Oral implant structure capable of being instantly planted in rear tooth area

Abstract

The invention discloses a structure for immediate implantation of an oral implant in a posterior tooth area, which comprises an implant connecting part, one end of which is recessed inwards to form a connecting area for fixing an abutment; the transition part is connected with the other end of the implant connecting part, and the transition part extends from the end face of the implant to the direction gradually deviating from the axis of the implant connecting part to form an expansion structure; at least two pyramid pieces are arranged at the tail end of the expansion structure, are rotationally and symmetrically distributed about the geometric center point of the tail end of the expansion structure, and are used for penetrating and being fixed in the bone fossa. Through the transition part below the connecting part of the implant and the plurality of pyramid pieces arranged at the bottom end, the implant structure can be inserted into a denture bone tissue for retention on the premise that a traditional bone drill is not used for preparing a hole in an interroot bone septum, so that the initial stability is effectively obtained.

Description

Technical Field

[0001] This invention belongs to the field of dental implantology, and more specifically, relates to a dental implant structure for immediate implantation in the posterior tooth region. Background Technology

[0002] Currently, immediate implantation in the posterior region has become one of the commonly used techniques in clinical dental implantology. It refers to the immediate placement of implants while extracting posterior teeth that cannot be saved. The advantages of immediate implantation include: fewer surgical procedures, shorter treatment time, and the ability to counteract bone resorption in the extraction socket, making it popular with both patients and dentists. However, immediate implantation in the posterior region is a complex surgical procedure. The biggest challenge in implant placement is how to fully utilize the interperitoneal septum (the bone between the tooth roots) within the extraction socket to provide good initial stability for the implant.

[0003] Clinical studies have confirmed that initial stability is a key factor for the success of immediate implantation. Poor stability often leads to the implant failing to integrate with the bone tissue, resulting in treatment failure. Therefore, achieving good initial stability is the most important treatment goal for immediate implantation. From an anatomical perspective, posterior teeth are mostly multi-rooted teeth with irregularly shaped extraction sockets, and their size is often larger than the diameter of the implant. In most cases, the interroot septum between the tooth roots can be used to provide stability for the immediate implant. This involves preparing a hole in the interroot septum with a bone drill, screwing the implant in to contact the interroot septum, thereby achieving initial stability.

[0004] However, due to limitations imposed by anatomical factors such as root height, root convergence, inferior alveolar nerve canal, and the location of the maxillary sinus floor, as well as the influence of factors such as bone resorption caused by periapical inflammation, the height and width of the interosseous bone septum in the extraction socket of the posterior teeth are often limited. If a traditional bone drill is used to prepare the implant socket during immediate implantation, the bone septum is often lost due to bone removal, making it difficult for the immediate implant to achieve initial stability and increasing the risk of implant bone healing failure.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an immediate implant structure for posterior teeth. Through the transition part below the implant connection and the multiple pyramidal pieces set at the bottom end, the implant structure can be embedded into the bone tissue of the tooth socket for fixation without the use of traditional bone drills to prepare holes in the interosseous bone septum, thus effectively achieving initial stability.

[0007] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is to provide an immediate implant structure for posterior teeth, including an implant connection part, one end of which is recessed inward to form a connection area for fixing the abutment; The transition section connects to the other end of the implant connection section. The transition section extends from the end face of the implant in a direction that gradually deviates from the axis of the implant connection section, forming an expanded structure. The end of the expansion structure is provided with at least two pyramidal members, which are rotationally symmetrical about the geometric center point of the end of the expansion structure, for insertion and fixation in the bone socket.

[0008] Furthermore, the connection between the transition section and the implant connection section is smooth.

[0009] Furthermore, the tendency of the transition portion to extend away from the axis of the implant connection portion first increases and then decreases, forming an expanded structure with a curved outer surface.

[0010] Furthermore, the center of each pyramid is located on the vertical line from the geometric center of the base of the pyramid, and its center is positioned near the edge of the transition end face.

[0011] Furthermore, the orthographic projection of the pyramidal component onto the end face of the transition section to which it is connected is entirely within the end face of the transition section.

[0012] Furthermore, the end face of the pyramidal component and the transition section are connected by threads.

[0013] Furthermore, the end face of the transition section is provided with multiple threaded holes arranged in an array around its geometric center. Each threaded hole is threaded with an adjusting post, and an adjusting shim is threaded through the adjusting post. The pyramidal part is threadedly connected to the adjusting post to be fixed to the end face of the fixing section.

[0014] Furthermore, the portion of the transition section near the pyramidal component is hollow inside, and multiple micro-side holes are provided through the outer periphery of the transition section to connect the hollow part of the transition section with the outside.

[0015] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: (1) The present invention, through the transition part below the implant connection and the multiple pyramidal parts set at the bottom end, enables the implant structure to be embedded into the tooth socket bone tissue for fixation without using a traditional bone drill to prepare a hole in the interosseous bone septum, thus effectively achieving initial stability.

[0016] (2) By setting the transition part of the implant structure and the implant connection part to smoothly transition at the connection, when subjected to vertical / lateral biting force, the force will be transmitted from the implant connection part to the expansion structure corresponding to the transition part. After the smooth transition design, there will be no microcracks and fatigue after repeated stress.

[0017] (3) The present invention limits the extension of the transition part away from the axis of the implant connection part to increase and then decrease, forming an expansion structure with a curved outer surface. It can gradually fit the bone wall shape of the root of the extraction socket from the top to the bottom of the expansion structure, which is widened and then gradually narrowed. This achieves no obvious gaps or local overpressure in the entire expansion structure, greatly reduces the amount of bone powder filling, and reduces the risk of postoperative bone powder displacement and infection.

[0018] (4) The present invention connects the pyramidal component to the end face of the transition part through the adjustment column, and one or more adjustment shims are provided on the adjustment column. According to the specific adjustment angle, the corresponding number of adjustment shims are placed on the adjustment column to realize the small angle adjustment of the pyramidal component, so that it can be inserted into the bone septum position more stably and accurately.

[0019] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0020] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 This is a front view of the implant structure of the present invention; Figure 2 This is a bottom view of the implant structure of the present invention; Figure 3 This is a partial cross-sectional view of the implant structure of the present invention; Figure 4 This is a cross-sectional view of the implant structure of the present invention; Figure 5 This is a cross-sectional view of the transition section of the present invention; Figure 6 This is a structural schematic diagram showing the connection relationship between the pyramidal component and the adjusting column of the present invention; Figure 7 This is a schematic diagram of the connection relationship between the adjusting column and the screw of the present invention.

[0021] In the picture: 1. Implant connection area; 11. Screw area; 12. Anti-rotation area; 13. Taper area; 2. Transition section; 21. Hollow cavity; 22. Micro-side hole; 3. Pyramidal component; 31. Screw; 4. Adjusting column; 41. Adjusting shim.

[0022] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0024] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] like Figures 1 to 7 As shown, the present invention provides an immediate implantation dental implant structure for the posterior tooth region, comprising, The implant connection part 1 has one end recessed inward to form a connection area for fixing the abutment; The transition section 2 is connected to the other end of the implant connection section 1. The transition section 2 extends from the end face of the implant in a direction that gradually deviates from the axis of the implant connection section 1, forming an expanded structure. The end of the expansion structure is provided with at least two pyramidal members 3, which are rotationally symmetrical about the geometric center point of the end of the expansion structure, for inserting into and fixing in the bone socket.

[0027] In this invention, the implant connection part 1 is cylindrical in shape and has a certain length. The upper end of the implant is concave to form an abutment for installing and fixing a temporary or permanent crown. Specifically, the connection area of ​​the implant includes a screw area 11, an anti-rotation area 12, and a tapered area 13, which are sequentially connected from the bottom of the concave area. The screw area 11 has an internal thread structure formed by the inner circumferential wall of the concave area. At least one end of the abutment has an external thread that matches the internal thread structure of the screw area 11, and the connection is quickly achieved through thread tightening. The internal thread is a triangular thread with a thread height of 2-2.5 mm, a diameter of 1.6-1.8 mm, a tooth height of 0.3-0.4 mm, and a pitch of 0.6-0.8 mm. Preferably, an elastic washer groove is machined at the bottom of the spiral area, and a nickel-titanium alloy elastic washer is embedded therein. After the washer is tightened on the external thread of the abutment, it generates continuous elastic pressure, which counteracts the thread loosening torque caused by chewing vibration, making the connection between the abutment and the spiral area more secure and reliable.

[0028] In addition, the anti-rotation zone 12 adopts a hexagonal or octagonal through hole, which is connected to the spiral zone. The anti-rotation zone 12 is 1-1.5mm high. By limiting the interaction between the surfaces, the abutment can be prevented from rotating around the axis of the implant structure, effectively ensuring that the abutment will not move axially when subjected to circumferential biting force.

[0029] Finally, the tapered section is located at the top of the implant connection area, with a specific taper design of 6-12° and a height of 2-2.5mm. The tapered surface of this section helps to position and guide the abutment into the bottom of the connection area, ensuring concentric positioning of the implant structure and abutment. This effectively solves problems such as "high occlusal point" and "uneven gingival compression" caused by positioning deviations between the implant structure and abutment. When the implant structure is subjected to vertical occlusal force, the tapered surface of the section can distribute the force along the "cone surface normal direction" to the implant structure, rather than concentrating it in the spiral section, thus avoiding "thread fatigue damage" caused by long-term axial force on the spiral section.

[0030] A transition section 2 is connected to the bottom of the implant connector 1. This transition section 2 is a cylinder, with its longitudinal section based on the central axis of the implant connector 1. The contours on both sides gradually extend downwards away from the central axis, forming an expansion structure resembling a frustum. The smooth curved surface of this expansion structure can form surface contact with the bone wall, dispersing local stress over a wider area. This aligns with the physiological characteristics of moderate stress promoting osseointegration and excessive stress leading to bone resorption. Simultaneously, at least two pyramidal elements 3 are provided at the bottom of this expansion structure. Due to the multi-root structure of posterior teeth, the extraction socket is separated by 1-2 interroot septa (1 for double roots, 2 for triple roots), forming "2-3 independent depressions" (corresponding to the periroot space of the original tooth root). By setting two or three pyramidal elements 3, these depressions can enter the prepared bone socket. Furthermore, the expansion structure and the overall occlusion of the socket fully utilize the bone tissue of the interroot septa, achieving good initial stability. This eliminates the need for expensive implant machines and various types of implant bone drills, simplifying the implant preparation process.

[0031] It should be noted that during the application of the implant structure, in order to ensure that the pyramidal component 3 can effectively and accurately correspond to the interosseous septum, an additional bone preparation tool is prepared. The head of the bone preparation tool is also composed of a triangular or quadrangular pyramid, and its shape and size are exactly the same as the pyramidal component of the implant fixation part. The bone preparation tool inserts its sharp cutting head into the interosseous septum to prepare the bone.

[0032] The specific procedure for using the aforementioned implant structure is as follows: The affected tooth is extracted, the soft tissue is carefully cleaned, and the interosseous bone septum is exposed. The bone preparation instrument is placed in the extraction socket, aligned with the interosseous bone septum, and its angle is adjusted to match the ideal implant angle. A resin-bonded mallet is used to gently tap the handle of the bone preparation instrument, causing the cone-shaped tip of the instrument to penetrate the bone tissue, thus completing the preparation of the interosseous bone septum. Simultaneously, an implant applicator, a temporary carrier for the implant structure, is provided. The implant structure is placed in the carrier section of the applicator and transferred into the oral cavity. The handle of the applicator is then gently tapped again with a resin-bonded mallet to position the implant structure.

[0033] In summary, by using the transition section 2 below the implant connector 1 and the multiple pyramidal pieces 3 at the bottom, the implant can be inserted into the bone socket prepared by the bone preparation tool, thereby achieving immediate implantation stability. Without using a traditional bone drill to prepare a hole in the interosseous bone septum, the implant structure effectively overcomes the problems of bone loss in the interosseous bone septum caused by traditional bone drill preparation and the inability of the implant to achieve initial stability, thus naturally expanding the adaptability of immediate implantation in the posterior tooth region.

[0034] Furthermore, the connection between the transition section 2 and the implant connection section 1 is smooth.

[0035] In this invention, the diameter of the transition portion 2 at the connection point with the implant connection portion 1 is nearly the same, and there is no step-like transition. Therefore, when the implant structure is subjected to vertical / lateral biting forces, the force will be transmitted from the implant connection portion 1 to the expansion structure corresponding to the transition portion 2. If the implant connection portion 1 and the transition portion 2 are at a right angle, the force will be transmitted to this point, forming a stress concentration point due to the abrupt change in shape. Long-term use can easily lead to microcracks in the connection portion, and fatigue after repeated stress.

[0036] Furthermore, the tendency of the transition portion 2 to extend away from the axis of the implant connection portion 1 first increases and then decreases, forming an expanded structure with a curved outer surface.

[0037] In this invention, by limiting the extension trend of the expansion structure, on the one hand, it avoids a linear expansion of the expansion structure away from the trend, which could easily lead to the middle of the implant fitting the wide part of the extraction socket, but with a gap appearing at the bottom due to the slight narrowing of the extraction socket; on the other hand, if the expansion structure has a step-like abrupt decrease away from the trend, it may put pressure on the bone wall formation point at the abrupt change. In this embodiment, the expansion structure is a gentle curved surface that first increases and then gradually decreases, which can gradually fit the bone wall morphology of the extraction socket from the top of the expansion structure (near the implant connection part 1) to the bottom (near the pyramidal part 3), which has a large widening range and gradually narrows. This achieves no obvious gaps and no local overpressure throughout the expansion structure, greatly reducing the amount of bone powder filling (in most cases, no bone powder is needed), and reducing the risk of postoperative bone powder displacement and infection.

[0038] In addition, the expansion structure extends downward from the implant connection 1, and its outer diameter increases continuously. On the one hand, it provides an assembly position for the pyramidal part 3; on the other hand, it increases the contact area with the bone wall of the extraction socket, which helps to improve the initial stability of the implant structure; and from a mechanical point of view, when the implant is subjected to the same occlusal force, the stress in the end area will be dispersed, which is beneficial to the long-term stability of the bone tissue.

[0039] Furthermore, the center of each pyramid 3 is located on the vertical line from the geometric center of the bottom surface of the pyramid 3, and its center is positioned near the edge of the end face of the transition section 2.

[0040] In this invention, the center of the pyramid 3 is eccentrically positioned relative to the geometric center of its base, thus making the pyramid 3 a non-regular pyramid. Specifically, the inclination of the pyramid surface closer to the geometric center is greater than that of the other pyramid surfaces. Consequently, the opposing pyramid surfaces of the two pyramids 3 gradually open, forming a figure-eight shape, which then conforms to the bone septum after tooth extraction.

[0041] When the pyramidal component 3 is perpendicular to the bottom surface of the implant end (i.e., without deviation), it can only penetrate the central area of ​​the septum, while the outward expansion depressions on both sides of the septum cannot be utilized, resulting in wasted retention force. However, in the embodiment of the present invention, the pyramidal component 3 with a figure-eight inclination can expand outward along the bifurcation direction of the septum. For example, the two pyramidal components 3 of the extraction socket of a double molar are tilted to both sides, accurately penetrating the depression areas on both sides of the septum. The three pyramidal components 3 of the three molars are tilted in a Y-shape, respectively aligning with the three depressions, realizing the full utilization of the septum area and avoiding bone damage caused by the pyramid penetrating the alveolar bone wall (ineffective area).

[0042] In addition, in clinical practice, the interosseous septum often has a natural tilt of 5-10°. For example, the maxillary molar septum tilts towards the buccal side. The vertical pyramidal piece 3 is prone to penetrating too deeply and piercing the septum due to mismatched angles, which may damage the nerves and blood vessels below, or it may penetrate too shallowly, resulting in insufficient retention.

[0043] Furthermore, the orthographic projection of the pyramid 3 onto the end face of the transition portion 2 to which it is connected is entirely within the end face of the transition portion 2.

[0044] In this invention, when the implant structure is subjected to lateral occlusal force, the pyramidal component 3 will experience a slight lateral displacement. If the projection exceeds this displacement, the excess edge will create point pressure on the outer wall of the bone septum, which may lead to bone resorption in the pressure area over time, resulting in reduced bone mass around the implant and decreased stability. However, in this embodiment, when the projection is completely recessed within the lower end face of the expansion structure, the lateral displacement of the pyramidal component 3 is limited by the end face of the transition portion 2. The force is transmitted to the expansion structure through the transition portion 2 and then evenly distributed to the bone wall, effectively improving the stability of the implant.

[0045] Importantly, immediate implantation requires precise alignment with the interosseous bone septum within a narrow oral cavity. The projected inward design simplifies the procedure and improves the efficiency and accuracy of the surgeon's work.

[0046] Furthermore, the end face of the pyramidal member 3 and the transition section 2 are connected by threads.

[0047] In this invention, a screw 31 is provided at the top of the pyramid 3 to thread and fix the pyramid 3 to the transition part 2, enabling quick assembly. When the pyramid 3 needs to be replaced, it can be loosened and replaced at any time, saving time and effort.

[0048] Furthermore, the end face of the transition part 2 is provided with a plurality of threaded holes arranged in an array around its geometric center. Each threaded hole is threadedly connected to an adjusting post 4, and an adjusting shim 41 is threaded through the adjusting post 4. The pyramidal part 3 is threadedly connected to the adjusting post to be fixed to the end face of the fixing part.

[0049] In this invention, multiple threaded holes with equal angular intervals are provided circumferentially at the bottom end of the transition section 2, and the outer periphery of the adjusting post 4 is provided with external threads that match the threaded holes. Specifically, each threaded hole is arranged at equal angular intervals with the geometric center of the bottom end of the transition section 2 as the center. Thus, depending on the width of the diaphragm, an implant structure containing or assembling a corresponding number of pyramidal members 3 can be selected.

[0050] Based on the actual angle of the interosseous septum, the angle of the pyramidal component 3 needs to be adjusted slightly. Therefore, depending on the specific adjustment angle, a corresponding number of adjusting shims 41 are placed on the adjusting post 4. In practice, the pyramidal component 3 is spirally connected to the adjusting post 4, and then the corresponding adjusting shims 41 are passed through the adjusting post 4. The adjusting post 4 is then screwed tightly onto the transition section 2, completing the overall assembly of the implant structure.

[0051] Furthermore, the portion of the transition section 2 near the pyramidal member 3 is hollow inside, and multiple micro-side holes 22 are provided through the outer periphery of the transition section 2 to connect the hollow portion of the transition section 2 with the outside.

[0052] In this invention, a hollow cavity 21 is provided on the side of the transition portion 2 near the pyramidal member 3, and multiple micro-side holes 22 are provided through the outer periphery of the transition portion 2, so that the hollow cavity 21 of the transition portion 2 is connected to the outside. That is, after surgery, bone tissue can grow into the interior of the end through the side holes, forming an integrated bone and implant structure, thereby improving long-term stability; in addition, the side holes can accommodate a small amount of bone powder, promoting the fusion of bone powder with the body's own bone tissue.

[0053] The steps for using the entire implant structure are as follows: 1. Before extracting posterior teeth that cannot be saved, perform a CBCT examination on the patient to measure the height and width of the interosseous septum. When the width of the interosseous septum is greater than 3mm, select an implant with 3-4 pyramids in the retention part. When the width of the interosseous septum is less than 3mm, select an implant with 2 pyramids. Select an implant with appropriate implant length and appropriate pyramid height according to the height of the interosseous septum.

[0054] 2. Remove the affected tooth, carefully clean the soft tissue, expose the interosseous bone septum, place the prepared bone preparation tool in the extraction socket, align it with the interosseous bone septum, and adjust the angle to match the ideal implant angle. Use a resin elastic bone mallet to gently tap the handle of the bone preparation tool so that the cone of the tool head penetrates into the bone tissue, thus completing the preparation of the interosseous bone septum.

[0055] 3. Place the implant structure in the carrier of the prepared implanter, transfer it into the oral cavity, and gently tap the handle of the implanter again with a flexible drumstick to position the implant structure. Check the direction and depth of the implant.

[0056] 4. Use bone graft material to fill the gap around the implant, connect the healing abutment or sealing screw, suture the wound, and the implantation procedure is complete.

[0057] 5. After the implant has healed for 4-6 months, a dental model is taken, a suitable abutment is selected, and the upper crown is fabricated.

[0058] 6. In clinical crown placement, the abutment is first placed within the implant structure, and torque is applied to tighten the abutment. Then, the implant crown is placed, the occlusion is adjusted, and the crown is permanently bonded to complete the implant crown placement, thus ending the implant treatment.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A dental implant structure for immediate implantation in the posterior region, characterized in that: include, The implant connection portion has one end recessed inward to form a connection area for fixing the abutment; The transition section connects to the other end of the implant connection section. The transition section extends from the end face of the implant in a direction that gradually deviates from the axis of the implant connection section, forming an expanded structure. The end of the expansion structure is provided with at least two pyramidal members, which are rotationally symmetrical about the geometric center point of the end of the expansion structure, for insertion and fixation in the bone socket.

2. The immediate implant structure for posterior teeth as described in claim 1, characterized in that: The transition between the transition section and the implant connection section is smooth.

3. The immediate implant structure for posterior teeth as described in claim 2, characterized in that: The transition section extends away from the axis of the implant connection, initially increasing and then decreasing in direction, forming an expanded structure with a curved outer surface.

4. A posterior dental implant structure according to any one of claims 1-3, characterized in that: The center of each pyramid is located on a vertical line offset from the geometric center of the base of the pyramid, and its center is positioned near the edge of the transition end face.

5. The immediate implant structure for posterior teeth as described in claim 4, characterized in that: The orthographic projection of the pyramidal component onto the end face of the transition section to which it is connected lies entirely within the end face of the transition section.

6. The immediate implant structure for posterior teeth as described in claim 5, characterized in that: The end face of the pyramidal component and the transition section are connected by threads.

7. The immediate implant structure for posterior teeth as described in claim 6, characterized in that: The end face of the transition section is provided with multiple threaded holes arranged in an array around its geometric center. Each threaded hole is threaded with an adjusting post, and an adjusting shim is threaded through the adjusting post. The pyramidal part is threadedly connected to the adjusting post to be fixed to the end face of the fixing section.

8. The immediate implant structure for posterior teeth as described in claim 7, characterized in that: The transition section near the pyramidal component is hollow inside, and multiple micro-side holes are provided through the outer periphery of the transition section to connect the hollow part of the transition section with the outside.

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