Orthodontic force production closed coil springs
by
Russell I. Webb,* Angelo A. Caputo, MS., Ph.D.,** and Spiro J. Chaconas, D.D.S., M.S.*** Los Angrles,
C&f.
c
losed coil springs have been in use for orthodontic tooth movement for many years. To date, several studies have been made on the optimum force required for specific tooth movement, but few experimental data are available on force production by intraoral closed coil springs. Current recommendations for the use of closed coil springs direct that the springs be extended one third to one half of their original length. The amount of force generated by this activation of any spring is currently unobtainable from either literature of manufacturer. The purpose of this study was to determine the force produced by closed coil springs to aid the clinician in the proper selection of coil springs for optimum tooth movement. Review of literature Several studies have been made on the amount of force required for specific tooth movements. Storey and Smith’ reported that 150 to 200 grams is the optimum force range for retraction of the lower canine tooth. Reitan’ has reported that the maximum force needed for continuous bodily movement of canine teeth is 250 grams. Burstone and Groves3 found the optimum force for the retraction of anterior teeth to be 50 to 75 grams. In 195 1, Bell’ studied nine closed wound coil springs and advised the user to activate the spring by elongating it one half of its original length during placement. A theoretical apprach to the mechanics of coil springs was presented by Kobayashi and Muramatsu” in 1972. They found a “preliminary tensile stress” portion of force production where the deformation against a load did not start until 70 grams of force was added. They also found the force extension curve to be a straight line until it reached 500 grams of load, at which time the deformation against the load markedly increased because of inelastic deformation. Presented in part at the 1976 Session of the International Association for Dental Research, Beach, Fla. This study was funded by the California Dental Association and by Biomedical Rewwh Grant No. RR 05304. *Dental Student, UCLA School of Dentistry. **Professor and Chairman, UCLA Biomaterials section. ***Professor and Chairman, UCLA Orthodontic Section.
OCKL-9416/78/100405+05$00
50/O 01978
The C. V. Mosby Cu.
Miami Support
405
Am. J. Orthod. October 1978
Unitek Force W-n) 4.
3.
2.
1.
El
Hi
1. 2. 3.
.009%036 005'~.032 009a30
4.
mxD22
T
200
m:: 100
I 2
0,
I 4
I 6
I
I
Ex8te&
Fig.
1. Force-extension
curves
of springs
I 12
1 14
I 16
I 18
1 20
I 22
(mm)
with
0.009
inch
wire
size
with four
different
lumen
sizes.
Materials and methods Nineteen closed coil springs reflecting the variables of wire size (0.006 to 0.009 inch), lumen size (0.022 to 0.036 inch), and four wire types from three manufacturers were selected for testing. Force extension tests were performed on 20 mm. lengths of each spring with the use of an Instron test machine.* A few turns of the wire at each end of the spring were separated and bent at an angle to the rest of the spring and attached to the machine by means of a hook of orthodontic wire. Ten samples of each spring were extended through a range of from 0 to 4.50 grams, and continuous curves of force versus distance were obtained. A table of force/extension values for several initial spring lengths was constructed with the use of data analyzed by the UCLA Health Science Computer Facility. Results The test data reveal that wire size, lumen size, and wire type all affect the forceextension characteristics of closed springs and that certain springs would be better suited for specific tooth-movement situations than others. Fig. 1 illustrates the force-extension curves comparing springs of 0.009-inch wire size with four different lumen sizes. It can be seen that the spring with the smaller lumen size, represented by curve 4, requires a smaller extension to give a certain force increment than does the spring with the larger lumen size, represented by curve 1. A change of 2 mm. extension results in a change of 100 grams in curve 4 and only 30 grams in curve I. The relationship between springs with a constant lumen size of 0.22 inch and wire size varying from 0.009 inch to 0.006 inch is shown in Fig. 2. The larger wire size (curve 4) produces the greatest increment of force per given extension, as well as the greatest amount of force in the linear range of the curve. Here, again, the smaller wire will remain *Instron
Corp.
Canton,
Mass.
Volume 74 Number 4
Unitek
I 2
Fig.
2. Force-extension
curves
I
I
1
4
6
aExteE.ion’fmmi
of springs
with
I
0 Hi T Unitek (i3 Permachrome
II
11 12345678
1
I
I
1
four
1
wire
3. Force-extension
curves
of 0.009
L
inch
sizes
Unitek
fi
Extension Fig.
I
by 0.030
Hi T
I
1
I
16
18
20
and
a constant
0.022
inch
lumen
size.
I
I1 9
10
I 11
I 12
I 13
I‘ 14
15
(mm) inch
springs
from
different
manufacturers.
in a given force range for a greater variation of extension than the larger wires, but a smaller amount of force is obtainable from the smaller wires. Fig. 3 illustrates the comparison between springs with a given wire size and lumen size from different manufacturers. it can be seen that the type of wire affects the force extension curve, and that closed coil springs of similar sizes from different manufacturers show definite variation. It is not enough, then, to merely use a specific spring size. The specific wire type must also be designated.
Am. J. Orthod. October 1978
Unitek 4,.009x1)22 5. co8 x1)22 6. .077~.022
:e J)
7. .006 x.022
2
4
6
8
10
Extension Fig. 4. The
relationship
of the current
recommended
12
14
11. 12. 13. 14.
.009x.022 .008x022 007x.022 .006x.022
16
18
Hi Hi Hi Hi
T T T T
f%%rKi
Perma Ferma Perma
J
20
(mm) extension
(shaded)
to the force
extension
curves.
Discussion For closed coil springs, increasing the wire size will increase both the maximum production of force and the force produced by a given activation. Decreasing the lumen size will produce the same effects on the performance. Springs with lower slopes will remain in a given force range longer and thus will be preferable for tooth movement. This means that springs with larger lumen sizes and smaller wire sizes would be indicated for orthodontic use because of their more constant force production, but a limit to the size must be imposed in order to remain within recommended force ranges. Current recommendations for the use of closed coil springs direct that the springs be extended from one third to one half of their original length. It can be seen from Fig. 4 that this procedure would give a wide range of force, depending on the spring being used. Springs of 20 mm. are represented with 30 to 50 percent range area between 6 and 10 mm. extension (shaded area). The amount of force from spring 14 with the recommended extension would be uncertain since the linear range has not been reached. Springs 4 and 11 would be either out of the linear force production range or at an undesirably high force. For the rest of the springs the force obtained would vary from 200-300 grams in springs 5 and I 2 to 7% 100 grams in spring 7. The amount of force generated by the 30 to 50 percent extension of any of the springs studied was unobtainable from either literature or the manufacturer. Summary and conclusions The effects of wire size, lumen size, and wire type on the production of force by closed coil springs were determined. Force production was affected as follows: (1) Keeping the lumen size constant, an increase in wire size produced an increase in force. (2)
Volume 74 Number
4
Keeping the wire size constant, an increase in lumen size produced For a given wire size, force varied with different wire types. This study has shown that the current recommendations for springs produce forces of greater magnitude than is necessary movement. The clinician should take care to select the proper specific clinical situations. REFERENCES I. Storey, E., and Smith, R.: The importance of force 2. Reitan, R.: Some factors determining the evaluation 1957. 3. Burstone, C. J.. and Groves, M. H.. Jr.: Threshold movement, J. Dent. Res. 39: 695, 1960. 4. Bell, W. R.: A study of applied forces as related to 151-154, 19.51. S. Kobayashi, K., and Muramatsu, A.: Mechanics of 1972.
THE JOURNAL October,
60 YEARS
a decrease in force. (3) the use of closed coil for orthodontic tooth closed coil spring for
in orthodontics, Aust. Dent. J. 56: 291-304, 1952. of forces in orthodontics, AM. J. ORTHOD. 43: 32-45, and optimum
force
the use of elastics orthodontic
springs,
values
for maxillary
and coil springs, J. Jap.
Stomatol.
anterior
Angle Sot.
Orthod. 39:
tooth 21: I-IS,
AGO
1918
in order to make orthodontia an absolute science two capital principles must be observed: First, the throwing overboard of all orthodontic quacks, witches, guessers, take-a-chanters, sole-dependents upon Nature, and of all who make their patients the subjects of their ignorance by clumsily experimenting upon them; and second, a strict, faithful, uncompromising adherence to the laws of science-an adherence which can not and will not tolerate the contaminating association with any and all orthodontic alchemists who mix 1 carat of the gold of science with 23 carats of the mica of quackery, and who then proclaim: “Behold, this is science!” (Rudolph L. Hanau: Dental Engineering: Is It Justified? The International Journal of Orthodontia, predecessor of the American Journal of Orthodontics, 4: 520, 1918.)
by
Russell I. Webb,* Angelo A. Caputo, MS., Ph.D.,** and Spiro J. Chaconas, D.D.S., M.S.*** Los Angrles,
C&f.
c
losed coil springs have been in use for orthodontic tooth movement for many years. To date, several studies have been made on the optimum force required for specific tooth movement, but few experimental data are available on force production by intraoral closed coil springs. Current recommendations for the use of closed coil springs direct that the springs be extended one third to one half of their original length. The amount of force generated by this activation of any spring is currently unobtainable from either literature of manufacturer. The purpose of this study was to determine the force produced by closed coil springs to aid the clinician in the proper selection of coil springs for optimum tooth movement. Review of literature Several studies have been made on the amount of force required for specific tooth movements. Storey and Smith’ reported that 150 to 200 grams is the optimum force range for retraction of the lower canine tooth. Reitan’ has reported that the maximum force needed for continuous bodily movement of canine teeth is 250 grams. Burstone and Groves3 found the optimum force for the retraction of anterior teeth to be 50 to 75 grams. In 195 1, Bell’ studied nine closed wound coil springs and advised the user to activate the spring by elongating it one half of its original length during placement. A theoretical apprach to the mechanics of coil springs was presented by Kobayashi and Muramatsu” in 1972. They found a “preliminary tensile stress” portion of force production where the deformation against a load did not start until 70 grams of force was added. They also found the force extension curve to be a straight line until it reached 500 grams of load, at which time the deformation against the load markedly increased because of inelastic deformation. Presented in part at the 1976 Session of the International Association for Dental Research, Beach, Fla. This study was funded by the California Dental Association and by Biomedical Rewwh Grant No. RR 05304. *Dental Student, UCLA School of Dentistry. **Professor and Chairman, UCLA Biomaterials section. ***Professor and Chairman, UCLA Orthodontic Section.
OCKL-9416/78/100405+05$00
50/O 01978
The C. V. Mosby Cu.
Miami Support
405
Am. J. Orthod. October 1978
Unitek Force W-n) 4.
3.
2.
1.
El
Hi
1. 2. 3.
.009%036 005'~.032 009a30
4.
mxD22
T
200
m:: 100
I 2
0,
I 4
I 6
I
I
Ex8te&
Fig.
1. Force-extension
curves
of springs
I 12
1 14
I 16
I 18
1 20
I 22
(mm)
with
0.009
inch
wire
size
with four
different
lumen
sizes.
Materials and methods Nineteen closed coil springs reflecting the variables of wire size (0.006 to 0.009 inch), lumen size (0.022 to 0.036 inch), and four wire types from three manufacturers were selected for testing. Force extension tests were performed on 20 mm. lengths of each spring with the use of an Instron test machine.* A few turns of the wire at each end of the spring were separated and bent at an angle to the rest of the spring and attached to the machine by means of a hook of orthodontic wire. Ten samples of each spring were extended through a range of from 0 to 4.50 grams, and continuous curves of force versus distance were obtained. A table of force/extension values for several initial spring lengths was constructed with the use of data analyzed by the UCLA Health Science Computer Facility. Results The test data reveal that wire size, lumen size, and wire type all affect the forceextension characteristics of closed springs and that certain springs would be better suited for specific tooth-movement situations than others. Fig. 1 illustrates the force-extension curves comparing springs of 0.009-inch wire size with four different lumen sizes. It can be seen that the spring with the smaller lumen size, represented by curve 4, requires a smaller extension to give a certain force increment than does the spring with the larger lumen size, represented by curve 1. A change of 2 mm. extension results in a change of 100 grams in curve 4 and only 30 grams in curve I. The relationship between springs with a constant lumen size of 0.22 inch and wire size varying from 0.009 inch to 0.006 inch is shown in Fig. 2. The larger wire size (curve 4) produces the greatest increment of force per given extension, as well as the greatest amount of force in the linear range of the curve. Here, again, the smaller wire will remain *Instron
Corp.
Canton,
Mass.
Volume 74 Number 4
Unitek
I 2
Fig.
2. Force-extension
curves
I
I
1
4
6
aExteE.ion’fmmi
of springs
with
I
0 Hi T Unitek (i3 Permachrome
II
11 12345678
1
I
I
1
four
1
wire
3. Force-extension
curves
of 0.009
L
inch
sizes
Unitek
fi
Extension Fig.
I
by 0.030
Hi T
I
1
I
16
18
20
and
a constant
0.022
inch
lumen
size.
I
I1 9
10
I 11
I 12
I 13
I‘ 14
15
(mm) inch
springs
from
different
manufacturers.
in a given force range for a greater variation of extension than the larger wires, but a smaller amount of force is obtainable from the smaller wires. Fig. 3 illustrates the comparison between springs with a given wire size and lumen size from different manufacturers. it can be seen that the type of wire affects the force extension curve, and that closed coil springs of similar sizes from different manufacturers show definite variation. It is not enough, then, to merely use a specific spring size. The specific wire type must also be designated.
Am. J. Orthod. October 1978
Unitek 4,.009x1)22 5. co8 x1)22 6. .077~.022
:e J)
7. .006 x.022
2
4
6
8
10
Extension Fig. 4. The
relationship
of the current
recommended
12
14
11. 12. 13. 14.
.009x.022 .008x022 007x.022 .006x.022
16
18
Hi Hi Hi Hi
T T T T
f%%rKi
Perma Ferma Perma
J
20
(mm) extension
(shaded)
to the force
extension
curves.
Discussion For closed coil springs, increasing the wire size will increase both the maximum production of force and the force produced by a given activation. Decreasing the lumen size will produce the same effects on the performance. Springs with lower slopes will remain in a given force range longer and thus will be preferable for tooth movement. This means that springs with larger lumen sizes and smaller wire sizes would be indicated for orthodontic use because of their more constant force production, but a limit to the size must be imposed in order to remain within recommended force ranges. Current recommendations for the use of closed coil springs direct that the springs be extended from one third to one half of their original length. It can be seen from Fig. 4 that this procedure would give a wide range of force, depending on the spring being used. Springs of 20 mm. are represented with 30 to 50 percent range area between 6 and 10 mm. extension (shaded area). The amount of force from spring 14 with the recommended extension would be uncertain since the linear range has not been reached. Springs 4 and 11 would be either out of the linear force production range or at an undesirably high force. For the rest of the springs the force obtained would vary from 200-300 grams in springs 5 and I 2 to 7% 100 grams in spring 7. The amount of force generated by the 30 to 50 percent extension of any of the springs studied was unobtainable from either literature or the manufacturer. Summary and conclusions The effects of wire size, lumen size, and wire type on the production of force by closed coil springs were determined. Force production was affected as follows: (1) Keeping the lumen size constant, an increase in wire size produced an increase in force. (2)
Volume 74 Number
4
Keeping the wire size constant, an increase in lumen size produced For a given wire size, force varied with different wire types. This study has shown that the current recommendations for springs produce forces of greater magnitude than is necessary movement. The clinician should take care to select the proper specific clinical situations. REFERENCES I. Storey, E., and Smith, R.: The importance of force 2. Reitan, R.: Some factors determining the evaluation 1957. 3. Burstone, C. J.. and Groves, M. H.. Jr.: Threshold movement, J. Dent. Res. 39: 695, 1960. 4. Bell, W. R.: A study of applied forces as related to 151-154, 19.51. S. Kobayashi, K., and Muramatsu, A.: Mechanics of 1972.
THE JOURNAL October,
60 YEARS
a decrease in force. (3) the use of closed coil for orthodontic tooth closed coil spring for
in orthodontics, Aust. Dent. J. 56: 291-304, 1952. of forces in orthodontics, AM. J. ORTHOD. 43: 32-45, and optimum
force
the use of elastics orthodontic
springs,
values
for maxillary
and coil springs, J. Jap.
Stomatol.
anterior
Angle Sot.
Orthod. 39:
tooth 21: I-IS,
AGO
1918
in order to make orthodontia an absolute science two capital principles must be observed: First, the throwing overboard of all orthodontic quacks, witches, guessers, take-a-chanters, sole-dependents upon Nature, and of all who make their patients the subjects of their ignorance by clumsily experimenting upon them; and second, a strict, faithful, uncompromising adherence to the laws of science-an adherence which can not and will not tolerate the contaminating association with any and all orthodontic alchemists who mix 1 carat of the gold of science with 23 carats of the mica of quackery, and who then proclaim: “Behold, this is science!” (Rudolph L. Hanau: Dental Engineering: Is It Justified? The International Journal of Orthodontia, predecessor of the American Journal of Orthodontics, 4: 520, 1918.)
