DENTAL HANDPIECE AND PUSH BUTTON FOR A DENTAL HANDPIECE

Abstract

The invention relates to a dental handpiece with a manually operable push button for actuating the trigger mechanism, wherein the push button is double-walled with an outer cover plate and an inner contact element, wherein for actuating the push button an upper side of the outer cover plate is pressable by a user against a bias, thereby actuating an actuator by an underside of the inner contact element to actuate the trigger mechanism, wherein a thermal insulation layer extends between the outer cover plate and the inner contact element which causes a thermal decoupling of the outer cover plate from the inner contact element.

Claims

1. Dental handpiece (10) having a head (12) for receiving rotatable dental tools, comprising: a housing (14) for accommodating components of the head (12), a tool clamping device (16) accommodated by the housing (14) for clamping a dental tool such that the clamped dental tool is rotatably drivable in the head (12), a trigger mechanism for releasing the clamping of the rotatable dental tool in order to insert the dental tool into the tool clamping device (16) and to remove the dental tool from the tool clamping device (16), a manually operable push button (36) for actuating the trigger mechanism, wherein the push button (36) is double-walled with an outer cover plate (42) and an inner contact element (54), wherein for actuating the push button (36) an upper side (42b) of the outer cover plate (42) is pressable by a user against a bias, thereby actuating an actuator (18) by an underside (54a) of the inner contact element (54) to actuate the trigger mechanism, wherein a thermal insulation layer (80) extends between the outer cover plate (42) and the inner contact element (54), effecting a thermal decoupling of the outer cover plate (42) from the inner contact element (54).

2. Dental handpiece (10) according to claim 1, wherein the thermal insulation layer (80) is provided in the form of a thermally insulating gap (78) which extends in a plane transverse to the axis of rotation (38) of the rotatable dental tool between an underside (42a) of the outer cover plate (42) and an upper side (54b) of the inner contact element (54).

3. Dental handpiece (10) according to claim 2, wherein the spatial extension of the thermal insulation layer (80) in at least one direction of a plane transverse to the axis of rotation (38) of the rotatable dental tool corresponds to at least 40%, preferably at least 50%, preferably at least 70%, of the diameter of the push button.

4. Dental handpiece (10) according to one claim 1, wherein frictional heat, which is generated in the inner contact element (54) when the inner contact element (54) contacts the rotating actuator (18) at a contact point (64), is dissipated in the inner contact element (54) predominantly radially outward from the contact point (64).

5. Dental handpiece (10) according to claim 4, wherein the material and the processing of the inner contact element (54) and/or the actuator (18) are selected such that the contact element and/or the actuator, at the contact point (64) of the underside (54a) of the inner contact element (54) with the actuator (18), has an average surface roughness Rz<3.5 μm, preferably Rz<2.5 μm, preferably in the range of Rz=1.5 μm+/−1 μm and/or a profile depth Pt<6 μm, preferably Pt<4.5 μm, preferably in the range of Pt=3 μm+/−1.5 μm.

6. Dental handpiece (10) according to claim 1, wherein the inner contact element (54) is made of a material with a thermal conductivity of less than or equal to 30 W/(mk), preferably in the range between 10 W/(mK) and 25 W/(mK), preferably in the range of 15 W/(mK)+/−5 W/(mK).

7. Dental handpiece (10) according to claim 1, wherein the inner contact element (54) is made of metal, for example of a stainless martensitic alloy.

8. Dental handpiece (10) according to claim 4, wherein the inner contact element (54), in the region of the contact point (64) between the inner contact element (54) and the rotating actuator (18), has a thickness (h) which is less than or equal to 1 mm, preferably less than or equal to 0.6 mm, preferably less than or equal to 0.5 mm, preferably between 0.1 mm and 0.6 mm, preferably in the range of 0.4 mm+/−0.2 mm.

9. Dental handpiece (10) according to claim 1, wherein the thermal insulation layer (80) has a thickness (H) of less than or equal to 0.5 mm, preferably less than or equal to 0.3 mm, preferably less than or equal to 0.2 mm, preferably between 0.01 mm and 0.2 mm, preferably in the range of 0.12 mm+/−0.05 mm.

10. Dental handpiece (10) according to claim 1, wherein the inner contact element (54) is made as a separate part from the outer cover plate (42) and is joined to the outer cover plate (42) or other parts of the push button (36) by a bonded joint, for example by welding, by positive locking or by a press-fit connection.

11. Dental handpiece (10) according to claim 1, wherein the push button (36) is hat-shaped, such that a circumferential wall (48) extends from the outer cover plate (42), wherein the push button (36) has an annular stop (76, 112) at the outer cover plate (42) or at the circumferential wall (48), and wherein the inner contact element rests on the annular stop (76, 112).

12. Dental handpiece (10) according to claim 11, wherein the inner contact element (54) is made as a separate part from the outer cover plate (42) and wherein the inner contact element (54) loosely lies in the hat-shaped push button (36) and is pushed by a spring (56) against the annular stop (76), or the inner contact element (54) is pressed in the hat-shaped push button (36) by means of a press-fit, or the inner contact element (54) is joined to the hat-shaped push button (36) by a bonded joint, for example by welding.

13. Dental handpiece (10) according to claim 1, wherein the inner contact element (54) has a peripheral support ring (126), a central actuation portion (124), and spokes (128), wherein the central actuation portion (124) is suspended in the peripheral support ring (126) by means of spokes (128), such that recesses (122) are formed between the spokes (128), and for example wherein the spokes (128) radially do not extend in a straight line.

14. Dental handpiece (10) according to claim 1, having a push button (36) being adapted for installation in a head (12) of the dental handpiece (10) for receiving dental tools, and for actuating a trigger mechanism in the head (12) for clamping and releasing a dental tool, wherein the push button (36) is double-walled with an outer cover plate (42) and an inner contact element (54), wherein for actuating the push button (36) an upper side (42b) of the outer cover plate (42) is pressable by a user against a bias, thereby actuating an actuator (18) by an underside (54a) of the inner contact element (54) to actuate the trigger mechanism when the push button is installed in the head (12) of the dental handpiece (10), wherein a thermal insulation layer (80) extends between the outer cover plate (42) and the inner contact element (54), which effects a thermal decoupling of the outer cover plate (42) from the inner contact element (54).

15. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0068] It is shown in:

[0069] FIG. 1 a schematic view of a handpiece coupled to a supply hose,

[0070] FIG. 2 a cross section through a handpiece according to an exemplary embodiment of the invention,

[0071] FIG. 3 an enlarged cross-section through the head of the handpiece of FIG. 2,

[0072] FIG. 4 a cross-sectional view of the push button of FIGS. 2 and 3,

[0073] FIG. 5 a schematic cross section through the upper region of the head according to a further embodiment of the invention,

[0074] FIG. 6 a schematic cross-section through the head of FIG. 5 with a partially pressed push button,

[0075] FIGS. 7-13 schematic cross sections through push buttons according to further embodiments of the invention,

[0076] FIG. 14 a schematic plan view of an inner contact element according to a further embodiment of the invention, and

[0077] FIG. 15 a schematic view of a dental treatment unit.

DETAILED DESCRIPTION OF THE INVENTION

[0078] Referring to FIG. 1, the dental handpiece 10 is coupled to a coupling piece 2 by means of a standard interface, e.g. an ISO interface. The coupling piece 2 is located at a free end of the supply hose 4 of a base unit 6 (see FIG. 15). A dental tool 8, in this example a dental drill, is inserted into the dental handpiece 10.

[0079] Referring to FIGS. 1 and 2, the dental handpiece 10 comprises a rod-like handle 11 and a head 12, which is attached to the distal end of the dental handpiece 10 or the rod-like handle 11. The head 12 comprises a generally cylindrical housing 14, which is tapered at its lower end, and in which the tool clamping device 16 and other components of the tool drive are installed.

[0080] Referring to FIG. 3, a linear actuator or plunger 18, as part of the tool clamping device 16, is mounted by means of ball bearings 20 in a ball bearing receiving sleeve 22 of a holder 24. The usual construction of a head of a dental handpiece with a corresponding tool clamping device is generally known to the person skilled in the art.

[0081] At the upper end of the head 12 is a cover system or lid system 30 with a threaded sleeve 32 which is screwed into an internal thread 34 of the head housing 14 from above. In the threaded sleeve 32, a cover or lid is used as a push button 36, which is axially (relative to the axis of rotation 38 of the tool) displaceable or movable. In this example, the cover or push button 36 is hat-shaped with an upper or outer cover wall or plate 42, which is slightly curved to the outside on the upper side in this example, and with an annular wall 48 or jacket, which adjoins the peripheral edge portion 44 of the outer cover plate 42 and extends axially with respect to the axis of rotation 38 downwardly from the peripheral edge portion 44. At the lower end of the annular wall 48, which is the free end of the annular wall 48 opposite to the outer cover plate 42, the annular or circumferential wall 48 has an outer collar or stop ring 50 which, in this example, provides an upper stop against an inner stop ring 52 of the threaded sleeve 32, and which holds the lid or push button 36 in the head housing or in the threaded sleeve 32.

[0082] The push button 36 is double-walled in a plane transverse to the axis of rotation 38, wherein the outer cover plate 42 forms a first layer of the two layers of the double wall. The second layer of the two layers of the double wall is formed by an inner contact member or inner contact element 54, in this example in the form of an inner contact plate, which is inserted from below into the hat-shaped cover or push button 36. The push button 36 is biased by a coil spring 56, which is supported at its lower end on an end plate 58 and at its upper end at the underside 54a of the inner contact plate 54. More generally, the spring 56 engages the inner contact element or plate 54. The bias of the spring 56 results in an actuating force for the push button 36 approximately in the range of 1 N to 5 N in the idle stroke range until touching the plunger head 62. The actuating force for actuating the trigger mechanism, however, is about 50 N.

[0083] To clamp the dental tool 8, the user typically pushes with a finger on the upper side 42b of the outer cover plate 42 to depress the push button 36 axially against the bias of the push button spring 56. In doing so, the user first overcomes the idle stroke between the underside 54a of the inner contact plate 54 and the plunger head 62, which forms the free upper end of the plunger 18, until the underside or lower surface 54a contacts the free upper end of the plunger 18. As the plunger head 62 or the free upper end of the plunger 18 is formed convexly, a relatively small contact point 64 between the inner contact plate 54 and the plunger head 62 is created. If the user pushes the push button 36 further down, the push button 36 actuates the plunger 18, i.e. pushes the plunger 18 downwards, by means of the pressure of the inner contact plate 54 on the plunger head 62, whereby the trigger mechanism of the tool clamping device 16 is actuated. When the trigger mechanism of the tool clamping device 16 is actuated, the tool clamping device 16 is in a release state (not shown) in which the dental tool 8, e.g. a dental drill, can be inserted or removed in the tool clamping device 16 (not shown).

[0084] An outer collar 66 on the ball bearing sleeve 22 forms a lower stop for the push button 36, which is put like a hat over the ball bearing sleeve 22 and on further actuation over the ball bearing 20.

[0085] In the present exemplary embodiment, the outer cover plate 42 has, on its underside 42a, a recess 70 with a diameter d=4.7 mm. The diameter of the inner contact plate 54 in this example is D=5.8 mm.

[0086] The central recess 70 is bounded outwards by a peripheral circumferential shoulder or ledge 72, so that an annular step 74 is formed at the outer circumference of the recess 70. Accordingly, the underside or lower surface 42a of the outer cover plate 42 has a peripheral support or bearing surface 76 for the inner contact plate 54. Accordingly, the inner contact plate 54 peripherally annularly engages the outer cover plate 42 from below and thereby forms the inner second layer of the double wall in the centrally double-walled region of push button 36.

[0087] Thus, the recess 70 forms a central gap or cavity 78 which extends in both dimensions in the plane transverse to the axis of rotation 38 between the outer cover plate 42 and the inner contact plate 54. In the present example, the cavity 78 is unfilled, i.e. air under atmospheric pressure is present in the cavity 78. Thus, the cavity 78 forms a thermal insulation layer 80, which extends flatly in the two dimensions of the plane transverse to the axis of rotation 38 between the outer cover plate 42 and the inner contact plate 54, and effects a thermal insulation against heat flow from the inner contact plate 54 to the outer cover plate 42 in a central region 82 of the push button 36. The contact between the inner contact plate 54 and the peripheral annular support or bearing surface 76 creates a thermal bridge 84 from the inner contact plate 54 to the push button 36 or, in this example, to the outer cover plate 42. Thus, the thermal bridge 84 is not in the central or near-axis region 82 of the push button 36 or the outer cover plate 42, but in the peripheral edge portion or region 44 of the outer cover plate 42, i.e. in the radial periphery 37 of the push button 36.

[0088] If the push button 36 is undesirably actuated during rotation of the plunger 18, e.g. accidentally actuated so far that the inner contact plate 54 might come into contact with the plunger head 62 at the central contact point 64, frictional heat is initially generated at the central contact point 64. The thermal conductivity of the material of the inner contact plate 54 is higher than the thermal conductivity of the thermal insulation layer 80, which is, in this example, an air layer. Therefore, the frictional heat generated at the contact point 64 is guided predominantly or essentially radially outwards within the inner contact plate 54. The annular contact region 85 between the upper side or upper surface 54b of the inner contact plate 54 and the outer cover plate 42, which forms the thermal bridge 84 between the inner contact plate 54 and the push button 36, is located peripherally relatively far away from the rotation axis 38 so that the generated frictional heat is distributed peripherally on a relatively large perimeter into the peripheral edge region 44 of the outer cover plate 42. This provides, inter alia, that the maximum temperature of the upper side or upper surface 42b of the outer cover plate 42 remains within acceptable limits in the areas which are in danger of being touched. In the example shown in FIGS. 2-4, the thermal bridge 84 is located radially outside of the inner diameter of the bearing 20 or radially outside of the diameter of the plunger 16.

[0089] In other words, the inner contact element 54 and the thermal insulation layer 80 extend radially into the radial periphery 37 of the push button 36, so that the thermal bridge 84 is located in the radial periphery 37 of the push button 36.

[0090] In the present example, the diameter d of the thermal insulation layer 80 is about 75% of the inner diameter Di of the push button 36. Preferably, this ratio d/Di may be at least 40%, at least 50% or at least 70%.

[0091] In the example shown in FIGS. 2-4, the inner contact plate 54 is made of stainless steel, in the present example made of hardened, acid- and rust-resistant martensitic steel, which allows easy manufacture. In this example, the thickness of the inner contact plate 54 is approximately h=0.4 mm in the central region, in particular in the region of the contact point 64. In an annular peripheral portion or region 53, the thickness of the inner contact plate 54 is somewhat reduced in this example. In this example, the thickness H of the thermal insulation layer 80 or the height of the recess 70 is about 0.12 mm in the central region 82. Thus, the overall height caused by the inner contact plate 54 and the thermal insulation layer 80 is only increased by about 0.52 mm in this example. In the present example, the upper side 54b has a slight central thinning 57, which contributes to the thickness H of the thermal insulation layer 80 in the central region 82. The thinning 57 in the central region of the inner contact plate 54 and a second central recess 94 in the outer cover plate 42 (see FIG. 10), which forms a thinning of the outer cover plate 42, provide a further safety margin against deformation of the inner contact plate 54 or the outer cover plate 42. Therewith, an undesirable contact between the inner contact plate 54 and the outer cover plate 42 in the central region 82 of the push button 36 can be prevented even better.

[0092] The use of an acid- and rust-resistant martensitic stainless steel for the inner contact plate 54 advantageously provides a high strength or stability against deformation with a comparatively small thickness h. Furthermore, such a martensitic steel advantageously has a smooth or even surface, so that a relatively lower coefficient of friction is provided at the contact point 64 with the plunger head 62. The plunger head 62 is also made of an acid- and rust-resistant steel, so that in this example there is a steel-to-steel contact at the central contact point 64. In particular, the inner contact plate 54 directly contacts and actuates the plunger head 62 without the need for additional spherical elements. As a result, the heat development can be reduced already at the contact point 64 with respect to materials having a higher coefficient of friction. In addition, the inner contact plate 54 made of such a martensitic steel is easy to process and may be produced precisely and inexpensively by etching. At the same time, the acid- and rust-resistant, preferably martensitic, steel used for this example has a coefficient of thermal conduction λ=15 W/(mK), which is relatively low compared to other steels.

[0093] In particular, the relatively low thermal conductivity, the low coefficient of friction and the predominantly radial heat dissipation into the peripheral edge region 44 or in the radial periphery 37 of the push button 36 synergistically interact, so that the maximum temperature at points of the push button 36, which are in danger of being touched, can be kept within acceptable limits even at a long-term contact of the inner contact plate 54 with the plunger head 62 under the maximum possible contact pressure.

[0094] In the push button 36, the inner contact plate 54 engages the peripheral bearing surface 76, which surrounds the cavity 78 and forms a peripheral annular stop. In this example, the annular wall 48 or jacket of the push button 36 has a peripheral shoulder or ledge 77 which centers the inner contact plate 54 and forms an annular press fit or interference fit 86. In this example, the inner contact plate 54 has on its underside 54a an annular extension 55, which centers the spring 56, but may also contribute to increase the flexural rigidity of the inner contact plate 54.

[0095] FIG. 5 shows schematically a simplified embodiment comprising a flat or planar inner contact plate 54 without the annular extension 55 and comprising a push button 36 without the peripheral shoulder or ledge 77. In this example, the inner contact plate 54 lies only loosely in the push button 36 at the peripheral bearing surface 76, which surrounds the cavity 78 and forms a peripheral annular stop. In the illustrated assembled state, the inner contact plate 54 is biased or pressed by the spring 56 against the peripheral annular stop 76 or peripheral bearing surface of the underside 42a of the outer cover plate 42.

[0096] Referring to FIG. 6, illustratively, the push button 36 of FIG. 5 is actuated about the axial idle stroke 60 so that the inner contact plate 54 contacts the plunger head 62, however, the plunger 18 has not yet actuated the trigger mechanism.

[0097] Referring to FIG. 7, the push button 36 also has an annular press fit 86 such that the inner contact plate 54 is press fit from below into the inner press fit or interference fit 86 in the push button 36. Also in the examples with the interference fit 86, the thermal contact, i.e. the thermal bridge 84 between the inner contact plate 54 and the push button 36 is located substantially in the peripheral edge region 44, namely substantially via the press fit 86 and the annular peripheral bearing surface 76. Otherwise, the embodiment corresponds to that in FIG. 5.

[0098] Referring to FIG. 8, the inner contact plate 54 may be joined to the push button 36 by a material bond, for example by welding. The inner contact plate 54, e.g. may be welded annularly with the peripheral bearing surface 76 or annular stop, as symbolized at the reference numeral 88 as a welding seam, or be welded radially to the circumferential annular wall 48, as symbolized at the reference numeral 90 as a welding seam. Laser welding is considered as the preferred welding method.

[0099] Referring to FIG. 9, the inner contact plate 54 may be positively locked or form-locked in a radial annular groove 92. Also in this embodiment, the thermal bridge 84 is created exclusively in the peripheral edge region 44 of the outer cover plate 42.

[0100] Referring to FIG. 10, the gap or cavity 78 or the thermal insulation layer 80 may be formed by two or more steps. For this purpose, the outer cover plate 42 may have on its underside 42a a first recess 70 with a comparatively large diameter d and a second central recess 94 with a smaller diameter dl. Accordingly, the thermal insulation layer 80 has a thickness H′ in an annular portion 96 and a thickness H in a central portion 98, wherein the thickness H is larger than the thickness H′. In addition to the predominantly radial dissipation of the frictional heat by means of heat conduction within the inner contact plate 42 this provides a reduction of heat transfer from the inner contact plate 54 to the central or near-axis region 82 of the outer cover plate 42.

[0101] Referring to FIG. 11, the inner contact element 54 is curved and has a central convex portion or dome 102 which extends away from the outer cover plate 42 to form the central cavity 78 or the thermal isolation layer 80 under the dome. Also in this example, the thermal bridge 84 is located in the peripheral edge region 44 of the outer cover plate 42. In this example, the diameter d of the cavity 78 or the thermal insulation layer 80 corresponds to about 80% of the inner diameter Di of the push button 36.

[0102] Referring to FIG. 12, the inner contact element 54 may be hat-shaped like the push button 36. In this example, the inner contact element 54 has a cover plate 104 extending in the plane transverse to the axis of rotation 38 and a peripheral annular wall 108 adjoining the peripheral edge 106 of the cover plate 104 and extending axially downwards. At the lower end of the peripheral annular wall 108 a circumferential and radially outwardly extending collar 110 is arranged. The circumferential collar 110 axially abuts from below against an annular stop 112 of the peripheral annular wall 48 of the push button 36. Thus, the circumferential annular stop 112 is axially offset downwardly with respect to the underside 42a of the horizontal outer cover plate 42. Again, the inner contact element 54 may be loosely inserted into the push button 36, may be welded to the annular stop 112, may be press-fitted or may be latched with positive locking. Due to the axial offset of the thermal bridge 84 created between the collar 110 and the annular stop 112, the thermal bridge 84 between the inner contact element 54 and the push button 36 and, therewith, the heat dissipation onto the push button 36 are displaced even further radially outwards and additionally axially downwards. This delays the heat transport, and the heat energy which is transmitted onto the push button 36 via the thermal bridge 84 spreads further away from the central region 82 of the push button 36 or the upper side 42b of the outer cover plate 42.

[0103] In this example, the gap or cavity 78 between the inner contact element 54 and the push button 36, forming the thermal insulation layer 80, also has two areas, namely a base portion 114 extending in the plane transverse to the axis of rotation 38 and a jacket area or shell portion 116 located between the peripheral annular walls 48 and 108. In other words, in this example, the thermal insulation layer 80 is also hat-shaped.

[0104] Optionally, the outer cover plate 42 may have a thinning 71, which increases the thickness H of the thermal insulation layer 80 and forms a safety margin against deformation.

[0105] In the embodiment of FIG. 12, the outer hat-shaped part of the push button 36 is integrally formed, wherein the annular stop 112 is provided as an annular recess in the annular wall 48.

[0106] Referring to FIG. 13, the annular stop 112 may be provided by a spacer ring 118 inserted into a conventional push button 36. This embodiment has the advantage that the design of the push button 36 need not to be changed relative to conventional handpieces, which may provide advantages in the production.

[0107] Referring to FIGS. 12 and 13, the inner contact element 54 is made as a metal turned part in these examples. In the embodiments of FIGS. 12 and 13, the thermal bridge 84 between the inner contact element 54 and the push button 36 is also located in the radial periphery 37 of the push button 36, but not on the outer cover plate 42, but in the area of the circumferential annular wall 48, i.e. in the jacket area of the push button 36.

[0108] Referring to FIG. 14, the heat dissipation within the inner contact element or the inner contact plate 54 may be further reduced by recesses 122 in the inner contact element 54. In this exemplary embodiment, the inner contact plate 54 has a central actuation portion 124, which actuates the plunger head 62, and a peripheral support ring 126. The central actuation portion 124 is connected to the peripheral support ring 126 by means of a plurality of spokes 128, in this example four spokes 128. Recesses 122 are located between the spokes 128. In this example, the spokes 128 are not radially straight, but are curved to lengthen the path for the heat flow I 130 from the central actuation portion 124 to the peripheral support ring 126.

[0109] Although the use of hardened martensitic stainless steel for the inner contact plate 54 has advantages due to the low coefficients of friction with the plunger head 62, it shall not be excluded that the inner contact element or inner contact plate 54 may be made out of austenitic (acid- and rust-resistant) steel or out of a ceramic material. Although, ceramic materials typically provide a higher coefficient of friction, this may nevertheless be acceptable, if the thermal bridge 84 between the inner contact plate 54 and the push button 36 is located in the radial periphery 37 of the push button 36.

[0110] Referring to FIG. 15, the supply hose 4 is connected to a base unit 6 of a dental treatment unit 140, which also includes a treatment chair 142 and a patient lighting 144. The base unit 6 supplies several, in this example two, dental handpieces 10, 10′ with compressed air, electrical energy, light and/or water. For example, the first handpiece 10 is a motor-driven or electrical handpiece and the second handpiece 10′ is a flow-driven or air-driven handpiece. The base unit 6 also supplies a sprayvit 146 and an ultrasonic scaler 148.

[0111] It should be noted that the directional information like above or below, left or right, are not absolute, but refer to the orientation shown in the figures of the dental handpiece 10 and push button 36, in which the push button 36 is located above and the clamped dental tool 8 is located below.

[0112] It is apparent to those skilled in the art that the above-described embodiments are to be understood as exemplary and that the invention is not limited to these embodiments, but may be varied in many ways without departing from the scope of the claims. Furthermore, it will be understood that the features, whether disclosed in the specification, the claims, the figures, or otherwise, do individually define essential components of the invention, even if described together with other features. Thus, every such feature is to be understood to be disclosed separately and independent of each other. The description of features of each embodiment also applies to each of the other embodiments.

LIST OF REFERENCE NUMERALS

[0113] 2 coupling piece [0114] 4 supply hose [0115] 6 base unit [0116] 8 dental tool [0117] 10 dental handpiece [0118] 11 rod-like handle [0119] 12 head [0120] 14 housing [0121] 16 tool clamping device [0122] 18 actuator, plunger, release pin, or tappet [0123] 20 ball bearing [0124] 22 ball bearing receiving sleeve [0125] 24 holder [0126] 30 cover system [0127] 32 threaded sleeve [0128] 34 internal thread [0129] 36 push button [0130] 37 radial periphery [0131] 38 axis of rotation [0132] 42 outer cover plate [0133] 42a underside of the outer cover plate [0134] 42b upper side of the outer cover plate [0135] 44 peripheral edge region [0136] 48 circumferential or annular wall [0137] 50 stop ring of the annular wall [0138] 52 stop ring of the threaded sleeve [0139] 53 annular peripheral region [0140] 54 inner contact element, inner contact plate [0141] 54a underside [0142] 54b upper side [0143] 55 annular extension [0144] 56 spring [0145] 57 central thinning [0146] 58 end plate [0147] 60 idle stroke [0148] 62 actuator/plunger head [0149] 64 contact point [0150] 66 outer collar [0151] 70 recess [0152] 71 thinning [0153] 72 circumferential shoulder or ledge [0154] 74 annular step [0155] 76 peripheral bearing surface, annular stop [0156] 77 peripheral shoulder or ledge [0157] 78 gap, cavity [0158] 80 thermal insulation layer [0159] 82 central region of the push button [0160] 84 thermal bridge [0161] 85 annular contact region [0162] 86 annular interference fit [0163] 88 welding seam [0164] 90 welding seam [0165] 92 annular groove [0166] 94 second central recess [0167] 96 annular portion [0168] 98 central portion of the thermal insulation layer [0169] 102 dome [0170] 104 cover plate [0171] 106 peripheral edge of the cover plate [0172] 108 peripheral annular wall [0173] 110 collar [0174] 112 annular stop [0175] 114 base portion of the thermal insulation layer [0176] 116 shell portion [0177] 118 spacer ring [0178] 122 recesses [0179] 124 central actuation portion [0180] 126 peripheral support ring [0181] 128 spokes [0182] 130 heat flow [0183] 140 dental treatment unit [0184] 142 treatment chair [0185] 144 patient illumination [0186] 146 sprayvit [0187] 148 ultrasonic scaler