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Effects of prestretching on forceEffects of prestretching on force
degradation of synthetic elastomericdegradation of synthetic elastomeric
chains – AJO oct-2005chains – AJO oct-2005
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 Introduction:Introduction: The purpose of this studyThe purpose of this study
was to evaluate the effects ofwas to evaluate the effects of
prestretching on time-dependant forceprestretching on time-dependant force
decay of synthetic elastomeric chainsdecay of synthetic elastomeric chains

 Orthodontic elastics in form of ring,Orthodontic elastics in form of ring,
module, chain, are widely used to applymodule, chain, are widely used to apply
the forces needed for tooth movement.the forces needed for tooth movement.
 The elastics are made of either latex orThe elastics are made of either latex or
synthetic rubber.synthetic rubber.
 Latex, a naturally extracted rubber, is usedLatex, a naturally extracted rubber, is used
primarily for extraoral or intermaxillaryprimarily for extraoral or intermaxillary
force delivery.force delivery.

 Synthetic rubber is made of polyurethaneSynthetic rubber is made of polyurethane
with additives to improve both strengthwith additives to improve both strength
and resistance to free radicals that canand resistance to free radicals that can
weaken the polymer structureweaken the polymer structure
 Synthetic elastomeric chain isSynthetic elastomeric chain is
inexpensive, hygienic, and easilyinexpensive, hygienic, and easily
manipulated and requires little or nomanipulated and requires little or no
patient cooperationpatient cooperation

 However, it absorbs saliva, stains, andHowever, it absorbs saliva, stains, and
deforms permanently after it is stretched indeforms permanently after it is stretched in
the oral cavity.the oral cavity.
 It loses its force rapidly because of stressIt loses its force rapidly because of stress
relaxation and can result in a lessrelaxation and can result in a less
desirable force value to conduct toothdesirable force value to conduct tooth
movement.movement.

 Previous studies have shown that it might losePrevious studies have shown that it might lose
50% to 70% of its initial force during the first day50% to 70% of its initial force during the first day
of load application and 10% more by 3 weeks,of load application and 10% more by 3 weeks,
and retain only 30% to 40% of the original forceand retain only 30% to 40% of the original force
after 4 weeks.after 4 weeks.
 To counteract the rapid loss of force, AndreasenTo counteract the rapid loss of force, Andreasen
and Bishara suggested that one should over-and Bishara suggested that one should over-
stretch the synthetic elastomeric chain to inducestretch the synthetic elastomeric chain to induce
a much greater initial forcea much greater initial force

 But this could cause greaterBut this could cause greater patient discomfortpatient discomfort
and undermining resorptionand undermining resorption..
 Kovatch et alKovatch et al suggestedsuggested to stretch the chainto stretch the chain
more slowlymore slowly into place to reduce the forceinto place to reduce the force
decay for an extended period of time.decay for an extended period of time.
 Ferriter et alFerriter et al reported that an oral pH belowreported that an oral pH below
7.267.26 retarded the rate of force decayretarded the rate of force decay of theof the
chain elastics..chain elastics..

 Another method to reduce force decay isAnother method to reduce force decay is
to prestretch the elastomeric chain beforeto prestretch the elastomeric chain before
it is stretched with tension on teethit is stretched with tension on teeth
 Brooks and Hershey found that, when theBrooks and Hershey found that, when the
elastomeric modules were heated, theelastomeric modules were heated, the
force decreased to approximately 30% offorce decreased to approximately 30% of
the initial force at 1 hour and to 20% at 4the initial force at 1 hour and to 20% at 4
weeks.weeks.

 When modules were prestretched and thenWhen modules were prestretched and then
heated, the remaining force was about 50% at 1heated, the remaining force was about 50% at 1
hour and 31% at 4 weekshour and 31% at 4 weeks..
 They suggested that prestretching could partiallyThey suggested that prestretching could partially
offset the reduction in force caused by heatoffset the reduction in force caused by heat
 Young and SandrikYoung and Sandrik reported thatreported that
instantaneously prestretching elastomeric chainsinstantaneously prestretching elastomeric chains
in air significantlyin air significantly increased the remainingincreased the remaining
force after 24 hours by 17% to 25%force after 24 hours by 17% to 25% whenwhen
compared with the unprestretched controls.compared with the unprestretched controls.

 Chang studied the force decay of modulesChang studied the force decay of modules
instantaneously prestretched in air to 100%, 200%, andinstantaneously prestretched in air to 100%, 200%, and
300%.300%.
 He found that the initial force of the 100% prestretchedHe found that the initial force of the 100% prestretched
modules was significantly lower than that of themodules was significantly lower than that of the
unprestretched control, but the remaining force after 1unprestretched control, but the remaining force after 1
hour was similar to that of the control group.hour was similar to that of the control group.
 The 200% and 300% prestretching caused significantThe 200% and 300% prestretching caused significant
reduction in initial force and remaining forces from 1 hourreduction in initial force and remaining forces from 1 hour
to 3 weeks.to 3 weeks.
 Therefore, he suggested 100% prestretching for clinicalTherefore, he suggested 100% prestretching for clinical
useuse

 Brantley et al reported a 45% force loss inBrantley et al reported a 45% force loss in
modules prestretched for 3 weeks whenmodules prestretched for 3 weeks when
tested in water after 3 weeks, but a 65%tested in water after 3 weeks, but a 65%
force loss in the controls under the sameforce loss in the controls under the same
test condition.test condition.
 They also found that prestretching in waterThey also found that prestretching in water
was better than in air in terms ofwas better than in air in terms of
decreasing the force decay.decreasing the force decay.

 Williams and von Fraunhofer observedWilliams and von Fraunhofer observed
that 100% prestretching for 10 secondsthat 100% prestretching for 10 seconds
decreased force decay by only 4% to 6%.decreased force decay by only 4% to 6%.
 Baty et al concluded that the benefits ofBaty et al concluded that the benefits of
prestretching were small and probably notprestretching were small and probably not
clinically significant.clinically significant.

Materials and methodMaterials and method
 Two module lengths, 5-unit (12.5 mm) and 6-unitTwo module lengths, 5-unit (12.5 mm) and 6-unit
(15.5 mm), of clear, closed loop chain(15.5 mm), of clear, closed loop chain
(Generation II, Ormco, Glendora, Calif) were(Generation II, Ormco, Glendora, Calif) were
tested.tested.
 Eight frames for stretching modules wereEight frames for stretching modules were
fabricated from clear resin in which 2 rows offabricated from clear resin in which 2 rows of
1.8-mm diameter dowel pins were embedded.1.8-mm diameter dowel pins were embedded.
 There were 12 pins in each row, and theThere were 12 pins in each row, and the
distance between the rows was 25 mm for 4distance between the rows was 25 mm for 4
frames and 31 mm for the other 4 frames.frames and 31 mm for the other 4 frames.

Elastomeric chains stretched toElastomeric chains stretched to
pins on frame.pins on frame.

 The prestretched (experimental) modules wereThe prestretched (experimental) modules were
made by stretching the 5-unit to 25 mm pinsmade by stretching the 5-unit to 25 mm pins
(100%) and the 6-unit to 31 mm pins (100%);(100%) and the 6-unit to 31 mm pins (100%);
they were then stored in 37°C water for 1 hour,they were then stored in 37°C water for 1 hour,
24 hours, 2 weeks, and 4 weeks.24 hours, 2 weeks, and 4 weeks.
 The control modules were not prestretched.The control modules were not prestretched.
 There were 10 groups, 5 groups of 5-unitThere were 10 groups, 5 groups of 5-unit
modules (control and 4 storage times) and 5modules (control and 4 storage times) and 5
groups of 6-unit modules (control and 4 storagegroups of 6-unit modules (control and 4 storage
times).times).
 Each group had 12 pieces of chainEach group had 12 pieces of chain

 To test the force decay, a new frame with 12To test the force decay, a new frame with 12
pairs of pins was made for each group, and thepairs of pins was made for each group, and the
distance between the rows was 30 mm. Fordistance between the rows was 30 mm. For
each group, the samples were stretched on theeach group, the samples were stretched on the
pins (30 mm) and stored in 37°C distilled waterpins (30 mm) and stored in 37°C distilled water
 Then each stretched sample was removed fromThen each stretched sample was removed from
the pins and directly attached to a digital forcethe pins and directly attached to a digital force
gauge (DPS-2R, IMADA, Tokyo, Japan) set atgauge (DPS-2R, IMADA, Tokyo, Japan) set at
30 mm in length, and its exerted force was30 mm in length, and its exerted force was
measured at the initial time, 1 hour, 24 hours,measured at the initial time, 1 hour, 24 hours,
and weekly for 4 weeksand weekly for 4 weeks

Elastomeric chains stretched toElastomeric chains stretched to
pins (30 mm) on frame.pins (30 mm) on frame.

AA, Digital force gauge;, Digital force gauge; BB, chain was, chain was
stretched to 30 mm and force wasstretched to 30 mm and force was
measuredmeasured

 The mean and standard deviation of the force valueThe mean and standard deviation of the force value
and the percentage of initial force remaining wereand the percentage of initial force remaining were
calculatedcalculated for each group, and the Student pairedfor each group, and the Student paired tt testtest
was used to evaluate whether the initial force remainingwas used to evaluate whether the initial force remaining
was reduced significantly between the time intervals inwas reduced significantly between the time intervals in
each group.each group.
 One-way analysis of variance (ANOVA) and the DuncanOne-way analysis of variance (ANOVA) and the Duncan
multiple range test were used to compare the force valuemultiple range test were used to compare the force value
and the percentage of initial force remaining in theand the percentage of initial force remaining in the
control and the prestretched groups.control and the prestretched groups.
 The level of statistical significance was predetermined atThe level of statistical significance was predetermined at
PP < .05< .05

ResultsResults
 The initial forces of the prestretched groupsThe initial forces of the prestretched groups
(329.3-344.8 g) were significantly lower(329.3-344.8 g) were significantly lower thanthan
the force of the control group (358.8 g) (P < .05).the force of the control group (358.8 g) (P < .05).
 In the first hour,In the first hour, a rapid and statisticallya rapid and statistically
significant loss of force occurred in both thesignificant loss of force occurred in both the
control (100 g or 27.9%) and the prestretchedcontrol (100 g or 27.9%) and the prestretched
groups (69-85 g or 21%-24.7%),groups (69-85 g or 21%-24.7%),

 From 1 hour to 24 hoursFrom 1 hour to 24 hours, a statistically, a statistically
significant force loss was also noted in thesignificant force loss was also noted in the
control (28.7 g or 8%) and the prestretchedcontrol (28.7 g or 8%) and the prestretched
groups (24.3-27.8 g or 7.1%-8.1%).groups (24.3-27.8 g or 7.1%-8.1%).
 From 24 hours to 4 weeksFrom 24 hours to 4 weeks, a limited and, a limited and
steady force loss was found in all groups (9.6steady force loss was found in all groups (9.6
g/week for the control and 8.5-11.3 g/week forg/week for the control and 8.5-11.3 g/week for
the prestretched groups).the prestretched groups).

 At the end of fourth week, the residualAt the end of fourth week, the residual
forces wereforces were 191.7 g for the control191.7 g for the control
groupgroup andand 189.3 to 198.8 g for the189.3 to 198.8 g for the
prestretched groups.prestretched groups.

Mean force value graphics for 5-Mean force value graphics for 5-
unit modulesunit modules

Force values for the 6-unit groupsForce values for the 6-unit groups
 The 4 prestretched groups (205.6-240.3 g) hadThe 4 prestretched groups (205.6-240.3 g) had
statistically significantly lower initial forces thanstatistically significantly lower initial forces than
the control group (333.1 g).the control group (333.1 g).
 A rapid force loss occurred in both the controlA rapid force loss occurred in both the control
(110.8 g or 33.2%) and prestretched groups(110.8 g or 33.2%) and prestretched groups
(11.8-23.1 g or 5.4%-10.3%) in the first hour ((11.8-23.1 g or 5.4%-10.3%) in the first hour (PP
< .05).< .05).
 A statistically significant force loss was alsoA statistically significant force loss was also
noted from 1 hour to 24 hours in the controlnoted from 1 hour to 24 hours in the control
(27.6 g or 8.4%) and the prestretched groups (9-(27.6 g or 8.4%) and the prestretched groups (9-
21.3 g or 4.1%-8.8%).21.3 g or 4.1%-8.8%).

 From 24 hours to 4 weeks, a limited andFrom 24 hours to 4 weeks, a limited and
steady force loss was seen in all groupssteady force loss was seen in all groups
(8.5 g/week for the control and 4.5-8.6(8.5 g/week for the control and 4.5-8.6
g/week for the prestretched groups).g/week for the prestretched groups).
 At the end of fourth week, the remainingAt the end of fourth week, the remaining
force of the control was 160.9 g, and thatforce of the control was 160.9 g, and that
of the prestretched groups ranged fromof the prestretched groups ranged from
151.3 to 167.5 g.151.3 to 167.5 g.

Mean force value graphics for 6-Mean force value graphics for 6-
unit modulesunit modules

DiscussionDiscussion
 In this study, a testing distance of 30 mmIn this study, a testing distance of 30 mm
was used, approximately the averagewas used, approximately the average
length from the mid-position between thelength from the mid-position between the
maxillary lateral incisor and the canine tomaxillary lateral incisor and the canine to
the mesial hook on the maxillary firstthe mesial hook on the maxillary first
molar band.molar band.
 The amounts of stretch were 140% in 5-The amounts of stretch were 140% in 5-
unit modules and 93.5% in 6-unitunit modules and 93.5% in 6-unit
modules.modules.

 Initial forces produced by both 5-unitInitial forces produced by both 5-unit
(358.8 g) and 6-unit (333.1 g)(358.8 g) and 6-unit (333.1 g) controlcontrol
modulesmodules were relatively high, more thanwere relatively high, more than
the orthodontic force suggested by Storeythe orthodontic force suggested by Storey
and Smith, Reitan, and Proffit.and Smith, Reitan, and Proffit.
 However, in 1 hour, the forces droppedHowever, in 1 hour, the forces dropped
significantly to 258.8 g (5-unit) and 222.3 gsignificantly to 258.8 g (5-unit) and 222.3 g
(6-unit), more acceptable levels(6-unit), more acceptable levels

 These findings were similar to the reportsThese findings were similar to the reports
by De Genova et al and Chang, who foundby De Genova et al and Chang, who found
that all control modules lost considerablethat all control modules lost considerable
force with timeforce with time
 The largest loss occurred within the firstThe largest loss occurred within the first
hour after which the force decay ratehour after which the force decay rate
gradually tapered offgradually tapered off

 In this study, the initial forces were 329.3In this study, the initial forces were 329.3
to 344.8 g for the prestretched 5-unitto 344.8 g for the prestretched 5-unit
groups and 205.6 to 240.3 g for the 6-unitgroups and 205.6 to 240.3 g for the 6-unit
groups.groups.
 It seemed thatIt seemed that prestretching wasprestretching was
advantageous in the case of 6-unitadvantageous in the case of 6-unit
modules because the resulting initialmodules because the resulting initial
force was closer to the optimal forceforce was closer to the optimal force..

 Interestingly, after 1 hour, there was aInterestingly, after 1 hour, there was a
steep force decline in all control andsteep force decline in all control and
experimental groups.experimental groups.
 Similar remaining forces were notedSimilar remaining forces were noted
among all 5-unit control and experimentalamong all 5-unit control and experimental
groups, and small differences were seengroups, and small differences were seen
among the 6-unit groups.among the 6-unit groups.

 Remaining forces at 1 hour in the 5-unit groupsRemaining forces at 1 hour in the 5-unit groups
were between 258.8 and 263 g, and those in thewere between 258.8 and 263 g, and those in the
6-unit groups were between 192.3 and 222.3 g.6-unit groups were between 192.3 and 222.3 g.
All values were within the acceptable optimalAll values were within the acceptable optimal
force range.force range.
 Prestretching lowered the initial force byPrestretching lowered the initial force by
3.9% to 8.2% in the 5-unit and 27.9% to 38.3%3.9% to 8.2% in the 5-unit and 27.9% to 38.3%
in the 6-unit groupsin the 6-unit groups..
 However, Brantley et al found a greaterHowever, Brantley et al found a greater
decrease in initial force, 53.9% to 56.8%, afterdecrease in initial force, 53.9% to 56.8%, after
prestretching modules in 37°C water for 24prestretching modules in 37°C water for 24
hours and 3 weeks.hours and 3 weeks.

 After 1 hourAfter 1 hour, there was a mean force, there was a mean force
decay of 100 g (27.9%) in the 5-unitdecay of 100 g (27.9%) in the 5-unit
control and 110.8 g (33.2%) in the 6-unitcontrol and 110.8 g (33.2%) in the 6-unit
control groupscontrol groups
 In prestretched groups, the force decay inIn prestretched groups, the force decay in
the first hour was 69 to 85 g (21.0% tothe first hour was 69 to 85 g (21.0% to
24.7%) for 5-unit and 11.8 to 23.1 g (5.4%24.7%) for 5-unit and 11.8 to 23.1 g (5.4%
to 10.3%) for 6-unit modulesto 10.3%) for 6-unit modules

 Significant force decay occurred from 1Significant force decay occurred from 1
hour to 24 hours in all groups.hour to 24 hours in all groups.
 The force decay from 24 hours to 4The force decay from 24 hours to 4
weeks was small and steady for allweeks was small and steady for all
groups.groups.
 Clinically, there should be no significantClinically, there should be no significant
differences in the weekly force decay ofdifferences in the weekly force decay of
the control and prestretched groups.the control and prestretched groups.

 In terms ofIn terms of initial force remaininginitial force remaining, generally, generally
the 5- and 6-unit presretched groups showed athe 5- and 6-unit presretched groups showed a
higher percentage from 1 hour to 4 weeks thanhigher percentage from 1 hour to 4 weeks than
the controlsthe controls
 From 1 hour to 4 weeks,From 1 hour to 4 weeks, the percentage ofthe percentage of
force remainingforce remaining was reduced by 18.7% in thewas reduced by 18.7% in the
control and 18% to 21.6% in the prestretched 5-control and 18% to 21.6% in the prestretched 5-
unit groups; it was reduced by 18.5% in theunit groups; it was reduced by 18.5% in the
control and 12.3% to 23.1% in the prestrecthedcontrol and 12.3% to 23.1% in the prestrecthed
6-unit groups.6-unit groups.

 Results showed that, at 4 weeks,Results showed that, at 4 weeks, similarsimilar
remaining forces were present betweenremaining forces were present between
the control and prestretched groupsthe control and prestretched groups ofof
5- (189.3-198.8 g) and 6-unit (151.3-167.55- (189.3-198.8 g) and 6-unit (151.3-167.5
g) modules.g) modules.
 These force values are sufficient to moveThese force values are sufficient to move
teeth.teeth.
 Thus, clinically it might not be necessaryThus, clinically it might not be necessary
to replace the chain earlier than 4 weeksto replace the chain earlier than 4 weeks

 When compared with the 5-unitWhen compared with the 5-unit
prestretched modules, the 6-unitprestretched modules, the 6-unit
prestretched modules showed greaterprestretched modules showed greater
reductions in initial force but less forcereductions in initial force but less force
decay during the first hour than thedecay during the first hour than the
corresponding control.corresponding control.
 The difference might be due to theThe difference might be due to the
different degree of stretch tested (140%different degree of stretch tested (140%
for the 5-unit and 93.5% for the 6-unit).for the 5-unit and 93.5% for the 6-unit).

ConclusionsConclusions
 The prestretched 5- and 6-unit modules hadThe prestretched 5- and 6-unit modules had
significantly lower initial forces than thesignificantly lower initial forces than the
corresponding controls (corresponding controls (PP < .05).< .05).
 All prestretched and control groups showedAll prestretched and control groups showed
significant force decay during the first hour (significant force decay during the first hour (PP < .< .
05)05)
 From 1 hour to 4 weeks, a similar rate of forceFrom 1 hour to 4 weeks, a similar rate of force
decay was seen between the prestretched anddecay was seen between the prestretched and
the control groups.the control groups.
 After 4 weeks, similar remaining forces wereAfter 4 weeks, similar remaining forces were
found between the prestretched and the controlfound between the prestretched and the control
groupsgroups

 The effects of prestretching were evidentThe effects of prestretching were evident
only in the first hour. Thus, the benefit ofonly in the first hour. Thus, the benefit of
the prestretching technique in thethe prestretching technique in the
synthetic elastomeric chain used in thissynthetic elastomeric chain used in this
study is questionable.study is questionable.

Force delivery properties ofForce delivery properties of
colored elastomeric modulescolored elastomeric modules
 David L. Baty, DDS, MSc, John E. Volz, DDS,David L. Baty, DDS, MSc, John E. Volz, DDS,
MPA, and Joseph A. von Fraunhofer, MSc,MPA, and Joseph A. von Fraunhofer, MSc,
PhD, FRSCPhD, FRSC
 Ft. Riley, Kan., and Ft. Knox, and Louisville,Ft. Riley, Kan., and Ft. Knox, and Louisville,
Ky.Ky.
-JULY 1994, AJO-JULY 1994, AJO

 The force required to achieve physiologicThe force required to achieve physiologic
tooth movement is the subject of sometooth movement is the subject of some
controversy, but it is generally agreed thatcontroversy, but it is generally agreed that
light continuous forces are optimal.light continuous forces are optimal.
 Storey and Smith stated that 175 to 300 gfStorey and Smith stated that 175 to 300 gf
would allow for canine retraction withoutwould allow for canine retraction without
causing damage to the periodontalcausing damage to the periodontal
ligament.ligament.

 HixonHixon recommended force levels based on therecommended force levels based on the
root surface area to be moved (generally aboutroot surface area to be moved (generally about
350 gm for a canine).350 gm for a canine).
 Boester and JohnsonBoester and Johnson stated that canines couldstated that canines could
be retracted with forces between 100 to 300 gm.be retracted with forces between 100 to 300 gm.
 However, if the force level fell below 55 gm,However, if the force level fell below 55 gm,
canine movement essentially ceasedcanine movement essentially ceased

 Andreasen and Bishara found thatAndreasen and Bishara found that
Alastiks (Unitek Corp., Monrovia, Calif.)Alastiks (Unitek Corp., Monrovia, Calif.)
suffered a 74% loss of force deliverysuffered a 74% loss of force delivery
capability after 24 hours of loadcapability after 24 hours of load..
 Elastomeric modules can be extended toElastomeric modules can be extended to
deliver light forces, butdeliver light forces, but the degree ofthe degree of
distraction required to deliver a forcedistraction required to deliver a force
compatible with physiologically soundcompatible with physiologically sound
tooth movement is still not completelytooth movement is still not completely
characterized.characterized.

 Andreasen and BisharaAndreasen and Bishara recommended thatrecommended that
elastomeric chains, needed to be extendedelastomeric chains, needed to be extended toto
four times theirfour times their original lengthoriginal length to compensateto compensate
for the large force loss during the first day.for the large force loss during the first day.
 WongWong recommended that an increase of only arecommended that an increase of only a
third would provide sufficient force deliverythird would provide sufficient force delivery
without exceeding the elastic limitwithout exceeding the elastic limit
 RockRock suggested extending the chains by 50% tosuggested extending the chains by 50% to
70% of their original length.70% of their original length.

 Significant effects on force decay behavior wereSignificant effects on force decay behavior were
found with thermal cycling in artificial salivafound with thermal cycling in artificial saliva (De(De
Genova) when chains were exposed to simulated oralGenova) when chains were exposed to simulated oral
conditions, and also in vivo conditions (Ash andconditions, and also in vivo conditions (Ash and
Nikolai,Andreasen and Bishara), as well as different pHNikolai,Andreasen and Bishara), as well as different pH
media (Ferriter et al.).media (Ferriter et al.).
 Long-term storage of elastomeric chains in waterLong-term storage of elastomeric chains in water
was found to substantially increase the force decaywas found to substantially increase the force decay
ratesrates (Huget et al.).(Huget et al.).

 The present study was undertaken toThe present study was undertaken to
examine the force delivery behavior ofexamine the force delivery behavior of
a variety of new colored "power"a variety of new colored "power"
chains and to determine theirchains and to determine their
dimensional stability with respect todimensional stability with respect to
immersion in a fluid environment.immersion in a fluid environment.

MATERIALS AND METHODSMATERIALS AND METHODS
 Four different colored elastomericFour different colored elastomeric
chains from three manufacturers werechains from three manufacturers were
studied, all having the short-filamentstudied, all having the short-filament
configurationconfiguration
 All chains were subjected to a force-All chains were subjected to a force-
delivery study to determine thedelivery study to determine the
distraction required to generate 150 anddistraction required to generate 150 and
300 gf.300 gf.
 The chains were also stored in a fluidThe chains were also stored in a fluid
environment to assess the effects ofenvironment to assess the effects of
liquid on the force delivery behaviorliquid on the force delivery behavior

 Five specimens of each chain,Five specimens of each chain,
trimmed to four loops with an extratrimmed to four loops with an extra
half loop at each end to preventhalf loop at each end to prevent
distortion while cutting, were testeddistortion while cutting, were tested
immediately (0 hours), 1 hour, 4immediately (0 hours), 1 hour, 4
hours, 24 hours, 1 week, 2 weeks,hours, 24 hours, 1 week, 2 weeks,
and 3 weeks after storage in air,and 3 weeks after storage in air,
distilled water, and artificial saliva,distilled water, and artificial saliva,
Oralube at 37 ± 0.5° C before testing.Oralube at 37 ± 0.5° C before testing.

 Each specimen was removed from its storageEach specimen was removed from its storage
container and suspended between two hooks oncontainer and suspended between two hooks on
a universal testing machinea universal testing machine
 The sample chain was distracted at a crossheadThe sample chain was distracted at a crosshead
speed of 50 mm/min, and the output of thespeed of 50 mm/min, and the output of the
transducer attached to the crosshead was fed totransducer attached to the crosshead was fed to
an internal x-y chart recorder that automaticallyan internal x-y chart recorder that automatically
plotted force versus displacement curves.plotted force versus displacement curves.

 Each curve was analyzed to determine the distractionEach curve was analyzed to determine the distraction
required to generate 150 and 300 gf (total of 2280required to generate 150 and 300 gf (total of 2280
measurements). The data were analyzed with a 4-factormeasurements). The data were analyzed with a 4-factor
factorial analysis of variancefactorial analysis of variance
 Interactions above the second order were consideredInteractions above the second order were considered
clinically and scientifically uninterpretable and wereclinically and scientifically uninterpretable and were
collapsed into the error term.collapsed into the error term.
 Follow upFollow up Bonferroni simultaneous t testsBonferroni simultaneous t tests were usedwere used
to assess differences among sets of means withto assess differences among sets of means with
statistical significance set at a family-wise a priority of pstatistical significance set at a family-wise a priority of p
< 0.05.< 0.05.

Second part of experimentSecond part of experiment
 Dimensional stability was evaluated byDimensional stability was evaluated by
exposing the elastomeric chains to aexposing the elastomeric chains to a
simulated oral environment over a 3-weeksimulated oral environment over a 3-week
periodperiod..
 Four samples of each chain were trimmed to theFour samples of each chain were trimmed to the
same specifications of those in the force deliverysame specifications of those in the force delivery
study,study,
 Each specimen was initially measured inEach specimen was initially measured in
four dimensions: length, width, diameter offour dimensions: length, width, diameter of
the lumen, and thicknessthe lumen, and thickness..

 The chains were then placed in artificialThe chains were then placed in artificial
saliva (Oralube) and stored in an incubatorsaliva (Oralube) and stored in an incubator
(37 ± 0.5° C).(37 ± 0.5° C).
 At intervals of 1, 2, and 3 weeks, theAt intervals of 1, 2, and 3 weeks, the
chains were again measured in the samechains were again measured in the same
manner for a total of 768 measurements.manner for a total of 768 measurements.

 Data were analyzed with a 3-factor factorialData were analyzed with a 3-factor factorial
analysis of variance for each dimension withanalysis of variance for each dimension with
interactions above the second order againinteractions above the second order again
collapsed into the error term.collapsed into the error term.
 The Bonferroni simultaneous t tests (family-The Bonferroni simultaneous t tests (family-
wise a priori a = p < 0.05)wise a priori a = p < 0.05) was used to assesswas used to assess
the statistical significance of the differencethe statistical significance of the difference
among sets of means.among sets of means.

RESULTSRESULTS
 The study generated a large number ofThe study generated a large number of
observations (2280 in the force deliveryobservations (2280 in the force delivery
study and 768 in the dimensional stabilitystudy and 768 in the dimensional stability
study) with very little within groupstudy) with very little within group
variability.variability.

 The distraction of the elastomericThe distraction of the elastomeric
chains for a force of 150 gm waschains for a force of 150 gm was
approximately 3 mm and 7 mm for aapproximately 3 mm and 7 mm for a
force of 300 gm.force of 300 gm.

 MaselMasel 4-link chains originally measured an average of4-link chains originally measured an average of
11.69 mm in length and needed 3.13 mm of extension11.69 mm in length and needed 3.13 mm of extension
(23.7%) to generate 150 gm and 6.53 mm (55.9%)(23.7%) to generate 150 gm and 6.53 mm (55.9%)
distraction to achieve 300 gm of force delivery.distraction to achieve 300 gm of force delivery.
 OrmcoOrmco chains required 2.46 mm (21.7%) and 5.88 mmchains required 2.46 mm (21.7%) and 5.88 mm
(51.9%) to deliver 150 gm and 300 gm, respectively, from(51.9%) to deliver 150 gm and 300 gm, respectively, from
an initial length of 11.34 mm.an initial length of 11.34 mm.
 Unitek chainsUnitek chains were 12.22 mm in length at the originalwere 12.22 mm in length at the original
measurements and required extensions of 3.04 mm (24.9%)measurements and required extensions of 3.04 mm (24.9%)
and 6.96 mm (56.9%) to generate forces of 150 gm and 300and 6.96 mm (56.9%) to generate forces of 150 gm and 300
gm.gm.

 None of the Masel chains stored in air showed aNone of the Masel chains stored in air showed a
change in the distraction-force delivery behaviorchange in the distraction-force delivery behavior
 After storage in bothAfter storage in both water and Oralubewater and Oralube, all Masel, all Masel
chainschains showed an increase in required distractionshowed an increase in required distraction
(compared to that in air)(compared to that in air)
 The greatest required distraction in all cases wasThe greatest required distraction in all cases was
observed at 24 hoursobserved at 24 hours
 The differences in the distraction-force behavior inThe differences in the distraction-force behavior in
water and Oralube did not exceed 10%water and Oralube did not exceed 10% at any givenat any given
time period for any of the colored chains.time period for any of the colored chains.

 Ormco chains did not exhibit a change >10% in air atOrmco chains did not exhibit a change >10% in air at
any test period.any test period.
 However, in water and Oralube, all chains,However, in water and Oralube, all chains, requiredrequired
more than a 10% increase in extension after 4 hoursmore than a 10% increase in extension after 4 hours
to deliver 150 gfto deliver 150 gf..
 At the 300 gf level, all colors of Ormco chainsAt the 300 gf level, all colors of Ormco chains
required at least a 10% increase in distractionrequired at least a 10% increase in distraction inin
both water and Oralube to achieve the desired forceboth water and Oralube to achieve the desired force
level after 1 hourlevel after 1 hour

 The increased distractionThe increased distraction to generate 150 gf atto generate 150 gf at
24 hours24 hours in waterin water ranged from 14% (gray) toranged from 14% (gray) to
29% (green)29% (green) andand at 300 gm the range wasat 300 gm the range was
27% (gray and pink) to 39% (green).27% (gray and pink) to 39% (green).
 In OralubeIn Oralube, the required extension increase was, the required extension increase was
again greatest at 24 hours, rangingagain greatest at 24 hours, ranging from 19%from 19%
(gray) to 38% (green) for 150 gf(gray) to 38% (green) for 150 gf andand 31%31%
(pink) to 50% (green) for a force delivery of(pink) to 50% (green) for a force delivery of
300 gm.300 gm.

 Unitek chainsUnitek chains, when stored in air,, when stored in air,
required no increase in extension torequired no increase in extension to
generate the desired force levelsgenerate the desired force levels
 Tendency to become stiffer, requiring lessTendency to become stiffer, requiring less
distraction to deliver 150 gm and 300 gmdistraction to deliver 150 gm and 300 gm
as storage time increased.as storage time increased.
 At 504 hours, all Unitek chains, with theAt 504 hours, all Unitek chains, with the
exception of gray and pink at the 300 gmexception of gray and pink at the 300 gm
level, required at least 10% less distractionlevel, required at least 10% less distraction
to achieve both 150 and 300 gf.to achieve both 150 and 300 gf.

 All chains needed more than 10% increase inAll chains needed more than 10% increase in
distraction at 4 hours and 24 hours in water anddistraction at 4 hours and 24 hours in water and
Oralube to deliver 150 gf.Oralube to deliver 150 gf.
 For a force of 300 gm after storage in both waterFor a force of 300 gm after storage in both water
and Oralube, all colors of Unitek chains requiredand Oralube, all colors of Unitek chains required
an increase in distraction that exceeded 10%an increase in distraction that exceeded 10%
level after 24 hourslevel after 24 hours
 This increase in distraction gradually diminishedThis increase in distraction gradually diminished
to the end of the testing period, as these chainsto the end of the testing period, as these chains
become stiffbecome stiff

 In general, all chains exhibited an initial increaseIn general, all chains exhibited an initial increase
in dimensions at 1 week with little changein dimensions at 1 week with little change
thereafter.thereafter.
 Although there were statistically significantAlthough there were statistically significant
differences between the various chains,differences between the various chains, thesethese
differences never exceeded 6% from thedifferences never exceeded 6% from the
original dimensionsoriginal dimensions, thus appearing to be, thus appearing to be
clinically unimportant.clinically unimportant.

DISCUSSIONDISCUSSION
 The chains in this study initially requiredThe chains in this study initially required
an extension of 52% to 57% to generate aan extension of 52% to 57% to generate a
force level of 300 gm, a finding that wouldforce level of 300 gm, a finding that would
seem to concur with those of Rock whoseem to concur with those of Rock who
recommended distractions of 50% to 70%recommended distractions of 50% to 70%

 After the first 4 to 24 hours of storage in fluids, theAfter the first 4 to 24 hours of storage in fluids, the
chains required an additional increase in extension ofchains required an additional increase in extension of
20% to 40% to generate 300 gf.20% to 40% to generate 300 gf.
 when the chains are held at constant extension,when the chains are held at constant extension,
there is a decay of force delivery capability of athere is a decay of force delivery capability of a
comparable amount.comparable amount.
 Thus with an initial extension of 50% to 70% and a 20%Thus with an initial extension of 50% to 70% and a 20%
to 40% decay of force delivery, the residual force wouldto 40% decay of force delivery, the residual force would
still remain in the 100 to 300 gm range required forstill remain in the 100 to 300 gm range required for
efficient tooth movement, as stated by Boester andefficient tooth movement, as stated by Boester and
Johnson.Johnson.

 It was noted that there wasIt was noted that there was an increase inan increase in
required distractionrequired distraction for force delivery offor force delivery of
all chains exposed to fluids during the firstall chains exposed to fluids during the first
week as well asweek as well as an increase of thean increase of the
original dimensions of the chainsoriginal dimensions of the chains

 Williams and von Fraunhofer15 in 1989 showedWilliams and von Fraunhofer15 in 1989 showed
that the force delivery properties of tooth-coloredthat the force delivery properties of tooth-colored
elastomeric chains were significantly affected byelastomeric chains were significantly affected by
the filler material used in tinting the chains.the filler material used in tinting the chains.
 The present study appears to support thisThe present study appears to support this
conclusion in chains of certain colors from aconclusion in chains of certain colors from a
particular manufacturer.particular manufacturer.
 Masel and Unitek chains were not clinicallyMasel and Unitek chains were not clinically
affected by the addition of coloring material, butaffected by the addition of coloring material, but
those of Ormco, especially the purple and greenthose of Ormco, especially the purple and green
chains, consistently required more extension thanchains, consistently required more extension than
that company's standard gray chain whenthat company's standard gray chain when
exposed to a fluid environment.exposed to a fluid environment.

SUMMARY ANDSUMMARY AND
CONCLUSIONSCONCLUSIONS
 All the colored elastomeric chains in this studyAll the colored elastomeric chains in this study
appeared capable of generating force levelsappeared capable of generating force levels
compatible with physiologically sound toothcompatible with physiologically sound tooth
movement.movement.
 TheThe distractiondistraction necessary to deliver a force ofnecessary to deliver a force of
150 or 300 gm150 or 300 gm increased for all chains afterincreased for all chains after
the first 4 to 24 hoursthe first 4 to 24 hours exposure to distilledexposure to distilled
water and artificial saliva.water and artificial saliva.

 The distraction required to achieve theThe distraction required to achieve the
desired force levels, especially afterdesired force levels, especially after
storage in fluid media, varied with thestorage in fluid media, varied with the
manufacturemanufacture
 All the tested chains appeared to retainAll the tested chains appeared to retain
force delivery capabilities after 3 weeksforce delivery capabilities after 3 weeks
storage in a fluid medium.storage in a fluid medium.

 Changes in dimension were observed for theChanges in dimension were observed for the
chains on storage in fluid mediachains on storage in fluid media
 The force delivery behavior of chains varies withThe force delivery behavior of chains varies with
the manufacturer of the chain.the manufacturer of the chain.
 EXAMPLE -Masel chains are not the same asEXAMPLE -Masel chains are not the same as
Ormco or Unitek chains, but all colors of MaselOrmco or Unitek chains, but all colors of Masel
chains appear to behave similarly.chains appear to behave similarly.

Relaxation of Elastomeric ChainsRelaxation of Elastomeric Chains
DENNIS M. KILLIANY, DDS, MSDDENNIS M. KILLIANY, DDS, MSD
JOHN DUPLESSIS, DMD, JCO 1985,VOL19JOHN DUPLESSIS, DMD, JCO 1985,VOL19

 Ideally, an elastomeric chain shouldIdeally, an elastomeric chain should
undergo minimal relaxation and maintain aundergo minimal relaxation and maintain a
constant force level.constant force level.
 However, there is usually aHowever, there is usually a relaxation ofrelaxation of
more than half of the force in the firstmore than half of the force in the first
24 hours, followed by a gradual24 hours, followed by a gradual
additional decline.additional decline.

 An initial force heavier than desiredAn initial force heavier than desired
would have to be used if one were towould have to be used if one were to
offset the initial relaxation and produceoffset the initial relaxation and produce
adequate force to move teeth.adequate force to move teeth.

 A new syntheticA new synthetic elastomeric chain,elastomeric chain,
Energy ChainEnergy Chain, appears to possess better, appears to possess better
properties than many other conventionalproperties than many other conventional
types of elastomeric chains.types of elastomeric chains.
 The purpose of this study was to verifyThe purpose of this study was to verify
this clinical observation underthis clinical observation under
laboratory conditionslaboratory conditions..

 Two elastomeric chains were evaluated:Two elastomeric chains were evaluated:
closed Energy Chain and short Plasticclosed Energy Chain and short Plastic
Chain (representative of conventionalChain (representative of conventional
synthetic elastomeric chains)synthetic elastomeric chains)

ProcedureProcedure
 Ten pieces of chain, each with an initial length ofTen pieces of chain, each with an initial length of
19mm, were tested for each group.19mm, were tested for each group.
 This length was selected so that each piece ofThis length was selected so that each piece of
chain was closed at both ends (seven moduleschain was closed at both ends (seven modules
for Energy Chain and six for Plastic Chain).for Energy Chain and six for Plastic Chain).
 Frames were constructed on which to stretch theFrames were constructed on which to stretch the
elastics to 38mm, orelastics to 38mm, or twice their initial lengthtwice their initial length..

 Each chain was stretched, held by theEach chain was stretched, held by the
Instron machine, and allowed toInstron machine, and allowed to
equilibrate for one minute before the forceequilibrate for one minute before the force
was recorded.was recorded.
 Forces were measured on an InstronForces were measured on an Instron
Machine at 24 hours, 72 hours, andMachine at 24 hours, 72 hours, and
weekly for eight weeks.weekly for eight weeks.

 All samples were stretched while stored inAll samples were stretched while stored in
a common pool of saliva maintained ata common pool of saliva maintained at
body temperature.body temperature.
 The saliva was changed every three daysThe saliva was changed every three days
throughout the experiment.throughout the experiment.

ResultsResults
 There was a significant differenceThere was a significant difference
between the two materials for thebetween the two materials for the
percentage of initial force maintained atpercentage of initial force maintained at
each time periodeach time period

 Although Plastic Chain had a greater initial force,Although Plastic Chain had a greater initial force,
Energy Chain produced a greater force afterEnergy Chain produced a greater force after
eight weekseight weeks than Plastic Chain did after onethan Plastic Chain did after one
day,day, and maintained a higher percentage ofand maintained a higher percentage of
its initial forceits initial force..
 While Energy Chain appears to be a significantWhile Energy Chain appears to be a significant
and desirable improvement, it remains to beand desirable improvement, it remains to be
proven in the oral cavity..proven in the oral cavity..

 Although all chains were intact and functional after eightAlthough all chains were intact and functional after eight
weeks in this test, it should not be concluded that theyweeks in this test, it should not be concluded that they
would perform in exactly the same way in the mouth.would perform in exactly the same way in the mouth.
 Clinical observations indicate that a single piece ofClinical observations indicate that a single piece of
Energy Chain may be used for six weeks or longer, butEnergy Chain may be used for six weeks or longer, but
that the material can fray and tear when used too long.that the material can fray and tear when used too long.
 Still, this product seems to represent the first of a newStill, this product seems to represent the first of a new
generation of improved synthetic elastomeric chainsgeneration of improved synthetic elastomeric chains

Thank youThank you
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