US2122619A

US2122619A - Dental instrument

Info

Publication number: US2122619A
Application number: US99613A
Authority: US
Inventors: John F Mcmath
Original assignee: Individual
Current assignee: Individual
Priority date: 1936-09-05
Filing date: 1936-09-05
Publication date: 1938-07-05
Anticipated expiration: 1955-07-05

Description

July 5, 1938;. J, F. MCMATH 2,122,619

E DENTAL INSTRUMENT Filed Sept. 5, 1936 3 Sheets-Sheet 1 j? F'lf* INVENTR. Joh/7 f /k/F/W//y ATTORNEY.

. July s, 193s. J. F. MCM'ATH 2,122,619

DENTAL IN S TRUMENT Filed Sept. 5, 1936 3 Sheets-Sheet 2 INVENTOR. i Job/7 F. MF/Wa/ ATTORNEY July 5, 1.938.

J. F. McMATg-l 2,122,619

DENTAL I NS TRUMEN T Filed Sept. 5, 1956 3 Sheets-Sheet 3 INVENTOR. Job/7 /WF/Mi/ ATTORNEY.

Patented July 5, 1938 PATENT orner.

2,122,619 DENTAL INSTRUMENT' JohnF. McMath, Oakland, Calif.

Application September 5, 1936, Serial No. 99,613

11 Claims.

My invention relates to dental instruments, and 'more particularly to tooth cleaning tools, such as tooth brushes, having oscillatable heads. This application is a continuation-in-part of my copending application, Serial No. 703,704, led Dec. 23, 1933.

It is desirable for eicacious operation of a dental instrument, such as a tooth brush, in the mouth of a person, that the tool or brush have oscillatory or relative pivotal movement with respect to the handle upon which it is mounted. This is so because, as the relative movement occurs, a rack and pinion-like effect occurs between the bristles of the tooth brush and the interstices or spaces between the teeth, to cause the bristles to enter such spaces and thus effect thorough cleansing in a very vital spot. With the conventional type of tooth brush, where the handle is rigidly fixed to the head of the brush, the ends of the bristles merely ride over the spaces or interstices between the teeth, resulting in lack of cleaning efficiency.

Pivotal or oscillatory mountings for the tool on the handle have been employed, as is taught in the patents to Newlon et al (Br.) No. 17,808 of 1915; Weis No. 1,706,555; Czencz No. 1,776,312; and my own prior Patent No. 1,968,303.

However, with respect to pivotal Yinstruments having oscillatable tools, there existed the problem of providing a construction which would .avoid pinching of delicate mouth tissues or membranes as relative movement between the handle and the tool occurred, and of providing a pivotal connecting means between the handle and the tool, which would not result in unduly increasing the external dimensions of the tool. Obviously, with any ordinary type of movable tool and handle connection, the mouth membranes will be caught and pinched, thus rendering impractical such advantageous arrangement. As for the problem of providing a small mounting of the character related, which does not require substantial increase in size of any given size tooth brush or tool, it is apparent that ,A the mouth is limited as to space.

1. Means for connecting the dental tool for relative movement with respect to the handle therefor, in a manner to preclude pinching of mouth membranes as such relative movement occurs;

2. Connecting means, of the character related, arranged within substantially the normal dimensions of the tool, especially the side extremities or widthwise dimensions of the tool, to thereby afford complete and normal useage of the tool vention comprises a tool including a head having 1 edge extremities, namely opposite end edges, and opposite side edges joined to the end edges. Suitable cleaning means, such as the usual brush bristles, or any other suitable means such as a resilient cleaning sponge or pad, is secured to f one face or surface of the head. 'I'he handle for the instrument has a portion extending past one end extremity or edge of the tool, and is connected to the tool, between the opposite side edges, forrelative pivotal movement with respect thereto, so as to enable oscillatory movement of the tool with reference to the handle.

Means, conned substantially within the area bounded by the edge extremities of the tool, is provided to limit oscillatory movement of the tool i with respect to the handle; and the parts are so connected adjacent the end edge or extremity past which the handle extends, as to provide shield means for precluding pinching of mouth membranes within the limits of the relative f movement permitted. rThis is primarily accomplished by having at least some portions of the tool and the handle adjacent the extremity referred to, always in cooperating overlapping relationship within the limits of movement allowed,

so as to leave no opening in which membranes can be caught as the relative movement occurs. Inasmuch as the connecting and motion limiting means between the tool and the handle, are conned substantially within the area bounded by i the edge extremities of the tool, particularly the side edge extremities which determine the widthwise dimensions` of the tool, increase, in the efcan be used in the mouth with comfort.

Reference will now be made to the drawings for a more detailed description of the invention:

Fig. l is a plan perspective view of tooth brush constructed in accordance with my invention.

Fig. 2 is a sectional elevation of the brush shown in Fig. 1.

Fig. 3 is a bottom view or the brush head, namely a view looking toward the bristle face of the brush head.

Fig. 4 is a side view of a tooth brush of modied design, the brush head being shown in section.

Fig. 5 is a transverse sectional View of the brush taken on the line 5 5 of Fig. 4.

Fig. 6 is a perspective view of another embodiment or the invention, illustrating the tool and the handle detached from each other. A portion of the handle is broken away to shorten the view.

Fig. 'l is a longitudinal sectional View through the tool taken in la plane indicated by line 'I--l in Fig. 6, illustrating the tool and the handle connected together.

Fig. 8 is a plan View of a further modied form of the invention.

Fig. 9 is a longitudinal sectional view taken in a plane indicated by line 9x9 in Fig. 8.

Fig. 10 is plan View of another form of device.

Fig. 10a is an end elevation looking in the direction or" arrow Illa in Fig. 10; the handle being shown in section.

ll is a longitudinal sectional view taken in a plane indicated by line II-II in Fig. 10.

Fig. l2 is a plan view of a still further embodiment of the invention.

Fig. 13 is a longitudinal section taken in a plane indicated by line I3-I3 in Fig. 12.

Fig, 14 is a fragmentary longitudinal sectional view, through the preferred form of instrument.

Fig. 15 is an underA elevational View looking in the direction of arrow I5 in Fig. 14; the tool head in Fig. l5 being shown in phantom lines.

-As illustrated in Figs. l through of the drawings, the connection of invention as applied to a tooth brush comprises a tool including brush head 6 formed with a back surface or face 1; to the opposite face of the head are secured cleaning means such as brush bristles 8. Provided in the head E and longitudinally extending inwardly from one end or edge extremity IIl thereof, between the opposite side edge extremities joining such end extremity, is a slot or recess I2 which is arranged to receive an extension piece or tang I 3 forming a portion of brush handle I6. The tang portion of the handle I6 is thus conned between the widthwise dimensions or sid-e edges of the tool. Slot I2 is open at both the back and the front of head E or in other words at each of the opposite surfaces or faces of the head; and the extension I3 of the brush handle is of a width substantially equal to the width of slot or recess I2. Means for pivotally connecting the tool head and the handle includes a pin Il extending transversely through the head, and engaging the extension piece I3 within the slot and adjacent the opposed ends I8 and 2| of the slot and the extension, respectively.

The pivotal movement of the head relative to the handle is arranged to be limited, so that some part of the handle extension I3 adjacent the end extremity vII always is in cooperating overlapping relationship with such extremity, and is shielded in slot I2 adjacent extremity I I. Thus,

' within the limits of the relative movement permitted, no opening is vever formed between the handle and the head adjacent extremity II, in

which mouth membranescan be caught. In iact, as may be best seen from Fig. 2, the depth of extension I3 is arranged less than the depth of the brush head, to thereby permit the limited relative oscillation of the head about the extension without causing an appreciable uncovering of the handle extension at all.

As a means for limiting oscillation of the head about pin Il which provides the pivot for the movable connection between the tool and the handle, the upper end portions 22 and 23 or" the opposed slot and extension ends I3 and 2i, respectively, are arranged to cooperate to provide one stop means for limiting upward movement of handle I6, as is illustrated by thesolid line position in Fig. 2. Such portions 22 and 23, in the dotted line positionof the handle shown in Fig. 2, are formed so as to be divergently disposed with reference to pin Il, to allow the limited movement of the handle in a counterclookwise direction from the dotted line position to the full line position in Fig. 2. The other stop means for limiting downward movement of the handle, in a clock-wise direction from the solid line to the dotted line position shown in Fig. 2, is provided by the lower portions 2S and 2'! which form contnuatlons of portions 22 and 23, respectively.

Such portions 26 and 2l slant at a comparatively sharp angle from portions 22 and 23, respectively, toward the open end or extremity of slot or recess I2 and, hence, cooperate with stop portions 22 and 23 to restrict movement of the handle to an extent materially less than 45, to thereby provide for a portion of the handle adjacent the end edgeextremity II of the head, at the open end o1" slot I2, always to work or remain in the slot, as relative movement between the tool and the handle occurs.` In effect, some portions of the handle and the head are always in overlapping relationship adjacent extremity II, and this coupled with the open-ended slot construction in the head, causes the end extremity of the head past-which the handle extends, to serve as a shield for the movable portion of the handle. This avoids pinching of delicate mouth tissues or membranes, as the desirable oscillatory movement occurs.

In this manner, suiicient amplitude of oscillation is afforded the tool during cleaning of the teeth, to allow effective cleansing vin the spaces occurring between the teeth; and the handle will be substantiallyT always in line with the head 6, as exists in known constructions where the brush or tool head is xed against movement with ref= erence to the handle, to offer no inconvenience in manipulation. With the movable connection between the handle and the brush head and the stop means, made substantially entirely within the connes or edge extremities of the head, it will be understood that no increase in the overall size of the tooth brush is made necessary by such connection, and that, therefore, the use of the tooth brush in the mouth as to mouth opening and length of brush stroke, will be unchanged from that of the usual brush.

As shown in Figs. 1 and 2, the face or surface of the head, to which the cleaning means is secured, is convexly curved about the pivotal connection of the head and the handle, and the bristles are arranged with their longitudinal axes generally radially of the connection. As a resnlt, theirorces incident on the bristles during the brushing of the teeth upon oscillation of the brush head, will be applied generally longitudi- :is .substituted for the pin l1, a pair of pin extensions *.28 formed preferably as a part of the handle or tang extension I3 and arranged to seat in `a recess Y29 extending transversely across the upper face of the brush head. Retention of the :pinextensions 23 in the recess is effected by means of .aspiing yoke 31| fitting over the head,

and releasably engaging at its ends in depres- .sions.3,2 formed in the side edge extremities of the head.. In this arrangement, the yoke serves as la means yfor limiting .oscillation Yof `the head in one direction. Because of the spring yoke 3|, which, as previously stated, is releasably held, lthe tool may be 'readily replaced by a Anew one when Vthe brush bristles become worn from use. .Obyiously, the tool may have other cleaning means in place of brush bristles 8 secured to the the head, such as a cleaning sponge orpad.

In both modifications thus far described, it will he observed vthat the connection betwen the tool `and the handle is coniined substantially within the width-wise .dimensions or side edge extremities of 4the tool. In actuality, such connection is confined substantially within the area bounded by the .edge .extremities of the tool, namely the opposite end extremities and the opposite side extremities. This avoids increase in effective size of the tool, as exists yin prior known constructions wherein the tool is movable relative to the handle and motion limiting means provided. As a result, no inconvenience or discomfort obtains when the tool is used in the mouth. Furthermore, the motion limiting means, which restricts oscillatory movement of the head relative to the handle, serves to maintain at least some parts of the handle .and the head at the extremity past which the rhandle extends, in cooperating overlapping engagement, to thus provide shield means which prevents pinching of mouth membranes .as such .oscillatory movement occurs.

Figs. 6 and '7 illustrate another embodiment of the invention in which the principles disclosed in Figs. 1 through 5 are employed. In such embodiment, the face or surface 40 of tool head 4l is formed with inwardly extending groove 42 which communicates with recess or slot 43 in the end edge or extremity 44. Such recess is open at both surface 4D of the head and the opposite surface 45 .to which the brush bristles 4] are secured, but does not extend inwardly lall the way .tothe .central portion yof the head as occurs in the modifications of Figs. 1 through 5,. It will be noted that recess 43 extends inwardly only to a position adjacent the end of the brush bristles.

Extension or tang portion 48 of tool handle 4.9, is pivotally connected to the tool to allow `limited oscillatory movement of the tool with respect to the handle, in such manner that a projecting portion 5l on the handle extension, always Works or lies in recess 43, or in other words overlaps extremity 44. This is accomplished by positioning portion 52 of extension 48 over head 4| above groove 42, and between the side edges or extremities 53 of the head. The pivotal connecting means includes fork 54 pivotally connected to the end of portion 52, and which is adapted to be detachably or removably seated in apertures 56 formed in the head.

Portion 52 is provided with downwardly extending pin memberV 51 rigidly secured thereto,

and which is adapted to enter aperture 58 between apertures 56. Apertures 58 is of larger diameter than the diameter of pin 5l, to thus allow the limited pivotal or oscillatory movement of the tool with respect to the handle. This limited movement, as previously explained, is

such as to provide the shield means adjacent the portion of the handle extending past edge extremity 44, to preclude pinching of mouth membranes as the movement occurs. Fig. '7 illustrates in the solid and dotted line positions, the limits of movement of the handle. In the dotted line position of the handle, it will be observed that groove 42 accommodates the under edge of portion v52 which passes over the head between opposite side edges 53.

The modiiication of Figs. 6 and 7 is desirable because, inasmuch as recess 43 does not extend inwardly to the central portion of the tool 4but only to the end of bristles 4l, the longitudinal rows of bristles may be placed closely together within a minimum width of .tool head. Although portion 52 of the handle passes over the head and the overall depth of the tool is, consequently, increased, nevertheless, the pivotal connection between the tool and the handle and the motion limiting means a-re confined within the area bounded by the side edge extremities of the tool, or in other words between the width-wise dimensions of the tool, to thereby avoid increase in size of such dimensions which is undesirable. The increased depth of the tool, offers no discomfort in manipulation because such increase is on the face of the head opposite the cleaning means face, andthe mouth can readily accommodate this.

As with respect to the previously described modifications, the tool can be readily removed from the handle, merely by pulling the handle so that the prongs of fork 54 and the pin 51, leave

apertures

56 and 58, respectively; and a new tool can be readily substituted therefor.

Figs. 8 and 9 depict a further modification-similar to that illustrated in Figs. 6 and '7, but in which the slot or recess adjacent the end edge or extremity 60 past which handle 6l extends, is omitted. In the construction of Figs. 8 and 9, extremity 60 is formed with a curvature concentric with the pivotal axis 62 of the connection between the handle 6l and the tool; such connection being the same as that described with reference to Figs. 6 and '7. Also, portion 53 of the handle, which always overlaps extremity 60, is formed with a curvature complementary to the curva.- ture of extremity 6|, so as to cooperate with such extremity in providing the shield means for preventing formation of an open space in which mouth membranes can be caught as relative movement between the handle and the tool occurs.

The motion limiting means in Figs. 8 and 9 restricts relative movement of the handle with respect to the tool within the full line and dotted line positions of the handle, shown in Fig. 9. Thus, such motion limiting means, as in the previously described modications, always serves to provide a portion of the head and the handle in shielding cooperation, adjacent the end edge or extremity past which the handle extends.

An additional embodiment of the invention is shown in Figs. 10 through l1, in which the brush bristles themselves serve as the shield means' to prevent formation of an open space in which mouth membranes can be caught. Brush bristles 65 extend in longitudinal rows closely adjacent ally connected to the handle at 18.

Vto'both of the opposite end edges or extremities A68 of tool head 61; and the portion 68 of the handle which extends past one end extremity 66, passes through the space between the intermediate rows of bristles. Such portion 68 of the handle is formed with an up-turned end 68 which is pivotally connected to pin 69 removably held in the head; the end 68 entering tapered aperture 18, the sides of which serve to limit motion of the handle with respect to the tool.

Figs. 12 and 13 illustrate a still further form of the invention, in which a resilient shield or pad, preferably of sponge rubber, is provided adjacent the end edge or extremity of the tool, past which vthe handle extends, to cooperate in preventing pinching of mouth membranes. In such form, the handle 1| and the tool head 'E2 are pivotally secured for limited oscillatory movement in the manner disclosed in Figs. 6` and 7; and recess 13 ls formed in the end edge or extremity 74 past which the handle extends. Shield portion 'l5 on the handle lies in recess 13 and overlaps edge or extremity 14.

Extremity 'I4 is formed with a curvature eccentric to the pivotal axis 16; and a rubber pad or insert TI, having a complementary curvature adjacent extremity M, is formed with a slot in which portion 75 of the handle lies and is pivot- Because of the complementary eccentric curvatures of extremity 'i4 and pad 71 adjacent the extremity, the pad will remain engaged with the extremity as relative movement between the tool and handle occurs. This cooperates with the shield means 1' formed by the portion 'l5 of the handle which overlaps extremity T4, to insure against pinching of mouth membranes as the limited relative movement occurs.

The preferred construction employs a resilient or spring latch connection between the tool and l the handle, which enables ready attachment and disconnection between these parts. Such construction is illustrated in Figs. 14 and l5, and comprises head 89 having brush bristles 8| secured, in the usual manner, to face 82 thereof. In the opposite face 83 of the head is formed a longitudinally or axially extending groove 84 which runs inwardly from end extremity or edge 88 of the head and which communicates with recess 8'! at such end extremity. Groove 84 and recess 8l', as with respect to prior modifications, are located between the opposite side edges of the head, which join end edge 88.

Handle 88 has tang or extension 89v which extends over the head past end edge or extremity 86, and between the opposite side edges of the head, and is of substantially the same width and depth as that of groove 84 to lie completely in the groove in one extreme position of the handle. Extension 89 is adapted for pivotal connection to the tool on pin 9|, lying transversely in the head, in a manner to be subsequently explained. As with respect to the modification of Figs. 6 and 7, extension 89 has shield portion 92 which lies in recess 81 and always overlaps extremity 88. An end projection 93 on shield portion 92 extends over the cleaning element face 82 of the head, to provide stop meansfor engaging such face 82 in another extreme position of the handle. Thus, the handle portion 89 extends over one face 89 of the head and provides stop means for limiting movement of the handle in one direction, as illustrated by the full line position in Fig. 14; and the projection 93 on shield portion 92 of the handle, is adapted to engage the opposite face 82 of the head for limiting movement of the handle in the opposite direction, as is illustrated by the broken line position in Fig. 14. Pinching of mouth membranes as relative movement between y the handle and the tool occurs, is hence avoided in the manner previously described. It will be noted that because groove 84 is adapted to receive extension 89, a compact structure obtains.

Ihe spring latch connection between' the handle and the tool will now be described. Extension 89 is hollow inside and open underneath, as can be seen more clearly from Fig. 15. At its far end, it is formed with a bayonet slot orrecess 96 in which pivot pin 9| is adapted to be engaged,

as shown in Fig. 14. A generally L-shaped leaf spring member 91 is mounted within extension 89, with one leg 98 thereof welded between the sides of projection 93. The other leg of the spring extends longitudinally or axially along handle extension 89, and has a hook portion 99 lying ,in recess 98. Such hookA portion normally engages inturned flanges |8| on extension 89; the flanges lill thus providing an abutment for the spring which, because of being anchored to projection 93, can be shifted or moved axially'along the handle extension, to separate hook 99 from abutment ||I|.

In connecting the tool and the handle, it is only necessary to rst position pin 9| between hook99 and abutment Il, and press down on the handle while moving it axially in the direction of edge 89, to separate the hook 99 from abutment |8|,.and thereby cause pin 9| to snap into bayonet slot or recess 96. The spring bearing against pin 9| will then hold the pin securely in the horizontal portion of the bayonet slot, so that during manipulation of the tool in the mouth, it cannot become detached from the handle. Detachment of the tool from the handle can be readily effected in a reverse manner.

In all embodiments of the invention, even though relative movement occurs between the handle and the tool, pinching of mouth membranes at the extremity of the tool past which the handle extends, is avoided. At the same time, the external edge dimensions of the tool, especially the width-wise dimensions, are not increased. Thus, the tool can be employed comfortably inthe mouth. As previously related, any suitable cleaning means, instead of brush bristles, can be employed in any of the modications described.

I claim:

- 1. A dental instrument comprising a tool including a head having edge extremities, a handle having a portion extending past one extremity and positioned between opposite extremities joining said one extremity, and means conned substantially between said opposite extremities for connecting said tool and said handle for limited relative pivotal movement therebetween, the llmits of movement being such as to preclude reversal of the position of said handle and to cause said handle portion to extend always past said one extremity, the handle having a part adjacent said one extremity to cooperate with such extremity in providing shield means for precluding pinching of mouth membranes within the limits of relative movement between said handle and said tool.

2. A dental instrument comprising a tool including a head, a handle having a portion extending past an end extremity of said head and positioned between opposite side extremities joining saidv end extremity, means substantially between said opposite side extremities for connecting said tool and said handle for relative pivotal movement therebetween, and stop means coniined substantially between said opposite side extremities for limiting said relative movement, the handle having a part adjacent said end extremity adapted to overlap such extremity within the limits of said relative movement to thereby cooperate with said end extremity in preventing for-l mation of an open space in which mouth membranes can be caught. Y

3. A dental instrument comprising a tool including a head, a handle having a portion extending past an end extremity of said head and over said head between opposite side extremities .joining said end extremity, means substantially between said opposite side extremities for connecting said tool and said handle for relative pivotal movement therebetween, and stop means confined substantially between said opposite side extremities for limiting said relative movement, the handle having a part adjacent said end extremity adapted to overlap such extremity within the limits of said relative movement to thereby cooperate with said end extremity in providing shield means for precluding pinching of mouth membranes.

4. A dental instrument comprising a tool including a head having a recess extending inwardly from an end extremity thereof, a handle having a portion extending past said end extremity and positioned between opposite side extremities joining such end extremity, means substantially between said opposite side extremities for connecting said tool and said handle for relative pivotal movement therebetween, and stop-means conned substantially between said opposite side extremities for limiting such relative movement, the handle having a part adjacent said end extremity adapted to lie substantially in said recess and o-verlap such extremity within the limits of Said relative movement.

5. A dental instrument comprising a tool having edge extremities, a handle having a portion extending past one extremity and positioned between opposite extremities joining said one extremity, means conned substantially between such opposite extremities for connecting said tool and said handle for limited relative movement therebetween, and means adjacent said one extremity including a resilient pad for providing a shield to preclude pinching of mouth membranes as such limited relative movement occurs.

6. A dental instrument comprising a tool head having cleaning means secured to a face thereof and a recess extending inwardly from an end extremity thereof between and in the direction of opposite side extremities joining said end extremity and forming the lengthwise extremities of said head, to a position adjacent an end of said cleaning means, a handle having a portion extending past said end extremity between and in the direction of said opposite side extremities and a second portion adapted to lie in said recess and overlap said extremity, means substantially between said opposite side extremities for connecting said tool and said handle for free relative pivotal movement therebetween during working operation of said instrument while cleaning, and means confined substantially between said opposite side extremities for limiting such relative movement so that at least some part of said second handle portion always works in said recess.

7. A dental instrument comprising a tool head having cleaning means secured to a face thereof and a recess extending inwardly from an end extremity thereof to a position adjacent an end of said cleaning means, a handle having a portion extending past said end extremity over the opposite face of said head and between opposite side extremities joining said end extremity, means substantially between said opposite side extremities for detachably connecting said tool and said handle for relative pivotal movement therebetween, said portion of said handle being engageable with said opposite face of said head to limit said pivotal movement in one direction, a second portion on said handle .adapted to lie in said recess and overlap said extremity, and means on said second portion of said handle for engaging said rst mentioned face of said head to limit said pivotal movement in an opposite direction.

8. A dental instrument comprising a tool; a handle; and means for detachably connecting said tool and said handle for free relative pivotal movement therebetween within a predetermined range of movement during working operation of said tool comprising a pin in said tool, said handle having .a recess in which the pin is engageable, and resilient means adjacent said handle recess and engageable with said pin for maintaining engagement between the pin and the handle.

9. A dental instrument comprising a tool head; va handle; and means for detachably connecting said tool and said handle for free relative pivotal movement therebetween within a predetermined range of movement during working operation of said tool comprising a pin in said head, said handle having a recess in which the pin is engageable, and a spring movable axially along said handle and having a hook in said recess adapted to embrace and hook over said pin.

l0. A dental instrument comprising a tool head having an end extremity, a handle extending past said end extremity and positioned between opposite side extremities forming the lengthwise extremities of said head, a pin in said head and extending transversely between and normal to said opposite lengthwise extremities, means for detachably connecting said head and said handle for relative free pivotal movement therebetween in a plane normal to said head during Working operation of said tool comprising a spring latch connection between said handle and said pin, means confined substantially between said opposite lengthwise extremities for limiting said relative movement within .a predetermined range of movement, and shield means adjacent said end extremity for precluding pinching of mouth membranes as such limited relative movementI occurs.

ll. A dental instrument comprising a tool having edge extremities, a handle having a portion extending past one extremity and positioned between opposite extremities joining said one extremity, means confined substantially between said opposite extremities for connecting said tool and said handle for free relative movement therebetween in a plane normal to said tool during working operation oi" said tool, and means substantially between said opposite extremities for conning such relative movement within limits precluding reversal of the position of said handle with respect to said tool to cause said handle to extend always past said one extremity.

JOHN F. MCMATH.