Dental handpiece

Abstract

We provide a dental handpiece with a simple structure that suppresses the generation of heat itself. [Solution] The dental handpiece according to this disclosure is a dental handpiece that rotates a cutting tool. The dental handpiece comprises a head 6 that rotatably houses a cutting tool 3, a first bearing provided on the insertion side into which the cutting tool 3 is inserted into the head 6 and which rotatably holds the cutting tool 3, a second bearing provided on the opposite side of the head 6 from the insertion side and which rotatably holds the cutting tool 3, and a drive mechanism that rotates the cutting tool 3 held by the first bearing and the second bearing. The first bearing and the second bearing have ball-holding cages made of different materials.

Description

Technical Field

[0001] The present disclosure relates to a dental handpiece.

Background Art

[0002] A dental handpiece cuts teeth by rotating at high speed while holding a cutting tool with a holding mechanism provided inside the head. The cutting tool is held by the holding mechanism, and the holding mechanism is rotatably held inside the head by a bearing.

[0003] Japanese Patent No. 6420073 (Patent Document 1) describes that since the cutting tool and the portion holding it rotate at a high speed of 200,000 revolutions per minute, problems such as abnormal heat generation of the cutting tool and the portion holding it may occur.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the dental handpiece described in Japanese Patent No. 6420073 (Patent Document 1) and the like, only the provision of a mechanism for detecting heat generation is described, and no configuration for suppressing the generation of heat itself is described. Further, in the dental handpiece described in Japanese Patent No. 6420073 (Patent Document 1) and the like, since a mechanism for detecting heat generation needs to be provided, the configuration becomes complicated and the manufacturing cost also increases.

[0006] This disclosure has been made in view of the above-mentioned problems, and its purpose is to provide a dental handpiece with a simple configuration that suppresses the generation of heat itself. [Means for solving the problem]

[0007] The dental handpiece of this disclosure is a dental handpiece that rotates a cutting tool. The dental handpiece comprises a head that rotatably houses a cutting tool, a first bearing provided on the insertion side into which the cutting tool is inserted into the head and which rotatably holds the cutting tool, a second bearing provided on the opposite side of the head from the insertion side and which rotatably holds the cutting tool, and a drive mechanism that rotates the cutting tool held by the first and second bearings. The cages that hold the balls of the first and second bearings are formed of different materials. [Effects of the Invention]

[0008] According to this disclosure, in a dental handpiece, the first bearing and the second bearing have ball-holding cages made of different materials, thereby suppressing the generation of heat. [Brief explanation of the drawing]

[0009] [Figure 1] This is an external view showing the appearance of a dental handpiece according to an embodiment. [Figure 2] This is a diagram illustrating the internal structure of the head. [Figure 3] This is a plan view of the bearing. [Figure 4] This is a disassembled perspective view of a bearing. [Figure 5] This diagram illustrates the evaluation of the retainer's durability in an autoclave. [Figure 6] This is a cross-sectional view illustrating another assessment of the retainer's autoclave resistance. [Figure 7] This diagram shows the combination of materials for the front and rear retainers. [Modes for carrying out the invention]

[0010] Embodiments of this disclosure will be described in detail with reference to the drawings. In the drawings, identical or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0011] [Components of a dental handpiece] Figure 1 is an external view showing the appearance of a dental handpiece 1 according to an embodiment. As shown in Figure 1, the dental handpiece 1 comprises a connector 2, a body 4, a neck 5, and a head 6. The connector 2, body 4, neck 5, and head 6 are arranged in this order from one end (proximal end) to the other end (tip) in the longitudinal direction of the dental handpiece 1.

[0012] The connector 2, located on the proximal end of the dental handpiece 1 in the longitudinal direction, is for connecting to a pipe that supplies driving air. The connector 2 is detachably configured to attach to the proximal end of the dental handpiece 1, and when connected to the proximal end of the dental handpiece 1, driving air is supplied to the head 6. The head 6, located on the tip of the dental handpiece 1 in the longitudinal direction, is the part that rotatably houses the cutting tool 3. The cutting tool 3 is configured to cut teeth by rotating at high speed.

[0013] In this embodiment, the drive mechanism of the dental handpiece 1 is an air turbine provided in the head 6 and the driving air supplied to the air turbine. In other words, the dental handpiece 1 is an air turbine handpiece that rotates the cutting tool 3 using an air turbine. However, the drive mechanism of the dental handpiece 1 is not limited to an air turbine, etc., and may also be a motor. In other words, the dental handpiece 1 may be a motor handpiece that rotates the cutting tool 3 using a motor.

[0014] The body 4 is configured to be detachable from the connection part 2. The body 4 is arranged on the proximal end side of the dental handpiece 1. The body 4 gradually decreases in diameter toward the distal end side of the dental handpiece 1. The body 4 includes a substantially cylindrical housing. The body 4 is a part that is grasped by users such as the operator and the maintenance worker.

[0015] When the operator holds the dental handpiece 1 with the cutting tool 3 facing downward, the head 6 facing upward, and the body 4 horizontal, the neck 5 bends upward at the central part in the longitudinal direction. The neck 5 gradually decreases in diameter toward the distal end side of the dental handpiece 1. The neck 5 includes a substantially cylindrical housing.

[0016] The head 6 is connected to the body 4 via the neck 5. The head 6 includes a substantially cylindrical housing having an axial direction in a direction substantially orthogonal to the longitudinal direction of the neck 5 (the vertical direction in FIG. 1).

[0017] FIG. 2 is a cross-sectional view for explaining the internal structure of the head 6. Referring to FIG. 2, the head 6 includes an air turbine 60, a holding mechanism 70, a rotating mechanism 80, and a release mechanism 90. The cutting tool 3 is held by the holding mechanism 70, and the holding mechanism 70 is held inside the head by the rotating mechanism 80. Since the air turbine 60 is fixed to the holding mechanism 70, the cutting tool 3 held by the holding mechanism 70 is rotated by receiving the driving air supplied from the connection part 2 and rotating.

[0018] The holding mechanism 70 holds the cutting tool 3. The holding mechanism 70 has a rotating cylinder 71, a slide ring 72, a ring holder 73, a chuck 74, and an elastic body 75.

[0019] The rotating cylinder 71 is configured to allow insertion of the cutting tool 3. The chuck 74 is configured to detachably hold the cutting tool 3 inserted into the rotating cylinder 71. The elastic body 75 is configured to bias the chuck 74 so that it engages with the cutting tool 3. In other words, the holding mechanism 70 can attach the cutting tool 3 by biasing the chuck 74 with the elastic body 75 so that it engages with the cutting tool 3 inserted into the rotating cylinder 71.

[0020] The slide ring 72 is housed on the rear side of the head 6 (opposite the insertion side of the head 6) relative to the elastic body 75, and by pressing it, the elastic body 75 can be compressed toward the front side of the head 6 of the cutting tool 3 (the insertion side into the head 6). When the elastic body 75 is compressed toward the front side of the head 6 of the cutting tool 3 by the slide ring 72, the force that the elastic body 75 exerts on the chuck 74 is weakened, making it possible to remove the cutting tool 3 from the chuck 74. In other words, the holding mechanism 70 can remove the cutting tool 3 inserted into the rotating cylinder 71 by pressing the slide ring 72.

[0021] The ring holder 73 is substantially cylindrical in shape and is located on the rear side of the head 6, relative to the slide ring 72. The ring holder 73 can restrict the position of the cutting tool 3 when it is mounted.

[0022] The rotating mechanism 80 includes a bearing 81 (first bearing) provided on the insertion side (front side) where the cutting tool 3 is inserted into the head 6, and a bearing 82 (second bearing) provided on the opposite side of the head 6 from the insertion side (rear side). Bearings 81 and 82 rotatably hold the cutting tool 3 via a holding mechanism 70. If it is not necessary to be able to attach and detach the cutting tool 3 from the head 6, bearings 81 and 82 may rotatably hold the cutting tool 3 directly.

[0023] The release mechanism 90 is a mechanism for changing the state of the holding mechanism 70 to a released state in which the cutting tool 3 can be removed from the holding mechanism 70. The release mechanism 90 has a cap 91, a cap ring 92, and a push cap 93. The cap 91 is attached to the rear side of the head 6, and the push cap 93 is attached to the cap 91 with the cap ring 92 in a pressable state. By pushing the push cap 93 towards the front side of the head 6, the push cap 93 presses the slide ring 72 of the holding mechanism 70, releasing the holding mechanism 70.

[0024] The bearings 81 and 82, which constitute the rotating mechanism 80, will be explained in more detail using the figures. Figure 3 is a plan view of bearings 81 and 82. Figure 4 is an exploded perspective view of bearings 81 and 82. The bearing 81, which is provided on the front side of the head 6, and the bearing 82, which is provided on the rear side of the head 6, will be described below assuming that they have the same structure and the same size, except that the material of the cage that holds the balls is different. Here, bearings 81 and 82 being the same size means, for example, that the difference between the outer diameter and inner diameter of bearings 81 and 82 is the same. Note that bearings 81 and 82 only need to have different cage materials, and their structure and size may be different.

[0025] The bearings 81 and 82 include an inner ring 801, an outer ring 802, a cage 803, and a plurality of balls 804. The plurality of balls 804 are positioned between the inner ring 801 and the outer ring 802. The cage 803 is positioned between the inner ring 801 and the outer ring 802 in the bearings 81 and 82. The material of the inner ring 801, the outer ring 802, the cage 803, and the plurality of balls 804 is not particularly limited and may be made of metal, resin, or the like.

[0026] The bearings 81 and 82 are used to rotatably hold the rotating cylinder 71 into which the cutting tool 3 is inserted. The bearings 81 and 82 rotate at high speeds of several hundred thousand revolutions per minute, and if they break, they will generate heat due to friction. Therefore, the bearings 81 and 82 used in the dental handpiece 1 need to be durable enough to withstand use for a specified period of time without breaking.

[0027] Furthermore, among the components that make up bearings 81 and 82, the cage 803 is more prone to damage than other components, and especially when a resin cage 803 is used, the durability of bearings 81 and 82 depends on the cage 803. In other words, the durability of the cage 803 is necessary for bearings 81 and 82 used in dental handpiece 1.

[0028] Furthermore, the dental handpiece 1 is autoclaved (for example, at 135°C for 10 minutes) after use for sterilization. Therefore, it is thought that the bearings 81 and 82, and especially the resin retainer 803, deteriorate with each autoclaving. The bearings 81 and 82 used in the dental handpiece 1 need to be durable enough to withstand a predetermined number of autoclaves and use for a predetermined time without breaking. In other words, the bearings 81 and 82 need to be resistant to autoclaving.

[0029] In dental handpiece 1, the cutting tool 3 is rotated using two bearings 81 and 82. When bearings 81 and 82 fail and generate heat, the amount of heat generated is greater when both bearings 81 and 82 fail and generate heat compared to when one of the two bearings 81 and 82 fails and generates heat. Therefore, by reducing the risk of both bearings 81 and 82 failing at similar times, it is possible to suppress the occurrence of high-heat generation itself. Accordingly, in dental handpiece 1, the holders 803 that hold the balls of bearings 81 and 82 are made of different materials to reduce the risk of both bearings 81 and 82 failing at similar times.

[0030] Furthermore, considering the structure of the dental handpiece 1, the load during cutting by the cutting tool 3 differs between the bearing 81 located on the front side and the bearing 82 located on the rear side of the head 6. The bearing 82 located on the rear side of the head 6, which is further from the cutting edge of the cutting tool 3, experiences a greater load than the bearing 81 located on the front side of the head 6, which is closer to the cutting edge of the cutting tool 3. Therefore, the bearing 82 located on the rear side of the head 6 needs to be more resistant to breakage than the bearing 81 located on the front side of the head 6, and it is preferable that the bearing 82 has higher autoclave resistance than the bearing 81. In particular, it is preferable that the cage 803 of the bearing 82 has higher autoclave resistance than the cage 803 of the bearing 81. Specifically, it is preferable to use polyamide-imide (PAI) resin for the cage 803 of the bearing 81 and polyimide (PI) resin for the cage 803 of the bearing 82.

[0031] Furthermore, in dental handpieces 1, water is generally injected from the front of the head 6 for the purpose of cooling the cutting tool 3. Therefore, even if the bearing 81 on the front side breaks and generates heat, the front side of the head 6 can be cooled by injecting water. On the other hand, even if the bearing 82 on the rear side of the head 6 breaks and generates heat, cooling by injecting water cannot be expected. Therefore, it is necessary to make the bearing 82 on the rear side of the head 6, which cannot be cooled, more resistant to breakage than the bearing 81 on the front side of the head 6, and it is preferable that the bearing 82 has higher autoclave resistance than the bearing 81. In particular, it is preferable that the cage 803 of the bearing 82 has higher autoclave resistance than the cage 803 of the bearing 81.

[0032] The autoclave durability of bearings 81 and 82 refers to their ability to withstand autoclave cycles a predetermined number of times and use for a predetermined period of time without breaking. Bearing 82 is considered to have higher autoclave durability than bearing 81 if it undergoes the same number of autoclave cycles, while bearing 82 takes longer to break. Similarly, bearing 82's cage 803 is considered to have higher autoclave durability than bearing 81's cage 803 if it undergoes the same number of autoclave cycles, while bearing 82's cage 803 takes longer to break. In practice, to evaluate the autoclave durability of bearings 81 and 82, one could, for example, autoclave them 1000 times and measure the time until they break, but this evaluation is time-consuming.

[0033] Therefore, the durability against autoclaving is evaluated by comparing the fracture strength and fatigue strength of the retainer 803. Note that the indicators used to evaluate durability are not limited to the fracture strength and fatigue strength of the retainer 803; other indicators, such as impact resistance, may also be used. Figure 5 is a diagram illustrating the evaluation of the durability of the retainer 803 against autoclaving. Figure 5 shows a graph comparing the fracture strength against the number of autoclave cycles for a retainer 803 made of polyamide-imide (PAI) resin and a retainer 803 made of polyimide (PI) resin. The horizontal axis of Figure 5 represents the number of autoclave cycles, and the vertical axis represents the fracture strength (in N). The fracture strength of the retainer 803 is the force applied when fracture occurs when force is applied radially to the retainer 803.

[0034] As shown in Graph B, the fracture strength of the retainer 803 made of polyamide-imide (PAI) resin decreases as the number of autoclave cycles increases. On the other hand, as shown in Graph A, the fracture strength of the retainer 803 made of polyimide (PI) resin does not change much even as the number of autoclave cycles increases. For example, when the number of autoclave cycles is 1000, the fracture strength of the retainer 803 made of polyamide-imide (PAI) resin is 4.6 N, while the fracture strength of the retainer 803 made of polyimide (PI) resin is 7.4 N. The fracture strength of the retainer 803 made of polyimide (PI) resin is approximately 1.6 times that of the retainer 803 made of polyamide-imide (PAI) resin. Therefore, based on the evaluation using the fracture strength of the retainer 803, it can be seen that the retainer 803 made of polyimide (PI) resin has higher autoclave durability than the retainer 803 made of polyamide-imide (PAI) resin.

[0035] Figure 6 illustrates another evaluation of the autoclavability of the retainer 803. Figure 6 shows a graph comparing the fatigue strength of a retainer 803 made of polyamide-imide (PAI) resin and a retainer 803 made of polyimide (PI) resin. Figure 6 shows the fatigue strength after 0 autoclave cycles, and after 500 or 1000 autoclave cycles. The fatigue strength of the retainer 803 is determined by the number of cycles at which failure occurs when a radial load (e.g., 4N) is repeatedly applied to the retainer 803. Therefore, the vertical axis in Figure 6 represents the number of load cycles at which failure occurs.

[0036] As shown in Graph C, the polyamide-imide (PAI) resin-based cage 803 has a fatigue strength of 24,645 cycles when the number of autoclaves is 0, and as shown in Graph D, it has a fatigue strength of 76 cycles when the number of autoclaves is 500. On the other hand, as shown in Graph E, the polyimide (PI) resin-based cage 803 has a fatigue strength of 187,695 cycles when the number of autoclaves is 0, and as shown in Graph F, it has a fatigue strength of 141,800 cycles when the number of autoclaves is 1,000. Despite the increase in the number of autoclaves from 500 to 1,000, the fatigue strength of the polyamide-imide (PAI) resin-based cage 803 is 76 cycles, while the fatigue strength of the polyimide (PI) resin-based cage 803 is 141,800 cycles. The fatigue strength of the retainer 803 made of polyimide (PI) resin is approximately 1865 times that of the retainer 803 made of polyamide-imide (PAI) resin. Therefore, even in evaluations using the fatigue strength of the retainer 803, it can be seen that the retainer 803 made of polyimide (PI) resin has higher autoclave resistance than the retainer 803 made of polyamide-imide (PAI) resin.

[0037] In other words, due to their durability against autoclaving, it is preferable to use polyamide-imide (PAI) resin for the cage 803 of the bearing 81 located on the front side of the head 6, and polyimide (PI) resin for the cage 803 of the bearing 82 located on the rear side of the head 6. Polyetheretherketone (PEEK) resin is a material that has higher autoclavability than polyamide-imide (PAI) resin. Therefore, due to their durability against autoclaving, it is also possible to use polyamide-imide (PAI) resin for the cage 803 of the bearing 81 located on the front side of the head 6, and polyetheretherketone (PEEK) resin for the cage 803 of the bearing 82 located on the rear side of the head 6.

[0038] Furthermore, when comparing the autoclave resistance of polyimide (PI) resin and polyetheretherketone (PEEK) resin, polyimide (PI) resin is more durable than polyetheretherketone (PEEK) resin. Therefore, for reasons of autoclave resistance, polyetheretherketone (PEEK) resin may be used for the cage 803 of bearing 81 located on the front side of head 6, and polyimide (PI) resin may be used for the cage 803 of bearing 82 located on the rear side of head 6.

[0039] Figure 7 shows the combination of materials for the front and rear cages 803. In Figure 7, the left column shows the material names for the cages 803 of the bearing 81 installed on the front side of the head 6, and the right column shows the material names for the cages 803 of the bearing 81 installed on the rear side of the head 6, corresponding to the left column. Note that the materials shown in Figure 7 are just examples, and the materials used for the cages 803 of the bearing 81 installed on the front side of the head 6 and the cages 803 of the bearing 82 installed on the rear side of the head 6 should be determined based on their durability against autoclave.

[0040] (modified version) It was explained that polyamide-imide (PAI) resin is used for the cage 803 of bearing 81, which is provided on the front side of head 6, and polyimide (PI) resin is used for the cage 803 of bearing 82, which is provided on the rear side of head 6. However, it is not limited to this, and polyamide-imide (PAI) resin may be used for at least one of the materials of the inner ring 801, outer ring 802, and ball 804 of bearing 81, and polyimide (PI) resin may be used for at least one of the materials of the inner ring 801, outer ring 802, and ball 804 of bearing 82.

[0041] It was explained that polyamide-imide (PAI) resin is used for the cage 803 of bearing 81, which is provided on the front side of head 6, and polyetheretherketone (PEEK) resin is used for the cage 803 of bearing 82, which is provided on the rear side of head 6. However, it is not limited to this, and polyamide-imide (PAI) resin may be used for at least one of the inner ring 801, outer ring 802, and ball 804 of bearing 81, and polyetheretherketone (PEEK) resin may be used for at least one of the inner ring 801, outer ring 802, and ball 804 of bearing 82.

[0042] It was explained that polyetheretherketone (PEEK) resin is used for the cage 803 of bearing 81, which is provided on the front side of head 6, and polyimide (PI) resin is used for the cage 803 of bearing 82, which is provided on the rear side of head 6. However, it is not limited to this, and polyetheretherketone (PEEK) resin may be used for at least one of the materials of the inner ring 801, outer ring 802, and ball 804 of bearing 81, and polyimide (PI) resin may be used for at least one of the materials of the inner ring 801, outer ring 802, and ball 804 of bearing 82.

[0043] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0044] 1 Dental handpiece, 2 Connector, 3 Cutting tool, 4 Body, 5 Neck, 6 Head, 60 Air turbine, 70 Holding mechanism, 71 Rotating cylinder, 72 Slide ring, 73 Ring holder, 74 Chuck, 75 Elastic body, 80 Rotating mechanism, 81, 82 Bearings, 90 Release mechanism, 91 Cap, 92 Cap ring, 93 Push cap, 801 Inner ring, 802 Outer ring, 803 Retainer, 804 Ball.

Claims

1. A dental handpiece that rotates and drives a cutting tool, A head that rotatably houses the cutting tool, The head is provided with a first bearing on the insertion side into which the cutting tool is inserted, which rotatably holds the cutting tool, A second bearing is provided on the side of the head opposite to the insertion side, which rotatably holds the cutting tool. The system includes a drive mechanism for rotating the cutting tool held by the first bearing and the second bearing, The first bearing and the second bearing are dental handpieces in which the ball-holding cages are made of different materials.

2. The dental handpiece according to claim 1, wherein the first bearing and the second bearing have the same size of the retainer.

3. The dental handpiece according to claim 1, wherein the first bearing and the second bearing have the same difference between their outer and inner diameters.

4. The dental handpiece according to any one of claims 1 to 3, wherein the second bearing has higher autoclave resistance compared to the first bearing.

5. The dental handpiece according to any one of claims 1 to 3, wherein the retainer of the second bearing has higher autoclave resistance than the retainer of the first bearing.

6. The dental handpiece according to claim 5, wherein the durability of the retainer against autoclaving is evaluated based on the fracture strength of the retainer against the number of autoclave cycles.

7. The dental handpiece according to any one of claims 1 to 3, wherein at least the cage of the first bearing is made of polyamide-imide (PAI) resin, and at least the cage of the second bearing is made of polyimide (PI) resin.

8. The dental handpiece according to any one of claims 1 to 3, wherein at least the cage of the first bearing is made of polyamide-imide (PAI) resin, and at least the cage of the second bearing is made of polyetheretherketone (PEEK) resin.

9. The dental handpiece according to any one of claims 1 to 3, wherein at least the cage of the first bearing is made of polyetheretherketone (PEEK) resin, and at least the cage of the second bearing is made of polyimide (PI) resin.

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