US3729824A

US3729824A - Orthodontic arch wire

Info

Publication number: US3729824A
Application number: US00095699A
Authority: US
Inventors: D Baues; R Marini; D Mccauley
Original assignee: G A C INTERNATIONAL Inc
Current assignee: G A C INTERNATIONAL Inc
Priority date: 1970-12-07
Filing date: 1970-12-07
Publication date: 1973-05-01
Anticipated expiration: 1990-05-01
Also published as: JPS5038430B1

Abstract

Orthodontic arch wire comprising three segments of wire twisted together to form a single stranded arch wire with turns which have an angle with the longitudinal axis of the wire of sufficient magnitude but less than 90* and which have a sufficient number of turns per inch of length of wire such that the wire has the characteristics that it does not fray when cut and the segments do not separate when bent at an angle of at least 90* and when the ends thereof are flicked repeatedly. The twisted wire is preferably subjected to precipitation hardening at a temperature of from about 950* to about 975* Fahrenheit to increase its tensile strength. Apparatus for twisting the wire comprises a rotatable chuck and a fixed chuck mounted on a slidable shaft, each chuck having a pair of posts for forming a continuous length of wire into three spaced substantially equal and parallel segments. Affixed to the end of the slidable shaft is a weight for maintaining the parallel segments of wire under substantially constant tension. A set screw engageable with a V slot in the shaft prevents rotation of the shaft during twisting of the wire but permits rotation thereof after completion of twisting to relieve torsional stresses in the wire built up during the twisting operation. A method of forming the arch wire is also disclosed.

Description

United States Patent 1 Baues et al.

[ ORTHODONTIC ARCH WIRE [75] Inventors: Dietrich Baues, Jackson Heights; Richard Marini, Bellerose; Donald McCauley, Huntington, all of NY.

[73] Assignee: G.A.C. International, Inc., Farmingdale, L.l., N.Y.

[22] Filed: Dec. 7, 1970 [21 Appl. No.: 95,699

[52] US. Cl. ..32/l4 A [5 I] Int. Cl ..A6lc 7/00 [58] Field ofSearch ..l40/l49, 11];

32/14 A, 14 B, 14D

[56] References Cited UNITED STATES PATENTS 3,444,621 5/1969 Pletcher .32/14 A Primary Examiner-Robert Peshock AttorneyKenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT Orthodontic arch wire comprising three segments of [451 May 1,1973

wire twisted together to form a single stranded arch wire with turns which have an angle with the longitudinal axis of the wire of sufficient magnitude but less than 90 and which have a sufficient number of turns per inch of length of wire such that the wire has the characteristics that it does not fray when cut and the segments do not separate when bent at an angle of at least 90 and when the ends thereof are flicked repeatedly. The twisted wire is preferably subjected to precipitation hardening at a temperature of from about 950 to about 975 Fahrenheit to increase its tensile strength. Apparatus for twisting the wire comprises a rotatable chuck and a fixed chuck mounted on a slidable shaft, each chuck having a pair of posts for forming a continuous length of wire into three spaced substantially equal and parallel segments. Affixed to the end of the slidable shaft is a weight for maintaining the parallel segments of wire under substantially constant tension. A set screw engageable with a V slot in the shaft prevents rotation of the shaft during twisting of the wire but permits rotation thereof after completion of twisting to relieve torsional stresses in the wire built up during the twisting operation. A method of forming the arch wire is also disclosed. 1

14 Claims, 8 Drawing Figures Patented May 1, 1973 I N VEN TORS ORTHODONTIC ARCH WIRE FIELD OF THE INVENTION This invention relates to the field of orthodontic appliances and more particularly to new and improved orthodontic arch wire and to new and improved method and apparatus for making same.

BACKGROUND OF THE INVENTION Orthodontic appliances are known for straightening maloccluded teeth and for establishing the normal dental arch of the teeth. It has been proposed to use orthodontic arch wire comprising strands of twisted wire. Thus, US. Pat. No. 3,052,981 discloses an orthodontic arch wire comprised of three individual pieces of wire twisted in the form of a helix of zero diameter having turns whose planes are perpendicular to the axis of the wire. It has been found that this wire is extremely difficult to manufacture since the strands have a tendency to break during the twisting operation before the desired Configuration of the turns is achieved. US. Pat. No. 3,444,621 also discloses an arch wire comprised of three individual pieces of twisted wire which are twisted only enough to keep the wire from unraveling when tension is removed from the wire. It has been found that this wire is susceptible to fraying when cut and separating when flicked or bent at right angles. In addition, in order to prevent the individual strands from separating, it has been found necessary to solder the ends of this wire.

OBJECTS OF THE INVENTION It is thus an object of the present invention to provide new and improved arch wire for orthodontic appliances which is effective in straightening maloccluded teeth and establishing the normal dental arch thereof.

It is another object of the present invention to provide new and improved orthodontic arch wire which has good spring temper and which is easy to handle, which does not fray when cut and the strands of which do not separate when bent or repeatedly flicked.

It is yet another object of the present invention to provide new and improved method and apparatus for making orthodontic arch wire in a safe, efficient and economic manner.

SUMMARY OF THE INVENTION These and other objects and advantages are achieved according to the present invention wherein new and improved arch wire is provided which is effective in straightening maloccluded teeth and establishing the normal dental arch thereof. Said arch wire has good spring temper. is easy to handle, does not fray when cut and the strands of which do not separate when bent or repeatedly flicked. According to the apparatus and method of the present invention, orthodontic arch wire is produced in a safe efficient and economic manner.

In generaL the orthodontic arch wire of the present invention comprises three segments twisted together to form a signal stranded arch wire with turns which have an angle with the longitudinal axis of the wire of sufficient magnitude preferably in the range of about at least l6 r but less than 90 and which have a sufficient number of turns per inch of length of wire generally at least about 28 turns per inch such that the wire has the characteristics that it does not fray when out and the segments do not separate when bent at an angle of at leastand when the ends thereof are flicked repeatedly.

According to an aspect of the method of the present invention, after a continuous length of wire has been formed into three spaced substantially parallel segments and twisted to obtain the desired turn angle and turns per inch, the tensile strength of the twisted wire is subjected to precipitation hardening at a temperature of from about 950 to about 975 Fahrenheit.

One embodiment of the apparatus of the present invention comprises means for holding three segments of a continuous length of wire in spaced, parallel relationship, weight means for tensioning of the wire segments during twisting thereof and means for twisting the wire segments into a single orthodontic arch wire. According to one aspect of the apparatus of this invention means are provided for relieving the torsional stresses in the twisted wire after it has been twisted. According to another aspect of such apparatus, said twisting means comprises a rotatable chuck and a stationary chuck movably mounted to and away from said rotatable chuck and said holding means comprises a pair of posts mounted on each of said chuck about which said length of wire is wound in three spaced, substantially parallel segments.

DESCRIPTION OF THE DRAWINGS FIG. 3 is a partial perspective view of one of the chucks of FIG. 1;

FIG. 4 is a sectional elevational taken along line 4-4 of FIG. ll;

FIG. 5 is a partial perspective view of a preferred embodiment of the orthodontic arch wire of the present invention;

FIGS. 6 and 7 are diagrammatic views of preferred configurations of a continuous length of wire formed into three parallel segments prior to being twisted into the arch wire of the present invention; and

FIG. 8 is a perspective view illustrating the application of the orthodontic arch wire of FIG. 5 to the correction of a set of lower teeth.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the Figures there is shown a preferred embodiment of the orthodontic arch wire of the present invention and preferred apparatus for making same. According to the present invention new and improved orthodontic arch wire is provided for use in dental appliances for straightening maloccluded teeth and establishing the proper dental arch therefor. FIG. 8 shows a lower set of teeth 10 having individual teeth 12 to which a dental appliance 14 has been attached for orthodontic purposes. Appliance 14 comprises teeth bands 16 having lugs 18 to which is attached orthodontic arch wire 20. The function of arch wire 20 is to urge maloccluded teeth through bands 16 into their normal position and to establish alignment of the teeth into a proper dental arch. Thus, arch wire 20 must possess sufficient flexibility and tensile strength to accomplish these functions and in addition must be easy to handle by the orthodontist fitting the arch wire to the patients teeth.

According to the present invention, a continuous length of wire is formed into three spaced, substantially equal and parallel segments (FIGS. 6 and 7 the segments being twisted together to form a single stranded arch wire with turns which have an angle with the 1ongitudinal axis of the wire of sufficient magnitude and which have a sufficient number of turns per inch of wire such that the wire has the characteristics that it does not fray when cut and the segments do not separate when bent at an angle of at least 90 and when the ends thereof are flicked repeatedly but which have an angle which is substantially less than 90 with the longitudinal axis of the wire. As shown in FIG. 5, arch wire 20 comprises

segments

22, 24 and 26 twisted together to form turns 28. The turn angle and turns per inch of wire 20 will depend upon the desired overall diameter of arch wire 20 and the diameter of

wire segments

22, 24 and 26 used to form arch wire 20. In order to be usable with standard orthodontic appliances, arch wire 20 preferably has an overall diameter of from about 0.0145 inches to about 0.0215 inches and is made from wire segments having a diameter of from about 0.006 inches to about 0.010 inches.

In general, the diameter of

wire segments

22, 24, 26 and the overall diameter of arch wire 20 will determine to some extent the angle of turn with the longitudinal axis and the number of turns per inch of length of the orthodontic arch wire of the present invention. Table I gives examples of arch wire 20 considered to be within the scope of the present invention.

Arch wire 20 may be made from any material well v 32 is split in half at its free end and is provided with

posts

42 and 44 the purpose of which will be described in greater detail hereinafter.

Stationary chuck 50 is also split at its free end and is provided with separable member 56 secured thereto by clamp screw 58 and is also provided with

posts

52 and 54. Chuck 50 is secured to the end of a shaft 60 by clamp screw 61 projecting into groove 63 on the end of shaft 60. Shaft 60 is slidably mounted in bore 62 of block 64. Block 64 is provided with threaded bore 66 (FIG. 4) communicating at right angles with bore 62 and set screw 68 threaded in bore 66. Screw 68 is adapted to project into a V shaped channel 70 in shaft 60. The purpose of set screw 68 and channel 70 will be more fully explained hereinafter.

In order to tension the wire during the twisting operation 30, shaft 60 is biased away from chuck 32 by means of weight 72 secured to shaft60 by means of rope 74 secured to shaft 60 by means of eye bolt 76. Rope 74 passes over frictionless pulley 78 mounted on base member 80 by suitable brackets (not shown). Motor 38, counter 36 and block 64 are also mounted on base member 80.

A rotatable wire feed stand 82 is also mounted on base member 80 and comprises base 84, vertical pivot 86 mounted on base 84, turntable 88 rotatably mounted on pivot 86, and posts 90 mounted for sliding movement in slots 92 of turntable 88. A coil of wire 94 is supported on turntable 88, disposed about posts 86 which are adjusted to press against the inner loops of the coil. Post 86 may be adjusted to accommodate coils of wires of different diameters.

In operation, set screw 68 is tightly clamped to shaft 60 to permit the securing of a length of wire 94 between chucks 32 and 50 without the biasing influence of weight 72 on the wire during this operation. A length of wire 94 is unwound from stand 82, such unwinding being facilitated by the rotation of turntable 88, and the end thereof is inserted between member 56 and chuck 50 and is securely clamped by screw 58. Wire 94 is then formed into three spaced, substantially equal and parallel segments by passing it around posts 52 and 54 and

posts

44 and 42 respectively of chucks 50 and 32 and severing the desired length thereof from the coil and clamping the severed end between member 41 and chuck 32 by means of screw 43.

FIGS. 6 and 7 diagrammatically illustrate two preferred configurations for forming wire 94 about

posts

52, 54 and 44, 42. FIG. 6 shows wire 94 being looped about the posts in the configuration of the letter S and FIG. 7 shows wire 94 being looped about the posts in the configuration of a distorted numeral 6. In either case, posts 52, 54 and 44, 42 support the three segments of wire 94 is spaced, substantially parallel relationship, the three segments being substantially equal in length. It has been found that wire formed in this manner prior to the twisting operation, will be substantially free of kinking during twisting thus greatly increasing the efficiency of the operation.

After wire 94 has been securely clamped in chucks 32 and 50, set screw 68 is backed off sufficiently to permit shaft 60 to slide in bore 62 while preventing rotation thereof. Weight 72 now acts on shaft 60 to bias it away from chuck 32 thus subjecting the segments of wire 94 to the desired tension. The value of weight 72 and consequently the amount of tension applied to wire 94 will vary according to the physical characteristics and diameter of wire 94 and the length of span between chucks 32 and 50. Thus, in general, the longer the span of wire to be twisted and the thicker in diameter such 5 wire is, the greater the weight 72 that must be used to apply the desired tension during the twisting operation.

It has been found, that by maintaining a constant bias on shaft 60 and thereby a constant tension on wire 94 during the twisting operation, wire breakage is greatly minimized and the incidence of wire kinkage is also substantially reduced.

Rotation of chuck 32 is now initiated to twist wire 94, by starting motor 38 which is connected to chuck 32 by means of shaft 40, counter 36 and shaft 34'. As the wire is twisted, the length thereof will be reduced and shaft 60 will slide in block 64. The number of revolutions that wire 94 is twisted is indicated by counter 36 and will depend to a great extent on the characteristics and length of the wire being twisted. In general, the wire must be twisted a sufficient number of revolutions so that there is formed a single stranded arch wire with turns which have an angle with the longitudinal axis of the wire of sufficient magnitude and which have a sufficient number of turns per inch of length of wire such that the wire has the characteristics that it does not fray when cut and the segments do not separate when bent at an angle of at least 90 and when the ends thereof are flicked repeatedly but which have an angle which is substantially less than 90 with the longitudinal axis of the wire.

Following Tables II V illustrate a number of samples of twisted wire formed on apparatus 30, as described hereinabove, from continuous lengths of wire having diameters of 0.007 inches, 0.008 inches, 0.009 inches and 0.010 inches. Each sample was twisted according to the conditions indicated and then cut with a conventional wire cutter and the cut ends bent at an angle of at least 90 with the aid of a conventional pair of pliers and subjected to repeated flicking with a finger. A standard optical comparator (such as made by Scherr-Tumico, Inc. of St. James, Minn.) was used to facilitate measurement of the turns per inch and turn angle of the twisted wire. As is known optical comparators enlarge the image of an object and project the enlarged image on a screen.

In following Table 11 each of the samples was formed from wire segments of 0.007 inches diameter having an initial length of 40 inches. A tensioning weight of 2.2 lbs. was applied.

TABLE II No. of Angle Rcvolu- Overall Turns/ Of Turn lions dia.(in.) Inch (deg) Remarks 50 Sample unwound before test 100 0.0138 1% 3%" Frayed before snapping Unraveled at 90 Turn. 00 0.0144 1 1% 5 Frayed on 3rd snap Unraveled on 90 Tum. 300 0.0148 18 955 Did not separate when cut.

Separated on 4th snap. Unraveled on 120 Tum.

In following Table III each of the samples was formed from wire segments of 0.008 inches diameter having an initial length of 40 5 1 inches. A tensioning weight of 5 .75 lbs. was applied.

TABLE 111 No. of Angle Revolu- Overall Tums/ of Turn tions Dia. (in.) Inch (deg) Remarks 50 Sample unwound before test 100 0.0157 2 116 Falls apart on cutting 200 0.0168 12 65? Frayed on 3rd snap. Unraveled on Turn.

300 0.0169 19 be 11 No Fraying on multiple Snaps. Unraveled on 90 Turn.

400 0.0170 28 16 k No Praying on multiple snaps. Did not unravel on 90 Turn.

450 0.0169 32 17 16 No Fraying on multiple snaps. Did not unravel on 90 Turn.

500 0.0170 36 21 No Fraying on multiple snaps. Did not unravel on 90 Turn.

600 0.0169 44 29 No Fraying on multiple snaps. No unraveling on 90 Bend.

In following Table IV each of the samples was formed from wire segments of 0.009 inches diameter having an initial length of 40 inches. A tensioning weight of 5.4 lbs. was applied.

TABLE IV No. of Angle Revolu- Overall Tums/ of Turn lions Dia. (in.) Inch (deg) Remarks 50 Sample unwound before test unraveling on 90 Bend.

No Praying on multiple snaps. No unraveling on 90 Bend.

6.75 lbs. was applied.

TABLE V No. of Angle Revolu- Overall Turns/ of Turn tions Dia. in.) inch (deg) Remarks 50 Sample unwound before test 100 0.0201 4 92 4 Frayed on 1st snap.

Unraveled on 90 Turn.

200 0.0214 12 8 95 Frayed on 2nd snap.

Unraveled on 90 Turn.

300 0.0215 20 Frayed on 3rd snap. Unraveled on 90 Turn.

400 0.0215 28 24 No Fraying on multiple snaps. No unraveling on 90 Turn.

500 0.0215 37 27 No Fraying on multiple snaps. No unraveling on 90 Turn.

600 0.0216 46 55 32 No Fraying on multiple snaps. No unraveling on 90 Turn.

After the segments of wire 94 have been twisted the desired number of revolutions to form the orthodontic arch wire according to the present invention, the torsional stresses built up therein during the twisting operation may be relieved by moving shaft 60 toward chuck 32 thus relieving the tension on wire 94 and by backing screw 61 out of channel 63 to permit rotation of chuck 50. Thereafter, the twisted arch wire may be cut at both ends without fear of unsafe whiplash or wire kinkage and the unwanted end pieces removed from chucks 32 and 50.

The tensile strength of the orthodontic arch wire is preferably increased by precipitation hardening. Where the arch wire is comprised of stainless steel, the arch wire is placed in a vessel filled with an inert gas such as argon and heated for a period of about an hour at a temperature of from about 950 to 975 Fahrenheit. The wire is then allowed to cool to ambient temperature. It has been found that arch wire treated in this manner has increased tensile strength over untreated wire.

Additional examples of arch wire within the scope of the present invention are as follows:

Example N Overall diameter 0.0215 inches Angle of turn with long. axis 41 degrees Number of turns per inch 46 Example 0 Overall diameter 0.0195 inches Angle of turn with long. axis 30 degrees Number of turns per inch 45 Although specific examples of the present invention have been given hereinabove, it will be understood that such examples are illustrative only and are not to be taken as limiting the scope of the present invention.

What is claimed is:

1. Orthodontic arch wire comprising three segments of wire twisted together, said twisted arch wire having turns which have an angle with the longitudinal axis of the wire of sufficient magnitude but less than and which have at least 28 turns per inch of length of wire such that said wire has the characteristics that it does not fray when out and the segments do not separate when bent at an angle of at least 90 and when the ends thereof are flicked repeatedly.

2. The orthodontic arch wire of claim 1 wherein said wire segments have a diameter of from about 0.007 inches to about 0.010 inches.

3. The orthodontic arch wire of claim 2 wherein said turns of said twisted arch wire have an angle of at least about 16 k" with the longitudinal axis of sad wire but of substantially less than 90 with said axis.

4. The orthodontic arch wire of claim 2 wherein said turns of said twisted arch wire have an angle of from about 16 k" to about 41 with the longitudinal axis of said wire.

5. The orthodontic arch wire of claim 2 wherein said twisted arch wire has from about 28 to about 46 A turns per inch of length of said wire.

6. The orthodontic arch wire of claim 2 wherein said turns of said twisted arch wire have an angle of from about 16 76 to about 41 with the longitudinal axis of said wire and said wire has from about 28 to about 46 it turns per inch of length of said wire.

7. The orthodontic arch wire of claim 1 wherein said turns of said twisted arch wire have an angle of at least about 16 36 with the longitudinal axis of said wire but of substantially less than 90 with said axis.

8. The orthodontic arch wire of claim 1 wherein said turns of said twisted arch wire have an angle of from about 16 6 to about 41 with the longitudinal axis of said wire.

9. The orthodontic arch wire of claim 1 wherein said twisted arch wire has from about 28 to about 46 /2 turns per inch of length of said wire.

10. The orthodontic arch wire of claim 1 wherein said turns of said twisted arch wire have an angle of from about 16 to about 41 with the longitudinal axis of said wire and said wire has from about 28 to about 46 )6 turns per inch of length of said wire.

11. The orthodontic arch wire of claim 1 wherein said wire segments have a diameter of about 0.007 inches, wherein said turns of said twisted arch wire have an angle of from about 20 to about 29 with the longitudinal axis of said wire and wherein said wire has from about 33 to about 42 turns per inch of length thereof.

12. The orthodontic arch wire of claim 1 wherein said wire segments have a diameter of about 0.008 inches, wherein said turns of said twisted arch wire have an angle of from about 16 1? to about 29 with the longitudinal axis of said wire and wherein said wire has from about 28 to about 44 turns per inch of length thereof.

13. The orthodontic arch wire of claim 1 wherein said wire segments have a diameter of about 0.009 inches, wherein said turns of said twisted arch wire inches, wherein said turns of said twisted arch wire have an angle of from about 24 to about 32 with the longitudinal axis of said wire and wherein said wire has from about 28 to about 46 1$ turns per inch of length thereof.

UNITED STATES PATENT @FFFCE CERTWECATE CF QORRECTEON Inventor(s) Dietrich Baues; Richard Marini 80 Donald McCauley It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, Table I, Example B has been printed twic and should read as follows:

Column 3, Table I, Example F, "0.169" should be --0.0169-- Column 4, line 53, place quotation marks around letter S.

Column 8, claim 3, line 20, correct spelling of "said".

Signed and'sealed this 29th day of January 1974.

(SEAL) Attestt EDWARD M.PLETCHER,JR. RENE D. TEGTMEYER Attest ng Officer Acting Commissioner of Patents ORM PO-1050(10-69) USCOMM-DC 60376-1 69 U.S GOVERNMENT PRINTING OFFICE: 1969 O--366'334

Claims

1. Orthodontic arch wire comprising three segments of wire twisted together, said twisted arch wire having turns which have an angle with the longitudinal axis of the wire of sufficient magnitude but less than 90* and which have at least 28 turns per inch of length of wire such that said wire has the characteristics that it does not fray when cut and the segments do not separate when bent at an angle of at least 90* and when the ends thereof are flicked repeatedly.

3. The orthodontic arch wire of claim 2 wherein said turns of said twisted arch wire have an angle of at least about 16 1/2 * with the longitudinal axis of sad wire but of substantially less than 90* with said axis.

4. The orthodontic arch wire of claim 2 wherein said turns of said twisted arch wire have an angle of from about 16 to about 41* with the longitudinal axis of said wire.

5. The orthodontic arch wire of claim 2 wherein said twisted arch wire has from about 28 to about 46 1/2 turns per inch of length of said wire.

6. The orthodontic arch wire of claim 2 wherein said turns of said twisted arch wire have an angle of from about 16 1/2 * to about 41* with the longitudinal axis of said wire and said wire has from about 28 to about 46 1/2 turns per inch of length of said wire.

7. The orthodontic arch wire of claim 1 wherein said turns of said twisted arch wire have an angle of at least about 16 1/2 * with the longitudinal axis of said wire but of substantially less than 90* with said axis.

8. The orthodontic arch wire of claim 1 wherein said turns of said twisted arch wire have an angle of from about 16 1/2 * to about 41* with the longitudinal axis of said wire.

9. The orthodontic arch wire of claim 1 wherein said twisted arch wire has from about 28 to about 46 1/2 turns per inch of length of said wire.

10. The orthodontic arch wire of claim 1 wherein said turns of said twisted arch wire have an angle of from about 16 1/2 * to about 41* with the longitudinal axis of said wire and said wire has from about 28 to about 46 1/2 turns per inch of length of said wire.

11. The orthodontic arch wire of claim 1 wherein said wire segments have a diameter of about 0.007 inches, wherein said turns of said twisted arch wire have an angle of from about 20* to about 29 1/2 * with the longitudinal axis of said wire and wherein said wire has from about 33 to about 42 turns per inch of length thereof.

12. The orthodontic arch wire of claim 1 wherein said wire segments have a diameter of about 0.008 inches, wherein said turns of said twisted arch wire have an angle of from about 16 1/2 * to about 29* with the longitudinal axis of said wire and wherein said wire has from about 28 to about 44 turns per inch of length thereof.

13. The orthodontic arch wire of claim 1 wherein said wire segments have a diameter of about 0.009 inches, wherein said turns of said twisted arch wire have an angle of from about 19 1/2 * to about 29* with the longitudinal axis of said wire and wherein said wire has from about 28 to about 45 turns per inch of length thereof.

14. The orthodontic arch wire of claim 1 wherein said wire segments have a diameter of about 0.010 inches, wherein said turns of said twisted arch wire have an angle of from about 24* to about 32* with the longitudinal axis of said wire and wherein said wIre has from about 28 to about 46 1/2 turns per inch of length thereof.