bearings (14 ) adapted to snap into the circumferential groove (9). 7. Navigation system (1) according to claim 6, characterized in that said second magnetic tracking device (15) is integrated in a plastic or metal support (16), sterilizable and sealed, which comprises an attachment portion (16a) adapted to cooperate with the attachment element (12). 8. Navigation system (1) according to claim 7, characterized by the fact that said attachment element (12) has a polygonal plan conformation on the side wall of which a circumferential groove is obtained and that said attachment portion (16a) of said support (16) has a polygonal opening suitable for housing the coupling head and a plurality of spring bearings adapted to snap-engage the circumferential groove. 9. Navigation system (1) according to any one of claims 5-8, characterized in that it also comprises a radiographic grid intended to be used during instrumental diagnostic tests to which the patient is subjected before the dental / oral-maxillofacial operation ; the fixing unit (4) being able to connect said radiographic grid in a solid manner to the specific portion of interest; said radiographic grid comprising an attachment adapted to cooperate with the attachment element (12). Navigation system (1) according to any preceding claim, characterized in that the medical-surgical instrument (3) comprises a motor shielded in such a way as not to create magnetic interference to the magnetic tracking system. 11. Navigation system (1) according to any preceding claim, characterized in that the central processing and control unit (2) is also configured to perform a calibration of the magnetic tracking system which takes into account a any magnetic interference created by a motor of the medical-surgical instrument (3) in such a way as to ensure correct operation of the magnetic tracking system. Navigation system (1) according to any preceding claim, wherein the second magnetic tracking device (15) comprises a magnetic field emitter configured to emit a predefined magnetic field; and in which the first magnetic tracking device comprises a first position sensor configured to detect the magnetic field emitted by the magnetic field emitter and to determine, on the basis of the detected magnetic field, the position of the medical-surgical instrument (3) with respect to the specific portion of interest. Navigation system (1) according to any one of claims 1-11, wherein the magnetic tracking system also comprises a magnetic field emitter which is configured to emit a predefined magnetic field and which is intended to be disposed in proximity the first and second (15) magnetic tracking device; in which the first magnetic tracking device comprises a first position sensor configured to detect the magnetic field emitted by the magnetic field emitter and to determine, on the basis of the detected magnetic field, the position of the medical-surgical instrument (3) with respect to the magnetic field emitter; wherein the second magnetic tracking device (15) comprises a second position sensor configured to detect the magnetic field emitted by the magnetic field emitter and to determine, on the basis of the magnetic field detected, the position of the specific portion of interest with respect to to the magnetic field emitter; and in which the magnetic tracking system is configured to determine the position of the medical-surgical instrument (3) with respect to the specific portion of interest on the basis of the positions determined by the first and second position sensors. Navigation system (1) according to claim 12 or 13, wherein the first magnetic tracking device also comprises a first inclinometer / accelerometer; wherein the second magnetic tracking device also comprises a second inclinometer / accelerometer; in which the magnetic tracking system is also configured to determine in real time during the dental / oro-maxillofacial intervention, by means of the first and second inclinometer / accelerometer, an inclination of the medical-surgical instrument (3) and to provide to the central processing and control unit (2) said determined inclination; and in which the central processing and control unit (2) is also configured to display on the screen (5) in real time during the dental / oromaxillofacial intervention said inclination of the medical surgical instrument (3). Navigation system (1) according to any preceding claim, further comprising a point digitizer which is configured to digitize anatomical structures of the patient and to supply said digitized anatomical structures to the central processing and control unit (2). Navigation system (1) according to claim 15 when it depends on claim 14, wherein the magnetic tracking system also comprises a third magnetic tracking device which is attached to the point digitizer and which includes a third inclinometer / accelerometer for determining the inclination of the point digitizer and a third position sensor to determine the position of the point digitizer; in which said magnetic tracking system is also configured to provide the central processing and control unit (2) with the inclination and position of the point digitizer; and in which the central processing and control unit (2) is also configured to display on the screen (5) in real time during the dental / oromaxillofacial intervention: â € ¢ a three-dimensional reconstruction of the patient's anatomical structures generated on the basis of the digitized anatomical structures provided by the point digitizer, the inclination and position of the point digitizer provided by the magnetic tracking system and data obtained from instrumental diagnostic tests the patient underwent before the dental / oromaxillofacial surgery; and â € ¢ a three-dimensional reconstruction of the medical-surgical device (3) referenced with respect to the three-dimensional reconstruction of the anatomical structures and generated on the basis of the position of the medical surgical instrument (3) with respect to the specific portion of interest and the inclination of the medical surgical instrument (3 ) provided by the magnetic tracking system. 17. Navigation system (1) according to claim 16, in which the central processing and control unit (2) is also coupled to a signaling device, comprises a user interface operable by a user to identify anatomical structures of the patient that must not be touched during the dental / oro-maxillofacial surgery and is also configured to signal, through the signaling device and on the basis of the position of the medical surgical instrument (3) with respect to the specific portion of interest and the inclination of the medical-surgical instrument (3) provided by the magnetic tracking system, which the medical-surgical instrument (3) is close to said anatomical structures identified. 18. Software product comprising portions of code that can be loaded into a memory of a processor of a navigation system such as that claimed in any preceding claim, executable by said processor and such as to cause that, when executed, said processor becomes configured as the unit central processing and control (2).