Automatic tooth taking method

Abstract

The invention relates to the technical field of dentistry, and discloses an automatic tooth taking method, which comprises the following steps: setting and processing a first notch, cutting a connecting end of a support rod through computer numerical control processing equipment to obtain the first notch, and enabling the first notch to be positioned at one end, connected with a false tooth, of the support rod; adhesive is fixed, specifically, the adhesive is fixed to the first notch, and the adhesive is a soluble / meltable substance; solidification of the adhesive: changing the environment and self conditions to enable the adhesive to be solidified; a second notch is formed and machined, the connecting end of the supporting rod is cut through the equipment to obtain the second notch, and after cutting, the supporting rod is connected with the false tooth through the adhesive but is not connected with the false tooth; and stripping the adhesive, namely changing the state of the adhesive through dissolving or melting treatment, so that the adhesive is separated from the false tooth. By the adoption of the method, the false teeth can be detached from the porcelain block through the equipment, the false teeth are prevented from being damaged or damaged due to artificial tooth grinding, cutting and taking, and high-precision and high-efficiency automatic tooth taking of the equipment can be achieved.

Description

Technical Field

[0001] The present application relates to the field of dental technology, and in particular to an automatic tooth extraction method. Background Art

[0002] Due to various factors, many people face oral problems, and the demand for dentures is increasing. With the improvement of living standards, people's requirements for the quality of dentures are also increasing. In the process of denture production, the processed dentures are fixed on the porcelain block by support rods, and then the dentures need to be separated and removed from the porcelain block.

[0003] The existing tooth extraction operation is done manually. The processing personnel first use an electrically driven diamond slicer to cut off the support rods between the denture and the porcelain block in sequence to separate the denture from the porcelain block. The outer wall of the separated denture has residual support rods. Then the processing personnel use an electrically driven grinding head to grind off the excess porcelain piles on the outer wall of the denture, so that the wall of the denture meets the processing requirements for dentures in clinical applications of oral restoration.

[0004] The main disadvantages of manual tooth extraction are that it takes a lot of time to manually cut off the support rods and grind off the porcelain posts remaining on the outer wall of the denture, which prolongs the denture processing cycle and reduces efficiency; it is easy to cause denture defects or damage, resulting in a decrease in processing yield; the denture shape and surface accuracy are low, which is not conducive to clinical restoration; the dust generated by manual tooth extraction affects the health of operators and pollutes the environment, and there is room for improvement. Summary of the invention

[0005] In order to realize mechanical and automated tooth extraction, avoid damage or defects to dentures caused by manual tooth extraction, improve processing efficiency and the accuracy and quality of dentures, reduce production costs and shorten production cycles, the present application provides an automatic tooth extraction method.

[0006] The present application provides an automatic tooth extraction method, which adopts the following technical solution: A method for automatically removing teeth, comprising the following steps Based on the denture cut from the zirconia block and its support rod, a first incision is set for processing, and a first incision is cut on the connecting end of the support rod by a computer numerical control processing device, wherein the first incision is located at one end of the support rod connected to the denture; Setting an adhesive, setting an adhesive at the position of the incision, wherein the adhesive is a soluble or meltable substance, or other physically decomposable or chemically decomposable substance; Solidification of the adhesive, changing the environment and / or its own conditions so that the adhesive solidifies and forms an adhesive bonded to the denture; Processing a second incision, cutting a second incision on the connecting end of the support rod and the denture by computer numerical control processing equipment, and connecting the cut support rod to the denture through the adhesive; The peeling of the adhesive is to change the physical state of the adhesive by dissolving or melting or other physical or chemical decomposition methods, so that the adhesive is separated from the denture.

[0007] By adopting the above technical scheme, firstly, a first incision is made at one end of the support rod near the denture by computer numerical control processing equipment; then, the adhesive is fixed at the first incision, and the adhesive is solidified by changing the external environment and / or the adhesive itself, and the adhesive bonds the denture and the support rod; then a second incision is made, and the computer numerical control processing equipment cuts off the part where the support rod is connected to the denture, and the denture is connected to the support rod by the adhesive, and the opening of the second incision separates the support rod from the outer wall of the denture; finally, by changing the external environment or changing the state of the adhesive itself, the physical state of the adhesive changes, and the adhesive is separated from the outer wall of the denture, so as to realize the stripping of the denture. Since computer numerical control processing equipment is used throughout the process to cut the connection between the support rod and the denture, the accuracy of the cutting and cutting surface processing of the connecting end of the support rod and the denture is guaranteed, and at the same time, the damage to the denture wall caused by the cutting process can be avoided, and manual work can be eliminated to realize mechanical automation processing, thereby improving work efficiency, shortening production cycle, reducing production costs, and improving the accuracy and quality of the denture.

[0008] Optionally, the cross-sectional shape and size of the support rods are changed according to the deployment position and direction of the support rods on the denture, the number of support rods deployed, and the size requirements of the subsequent adhesive.

[0009] By adopting the above technical solution, the shape of one end of the support rod to be cut is set in a rod shape, so that the computer numerical control processing equipment can cut the support rod more smoothly and efficiently; the diameter of the support rod changes with the change of the volume and shape of the denture to better support the denture and improve the stability of the fixed denture during processing.

[0010] Optionally, the interface domain where one end of the first incision is connected to the denture and the area where the other end of the first incision is connected to the support rod are the cuttable parts when cutting the second incision; in this cuttable part, the separation incision with an allowable width can be set by calculation and processing strategy including the shape and size of the tool blade, and the separation incision constitutes a spatial difference set from the cut surface domain of the support rod and the interface domain connected to the denture, calculates the difference set of the separation incision at the first incision on each support rod, and completes the cutting of the difference set spatial part of the first incision according to the difference set area through computer-controlled processing equipment.

[0011] Optionally, after completing the support rod connection differential cutting, the ceramic block is placed in a tooling or a holding container, and the receiving bottom of the tooling or the holding container is provided with a soft supporting pad or a buffer structure; the physical state of the adhesive is changed so that the adhesive is separated from the denture, including full separation, in which the denture is completely separated from the zirconia embryo, and semi-separation, in which the adhesive is semi-melted / semi-dissolved and softened; for semi-separation, a mechanical soft push rod is used to lightly press the denture to separate it from the zirconia embryo, and the position of the denture falling on the soft supporting pad corresponds to its position on the zirconium block.

[0012] By adopting the above technical solution, the peeling of multiple adhesives is carried out simultaneously. After the denture is separated from the porcelain block, it falls on the soft support pad or the buffer structure. The setting of the soft support pad and the buffer structure reduces the damage to the denture. The number and indication of the denture on the zirconium block are arranged before processing, so if the falling position corresponds to it, then the number and indication of the denture falling on the soft pad are known, so that it can be automatically picked by the machine.

[0013] Optionally, additives are mixed into the adhesive, and the additives are used to improve the application of the adhesive and to improve the adhesion, rigidity and strength of the adhesive.

[0014] By adopting the above technical solution, the bonding of the adhesive is made more convenient, the connection strength between the denture and the support rod is improved, and the damage caused by insufficient strength support during the processing of the denture is reduced.

[0015] Optionally, after the adhesive is fixed to form an adhesive, the ceramic block is put back into the computer numerical control device, and a secondary clamping overlap positioning structure and a fixture are used when putting it back.

[0016] By adopting the above technical solution, the position of the ceramic block on the computer numerical control processing equipment is fixed before and after the adhesive is fixed, which is convenient for cutting the support rod and improves the processing accuracy of the denture.

[0017] Optionally, a first alignment mechanism is provided on a fixture on the computer numerical control processing equipment, the ceramic block is mounted on a clamping set, and a first alignment pair corresponding to the first alignment mechanism is provided on the clamping set.

[0018] By adopting the above technical solution, the processing personnel install the ceramic block on the clamping set, and the first alignment pair is matched with the first alignment mechanism, so that the fixation of the clamping set and the fixture is more convenient, which improves the processing accuracy and makes the fixation of the ceramic block faster.

[0019] Optionally, a second alignment mechanism is provided on the clamping set, and a second alignment pair corresponding to the second alignment mechanism is provided on the ceramic block fixing ring, and the ceramic block is put back onto the clamping set for alignment and fastening.

[0020] By adopting the above technical solution, the positioning and fixing between the ceramic block fixing ring and the clamping set is made more convenient.

[0021] Optionally, the width of the first incision is greater than or equal to the width of the second incision.

[0022] In summary, the present application includes at least one of the following beneficial technical effects: 1. The denture is fixed on the porcelain block by a support rod. The separation of the denture and the porcelain block is completed by computer numerical control processing equipment. The denture is bonded and fixed with a meltable / dissolving adhesive. The denture is made to fall off by melting / dissolving the adhesive. The support rod is cut by computer numerical control processing equipment to reduce and avoid the possibility of damage to the denture caused by cutting the support rod to extract the tooth. At the same time, it can greatly reduce manpower input, significantly shorten the rod cutting time, greatly reduce the rod cutting breakage rate, and reduce processing costs exponentially.

[0023] 2. While computer numerical control processing equipment is used to cut the support rod, the interface surface between the support rod and the denture, that is, the related surface between the outer contour of the denture and the support rod is obtained by mechanical automation processing and milling. This ensures the accuracy of the cutting and cutting processing of the connection end of the support rod and the denture, improves the complete suitability of clinical prosthetic restoration, reduces and avoids the uncertainty, irregularity, large errors and damage to the interface surface obtained by manual grinding, and at the same time can significantly improve the surface grinding efficiency, shorten the relevant processing cycle, significantly improve the surface quality of the denture, reduce the relevant production cost and save labor input.

[0024] 3. Before fixing the adhesive, the ceramic block needs to be removed from the CNC machining equipment. After fixing the adhesive, the ceramic block needs to be reinstalled on the CNC machining equipment. A secondary clamping overlap positioning structure and fixture are set up to make the fixation of the ceramic block more convenient and the fixed position of the ceramic block more accurate, thereby making the cutting process more accurate.

[0025] 4. When using paraffin or other liquid injection adhesive materials, consider adding gypsum powder and other strengthening agents, or VA acetic acid cold-setting and hot-melting strengthening and fluxing agents, and control the added ratio so that the injection material can solidify faster and the adhesion, rigidity and strength of the material after solidification are improved.

[0026] 5. The tooth extraction method and technology applied for by the present invention, except for the auxiliary operations of placing adhesives and secondary clamping and overlapping positioning, which are handled manually, the rest are automatically completed by computer numerical control processing equipment. Therefore, the tooth extraction method and technology realizes mechanical automation of tooth extraction; if the auxiliary operation mechanical automation is added, it can constitute fully automated tooth extraction, which can provide a basic means for the complete automated manufacturing of oral restorations and digital economy.

[0027] 6. The use of mechanical automated tooth extraction can greatly reduce the health impact of dust on operators through the equipment's dust suction and dust removal devices, and at the same time greatly reduce the pollution of dust to the environment, which is beneficial to health and green production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the automatic tooth extraction method in an embodiment of the present application.

[0029] Figure 2 It is a schematic structural diagram of the denture according to an embodiment of the present application, and is used to show the first incision set on the support rod.

[0030] Figure 3 It is a schematic diagram used to show the first incision cut on the support rod in the embodiment of the present application.

[0031] Figure 4 It is a schematic diagram for illustrating the second cutout set on the support rod in an embodiment of the present application.

[0032] Figure 5 It is a schematic diagram of the structure used to show that the adhesive applied to the support rod is not solidified in the embodiment of the present application.

[0033] Figure 6 It is a schematic diagram of the structure after the adhesive on the support rod in the embodiment of the present application solidifies.

[0034] Reference numerals: 1, first cut; 1', first incision; 2, adhesive; 3, support rod; 4, second cut; 4', fourth incision. DETAILED DESCRIPTION

[0035] The following is combined with Figure 1-6 This application is described in further detail.

[0036] In this application specification, the patent terminology of automatic tooth extraction is defined as follows: support rod 3: a complete support rod for supporting the denture set in the cutting arrangement stage; first cut body 1: an upper half cut set on the complete support rod, but not processed, which is located at the end of the support rod connected to the denture; First incision 1': the opening on the support rod after the first cut body 1 is cut off; support rod 3': the support rod after the first cut body 1 is cut off from the support rod 3; adhesive 2: the adhesive material piled up and covered on the first incision 1'; adhesive 2': the adhesive for fixing the denture that is solidified after being piled up and covered on the first incision 1; Second cut 4: the lower half cut set on the support rod 3', but not processed, which is located at the end of the support rod connected to the denture, and is adjacent to the first cut 1; the shape and size of the second cut 4 are determined by the difference set, and include the necessary overcut area; second cut 4': the processed shape and size of the second cut 4 actually cut off; support rod 3": the support rod after the second cut 4 is cut off from the support rod 3', and it is separated from the denture.

[0037] Embodiment 1, Embodiment 1 of the present application discloses a method for automatic tooth extraction.

[0038] Reference Figure 1 and Figure 2 The denture and the support rod 3 are formed by cutting on the zirconia block through computer numerical control processing equipment. In the present application, the support rod 3 is preferably set to be rod-shaped. During the cutting process, as the volume of the denture increases, the rod diameter of the support rod 3 gradually increases, and as the shape of the denture and the deployment position of the support rod are different, the cross-sectional shape and size of the support rod 3 will change, which is beneficial to improve the stability of the support rod 3 in supporting the denture.

[0039] Reference Figure 2 and Figure 3 After the processing of the denture and the support rod 3 on the zirconia block is completed, the zirconia block is fixed on the computer numerical control processing equipment, and the corresponding software program is input into the control computer of the computer numerical control processing equipment. According to the shape and cross-sectional diameter of the support rod 3, a first cut body 1 is set at the corresponding end of the support rod 3 close to the denture, and a first incision 1' is opened on the outer wall of the end of the support rod 3 close to the denture by the computer numerical control processing equipment. Figure 4 and Figure 5 Then, an adhesive 2 is set in the first incision 1' by injection or extrusion. In the present application, the adhesive 2 can be a liquid special paraffin with slow fluidity that can be injected and can be cured quickly after injection. The curing conditions include specific temperature, pressure or vacuum process, and can also include fixed catalytic conditions, such as a single group or multiple groups of additives with good biocompatibility. The cured adhesive 2 is adhesive 2'.

[0040] Reference Figure 4 and Figure 5 The adhesive 2 can also be a flexible material with good fluidity for injection, such as a paste or a soft body, which is placed at the first incision 1' by injection or extrusion pressure, and the material is cured faster through temperature and pressure conditions, or time and solidification agents; the adhesive 2 can also be an EVA composite material, in which the molten fluidity suitable for injection or extrusion, as well as the melting point, Vicat softening point and curing properties at room temperature and pressure are obtained by controlling the VA acetic acid ratio and melt index of its precursor.

[0041] Reference Figure 4 and Figure 5Due to the fluidity of the adhesive 2, the adhesive 2 will flow and wrap around the end of the support rod 3' close to the denture. Figure 4 and Figure 6 The volume of the solidified adhesive 2' is larger than the volume of the first incision 1', and the adhesive 2' plays a role in bonding and fixing the support rod 3' and the denture, thereby improving the stability of the denture after the ceramic block at the first cut body 1 is removed.

[0042] Reference Figure 6 After fixing the adhesive 2', the ceramic block with the adhesive 2' is fixed on the computer numerical control processing equipment. A specially designed secondary clamping overlap positioning structure and its fixture are used for fixing. In the present application, the secondary clamping overlap structure can be a movable fixture based on the fixed clamp on the computer numerical control processing equipment. The movable fixture is provided with a unique first alignment mechanism. The ceramic block is installed on the clamping set. The clamping set is provided with a first alignment pair corresponding to the alignment mechanism. The clamping set is placed on the mobile workbench fixture. The first alignment mechanism cooperates with the first alignment pair to fasten the clamping set to the mobile workbench fixture to fix the ceramic block, thereby achieving fixation of the ceramic block and making the fixation of the ceramic block faster.

[0043] In the present application, the first alignment mechanism can be a plurality of protrusions fixed on the movable workbench clamp, and the corresponding first alignment pair can be a plurality of grooves opened on the outer wall of the clamping set, and the protrusions and the grooves are arranged in a one-to-one correspondence; the first alignment mechanism and the first alignment pair can also be other components for fast and precise positioning.

[0044] Reference Figure 4 A second cutting body 4 is provided at one end of the support rod 3' close to the denture. In this cutting portion, a cutting incision with an allowable width is set by calculating a processing strategy including the tool blade size. The incision forms a spatial difference set from the interface domain connected to the cut surface domain of the support rod and the denture, and the difference set of the cutting incision at the first incision 1' on each support rod 3' is calculated.

[0045] Reference Figure 4 In the present application, the second incision 4' is opened by using the difference set fitting cutting method and the difference set overcutting cutting method. When fitting cutting, only the calculated difference set area is cut, while when overcutting, the area cut off will be more than the difference set area. The crown surface at the connection of the restoration crown is fitted and overcut, and the overcut of the non-connection part does not need to be fitted, which is arbitrary. Therefore, overcutting is more conducive to the unpeeled and cut residual porcelain body that may be caused by insufficient calculation and processing accuracy, resulting in incomplete difference set cutting, which still requires manual peeling and post-processing.

[0046] Reference Figure 4 and Figure 5In the process of pouring or dripping the adhesive 2 into the first incision 1', due to the flow of the adhesive 2, its shape and size have a large range of variation, so that the solidified adhesive 2 presents different shapes. Therefore, when the differential cutting feed is performed, it is easy to cause feed failures such as collision and breakage due to the uncertain range. In the process of cutting the support rod 3' of the present application, the cutting knife on the computer numerical control processing equipment starts to operate from a position far away from the outer wall of the adhesive 2', so that part of the feed is empty cutting and the other part is real cutting. Avoid feed failures such as collision and breakage due to the uncertain range.

[0047] Reference Figure 4 and Figure 5 The notch cut out in the process of cutting the support rod 3' is the second incision 4'. In the present application, the width of the second incision 4' is less than or equal to the width of the first incision 1'. In the process of cutting the support rod 3', it is only necessary to cut a gap between the denture and the support rod 3'. By limiting the width of the second incision 4', it has the effect of reducing the probability of damaging the denture while reducing the amount of cuttings.

[0048] Reference Figure 5 and Figure 6 , peeling of adhesive 2', after completing the cutting of support rod 3', take out the ceramic block on the cut support rod 3", and peeling of adhesive 2'. Put the ceramic block with denture into the corresponding tooling, the bottom of the tooling is provided with a soft support pad or a buffer structure, according to the type of tooling used, the adhesive 2' is peeled off according to the corresponding prescribed processing procedures, and the peeled ceramic block falls into the soft support pad or buffer structure to act as a buffer, thereby reducing the damage to the denture during the separation process.

[0049] The separation of the adhesive 2' and the denture includes full separation, in which the denture is completely separated from the zirconia embryo, and semi-separation, in which the adhesive 2' is semi-melted / semi-dissolved and softened; for semi-separation, a mechanical soft ejector is used to gently press the denture to separate it from the zirconia ligand, and the denture falls to the position of the soft pad after it falls off, which is basically consistent with its position on the pick block. Because the number and indication of the denture on the zirconium block are arranged before processing, if the falling position corresponds to it, then the number and indication of the denture that falls on the soft pad are known, so that it can be automatically picked by the machine.

[0050] In the first embodiment of the present application, the implementation principle of an automatic tooth extraction method is as follows: a first incision 1' is opened on one end of a support rod 3 close to a denture by means of computer numerical control processing equipment, an adhesive 2' is fixed on the inner wall of the first incision 1', the adhesive 2' assists the support rod 3' in supporting the denture, and then the remaining porcelain block on the support rod 3' close to the first incision 1' is cut off, and the denture is fixed to the support rod 3" under the bonding and fixation of the adhesive 2', and finally the denture is made to fall off by changing the shape of the adhesive 2', and the cutting of the denture during the separation process is completed by means of computer numerical control processing equipment, and no manual cutting is required, thereby reducing the damage to the denture caused during the cutting process.

[0051] Embodiment 2: Embodiment 2 is different from Embodiment 1 in that a secondary clamping and overlapping positioning method is adopted between a movable clamp and a fixed clamp, a second alignment mechanism is provided on the movable clamp, and a second alignment pair corresponding to the second alignment mechanism is provided on the fixed clamp. The ceramic block is put back on the clamping set and aligned and fastened to complete the secondary clamping and overlapping positioning, ensuring that the position and direction of the ceramic block after clamping accurately matches the position and direction before disassembly, making the fixation of the ceramic block more convenient.

[0052] In the present application, the second alignment mechanism can be a plurality of protrusions fixed on the movable workbench clamp, and the corresponding second alignment pair can be a plurality of grooves opened on the outer wall of the clamping set, and the protrusions and the grooves are arranged in a one-to-one correspondence; the second alignment mechanism and the second alignment pair can also be other components for fast and precise positioning.

[0053] The implementation principle of the second embodiment of the present application, a method for automatic tooth extraction, is the same as that of the first embodiment.

[0054] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for automatic tooth extraction, characterized in that: The following steps are included Based on a denture cut from a zirconia block and a support rod (3), a first cut body (1) is provided for processing, and the first cut body (1) is cut at a connection end of the support rod (3) by computer numerical control processing equipment to obtain a first cut (1'), wherein the first cut (1') is located at one end of the support rod (3') connected to the denture; Providing an adhesive (2), wherein the adhesive (2) is provided at the position of the first incision (1'), wherein the adhesive (2) is a soluble or meltable substance, or other substances that can be physically decomposed or chemically dissolved; Solidification of the adhesive (2), changing the environment and / or the self-conditions so that the adhesive (2) solidifies to form an adhesive (2') fixed to the denture; Processing the second cut body (4), cutting the second cut body (4) at the connection end between the support rod (3') and the denture by computer numerical control processing equipment to obtain a second cut (4'), and connecting the cut support rod (3") to the denture by means of the adhesive (2'); The adhesive (2') is peeled off by changing the physical state of the adhesive (2') by dissolving or melting or other physical decomposition or chemical dissolution methods, so that the adhesive (2') is separated from the denture.

2. The method for automatic tooth extraction according to claim 1, characterized in that: The cross section of the support rod (3) connected to one end of the denture is arranged in a rod shape, and as the volume of the denture increases, the rod diameter of the support rod (3) increases accordingly.

3. The automatic tooth extraction method according to claim 1, characterized in that: The interface domain where one end of the first incision (1') is connected to the denture and the area where the other end of the first incision (1') is connected to the support rod (3') is a cuttable portion for cutting the second cut body (4); in this cuttable portion, a separation incision with an allowable width can be set by calculation and a processing strategy including the shape and size of the tool blade, and the separation incision forms a spatial difference set from the cut surface domain of the support rod and the interface domain connected to the denture, calculates the difference set of the separation incision at the first incision (1') on each support rod (3'), and completes the difference set spatial part cutting at the first incision (1') according to the difference set area through computer-controlled processing equipment.

4. The automatic tooth extraction method according to claim 1, characterized in that: After the support rod (3') is connected to the differential cutting, the ceramic block is placed in a tool or a container, and the receiving bottom of the tool or the container is provided with a soft supporting pad or a buffer structure; the physical state of the adhesive (2') is changed so that the adhesive (2') is separated from the denture, including full separation, in which the denture is completely separated from the zirconia embryo, and semi-separation, in which the adhesive (2') is semi-melted / semi-dissolved and softened; for semi-separation, a mechanical soft ejector is used to lightly press the denture to separate it from the zirconia embryo and place it on the soft supporting pad. The position of the denture corresponding to its position on the zirconium block.

5. The automatic tooth extraction method according to claim 1, characterized in that: The adhesive (2) is mixed with an additive, and the additive is used to improve the application of the adhesive (2) and improve the adhesion, rigidity and strength of the adhesive (2').

6. The automatic tooth extraction method according to claim 1, characterized in that: After the adhesive (2) is fixed to form an adhesive (2'), the ceramic block is placed back into the computer numerical control device, and a secondary clamping overlap positioning structure and a fixture are used when placing it back.

7. The automatic tooth extraction method according to claim 6, characterized in that: A first alignment mechanism is arranged on a fixture on the computer numerical control processing equipment, the ceramic block is mounted on a clamping set, and a first alignment pair corresponding to the first alignment mechanism is arranged on the clamping set.

8. The automatic tooth extraction method according to claim 6, characterized in that: The clamping set is provided with a second alignment mechanism, and the ceramic block fixing ring is provided with a second alignment pair corresponding to the second alignment mechanism, and the ceramic block is put back onto the clamping set for alignment and fastening.

9. The automatic tooth extraction method according to claim 1 or 3, characterized in that: The width of the first incision (1') is greater than or equal to the width of the second incision (4').

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