Crushed bone collection type implant and implant assembly

Abstract

The utility model relates to a crushed bone collection type implant and an implant assembly. The crushed bone collection type implant comprises a main body, a containing hole formed in the coronal end of the main body and used for containing a dental crown prosthesis, and a cutting part formed in the tip end of a vertebral body of the main body, the first thread and the second thread are arranged on the two sides of the main body in the axial direction respectively, the spiral groove is spirally formed in the cutting part along the outer side wall of the main body, the groove is formed in the end of the spiral groove, the spiral direction of the spiral groove is the same as that of the first thread, and the lead angle of the spiral groove is larger than that of the first thread; and the second thread is arranged in the coronal end direction of the groove. Through the arrangement, crushed bones are collected into the groove, so that stable osseointegration is conveniently formed between an alveolar bone and the implant, and the combination speed and firmness of the implant are improved.

Description

Technical Field

[0001] The utility model relates to the field of implants, in particular to a bone crushing collection type implant and an implant component. Background Art

[0002] Oral implant components, also known as dental implants, are surgically implanted into the alveolar bone of an edentulous area. After the surgical wound heals, a prosthetic device is installed over the implant to restore the tooth. With the continuous development of oral implant technology, dental implant technology has become increasingly mature and stable. Dental implant technology involves the placement of highly biocompatible titanium alloy artificial implants into the alveolar bone, followed by fixation and suturing. Because of the strong chewing force they provide, it has become the preferred treatment option for patients with edentulous disease.

[0003] Dental implants in the prior art require a physiological or pathological remodeling process (such as peri-implantitis) for bone integration, and are easily affected by changes in the bone level of the implant neck. Early bone loss, especially loss of the labial bone wall, is a major risk factor for peri-implantitis. Soft tissue loss and corresponding aesthetic problems are also easily associated with bone loss. Furthermore, during the implantation process of existing implants, bone chips removed by cutting are washed away, which easily leads to waste of autologous bone, resulting in insufficient bone integration and slow integration speed in the later stage. Therefore, there is a need to improve existing oral implant components. Utility Model Content

[0004] To this end, the technical problem to be solved by the present invention is to overcome the problem in the prior art that during the implantation process, the bone chips cut off are washed away, which easily leads to waste of autologous bone, insufficient bone bonding strength and slow bonding speed in the later stage, thereby providing a bone chip collection implant.

[0005] In order to solve the above technical problems, the present invention provides a bone fragment collection implant, comprising:

[0006] Implant structure, comprising: a main body, a receiving hole provided at the coronal end of the main body for accommodating a crown prosthesis, and a cutting portion provided at the tip of the vertebral body of the main body;

[0007] A collecting groove mechanism includes: a first thread and a second thread respectively arranged on both sides of the main body in the axial direction, a spiral groove spirally opened from the cutting portion along the outer wall of the main body, and a groove opened at the end of the spiral groove, the spiral groove and the first thread have the same spiral direction, the thread lead angle of the spiral groove is greater than the thread lead angle of the first thread, the second thread is arranged on the side of the groove close to the coronal end direction, the outer diameter of the groove is not greater than the outer diameter of the adjacent second thread, and the spiral groove and the groove are connected through the first thread groove between adjacent first threads.

[0008] In one embodiment of the present invention, the first thread and the second thread are transitionally connected to spirally surround the outer wall of the vertebral body, the first thread is opened on the tip side of the main body, the second thread is opened on the coronal side of the main body, and the groove is opened on the first thread adjacent to the second thread.

[0009] In one embodiment of the present invention, the first thread and the second thread are right-hand threads, the spiral groove is opened on the first thread along its spiral line direction, the first thread is provided with a groove body for the spiral groove to extend to the outer wall of the vertebral body, and the bottom diameter of the groove body is smaller than the bottom diameter of the first thread groove.

[0010] In one embodiment of the present invention, the first thread groove is further provided with a guide member, which is arranged between adjacent first threads and on the right side of the line connecting adjacent groove bodies. The guide member includes a guide portion and a guide groove, and a first inclined surface and a second inclined surface are respectively provided on both sides of the guide portion. The angle of the first inclined surface is not less than the angle of the adjacent groove body side wall, and the first inclined surface and the adjacent groove body side wall have a smooth transition. The second inclined surface is a concave arc surface, and the guide groove is opened between adjacent groove bodies and parallel to the bottom of the spiral groove.

[0011] In one embodiment of the present invention, the distance between the end of the spiral groove and the groove is 0.5 mm-1 mm, and the depth of the groove is 0.2 mm-0.4 mm.

[0012] In one embodiment of the present invention, the taper of the main body is 5°-25°, the pitch of the first thread is greater than the pitch of the second thread, and a plurality of through holes are axially penetrated through the first thread adjacent to the second thread.

[0013] In one embodiment of the present invention, a groove body is formed on the first thread, and the spiral groove body and the first thread groove between adjacent groove bodies constitute the angle of the left side wall of the groove body is greater than the angle of the right side wall.

[0014] In one embodiment of the present invention, the diameter of the bottom wall of the trough body is smaller than the outer diameter of the cone at the corresponding bottom wall position, the outer diameter of the first thread of the cutting portion gradually increases toward the coronal end, the outer diameters of the remaining first threads are the same, the height of the first thread gradually decreases toward the coronal end, and the height of the side wall of the trough body outside the cutting portion gradually decreases toward the coronal end.

[0015] In one embodiment of the present invention, a receiving groove is provided on the side wall of the second thread close to the groove, the side wall of the receiving groove close to the tightening direction is a first wall body, and the side wall of the receiving groove close to the loosening direction is a second wall body, and the opening angle of the first wall body is greater than that of the second wall body.

[0016] The utility model also discloses an implant assembly, comprising the above-mentioned bone fragment collection type implant and a dental crown prosthesis, wherein the dental crown prosthesis is threadedly connected to the main body.

[0017] The above technical solution of the utility model has the following advantages compared with the prior art:

[0018] The invention provides a bone-crushing collecting implant according to the present invention, wherein the spiral groove is arranged so that its spiral direction is the same as the first thread and the thread lead angle is greater than the first thread, so that the bone crushed by the cutting part can be collected in the groove along the spiral groove, the groove is opened at the end of the spiral groove, and its outer diameter is not greater than the outer diameter of the adjacent second thread, that is, the outer diameter of a circle of the groove opening is not greater than the outer diameter of the adjacent second thread, and the adjacent second thread is above the groove at the first thread, which can limit and block the bone chips in the groove, and the spiral groove and the groove are connected through the first thread groove between the adjacent first threads, so that the bone crushing can enter the groove smoothly, avoiding the bone crushing entering the second thread groove and affecting the closing of the implant and the alveolar bone. The second thread is arranged in the coronal end direction of the groove, which fits tightly with the alveolar bone, so that the pre-grooved seal in the implant and the alveolar bone is locked, facilitating the formation of a stable soft tissue closure, reducing the implant infection rate, and collecting the bone crushing in the groove, facilitating the formation of a stable bone connection between the alveolar bone and the implant, thereby improving the bonding speed and firmness of the implant. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the content of the utility model easier to understand, the utility model is further described in detail below based on the specific embodiments of the utility model and in conjunction with the accompanying drawings, wherein

[0020] Figure 1 It is a stereoscopic diagram of the implant of the utility model;

[0021] Figure 2 It is a structural diagram of the tank body of the utility model;

[0022] Figure 3 It is a structural schematic diagram of another tank body of the utility model;

[0023] Figure 4 It is a top view of the implant of the utility model;

[0024] Figure 5 It is a cross-sectional view of the implant of the utility model;

[0025] Figure 6 This utility model Figure 2 Magnified image in .

[0026] Explanation of the reference numerals in the specification: 1. Main body; 2. First thread; 3. Second thread; 4. Groove body; 5. Guide groove; 6. Groove; 7. Accommodating groove; 8. Cutting portion; 9. Through hole; 10. Accommodating hole; 11. Guide member; 12. First inclined surface; 13. Second inclined surface; 14. First thread groove; 15. Second thread groove. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention. Example

[0028] Reference Figure 1-6 As shown, the utility model is a bone-collecting implant, comprising:

[0029] Implant structure, comprising: a main body 1, provided in the coronal end of the main body 1 for accommodating a crown prosthesis receiving hole 10, provided in the main body 1 of the vertebral tip cutting portion 8;

[0030] The collecting groove mechanism includes: a first thread 2 and a second thread 3 respectively arranged on both sides of the main body 1 along the axial direction, a spiral groove spirally opened from the cutting portion 8 along the outer wall of the main body 1, and a groove 6 opened at the end of the spiral groove. The spiral groove and the first thread 2 have the same spiral direction and the thread lead angle is greater than the first thread 2. The second thread 3 is arranged in the coronal end direction of the groove 6. The outer diameter of the groove 6 is not greater than the outer diameter of the adjacent second thread 3. The spiral groove and the groove 6 are connected through the first thread groove 14 between the adjacent first threads 2.

[0031] The utility model discloses a bone-collecting implant, wherein the main body 1 is a conical structure and is used to be implanted in the alveolar bone. A receiving hole 10 is provided at the coronal end of the main body 1 for accommodating a crown prosthesis so that the prosthesis can be fixed on the implant. A cutting portion 8 is provided at the vertebral tip of the main body 1, and the cutting portion 8 is provided with a cutting edge. During the implantation of the implant into the alveolar bone, the cutting portion 8 can cut bone tissue and form a cavity matching the implant in the bone tissue. The first thread 2 and the second thread 3 are respectively arranged on both sides of the main body 1 along the axial direction, which is conducive to the stable implantation of the implant in the bone tissue. The spiral groove is spirally opened from the cutting portion 8 along the outer wall of the main body 1. The spiral groove is provided so that its spiral direction is the same as the first thread 2 and the thread lead angle is greater than the first thread 2, so that the bone fragments cut by the cutting portion 8 can be collected into the groove 6 along the spiral groove. The groove 6 is opened At the end of the spiral groove, its outer diameter is not greater than the outer diameter of the adjacent second thread 3, that is, the outer diameter of a circle of the groove 6 is not greater than the outer diameter of the adjacent second thread 3. The adjacent second thread 3 is above the groove 6 at the first thread 2, and can limit and block the bone chips in the groove 6. The spiral groove and the groove 6 are connected through the first thread groove 14 between the adjacent first threads 2, so that the broken bone can enter the groove 6 smoothly, and the bone chips are prevented from entering the second thread groove 15 and affecting the closure of the implant and the alveolar bone. The second thread 3 is arranged in the coronal end direction of the groove 6, and it fits tightly with the alveolar bone, so that the pre-grooved space in the implant and the alveolar bone is tightly sealed and locked, which is convenient for forming a stable soft tissue closure, reducing the infection rate of the implant, and collecting the broken bone into the groove 6, which is convenient for forming a stable bone bond between the alveolar bone and the implant, and improving the bonding speed and firmness of the implant.

[0032] See also Figure 2 、 Figure 6As shown, the first thread 2 and the second thread 3 are transitionally connected to spirally surround the outer wall of the vertebral body. The first thread 2 is opened on the tip side of the main body 1, and the second thread 3 is opened on the coronal side of the main body 1. The groove 6 is opened on the first thread 2 adjacent to the second thread 3. The first thread 2 is opened on the tip side of the main body 1, close to the cutting part 8; the second thread 3 is opened on the coronal side of the main body 1, away from the cutting part 8, so that during the implantation process, the first thread 2 first contacts the bone tissue and provides initial stability, and then the second thread 3 gradually occludes the bone tissue to further enhance the stability of the implant. The groove 6 is located near the junction of the first thread 2 and the second thread 3, so that the groove 6 can better collect the bone fragments guided by the spiral groove. At the same time, the groove 6 is adjacent to the second thread 3, so that the collected bone fragments can contact the bone tissue occluded by the second thread 3, promote local bone integration, and enable the patient's own bone chips and related tissues to form healing more safely and reliably in the groove 6, and the healed bone augmentation Embedded in the groove 6, a lock is formed between the implant and the alveolar bone to prevent the implant from loosening. In this embodiment, the total length of the implant is 12 mm, of which the length of the first thread 2 area is 9 mm, the length of the second thread 3 area is 3 mm, the pitch of the first thread 2 is 1.2 mm, the pitch of the second thread 3 is 0.8 mm, the axial length of the groove 6 is 2 mm, the circumferential angle is 45° and it is a circular arc surface, and the radial depth is 0.4 mm. During the implant surgery, the doctor first uses a drill to pre-groove the alveolar bone to prepare a bone socket, and then implants the implant into the bone socket. The cutting part 8 cuts the bone tissue, and the broken bone enters the groove 6 along the spiral groove. After 8 weeks, the implant is integrated with the bone tissue to obtain a stable secondary retention. The first thread 2 and the second thread 3 are transitionally connected and spirally wrapped around the surface of the implant to form a continuous thread, providing a stable force that gradually increases from the tip to the coronal end. The groove 6 is opened near the junction of the first thread 2 and the second thread 3, taking into account the dual functions of collecting broken bone and promoting local bone integration.

[0033] Continue to see Figure 2 、 Figure 6As shown, the first thread groove 14 is further provided with a guide member 11, which is arranged between adjacent first threads 2, and the guide member 11 is arranged on the right side of the line connecting the adjacent groove bodies 4. The guide member 11 includes a guide portion and a guide groove 5, and a first inclined surface 12 and a second inclined surface 13 are respectively provided on both sides of the guide portion. The angle of the first inclined surface 12 is not less than the angle of the side wall of the adjacent groove body 4, and is equal in this embodiment. The first inclined surface 12 and the adjacent side wall of the groove body 4 have a smooth transition, and the second inclined surface is a concave arc surface. The guide groove 5 is opened between adjacent groove bodies 4 and is parallel to the bottom of the spiral groove. The guide member 11 is used to guide the broken bones to enter the spiral groove and the groove 6 more smoothly. The guide 11 is located between the adjacent first threads 2 and is offset from the line connecting the adjacent groove bodies 4. On the right side, since the thread and the second thread 3 are right-hand threads, the implant will be tightened in the clockwise direction, that is, bone chips will be relatively transmitted in the counterclockwise direction along the spiral groove, and the bone chips will have a tendency to stick to the right. Through the provided guide 11, the first bevel 12 and the guide groove 5 cooperate to guide and transmit the bone chips of the first thread 2, avoiding bone chips from re-entering the first thread groove 14 from the groove body 4 for circulation. The groove body 4 refers to the groove between two adjacent thread peaks on the spiral groove. The guide 11 has an unequal cross-section, and a first bevel 12 and a second bevel 13 are respectively provided on both sides. The first bevel 12 has a smooth transition with the adjacent side wall of the groove body 4 without protrusions or edges, which can avoid the bone fragments from being blocked or accumulated during movement. The second bevel 13 is a concave arc surface, which reduces the impact on the tightening and loosening of the implant.

[0034] See also Figure 1-Figure 4 As shown, the distance between the end of the spiral groove and the groove 6 is 0.5mm-1mm, the depth of the groove 6 is 0.2mm-0.4mm, and a certain distance is set between the end of the spiral groove and the groove 6. The spacing is calculated as follows: a first vertical line is drawn upward from the right side wall of the spiral groove end, and a second vertical line is drawn on the left side wall of the groove 6. The vertical distance between the second vertical line at the left end point of the groove 6 and the first vertical line is the spacing. The spacing ranges from 0.5mm to 1mm, and is 0.6mm in this embodiment, so that bone chips can be transmitted in the top first thread 2 and enter the groove 6 as the rotation deflects. If the spacing is too small, the first thread groove 14 cannot be filled with enough bone chips, affecting the later autologous bone healing. If the spacing is too large, it may affect the smoothness of the bone fragments entering the groove 6 from the spiral groove. Therefore, controlling the spacing within the range of 0.5mm to 1mm can not only ensure the structural strength of the implant, but also achieve effective collection of bone fragments.

[0035] See also Figure 1-Figure 3As shown, the taper of the main body 1 is 5°-25°. The pitch of the first thread 2 is greater than the pitch of the second thread 3. Multiple through-holes 9 are axially extending through the first thread 2 adjacent to the second thread 3. The inner diameter of the through-holes 9 on the input side is larger than the inner diameter on the output side, facilitating the passage of bone chips through the first thread 2 and into the thread groove between the first and second threads 2 and 3, as well as into the groove 6 and receiving groove 7. In this embodiment, the taper angle is 15°. The tapered main body 1 contributes to the initial stability of the implant. During implantation, the tapered main body 1 forms a matching conical bone cavity within the bone tissue, ensuring closer contact between the implant and the bone tissue and improving initial retention. Furthermore, the tapered design enhances the implant's anti-rotational ability. Because the frictional contact area between the tapered surface and the bone tissue is greater than that of the cylindrical surface, especially the upper section, the tapered main body 1 can better resist rotational and lateral forces, maintaining implant stability. The first thread 2, located on the apical side of the implant, primarily serves as initial retention; the second thread 3, located on the coronal side, primarily serves to maintain long-term stability. The first thread 2 adopts a larger pitch to obtain sufficient retention force with fewer thread turns, reducing the stress on bone tissue. The second thread 3 adopts a smaller pitch to disperse the chewing force with more thread turns to maintain the long-term stability of the implant.

[0036] Continue to see Figure 1-Figure 3 As shown, the first thread 2 and the second thread 3 are right-hand threads, and the spiral groove is opened on the first thread 2 along the direction of its spiral line. The first thread 2 is provided with a groove body 4 for the spiral groove to extend to the outer wall of the vertebral body. The right-hand thread conforms to the doctor's operating habits and is convenient for the implantation and removal of the implant. The right-hand thread matches the rotation direction of most implant tools, which is conducive to applying torque and controlling the implantation depth. The spiral groove is opened on the first thread 2 along the direction of its spiral line and extends to the outer wall of the main body 1. The groove body 4 is provided on the first thread 2 for the spiral groove to pass through and extend, so that the spiral groove spirals along the outer wall of the main body 1 until it reaches the groove 6.

[0037] A groove body 4 is provided on the first thread 2, and the spiral groove groove body 4 and the first thread groove 14 between the adjacent groove bodies 4 are formed. The angle of the left side wall of the groove body 4 is greater than the angle of the right side wall. The spiral groove is composed of the groove body 4 provided on the first thread 2 and the first thread groove 14 between the adjacent groove bodies 4, wherein the groove body 4 refers to the recessed part in the spiral groove, and the first thread groove 14 refers to the part of the first thread 2 not occupied by the groove body 4. While ensuring the integrity of the first thread 2, effective collection of broken bones is achieved. The angle of the left side wall of the groove body 4 is greater than that of the right side, so that there is a larger space between the right side wall of the groove body 4 and the pre-groove of the alveolar bone, which is conducive to the transmission of bone chips along the spiral groove. At the same time, the end of the left side wall can scrape off the adhesion tissue and bone chips in the pre-groove, making the inner wall of the pre-groove smooth, which is conducive to bone growth.

[0038] The diameter of the bottom wall of the groove body 4 is smaller than the outer diameter of the vertebral body at the corresponding bottom wall position, which increases the cross-sectional area for the flow of bone chips. The outer diameter of the first thread 2 of the cutting portion 8 gradually increases toward the coronal end, and the outer diameters of the remaining first threads 2 are the same. The height of the first thread 2 gradually decreases toward the coronal end, and the height of the side wall of the groove body 4 outside the cutting portion 8 gradually decreases toward the coronal end, and the reduction amplitude is the same as the widening amplitude of the vertebral body, so that the outer diameter of the vertebral body thread outside the cutting portion 8 is the same.

[0039] See also Figure 1 As shown, a receiving groove 7 is provided on the side wall of the second thread 3 near the groove 6, and the side wall of the receiving groove 7 near the tightening direction is a first wall body, and the side wall of the receiving groove 7 near the loosening direction is a second wall body. The opening angle of the first wall body is greater than that of the second wall body, so that the first wall body can provide a larger contact area and bite force, thereby enhancing the friction locking effect between the implant and the bone tissue and improving the initial stability. In some embodiments, the surface of the receiving groove 7 is a porous tissue, and antibacterial and / or anti-inflammatory drugs are contained in the porous tissue to improve the antibacterial and anti-inflammatory effects of the implant and prevent infection. In some embodiments, the number of spiral grooves is multiple, and the number of spiral grooves can be optionally one, two, three or four. In some embodiments, the groove 6 can partially pass through the end of the first thread 2 to facilitate the passage of bone blood and other tissues from the end of the first thread 2.

[0040] This embodiment also discloses an implant assembly, including the above-mentioned bone fragment collection implant and a dental crown prosthesis, wherein the dental crown prosthesis is threadedly connected to the main body 1.

[0041] The implant assembly described in this embodiment is installed by implanting the implant into the pre-opened alveolar bone and then thread-locking the body body and the receiving hole 10, thereby completing the installation of the implant.

[0042] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this utility model.

Claims

1. A bone fragment collection implant, characterized in that: include: An implant structure comprising: a main body, the main body comprising a coronal end and a vertebral tip, the coronal end having a receiving hole for accommodating a crown prosthesis, the vertebral tip having a cutting portion; A collecting groove mechanism, comprising: a first thread and a second thread respectively arranged on both sides of the main body along the axial direction, a spiral groove spirally opened from the cutting portion along the outer side wall of the main body, and a groove opened at the end of the spiral groove, the spiral direction of the spiral groove and the first thread is the same, the thread lead angle of the spiral groove is greater than the thread lead angle of the first thread, the second thread is arranged on the side of the groove close to the coronal end direction, the outer diameter of the groove is not greater than the outer diameter of the adjacent second thread, and the spiral groove and the groove are connected through the first thread groove between the adjacent first threads.

2. The bone fragment collection implant according to claim 1, characterized in that: The first thread and the second thread are transitionally connected to spirally surround the outer wall of the vertebral body, the first thread is opened on the tip side of the body, the second thread is opened on the coronal side of the body, and the groove is opened on the first thread adjacent to the second thread.

3. The bone-collecting implant according to claim 1, characterized in that: The first thread and the second thread are right-hand threads, the spiral groove is opened on the first thread along its spiral line direction, the first thread is opened with a groove body for the spiral groove to extend to the outer wall of the vertebral body, and the bottom diameter of the groove body is smaller than the bottom diameter of the first thread groove.

4. The bone fragment collection implant according to claim 3, characterized in that: The first thread groove is also provided with a guide member, which is arranged between adjacent first threads and on the right side of the line connecting adjacent groove bodies. The guide member includes a guide portion and a guide groove. The guide portion has a first inclined surface and a second inclined surface on both sides thereof. The angle of the first inclined surface is not less than the angle of the adjacent groove body side wall. The first inclined surface and the adjacent groove body side wall have a smooth transition. The second inclined surface is a concave arc surface. The guide groove is opened between adjacent groove bodies and parallel to the bottom of the spiral groove.

5. The bone-collecting implant according to claim 2, characterized in that: The distance between the end of the spiral groove and the groove is 0.5mm-1mm, and the depth of the groove is 0.2mm-0.4mm.

6. The bone-collecting implant according to claim 1, characterized in that: The taper of the main body is 5°-25°, the pitch of the first thread is greater than the pitch of the second thread, and a plurality of through holes are formed in the axial direction through the first thread adjacent to the second thread.

7. The bone fragment collection implant according to claim 1 or 3, characterized in that: A groove body is formed on the first thread, and the spiral groove body and the first thread groove between adjacent groove bodies constitute the angle of the left side wall of the groove body is greater than the angle of the right side wall.

8. The bone fragment collection implant according to claim 7, characterized in that: The diameter of the bottom wall of the groove body is smaller than the outer diameter of the cone at the corresponding bottom wall position, the outer diameter of the first thread of the cutting portion gradually increases toward the coronal end, the outer diameters of the remaining first threads are the same, the height of the first thread gradually decreases toward the coronal end, and the height of the side wall of the groove body outside the cutting portion gradually decreases toward the coronal end.

9. The bone-collecting implant according to claim 1, characterized in that: The side wall of the second thread close to the groove is provided with a receiving groove, the side wall of the receiving groove close to the tightening direction is the first wall body, the side wall of the receiving groove close to the loosening direction is the second wall body, and the opening angle of the first wall body is greater than that of the second wall body.

10. An implant assembly, characterized in that: It comprises a bone-collecting implant according to any one of claims 1 to 9, and also comprises a crown prosthesis, wherein the crown prosthesis is threadedly connected to the main body.

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