Dental implant with conical coronal end

Abstract

The present invention relates to a dental implant comprising a core and a plurality of threads defined on the core. The implant has a first lower region in which an apical end is located, a second intermediate region, and a third coronal region, wherein the apical end has a conical form comprising at least one channel. The core further has at least one chamber comprising at least two segments, wherein a first segment of the chamber has a helical form and at least one second segment of the chamber has a linear form.

Description

[0001] “DENTAL IMPLANT WITH CONICAL CORONAL TIP” FIELD OF THE INVENTION

[0001] The present invention is part of the technical field of osseointegrated dental implants, with a specific focus on dental implants capable of providing better stress distribution across the bone and tissue heights they contact. BACKGROUND OF THE INVENTION

[0002] Osseointegrated implants are widely known medical components in dental practice, used for the placement of prosthetic structures, bone substitutes, or corrective components in the human skeleton. Briefly, specifically for dentistry, it is a structure made of biocompatible material, such as metal or ceramic, surgically inserted into a patient, and can be implanted in either the maxilla or mandible. The primary purpose of an implant is to replace the root of a lost tooth, acting as a support for prosthetic components.

[0003] The state of the art offers a series of procedures that enable the surgical implantation of these components. In general, in simplified terms, this type of surgery involves an incision in the soft tissue until the bone is reached, so that a hole can be drilled to house the dental implant, accessing different heights of bone tissue. This drilling step is currently performed using different types of drills, such as pilot drills, spherical drills, and helical drills, which perform different functions according to the specific needs of the patient, the surgical technique, and / or the location where the implant will be inserted.

[0004] In the field of implantology, dental implants with self-tapping capabilities (implants of the "self-tapping" type) are known in the state of the art, eliminating the need for drills to create threads, or implants with a rounded apex that prevent injury. An example can be seen in document US 5,312,256, which describes a dental implant with a cylindrical body and rounded apex, in which two sections with wide threads are incorporated to facilitate self-tapping and fixation in already threaded bone.

[0005] Another example of an osseointegrated dental implant can be seen in BR102017015490-4, which reveals an implant whose core is divided into two threaded portions with different proportions, possessing a chamber whose depth varies along its length. This implant is intended for use in various bone types, due to the constant installation torque and the gains in primary and secondary stability it provides.

[0006] However, despite advances in dental implant technology, current surgical techniques require the use of a wide range of drills, and if the drill sequence is not strictly followed, a number of problems can arise regarding the suitability to the different bone characteristics of the implant area, the most appropriate implant positioning, the osseointegration process, as well as aesthetic characteristics and the patient's well-being and comfort. Moreover, a proper drill sequence in implant technique directly influences the success of implant placement and, consequently, how forces from human activities, such as chewing, are distributed on the dental implant, especially in its cervical region.

[0007] For example, current surgical techniques generally use a pilot drill or a countersink drill to prepare the area corresponding to the cervical region of the implant. Especially in denser bones, the use of this drill is even more critical, as the absence of adequate initial preparation can result in excessive compression of the cortical bone in the cervical region during insertion, increasing the installation torque. This excess mechanical stress can cause compression necrosis and subsequent marginal bone resorption, compromising initial stability and the success of osseointegration.

[0008] It is important to note that the cervical region of a dental implant is the upper part of the implant, near the interface between the implant and the gum. This region is critical because it is where the implant emerges from the alveolar bone and approaches the soft tissues (gum), forming the peri-implant seal. The health and integrity of the cervical region are essential to prevent complications such as peri-implantitis, which can compromise osseointegration and long-term implant stability. This would be precisely the result of an unsuccessful implant. Furthermore, the technical characteristics of the implant's cervical region are crucial for both aesthetics and the distribution of masticatory forces.

[0009] In view of this entire scenario, it is clear that there are no provisions in the state of the art for dental implants whose cervical region presents a geometry that reduces stress in this region. In particular, the state of the art does not provide for a dental implant whose cervical region presents a conical coronal tip, specially designed to contribute to the distribution of forces received on the implant and those observed during the insertion process, where this implant is successfully installed independently of the use of a pilot drill or countersink, and is also a friendly implant to different types of bone tissue that may be found at the surgical site. OBJECTIVES OF THE INVENTION

[0010] It is an objective of the present invention to provide a dental implant capable of relieving the insertion stresses generated in the patient's bone during the surgical implant procedure, thus contributing positively to the osseointegration process.

[0011] It is also an objective of the present invention to provide a dental implant that allows its insertion into a patient's bone without the use of a pilot drill or countersink.

[0012] It is also an objective of the present invention to provide a dental implant capable of favoring the distribution of stresses received on the implant resulting from human activities, such as the masticatory function, for example. SUMMARY OF THE INVENTION

[0013] The aforementioned objectives are achieved by means of a dental implant with a core, a plurality of threads defined on the core, and at least one chamber. Said core is formed with a first inferior (apical) region, a second intermediate (medial) region, and a third region consisting of a coronal end. The coronal end possesses a truncated cone-shaped region comprising at least one canal.

[0014] According to additional or alternative embodiments of the present invention, the following features, and their possible variants, may also be present, alone or in combination: - the coronal end comprises a plurality of channels, preferably having channels along its entire length; - the coronal end has a groove positioned at the junction between the coronal end and the second intermediate region; - the coronal end has a truncated cone region above the most extreme channel of the coronal end; - the truncated cone region has a diameter that decreases towards the second region; - the inclination of the outer surface of the truncated cone coronal end forms a cone angle α, wherein the cone angle α is preferably 16°; - the coronal end has an internal orifice; - said internal orifice has a truncated cone shape with a cone angle β, wherein the cone angle β is preferably 16°;- the width of a crest of each thread of the plurality of threads increases gradually in a direction from an apical end (6) to the coronal end; - the at least one chamber comprises a first segment, a second segment and a third segment, wherein the first segment of the at least one chamber has a helical shape, and the second and third segments have linear shapes parallel to a geometric median axis of the implant; - the first and second segments of the at least one chamber are located in the first lower region of the implant; - the third segment of the at least one chamber is located in the second intermediate region of the implant; - the at least one chamber has a spherical bottom; - the at least one chamber has a flat bottom;and - at least one chamber is divided into two segments, where the first segment has a helical shape and is located in the first region, and the second segment has a linear shape and is located in the second region. DESCRIPTION OF THE FIGURES;

[0015] Preferred, but not limited, embodiments of the present invention are represented in the accompanying figures, as briefly described below.

[0016] Figure 1a shows a front view of a dental implant, according to an embodiment of the present invention.

[0017] Figure 1b is a graphical representation of a dental implant fixed in a breakable manner to an implant packaging support.

[0018] Figure 2a shows a cross-sectional front view of the coronal end of the implant of the present invention.

[0019] Figure 2b shows a representative diagram of the diameter relationship between the coronal region of the implant and the other regions in preferred embodiments of the present invention.

[0020] Figure 2c is a graphic representation of a cross-section providing a visualization of the end of the medial region and the beginning of the coronal region.

[0021] Figure 3a is a perspective view of an implant according to the present invention, illustrating in detail a chamber with a spherical bottom.

[0022] Figures 3b and 3c represent a perspective view of an implant according to the present invention, illustrating in detail a chamber with a flat bottom of varying widths.

[0023] Figures 4a-f refer to a front view of dental implants according to the present invention with different diameters.

[0024] Figure 5 represents a front cross-sectional view of the dental implant of the present invention within which a dental prosthesis is attached.

[0025] Figure 6 is a graphical representation indicating the path of a machining tool over an implant of the present invention.

[0026] Figures 7a-d illustrate, by way of example, the tools that can be used during the machining of the implant. DETAILED DESCRIPTION OF THE INVENTION

[0027] According to the general concept of the present invention, a dental implant 1 is disclosed comprising a core 2 on which a plurality of threads 4 are arranged. In one embodiment of this invention illustrated in Figure 1a, the dental implant 1 is formed with three distinct regions integrated with each other, namely, a first lower (apical) region 21, which has a length lr1 ranging from 2 to 8 mm and a shape that can be substantially conical, a second intermediate (medial) region 22, which has a length lr2 ranging from 2 to 16 mm and a shape that is conical in the core and substantially cylindrical in the outermost shape of the threads, and a third region (coronal or cervical) consisting of a coronal end 3, which has a length lr3 ranging from 0.5 to 3 mm and a shape that can be substantially truncated conical and of constant inclination over most of its length lr3.

[0028] Figure 2a illustrates the coronal end 3, which is the part of the implant closest to the gum after insertion into the patient's bone, in greater detail. As previously mentioned, this end is formed, for most of its length lr3, as a truncated cone-shaped portion with a constant inclination, whose diameter decreases from the third region to the second region 22. As can be seen in Figure 2a, the coronal end 3 has a maximum diameter dcormax that varies between 2.5 mm and 8 mm and a minimum diameter dcormin that varies between 2 mm and 6 mm. Furthermore, there is a groove 31.2 between the medial and cervical regions that defines the transition between these regions, as illustrated in Figure 1a and Figure 2c. In some diameters, the existence of the groove is also accompanied by a smaller diameter relative to the largest external diameter dmax observed in the medial region of the implant. Figure 2b contributes to this visualization.The geometry of the coronal, or cervical, region contributes to the implant minimizing bone compression in the cervical region, eliminating the need for a pilot drill (or countersink drill) and simplifying the drilling protocol.

[0029] In a preferred embodiment of the present invention, the coronal end 3 is provided with at least one radially arranged channel 31 on its surface, and even more preferably the presence of a plurality of channels 31 arranged along the entire length lr3, or most of it, of the coronal end 3. The width of each channel can vary between 0.1 mm and 0.2 mm, its height between 0.03 mm and 0.1 mm, and the spacing between one channel and another between 0.15 mm and 0.35 mm.

[0030] At this point, it is clarified that the coronal end 3 is formed, for most of its length lr3, as a truncated cone-shaped portion of constant inclination, whose diameter decreases from the third region to the second region 22. Figure 2a illustrates a cross-sectional and maximized representation of the cervical region, allowing one to clearly visualize that above the last canal, that is, the most extreme canal 31 of the coronal portion, there is a truncated cone region 31.1, whose diameter decreases from the second region 2 to the third region, thus closing the most extreme upper region of the implant. In other words, in the truncated cone region 31.1, there is a reversal in the direction of inclination relative to the inclination of most of the length lr3 of the coronal end 3.

[0031] Figure 2a further illustrates a cross-sectional front view of the coronal portion 3 of an embodiment of the implant 1 of the present invention, showing that the outer surface of the coronal region 3 has an inclination determined by a cone angle α, which can vary between 5° and 20°, preferably an angle of 16°.

[0032] The coronal end 3 also has an internal orifice 33 which, in an optional and non-limiting embodiment of the present invention, may also have a truncated cone shape, presenting an inclination with a cone angle β that varies between 5° and 20°, preferably a 16° Morse taper interface. The internal orifice 33 forms the implant interface to receive a dental prosthesis, whose abutment will be housed in an interior 8, which can be understood as a prosthetic interface 8 of said internal orifice 33, as can also be seen in Figure 5. In a preferred embodiment of this invention, the cone angles α and β are equal; however, in order to meet the particular anatomical needs of a patient, this relationship may be modified.

[0033] The proposed prosthetic interface 8 for the implant, in its preferred form, is a Morse taper type with a 16° angle and features an internal hexagonal indexer, which contributes to the correct positioning of abutments or prosthetic components, as well as having an internal thread. The prosthetic interface 8 allows the implant to be connected to the prosthetic components that will support the prosthesis and provide oral rehabilitation for the patient. In addition, it serves as an attachment point for instruments used in surgical and prosthetic procedures.

[0034] Although the descriptions above take into account an internal hole with a truncated cone shape, it should be noted that, from the perspective of a person skilled in the art, said hole may have other shapes suitable for various prosthetic interfaces without compromising the technical effects described in this application. That is, the internal hole 8 does not need to have the typical truncated cone shape of the Morse taper interface; it can also be designed with a shape adapted for different interfaces such as the external hexagon interface, Internal Fixture (IF), other types of cones, among others. Furthermore, it will be clear to a person skilled in the art that the interface 33 and its interior (prosthetic interface 8) are the physical means by which any type of intermediate component (abutment) connects to the implant, be it, for example, a healing abutment, a scanning abutment, an abutment, etc.

[0035] In relation to Figures 1a, 1b, and 2b, dental implant 1 is also illustrated with its first region 21 and second region 22. In one embodiment of the present invention, the second region 22 has an outer contour of cylindrical or substantially cylindrical shape with a diameter dmax, which is the maximum diameter of the implant, varying between 2.5 mm and 8.0 mm. That is, considering the threads established on the implant core, the shape obtained at this outermost diameter is a cylinder, or substantially close to a cylinder. Figure 2b clearly illustrates the aforementioned cylindrical outer shape, as well as illustrating the relationship between the diameters dmax and dcormax.

[0036] The aforementioned second region 22 extends from the coronal end 3 to the first region 21, comprising in this region part of the core 2 and a plurality of threads 4 machined on the surface of said core, preferably the plurality of threads 4 extending along its entire length. However, it must be borne in mind that obtaining the technical effects of the present invention is not limited to the use of a second region with a cylindrical or substantially cylindrical shape, as described, since it may have diverse geometries, such as, for example, a truncated cone shape.

[0037] In turn, the first region 21 of implant 1 extends from the end of the second region 22 to an apical end 6, which is the smallest diameter of implant 1. The first region 21 may have an external contour of truncated cone shape, encompassing in this region part of the core 2 and a plurality of threads 4 machined on its surface, preferably having threads 4 along its entire length.

[0038] In a preferred embodiment of the present invention illustrated in Figure 1, the plurality of threads 4 distributed over the implant core may present a progressive profile. This means that, as the threads extend along the core 2, there is a gradual increase in the width of the crest of each thread, this gradual increase referring to the apical to the coronal direction. In particular, said threads 4 begin at the apical end 6, where they have a thin and highly sharp crest, and extend along the core 2, presenting an increasingly larger crest width as they advance through the second intermediate region 22, becoming less sharp and increasing the stability of implant insertion, such that the last thread, which is the one closest to the beginning of the coronal end 3, has the greatest crest width.

[0039] To achieve a perfect visualization of the thread progression, Figure 6 illustrates a preferred embodiment of the present invention, in which the proposed thread is produced by a tool shaped to produce a trapezoidal thread. The thread has a trapezoidal profile achieved with one to three tool entries, preferably two tool entries, and a machining path with two tapers. The term tool entry can be understood as the number of different points from which the tool begins cutting the thread.

[0040] Thus, in the apical portion, the implant core is parallel to the external profile of the threads, as can be seen in sign P1 of Figure 6. Starting from the apical end, the thread has a taper that varies according to the length of the implant and gradually increases until it reaches the exit P5, in the groove of the cervical portion. That is, considering the external profile formed by the crest of the threads, the implant can have a conical profile P2 in the apical region and a cylindrical profile P3 in the medial region. Considering the profile formed by the core, the implant can have a conical profile P6 parallel to the conical profile P2 and a second conical profile P4 in the medial region, providing a gradual increase in the diameter of the core.

[0041] This gradual increase in core diameter consequently influences the thread thickness. For example, for implants with diameters between 3.5 and 6.0 mm, an acceptable thread pitch is in the range of 0.55 to 0.90 mm, with the maximum tool depth established in the range of 0.25 and 0.75 mm, respectively. To produce a trapezoidal thread shape, angles between 1 and 35 degrees can be applied to the sides of the trapezoid.

[0042] It should also be noted that the thread profile is determined by the profile of the tool selected for machining. Thus, a preferred embodiment of the present invention can be constructed with a trapezoid, preferably scalene, optionally isosceles or rectangular, with a depth determined by the tool entry level. Similarly, a person skilled in the art will be able to envision possible alterations to the threading patterns exemplified here, such as derivation, pitch, angles, thickness, larger or smaller diameter, orientation, number of starts, tool entry and exit positions, etc.

[0043] The above illustrative, non-limiting values, associated with the progressiveness of the threads and the shape of the coronal region, make the implant design versatile enough to achieve optimal performance in different bone types. That is, when the implant is used in low-density bone, the proposed geometry ensures greater compaction power and, consequently, increases stability during the installation procedure. On the other hand, when used in high-density bone, the interference volume is reduced, and consequently, adequate installation stability is obtained.

[0044] Again with regard to figure 1a, the implant 1 comprises at least one chamber 5 arranged along its length, and said at least one chamber 5 is composed of a plurality of segments. In the exemplary embodiment illustrated in figure 1, the at least one chamber 5 is provided with at least two, preferably three segments, namely a first segment 51, a second segment 52 and a third segment 53.

[0045] In one embodiment of the present invention, the first segment 51 extends helically and axially in part of, or all of, the first region 21 comprising the apical end 6 of the implant 1, having a length ls1 that varies between at least a fraction of the first region 21 and the entire first region 21. Regarding the second segment 52 of the chamber, it is also disposed in the first region 21 of the implant 1 (interconnected between the upper limit of region 51 and the lower limit of a region 53), but extends upwards linearly parallel to a geometric median axis 7, having a length ls2 that varies within fractions of this apical region. The third segment 53 is the portion of the chamber 5 that is located in part of, or all of, the second region 22 of the implant, also with a linear shape parallel to a geometric median axis 7, having a length ls3 that varies between at least a fraction of the second region 22 and the entire second region 22.In functional terms, the aforementioned first helical segment 51 facilitates the interaction between the implant and the bone, helping to pull the implant into the dental alveolus to its final position. In turn, the second and third linear segments 52 and 53 increase the cutting power of the implant and facilitate its installation in the bone alveolus, allowing for a considerable reduction in insertion resistance.

[0046] It is important to emphasize that the depth of chambers 5 is slightly greater than the depth of thread 4, providing a continuous and uninterrupted appearance. Preferably, it is manufactured using a spherical tool that produces a radius in the range of 0.5 to 2.0 mm along its entire length. At the apical end 6, chamber 5 preferably does not completely break the apex in order to avoid stripping of the implant 1 during insertion.

[0047] Although the invention has been described in terms of an exemplary embodiment in which at least one chamber 5 is divided into three segments, it is necessary to bear in mind that this embodiment is not limiting. That is, the technical effects described in this application can also be obtained by implants comprising chambers with different numbers of segments. By way of example, an alternative embodiment (not illustrated) of the implant of the present invention has at least one chamber divided into two segments, one of which is helical and extending along the entire first region, and the other linear and extending along the second region. The number of segments will depend on the size of the implant, with two segments being used in smaller implants, such as, for example, implants 8 to 10 mm in length.

[0048] The configurations shown in Figures 4a–4f illustrate how the chamber can vary according to the implant dimensions, with implants of diameters of 3.5 mm (Fig. 4a), 3.75 mm (Fig. 4b), 4 mm (Fig. 4c), 4.3 mm (Fig. 4d), 5.0 mm (Fig. 4e), and 6.0 mm (Fig. 4f) being shown respectively. The chamber can vary in length, becoming more or less extensive depending on the implant size, as well as in its geometry, potentially having, for example, a spherical or a flat bottom. This change in shape is achieved by modifying the profile of the machining tool selected, for example, using a CNC lathe. Therefore, it should be understood that the chambers can have other shapes such as oval, ovular, ellipsoidal, trapezoidal, polygonal, or various combinations of these shapes.

[0049] In an embodiment illustrated in Figure 3a, at least one chamber 5 of implant 1 has a spherical bottom 53. The spherical bottom 53 can have a diameter dfe ranging from 0.3 to 8.0 mm. In an alternative embodiment illustrated in Figures 3b and 3c, implant 1 is constructed with at least one flat-bottomed chamber 54. The implant in Figures 3b and 3c has a flat-bottomed chamber which, when compared to the spherical-bottomed one, extends for a greater length along the second region and has a greater width. In this way, it is possible to further increase the capacity for conducting bone material and generate greater bone cutting power.

[0050] Figures 7a-d represent, by way of example, tools that can be used during an implant machining process (1), illustrating, respectively, a threading tool, a turning tool, a regular implant chamber tool, and a wide implant chamber tool.

[0051] Through the characteristics described throughout this description, the invention guarantees significant advantages to the surgical procedure, as these characteristics ensure greater primary stability to the dental implant and allow for the relief of tensions arising from bone drilling, making the use of a pilot drill or countersink unnecessary. This makes the surgery less costly and technically less complex, in addition to avoiding potential injuries to the patient undergoing the procedure. With the use of the implant described herein, excellent stability can be expected during the implant placement procedure.

[0052] By providing a dental implant with a coronal end 3 with the geometry described throughout this description, the present invention ensures that the stresses generated during bone drilling and implant placement are relieved, since the proposed shape for the coronal end reduces interference between the implant and the bone. For example, the presence of the groove 31.2 allows for stress relief during implant insertion, which contributes to the technical effect of performing the operation without the use of a pilot drill or countersink.

[0053] In fact, the present invention achieves the result of stress distribution on the implant and bone not only through the proposed coronal end, but also as a result of the shape of the regions proposed in the implant described herein, as well as the distribution and shape of the channels described. Furthermore, the use of progressive threads enhances the proposed technical effects and makes the use of the implant of the present invention even more advantageous. With this, it is possible that the surgical procedure can be performed without the use of a pilot drill or countersink, since it becomes possible to reduce the volume of implant-bone interference by reducing the diameter in the coronal region, which provides stress relief at the site, allowing the implant to be installed without the aforementioned pilot drill or countersink.

[0054] It is noteworthy that the proposed dental implant is suitable for both immediate loading procedures (i.e., when the prosthesis is installed immediately after the insertion of the dental implant) and procedures where the prosthesis is placed later. The combination of proposed technical characteristics, as can be clearly observed by a technician in the field, provides the desired stability and torque for receiving abutments (intermediaries) and prostheses immediately after the implant procedure.

[0055] Finally, it is also important to emphasize that the description above aims solely to exemplify a particular embodiment of the invention in question. Therefore, it is clear that modifications, variations, and constructive combinations of the elements that perform the same function substantially in the same way to achieve the same results remain within the scope of protection delimited by the appended claims.

Claims

1 / 3 CLAIMS 1. Dental implant (1) comprising: a core (2); a plurality of threads (4) defined on the core (2); and at least one chamber (5); wherein the implant comprises a first lower region (21), a second intermediate region (22), and a third region consisting of a coronal end (3); and the dental implant (1) CHARACTERIZED in that the coronal end (3) has a truncated cone-shaped region comprising at least one canal (31).

2. Dental implant (1), according to claim 1, CHARACTERIZED in that the coronal end (3) comprises a plurality of canals (31), wherein it preferably has canals (31) along its entire length (lr3).

3. Dental implant (1), according to claim 1 or 2, CHARACTERIZED in that the coronal end (3) has a groove (31.2) positioned at the junction between the coronal end (3) and the second intermediate region (22). 4.Dental implant (1), according to any one of claims 1 to 3, CHARACTERIZED in that the coronal end (3) has a truncated cone region (31.1) above the most extreme canal (31) of the coronal end (3).

5. Dental implant (1), according to any one of claims 1 to 4, CHARACTERIZED in that the truncated cone region (31.1) has a diameter that decreases towards the second region (22).

6. Dental implant (1), according to any one of claims 1 to 5, CHARACTERIZED in that the inclination of the outer surface of the... 2 / 3 coronal end (3) truncated cone-shaped with a cone angle α, wherein the cone angle α is preferably 16°.

7. Dental implant (1), according to any one of claims 1 to 6, CHARACTERIZED in that the coronal end (3) has an internal orifice (33).

8. Dental implant (1), according to claim 7, CHARACTERIZED in that said internal orifice (33) has a truncated cone shape with a cone angle β, wherein the cone angle β is preferably 16°.

9. Dental implant (1), according to any one of claims 1 to 8, CHARACTERIZED in that the width of a crest of each thread (4) of the plurality of threads (4) increases gradually in a direction from an apical end (6) to the coronal end (3). 10.Dental implant (1), according to any one of claims 1 to 9, CHARACTERIZED in that at least one chamber (5) comprises a first segment (51), a second segment (52) and a third segment (53), wherein the first segment (51) of at least one chamber (5) has a helical shape, and the second (52) and third (53) segments have linear shapes parallel to a geometric median axis (7) of the implant.

11. Dental implant (1), according to claim 10, CHARACTERIZED in that the first segment (51) and the second segment (52) of at least one chamber (5) are arranged in the first lower region (21) of the implant (1).

12. Dental implant (1), according to claim 10 or 11, CHARACTERIZED in that the third segment (53) of at least one chamber (5) is arranged in the second intermediate region (22) of the implant (5).

13. Dental implant (1), according to any of the claims 1. 3 / 3 to 12, CHARACTERIZED in that at least one chamber (5) has a spherical bottom (53).

14. Dental implant (1), according to any one of claims 1 to 13, CHARACTERIZED in that at least one chamber (5) has a flat bottom (54).

15. Dental implant (1), according to any one of claims 1 to 9 or 13 to 14, CHARACTERIZED in that at least one chamber is divided into two segments, wherein the first segment has a helical shape and is disposed in the first region (21), and the second segment has a linear shape and is disposed in the second region (22).

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