Dental Instrument

Abstract

In a dental instrument for the treatment of dental roots by dental instruments such as broaches or reamers, means are provided for causing the instrument to alternately rotate in one direction and in the opposite direction, the means causing an angle of rotation of the instrument which is at the most equal to the angle which corresponds to its yield strength, or elastic limit.

Parent Case Text

This application is a continuation-in-part of application Ser. No. 438,364 of Mar. 3, 1965, and Ser. No. 494,629 of Oct. 11, 1965.

Description

The present invention is concerned with a dental instrument for the treatment of root canals and in particular for the reaming of such canals.

The root treatment of interior teeth does not generally present any mechanical difficulties. This is not the case, however, with molars. The penetration and enlarging of fine and curved root canals often presents delicate problems.

Until recently the method of broaching canals by hand with files, reamers or broaches incurred both mechanical and operative dangers and difficulties Naturally one such danger was the dropping of the instrument into the respiratory or digestive passages.

The classical maneuver for canal enlargement is the rotation of the instrument, limited to a quarter turn and coupled with an up and down movement. This alternate rotational movement can only be achieved very slowly by hand at the rate of about 150 times per minute. The degree of rotation is naturally not precise and the dentist can over step the degree of elasticity of the metal and thus cause breakage of the instrument. Depending on the type of instrument used, an exaggerated rotation can lead to the creation of "steps" in the canal wall and to false roots in broaching.

Additionally the slow progress made may tempt the dentist to force, but the instrument is liable to twist or jam. Keeping the mouth open as wide as possible is very tiring for the patient and if he closes his mouth suddenly, there may occur an accident. Also to be considered is the fact that the dentist's fingers are extended while working in bad conditions, which may lead to cramp and to the dulling of tactile sense. Too, the visibility of the dentist is almost nil as the fingers obstruct the view of the tooth and saliva may make the fingers and instruments slippery.

Previous attempts to mechanize the treatment of root canals have never succeeded because the danger of breaking the instrument was too great.

In the past dental handpieces have been provided in which the continuous rotation of a whole turn was transformed into an alternating movement. This was done however for the purpose of a massaging or in conjunction with an axial movement, the device being used as a hammer or amalgam condenser.

The invention in one modification provides a handpiece having a rotating driving shaft moving a circular tray continuously around; a lug secured to the tray around its periphery; a hollow circular cylinder having an axis perpendicular to the motor axis and having a longitudinal slot which cooperate with said lug; means for supporting the drilling tool inside said circular cylinder and a gear case surrounding the handpiece.

The invention will be better understood by reference to the following description made by way of nonlimiting example of a handpiece according to the invention, and with the annexed drawing in which:

FIG. 1 is a schematic cross-sectional view of a handpiece according to the invention according to one modification.

FIG. 2 is a cross-sectional view along the line II-II of FIG. 1.

FIG. 3 is a schematic view plan wise of the securing plate for the drilling tool.

FIG. 4 is the same as FIG. 1 for another modification.

FIG. 5 is a cross section taken along line III-III of FIG. 4.

FIG. 6 is a schematic view of an operating assembly according to either modification of the invention.

FIG. 7 is an enlarged cross-sectional view of a tooth being treated by a reamer according to the invention.

Referring to FIGS. 1 and 2, handle 1 of the inclined shaft contains an arm 2 which is directly linked to usual moving means for dental chairs (not shown). At the elbow 3 of the handle is secured, by means of a threaded elbow sleeve 4, the handpiece 5. Use of sleeve 4 allows the replacement of handpiece 5 by any other conventional handpiece, having continuous rotation.

Handpiece 5 comprises a moving shaft 6 actuated by arm 2 by means of pinion 7 cooperating with the interior teeth 8 on the end of arm 2. On motor shaft 6 is fixed a sleeve 9 bearing a circular disc 10. Disc 10 carries around its periphery a substantially conical pinion lug 11.

Perpendicularly to the axis of shaft 6, and in the interior of the gear case 12 of the tool, is mounted a hollow circular cylinder 13 having a longitudinal slot 14. Cylinder 13 is kept in motion inside gear case 12, at one end by tube 15 driven in the body of the head of the tool, and at the other end by a bushing 16.

Cylinder 13 is made integral, as will be explained later, with drilling tool 17. Lug 11 is mounted in such a way as to slide alternatively or reciprocally in slot 14 when disc 10 rotates continuously. On FIG. 2 is shown one of the two positions of cylinder 13, the radial surface of slot 14 making an angle of about 45.degree. with the axis of motor arm 6. For a position diametrically opposite pin 11, slot 14 will occupy a position symmetrical with respect to this axis. In FIG. 1 on the contrary, lug 11 occupies its highest position, the plane of slot 14 passing then through the lowest position of lug 11.

From a continuous circular rotating motion around the axis of arm 6, the present arrangement provides reciprocating rotary movement around a perpendicular axis of cylinder 13 bearing a broach or drilling tool or a nerve puller 17 so that the direction tool 17 rotates changes about every one quarter turn or 90.degree.. It is understood that the width of slot 14 as well as the height and shape of pin 11 are selected in such a way as to ensure their cooperation with a minimum of play and to prevent unhooking at the two extreme positions of slot 14, as shown in FIG. 2. The conical shape of the lug or pin 11 represented on FIGS. 1 and 2 is particularly adapted for this purpose.

The drilling tool 17 can be secured to the bottom part of a conventional mandrel 18, by welding, screwing or any other known means. Mandrel 18 is mounted inside cylinder 13 in tube 15. Cylinder 13 is closed at its upper end at 19 and has an opening 20 for passing the upper end 21 of the shank of mandrel 18. Opening 20 has a face cut 22 which cooperates with a flattened section 23 at the end 21 of the mandrel. Thus is ensured integral rotation of the shank of mandrel 18, and therefore of tool 17, with moving cylinder 13.

The shank of the mandrel is prevented from sliding along the axis of cylinder 13 by a locking plate 24 (FIG. 3). Plate 24 has an elongated opening 25 terminating by a bore 26 of increased diameter. In the extension of opening 25, on the side of bore 26, is located circular bore 27. This bore 27 allows the passage of a screw 28 which fixed plate 24 onto a fastener 29, having shoulder 30 and actuated by spiral spring 31 positioned in a hollow 32 of gear case 12. Elongated opening 25 cooperates with the end 21 of the shank of mandrel 18, which for this purpose has a circular groove 33. To insert tool 17, maneuvering piece 29 is pushed back, thus retracting plate 24, by pushing the shoulder 30 towards the left of FIG. 1, against the action of spring 31. Thus bore 26 is brought in front of end 21 and the tool can be inserted in bore 26 which has a greater diameter than that of end 21. When piece 29 is released, the latter returns to the position of FIG. 1, as a result of the action of spring 31; the shank of mandrel 18 is therefore prevented from disengaging from plate 24, groove 33 cooperating with elongated opening 25 which is slightly larger than the diameter of circular groove 33 while being smaller than the diameter of the shank of mandrel 18.

The other embodiment of the invention, shown in FIGS. 4--5 comprises a driving spindle 41, one extremity of which comprises a journal 42, to which is keyed a driving piece 43. The latter is intended to be coupled to a corresponding part of a conventional wrist joint. A plate 44, of rectangular shape in the specific example, is keyed to the other extremity of spindle 41. This plate is at right angles to the axis of driving spindle 41, and comprises a cylindrical first crankpin 5, fixed to plate 44 in the vicinity of its periphery. This axis of crankpin 45 is parallel to that of driving spindle 41. The latter is rotatively mounted within a cylindrical ring 46 keyed to the body 47 of the handpiece.

Said handpiece comprises a driven spindle 48, the axis of which is substantially coincident with that of the driving spindle 41, in the present specific example. A rectangular plate 49 is keyed to one of the extremities of driven spindle 48 through a cylindrical sleeve 50.

Plate 49 is at right angles to the axis of driven spindle 48 and it is in register with plate 44. It is provided with a cylindrical crankpin 51, substantially similar to crankpin 45, located in the vicinity of the periphery of plate 49. The axis of crankpin 51 is parallel to that of driven spindle 48.

The other extremity of driven spindle 48 is journaled within a cylindrical ring 52. Again, the sleeve 50 of plate 49 is journaled within a cylindrical ring 53. Rings 52 and 53 are keyed within a tubular sleeve 54 screwed on to the body 47 of the handpiece. The extremity 61 of the handpiece as shown in the FIG. is that of an ordinary handpiece. Driven spindle 48 is adapted to drive a canal dental instrument for boring a canal.

A fork-shaped swinging member 55 is pivotally mounted by one of its extremities about an axis at right angles to its plane and parallel to the axis of driving spindle 41. Said swinging member 55 is located between plates 44 and 49, and acts as a coupling member between driving spindle 41 and driven spindle 48. In the specific example shown in the FIG., the axle of swinging member 55 is constituted by a screw 56 fixed to a shoulder of the handpiece body 47. To this end, the body of the handpiece is formed of three parts made integral with one another by screws, which permits to easily assemble and disassemble said handpiece.

Swinging member 55 comprises two parallel legs 57 and 58, between which is a space forming a longitudinal groove adapted to house the two crankpins 45 and 51. To this end, the spacing between the axis of crankpin 45 and that of driving spindle 41 is smaller than the spacing between the axis of crankpin 51 and the axis of driven spindle 48, which substantially coincides with that of driving spindle 41.

Of course the same sort of coupling is obtained if the respective values of these spacings are reversed, i.e. if the axis of crankpin 45 is located farther from the common axis of spindles 41 and 48 than is the axis of crankpin 51.

When driving spindle 41 is rotatively driven, the swinging member 55 controlled by crankpin 45 will oscillate between two steady positions, viz, as shown in FIG. 2, the position drawn in full line and that drawn in dash and dots. This oscillating movement is transmitted, through crankpin 51 to the driven spindle 48 which oscillates within an angle defined by two axes 59 and 60 corresponding to the extreme positions of swinging member 55, as shown in FIG. 2. The nerve extractor driven by spindle 48 thus alternatively pivots in one direction and in the other direction, by a fraction of a full turn corresponding to the angle between axes 59 and 60. The rotation angle of the instrument is so chosen as to be at most equal to the angle corresponding to its yield strength, in order to avoid any possible breakage.

In the specific example shown, the axis of driving spindle 41 coincides with that of driven spindle 48. According to a further form of embodiment, these two axes no longer coincide but still remain parallel, and it is possible to define the spacing between these two axes as a function of the selected value of the instrument's angle of rotation.

It is also possible to design a handpiece according to the invention, in which the axes of the driving spindle 4 and of the driven spindle 48 make a small angle. The coupling of spindle 41 and spindle 48 make a small angle. The coupling of spindle 41 and spindle 48 is similarly achieved by means of the swinging member 56 which, depending upon the value of the angle between the axes, can be parallel to one of the plates 44 and 49, or located in a plane which substantially bisects the plane of the two plates.

According to a still further form of embodiment of the invention, it is possible to design a handpiece in which the swinging member is constituted by the plate 49 itself, in which is provided a groove similar to that between the legs 57 and 58 of swinging member 55, said groove being directed towards the axis of driven spindle 48 and adapted to house crankpins 45. In order to obtain a suitable transformation of the movement, it is necessary to shift the axis of driving spindle 41 and that of driven spindle 8 with respect to each other, while maintaining same substantially parallel. In this form of embodiment, the spacing between the axis of crankpin 45 and that of spindle 41 must be smaller than the spacing between the axis of driving spindle 41 and that of driven spindle 48.

Quite obviously, the present invention is not limited to the above forms of embodiments and several changes can be made therein without going beyond its scope, in particular, as regards the respective positions of the axes of driving spindle and of driven spindle, the nature of the coupling member (a swinging member or a groove in a plate), the respective positions of the axes of crank pins and the shape of the handpiece's body.

FIG. 5 shows the alternate movement effected by a broach which has four rows of very sharp barbs which very effectively scrape the walls of the canal as they progressively enlarge it. It is obvious that this amplitude will vary according to the working surfaces of the dental instrument. Thus if the broach has a continuous working surface, the amplitude of the instrument would be at the most equal to the yield strength of the shaft or to its torsive strength. Otherwise the amplitude is equal to 360.degree. divided by the number of active surfaces of the dental tool.

As a reaming instrument, the barbs of the nerve broach are able to be depressed by the canal walls more or less over the length of the stem making the diameter thereof variable. These thin barbs guide the tip of the broach through the curves in the canal and prevent it from directly attacking the canal walls. As this tip is also blunt (neither capable of penetrating nor of cutting) the danger of a false route, of lateral perforation or the creation of a "step" is avoided. Preferably the dental tool used in the present device will be of special steel which is not twisted during manufacture and has not undergone any previous tension. Traditionally the root treatment is carried out with an alternate quarter-turn movement, with the present device this can be effected at a rate of 3,000 turns per minute, that is, 20 times as fast as it would be by hand. The broach operates therefore at 3,000 quarter-turns per minute.

In a typical treatment, the tip of the broach is inserted in the opening of a canal. The instrument is then started up at an average speed of 3,000 r.p.m. From the beginning the dentist has a very definite tactile appreciation of the penetration. He then gives the broach an up and down movement of growing amplitude (1--3 mm.) about every second. This penetration is followed by the passage of a second and, if necessary, a third broach so as to obtain a canal diameter of sufficient width to accept a paste filler.

As shown in FIG. 7, the barbs 69 of the broach have flattened against the walls 64 of tooth 63. This FIG. which is copied from an X-ray picture shows that even flattened, the barbs of the broach keep their tip in the canal shaft.

Claims

We claim:

1. A dental instrument for treating nonlinear root canals of teeth comprising a handpiece, a broach having a slender shaft with a tip at one end and a shank at the opposite end, said shaft having sharp barbs projecting therefrom including barbs near the tip, said shaft being resiliently flexible within the elastic limit of the material of the shaft to permit lateral flexing to follow nonlinear root canals and being torsionally flexible to permit rotation of said shank about its longitudinal axis through a predetermined limiting angle of not less than 90.degree. of torsional flexion relative to said tip within the elastic limit of said material, socket means for holding said broach by its shank, bearing means rotatably supporting said socket means in said handpiece while holding it against axial movement, and drive means for rotationally oscillating said socket means about its longitudinal axis through a predetermined angle which is at least of the order of 90.degree. and at the most equal to said limiting angle of torsional flexion of said broach shank, whereby if the tip of said broach becomes fast in a root canal continued rotational oscillation of the shank of said broach by said socket means will not break the broach, lengthwise penetration of said broach into a root canal being effected solely by manipulation of said handpiece by an operator.

2. A dental instrument according to claim 1, in which said broach shank has a plurality of said barbs equally spaced around its circumference and in which the angle of oscillation of said socket means is not less than 360.degree. divided by the number of barbs around the circumference of said broach shank.

3. A dental instrument according to claim 1 in which said socket means comprises a hollow circular cylinder in which said broach shank is received, said cylinder having a longitudinal slot in its outer surface, and in which said drive means comprises a rotating shaft in said handpiece with an axis normal to the axis of said cylinder, an arm fixed on an end of said shaft adjacent said cylinder and a pinion lug carried by said arm eccentric of the axis of said shaft and engaging in said slot to oscillate said cylinder upon rotation of said shaft, said slot having a length at least equal to twice the eccentricity of said pinion lug.

4. A dental instrument according to claim 3, in which said shank comprises a mandrel integral at one end with the shank of said broach and having a circumferentially extending groove near its free end, and in which a manually operable spring loaded locking plate slidably mounted on said handpiece has a bore engageable in said groove to hold said shank releasably in said hollow cylinder.

5. A dental instrument for treating nonlinear root canals of teeth comprising a handpiece, a broach having a slender shaft with a tip at one end and a shank at the opposite end, said shaft having shaft barbs projecting therefrom including barbs near the tip, said shaft being resiliently flexible within the elastic limit of the material of the shaft to permit lateral flexing to follow nonlinear root canals and being torsionally flexible to permit rotation of said shank through a predetermined limiting angle of torsional flexion relative to said tip within the elastic limit of said material, socket means for holding said broach by its shank, bearing means rotatably supporting said socket means in said handpiece while holding it against axial movement, and drive means for rotationally oscillating said socket means through a predetermined angle which is at the most equal to said limiting angle of torsional flexion of said broach shank, whereby if the tip of said broach becomes fast in a root canal continued rotational oscillation of the shank of said broach by said socket means will not break the broach, penetration of said broach into a root canal being effected solely by manipulation of said handpiece by an operator said drive means comprising a driving spindle, a first plate fixed on one end thereof, a first crankpin carried by said plate and extending parallel to but offset from said driving spindle, a driven spindle coaxial with said driving spindle and in driving connection with said socket means, a second plate fixed on an end of said driven spindle and facing said first plate, a second crankpin carried by said second plate and extending parallel to the axes of said spindles but offset from said axes a distance less than the offset of said first crankpin, said crankpins overlapping one another in an axial direction and a fork-shaped member pivotally mounted to swing about a fixed pivot parallel to said spindle axes and offset from said axes a distance greater than the offset of said first crankpin, said fork-shaped member having a slot receiving both of said crankpins whereby rotation of said driving spindle produces oscillation of said fork-shaped member about its pivot which in turn produces oscillation of said driven spindle, the angle of oscillation of said driven spindle being determined by the respective offsets of said crankpins.