Applicator handpiece with open-ended coaxial cable

Abstract

The handpiece comprises an external conductor and an internal conductor placed in an inner cavity of the external conductor. An intermediate spacer made of dielectric material is placed inside the external conductor, between the external conductor and the internal conductor. The external conductor and the internal conductor are approximately coaxial to each other and form an open-ended coaxial cable. An energy delivery window is arranged in front of the external conductor and of the internal conductor. A cooling system removes heat in the area of the window, to limit heating of the skin of the patient during treatment.

Description

APPLICATOR HANDPIECE WITH OPEN-ENDED COAXIAL CABLEDESCRIPTIONTECHNICAL FIELD

[0001] The present invention relates to medical equipment and devices. More in particular, the invention relates to improvements to devices and equipment for medical-aesthetic treatments using electric fields.BACKGROUND ART

[0002] In the field of aesthetic treatments, techniques for the selective removal of adipose tissue are currently of great importance. To this end, various methods have been developed over the years, some of which are based on invasive surgical procedures. In less recent times, a treatment known as liposuction was widely used; this treatment allows portions of fat to be eliminated through suction, making small incisions of a few millimetres in the epidermis and subsequently inserting a cannula subcutaneously into the adipose tissue to be removed or reduced. Suction occurs manually using syringes, or with specific aspirators. In some cases, the localized use of ultrasound, vibrations or water jets is combined with suction to aid dissolution of the fat.

[0003] Due to its invasive nature, the procedure is carried out under local or general anaesthetic, depending on the amount and distribution of the tissue to be removed.

[0004] In some cases, to dissolve adipose tissue, a lipolysis procedure is used which involves injecting liquids (such as soy lecithin) suitable to cause lysis of the adipocytes, i.e., destruction of the cellular membranes and hence liquefaction of the adipocytes, into the adipose layers to be removed. The biological material resulting from lipolysis is then gradually absorbed by the organism.

[0005] In more recent times, laser liposuction techniques have been developed, consisting in sucking adipocytes using a suction cannula, after the fat has been dissolved using laser energy conveyed into the tissue through an optical fibre, inserted by means of a needle. In some cases, lipolysis is performed on the adipocytes using a laser and the resulting biological material is metabolized by the body instead of beingremoved by suction.

[0006] Laser lipolysis methods and devices are disclosed in US-B-6206873.

[0007] An alternative method uses cooling by means of pads that enclose plicae of abdominal tissue consisting of dermis and subcutaneous fat. Cooling remaining in place for a given time damages the adipocytes of the subcutaneous tissue and leads to necrosis. Subsequent elimination is carried out gradually by the body.

[0008] Already in less recent times, methods for destroying adipocytes via the percutaneous administration of energy have been proposed. For example, US-A- 5, 143,063 discloses an energy applicator to be applied to the dermis. The energy passes through the dermis to reach the adipose layers below, causing destruction of the adipocytes. This prior art document suggests the use of different forms of energy, such as ultrasound energy or electromagnetic microwave energy.

[0009] WO-A-96 / 40369 discloses an apparatus and a handpiece for treatments to remove adipose layers using microwaves. The handpiece has an antenna array that generates converging microwave beams to reach the desired temperature in the subcutaneous adipose layers.

[0010] EP-A-2767308 discloses devices and systems for applying energy in the form of microwaves, in order to remove subcutaneous adipose layers.

[0011] EP3422978 discloses an innovative device for medical and aesthetic treatments, in particular for the removal of subcutaneous adipose layers, which uses the emission of an electric field by a truncated coaxial guide, i.e., an open-ended coaxial cable. This device is particularly effective, but may be further improved, in particular to improve its efficiency in the treatment of some body regions, such as, in particular, the neck and the face.SUMMARY

[0012] According to one aspect, a handpiece is disclosed particularly adapted for the treatment of particularly small skin regions or areas, such as areas of the face or of the neck.

[0013] Substantially, an applicator handpiece for skin treatments is provided, which uses radio frequency energy, comprising an external conductor with an inner cavity and an internal conductor placed in the inner cavity of the external conductor, so that the external conductor surrounds the internal conductor. An intermediate spacer made of dielectric material is placed inside the external conductor, between the external conductor and the internal conductor. In advantageous embodiments, the external conductor and the internal conductor are approximately coaxial to each other and form an open-ended coaxial cable. The handpiece may further comprise an energy delivery window, arranged in front of the external conductor and of the internal conductor. The window may be closed by a closing element, transparent to the emission frequency of the open-ended coaxial cable waveguide. The handpiece also comprises a cooling system to prevent the epidermis of the patient being treated with the handpiece being damaged due to excessive heating.

[0014] Advantageously, the external conductor comprises an annular front surface; the internal conductor comprises a circular front surface, coaxial to the annular surface of the external conductor; and the cooling system comprises a cooling duct for circulation of a cooling fluid, formed in the external conductor, or in the spacer, or partly in the external conductor and partly in the spacer.

[0015] In particularly advantageous embodiments, the cooling duct is integrally formed in the external conductor. In advantageous embodiments, the cooling duct is formed by an additive manufacturing, i.e., 3D printing, process, with which the external conductor is manufactured.

[0016] Further features and embodiments of the handpiece are set forth in the appended claims and described below with reference to the accompanying drawings.BREVE DESCRIPTION OF THE DRAWINGS

[0017] The invention will be better understood by following the description and the accompanying drawings, which illustrate non-limiting examples of embodiments of the invention. More in particular, in the drawing:Fig.l shows an axonometric view of an applicator handpiece according to the invention in an embodiment;Fig.2 shows an axonometric view in partial section;Fig.3 shows a longitudinal section, according to the line HI-HI of Fig. 5, of the applicator handpiece along a plane containing the axis of the applicator handpiece;Fig.4 shows a cross section according to IV-IV of Fig.3;Fig.5 shows a view according to V-V of Fig.3;Fig.6 shows an enlargement of a detail of the front part of the handpiece in the view of Fig.3;Fig.7 shows an axonometric view of an applicator handpiece partially disassembled in a further embodiment; andFig.8 shows an axonometric view analogous to the view of Fig.2, of the handpiece of Fig.7.DETAILED DESCRIPTION

[0018] In the accompanying figures, the reference numeral 1 indicates an applicator handpiece in one embodiment. The applicator handpiece 1 may be connected via a cable, for example a coaxial cable 3, to a radio frequency generator, not shown.

[0019] The applicator handpiece 1 comprises an external conductor 5, or external electrode, with an inner cavity 7, in which an internal conductor 9, or internal electrode, is placed. The external conductor 5 surrounds the internal conductor 9. The outer wall of the front part of the external conductor 5 may have a cylindrical shape, so as to define a front surface 5 A with a circular outer edge. The inner cavity 7 of the external conductor 5 may have a cylindrical shape and hence define a circular inner edge of the front surface 5A. The circular outer edge may advantageously be bevelled or rounded, as shown with 5S in Fig.6, to facilitate sliding of the applicator handpiece on the surface of the epidermis during treatment.

[0020] In some embodiments, the inner cavity 7 may have an inner diameter De(Figs.3, 6), which can, for example, be between 5 mm and 20 mm, preferably between 8 mm and 15 mm.

[0021] The external conductor 5 and the internal conductor 9 are approximately coaxial to each other and are connected, respectively, to the external conductor (or sheath) and to the internal conductor of the coaxial cable 3.

[0022] An intermediate spacer 11 is placed in the cavity 7 of the external conductor5, between it and the internal conductor 9. The spacer 11 is made of dielectric material, to electrically isolate the external conductor 5 and the internal conductor 9 from each other. In some embodiments, for practicality of construction, the spacer 11 may be produced in two portions, respectively a rear portion 11 A and a front portion 1 IB. The two portions 11 A, 1 IB together form a dielectric that completely isolates the internal conductor 9 from the external conductor 5. The front portion 1 IB forms a flat annular front surface 11C, which is interposed between the annular front surface 5 A of the external conductor 5 and a flat circular front surface 9A of the internal conductor 9.

[0023] In some embodiments, the flat circular front surface 9A of the internal conductor 9 has a diameter Di (Figs.3, 6) that may be between 3 mm and 9 mm, preferably between 4 mm and 6 mm.

[0024] In some embodiments, the ratio between the inner diameter Di of the annular front surface 5A of the internal conductor and the outer diameter Deof the circular front surface 9 A of the internal conductor 9 may be between 1 and 3, preferably between 2 and 2.5.

[0025] The rear portion 11 A of the spacer 11 made of dielectric material may be cupshaped with a central hole for the coaxial cable 3 to pass through, and more precisely for its conductor or internal electrode, which is in electrical contact with the internal conductor 9 of the applicator handpiece 1, to pass through.

[0026] In the illustrated embodiment, the two portions 11 A, 11B of the insulating spacer 11 form an externally cylindrical body, the outer cylindrical surface of which is in contact with the inner cylindrical surface of the cavity 7 of the external conductor 5.

[0027] Internally, the two portions 11 A, 1 IB form a seat coaxial to the inner wall of the external conductor 5, with a variable diameter. More in particular, the rear part formed by the portion 11A of the spacer 11 has a larger diameter and the front part formed by the portion 1 IB of the spacer 11 has a smaller diameter. Both the rear part and the front part have a cylindrical shape and accommodate the internal conductor 9.

[0028] The internal conductor 9, or internal electrode, thus has a variable cross section, with larger diameter in the part closest to the coaxial cable 3, i.e., in the rearportion, and a smaller diameter in the distal part, i.e., in the front portion, farthest from the coaxial cable 3.

[0029] The external conductor 5 and the internal conductor 9 with the dielectric of the intermediate spacer 11 form an open-ended coaxial cable, i.e., a truncated coaxial guide.

[0030] The front surfaces 5A of the external conductor 5 and 9A of the internal conductor 9 are substantially orthogonal to the axis A-A of the handpiece, which coincides with the circular axis of symmetry of the front surfaces 5A, 9A.

[0031] At their front surfaces 5A, 9A, the two coaxial conductors 5 and 9 form an energy delivery window. The delivery window is indicated with the reference numeral 13. When the applicator handpiece 1 is electrically powered and is placed with the delivery window 13 on the epidermis of a patient being treated, an electric field, the force lines of which extend orthogonally to the front surface 9A of the internal conductor 9 and orthogonally to the front surface 5A of the external conductor 5, propagates within the epidermis and the adipose layers below.

[0032] More specifically, as indicated above, the portion 11 A of the spacer 11 is cupshaped with a perforated bottom for the coaxial cable 3 to pass through and a wall, for example cylindrical, which extends from the perforated bottom toward the distal part of the handpiece 1, i.e., toward the window 13. The seat for a portion of larger diameter of the internal conductor 9 is formed between the perforated bottom and the cylindrical wall. The portion 1 IB has an outer diameter equal to the portion 11 A of the spacer 11, but a cylindrical cavity defined by a cylindrical wall thereof, with an inner diameter smaller than the inner diameter of the first portion 11 A. Consequently, the internal conductor 9 may have a rear part with a larger diameter, in the part accommodated in the cavity of the portion 11 A, and a front part, i.e., closer to the window 13, with a smaller diameter, equal to Di.

[0033] In this way, it is possible to produce an electrical connection with the coaxial cable 3 via the part of the internal conductor 9 with larger diameter, which facilitates electrical connection, and allows the use of coaxial cables available on the market. At the same time, the front part of the internal conductor 9 may have a diameter Di of the correct size to obtain the desired shape of the electric field lines delivered from thehandpiece, without the need to excessively increase the diameter De of the cavity of the external conductor 5 and the outer diameter of said conductor 5.

[0034] In this way, a handpiece 1 with a front surface of limited size is obtained, particularly useful for treating regions of the human body that are particularly complex to irradiate, in particular the face.

[0035] The delivery window 13 may be closed by (or formed by) a closing element 15, for example made of sapphire or another material adapted for contact with the epidermis, transparent to the electric and magnetic field generated by the generator applied to the coaxial cable 3 and preferably with good thermal conductivity. The closing element 15 allows the passage of the electric field flux through the epidermis of the patient and removes heat from the epidermis treated by conduction.

[0036] The closing element 15 may be a disc-shaped element, of limited thickness, for example between 0.1 mm and 1.5 mm, preferably between 0.3 mm and 1.00 mm, in some embodiments approximately 0.5 mm. The closing element 15 may be housed in a recessed seat 17 formed by the front surface 5 A of the external conductor 5, by the annular flat front surface 11C of the dielectric spacer 11 and by the circular front surface 9A of the internal conductor, see in particular the detail of Fig.6.

[0037] Advantageously, the recessed seat 17 may have a depth substantially equal to the thickness of the closing element 15, so that this forms, with the peripheral part of the front surface 5A of the external conductor 5, a substantially continuous flat surface. Moreover, in this way, the perimeter surface of the closing element 15 is in contact with the cylindrical wall of the recessed seat 17 formed in the external conductor 5; the flat inner surface of the closing element 15 is in contact with the bottom of the recessed seat 17. The bottom of the recessed seat 17 is formed by a part of the front surface of the external conductor 5, by the front surface of the spacer 11 and by the front surface of the internal conductor 9.

[0038] With the arrangement described above, the distance, in axial direction, between the annular front surface 5 A of the external conductor 5 and the circular front surface 9A of the internal conductor 9 may be between 0 and the diameter Di of the circular front surface 9A of the internal conductor 9, preferably between 0 and 1 / 3 of the diameter of the circular front surface of the internal conductor, even morepreferably between 0 and 1 / 5 of the diameter of the circular front surface of the internal conductor. In practice, in the illustrated embodiment, in which the closing element 15 is embedded in the recessed seat 17, a part of the annular front surface 5 A of the external conductor 5 is coplanar to the flat circular surface 9A of the internal conductor and a part of the front surface 5 A of the external conductor 5 is spaced from the surface 9A by a length equal to the thickness of the closing element 15, for example 0.5 mm.

[0039] In practice, the closing element 15 of the window 13 may be in thermal contact with the annular front surface 5A of the external conductor 5, with the cylindrical surface formed in the external conductor 5 and defining the lateral wall of the recessed seat 17, with the flat annular surface 11C of the spacer 11 and with the flat circular surface of the internal conductor 9.

[0040] In other embodiments, the closing element 15 of the window 13 may be applied to the outside of a surface formed by the external conductor 5, by the internal conductor 9 and by the dielectric 11 and, more precisely: by an annular front surface of the external conductor 5, by an annular front surface of the dielectric 11 and by a circular front surface of the internal conductor 5, all these surfaces being coplanar to one another and in contact with the flat inner surface (i.e., facing the cavity 7) of the closing element 15.

[0041] This thermal contact allows efficient heat transfer from the outer surface of the closing element 15 toward the internal and external conductors 9 and 5 and toward the dielectric spacer 11, to obtain efficient cooling of the epidermis of the patient during treatment.

[0042] To obtain efficient cooling, the handpiece 1 may comprise a fluid cooling system, in particular a liquid cooling system. The coolant may simply be water when the cooling system comprises a cooling circuit that is contained only in the external conductor 5. In fact, in this case, due to the structure of the cooling system described below, the coolant does not interfere with the electric and magnetic field emitted by the handpiece 1. Moreover, in advantageous embodiments, the cooling circuit in which the cooling fluid circulates is hermetically closed and isolated relative to the delivery window 13, which prevents contact with the closing element 15 and minimizes the risk of leaks and of contact of the cooling fluid with the epidermis of the patient.

[0043] This allows great freedom of the choice of the coolant used, which will be selected mainly based on considerations regarding cost and heat exchange coefficient.

[0044] In some embodiments, the cooling system comprises a cooling duct for circulation of the cooling fluid, formed in the external conductor 5, or in the spacer 11, or partly in the external conductor 5 and partly in the spacer 11.

[0045] In the illustrated embodiment, the cooling system comprises a cooling duct 21 formed integrally in the external conductor 5, see in particular Fig.4.

[0046] In some embodiments, the cooling duct 21 extends around the axis A-A of the handpiece 1. For example, the cooling duct 21 may have an approximately annular extension and may extend for an angle of less than 360°, as visible in Fig.4. In this way, a flow in a constant direction (for example, clockwise or counter-clockwise) is established in the cooling duct 21 along the whole of its extension.

[0047] In the embodiment illustrated, the cooling duct 21 has two ends opposite each other, in fluid communication with an inlet connection and with an outlet connection. In some embodiments, the inlet connection and the outlet connections each comprise a rectilinear duct that extends parallel to the axis A-A of the handpiece 1. The rectilinear ducts are indicated with 21A and 21B. The reference numeral 23 indicates connections, for example threaded connections, connected to the ducts 21A, 21B and configured to connect the handpiece 1 to an external cooling circuit, not shown. The external cooling circuit comprises a heat exchanger, not shown, to remove heat from the coolant circulating in the handpiece 1, driven by a pump, again not shown. In some embodiments, the heat exchangers may be a liquid / air heat exchanger. In other embodiments, a liquid / liquid heat exchanger may be used. In further embodiments, the coolant may be cooled via one or more thermoelectric elements, such as Peltier cells.

[0048] Advantageously, in the illustrated embodiment, the annular cooling duct 21 and the rectilinear ducts 21A, 21B may be formed by additive manufacturing, i.e., by 3D printing, in the external conductor 5. In practice, the external conductor 5 may be manufactured by 3D printing, i.e., by additive manufacturing, so that the annular cooling duct 21 and the ducts 21A, 21B (rectilinear in the example of embodiment) are integrally formed inside the external conductor 5 during its production with a 3D printing process.

[0049] The external conductor 5 may be made of metallic material with high thermal and electrical conductivity, for example aluminium.

[0050] The structure of the cooling duct 21 with its inlet and outlet ducts 21A, 21B formed by additive manufacturing guarantees a sealed, leak-free cooling circuit. Moreover, the overall volume of the applicator handpiece 1 is particularly compact, due to integration of the cooling circuit in the thickness of the external conductor 9.

[0051] The only points of the cooling circuit in which leakages of cooling fluid may occur are located at the connections 23, which are positioned away from the area in which the handpiece 1 is applied to the patient. The connections 23 guarantee the seal, for example through a threaded connection. The cooling circuit inside the applicator handpiece 1 may be produced without sealing gaskets and the duct for circulation of the cooling fluid is made in one piece inside the material forming the external conductor 9.

[0052] Removal of heat from the area of epidermis being treated takes place by thermal conduction through the closing element 15 of the window 13 and from this mainly through the thickness of material of the external conductor 5 that closes the annular cooling duct 21 at the front. The cooling fluid removes heat from the closing element 15 along the whole of its perimeter, which makes cooling of the entire area of epidermis being treated efficient, also due to the high coefficient of thermal conduction of the material (sapphire or the like) of which the closing element 15 is formed and to the limited size of the front area of the applicator handpiece 1.

[0053] Forming the cooling duct integrally inside the external conductor 5 avoids the need to use gaskets or other sealed coupling elements, and also the need to use a coolant with insulating properties.

[0054] In fact, the entire cooling circuit remains confined inside a single block consisting of the material forming the external conductor 5, which may be grounded.

[0055] In practice, the annular cooling duct 21 has a closed cross section and is integrally formed by the external conductor. The cooling duct 21 is configured as an annular chamber formed in the external conductor, adj acent to the annular front surface 5 A of the external conductor 5. Advantageously, the annular chamber has an extensionthat is slightly less than 360° and is thus interrupted by a dividing wall 21C (see Fig.4) that separates an inlet end and an outlet end of the cooling fluid to guarantee uniform circulation of the cooling fluid in the annular chamber.

[0056] Figs.7 and 8 illustrate a further embodiment of a handpiece according to the invention. In these figures, the same reference numerals indicate the same or equivalent parts to those illustrated in Figs. 1 to 6. These parts will not be described again. The embodiment of Figs. 7 and 8 differs from the embodiment of Figs. 1 to 6 mainly in that the external conductor 5 is made of two parts 5.1 and 5.2 (which in Fig.7 are shown separated from each other), which may be manufactured separately and joined to each other, as shown in Fig.8. The part 5.1 may be joined to the part 5.2, for example, by welding or gluing. The two parts may also be joined in another way, for example by snap fastening, shrink fitting, threaded coupling, or the like. Advantageously, the two parts 5.1, 5.2 are joined to each other so as to prevent leaks towards the outside from the cooling duct 21, which in this embodiment may be produced on a front surface of the part 5.1, on a rear surface of the part 5.2, or partly on the front surface of the part 5.1 and partly on the rear surface of the part 5.2. After coupling, the two parts 5.1, 5.2 joined to each other with seal, close the cooling duct 21 toward the outside, preventing leaks.

[0057] While in the embodiment of Figs. 1 to 6 the cooling duct 21 is generated by additive manufacturing, i.e., by 3D printing, of a monobloc electrode 5, in the embodiment of Figs.7, 8 the cooling duct 21 may be produced in another way, for example by chip removal, or by moulding, in the two parts 5.1, 5.2, which are then coupled to each other.

Claims

Claims1. An applicator handpiece for skin treatments using radio frequency energy, comprising: an external conductor with an inner cavity; an internal conductor placed in the inner cavity of the external conductor, so that the external conductor surrounds the internal conductor; wherein the external conductor and the internal conductor are approximately coaxial to each other; and wherein the external conductor and the internal conductor form an open-ended coaxial cable; an energy delivery window, arranged in front of the external conductor and of the internal conductor; a cooling system; an intermediate spacer made of dielectric material placed inside the external conductor between the external conductor and the internal conductor; wherein the external conductor comprises an annular front surface; wherein the internal conductor comprises a circular front surface, coaxial to the annular front surface of the external conductor; and wherein the cooling system comprises a cooling duct, for circulating a cooling fluid, formed in the external conductor, or in the spacer, or partly in the external conductor and partly in the spacer.

2. The handpiece of claim 1, wherein the intermediate spacer comprises a rear portion and a front portion.

3. The handpiece of claim 2, wherein the rear portion and the front portion of the intermediate spacer form a dielectric that completely isolates the internal conductor from the external conductor.

4. The handpiece of claim 2 or 3, wherein the front portion of the intermediate spacer forms a flat annular front surface, which is interposed between the annular front surface of the external conductor and the flat circular front surface of the internal conductor.

5. The handpiece of claim 2, 3 or 4, wherein interiorly, the front portion and the rear portion of the intermediate spacer form a seat coaxial to the inner wall of the external conductor, with a larger diameter in the rear part and smaller diameter inthe front part; wherein the internal conductor has a rear portion with a cross section having a larger diameter and a front portion with a cross section having a smaller diameter; wherein one end of a coaxial cable is connected in the rear part and the front part forms the front surface of the internal conductor.

6. The handpiece of any one of the preceding claims, wherein the cooling system consists of a cooling circuit fully contained only in the external conductor, so that a coolant that circulates in the cooling circuit does not interfere with the electrical and magnetic field emitted by the handpiece.

7. The handpiece of claim 6, wherein the cooling duct extends around an axis of the external conductor and of the internal conductor.

8. The handpiece of any one of the preceding claims, wherein the cooling duct has an annular extension around an axis of the external conductor and of the internal conductor.

9. The applicator handpiece of any one of the preceding claims, wherein the cooling duct has a closed cross section and is integrally formed by the external conductor.

10. The applicator handpiece of any one of the preceding claims, wherein the cooling duct is configured as an annular chamber formed in the external conductor, adjacent to the annular front surface of the external conductor.

11. The applicator handpiece of claim 10, wherein the annular chamber has an extension of less than 360° and has a cooling fluid inlet end and a cooling fluid outlet end.

12. The applicator handpiece of any one of the preceding claims, wherein the distance, in axial direction, between the annular front surface of the external conductor and the circular front surface of the internal conductor is between 0 and the diameter of the circular front surface of the internal conductor, preferably between 0 and 1 / 3 of the diameter of the circular front surface of the internal conductor, even more preferably between 0 and 1 / 5 of the diameter of the circular front surface of the internal conductor.

13. The applicator handpiece of any one of the preceding claims, wherein the intermediate spacer comprises: an annular front surface; an outer lateral surface in contact with an inner surface of the external conductor; and an inner lateral surface in contact with an outer surface of the internal conductor.

14. The applicator handpiece of claim 13, wherein the annular front surface of the external conductor, the annular front surface of the spacer, and the circular front surface of the internal conductor form a recessed seat housing a closing element of the delivery window, which is transparent to the electrical field generated by the external conductor and by the internal conductor; and wherein the closing element is in contact with a perimeter edge with the external conductor and with a rear surface with the external conductor, the spacer and the internal conductor.

15. The applicator handpiece of claim 14, wherein the closing element of the delivery window is a disc-shaped element.

16. The applicator handpiece of any one of the preceding claims, wherein the cooling duct is formed by additive manufacturing inside a monolithic body forming at least a front portion of the external conductor.

17. The handpiece of claim 16, wherein the monolithic body forms the whole of the external conductor.

18. The handpiece of any one of claims 1 to 15, wherein the external conductor is formed by a main body and by a front end portion, coupled to each other with seal, and between which the cooling duct is formed.

19. The applicator handpiece of claim 18, when dependent on claim 13, wherein the recessed seat of the closing element of the delivery window is partly formed in the front end portion of the external conductor.

20. The applicator handpiece of claim 18 or 19, wherein the front end portion and the main body of the external conductor are joined to each other by welding, or by gluing, or by screw coupling members.

21. The applicator handpiece of any one of the preceding claims, wherein the cooling duct comprises a cooling fluid inlet end and a cooling fluid outletend in fluid communication with a cooling fluid inlet connection and a cooling fluid outlet connection.

22. The applicator handpiece of any one of the preceding claims, wherein the inner cavity of the external conductor has a diameter between 5 mm and 20 mm, preferably between 8 mm and 15 mm.

23. The applicator handpiece of any one of the preceding claims, wherein the internal conductor has a front surface with a diameter between 3 mm and 9 mm, preferably between 4 mm and 6 mm.

24. The applicator handpiece of any one of the preceding claims, wherein the ratio between the inner diameter of the external conductor and the outer diameter of the front surface of the internal conductor is between 1 and 3, preferably between 2 and 2.5.

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