FR2864441A1 - Hand-held instrument used in dentistry has one-piece body or shell comprising handle and head with apertures to receive inner components - Google Patents

Abstract

The instrument has a moulded metal or plastic one-piece body or shell (8) forming a head (4) and handle, with apertures for inserting inner components. The axes (6, 7) of the head and handle lie at an angle of 100 - 130 degrees to one another. The body/shell has an electrical connection through internal mechanical transmission components, comprising a sleeve (11), the outer ring of a bearing (12), a spring (13), the outer ring of a second bearing (14), a fixed ring (15) and a spring (16). The two springs are compression springs located round a transmission shaft.

Description

The invention relates to a new type of dental handpiece.

  The generally known dental handpieces are of two types straight handpieces and contra-angle handpieces.

  In the case of contra-angle handpieces, the body consists of a handle having an elbow and a head.

  This structure leads to an embodiment that imposes at least two parts for the body and very often three to allow the assembly of the internal organs, and which also imposes several bearings, at least three.

  It is obvious that this type of design does not reduce costs significantly.

  A first object of the invention is to propose a new concept of handpiece structure that can replace the current concept of handpieces, and allowing the realization of the body in one piece whether for handpieces with mechanical drive or for air turbine driven handpieces.

  This object is achieved by the invention which consists of a dental handpiece of the type comprising mechanical members including a tool holder assembly for fixing and rotating a dental instrument around a drive shaft. and a motion transmission assembly, said mechanical members being mounted within a body with a head and a handle, characterized in that the body is formed of a single piece or envelope, a portion of which serves as a handle and the other part is a head, the head having a first housing opening with at least one opening sized to allow the introduction of the head members and their assembly therein, the handle having a second longitudinal housing of rectilinear axis opening on the one hand end of the handle by an opening and on the other hand in the first housing by a lateral opening, the opening being dimensioned for perme the introduction of the internal organs of the handle and their assembly inside it.

  According to an alternative embodiment the handpiece comprises electrical connection means consisting of a chain of mechanical transmission members of the rotational movement ensuring the transmission of movement and electrical energy from a connection provided at the end of the handle to cooperate an external motor, and up to the instrument.

  According to another variant it comprises electrical connection means consisting of a conductive wire.

  According to another variant, the head contains a turbine and the body of the handpiece comprises fluid channels necessary for operation. Preferably, the inner housing of the head is capable of receiving a tool-holder assembly composed of the mechanical transmission members of the machine. the head, and to receive a loosening clamping means of the tool or instrument, said housing opening on the head by an opening closable by a plug or a cap, or by a push-button.

  Preferably, the handpiece comprises a device for fixing a dental instrument to a tool-holder assembly for fastening and rotating a dental tool or instrument around a drive shaft, said assembly comprising tool being integrated in a head of a dental handpiece, and coupled to a motion transmission assembly, integrated in a handle of said handpiece, and composed mainly of a deformable and elastic clamping-loosening means in belt shape, at least a portion of which has a section adapted to engage in an annular groove or groove which is provided in the upper part of the instrument and able to hold said instrument by clamping the instrument, said clamping means loosening also comprising means for exerting loosening forces canceling the clamping forces to release the instrument.

  Preferably said fixing device is removable relative to the tool holder.

  According to a variant, the belt of elastic deformable material has a substantially parallelogram shape with a central zone designed to grip the head of the instrument at a groove.

  According to another variant the deformable elastic belt has the form of a split ring or a split annular claw having an annular shoulder adapted to engage in an annular groove of the instrument and a conical portion to cooperate with a complementary part conical of a push button.

  According to the alternative embodiment and / or the working speed of the tool, the fixing device can comprise a push button, integral or not with the tool holder, and can be held for example by clipping into an opening of the head .

  The invention will be better understood from the following description given with reference to the following appended figures: FIG. 1: general three-dimensional view of a handpiece according to the invention, FIG. longitudinal section of the handpiece of Figure 1, - Figure 3: partial longitudinal sectional view of a non-limiting embodiment of the invention, - Figure 4: representation in volume and partial of another embodiment non-limiting embodiment comprising loosening clamping means in the form of elastic lozenge belt manually releasable, - FIG. 5: axial sectional view of the view of FIG. 4, FIG. 6: cross-sectional and partial sectional view of the head of FIG. , made at the level of the elastic belt, - Figure 7: representation in volume and partial section of the head of Figure 4, - Figure 8: axial sectional view of another non-limiting embodiment comprising a loosening clamping means c-shaped elastic belt releasable by the action of a push button, Figure 9: representation in volume and partial section of the embodiment of Figure 8, Figure 10: volume representation of the elastic belt of Figures 8 and 9, Figure 11 FIG. 12 is an axial sectional view of another non-limiting embodiment comprising a split-ring loosening clamping means, FIGS. 12 and 13: a volume representation of the pushbutton of FIG. 11, FIGS. volume representation of cleft claw ring release clamping means of FIG. 11, FIG. 16: volume representation of a pushbutton of FIG.

  General concept of the body of the handpiece.

  Reference is first made to the non-limiting examples of FIGS. 1 to 3.

  A handpiece (1) according to the invention consists of a body (2) in one piece comprising a portion serving as a handle (3) of rectilinear axis and a portion constituting a head (4), for fixing and driving an instrument (5) along a driving axis (6) which can be aligned with the axis of the handle (7) or can form a predetermined angle therebetween, between 90 and 180 and preferably between 100 and 130, as in the non-limiting example of the figures.

  The body is formed of an outer casing (8) or casing, monoblock or not, which may be electrically insulating and may for example be made of a polymer material, thermoplastic or thermosetting, (preferably polyether-ether ketone abbreviated PEEK in the following text) incorporating the mechanical components of the handle and the head and electrical connection means, ensuring the transmission of movement and electrical energy from a connection (9) provided at the end of the handle to cooperate with a external motor, not shown, to the instrument (5) fixed in the head (4).

  The contra-angle (1) according to the invention represented in FIGS. 1 to 3 has two axes (6) and (7) making it possible to limit the risks of friction specific to each bearing and this, in order to guarantee a most stable yield. this is why, in this case, ball bearings are also integrated in the casing (8). Such an arrangement of the contra-angle is particularly suitable for root canal treatment (endodontics) with apex locator.

  A handpiece according to the invention connected to and coupled to a motor can thus generate, for example, a rotation of an instrument (5) (channel instrument for example) and thereby convey a usable electric current for the detection of the apex. The electrical connection between the motor and the handpiece (see FIGS. 2 and 3) can be done by any means of connection, for example between a coupling finger of the motor and a coupling groove (10) of a socket (11). (or by telescopic pusher for example). The envelope (8), insulating, is maintained by the practitioner, and its head end (4) is environment the patient's mouth. In this configuration the chain of mechanical and electrical transmission members is constituted as follows in the handle: the electric current passes from the bushing (11) to a fixed outer ring of a first bearing (12), and to a first spring (13), then to a fixed outer ring of a second bearing (14), then to a ring (15) axially stopped by a first shoulder in the casing (8), then to a spring (16) stopped axially by a second shoulder of the casing (8).

  The first and second bearings (12, 14) carry a transmission shaft along the longitudinal axis (7) of the handle, or first axis of the handpiece (1), and the springs (13 and 16) are springs with compression whose turns are arranged externally to the transmission shaft (7).

  At this point, the electric current has thus passed through the handle portion of the counter-angle or the handpiece (1).

  Alternatively, one could imagine a wire from the motor end to the contact with the instrument or tool (5) The head (4) of the contra-angle, with its second axis or drive shaft ( 6), supports two ball bearings (angular contact if possible) namely an upper bearing (17) whose outer ring cooperates with the second spring (16) of the handle and a lower bearing (18) whose axial play is caught using a spring washer (19).

  By this type of bearing arrangement, the bearing balls are always in contact with the outer and inner rings thereof, thus ensuring the electrical connection between fixed parts and moving parts.

  A pinion (20) mounted on the drive shaft (6) has teeth (21) meshing with the teeth (22) of an output gear (23) of the handle.

  The pinion (20) is conductive and integral with the inner rings of the bearings, it provides electrical driving to the instrument (5) and the mechanical drive thereof. The electric current conveyed to the end of the instrument will delimit the apex by a resistance variation effect, taking into account the external insulation of the envelope (8) and a pushbutton (55). ) provided on the head (4) and will be described later.

  Concept of the fixing device and the clamping means loosening the instrument in the head.

  There are now described preferred but not limiting embodiments of a device for fixing an instrument in the head (4) and their devices for clamping and loosening the instrument.

  During a canal treatment for example, the accessibility of the molars is a guarantee of comfort and quality for the practitioner and the patient. This is why the Applicant has set itself the goal of proposing a tool assembly (24) composed of the mechanical transmission members of the head, which is the smallest and most compact possible.

  It has achieved its objective by designing: - a new compact and space-saving clamping-loosening means (25) forming part of a fastening assembly, consisting of a deformable elastic belt (25) made of plastic material (PEEK by example) or not, ensuring by itself the functions of tightening and loosening, the loosening being achieved by a manual action 2864441 6 centripetal on the belt and the tightening being achieved by a loosening of this action, an inner housing (26) in the head, adapted to receive the tool assembly (24) and its loosening clamping means (25), said housing opening on the head through an opening (27) closable by a plug or cap (28), or by a push button.

  This solution will be better understood on reading the two exemplary embodiments described below.

  First described a first embodiment in connection with Figures 4 to 7 and for which the loosening is controlled by a direct manual action on the belt.

  According to the housing (26) of the tool holder assembly (24), there is firstly a lower portion (29) cylindrical coaxial with the drive shaft (6) and whose diameter is adapted to receive the barrel (30) of the sprocket (20), and secondly a substantially cylindrical upper portion (31), also coaxial with the drive shaft (6), and of larger diameter and adapted to receive the toothing ( 21) of the pinion-fut with its engagement means of the instrument and the clamping-loosening device thereof described later.

  The opening (27) opening the upper portion of the housing (31) is closed by a plug or cap (28), preferably but not necessarily the same material as the casing (8).

  The upper part of the housing (31) also has a lateral opening (32) opening into an inner housing (33) of the handle (3) so as to allow meshing of the toothing of the pinion-fut (20) with the toothing the output gear (23) of the handle (3).

  The pinion-was rotated freely in the head and its axial resistance is ensured between on the one hand the bottom (34) of the upper part of the housing which forms a shoulder, and on the other hand the front face (35) of the plug. The resulting axial freedom of said sprocket is a few hundredths of a millimeter.

  The rotational movement of the output pinion (23) is transmitted to the pinion shaft (20) and then to the instrument (5) by means of a flat part (36) provided on the instrument and cooperating with a flat part (37) provided in the internal bore (38) of the sprocket.

  According to this example of FIGS. 4 to 7, the tightening tightening means is essentially composed of a belt (25) of deformable and elastic material having a substantially diamond-like shape with a central zone (39) designed to grip the head (40). the instrument at an annular groove (41) provided at the upper end of the instrument.

  The large diagonal diamond is provided so that its two ends project diametrically from the envelope of the head (4) by two projections (42) each placed in a notch (43) of the head, each notch (43) opening a part in the upper part (31) of the housing, on the other hand in the opening (27) receiving the cap.

  A direct manual centripetal action, on the two projections (42) simultaneously, loosens the instrument and the release of this action ensures the clamping of said instrument.

  The blanks (44) of the notches provide locking in rotation of the belt, which is centered in the head by means of recesses (45) provided near the projections (42) and resting on the periphery (46) of the part upper housing (26).

  The axial holding of the belt is provided on the one hand by a shoulder (47) provided in the bottom (48) of an axial cavity (49) of the cap for receiving the head of the instrument (40) and of on the other hand by the bottom (50) of the notches.

  In this way the belt does not touch the rotating part of the sprocket.

  In the free state, said belt cooperates with an upper shoulder (51) of the annular groove of the head of the instrument to make a first axial limitation of said instrument, the other axial limitation being provided by a flat part (52) of the sprocket cooperating with the end (53) transverse of the flat part of the instrument.

  Unlocking the instrument consists in exerting two diametrically opposed supports on the projections (42), directed towards the axis of rotation. These two forces cause an orthogonal component thus releasing the instrument. Pressing simultaneously and directly on the two ears of the belt (with your thumb and forefinger for example) ensures tightness in the mouth, compared to the push-button system, for example. The attachment of the instrument can be done without support on the two ears of the belt through the arrangement of a conical portion (64) formed in the underside of the central zone (39) in the belt, the axial displacement of the instrument translating a radial displacement of the belt, by elasticity, the belt returns to its shape to ensure the clamping function.

  A second embodiment of the clamping-loosening device in connection with FIGS. 8 to 10 is now described.

  The elastic belt (25) with a diamond shape and a central zone (39) for gripping the instrument, differs from the previous one by its ears (54) forming projections perpendicular to the plane of the belt and located on the same side thereof, and in that it is held axially and radially by the sprocket as shown in Figures 8 to 9.

  For this purpose: the two ends of the belt pass through two peripheral lights to (61) provided on the upper flange (62) of the pinion, diametrically opposed, and arranged in a plane transverse to the drive shaft (6), the two lugs (54) are locked in rotation by two notches (63) of said flange.

  Moreover, the head differs from the previous one in that the plug is replaced by a push button (55) with metal insert for example (to facilitate manufacturing).

  According to this embodiment, the push-button, made of PEEK for example, has several parts: an elastic ring (56) at the bottom end, which limits the axial freedom of the pinion-drum and retains the push-button on the head ( 4), an elastic zone (57) intermediate which acts as a return spring of the push button, a cylindrical insert (58) inside which, when pressing the push button, to control the deformation of the elastic belt, thus releasing the tool, for this purpose pressing on the push-button (55) compresses its spring (57) and makes the inner conical shape (59) of the insert (58) cooperate with complementary conical blanks (60) the ears of the belt. The resulting radial component on the ears (54) of the belt induces another radial deformation perpendicular to this primary component. This deformation allows the unlocking of the instrument.

  The introduction of the instrument into the head can be done by pressing the push button, or without pressing the push button, in this case a conical arrangement (64) in the underside of the central zone (39) of the belt allows the introduction of the instrument.

  Belt configuration helps to ensure centrifugal clamping during rotation.

  Push button concept Miniaturization is a constant research in the field of medical equipment such as, for example, the heads of contra-angles in dentistry. New materials such as thermoplastic or thermosetting polymer materials meet this expectation. Known mechanisms can be reconsidered taking into account the mechanical, physical and chemical characteristics of these new materials by reducing the number of components, improving the quality, and lowering the cost of the whole; these plastic parts can be machined or injected. Obviously, these plastic materials, in addition to miniaturization, thus provide lightness, slip ability, for dynamic equipment, good behavior to sterilization or disinfection, good elastic characteristics. This is why these plastic materials can be used in the realization of dental parts. The control of the tightening or loosening of the tool is usually done by a manual action on the push button of the head of the handpiece. According to the design, this push button can be integral with the dynamic assembly (rotating, vibrating, etc.) for endodontics, for example, and with a fixed push button, independent of the dynamic assembly.

  As an example of application has already been presented above a handpiece head carrying a strawberry tail with reference to Figures 2 and 3.

  It is recalled here that: a head body (4) monobloc or not with the handle (3), receives a rotating sprocket (20) rotated by an output gear (23) of the handle. The pinion-drum thus has a freedom in rotation and an axial connection ensured for example by ball bearings.

  Solutions without ball bearings as in FIGS. 5 and 7 can of course be envisaged, with plain bearings reported, or with plain bearings merged with the head body.

  The transmission of the milling rotation movement is ensured by the combination of the flat part (36) formed in the pinion-drum (4) and the flat part (37) of the tool. The axial holding of the tool is guaranteed in one direction by the shoulder of the flat part of the pinion-drum and by the shoulder of the flat part complementary to the tool.

  2864441 Io From this common description, we can distinguish two types of push button according to the invention namely: - a push button integral with the dynamic assembly called tool holder as that referenced (55) in Figures 3 and 16 , solution characterized by a permanent contact between the rotating lock assembly and the push button. In the idle state, the push button (55) (made of PEEK for example) provides an axial limitation of an elastic split ring (65) (made of PEEK for example) and therefore centers it with respect to the axis (6). The ring (65) is externally cylindrical and its inner wall comprises a cone-shaped upper flange (71), a transverse shoulder-shaped intermediate portion (66) directed towards the axis (6). The shoulder (66) of the elastic ring (65) retains, in the axial direction, the instrument (5) engaging the annular groove (41). The pushbutton (55) is guided radially in the bore (38) of the sprocket by one or more sectors or members (87) disposed on the underside of the pusher (55) and each terminated by a conical end serving to provide the or the supports on the elastic ring (65). The axial displacement of the push button (55) is limited between the upper and lower ends of one or more lights (68) formed in the upper body of the pinion-drum and in which cooperate one or more hooks (67) provided on the underside. push button. The elastic ring (65) exerts an axial component on the push button (55) reminding it to its initial position. Due to their radial elasticity, due to slots (69) provided between the hooks and the sectors (87) the hooks (67) allow the clipping of the push button in the barrel. Pressing the push button (55) allows the unlocking of the tool (5) via the conical portions (70) engaging in the complementary conical slope (71) of the elastic ring to disengage the shoulder (66). The introduction of the instrument (5) into the sprocket can be done automatically without pressing the push button thanks to the conical portion (73) provided on the underside of the elastic ring at the end of the shoulder (66).

  In FIG. 3, the tightening-loosening means is a split elastic ring open in a radial plane visible on the section plane of FIG. 3 and the means for exerting the loosening forces consist of the conical slope (71). .

  a push button independent of the dynamic assembly In maintained tool position, the solution is characterized by a separation of the pushbutton and the locking means.

  An embodiment of this type is shown by way of example in Figures 11 to 15.

  In the idle state, in dynamic mode or not, and without action on the pushbutton, a conical elastic annular claw (72), thanks to its arms (73) (for example 6 arms) each terminated by a shoulder (79) directed towards the axis (6), retains axially the tool (5). The claw (72) is integral with the rotating sprocket by engaging the peripheral projections (74) of the claw in corresponding openings (76) in the sprocket. A slot (77) completely through the claws allows the assembly and disassembly of the claw in the bore of the sprocket-barrel, giving it the necessary radial elasticity.

  The pushbutton (55) is retained axially and centered by elastic blades (75) cut in its cap in the opening (27) head; these blades mounted under tension in the head body provide elastic axial freedom (along the axis 6) of the push button. Figures 12 and 13 show these blades (75) in the stress position and show the clipping grooves (80) at the end of blades to clip the pusher (55) in the opening (27). A manual thrust on the push button results in an axial displacement of the conical base (78) of the push button, cooperating with the complementary cone (82) of the internal conical cavity of the arms of the claw; the loosening of the tool is then provided by the spacing of said arms and the disengagement of the shoulders (79). The manual support removed, the push button returns to its original position, the respective cones of the two parts (55) and (72) no longer in contact.

  According to this solution of FIGS. 1 to 15, the clamping-loosening means is the elastic conical claw (72) whose shoulders (79) are able to engage in the groove or annular groove (28) of the instrument, and the means for exerting the loosening forces and constituted by the conical inner shape (82) of said claw (72) whose radial deformation is guaranteed by the slot (77).

  Lubrication concept Referring now to FIG. 8 which is an axial section of FIG. 9 and showing that the head has a cavity (83) provided around or beside the barrel-sprocket shaft for containing a solid grease which is released at each use in small quantities through an orifice (84) of the partition wall (85) between the cavity and the barrel to lubricate the barrel.

  Assembly concept The envelope (8) can be made in one piece by molding a plastic material (for example PEEK) and therefore electrically insulating or a sintered material comprising metal inclusions (for example Metal Injection Molding abbreviated MIM) and conductor or any other material. This envelope comprises: in the head, a first housing (26) for mounting a tool holder and an instrument according to a drive shaft (6) said housing opening on either side of the head according to two openings, at least one of which, the opening (27) has dimensions adapted to allow the introduction of all the organs of the head and their assembly, in the handle, a second housing (33) axis rectilinear (7) opening on the one hand to the distal end of the handle by an opening (81) and opening on the other hand, at the end near the head, in the first housing (26) by a lateral opening (32). ) allowing the cooperation between the mechanical organs of the head and those of the handle. In addition, the opening (81) is dimensioned so as to be able to allow the introduction of all the members of the handle and their mounting inside thereof, along a rectilinear axis called the axis of the handle (7). ). To make a contra-angle, there is provided an envelope whose axes (6) and (9) form, for example, an angle of between 90 and 180, preferably between 100 and 130 and to make a right hand piece can be provided that the axes (6) and (7) are parallel and offset so as to maintain an opening (27) of the head for mounting the internal parts and the establishment of a cap of a push button.

  This concept is particularly advantageous because it makes it possible to: reduce the number of steps, or even eliminate them, reduce the cost of the handpiece, reduce the dimensions of the handpiece facilitate cleaning (smoothed shapes), improve hygiene (one piece so no interface).

Claims (4)

  1. Dental handpiece (1) of the type comprising mechanical members including a tool holder assembly for fixing and rotating a dental instrument around a drive shaft (6) and a set of motion transmission, said mechanical members being mounted inside a body (2) with a head (4) and a handle (3), characterized in that the body (2) is formed in one piece or envelope (8) of which one part serves as a handle (3) and the other part constitutes a head, the head comprising a first housing (26) opening with at least one opening (7) sized to allow the introduction of the organs of the head and their assembly inside thereof, the handle comprising a second longitudinal housing (33) of rectilinear axis (7) opening on the one hand end of the handle by an opening (81) and secondly in the first housing by a lateral opening (32), the opening (81) being of a size e to allow the introduction of the internal organs of the handle assembly and to the interior thereof.   2. Dental handpiece according to claim 1, characterized in that the axis (6) of the head and the axis (7) of the handle form between them a predetermined angle a for the realization of a contra-angle.   3. Dental handpiece according to claim 2, characterized in that a is between 100 and 130.   4. Dental handpiece according to claim 1, characterized in that the axis (6) of the head and the axis (7) of the handle are parallel and offset for the realization of a right handpiece.   5. Dental handpiece according to one of claims 1 to 4 characterized in that the casing (8) is made by molding.   6. Dental handpiece according to claim 5, characterized in that the casing (8) is made of polymer material.   7. Dental handpiece according to claim 6, characterized in that the casing (8) is preferably made of PEEK.   8. Handpiece according to one of claims 6 to 7 characterized in that it comprises electrical connection means constituted by a chain of mechanical transmission members of the rotational movement.   9. A handpiece according to claim 8, characterized in that the chain of mechanical and electrical transmission members is constituted as follows - in the handle the electric current passes from a socket (11) to a fixed outer ring a first bearing (12), and a first spring (13), then a fixed outer ring of a second bearing (14), then a ring (15) axially stopped by a first shoulder in the envelope (8), then to a spring (16) stopped axially by a second shoulder of the casing (8), the first and second bearings (12, 14) carrying a transmission shaft along the longitudinal axis (7) of the handle , or first axis of the handpiece (1), and the springs (13 and 16) being compression springs whose turns are arranged externally to the transmission shaft (7), - in the head (4) of the contra-angle, with its second axis or drive shaft (6) supporting two bearings namely an upper bearing (17) whose outer ring cooperates with the second spring (16) of the handle and a lower bearing (18) whose axial play is caught with a spring washer (19), a sprocket (20) mounted on the drive shaft (6) has teeth (21) interspersed with the teeth (22) of an output gear (23) of the handle, the sprocket (20) ) being conductive and integral with the inner rings of the bearings, it provides electrical driving to the instrument (5) and the mechanical drive thereof.   10. Handpiece according to one of claims 6 to 7, characterized in that 25 the electrical connection means consist of a conductive wire.   11. Handpiece according to claim 5, characterized in that the casing is made of MIM type material.   12. Handpiece according to one of claims 1 to 11 characterized in that the inner housing (26) of the head is adapted to receive a tool-holder assembly composed of the mechanical transmission members of the head, and to receive a loosening clamping means (25) of the tool or instrument (5), said housing opening onto the head through an opening (27) closable by a plug or cap (28), or by a push-button.   13. Dental handpiece according to one of claims 1 to 12 characterized in that the head contains a turbine and the body of the handpiece comprises fluid channels necessary for operation.   14. A dental handpiece according to one of claims 1 to 13 characterized in that the head has a cavity for containing a solid fat released at each use by an orifice of the wall separating the cavity and the barrel to lubricate the drum.   15. Dental handpiece according to one of claims 1 to 14, characterized in that it comprises a device for fixing a dental instrument to a tool holder assembly for fixing and driving in rotation of a dental tool or instrument around a drive shaft (6), said tool holder assembly (24) being integrated into a head (4) of a dental handpiece, and coupled to a motion transmission assembly, integrated in a handle (3) of said handpiece (1), and mainly composed of a deformable and elastic belt-shaped clamping-loosening means (25), at least a portion of which has a section adapted to s' engage in an annular groove or groove which is provided in the upper part of the instrument and able to hold said instrument by clamping, said loosening clamping means also comprising means for exerting loosening forces canceling the clamping forces in order to release the ins strument.   16. Dental handpiece according to claim 15 characterized in that the fixing device is removable relative to the tool holder (24).   17. Dental handpiece according to one of claims 15 to 16, characterized in that the belt (25) of elastic deformable material has a substantially parallelogram shape with a central zone (39) provided for gripping the head (40). of the instrument at a groove, the large diagonal of the parallelogram is provided so that its two ends protrude diametrically from the envelope of the head (4) by two projections (42) each placed in a notch (43) of the head, the two projections constituting means for manually and directly exerting loosening forces on the belt.   18. Dental handpiece according to claim 17, characterized in that the belt (25) comprises recesses (45) provided near the projections (42) and supported on the periphery (46) of a housing (26). ) of the head.   19. Dental handpiece according to claim 17, characterized in that the elastic belt (25) with a parallelogram shape and a central zone (39) for gripping the instrument comprises two lugs (54) 2864441 17 forming protrusions perpendicular to the plane of the belt and located on the same side thereof, the two ears constituting means for exerting loosening forces by means of a push-button placed on the head of the handpiece .   20. Dental handpiece according to claim 18, characterized in that the ears comprise conical flanges (60).   21. Dental handpiece according to one of claims 17 to 20, characterized in that the belt has a conical portion (64) formed on the underside of the central zone (39).   22. Dental handpiece according to claims 19 to 20 characterized in that the fixing device also comprises a push button in several parts, namely: a resilient ring (56) at the bottom end and holds the push button on the head (4), an elastic zone (57) intermediate which acts as a return spring of the push button, a cylindrical insert (58) inside which, when pressing the push button, to control the deformation of the elastic belt, thus freeing the tool.   23. Dental handpiece according to one of claims 20 to 22 characterized in that the insert (58) has an inner conical shape (59) to cooperate with the conical flanges (60) of the ears of the belt.   24. Dental handpiece according to one of claims 15 to 16 characterized in that the elastic deformable belt has the form of a split ring (65) or a split annular claw (72) having an annular shoulder (66). ) (79) adapted to engage an annular groove (28) of the instrument and a conical portion (71) to cooperate with a conical complementary portion of a push button.   25. Dental handpiece according to claim 24, characterized in that the split ring comprises a conical part (73) provided on the underside of the split ring for the introduction of the instrument.   26. Dental handpiece according to claim 25, characterized in that the fixing device further comprises a push button (55) guided axially by one or more sectors (87) disposed on the underside and each terminated by a conical end ( 70).   27. A dental handpiece according to claim 25, characterized in that the fixing device further comprises a push button (55) having elastic blades (75) cut in its cap and terminated by clipping grooves (80). ), and a conical base (78).   28. Dental handpiece according to any one of claims 15 to 16, characterized in that the fixing device further comprises a push button for exerting the loosening forces on the clamping-loosening means.   29. Dental handpiece according to claim 28, characterized in that the push button is secured to the tool holder.   30. Dental handpiece according to one of claims 28 to 29, characterized in that the push button is held by clipping in an opening of the head.