WO2022068118A1

WO2022068118A1 - Cranial screw

Info

Publication number: WO2022068118A1
Application number: PCT/CN2020/141955
Authority: WO
Inventors: 全华林; 王航; 宋春辉; 张伟健; 张高龙
Original assignee: 北京品驰医疗设备有限公司
Priority date: 2020-09-30
Filing date: 2020-12-31
Publication date: 2022-04-07
Also published as: CN112156357B; CN112156357A

Abstract

A cranial screw, which relates to the field of bone implants. The cranial screw comprises: a screw head (1) comprising a cambered face (11), a cylindrical face (12) and a conical face (13); a screw main body (2) comprising a straight cylinder (22) and a serrated asymmetric thread (23) on the straight cylinder (22); and a screw tail end (3) comprising a cone-like body (33) and a gradient thread (31) on the cone-like body (33), wherein the screw main body (2) and the screw tail end (3) have a screw pitch (P) of 0.60-0.75 mm; the gradient thread (31) has a top diameter and a bottom diameter which have uniform transition; and the cone-like body (33) has a tip angle (θ₂) of 48°-65°. The cranial screw, which has been subjected to parameter optimization, has the characteristics of easy tapping and high strength, can be smoothly tapped into bone under low torque by means of a special torque screwdriver (4), and achieves a good surgical fixation effect.

Description

a skull screw

technical field

The present invention relates to the field of bone implants, in particular, to a skull screw, which is mainly used for the fixation of medical instruments, especially electrode fixation devices, on the skull.

Background technique

In Deep Brain Stimulation (DBS) surgery, it is often necessary to fix the implanted device on the skull with fasteners, such as skull screws.

Skull screws are a type of bone screw. Bone screws are generally divided into self-tapping screws and non-self-tapping screws. The basic structure of the two kinds of screws includes a cylindrical body, the outer surface of the body is provided with a set of external threads, and the external threads cooperate with the threads cut into the bone. For both types of screws, the engagement between the external thread and the internal bone thread provides initial stabilization of the screw, and long-term stability of the screw is provided by new bone growth around the screw.

A non-self-tapping screw is a threaded hole in which the thread is screwed into the bone, and the screw itself does not participate in drilling and tapping. Self-tapping screws include cutting threads and flutes, and their tails have more obvious cones than non-self-tapping screws. The cutting thread of the self-tapping screw is similar to a metal tap, which can cut the bone tissue into the bone when drilling, and the chip groove is conducive to the scraping of the bone tissue and the export of debris, thereby reducing the frictional resistance when the screw is tapped.

Non-self-tapping screws require pre-drilling prior to installation, and although this greatly reduces torque during screw insertion, clinical trials have shown that this approach establishes insufficient bone/screw contact, while making the procedure compact and operative. Actions strive for simple DBS surgery, this method has limitations.

In view of this, the skull screw adopts the form of self-tapping screw, so it has the common structural features of self-tapping screw, such as cutting thread, tail cone, chip flute and so on.

However, the existing skull screws have shortcomings, which is that the comprehensive performance of the screw strength and self-tapping ability is difficult to guarantee. Specifically: when the screw strength is sufficient, the self-tapping performance is often poor, the screw introduction resistance is large, and the doctor's clinical operation At the same time, it may cause discomfort to the patient due to the increased torque; when the self-tapping performance of the screw is good, the strength of the screw is not enough, the screw is prone to breakage, and the safety and reliability are insufficient; performance can not meet the requirements.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a new type of easy-tapping high-strength skull screw by analyzing the influence of the main parameters of the skull screw on the structural strength and self-tapping performance of the screw, optimizing the combination of parameters, and effectively preventing the screw from being easily broken or required. The high screw-in torque exacerbates the problem of patient discomfort.

In order to achieve the above object, the present invention provides a skull screw,

Screw head, including arc surface, cylindrical surface and conical surface;

Screw bodies, including straight cylinders and serrated asymmetrical threads on the straight cylinders;

Screw tails, including vertebral bodies and tapered threads on vertebral bodies;

The pitch P of the screw body and the screw tail end is 0.60-0.75mm;

The gradual thread has a top diameter and a bottom diameter of uniform transition, and the tip angle θ ₂ of the cone-like body is 48°-65°.

Optionally, the size of the bottom diameter d ₂ is 1.2-1.3 mm.

Optionally, the outer circular surface of the straight cylinder is the same as the bottom diameter parting surface of the zigzag asymmetric thread; the top diameter and the bottom diameter of the zigzag asymmetric thread on each turn are respectively the same.

Optionally, both the zigzag asymmetric thread and the gradual thread have a specially designed tooth structure, the tooth structure has a narrow ridge-like platform at the top of the tooth, and the width e of the ridge-like platform is 0.05-0.15mm.

Optionally, the chamfering radius r ₅ of the top of the tooth is 0-0.05 mm; and/or, the tooth flank angle α of the side of the tooth structure close to the screw head is 3°-5° and/or, the tooth flank angle β of the tooth structure close to the tail end of the screw is 32°-38°

Optionally, a tooth bottom chamfer on the side of the tooth structure close to the tail end of the screw, the radius r ₃ of the tooth bottom chamfer is 0.25-0.3 mm; and/or, the tooth structure The tooth bottom chamfer on the side close to the screw head is chamfered, and the radius r ₄ of the tooth bottom chamfer is 0.05-0.1 mm.

Optionally, the tail end of the screw includes a chip flute, the chip flute passes through multiple threads, the number of turns of the multiple threads is not less than 2, and the cross-sectional angle θ of the chip flute ₃ is 75°-112° and includes a scraping edge with scraping action.

Optionally, the center of the arc surface is provided with a cross-shaped drive slot used as a drive interface for screw connection, the cross-shaped drive slot extends orthogonally outward from the center of the arc surface, and the extension length is between the cylinders. 60%-98% of the diameter d ₃ of the face; and/or, the radius r ₁ of the arc-shaped bottom of the cross-shaped drive groove is 90%-100% of the diameter d ₃ of the cylindrical surface; and/or, the ten The depth l of the font-shaped driving groove is 0.7-0.9 mm.

Optionally, the threads of the screw body and the screw tail end are single-threaded right-hand threads.

Optionally, the overall length of the screw is 5.8-6 mm; the diameter d ₃ of the cylindrical surface of the screw head is 2.95-3 mm; the top diameter d ₁ of the asymmetric thread of the screw body is 1.775-1.825 mm.

Compared with the prior art, the technical effect of the present invention is that the parameter-optimized skull screw has the characteristics of easy tapping and high strength, and can be successfully tapped into the bone with a special torque screwdriver at a low torque, and achieves relatively low torque. Good surgical fixation.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without creative work.

Fig. 1 is the side view of the skull screw of the present invention;

Figure 2 is an end view of the skull screw of the present invention;

Figure 3 is a bottom view of a longitudinal section of the skull screw flute of the present invention;

Figure 4 is a cross-sectional view of the skull screw of the present invention;

5 is a partial enlarged view of the thread profile of the skull screw of the present invention;

Fig. 6 and the partial side view of the torque screwdriver matched with the skull screw of the present invention;

Figure 7 is an end view of the torque driver for the skull screw of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The invention relates to a skull screw, which has the characteristics of easy tapping and high strength. "Easy-tapping" should be understood as the self-tapping performance of the screw is good, the screw-in torque is small, and the insertion into the bone is easy. Tensile compression and torsional strength are in line with surgical requirements. It should be pointed out that there is a certain negative correlation between the self-tapping performance and structural strength of cranial screws. Only by comprehensively weighing the structural parameters of the screw can the two performances achieve a better balance. "Easy tapping and high strength" refers to the excellent comprehensive performance of the two, not just the outstanding performance of a certain performance.

Under the condition that the overall length of the screw, the outer diameter of the screw head and the top diameter of the screw thread are unchanged, the skull screw provided by the present invention can be designed through the optimized combination of the remaining structural parameters of the screw, and the comprehensive performance of its self-tapping performance and structural strength can be achieved. Better than ordinary skull screws.

In order to make those skilled in the art better understand the solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

Figure 1 is a side view of the skull screw of the present invention. As shown in FIG. 1 , the screw of the present invention includes: screw head 1 , screw head arc surface 11 , arc cross-shaped driving groove 111 , screw head cylindrical surface 12 , screw head cone surface 13 , cone surface chamfer 131 , screw main body 2, screw main body polished rod 21, main body straight cylinder 22, main body zigzag asymmetric thread 23, large bottom chamfer of asymmetric thread body 231, asymmetric thread tooth bottom small chamfer 232 , The crest 233 of the asymmetric thread body, the screw tail end 3, the screw tail end tapered thread 31, the tapered thread cutting edge 311, the screw tail end chip groove 32, the chip groove scraping edge 321, and the tip angle of the screw tail end.

The main characteristic dimensions of the skull screw of the present invention are shown in FIG. 4 . Among them, the overall length of the screw is 6mm, the upper tolerance is 0, the lower tolerance is -0.2mm, the diameter _d3 of the cylindrical surface 12 of the screw head is 3mm, the upper tolerance is 0, the lower tolerance is -0.05mm, the screw body is asymmetrical thread The top diameter d ₁ of 23 is 1.8mm, the upper tolerance is +0.025mm, and the lower tolerance is -0.025mm. The aforementioned three dimensions are the basic dimensions of this embodiment, and the rest of the structural parameters of the screw are based on these parameters remain unchanged. Carry out optimal combination design.

The screw of the present invention is made of a group of medical-grade biocompatible materials capable of resisting high torque, including but not limited to titanium alloy, cobalt-chromium and high-strength resin polymer, and titanium alloy is preferred in terms of comprehensive performance and application maturity , The screws of this embodiment are made of titanium alloy material TC4 (GB/T13810).

The screw of the present invention does not impose strict restrictions on the thread and the direction of rotation of the thread, and can be selected according to actual application conditions. Generally speaking, for the self-tapping screw fixed on the skull, the introduction efficiency of single thread thread can meet the requirements, and the double thread thread can theoretically increase the introduction efficiency, but in the actual introduction process, due to the increase of the contact surface between the thread and the bone tissue, the friction force Increase, but increase the difficulty of screw introduction. In addition, right-hand threads are in line with the idiom that people "turn clockwise to tighten, and counterclockwise to loosen". Therefore, the thread of the screw in this embodiment is a single-thread right-hand thread.

The included angle _θ1 of the taper surface 13 of the screw head is at least 90° to prevent the screw from being easily pulled out axially. It is recommended that the included angle _θ1 be between 90° and 120°. In this embodiment, _θ1 is 100° .

The diameter of the arc of the arc surface 11 of the screw head is between 2 and ₃ times the diameter d3 of the cylindrical surface of the screw head, and the diameter of the arc of the arc surface 11 of the screw head is between 6-9 mm. Preferably, this embodiment The arc diameter of the arc surface 11 of the screw head is 6.36 mm.

As shown in FIG. 2, the cross-shaped driving groove 111 of the screw head extends orthogonally outward from the center of the arc surface 11, and the extension length is between 60%-98% of the diameter of the cylindrical surface of the screw head, and the optimal extension length is In order to ensure the maximum driving torque of the screw without destroying the integrity of the outer circle of the nail head and the structural strength. The bottom of the cross-shaped drive slot 111 is arc-shaped to reduce the amount of material removed from the screw head 1 when machining the cross-shaped drive slot 111, and to maximize the strength of the screw head. The outer circle radius r ₁ should be between 90%-100% of the diameter of the cylindrical surface of the screw head, and the depth l of the cross-shaped driving slot 111 should be between 0.7-0.9 mm. As shown in FIG. 4 , the extension length of the cross-shaped driving slot 111 in this embodiment is about 2.90 mm, the outer radius _r1 of the arc bottom of the cross-shaped driving slot 111 is 2.75 mm, and the depth l of the cross-shaped driving slot 111 is 0.75 mm. The structure is capable of providing sufficient torque to allow the screw to be driven into the skull and sufficient strength to resist torsional deformation of the head of the screw and the torque driver for the screw during installation. If the extension length of the cross-shaped driving slot 111 is less than 60% of the diameter of the cylindrical surface of the screw head, it will cause the screwdriver to be difficult to fit and provide a small torque; It will lead to low strength of the screw head and easy deformation. If the outer radius r ₁ of the cross-shaped drive slot 111 is less than 90% of the diameter of the cylindrical surface of the screw head, it will cause the cross-shaped drive slot to be difficult to fit with the tool and easy to slide the wire; if the outer radius r ₁ of the cross-shaped drive slot 111 is larger than the screw The diameter of the cylindrical surface of the head will lead to the strength of the cross-shaped drive groove and it is easy to break. If the depth l of the cross-shaped driving slot 111 is less than 0.7mm, it will cause the cross-shaped driving slot to be difficult to fit the tool and easy to slide the wire; Fragile.

As shown in FIG. 1 , there is a rounded chamfer 131 at the connection between the screw head 1 and the screw body 2 , and the rounded corner radius r ₂ is between 0-0.3 mm. It should be pointed out that for screws whose head and the contact surface of the fixation device need to be in strict and flat contact, rounding is not recommended at the connection between the head and the main body. In this embodiment, the rounded corners are used to make the transition between the screw head 1 and the screw body 2 evenly, to avoid stress concentration, and to better transmit the driving torque of the screw head 1 to the screw body 2. The rounded corners r ₂ is 0.3mm.

The screw body 2 has a straight cylindrical body 22 and a serrated asymmetrical thread 23, and the straight cylindrical body is more conducive to the screw structure having better strength. The outer circular surface of the straight cylinder 22 is the same as the bottom diameter parting surface of the thread 23 , and the top diameter and the bottom diameter of the threads 23 of each circle on the screw body 2 are respectively the same. Among them, under the condition that the top diameter d1 of the thread ₂₃ remains unchanged at 1.8mm, the bottom diameter _d2 of the thread 23 is 1.2mm to 1.3mm to obtain a better comprehensive performance between self-tapping performance and structural strength. 23 The bottom diameter d ₂ is 1.20mm. If the bottom diameter d ₂ of the thread 23 is less than 1.2 mm, the strength of the screw is low and it is easy to break; if the bottom diameter d ₂ of the thread 23 is greater than 1.3 mm, the feed rate of the screw is small and it is difficult to tap.

The thread profile of the screw body 2 is shown in Figure 5 . The chamfering radii r ₃ and r ₄ at the bottom of the tooth mainly affect the strength of the thread, the flank angles α and β of the tooth mainly affect the cutting efficiency of the thread, and the chamfering radius r ₅ at the top of the tooth is related to the ridge-like platform. _The size of the width e affects the strength and cutting efficiency of the thread at the same time, and is affected by the hardness of the screw itself and the hardness of the bone tissue to be cut. The width e of the shape platform should be smaller. After comprehensive analysis in this embodiment, various structural parameters of the tooth shape are optimized, including: the preferred value range of the chamfering radius r ₃ at the bottom of the tooth body close to the end of the screw is 0.25-0.3 mm, and it is close to the head of the screw. The preferred value range of the chamfering radius r ₄ at the bottom of the tooth on one side is 0.05-0.1 mm, and the preferred value range of the tooth flank angle α on the side close to the screw head is 3°-5°, close to the screw tail The preferred value range of the tooth flank angle β on the end side is 32°-38°, the preferred value range of the chamfer radius r ₅ of the tooth top is 0-0.05mm, and the preferred ridge-like platform width e is The value range is 0.05-0.15mm. In this embodiment, the selected structural parameters of the tooth type are: the bottom chamfers r ₃ and r ₄ of the tooth are 0.3 mm and 0.1 mm respectively, the flank angles α and β of the tooth are 3° and 35° respectively, The chamfer r5 at the top of the body and the width e of the ridge _- like platform are 0.05mm and 0.1mm, respectively. If the chamfering radius r3 at the bottom _of the tooth body is less than 0.25mm, the strength of the screw will be low, and the screw will be easily broken. If the chamfering radius r3 at the bottom _of the tooth body is greater than 0.3mm, the resistance surface of the screw will be large and it will be difficult to tap. The problem. Similarly, if the chamfer radius r ₄ at the bottom of the tooth is less than 0.05mm, the strength of the screw will be low, and the screw will be easily broken; if the chamfer radius r ₄ at the bottom of the tooth is greater than 0.1mm, the resistance surface of the screw will be large, The problem of not easy tapping. If the tooth flank angle α is less than 3°, the screw feed will be small and the tapping efficiency will be low; if the tooth flank angle α is greater than 5°, the screw feed will be too large. Due to the large feeding resistance, it is not easy to tap. Similarly, if the tooth flank angle β is less than 32°, the screw feed will be small and the tapping efficiency will be low; if the tooth flank angle β is greater than 38°, the screw feed will be excessive. Large, the feeding resistance is large, and it is not easy to tap. If the width e of the ridge-like platform is less than 0.05mm, the strength of the screw is low and it is easy to break; if the width e of the ridge-like platform is greater than 0.15mm, the screw feed resistance is large and it is not easy to tap. If the chamfer r ₅ at the top of the tooth is larger than 0.05mm, the width of the ridge-like platform will be too small and it will be easy to break.

The screw tail end 3 includes a cone-like body 33 and a gradient thread 31 on the cone-like body. The structure of the cone-like body 33 and the gradient thread 31 is conducive to the introduction and tapping of the screw tail end 3. The chip groove 32 on the gradient thread 31 has It is beneficial to export or accommodate bone tissue debris, so as to reduce the resistance of the screw to the bone tissue material, thereby reducing the screw-in torque. The number of turns of the chip flute 32 passing through the thread depends on the structural strength of the screw. On the premise that the strength of the screw meets the requirements, the more the number of turns of the thread passing through, the more conducive to the export of chips. As shown in FIG. 3 , the scraping edge 321 on the chip flute 32 also has the function of scraping the thread shape, and the scraping effect is affected by the size of the included angle θ ₃ of the chip flute section. Theoretically, the included angle θ3 _of the flute section is in the range of 45°-120°, and the smaller the angle, the better the scraping effect. It should be pointed out that the size of the included angle θ3 _of the chip flute section also affects the rate of chip ejection. In theory, within the range of 45°-120°, the larger the included angle, the faster the chip ejection efficiency. In general, the angle dimension θ3 _of the chip flute section is between 75°-112° to obtain a better value. The included angle dimension θ3 _of the chip flute section of the screw in this embodiment is 90°. If the included angle dimension θ3 _of the chip flute section is less than 75°, there will be problems such as less chip capacity or slow chip ejection, high screw feeding resistance, and difficulty in tapping; if the included angle dimension θ3 _of the chip flute section is greater than 112° , there will be problems of low screw strength and easy breakage.

The gradient thread 31 of the screw has a uniform transition top diameter and bottom diameter. Taking into account the hardness of the bone and the material of the screw at the same time, its tip angle θ ₂ is between 48°-65° to obtain the screw drilling efficiency and screw tail. The optimal balance of end strength. The tip angle θ ₂ of the tail end of the screw in this embodiment is 60°. If the angle of the tip angle is less than 48°, the strength of the tail end of the screw is low and it is easy to break; if the angle of the tip angle is greater than 65°, the tail end of the screw is difficult to feed and difficult to tap.

The screw body 2 and the screw tail 3 have the same pitch P. The basis for the design optimization of the pitch P is as follows:

The relationship between the screw pitch P and the driving torque M of the torque screwdriver, the transmission efficiency ε, and the axial output force F can be approximated as: F=(2π·ε·M)/P. When the driving torque M and the transmission efficiency ε are constant, the thread pitch P is inversely proportional to the axial output force, that is, the smaller the thread pitch P, the greater the axial output force F, and the greater the feed force in the screw bone; when the axial output force F and When the transmission efficiency ε is constant, the pitch P is proportional to the driving torque M, that is, the smaller the pitch P, the smaller the required driving torque M, and the smaller the screw-in torque. Therefore, in order to output a large axial output force under a small driving torque, the pitch P of the screw should be as small as possible.

However, the feed amount W of the screw is equal to the pitch P of the screw, that is, when the driving rate is constant, the smaller the pitch P, the smaller the feed amount W of the screw, and the corresponding clinical operation is as follows: the doctor drives the small pitch screw The torque of the screw is small, but the tapping rate of the screw is correspondingly slow, and the doctor needs to rotate more turns to completely fix the screw.

Therefore, the pitch P of the screw should obtain a certain intermediate value within a certain range, so that the driving torque of the screw is small and the screwing rate is fast. In this embodiment, the screw pitch P is preferably 0.60-0.75 mm, and the screw pitch P in the preferred example of this embodiment is 0.70 mm. If the pitch P is less than 0.60mm, the feed rate of the screw is small and the tapping efficiency is slow; if the pitch P is greater than 0.75mm, the screw feeding resistance is large and it is not easy to tap.

6 and 7 are respectively a partial side view and an end view of a torque screwdriver 4 matched with a skull screw according to an embodiment of the present invention. As shown in Figures 6 and 7, the cross-shaped bit 41 of the torque screwdriver 4 is installed in conjunction with the cross-shaped groove driving slot 111 of the screw head. When screwing in, the screwdriver is kept stable, the screwing speed is low and stable, and the operator operates in a standardized manner.

The screw of the present invention can be easily manufactured by using a modern lathe capable of cutting threads, and can also be processed and formed at one time by CNC, and the surface of the screw is deburred, polished and anodized. The screw torque test and fracture torsion angle are tested according to the method specified in YY/T0662, the maximum torque is ≥0.5N m, and the maximum fracture torsion angle is ≥150°. The hardness of the screw material is measured according to the method specified in GB/T4340.1, and the material hardness is greater than or equal to 260HV. The screw torque is tested according to YY/T1506-2016, and the average screw-in torque is 0.25N m.

The self-tapping performance and strength test of the screw of the invention and the traditional skull screw on the bovine bone can be completely and smoothly screwed into the bovine bone under a lower torque value, and the screw has no cracks. In the quantitative comparison experiment, under the same test conditions, the measured average complete screw-in torque value of the traditional skull screw is 0.282N.m, and the measured average screw-in torque value of the preferred embodiment skull screw is 0.226N.m. Compared with the traditional skull screw, the preferred embodiment The self-tapping performance optimization rate of the skull screw is 19.8%; the measured average breaking torque of the traditional skull screw is 0.49N.m, and the measured average breaking torque of the skull screw of the preferred embodiment is 0.51N.m. Compared with the traditional skull screw, the structural strength of the skull screw of the preferred embodiment The optimization rate is 4%. Because the skull screw of the preferred embodiment has better self-tapping performance compared with the traditional skull screw, and the introduction resistance is small, the possibility of fracture during the actual tapping process is smaller, and its self-tapping performance and structural strength are better than the traditional skull screw. .

The skull screw provided by the present invention has been described above. The principles and implementations of the present invention are described herein by using specific examples. The descriptions of the above embodiments are only used to help understand the method and the core idea of the present invention, and are not intended to limit the present invention. Therefore, for those skilled in the art, any modifications made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

A skull screw, characterized in that it comprises:

The screw head (1) includes an arc surface (11), a cylindrical surface (12) and a conical surface (13);

a screw body (2), comprising a straight cylinder (22) and a serrated asymmetric thread (23) on the straight cylinder;

The tail end of the screw (3) includes a vertebral body (33) and a gradient thread (31) on the vertebral body;

The pitch P of the screw main body (2) and the screw tail end (3) is 0.60-0.75mm;

The tapered thread (31) has a top diameter and a bottom diameter of uniform transition, and the tip angle θ2 of the cone - like body (33) is 48°-65°.
The screw according to claim 1, wherein the size of the bottom diameter d 2 is 1.2-1.3 mm.
The screw according to claim 2, characterized in that, the outer circular surface of the straight cylinder (22) is the same as the bottom diameter parting surface of the serrated asymmetric thread (23); The top diameter and bottom diameter of the symmetrical thread (23) on each circle are respectively the same.
The screw according to any one of claims 1-3, characterized in that both the serrated asymmetrical thread (23) and the gradual thread (31) have a specially designed tooth structure, and the tooth structure The top of the tooth has a narrow ridge-like platform (233), and the width e of the ridge-like platform (233) is 0.05-0.15 mm.
The screw of claim 4, wherein

The chamfering radius r 5 of the top of the tooth is 0-0.05 mm; and/or,

The tooth flank angle α on the side of the tooth structure close to the screw head (1) is 3°-5°; and/or,

The tooth flank angle β on the side of the tooth structure close to the screw tail end (3) is 32°-38°.
The screw of claim 4, wherein

The tooth bottom chamfer (231) on the side of the tooth structure close to the screw tail end ( 3 ), the radius r3 of the tooth bottom chamfer (231) is 0.25-0.3 mm; and/or,

A tooth bottom chamfer (232) on the side of the tooth structure close to the screw head (1), and a radius r 4 of the tooth bottom chamfer (232) is 0.05-0.1 mm.
The screw according to any one of claims 1-6, characterized in that, the screw tail end (3) comprises a chip flute (32), and the chip flute (32) passes through multiple turns of thread, The number of turns of the multi-turn thread is not less than 2 turns, the section angle θ3 of the chip flute (32) is 75°-112°, and a scraping edge (321) with scraping function is included.
The screw according to any one of claims 1-7, characterized in that, a cross-shaped driving slot (111) used as a driving interface for screw connection is provided at the center of the arc surface (11), and the ten The word-shaped driving groove (111) extends orthogonally outward from the center of the arc surface, and the extension length is between 60%-98% of the diameter d3 of the cylindrical surface (12); and/or,

The radius r 1 of the arc bottom of the cross-shaped driving groove (111) is 90%-100% of the diameter d 3 of the cylindrical surface (12); and/or,

The depth l of the cross-shaped driving groove (111) is 0.7-0.9 mm.
The screw according to any one of claims 1-8, characterized in that, the threads of the screw body (2) and the screw tail end (3) are single-thread right-hand threads.
The screw according to any one of claims 1-9, characterized in that, the overall length of the screw is 5.8-6 mm; the diameter d 3 of the cylindrical surface (12) of the screw head is 2.95-3 mm; the The top diameter d 1 of the asymmetric thread (23) of the screw body is 1.775-1.825 mm.