ES2725124B2 - Multifunction board for teaching intraoral surgical techniques - Google Patents

Description

D E S C R I P C I Ó N

MULTIFUNCTION BOARD FOR TEACHING SURGICAL TECHNIQUES

INTRAORAL

OBJECT OF THE INVENTION

The invention, as expressed in the statement of the present specification, refers to a multifunctional board for teaching intraoral surgical techniques that provides, for its intended purpose, advantages and novelty characteristics, which are described in detail below. , which represent an improvement of the current state of the art.

More specifically, the object of the invention focuses on an instrument structurally designed to be able to test surgical techniques in a safe environment and reproducing the existing conditions in the oral cavity, which allows acquiring a minimum level of skill in the technique in question, before to perform it in a clinical setting on real patients, being conceived and carried out in order to obtain numerous and notable advantages over other existing instruments with similar purposes.

FIELD OF APPLICATION OF THE INVENTION

The field of application of the present invention is framed within the technical sector of sanitary instruments, more specifically in that related to surgical simulators, also encompassing the scope of models for scientific or medical use, as a full-scale device for the demonstration, and may include anatomical models.

BACKGROUND OF THE INVENTION

As is known, the surgery of the oropharyngeal cavity has the function of preventing or correcting anatomical, evolutionary, traumatic and pathological defects of the oropharyngeal structures.

Training in surgical techniques consists of developing cognitive, clinical and technical skills that are traditionally acquired through observation and supervised practice. Although errors are inherent in learning curves, failures are not allowable in surgical practice, making training in an simulated surgical environment. This type of training provides the educator with the possibility of standardizing both the quality and the quantity of the practice that the disciple will carry out, and also the feedback and evaluation of the student's skills (both technical and non-technical), something that is not always possible in the real environment.

The effectiveness of the training received in this way will depend on the proximity of the situation reproduced with the real case to be simulated. The existing simulators for oral surgery are grouped into two main types: synthetic and animal. The former seek to reproduce in artificial material the appearance and consistency of human tissues, as well as the feedback obtained by the operator during the surgical technique, while using manikins to reproduce the conditions of the human oral cavity. These simulators have been partially successful in recreating the appearance of the surgical area, although tissue consistency and feedback from practice are very poor. However, the reproduction of the oral cavity is acceptable, although it has the drawback of not allowing the tutor to observe the development of the intervention without interrupting / conditioning the process.

The second group of simulators employs animal models whose selection for surgical training must take into account the availability of specimens, the social acceptability of the chosen animal, the costs, and the similarity between the animal tissue on which the learning takes place and the human tissue on which the procedure will be carried out in reality. Under these premises, it is possible to adequately simulate the appearance and consistency of human tissues, so that the feedback obtained by the operator is close to that obtained in actual surgical practice.

The main drawback of this approach is that the simulation is carried out on a table, so that the circumstances in which the operator acquires his training are very different from reality, which compromises the real usefulness of the simulation as a previous step to surgery on real patients.

It would therefore be desirable to have a simulator that reproduces, not only the characteristics of the human tissue on which the disciples will intervene after completing their training, but also the environment where these tissues will be located (in this case the oral cavity), since the object of the training is to enable the procedure to be performed in that particular environment and not in another. Furthermore, the ideal simulator should allow observation by the instructor without limitations and without interfering in the development of the practice by the disciple.

Therefore, the objective of the present invention is the development of an instrument that combines the possibility of using animal and synthetic elements in the same simulator, limiting access and lighting in the area to be operated, which, in addition, can be used on a conventional dental unit, stretcher or table (which allows its orientation in different planes of the space) and combines opaque and transparent coating, allowing the instructor's vision, while restricting that of the operator.

On the other hand, and as a reference to the state of the art, it should be noted that simulators and similar devices are known in the field that concerns here. Specifically, as the closest relevant documents, the following can be named:

Document US2007178429A1, which describes a dental model for training in oral and maxillofacial surgery techniques. The model consists of a head that is adapted to be mounted on a support structure, such as a simulation table or cart, and includes a mouth opening, delimited by an upper and a lower jaw, which are mounted on a base. The interior of the oral opening is provided with elements that imitate the tissues and structures of a real mouth, such as a tongue, teeth, uvula, bone, a gingival layer, etc., made of a synthetic material such as urethane, and attached to the head by a plurality of pins, screws, etc. The model also incorporates elements that imitate the behavior of structures in the mouth, such as nerves and blood vessels, connected to an electrical circuit that simulates the behavior of these structures when the surgeon maneuvers and emits indicators of the state of the structure. The set is subsequently delimited by a hemispherical piece that imitates a skull.

And document US2013236873A1 which refers to an apparatus for demonstration of salivary gland endoscopy techniques (sialoendoscopy or sialendoscopy) that includes a support structure consisting of a replica of a human lower jaw, in which a structure incorporating a duct structure to mimic the salivary glands. The support structure may include additional elements, such as an upper jaw, with articulation elements to pivot relative to the lower jaw, teeth, etc. A structure including the invention is also a movable language, since its inclusion is considered necessary to demonstrate the manipulation of such an element during some of the procedures that are intended to be taught.

However, it is not observed that any of the previous inventions, taken separately or in combination, describe the present invention. It can therefore be affirmed that, at least on the part of the applicant, the existence of any other multifunctional board for teaching intraoral surgical techniques, or any other invention of similar application, that has the same or similar technical, structural and constitutive characteristics is unknown. to those presented by the board that is claimed here.

EXPLANATION OF THE INVENTION

The multifunctional board for teaching intraoral surgical techniques that the invention proposes is configured, therefore, as a novelty within its field of application, since according to its implementation and exhaustively, the previously indicated objectives are satisfactorily achieved, being the characterizing details that make it possible and distinguish it conveniently included in the final claims that accompany the present description.

More specifically, what the invention proposes, as previously pointed out, is an instrument designed to test surgical techniques in a safe way, reproducing the existing conditions in the oral cavity, in order to be able to acquire a minimum level of skill in intraoral surgical techniques. , before performing it on real patients, which has numerous and notable advantages over other existing instruments with similar purposes.

For this, and more specifically, said instrument consists of a board (base) with two main components in the form of flat elements perpendicular to each other, one vertical (minor) and the other horizontal (major), the latter with a series of elements and grooves. to allow the holding of specimens and models, as well as the insertion of specific attachments according to the simulation to be carried out, on which a lid is placed and which also includes a liquid collection and evacuation system, as well as stabilization devices for the different work surfaces (eg table, dental equipment, or stretcher).

In addition, on the horizontal element or board itself (major component) and above the lid, a metal frame is fitted, on which a transparent plastic cover is installed in the back and slightly translucent in the front ( to the area after the insertion of the model), where it has a hole that simulates the mouth in maximum opening. This cover constitutes a simulator that reproduces the access and space existing in the oral cavity, restricts the available lighting and the approach by the surgeon in training, while allowing the inspection of the technique by the instructor.

The whole of the invention is thus a board to incorporate elements and form a medical simulator that has application in the surgical field of various medical specialties, such as dentistry, stomatology, oral and maxillofacial surgery, otorhinolaryngology, dermatology, and family and community medicine. The present invention allows surgical training to be obtained under conditions similar to those existing in the oral cavity, which is more effective than that obtainable by means of current simulators.

The described multifunctional board for teaching intraoral surgical techniques represents, therefore, an innovation with structural and constitutive characteristics unknown until now, reasons that together with its practical utility, provide it with sufficient grounds to obtain the exclusive privilege that is requested.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, the present descriptive memory, as an integral part thereof, is accompanied by a set of plans in which, by way of illustration and non-limiting the following has been represented:

Figure number 1.- Shows a schematic view in upper perspective, of an example of the multifunctional board, object of the invention, showing its general configuration and the main parts and elements it comprises, in the absence of including the frame and the cover.

Figures number 2 and 3.- They show respective views in lateral perspective of the board shown in figure 1, represented in figure 2 with an inclined plane and in figure 3 with lid and without inclined plane.

Figure number 4.- Shows a front-side perspective view of the board, according to the invention, incorporating the metal frame and the plastic cover, both represented schematically, their arrangement being appreciated on the vertical and horizontal elements of the board, as well as its configuration.

Figure number 5.- Shows a bottom perspective view of the board, showing the liquid drainage system that comprises under the horizontal element, with the connection provided for the rubber tube that directs the liquid where appropriate.

Figures 6a, 6b, and 6c.- They show schematic views of an embodiment of the mobile fastening means for hard tissues and their location in the lid, appreciating the parts it comprises. Specifically, Figure 6a shows a perspective view of one of said fastening elements alone; and Figures 6b and 6c both elevational and perspective views of the set of two fastening elements incorporated in the slot of the cover of the horizontal element of the board.

Figure 6 shows a schematic side elevation view of an embodiment of the mobile fastening means for hard tissues, the parts it comprises being appreciated.

Figures 7-A and 7-B. - They show respective views, in front and side perspective respectively, of an example of embodiment of the inclined plane comprising the board to guide the movement with the traction of the tongue.

Figure number 8.- Shows a rear perspective view of the board of the invention, according to the example shown in Figures 1 to 3.

Figure number 9.- Shows a perspective view of the area of the horizontal element in which the hole is located with pressure screws that constitute the fastening system for synthetic models and for the inclined plane.

And figure number 10.- Shows a schematic perspective view of the fastening system of the piercing rod to the horizontal element of the multifunctional board, showing the arrangement of the same that allows its displacement with the opposition of the resistance exerted by the spring, at the same time that it allows its dismantling for washing and sterilization.

PREFERRED EMBODIMENT OF THE INVENTION

In view of the aforementioned figures, one can observe in each of them two non-limiting examples of the multifunctional board for teaching intra-oral surgical techniques of the invention, which comprises the parts and elements indicated and described in detail below, from according to the numbering adopted, according to the following list:

1. board

2. vertical element

3. horizontal element

4. First set holding hard tissue specimens

5. second set holding soft tissue specimens

6. third fastening set for inclined plane or synthetic models

7. liquid evacuation drain

8. eyelets for fastening to dental chair

9. suction cups

10. horizontal element cover with multiple perforations to avoid water accumulation 11. plastic cover

12. Transparent section of plastic cover

13. slightly translucent section of plastic cover

14. lateral reinforcements for liquid control

15. Lid support pivots and guides for fastening metal frame

16. side edges

17. legs

18. Sliding Slot Hard Tissue Fastening System

19. nut to secure hard tissue fastener assembly fasteners in slit slot on lid

20. butterfly screw

21. center rail of the cap for displacement of the piercing stem therein 22. piercing stem of the soft tissue holding assembly

23. movable piercing rod anchor

24. guide of the mobile anchorage of the pointed rod

25. spring attached to the piercing rod

26. opening in lid to accommodate synthetic model or inclined plane

27. inclined plane to reproduce lingual movements

28. depression of the horizontal element to hold synthetic models

29. holes in the cover to house the pivots of the horizontal element

30. circular hole in the plastic cover simulating the oral cavity in maximum opening

Thus, as observed in said figure 1, the board (1) in question is configured, essentially, from two flat elements perpendicular to each other, one vertical (2), which is preferably transparent in its upper part, and another horizontal (3), where a series of fastening sets (4, 5, 6) are located to hold different types of specimens and anatomical models, as well as the insertion of specific attachments according to the simulation to be performed, which, both of origin Biological as well as synthetic, they can be new and different with each use, said fastening assemblies (4, 5, 6) being provided with movement and shape to emulate the movement and orientation thereof with the traction of said specimens in surgical practice.

Preferably, in addition, the board (1) also includes means for collecting and evacuating liquids through a drain (7), as well as stabilization and / or fixing devices (8, 9) to different work surfaces (ex: table, dental equipment, or stretcher).

In any case, the board (1) is designed so that, on the horizontal element (3) or board itself, a cover (10) fits and on it a metal frame (not shown in the figures) which, in turn, it is covered with a plastic cover (11), which has a transparent section (12) on its side and rear and another slightly translucent section (13) on the front, where it has a hole (29) that simulates the mouth in maximum opening. This plastic cover (11), appreciable in figure 4, has a volumetric configuration such that it reproduces the access and space existing in the oral cavity, restricts the available lighting and the approach by the surgeon in training, while allowing inspection of the technique by the instructor.

In the preferred embodiment, the board (1) is formed from two rectangular flat elements of equal width and different length arranged one vertically (2) and the other horizontally (3), that is, with an angle of 90 degrees , facing the same ends. He vertical element (2), of smaller size, whose length is less than half that of the larger horizontal element (3), has on its outer lateral edges, near its upper and lower limits, on both sides, some rings support (8), solidly attached to the body, whose purpose is to act as stabilization and fixation devices for the tabletop (1) by allowing the passage of straps to stabilize the tabletop (1) in different situations (for example, the back of the dental chair ). In addition, preferably, the union of both rectangular elements (2, 3) is reinforced by lateral reinforcements (14), consisting of two triangular sections, on both sides, whose object is, in addition, to conduct the liquids resulting from the cooling of the rotary instruments used in surgical practice towards the horizontal element (3) that is provided with the evacuation system with drain (7) thereof located at the bottom of the panel (1).

For its part, the larger horizontal rectangular element (3) constitutes the main part of the board as it is shaped like a board itself, and its particular configuration shows its usefulness in simulating various surgical techniques on a wide range of animal tissues. and synthetic models, for which it has a series of attachments.

Specifically, this horizontal element (3) has, in the proximity of its four inner corners, some pivots (15) to support the cover (10) so that it is located at least 1 cm below the lateral edges (16 ) that surround this horizontal element (3) and that will merge with the aforementioned triangular lateral reinforcements (14) of the vertical element (2), and whose purpose is to confine the liquids collected in them within the board (1) and avoid their spillage. The cover (10), in addition, also has perforations designed so that the liquids produced in surgical practice do not accumulate on it and fall on the base of the horizontal element (3) located below it.

Preferably, in addition, on the underside of the horizontal element (3) and in its four corners, the existence of legs (17), about two centimeters in length, which end in a suction cup (9) is contemplated in order to Serve as a device to stabilize the simulator on a table.

In addition, the horizontal element (3) has a drain hole (7) as a liquid evacuation system to which, optionally, a connection is attached for the connection of a rubber tube (not shown) that allows directing them where appropriate.

In any case, this larger rectangular horizontal element (3) integrates, coupled between the element itself and the cover (10) that covers it, different fastening assemblies for the different types of specimen to be used, which preferably consist of the following:

- A first clamping assembly (4) for animal hard tissues (eg: pig's jaw), which is incorporated in the lid (10), preferably, in a rectangular slot (18), as shown in the example in Figures 3 and 6C, arranged transversely in the middle third of the cover (10), being made up of two movable fasteners (4) that move along said slot (18), as seen in Figures 6-A, 6 -B and 6-C.

Specifically, as seen in said figure 6A, the fasteners (4) that are incorporated in said slot (18) comprise two supports, placed facing each other that can be fixed in the slot at the desired distance by means of a nut (19 ) lower and that have a screw with butterfly lock (20) that act as a means of pressure clamping. The purpose of these devices is to stabilize the jaw (or other hard animal tissue) by pressing it between the screws (20) of both supports (4). In addition, and since their fixation is mobile, they can be adapted to the different widths that the specimens could present.

- And, a second fastening set (5) for animal soft tissues (eg: pig's tongue) that is also incorporated between the horizontal element (3) and the cover (10), which has a central rail (21 ) longitudinal that begins in the rear third of the cover (10) and continues in the direction of its front or opposite part and which serves to accommodate a piercing stem (22), which on its underside has a movable anchor (23) that is It moves on a guide (24), made up of two parallel bands fixed to the horizontal element of the board, sufficiently raised to allow the movement of the piercing rod (22), which is also attached to a spring (25) that tends to place it in the most posterior position of the guide (24) and that is anchored more posteriorly on the base of the horizontal element (3). The movable anchor (23), shown in detail in Figure 10, has a thread on which the piercing rod (22) is placed where the animal specimen is nailed, its end then being covered with a blunt stop (not shown). With all this, this clamping assembly (5) seeks to reproduce the anterior movement of the tongue when it is subjected to traction by the operator.

In order to better reproduce this movement, the board (1) preferably has a third clamping assembly (6), consisting of a group of pressure bolts with a wheel lock (Fig 9) located on the horizontal element (3 ) below and on both sides of an opening (26) of the cover (10) provided in front of the hard tissue clamping assembly (4), where an inclined plane (27) is fixed, consisting of a piece with a top surface decreasing towards the back of the horizontal element (3), with a partially curved profile and a hemieliptic section, as seen in Figures 7-A and 7-B, whose mission is to guide the movement of the tongue sideways and upwards under traction, just as it would in a real situation.

In an alternative option, the board (1), replacing the described inclined plane (27) (Fig 7B), allows to fix synthetic models, for which it has a depression (28) practiced in the horizontal element (3) under the the aforementioned box-shaped opening (26), one centimeter deep, on whose sides the pressure screws of the aforementioned third clamping assembly (6) are installed, as seen in figure 9, terminated in a wheel, which when pressed they will put pressure on the synthetic model, stabilizing it in this way.

Finally, it should be noted that the metal frame on which the plastic cover (11) is incorporated, preferably, is made up of a structure of steel threads that describe a parallelepiped partially truncated in its anterior portion, which fits into four pivots (15 ) of the horizontal element (3), as already indicated, having holes (29) coinciding with the position thereof in the cover (10) to accommodate said pivots. This frame serves as scaffolding for the plastic cover (11) with which it is covered as a lining, being, as previously mentioned, slightly translucent in its front part (13) and transparent in the back part (12). Furthermore, in the front part, and coinciding with the inclined section of the frame, it has a hollow (30) that defines a circular opening of 7 cm radius, its lower limit contacting the anterior crossbar that said frame presents.

Once the nature of the present invention has been described, as well as the way to put it into practice, it is not considered necessary to make its explanation more extensive so that any expert in the field understands its scope and the advantages derived from it, stating that: within its essentiality, it may be practiced in other forms of embodiment that differ in detail from that indicated by way of example, and to which it will also achieve the protection that is provided as long as its fundamental principle is not altered, changed or modified.

Claims (19)

1. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, characterized in that it is configured from two flat elements perpendicular to each other, one vertical (2) and the other horizontal (3), where a series of fastening assemblies are located (4, 5, 6) to hold different types of anatomical specimens and models, as well as the insertion of specific attachments according to the simulation to be carried out, both of biological and synthetic origin, said fastening assemblies (4, 5, 6) being provided with movement and way to emulate the movement and orientation of the same with the traction of said specimens in surgical practice; and because , on the horizontal element (3), a cover (10) and a metal frame fit onto which, in turn, a plastic cover (11) is installed, the configuration of which reproduces the access and space existing in the oral cavity, presenting a transparent section (12) in its lateral and posterior part and another slightly translucent section (13) in the anterior part, where it has a hole (29) that simulates the mouth in maximum opening. 2. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 1, characterized in that it also includes means for collecting and evacuating liquids through a drain (7). 3. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 2, characterized in that the union of both elements (2, 3) is reinforced by lateral reinforcements (14), consisting of two triangular sections, on both sides, whose object is, in addition, to direct the liquids product of the refrigeration of the rotating instruments towards the evacuation device (7) located in the lower part of the board (1). 4. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 3, characterized in that the cover (10) of the horizontal element (3) is located at least 1 cm below the lateral edges (16) that surround this horizontal element (3) and that merge with the triangular lateral reinforcements (14) of the vertical element (2). 5. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 4, characterized in that the cover (10) has perforations so that the liquids produced in the surgical practice do not accumulate on it and fall on the base of the horizontal element (3) located below it. 6. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to any of claims 1 to 5, characterized in that it also includes stabilization and / or fixing devices (8, 9) to different work surfaces. 7. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 6, characterized in that, as stabilization and / or fixation devices to work surfaces, the vertical element (2) has, on its external lateral edges, fastening (8) for the passage of belts to stabilize the tabletop (1) in different situations, for example, to the back of the dental chair. 8. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 6 or 7, characterized in that, as stabilization and / or fixation devices to work surfaces, in the lower part of the horizontal element (3), the existence of with legs (17), about two centimeters long, ending in a suction cup (9) whose purpose is to stabilize the simulator on a table. 9. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to any of claims 1 to 8, characterized in that the two vertical (2) and horizontal (3) flat elements are of equal width and different length arranged at an angle of 90 degrees, facing the equal ends. 10. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 9, characterized in that the vertical element (2) is smaller in size, and its length is less than half that of the horizontal element (3) that is greater. 11. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to any of claims 1 to 10, characterized in that, for fastening animal hard tissues (ex: pig's jaw), it comprises a first clamping assembly, made up of two mobile moving clamps (4) incorporated in a rectangular slot (18) arranged transversely in the middle third of the cover (10). 12. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 11, characterized in that the fasteners (4) comprise two supports, placed facing each other that can be fixed in the slot at the desired distance by means of a lower nut (19) and that they have a screw with butterfly closure (20) that act as a means of clamping by pressure. 13. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to any of claims 1 to 12, characterized in that, as fastening elements for animal soft tissues (eg: pig's tongue), it comprises a second fastening set (5) with a piercing stem (22), located in a movable anchor (23), where the animal specimen is nailed. 14. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 13, characterized in that the second clamping assembly (5) is incorporated between the horizontal element (3) and the cover (10), in a central rail (21) longitudinal that serves to accommodate the piercing rod (22), which on its underside has a movable anchor (23) that moves on a guide (24) formed by two parallel bands fixed to the horizontal element (3), raised to allow the displacement of the sharp rod (22), which is also attached to a spring (25) which tends to place it in the most posterior position of the guide (24) and which is anchored further on the base of the horizontal element (3). 15. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to any of claims 1 to 14, characterized in that it comprises a third set of fastening (6), consisting of a group of pressure screws with wheel closure located on the horizontal element (3) under and on both sides of an opening (26) of the cover (10) provided in front of the hard tissue holding assembly (4), where an inclined plane (27) is fixed whose mission is to guide sideways and upwards the movement of a tongue under traction. 16. - MULTIFUNCTION BOARD FOR TEACHING SURGICAL TECHNIQUES INTRAORAL, according to claim 15, characterized in that the inclined plane (27) is a piece with an upper surface decreasing towards the rear of the horizontal element (3), with a partially curved profile and a hemieliptic section. 17.- MULTIFUNCTIONAL BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 15 or 16, characterized in that the third clamping assembly (6) has a box-shaped depression (28) made in the horizontal element (3), under the opening (26) of the cover (10), one centimeter deep, on whose sides the set screws with wheel ends are installed to fix synthetic models to replace the inclined plane (27). 18. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to any of claims 1 to 17, characterized in that the metal frame is made up of a structure of steel threads that describe a parallelepiped partially truncated in its anterior portion, which is fixed in four support pivots (15) made for this purpose in the horizontal element (3). 19. - MULTIFUNCTION BOARD FOR TEACHING INTRAORAL SURGICAL TECHNIQUES, according to claim 18, characterized in that the plastic cover (5) covers the metal frame as a lining, being, translucent in its front part (13) and transparent in the posterior part ( 12), and, coinciding with the inclined section of the frame, provided with a hole (30) that defines a circular opening of 7 cm radius.