JP3460163B2 - Small fluid driven turbine handpiece with synthetic resin cap - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a new capping system applied to small fluid driven turbine handpieces such as dental air turbine handpieces. More recently, according to the present invention, the cap and the housing of the head portion, which are the main components of this type of handpiece, are made of synthetic resin, and both members are fixed by utilizing the elastic deformation of the synthetic resin. The present invention relates to such a small fluid turbine handpiece.

[0002]

2. Description of the Related Art Conventionally, small fluid-driven turbine handpieces have been used, for example, for cutting materials, or for medical purposes, orthopedics in surgery (eg, brain surgery, orthopedics, oral surgery, otolaryngology, etc.). Or in plastic surgery, ・ In dental treatment of teeth, cutting bones and teeth,
It is widely used for opening, cutting, cutting and polishing. Among the small fluid-driven turbine handpieces described above, a small-sized dental fluid-driven turbine handpiece that uses pressurized air as a pressurized fluid that is a drive medium of a turbine is called a dental air turbine handpiece. For the sake of convenience of explanation, the prior art and the present invention will be described below using the dental air turbine handpiece as an example. The external shape of the dental air turbine handpiece is as shown in FIG.

As shown in FIG. 1, the dental air turbine handpiece (A) comprises a head portion (H) and a grip portion (G). The neck portion (N) of the grip portion (G) is connected to the head portion (H) and supplies / exhausts pressurized air to / from an air turbine arranged in the head portion (H). Has inside. Further, the head portion (H) is provided with a cap (C) on the upper portion and a tooth treatment tool (T), for example, a cutting tool, on the lower portion.

The air turbine arranged in the head portion (H) is composed of a rotating shaft which is rotationally driven by pressurized air and an impeller (turbine blade) arranged on the outer peripheral surface of the rotating shaft. The turbine unit is referred to below. Since the turbine system is supported by the bearing mechanism, the unit including the bearing mechanism may be hereinafter referred to as a turbine unit.

As shown in FIG. 2, the turbine unit (B) is arranged in the chamber (11) of the head housing (1) of the head portion (H). The turbine unit (B) is configured to have an impeller (3) on the outer peripheral portion of the rotary shaft (2), and the rotary shaft (2) is provided inside the head housing (1) with a bearing portion (4). It is rotatably supported via. As shown in the figure, the head portion (H) is composed of a head housing (1) and a cap (C), and the rotating shaft (2) and the impeller of the turbine unit (B) are provided inside the head housing (1). Chamber (1) for arranging (3)
1) is configured. Generally, since the head portion (H), and hence the head housing (1) and the cap (C) are made of metal, both members are screwed (CH) as shown in the drawing. Although not shown, an O-ring is also used to maintain airtightness. Furthermore, in recent years, a disposable type dental handpiece in which the head housing (1) and the cap (C) are made of synthetic resin and which are adhered and fixed with an adhesive is also seen.

A tool shaft (5) such as a dental cutting tool is detachably fixed and held at the axial center of the rotary shaft (2) of the turbine unit (B), and various dental treatments are performed. In addition, in the illustrated one, the rotary shaft (2)
Has a chuck (51) of a friction type chuck mechanism for gripping the tool shaft (5) therein. Needless to say, a one-touch chuck mechanism known as a chuck mechanism may be used.

Another configuration of this type of dental air turbine handpiece (A) will be described with reference to FIG. As shown in FIG. 2, the bearing portion (4) includes an inner ring (inner race) (41), an outer ring (outer race) (42),
The ball bearing is composed of a ball (43) and a retainer (44). In addition, an O-ring for centering and a known mechanism for increasing shaft rigidity are provided on the outer periphery and the side of the bearing portion (4). Shown is a ball (43)
However, it may be a known air bearing mechanism called an air bearing. In the conventional dental air turbine handpiece (A), the treatment site is irradiated to the head housing (1) of the head portion (H) or the main body (6) of the neck portion (N), which is not shown. An illumination system for doing so, a water supply path for irrigating the treatment site with water or physiological saline to remove the cutting heat of the bones and teeth, or for cleaning may be provided.

FIG. 3 illustrates a manner of supplying / exhausting pressurized air of a conventional dental air turbine handpiece (A). That is, in the conventional dental air turbine handpiece (A), pressurized air is supplied to the air supply passage (7) arranged in the main body (6) of the neck portion (N), and the pressurized air is supplied. After it is introduced into the chamber (11) through the air supply port (71) and injected into the impeller (3) to generate a rotational driving force on the rotating shaft (2), it is introduced into the main body (6) of the neck portion (N). It is performed by guiding the gas from the exhaust port (81) provided to the exhaust passage (8) to exhaust the gas. In the figure, in the arrow line showing the pressurized air flow in the chamber (11) of the head part (H), the solid line arrow line circulates between the inner wall surface of the chamber (11) and the impeller (3). The components, and the dotted lines indicate the components circulating in the space formed between the upper and lower inner wall surfaces of the chamber (11) and the upper and lower portions of the impeller (3). And the exhaust of these components is shown as exhaust flow (b). As an exhaust mode, there is a new system that reduces these circulating components as much as possible, but this point will be described later (see the section "Problems to be solved by the invention").

Many problems have been pointed out with respect to the conventional dental air turbine handpiece having the above structure. For example, head housing (1) and cap (C)
However, the problem of sterilization / sterilization processability has been pointed out in the fixing method of (1), that is, the fixing method of the screwing mechanism through the O-ring. More specifically, in order to cope with the AIDS problem, hepatitis C, etc., whether or not the above-mentioned fixing method can sufficiently prevent sterilization and sterilization after use, as well as prevent invasion of the fixing site of pathogenic bacteria, or It has been pointed out that the turbine unit, including the durability, is durable under the severe conditions during processing in a high-pressure steam sterilizer.

In addition, under the fixing method of the above mechanism, when disassembling and assembling is considered, the workability is poor, and the conventional metal and expensive dental air turbine and the head described above are used. Since it is extremely uneconomical to dispose of a synthetic resin disposable type dental handpiece, in which the housing (1) and the cap (C) are adhesively fixed, in order to deal with the above-mentioned AIDS and hepatitis C after a predetermined number of times of use. However, due to the efficiency and certainty of sterilization / sterilization treatment and the ease of turbine unit replacement, a new economical fixing method is being demanded, and other problems are addressed.

[0011]

Among the problems of the above-mentioned conventional dental air turbine handpiece, the present invention particularly makes the head part synthetic resin, and the main components of the head housing and cap are It proposes an economical new fixing method with the above requirements in mind.

The direct trigger of the present invention is the development of a handpiece incorporating a new air supply / exhaust mechanism in order to improve the performance of the above-mentioned conventional metal dental air turbine handpiece. A small fluid-driven turbine handpiece incorporating the above-described new air supply / exhaust mechanism was previously filed by the present inventors (for example, Japanese Patent Application No. 6-3640).
See No. 4. Hereinafter, this is referred to as the previous application of the present inventors. The outline is shown in FIGS. 4 to 5 corresponding to FIGS.

The outline of the earlier application of the present inventors is shown in FIGS. 4 to 5, and the same symbols (alphabetic letters and numerals) have the same meaning contents as in FIGS. , Easily understood. The decisive difference between them (the ones in FIGS. 4 to 5 and the ones in FIGS. 2 to 3) lies in the air supply / exhaust mechanism. The previous application of the present inventors (FIGS. 4 to 5) is provided with exhaust ports (8, 9) in the vicinity of the air supply port (7). The new air supply / exhaust system allows the exhaust flow (a) (see FIG. 5) to flow in the conventional manner (see FIG. 3 (b)).
It is completely different from the one shown in. In other words, the prior application of the inventors of the present invention is a system in which the pressurized air flow is not circulated in the chamber (11) (non-circulation), and the pressurized air injected into the chamber (11) is used. The flow is exhausted immediately. By adopting the above-mentioned new air supply / exhaust system, the rotation speed of the tool (T) is 35 to 50 from the conventional level of about 20 to 350,000 rpm.
Greatly improved to 10,000 rpm level and large torque can be obtained.
In addition, another major structural difference between the two is that the distance (d ₁ ) between the upper and lower wall surfaces of the chamber (11) and the turbine blade (3) (see FIGS. 4 and 2) is significantly different. You can increase your presence.

In the process of developing the small fluid-driven air turbine handpiece which is the previous application of the present inventors,
The idea of using plastic for the head was born. This is because the pressurized air flow injected into the chamber (11) is immediately exhausted to the outside of the system as described above, so that the chamber (11) and the cap (C) that covers the chamber (11) are ) Does not apply a large load to the head housing (1) and the cap (C), that is, the head housing (1) and the cap (C) which are easily removable can be made of plastic. The idea was born. The present invention was developed based on the background described above, and a small fluid-driven turbine handpiece having a synthetic resin cap with excellent characteristics capable of meeting the problems and requirements described above is provided. Provided.

[0015]

The present invention will be summarized as follows.
A first invention is a chamber of a synthetic resin head housing.
A small fluid driven turbine handpiece having a synthetic resin head housing which is to be crowned by synthetic resin cap with a built-in turbine unit which is rotationally driven by a pressurized fluid in the chromatography, and a turbine unit
The pressurized fluid after rotating the
Supply of pressurized fluid that does not circulate inside the chamber
In a small fluid-driven turbine handpiece having a discharge mechanism , (i) in either the outer peripheral portion or the inner peripheral portion of the cap and the inner peripheral portion or the outer peripheral portion of the head housing, in the circumferential direction thereof. A convex piece is arranged continuously or discontinuously, and (ii) a concave groove for fitting the convex piece is arranged on the other side to constitute an engaging means by elastic deformation. The present invention relates to a small fluid-driven turbine handpiece characterized in that a cap and a head housing are fixed by means of.

A second aspect of the invention is a synthetic resin head housing.
Rotated by pressurized fluid in the housing chamber
That a synthetic resin cap with a built-in turbine unit A compact fluid driven turbine handpiece having a synthetic resin head housing to be crowned, or
The pressurized fluid after rotating the turbine unit
Circulate in the chamber of the synthetic resin head housing
Small fluid drive unit with no pressurized fluid supply / discharge mechanism
In over bottle handpiece, either one of the inner peripheral portion or the outer peripheral portion of (i) the outer peripheral portion or the inner peripheral portion of the cap and the head housing, with disposing the convex protrusion having a convex lead portion, ( ii) On the other hand, a concave groove having a concave lead portion that guides and fits the convex lead portion of the convex protrusion is provided to form an engaging means, and the cap and the head housing are fixed by the engaging means. And a small fluid-driven turbine handpiece.

Furthermore, a third invention is a synthetic resin head.
Rotation driven by pressurized fluid in chamber of housing
A small fluid driven turbine handpiece having a synthetic resin head housing which is to be crowned by synthetic resin cap with a built-in turbine unit to be,
And the pressurized fluid after rotating the turbine unit
Flow into the chamber of the synthetic resin head housing.
Compact fluid drive with a pressurized fluid supply / discharge mechanism
In the turbine handpiece , (i) a convex protrusion is provided on either the outer peripheral portion of the cap and the inner peripheral portion or the outer peripheral portion of the head housing, and (ii) the convex protrusion is guided to the other. The engaging means is formed by arranging an L-shaped or inverted L-shaped concave groove to be fitted with each other,
The present invention relates to a small fluid drive turbine handpiece characterized in that the cap and the head housing are fixed by the engaging means.

In the above-mentioned first to third inventions,
In addition to the respective engaging means, rotation preventing means may be added to both members of the synthetic resin cap and the synthetic resin head housing to prevent rotation of both members in cooperation with each other. .

Hereinafter, the technical constitution and embodiments of the present invention will be described in detail with reference to the drawings. Needless to say, the present invention is not limited to the illustrated one.

FIGS. 6 (1) and 6 (2) show a fixing (engaging) means arranged in the cap (C) and the head housing (1) of the head portion (H) of the first embodiment of the present invention. It is a figure explaining. In the present invention, the cap (C) and the head housing (1) are made of a synthetic resin, preferably a synthetic resin having a heat distortion temperature of 150 ° C. or higher in consideration of heat distortion resistance in an autoclave for sterilization. To be done. If the heat distortion temperature characteristic is specified by the characteristic under load, the ASTM
D-648 (load: 6.4 Kgf / cm ² ) at 135 ° C. or higher is preferable. As the synthetic resin satisfying the above-mentioned conditions, a thermoplastic resin or a thermosetting resin may be used as long as injection molding or compression molding is possible. Examples of the injection-moldable synthetic resin include wholly aromatic polyester polymer resin, polyamideimide resin, polyethernitrile resin, polyetherimide resin, polyetheretherketone resin, polyimide resin, polyethersulfone resin, and polyphenylenesulfide resin. Or these reinforced resins and the like. The reinforcing material applied to the reinforcing resin is a desired fiber reinforcing material such as carbon fiber or glass fiber, or ZnO, Ag, Ti.
A reinforcing material having an antibacterial filler such as O2 or hydroxyapatite may be used.

As shown, the fixing (engaging) means of the first embodiment is of the following form. (i) On the cap (C) side, at the outer periphery of the cap,
A convex piece (C ₁ ) is arranged in the circumferential direction. (ii) On the other hand, a concave groove (H ₁ ) for fitting the convex piece (C ₁ ) is provided on the side of the head housing (1). The convex piece (C ₁ ) and the concave groove (H ₁ ) are fitted and fixed to each other by elastic deformation of the synthetic resin. In the present invention, various modifications can be made to the first embodiment. For example, the convex piece and the concave groove may be formed on opposite members. Further, in FIG. 6, the convex piece is arranged on the outer peripheral portion of the cap, and the concave groove is arranged on the inner peripheral portion of the head housing. On the contrary, the convex piece is arranged on the outer peripheral portion of the head housing, A concave groove may be provided on the inner peripheral portion of the cap, a concave groove may be provided on the outer peripheral portion of the head housing, and a convex piece may be provided on the inner peripheral portion of the cap. Furthermore, the convex piece and the concave groove may be arranged (continuously) over the entire circumference in the circumferential direction or intermittently (discontinuously). Further, the number of convex pieces and concave grooves may be two or more.

In FIGS. 6 (1) and 6 (2), the protrusion (C) protruding below the upper end (cap) of the cap (C).
₂ ) and the corresponding recessed portion (H ₂ ) of the head housing (1) serve to accurately position both members and prevent rotation. That is, the protrusion (C ₂ ) and the recess (H
₂ ) is fitted and fixed so that both members are accurately positioned and rotation of the cap (C) about the turbine unit axis is prevented. This embodiment is similar to that shown in FIG.
In the air supply / exhaust system for the pressurized air to the turbine unit (B) described above, it becomes important when arranging the exhaust ports at the upper and lower adjacent portions of the air supply port. That is, when the exhaust port is formed by using the cap (C), the positioning means is important. In addition, (C ₃ ) of the cap (C) portion shown in FIG. 6 (1) is a guide hole for inserting a tool when the cap (C) is fixed to or removed from the head housing (1).

7 (1) and 7 (2) show a cap (C) and a fixing (engaging) means provided in the head housing (1) of the head portion (H) of the second embodiment of the present invention. It is a figure explaining. The fixing (engaging) means of the second embodiment is of the following form. (i) On the cap (C) side, at the outer periphery of the cap,
A projecting protrusion (C ₄ ) having a projecting lead portion is provided. (ii) On the other hand, a concave groove (H ₃ ) having a concave lead portion for fitting and guiding the convex lead portion of the convex protrusion (C ₄ ) is provided on the side of the head housing (1). The convex lead portion (or the concave lead portion) has a function of engaging the engaging means of both members and guiding (leading) to the lead portion to reach a predetermined engaged state. .

In FIGS. 7A and 7B, (C ₅ ) of the cap (C) and (H ₄ ) of the head housing (1).
Is a rotation preventing means for positioning and preventing loosening of both members when they are fixed. Various modifications can be made to the second embodiment as well. For example, the convex projections (C ₄ ) and the concave grooves (H ₃ ) may be formed on opposite members, that is, the convex projections and the concave grooves may be formed on the inner peripheral portion of the cap as in the first embodiment. It may be formed on the outer periphery of the head housing. Furthermore, two or more convex protrusions and concave grooves may be provided for each member. Further, although not shown, an O-ring may be arranged between the cap and the head housing in order to improve coaxiality and airtightness. Incidentally, (C ₆ ) of the cap (C) is a guide hole for inserting a tool when the cap (C) is fixed to the head housing (1) or removed.

FIGS. 8 (1), 8 (2) and 8 (3) show the fixing (retention) provided on the head housing (1) of the cap (C) and the head portion (H) of the third embodiment of the present invention. FIG. 6 is a diagram for explaining the means. The fixing (engaging) means of the third embodiment is
It is of the following aspect. (i) On the cap (C) side, at the outer periphery of the cap,
Protrusions (C ₇ ) are provided. (ii) On the other hand, on the side of the head housing (1), an L-shaped concave groove (H ₅ ) into which the convex protrusion (C ₇ ) is fitted is provided. And both members (cap and head housing)
The fixation of the convex protrusion (C ₇ ) is performed by connecting the L-shaped concave groove (H
₅ ), and both members are rotated and tightened at the bottom of the L-shaped groove. The convex portion (H ₆ ) formed in the L-shaped concave groove (H ₅ ) is of a size that elastically deforms mutually with the convex protrusion (C ₇ ), and the cap (C) The convex protrusion (C ₇ ) of the portion passes through the convex portion (H ₆ ) and is accommodated in the accommodating chamber (H ₇ ) formed at the tip of the L-shaped concave groove which is the final fixing position. Therefore, at this position, the cap (C) is fixed stably and without being loosened.

Various modifications can be made to the third embodiment. For example, the convex protrusion (C ₇ ) and the L-shaped concave groove (H ₅ ) may be formed on opposite members.
That is, similar to the first embodiment, the convex protrusion and the concave groove may be formed on the inner peripheral portion of the cap and the outer peripheral portion of the head housing.
Further, two or more convex projections and concave grooves may be provided for each member, and the L-shape may be an inverted L-shape. Furthermore, L
The V-shaped concave groove may have the shape shown in FIG. 9 (1) and 9 (2), the L-shaped groove (H ₈ ) has a shape (tapered) different from that of the convex portion (H ₆ ) shown in FIGS. 8 (2) and 8 (3). It has a convex portion (H ₉ ). In FIG. 9, (H ₁₀ ) is the projection (C) of the cap (C) at the final fixing position of both members.
_This is the room that houses ₇ ). In addition, the raised part is L
The anti-rotation means of the second embodiment may be provided separately instead of forming the V-shaped concave groove. In the above embodiment,
Although not shown, it goes without saying that an O-ring may be provided between the cap and the head housing in order to enhance the coaxiality and airtightness.

[0027]

INDUSTRIAL APPLICABILITY The present invention relates to a small-sized fluid-driven turbine handpiece represented by a dental air turbine handpiece, in which a head portion is made of plastic, particularly a removable cap portion in relation to a high pressure fluid supply / discharge system. It is confirmed that the plastic housing of the head housing can be realized, and an economical new fixing method can be provided instead of the conventional screwing mechanism using the O-ring.

The method of fixing both members of the present invention on the assumption that the cap portion and the head housing portion are made of plastic is sterilized to prevent infections such as AIDS and hepatitis C, which are strongly required for this type of handpiece. -It has excellent sterilization processability and exhibits durability against corrosion and chemicals during sterilization process. Further, the workability when disposing and replacing the turbine unit in the head housing is also excellent. In addition, it is made of plastic and is lightweight and excellent in cost performance. According to the invention,
A small fluid drive turbine having a cap and head housing made of synthetic resin, and a structure that replaces the conventional fixing method in which both members are fixed by screws through an O-ring, and has the above-mentioned excellent advantages. A handpiece is provided.

[Brief description of drawings]

FIG. 1 is a perspective view of a dental air turbine handpiece.

FIG. 2 is a cross-sectional view taken along the axis of the tool (T) shown in FIG.

3 is a cross-sectional view taken along line I-I of FIG.

FIG. 4 is a cross-sectional view of a dental air turbine handpiece having another internal structure, and is a view corresponding to FIG. 2.

5 is a sectional view taken along line II-II of FIG.

FIG. 6 is a diagram for explaining the fixing means of the first embodiment arranged on the cap and head housing of the present invention.

FIG. 7 is a diagram for explaining the fixing means of the second embodiment arranged on the cap and head housing of the present invention.

FIG. 8 is a diagram for explaining the fixing means of the third embodiment arranged on the cap and head housing of the present invention.

FIG. 9 is a diagram illustrating another fixing means arranged in the head housing of the present invention.

[Explanation of symbols]

A ………… Dental air turbine handpiece H ………… Head C ………… Cap N ………… Neck part G ………… Grip part B ………… Turbine unit 1 ………… Head housing 11 ………… Chamber 2 ………… Rotation axis 3 ………… Impeller (turbine blade) 4 ………… Bearing 5 ………… Tool axis 51 ………… Chuck 6 ………… Neck body 7 ………… Air supply route 8, 9 ………… Exhaust path

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shigeo Kobayashi, 43, Nukuda, Kumana City, Mie Prefecture 2 (72) Minor Ayukawa 5-111-105 Otoyama Takeen, Hachiman City, Kyoto City (56) References 6-181934 (JP, A) Actual development 2-123939 (JP, U) Actual development 64-14656 (JP, U) Actual development 4-38936 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61C 1/00-1/18 B65D 41/00-41/30

Claims (8)

(57) [Claims] 1. A chamber of a synthetic resin head housing.
A small fluid driven turbine handpiece having a synthetic resin head housing which is to be crowned by synthetic resin cap with a built-in turbine unit which is rotationally driven by a pressurized fluid in the chromatography, and a turbine unit
The pressurized fluid after rotating the
Supply of pressurized fluid that does not circulate inside the chamber
In a small fluid-driven turbine handpiece having a discharge mechanism , (i) in either the outer peripheral portion or the inner peripheral portion of the cap and the inner peripheral portion or the outer peripheral portion of the head housing, in the circumferential direction thereof. A convex piece is arranged continuously or discontinuously, and (ii) a concave groove for fitting the convex piece is arranged on the other side to constitute an engaging means by elastic deformation. A small fluid-driven turbine handpiece characterized in that the cap and the head housing are fixed by the. 2. The cap and the head housing have a rotation preventing means including a convex portion provided on either one of the cap and the head housing, and a concave portion engaging with the convex portion arranged on the other. 1. The small fluid-driven turbine handpiece according to 1. 3. A chamber of a synthetic resin head housing.
A small fluid driven turbine handpiece having a synthetic resin head housing which is to be crowned by synthetic resin cap with a built-in turbine unit which is rotationally driven by a pressurized fluid in the chromatography, and a turbine unit
The pressurized fluid after rotating the
Supply of pressurized fluid that does not circulate inside the chamber
In a small fluid-driven turbine handpiece having a discharge mechanism , (i) a convex lead portion is provided on either the outer peripheral portion or inner peripheral portion of the cap and the inner peripheral portion or outer peripheral portion of the head housing. And (ii) a concave groove having a concave lead portion that guides and fits the convex lead portion of the convex protrusion is provided on the other side to form an engaging means. A small fluid-driven turbine handpiece characterized in that the cap and the head housing are fixed by the engaging means. 4. The cap and the head housing have a rotation preventing means composed of a convex portion provided on either one of them and a concave portion engaging with the convex portion provided on the other. The small fluid-driven turbine handpiece according to item 3. 5. The small fluid-driven turbine handpiece according to claim 3, wherein two or more convex protrusions having convex lead portions and concave grooves having concave lead portions are arranged. 6. A chamber of a synthetic resin head housing.
A small fluid driven turbine handpiece having a synthetic resin head housing which is to be crowned by synthetic resin cap with a built-in turbine unit which is rotationally driven by a pressurized fluid in the chromatography, and a turbine unit
The pressurized fluid after rotating the
Supply of pressurized fluid that does not circulate inside the chamber
In a small fluid-driven turbine handpiece having a discharge mechanism , (i) a convex protrusion is provided on either the outer peripheral portion of the cap and the inner or outer peripheral portion of the head housing. (Ii) On the other hand, an engaging means is provided which is provided with an L-shaped or inverted L-shaped concave groove for guiding and fitting the convex projection.
A small fluid-driven turbine handpiece characterized in that the cap and the head housing are fixed by the engaging means. 7. The small fluid-driven turbine handpiece according to claim 6, wherein two or more convex protrusions and L-shaped or inverted L-shaped concave grooves are provided. 8. The miniature fluid-driven turbine handpiece according to claim 6, wherein the L-shaped or inverted L-shaped concave groove is provided with rotation preventing means having a raised portion for preventing loosening of the convex protrusion.