Patent Publication Number: US-2022226072-A1

Title: Head assembly for dental contra-angle hand-piece and dental contra-angle hand-piece

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present disclosure is a continuation-in-part application of the international patent application PCT/CN2021/081589 which claims priority to the Chinese patent application with the filing No. 202110017563.1 filed with the Chinese Patent Office on Jan. 7, 2021, and entitled “Head Assembly for Dental Contra-angle Hand-piece and Dental Contra-angle Hand-piece”, the contents of each of which are incorporated herein by reference in entirety. 
     The present disclosure also claims priority to the Chinese patent application with the filing No. 202210349369.8 filed with the Chinese Patent Office on Apr. 1, 2022, and entitled “Head Module for Dental Contra-angle Hand-piece and Dental Contra-angle Hand-piece”, the contents of which are incorporated herein by reference in entirety Technical Field 
     The present disclosure relates to the field of medical equipment, in particular to a head assembly for a dental contra-angle hand-piece and a dental contra-angle hand-piece. 
    
    
     BACKGROUND 
     The existing dental contra-angle hand-pieces mainly include two types, i.e. inner-water-channel dental contra-angle hand-pieces and outer-water-channel dental contra-angle hand-pieces. The inner-water-channel dental contra-angle hand-pieces are frequently used, that is, a water path and a gas path are provided inside the dental contra-angle hand-piece, water and gas are transmitted by a motor to the water path and the gas path in the dental contra-angle hand-piece, and the water and the gas are sprayed out from a front end of a head to form atomized water. The water sprayed out by the dental contra-angle hand-piece needs to be delivered via the water path of the motor, and the water path of the motor cannot be disinfected or sterilized, so when the clinical treatment of diseases such as oral diseases requires sterile operation with physiological saline or other sterile solutions, the existing inner-water-channel dental contra-angle hand-pieces cannot realize the same, and a dedicated outer-water-channel dental contra-angle hand-piece is needed, resulting in inconvenient use. In addition, the existing outer-water-channel dental contra-angle hand-pieces are not provided with a built-in water path, and cooling water cannot be directly provided by a dental chair when a sterile environment is not needed, resulting in inconvenient use. 
     It has been found from researches that the existing dental contra-angle hand-pieces have the following defects: a single function and inconvenient use. 
     SUMMARY 
     Embodiments of the present application provide a head assembly for a dental contra-angle hand-piece, including: 
     a hand-piece main body, wherein the hand-piece main body is provided with a first flow channel and a second flow channel independent from each other, the first flow channel is configured to be in communication with a liquid outlet of a motor, and the second flow channel is configured to be in communication with an external pipeline; 
     an inner water pipe, wherein the inner water pipe is connected to the hand-piece main body; and 
     a reversing valve, wherein the reversing valve is provided with a confluence channel; the reversing valve is movably connected to the hand-piece main body, the reversing valve is configured to enable the first flow channel and the second flow channel to alternatively be in communication with the inner water pipe through the confluence channel, when moving relative to the hand-piece main body. 
     Optionally, in one or more embodiments, the head assembly includes; 
     a hand-piece main body, wherein the hand-piece main body is provided with a first flow channel and a second flow channel independent from each other, the first flow channel is configured to be in communication with a liquid outlet of a motor, and the second flow channel is configured to be in communication with an external pipeline; 
     a reversing valve, wherein the reversing valve is provided with a confluence channel, and a first port and a second port both in communication with the confluence channel; the reversing valve is movably connected with the hand-piece main body so as to be switched between a first operation position and a second operation position; when the reversing valve is located in the first operation position, the first port is in communication with the first flow channel and the second port is discommunicated from the second flow channel; and when the reversing valve is located in the second operation position, the first port is discommunicated from the first flow channel and the second port is in communication with the second flow channel; and 
     an inner water pipe, wherein the inner water pipe is in communication with the confluence channel, and is configured to deliver a fluid to a head portion of the hand-piece main body. 
     Optionally, in one or more embodiments, the hand-piece main body is provided with a fitting hole, the first flow channel and the second flow channel are both in communication with the fitting hole; the reversing valve is provided in the fitting hole, and the reversing valve is configured to slidably cooperate with the hand-piece main body in an extending direction of the hand-piece main body, so as to enable the reversing valve to be switched between the first operation position and the second operation position. 
     Optionally, in one or more embodiments, the hand-piece main body has a front end configured to extend into an oral cavity and a rear end configured to be close to an operator, the fitting hole is provided on an end surface where the rear end is located, and the second flow channel is provided closer to the rear end than the first flow channel. 
     Optionally, in one or more embodiments, the dental contra-angle hand-piece further includes a toggle member, the toggle member is connected to the reversing valve, the toggle member protrudes from an outer circumferential wall of the hand-piece main body, and the toggle member slidably cooperates with the hand-piece main body in the extending direction of the hand-piece main body, so as to drive the reversing valve to be switched between the first operation position and the second operation position. 
     Optionally, in one or more embodiments, the hand-piece main body is provided with a first limiting portion and a second limiting portion arranged at an interval in the extending direction of the hand-piece main body, the toggle member is located between the first limiting portion and the second limiting portion, and the first limiting portion and the second limiting portion are configured to alternatively abut against the toggle member, so as to limit a sliding range of the toggle member. 
     Optionally, in one or more embodiments, when the reversing valve is located in the first operation position, the toggle member abuts against the first limiting portion; and when the reversing valve is located in the second operation position, the toggle member abuts against the second limiting portion. 
     Optionally, in one or more embodiments, when the reversing valve is switched between the first operation position and the second operation position, a flow rate is adjusted by adjusting an overlapped area of the first port and the first flow channel during the communication between the first port and the first flow channel; and the flow rate is adjusted by adjusting an overlapped area of the second port and the second flow channel during the communication between the second port and the second flow channel. 
     Optionally, in one or more embodiments, the hand-piece main body is further provided with an operation hole in communication with the fitting hole, the operation hole is located on an outer circumferential wall of the hand-piece main body, the operation hole is a strip-shaped hole and extends along the extending direction of the hand-piece main body, the first limiting portion and the second limiting portion are provided on a hole wall of the operation hole, and the toggle member passes through the operation hole and protrudes from the outer circumferential wall of the hand-piece main body. 
     Optionally, in one or more embodiments, the hand-piece main body is provided with a pressure relief hole in communication with the fitting hole. 
     Optionally, in one or more embodiments, the inner water pipe is inserted into the confluence channel, and the inner water pipe is configured to slidably cooperate with the reversing valve in the extending direction of the hand-piece main body. 
     Optionally, in one or more embodiments, an inner circumferential wall of the hand-piece main body is further provided with an annular gas passage, and the annular gas passage is configured to be in communication with a gas outlet of the motor. 
     Optionally, in one or more embodiments, the head assembly further includes at least one sealing member, and the at least one sealing member is provided between the reversing valve and the hand-piece main body, and is configured to seal a gap between the hand-piece main body and the reversing valve. 
     Optionally, in one or more embodiments, an outer circumferential wall of the reversing valve is provided with at least one annular positioning groove, and the at least one sealing member is provided in the at least one annular positioning groove. 
     Optionally, in one or more embodiments, the at least one sealing member is a sealing ring, and the sealing ring is an O-ring, a V-ring, or a rectangular ring. 
     Optionally, in one or more embodiments, the hand-piece main body is provided with a transfer cavity in communication with the inner water pipe and a first mounting hole in communication with the transfer cavity, the reversing valve is rotatably connected to the first mounting hole and then rotatably connected to the hand-piece main body, and a first sealing ring is provided between the reversing valve and a hole wall of the first mounting hole. 
     Optionally, in one or more embodiments, the hand-piece main body is provided with a locking ring, and the locking ring abuts against a side of the reversing valve away from the hand-piece main body, so as to prevent the reversing valve from disengaging from the hand-piece main body via an orifice of a second mounting hole. 
     Optionally, in one or more embodiments, the reversing valve has an outer circumferential surface provided around an axis of rotation of the reversing valve and an inner end surface intersecting the axis of rotation; the confluence channel includes a first hole segment and a second hole segment, one end of the first hole segment is located on the outer circumferential surface, and the other end of the first hole segment is in communication with one end of the second hole segment, the other end of the second hole segment is located on the inner end surface, the end of the second hole segment located on the inner end surface is eccentrically arranged with respect to the axis of rotation; and 
     the reversing valve has a first operation position and a second operation position which are switchable with each other when the reversing valve rotates relative to the hand-piece main body, wherein when the reversing valve is located in the first operation position, the first flow channel, the second hole segment, the first hole segment, and the transfer cavity are in communication in sequence, and the reversing valve blocks the second flow channel; and when the reversing valve is located in the second operation position, the second flow channel, the first hole segment, the second hole segment, and the transfer cavity are in communication in sequence, and the reversing valve blocks the first flow channel. 
     Optionally, in one or more embodiments, a second sealing ring is provided between the reversing valve and the hand-piece main body, and the reversing valve is configured to be rotatable relative to the second sealing ring, wherein when the reversing valve is located in the first operation position, an end of the second hole segment away from the first hole segment is located in a region surrounded by the second sealing ring, and the second hole segment is in communication with the first flow channel through the second sealing ring; and when the reversing valve is located in the second operation position, the reversing valve blocks the first flow channel through the second sealing ring. 
     Optionally, in one or more embodiments, the first flow channel includes an annular groove segment and a radial hole segment in communication with each other, the annular groove segment is provided around the axis of the hand-piece main body, the radial hole segment extends along a direction having an angle with the axis of the hand-piece main body, and the radial hole segment is configured to be in communication with the second hole segment through the second sealing ring when the reversing valve is located in the first operation position. 
     Optionally, in one or more embodiments, a third sealing ring is provided between the reversing valve and the hand-piece main body, and the reversing valve is configured to be rotatable relative to the third sealing ring, wherein when the reversing valve is located in the first operation position, the reversing valve blocks the second flow channel through the third sealing ring; and when the reversing valve is located in the second operation position, an end of the first hole segment away from the second hole segment is located in a region surrounded by the third sealing ring, and the first hole segment is in communication with the second flow channel through the third sealing ring. 
     Optionally, in one or more embodiments, a torque transmission portion is provided on the reversing valve, and the torque transmission portion is configured to be engaged with a force applying tool, so as to make the reversing valve rotate relative to the hand-piece main body under the driving of the force applying tool. 
     Optionally, in one or more embodiments, the torque transmission portion is provided as a protrusion or a groove. 
     Optionally, in one or more embodiments, at least one first limiting part is provided on the hand-piece main body, at least one second limiting part is provided on the reversing valve, and the at least one first limiting part and the at least one second limiting part are configured to abut against each other during rotation of the reversing valve relative to the hand-piece main body, so as to restrict a rotation range of the reversing valve. 
     Embodiments of the present disclosure further provide a dental contra-angle hand-piece, including the head assembly according to any one of the preceding embodiments. 
     Optionally, in one or more embodiments, the dental contra-angle hand-piece further includes a motor and an external pipeline, the motor is inserted into and matched with the hand-piece main body, and a liquid outlet of the motor is in communication with the first flow channel; and the external pipeline is inserted into the hand-piece main body and is in communication with the second flow channel. 
     Optionally, in one or more embodiments, an end surface where the rear end of the hand-piece main body close to an operator is located is provided with an insertion hole, and the motor is inserted into the insertion hole of the hand-piece main body. 
     Optionally, in one or more embodiments, the dental contra-angle hand-piece further includes a motor and an external pipeline, wherein both the motor and the external pipeline are connected to the hand-piece main body; the reversing valve of the head assembly is configured to make the liquid outlet of the motor and the external pipeline alternatively be in communication with the inner water pipe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more clearly illustrate technical solutions of embodiments of the present disclosure, accompanying drawings which need to be used in the embodiments will be introduced briefly below, and it should be understood that the accompanying drawings below merely show embodiments of the present disclosure, therefore, they should not be considered as limitation on the scope, and those ordinarily skilled in the art still could obtain other relevant accompanying drawings according to these accompanying drawings, without using any creative efforts. 
         FIG. 1  is a structural schematic view of a head assembly for a dental contra-angle hand-piece in an embodiment of the present disclosure; 
         FIG. 2  is an exploded structural schematic view of the head assembly for a dental contra-angle hand-piece in an embodiment of the present disclosure; 
         FIG. 3  is a sectional structural schematic view of the head assembly for a dental contra-angle hand-piece in an embodiment of the present disclosure; 
         FIG. 4  is a local enlarged structural schematic view of portion IV in  FIG. 3 ; 
         FIG. 5  is a partial sectional structural schematic view of a hand-piece main body in an embodiment of the present disclosure; 
         FIG. 6  is a sectional structural schematic view of a reversing valve and a toggle member in an embodiment of the present disclosure; 
         FIG. 7  is a partial structural schematic view of the head assembly for a dental contra-angle hand-piece in an embodiment of the present disclosure; 
         FIG. 8  is an exploded structural schematic view of the dental contra-angle hand-piece in an embodiment of the present disclosure; 
         FIG. 9  is a structural schematic view of another head assembly for a dental contra-angle hand-piece in an embodiment of the present disclosure; 
         FIG. 10  is a segmental structural schematic view of the another head assembly for a dental contra-angle hand-piece in an embodiment of the present disclosure; 
         FIG. 11  is an exploded structural schematic view of the another head assembly for a dental contra-angle hand-piece in an embodiment of the present disclosure; 
         FIG. 12  is a structural schematic view of a reversing valve in an embodiment of the present disclosure; 
         FIG. 13  is a segmental structural schematic view of the reversing valve in an embodiment of the present disclosure; 
         FIG. 14  is a structural schematic view of the head assembly when the reversing valve is located in a first operation position in an embodiment of the present disclosure; 
         FIG. 15  is a structural schematic view of the head assembly when the reversing valve is located in a second operation position in an embodiment of the present disclosure; and 
         FIG. 16  is a structural schematic view of the dental contra-angle hand-piece in an embodiment of the present disclosure. 
     
    
    
     REFERENCE SIGNS 
       0001 —head assembly;  100 —hand-piece main body;  101 —front end;  102 —rear end;  103 —insertion hole;  110 —first flow channel;  120 —second flow channel;  130 —fitting hole;  131 —insertion end;  140 —pressure relief hole;  150 —abutment surface;  160 —operation hole;  161 —first limiting portion;  162 —second limiting portion;  170 —annular gas passage;  200 —reversing valve;  201 —first end;  202 —second end;  210 —confluence channel;  220 —first port;  230 —second port;  240 —annular positioning groove;  300 —inner water pipe;  400 —toggle member;  500 —abutment ring;  600 —fastener;  700 —first sealing member;  800 —second sealing member;  900 —external pipeline;  001 —housing;  1001 —notch;  002 —motor;  2001 —liquid outlet;  2020 —gas outlet;  1100 —shell;  111 —second mounting hole;  112 —avoidance groove;  1200 —fixing seat;  1221 —annular groove segment;  1222 —radial hole segment;  124 —transfer cavity;  125 —first mounting hole;  126 —first limiting groove;  127 —second limiting groove;  128 —gas delivery channel;  1300 —press ring;  310 —sealing body;  311 —outer circumferential surface;  312 —inner end surface;  313 —confluence channel;  3131 —first hole segment;  3132 —second hole segment;  320 —force transmission body;  321 —torque transmission portion;  322 —second limiting part;  330 —annular limiting groove;  410 —first sealing ring;  510 —second sealing ring;  610 —third sealing ring;  700 —sealing structure;  800 —locking ring. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In order to make objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below in conjunction with accompanying drawings in the embodiments of the present disclosure, and apparently, the embodiments described are some but not all embodiments of the present disclosure. Generally, components in the embodiments of the present disclosure, as described and shown in the accompanying drawings herein, may be arranged and designed in various different configurations. 
     Therefore, the detailed description below of the embodiments of the present disclosure provided in the accompanying drawings is not intended to limit the claimed scope of the present disclosure, but merely illustrates chosen embodiments of the present disclosure. All of other embodiments obtained by those ordinarily skilled in the art based on the embodiments in the present disclosure without using any creative efforts shall fall within the scope of protection of the present disclosure. 
     It should be noted that similar reference signs and letters represent similar items in the following accompanying drawings, therefore, once a certain item is defined in one accompanying drawing, it is not needed to be further defined or explained in subsequent accompanying drawings. 
     In the description of the present disclosure, it should be indicated that orientation or positional relationships indicated by terms such as “center”, “upper”, “lower”, “left”, “right”, “vertical”, “horizontal”, “inner”, and “outer” are based on orientation or positional relationships as shown in the accompanying drawings, or orientation or positional relationships of a product of the present disclosure conventionally placed when in use, merely for facilitating describing the present disclosure and simplifying the description, rather than indicating or implying that related devices or elements have to be in the specific orientation, or configured or operated in a specific orientation, therefore, they should not be construed as limiting the present disclosure. Besides, terms such as “first”, “second”, and “third” are merely for distinctive description, but should not be construed as indicating or implying importance in the relativity. 
     Moreover, the terms “horizontal”, “vertical” and the like do not mean that the parts are required to be absolutely horizontal or overhanging, but may be slightly inclined. For example, for “horizontal”, it merely means that a structure is more horizontal in comparison with “vertical”, rather than being completely horizontal, while the structure can be slightly inclined. 
     In the description of the present disclosure, it should be further illustrated that, unless otherwise specifically specified and defined, the terms “set”, “install”, “link”, and “connect” should be understood in a broad sense, for example, a connection may be a fixed connection, a detachable connection, or an integrated connection; it may be a mechanical connection or an electrical connection; it may be direct joining or indirect joining through an intermediate medium, and it also may be inner communication between two elements. For those ordinarily skilled in the art, specific meanings of the above-mentioned terms in the present disclosure could be understood according to specific circumstances. 
     At present, the dental contra-angle hand-pieces mainly include two types of inner-water-channel contra-angle hand-pieces and outer-water-channel contra-angle hand-pieces. Water of the inner-water-channel contra-angle hand-piece is delivered by a motor to an inner water pipe; and water of the outer-water-channel contra-angle hand-pieces is delivered to an inner water pipe through an external pipeline. As the motor part of the inner water pipe is not easy to disinfect or clean, the inner-water-channel contra-angle hand-pieces are not suitable for delivering a sterile solution, at this time, the outer-water-channel contra-angle hand-piece needs to be used for processing, so the operation is complex, the labor intensity is high, and the efficiency is low. Meanwhile, when the outer-water-channel contra-angle hand-piece is used to deliver a liquid, the external pipeline of the outer-water-channel contra-angle hand-piece is close to a head of the hand-piece. In this way, a volume of a front end of the head assembly is increased, making the front end of the head assembly occupy a large space, while the oral cavity has a limited operation space, thus the operation is inconvenient. In other words, the existing dental contra-angle hand-pieces have a single function and are inconvenient to use. 
     It should be understood that the front end of the head assembly is the end located at the oral cavity, and atomized water formed by mixing the liquid and the gas can be sprayed out from the front end of the head. 
     Referring to  FIG. 1  to  FIG. 16 , in view of this, the present embodiment provides a head assembly (also called head module)  0001  for a dental contra-angle hand-piece, wherein the head assembly has both functions of inner-water-channel water delivery and outer-water-channel water delivery. In this way, when in use, the inner-water-channel water delivery and the outer-water-channel water delivery can be flexibly selected, enabling diversified functions, convenient switching, flexible and convenient operation, low labor intensity, high operation efficiency, wide application range and a low cost. 
     Referring to  FIG. 1  to  FIG. 4 , in the present embodiment, the head assembly  0001  for a dental contra-angle hand-piece includes: 
     a hand-piece main body (also called head main body)  100 , wherein the hand-piece main body  100  is provided with a first flow channel (also called first channel)  110  and a second flow channel (also called second channel)  120  independent from each other, the first flow channel  110  is configured to be in communication with a liquid outlet  2001  of a motor  002 , and the second flow channel  120  is configured to be in communication with an external pipeline (e.g., external water pipe)  900 ; 
     a reversing valve (also called adjusting valve)  200 , wherein the reversing valve  200  is provided with a confluence channel (also called reversing channel)  210 , and a first port  220  and a second port  230  which are both in communication with the confluence channel  210 ; the reversing valve  200  is movably connected with the hand-piece main body  100  so as to be switched between a first operation position and a second operation position; when the reversing valve is located in the first operation position, the first port  220  is in communication with the first flow channel  110  and the second port  230  is discommunicated from the second flow channel  120 ; and when the reversing valve is located in the second operation position, the first port  220  is discommunicated from the first flow channel  110  and the second port  230  is in communication with the second flow channel  120 ; and 
     an inner water pipe  300 , wherein the inner water pipe  300  is in communication with the confluence channel  210 , and is configured to deliver a fluid to a head portion of the hand-piece main body  100 . 
     For the dental contra-angle hand-piece head assembly provided by the present embodiment, a state of the head assembly can be adjusted as required according to a field situation when the clinical treatment is carried out, to correspondingly adjust it to achieve inner-water-channel or outer-water-channel water delivery, then the operation is convenient and reliable. Specifically, when the inner-water-channel water delivery is required, that is, when the water is delivered from the motor  002  to the inner water pipe  300 , the reversing valve  200  is adjusted so that the reversing valve  200  moves to the first operation position, and at this time, the first port  220  is in communication with the first flow channel  110 , the liquid outlet  2001  of the motor  002  is in communication with the first port  220  through the first flow channel  110 , and the first port  220  is in communication with the inner water pipe  300  through the confluence channel  210 , so that the water delivered by the motor  002  flows through the first flow channel  110 , the first port  220 , and the confluence channel  210  in sequence to the inner water pipe  300 , and flows out from the inner water pipe  300 , to be mixed with the gas to form a water mist. When the outer-water-channel water delivery is needed, that is, when the water is not delivered from the motor  002  to the inner water pipe  300 , but is delivered from the external pipeline  900  to the inner water pipe  300 , the reversing valve  200  is adjusted so that the reversing valve  200  moves to the second operation position, and the second port  230  is in communication with the second flow channel  120 , at this time, the external pipeline  900 , the second flow channel  120 , the second port  230 , the confluence channel  210 , and the inner water pipe  300  are in communication in sequence, so that the water delivered through the external pipeline  900  can smoothly flow into the inner water pipe  300 , and flow out from the inner water pipe  300 , to be mixed with the gas to form a water mist. Thus, the head assembly provided by the present embodiment can be switched between the state of inner-water-channel water delivery and the state of outer-water-channel water delivery, thus satisfying the use requirements of different scenarios, having diversified functions, being flexible and convenient to use, improving the operation efficiency and achieving safe and reliable operation. 
     Meanwhile, when the reversing valve  200  is switched between the first operation position and the second operation position, during the communication between the first port  220  and the first flow channel  110 , the overlapped portion of the first port  220  and the first flow channel  110  gradually increases, the flow rate can be adjusted by adjusting an overlapped area of the first port  220  and the first flow channel  110 , realizing the function of adjusting flow rate. Similarly, during the communication between the second port  230  and the second flow channel  120 , the flow rate can also be adjusted by adjusting the overlapped area of the second port  230  and the second flow channel  120 . 
     Referring to  FIG. 5 , in the present embodiment, optionally, the hand-piece main body  100  has a front end  101  which is close to a patient in an operation state and a rear end  102  used for being held by an operator, wherein the front end  101  may also be called as a head end, and the rear end  102  may also be called as a tail end. An end surface where the rear end  102  of the hand-piece main body  100  is located is provided with an insertion hole  103  for allowing the motor  002  to be inserted thereinto, an inner circumferential wall of the hand-piece main body  100  is provided with the first flow channel  110  in an annular shape, the first flow channel  110  is provided around an axis of the insertion hole  103 , an outer circumferential wall of the hand-piece main body  100  is provided with the second flow channel  120 , and the first flow channel  110  is located on a side of the second flow channel  120  close to the front end  101  of the hand-piece main body  100 . That is, the second flow channel  120  is provided close to the rear end  102  of the hand-piece main body  100 , in other words, the distance between the second flow channel  120  and the rear end  102  is smaller than the distance between the second flow channel  120  and the front end  101 , in this way, the external pipeline  900  in communication with the second flow channel  120  will not increase the volume of the head end, and when the head end extends into a patient&#39;s oral cavity, the external pipeline  900  will not enter the oral cavity. The head end has a small volume, and is easy to operate. 
     Optionally, the hand-piece main body  100  is further provided with a fitting hole  130  and a pressure relief hole  140  in communication with the fitting hole  130 , both the fitting hole  130  and the pressure relief hole  140  extend along a length direction of the hand-piece main body  100 , an end of the fitting hole  130  close to the front end  101  of the hand-piece main body  100  is an insertion end  131 , the pressure relief hole  140  is in communication with an end of the fitting hole  130  close to the rear end  102  of the hand-piece main body  100 , that is, the pressure relief hole  140  is located at a side of the fitting hole  130  close to the rear end  102  of the hand-piece main body  100 , and meanwhile, an end of the pressure relief hole  140  away from the fitting hole  130  extends to an end surface of the rear end  102  of the hand-piece main body  100 . 
     Optionally, the fitting hole  130  and the pressure relief hole  140  are both cylindrical holes, the fitting hole  130  is coaxial with the pressure relief hole  140 , and the diameter of the fitting hole  130  is greater than the diameter of the pressure relief hole  140 , so as to form an abutment surface  150  in an annular shape at a position where the fitting hole  130  is in communication with the pressure relief hole  140 . 
     It should be noted that the first flow channel  110  is in communication with the fitting hole  130  through a connecting hole, and the second flow channel  120  is in communication with the fitting hole  130 . 
     Optionally, the hand-piece main body  100  is further provided with an operation hole  160  in communication with the fitting hole  130 , the operation hole  160  is located on the outer circumferential wall of the hand-piece main body  100 , a hole wall of the operation hole  160  is provided with a first limiting portion  161  and a second limiting portion  162  arranged at an interval in an axial direction of the hand-piece main body  100 , and the first limiting portion  161  and the second limiting portion  162  are configured to limit a sliding range of the reversing valve  200  in an extending direction of the hand-piece main body  100 . 
     Optionally, the operation hole  160  may be a strip-shaped hole, and the operation hole  160  extends along the axial direction of the hand-piece main body  100 . With such configuration, the operation hole  160  has a small volume, occupies a small occupation space, and is easy to process, and the strength of the hand-piece main body  100  is not easily weakened. 
     Referring to  FIG. 6 , in the present embodiment, optionally, the reversing valve  200  is of a cylindrical structure, the reversing valve  200  is provided with the confluence channel  210  at a first end  201  in its axial direction, and the confluence channel  210  is spaced apart from a second end  202  of the reversing valve  200  in its axial direction. The first port  220  and the second port  230  are both provided on the circumferential wall of the reversing valve  200 , and are spaced apart from each other in a circumferential direction of the reversing valve  200 , for example, the first port  220  and the second port  230  are uniformly arranged at an interval in the circumferential direction of the reversing valve  200 , that is, angles of the first port  220  and the second port  230  in the circumferential direction of the reversing valve  200  are 180°. The first port  220  is located on a side of the second port  230  close to the first end  201 , that is, the second port is closer to the second end  202  than the first port  220 . 
     It should be noted that the reversing valve  200  may not be of a cylindrical structure, for example, may also be of a structure having an elliptical cross section or a square cross section, which may be set as needed. By providing the reversing valve  200  as a cylindrical structure, it is convenient to seal a gap between the reversing valve  200  and the hole wall of the fitting hole  130 . 
     When the reversing valve  200  is fitted with the hand-piece main body  100 , the second end  202  of the reversing valve  200  is inserted from the insertion end  131  of the fitting hole  130 , the first end  201  of the reversing valve  200  is corresponding to the insertion end  131 , and the inner water pipe  300  is inserted into the first end  201  of the reversing valve  200  from the insertion end  131 . With such design, the reversing valve  200  slidably cooperates with the fitting hole  130  in the axial direction of the fitting hole  130 , and when the reversing valve  200  slides to a first operation position, the first port  220  is in communication with the first flow channel  110  through the connecting hole, and the outer circumferential wall of the reversing valve  200  blocks the second flow channel  120 , at this time, the inner-water-channel water delivery can be carried out. When the reversing valve  200  slides to a second operation position, the outer circumferential wall of the reversing valve  200  blocks the connecting hole, and the second port  230  is in communication with the second flow channel  120 , and at this time, the outer-water-channel water delivery can be carried out. Meanwhile, when the second port  230  is close to the rear end  102  of the hand-piece main body  100 , and the second port  230  is connected to the external pipeline  900  through the second flow channel  120 , the external pipeline  900  is located at the rear end  102  of the hand-piece main body  100 , the external pipeline  900  is not located at the front end  101  of the hand-piece main body  100 , the front end  101  of the hand-piece main body  100  has a small volume, requires a small space when operating, and is convenient and flexible to operate in the oral cavity with limited space. 
     Referring to  FIG. 6  and  FIG. 7 , in the present embodiment, optionally, the head assembly for a dental contra-angle hand-piece further includes a toggle member  400 , an end of the toggle member  400  is in communication with the reversing valve  200 , and the toggle member  400  passes through the operation hole  160  and protrudes out from the outer circumferential wall of the hand-piece main body  100 . The toggle member  400  is located between the first limiting portion  161  and the second limiting portion  162 , and an outer wall of the toggle member  400  is in contact with the hole wall of the operation hole  160  in the circumferential direction of the hand-piece main body  100 , thereby preventing the reversing valve  200  from rotating in the fitting hole  130 , so that relative positions of the first port  220 , the second port  230 , the first flow channel  110 , and the second flow channel  120  are accurate and reliable. When the position of the reversing valve  200  needs to be switched, the toggle member  400  is operated so that the toggle member slides between the first limiting portion  161  and the second limiting portion  162 . Specifically, when the toggle member  400  moves to abut against the first limiting portion  161 , the reversing valve  200  is located in the first operation position, at this time, the first port  220  is in communication with the first flow channel  110 , and the second port  230  is not in communication with the second flow channel  120 ; when the toggle member  400  moves to abut against the second limiting portion  162 , the reversing valve  200  is located in the second operation position, at this time, the second port  230  is in communication with the second flow channel  120 , and the first port  220  is not in communication with the first flow channel  110 . Such configuration facilitates adjusting the position of the reversing valve  200  through the toggle member  400 , and meanwhile facilitates judging the operation state of the reversing valve  200  according to the position of the toggle member  400 , then the operation is convenient and reliable. 
     In addition, as there is the abutment surface  150  at a joint of the fitting hole  130  and the pressure relief hole  140 , when the revering valve  200  slides from the first operation position to the second operation position, the abutment surface  150  has a function of restricting the sliding of the revering valve  200 , thus preventing the revering valve  200  from sliding out from the pressure relief hole  140 . When the reversing valve  200  slides, the gas can be discharged from the pressure relief hole  140 . The reversing valve  200  flexibly slides, and is not easily stuck in the fitting hole  130 . Obviously, when the reversing valve  200  is located in the second operation position, the second end  202  of the reversing valve  200  does not necessarily abut against the abutment surface  150 , and it is also feasible to achieve limiting by only relying on the second limiting portion  162  abutting against the toggle member  400 . 
     It should be understood that in other embodiments, a driving mechanism can be provided to drive the toggle member  400  to move, so that the toggle member adjusts the position of the reversing valve  200 , then the reversing valve  200  can be switched between the first operation position and the second operation position. For example, the driving mechanism may be a motor screw transmission mechanism, a cylinder mechanism, a hydraulic cylinder mechanism, an electric push rod, or the like. 
     In addition, the operation positions of the reversing valve  200  also can be switched not by sliding linearly with respect to the hand-piece main body  100 , for example, in other embodiments, the operation positions of the reversing valve  200  can be switched by rotating with respect to the hand-piece main body  100 , or the operation positions of the reversing valve  200  is switched by sliding and simultaneously rotating with respect to the hand-piece main body  100 . 
     Referring to  FIG. 7 , in the present embodiment, optionally, the inner water pipe  300  is inserted into the confluence channel  210  from the first end  201  of the reversing valve  200  after passing through the insertion end  131 , and the inner water pipe  300  slidably cooperates with the confluence channel  210 , that is, when the reversing valve  200  slides relative to the fitting hole  130 , it meanwhile slides relative to the inner water pipe  300 , at the same time, the reversing valve  200  will not disengage from the innerwater pipe  300  during the sliding, and the connection stability between the two is high. 
     Optionally, the fitting hole  130  is provided therein with an abutment ring  500 , and the fitting hole  130  is provided with an inner thread on a hole wall thereof located at a side of the abutment ring  500  close to the insertion end  131 . The inner water pipe  300  is sheathed with a fastener  600  and a first sealing member  700 , the inner water pipe  300  penetrates through the abutment ring  500  and is inserted into the confluence channel  210 , the fastener  600  is screwed into the fitting hole  130 , and the first sealing member  700  is clamped between the fastener  600  and the abutment ring  500 , enabling good sealing performance and allowing it to be not easy to leak. 
     In the present embodiment, optionally, the head assembly for a dental contra-angle hand-piece further includes a plurality of second sealing members  800 , the plurality of second sealing members  800  are provided in the fitting hole  130 , located between the hole wall of the fitting hole  130  and the reversing valve  200 , and are configured to seal the hole wall of the fitting hole  130  and the outer circumferential wall of the reversing valve  200 . 
     It should be noted that the second sealing members  800  can be embedded in the fitting hole  130 , and after the reversing valve  200  is inserted into the fitting hole  130  from the insertion end  131  of the fitting hole  130 , the hole wall of the fitting hole  130  and the reversing valve  200  are sealed by the second sealing members  800 . Alternatively, the second sealing members  800  are sleeved over the reversing valve  200  and form with the reversing valve  200  a combined structure, and when the reversing valve  200  is inserted into the fitting hole  130 , the second sealing members  800  realize the sealing of the reversing valve  200  and the hole wall of the fitting hole  130 . In the present embodiment, illustration is made by taking the second sealing members  800  being sleeved over the reversing valve  200  as an example. 
     The number of second sealing members  800  is five, and all of the five second sealing members  800  are sleeved over the reversing valve  200 . Optionally, the outer circumferential wall of the reversing valve  200  is provided with five annular positioning grooves  240 , and the five second sealing members  800  are respectively provided in the five annular positioning grooves  240 . The second sealing members  800  have accurate and reliable positions, and are not easily displaced, rendering good sealing effect. 
     For convenience of description, it is assumed that in a direction from the first end  201  to the second end  202  of the reversing valve  200 , the five second sealing members  800  are sealing member a, sealing member b, sealing member c, sealing member d, and sealing member e, respectively, and when the five second sealing members  800  are fitted to the reversing valve  200 , the first port  220  on the reversing valve  200  is located between the sealing member c and the sealing member d, and the second port  230  on the reversing valve  200  is located between the sealing member d and the sealing member e. When the reversing valve  200  is located in the first operation position, the first flow channel  110  is in communication with the first port  220 , and both the first flow channel  110  and the first port  220  are located between the sealing member d and the sealing member e; when the reversing valve  200  is located in the second operation position, the second flow channel  120  is in communication with the second port  230 , the second flow channel  120  and the second port  230  are both located between the sealing member d and the sealing member e, and the first flow channel  110  is located between the sealing member b and the sealing member c. 
     It should be noted that both the first sealing member  700  and the second sealing member  800  may be sealing rings, and the sealing rings may be O-rings, V-rings, rectangular rings or the like. Shapes of the first sealing member  700  and the second sealing member  800  may be different. 
     In other embodiments, the head assembly for a dental contra-angle hand-piece further includes an external pipeline  900 , and the external pipeline  900  is inserted into the second port  230 . 
     It should be noted that, the inner circumferential wall of the hand-piece main body  100  is further provided with an annular gas passage  170  configured to be in communication with the gas outlet  2020  of the motor  002 , the annular gas passage  170  is in communication with a gas delivery pipe, the gas delivery pipe is configured to deliver the gas to the front end  101  of the hand-piece main body  100 , so that the gas and the water are mixed to form a water mist at the front end  101  of the hand-piece main body  100 . 
     In other embodiments, the hand-piece main body  100  is sheathed with a housing  001 , the toggle member  400  extends out of the housing  001 , and correspondingly, the housing  001  is provided with a through hole corresponding to the operation hole  160 . Meanwhile, the housing  001  is provided with a notch  1001  capable of exposing the second port  230  outside the housing  001 . 
     When the head assembly for a dental contra-angle hand-piece provided in the present embodiment is used, the position of the reversing valve  200  can be adjusted as needed, and when the reversing valve  200  is located in the first operation position, the first port  220  is in communication with the first flow channel  110 , and inner-water-channel water delivery can be realized. When the reversing valve  200  is located in the second operation position, the second port  230  is in communication with the second flow channel  120 , and outer-water-channel water delivery can be realized. The head assembly has diversified functions, is flexible to operate, and has high operation efficiency. Meanwhile, when the reversing valve  200  is in the first operation position, the reversing valve  200  can be properly adjusted, so that the overlapped area of the first port  220  and the first flow channel  110  is changed, thus adjusting the flow rate. Similarly, when the reversing valve  200  is in the second operation position, the overlapped area of the second port  230  and the second flow channel  120  can also be adjusted, thereby adjusting the flow rate. 
     Referring to  FIG. 8 , the present embodiment further provides a dental contra-angle hand-piece, including a motor  002  and the head assembly for a dental contra-angle hand-piece mentioned in the above embodiments, the motor  002  is inserted into the insertion hole  103  of the hand-piece main body  100 , and the liquid outlet  2001  of the motor  002  is in communication with the first flow channel  110 , the gas outlet  2020  of the motor  002  is in communication with the annular gas passage  170 , and the motor  002  is configured to supply water to the first flow channel  110  when the dental contra-angle hand-piece performs inner-water-channel water delivery, thus, the water flows from the first flow channel  110  and the first port  220  to the confluence channel  210 , and finally flows out from the inner water pipe  300 . 
     The dental contra-angle hand-piece provided by the present embodiment is capable of performing the inner-water-channel water delivery or the outer-water-channel water delivery as needed, has diversified functions, is flexible and reliable to operate, and has high safety. 
     Referring to  FIG. 9  to  FIG. 11 , in the present embodiment, a head assembly  0001  for a dental contra-angle hand-piece includes a hand-piece main body  100 , an inner water pipe  300 , and a reversing valve  200 . The hand-piece main body  100  is provided with a first flow channel  110  and a second flow channel  120  independent from each other, wherein the first flow channel  110  is configured to be in communication with a liquid outlet (or liquid delivery channel) of the motor  002 , and the second flow channel  120  is configured to be in communication with an external pipeline  900 . The inner water pipe  300  is connected to the hand-piece main body  100 . The reversing valve  200  is provided with a confluence channel  313 , the reversing valve  200  is rotatably connected to the hand-piece main body  100 , and the reversing valve  200  is configured to enable, when rotating relative to the hand-piece main body  100 , the first flow channel  110  and the second flow channel  120  to alternatively be in communication with the inner water pipe  300  through the confluence channel  313 . 
     It should be understood that the first flow channel  110  and the second flow channel  120  being alternatively in communication with the inner water pipe  300  through the confluence channel  313  means that when the reversing valve  200  is rotated, the confluence channel  313  of the reversing valve  200  can make the first flow channel  110  be in communication with the inner water pipe  300 , so as to realize the function of inner-water-channel water delivery, and at this time, the second flow channel  120  is not in communication with the inner water pipe  300 , and the liquid in the external pipeline  900  will not be delivered into the inner water pipe  300 ; similarly, when the reversing valve  200  is rotated, the confluence channel  313  of the reversing valve  200  can also make the second flow channel  120  in communication with the inner water pipe  300 , so as to realize the function of outer-water-channel water delivery, at this time, the first flow channel  110  is not in communication with the inner water pipe  300 , so that the liquid will not be delivered from the motor  002  into the inner water pipe  300 . 
     The operation principle of the head assembly  0001  for a dental contra-angle hand-piece provided in the present embodiment is as follows. 
     When needing to perform inner-water-channel water delivery, that is, when water is delivered from the motor  002  to the inner water pipe  300 , the reversing valve  200  is operated, to make the reversing valve  200  rotate relative to the hand-piece main body  100 , and during the rotation, the reversing valve  200  can move to a position where the first flow channel  110 , the confluence channel  313 , and the inner water pipe  300  are in communication in sequence, so that the motor  002  delivers the liquid from the first flow channel  110  to the confluence channel  313 , and then the liquid enters the inner water pipe  300  from the confluence channel  313 , thus realizing that the liquid is delivered from the motor  002  to the inner water pipe  300 , the liquid is mixed with the gas delivered by the motor  002  to form a water mist, and the water mist is sprayed out from a front end of the hand-piece main body  100 . 
     When needing to perform outer-water-channel water delivery, that is, when the water is not delivered from the motor  002  to the inner water pipe  300 , but is delivered from the external pipeline  900  to the inner water pipe  300 , the reversing valve  200  continues to rotate, to make the reversing valve  200  rotate to a position where the second flow channel  120 , the confluence channel  313 , and the inner water pipe  300  are in communication in sequence, so that the liquid delivered through the external pipeline  900  can smoothly flow to the inner water pipe  300  and flow out from the inner water pipe  300 , to be mixed with the gas to form a water mist. In this way, the operation state of the head assembly is adjusted as required according to the field situation when clinical treatment is carried out, so that it can be switched between two states of inner-water-channel water delivery and outer-water-channel water delivery, thus it is convenient and flexible to operate, and easy and convenient to use, and has a low cost. 
     Meanwhile, when the reversing valve is rotated with respect to the hand-piece main body, during the communication between the confluence channel and the first flow channel, an overlapped part of the confluence channel and the first flow channel is gradually increased, and the flow rate can be adjusted by adjusting an overlapped area of the confluence channel and the first flow channel, thereby achieving the function of adjusting flow rate. Similarly, during the communication between the confluence channel and the second flow channel, the flow rate can also be adjusted by adjusting the overlapped area of the confluence channel and the second flow channel. 
     With reference to  FIG. 10 , in the present embodiment, it needs to be noted that the hand-piece main body  100  is in an elongated shape, and two ends of the hand-piece main body  100  in a length extending direction thereof are respectively a front end  101  and a rear end  102 , wherein the front end  101  may also be referred to as a head end, the rear end  102  may also be referred to as a tail end, the front end  101  is configured to extend into a patient&#39;s oral cavity, and the rear end  102  is configured to be held by an operator. Optionally, the hand-piece main body  100  includes a shell  1100 , a fixing seat  1200 , and a press ring  1300 , wherein an end of the shell  1100  is configured to be open (i.e. the end is an opening), the fixing seat  1200  can be inserted into the shell  110  or pulled out from the shell  110  through the opening, the press ring  1300  is connected to the shell  1100 , and limits the fixing seat  1200  in the shell  1100 , and the fixing seat  120  will not freely slide out from the open end of the shell  1100 . The inner water pipe  300  is provided in the shell  1100 , and an end of the inner water pipe  300  is connected to the fixing seat  1200 . An end surface of the fixing seat  1200  close to the rear end  102  is provided with an insertion hole  103  configured to allow the motor  002  to insert thereinto, an axis of the insertion hole  103  extends along the length direction of the hand-piece main body  100 , and the hole wall of the insertion hole  103  is provided with the first flow channel  110  and a gas delivery channel  128  arranged at an interval in the length extending direction of the hand-piece main body  100 , and the gas delivery channel  128  is closer to the front end of the hand-piece main body  100  than the first flow channel  101 . The first flow channel  101  includes an annular groove segment  1221  and a radial hole segment  1222  arranged around the axis of the insertion hole  103 , the radial hole segment  1222  is in communication with the annular groove segment  1221 , and the radial hole segment  1222  extends along a direction perpendicular to the axis of the insertion hole  103 . Obviously, in other embodiments, the radial hole segment  1222  further may form, with the axis of the insertion hole  103 , an angle other than 90° and zero. When the motor  002  is inserted into the insertion hole  103 , a part of the motor  002  is butt-jointed to the open end of the shell  1100 , the liquid outlet of the motor  002  is in communication with the annular groove segment  1221 , and a gas delivery hole on the motor  002  is in communication with the gas delivery channel  128 . 
     It should be noted that the fixing seat  1200  can be fixedly connected to the shell  1100  by means of screws, snap structures or the like. 
     With reference to  FIG. 14 , meanwhile, the second flow channel  120  is provided on the fixing seat  1200 , and the second flow channel  120  is provided close to the rear end  102  of the hand-piece main body  100 , in other words, a distance between the second flow channel  120  and the rear end  102  is smaller than a distance between the second flow channel  120  and the front end  101 , in this way, the external pipeline  900  in communication with the second flow channel  120  is away from the front end, and will not increase the volume of the front end. When the front end is extended into the patient&#39;s oral cavity, the external pipeline  900  will not enter the oral cavity, in this way, the front end has a small volume, and is easy to operate. The fixing seat  1200  is further provided with a transfer cavity and a first mounting hole  125  in communication with the transfer cavity, and the transfer cavity is in communication with the inner water pipe  300 . The shell  1100  is provided with an avoidance groove  112  configured to avoid the external pipeline  900 , and the avoidance groove  112  is in communication with the second flow channel  120 . The shell  1100  is further provided with a second mounting hole  111  in communication with the first mounting hole  125 . The reversing valve  200  is rotatably connected to the first mounting hole  125  and the second mounting hole  111 , and a first sealing ring  410  is provided between the reversing valve  200  and a hole wall of the first mounting hole  125 , preventing the liquid in the transfer cavity from leaking from a gap between the first mounting hole  125  and the reversing valve  200 . In the above, an axis of the first mounting hole  125  is perpendicular to the extending direction of the hand-piece main body  100 . Obviously, in other embodiments, the axis of the first mounting hole  125  and the extending direction of the hand-piece main body  100  may also form an angle other than zero. A first limiting groove  126  and a second limiting groove  127  are further provided on a cavity wall of the transfer cavity, wherein the first limiting groove  126  and the second limiting groove  127  can both be provided as circular grooves, and an end of the radial hole segment  1222  away from the annular groove segment  1221  is located on a groove bottom wall of the first limiting groove  126 ; and an end of the second flow channel  120  is located on a groove bottom wall of the second limiting groove  127 . The first limiting groove  126  and the second limiting groove  127  are respectively provided with a second sealing ring  510  and a third sealing ring  610 , wherein the second sealing ring  510  is in communication with the radial hole segment  1222 , and the third sealing ring  610  is in communication with the second flow channel  120 ; further, an annular end surface of the third sealing ring  610  away from the groove bottom wall of the second limiting groove  127  is a sealing surface, and the sealing surface is a partial spherical surface or a partial cylindrical surface. 
     Further, a sealing structure  700  is provided in the transfer cavity  124 , which can prevent the liquid in the transfer cavity  124  from leaking from a connection gap between the shell  1100  and the fixing seat  1200 . 
     Referring to  FIG. 12  to  FIG. 13 , in the present embodiment, optionally, the reversing valve  200  includes a sealing body  310  and a force transmission body  320  connected to each other, and the sealing body  310  and the force transmission body  320  may be configured as an integrated structure. The sealing body  310  has an outer circumferential surface  311  and an inner end surface  312  connected to the outer circumferential surface  311 , the outer circumferential surface  311  is a partial spherical surface or a cylindrical surface, the inner end surface  312  is a circular surface, and the force transmission body  320  is located at an end of the sealing body  310  in an axial direction thereof, that is, the inner end surface  312  of the sealing body  310  is located at an end of the sealing body  310  away from the force transmission body  320 . The axis of the sealing body  310  is an axis of rotation of the reversing valve  200 . The confluence channel  313  includes a first hole segment  3131  and a second hole segment  3132 , wherein one end of the first hole segment  3131  is located on the outer circumferential surface  311 , and the other end of the first hole segment  3131  is in communication with one end of the second hole segment  3132 , the other end of the second hole segment  3132  is located on the inner end surface  312 , the end of the second hole segment  3132  located on the inner end surface  312  is eccentrically arranged with respect to the axis of rotation, and further, a center of the inner end surface  312  is located outside a region surrounded by an outer contour of one end of the second hole segment  3132  located at the inner end surface  312 . An annular limiting groove  330  is formed at a position where the sealing body  310  is connected with the force transmission body  320 , and the first sealing ring  410  is embedded in the annular limiting groove  330 . During fitting, the reversing valve  200  passes through the second mounting hole  111  and is inserted into the first mounting hole  125 , the inner end surface  312  abuts against the second sealing ring  510 , and the outer circumferential face  311  abuts against the third sealing ring  610 . Moreover, a part of the force transmission body  320  away from the sealing body  310  may protrude out from a port of the second mounting hole  111  away from the first mounting hole  125 , facilitating in operating the force transmission body  320  to make the same drive the sealing body  310  to rotate. 
     It should be understood that, the outer circumferential surface  311  cooperates with the third sealing ring  610 , here, when the reversing valve  200  is rotated relative to the hand-piece main body  100 , the sealing body  310  will be rotated relative to the third sealing ring  610  and the second sealing ring  510 , and the outer circumferential surface  311  will be rotated relative to the third sealing ring  610 , a sealing surface of the third sealing ring  610  fits with the outer circumferential surface  311  of the sealing body  310 , so that during the rotation, the sealing state is always maintained and dynamic sealing is realized. In this way, when the sealing surface of the third sealing ring  610  is a spherical surface, the outer circumferential surface  311  of the sealing body  310  is also correspondingly provided as a spherical surface. Similarly, when the sealing surface of the third sealing ring  610  is a cylindrical surface, the outer circumferential surface  311  of the sealing body  310  is also correspondingly provided as a cylindrical surface. 
     Referring to  FIG. 14  and  FIG. 15 , in the present embodiment, it may be noted that the reversing valve  200  has a first operation position and a second operation position which are switchable with each other when the reversing valve is rotated relative to the hand-piece main body  100 . When the reversing valve  200  is located in the first operation position, the first flow channel  110 , the second hole segment  3132 , the first hole segment  3131 , and the transfer cavity are in communication in sequence, an end of the second hole segment  3132  away from the first hole segment  3131  is located in a region surrounded by the second sealing ring  510 , the second hole segment  3132  is in communication with the radial hole segment  1222  of the first flow channel  110  through the second sealing ring  510 , and the outer circumferential surface  311  of the sealing body  310  blocks the second flow channel  120  through the third sealing ring  610 . When the reversing valve  200  is located in the second operation position, the second flow channel  120 , the first hole segment  3131 , the second hole segment  3132 , and the transfer cavity are in communication in sequence, an end of the first hole segment  3131  away from the second hole segment  3132  is located in a region surrounded by the third sealing ring  610 , the first hole segment  3131  is in communication with the second flow channel  120  through the third sealing ring  610 , and the inner end surface  312  of the sealing body  310  blocks the first flow channel  110  through the second sealing ring  510 . 
     It should be understood that, when the reversing valve is located in the first operation position, the head assembly  0001  for a dental contra-angle hand-piece can perform the inner-water-channel water delivery; and when the reversing valve is located in the second operation position, the head assembly  0001  can perform the outer-water-channel water delivery. 
     Optionally, a torque transmission portion  321  is provided on an end surface of the force transmission body  320  away from the sealing body  310 , and the torque transmission portion  321  is configured to be engaged with a force applying tool, so as to make the reversing valve  200  rotate relative to the hand-piece main body  100  under the driving of the force applying tool. The force applying tool may be a wrench, a screw driver, or the like. The torque transmission portion  321  may be a protrusion or a groove, and both the protrusion and the groove may be in a strip-shaped structure. 
     In other embodiments, optionally, at least one first limiting part may be provided on the shell  110 , and at least one second limiting part  322  may be provided on the force transmission body  320 . The first limiting part and the second limiting part  322  may both be protrusions. When the reversing valve  200  is rotated relative to the hand-piece main body  100 , the first limiting part can abut against the second limiting part  322 , thereby limiting a rotation angle of the reversing valve  200 . Specifically, there are two first limiting parts, and one second limiting part  322 . When the second limiting part  322  abuts against one of the first limiting parts, the reversing valve  200  is located in the first operation position, and when the second limiting part  322  abuts against the other one of the first limiting parts, the reversing valve  200  is located in the second operation position. Without doubt, in other embodiments, there may be one first limiting part and two second limiting parts  322 . 
     Alternatively, in other embodiments, the first limiting part can be provided on the fixing seat  120 . Alternatively, one of the first limiting part and the second limiting part  322  is a protrusion, and the other is a groove. 
     Referring to  FIG. 14 , in other embodiments, optionally, a locking ring  800  is mounted on the shell  1100  in a position corresponding to the second mounting hole  111 , and the locking ring  800  may be detachably connected to the shell  1100  by a screw or a snap member. After the locking ring  800  is connected to the shell  1100 , the locking ring  800  abuts against a side of the force transmission body  320  away from the shell  1100 , so as to prevent the reversing valve  200  from disengaging from the hand-piece main body  100  via an orifice of the second mounting hole  111 . 
     In other embodiments, optionally, two confluence channels  313  may be provided on the reversing valve  200 , and when the reversing valve  200  is located in the first operation position, a channel A makes the first flow channel  110  be in communication with the inner water pipe  300 , and the second flow channel  120  is discommunicated from the inner water pipe  300 . When the reversing valve  200  is located in the second operation position, a channel B makes the second flow channel  120  be in communication with the inner water pipe  300 , and the first flow channel  110  is discommunicated from the inner water pipe  300 . 
     The head assembly  0001  for a dental contra-angle hand-piece provided in the present embodiment can be switched between the state of inner-water-channel delivery and the state of outer-water-channel delivery as required, is flexible and convenient to use, and has a wide application range, and a low cost. 
     Referring to  FIG. 9  and  FIG. 16 , the present embodiment further provides a dental contra-angle hand-piece, including a motor  002 , an external pipeline  900 , and the head assembly  0001  for a dental contra-angle hand-piece described in the above embodiments, wherein both the motor  002  and the external pipeline  900  are connected to the hand-piece main body  100 ; the reversing valve  200  of the head assembly  0001  is configured to make the liquid outlet of the motor  002  and the external pipeline  900  alternatively be in communication with the inner water pipe  300 . When the dental contra-angle hand-piece is used, the state of the head assembly can be adjusted as required according to the field situation, so that it can be switched between two states of inner-water-channel water delivery and outer-water-channel water delivery, and is convenient and flexible to operate, and convenient to use. 
     The above-mentioned are merely for preferred embodiments of the present disclosure and not used to limit the present disclosure. For one skilled in the art, various modifications and changes may be made to the present disclosure. Any modifications, equivalent substitutions, improvements and so on, made within the spirit and principle of the present disclosure, should be covered within the scope of protection of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The head assembly for a dental contra-angle hand-piece provided by the present disclosure includes a hand-piece main body, an inner water tube and a reversing valve, wherein the hand-piece main body is provided with a first flow channel and a second flow channel independent from each other, the first flow channel is configured to be in communication with a liquid outlet of a motor, and the second flow channel is configured to be in communication with an external pipeline; the inner water pipe is connected to the hand-piece main body; the reversing valve is provided with a confluence channel; the reversing valve is movably connected to the hand-piece main body, the reversing valve is configured to enable, when moving relative to the hand-piece main body, the first flow channel and the second flow channel to alternatively be in communication with the inner water pipe through the confluence channel. the dental contra-angle hand-piece provided by the present disclosure includes the head assembly mentioned above. The head assembly and the dental contra-angle hand-piece including the same can be switched between the state of inner-water-channel water delivery and the state of outer-water-channel water delivery, so as to satisfy the use requirements of different scenarios, has flexible and convenient use, and is safe and reliable; and the dental contra-angle hand-piece can perform the inner-water-channel water delivery or the outer-water-channel water delivery as needed, have diversified functions, flexible and reliable operation, and high safety.