Six months was a familiar landmark time period for most orthodontists, and it was likely that most patients will still be complying with their retainer wear and so it was chosen.
It was calculated that a total sample size of 388 subjects would give a power of 80% with a 5% significance level to detect a true difference in contactpoint displacement of greater than 0.2 mm. at least 400 patients (200 in each group) would be recruited to allow for dropouts and loss to follow-up
was chosen, based on equal numbers of both types of and were blind to the fact that they were making retainers for patients included in the trial.
It was found that the VFRs were significantly better at retaining the labial segments than the Hawley retainers.
The effectiveness of
Hawley and vacuum
formed retainers: a single
INDIAN DENTAL ACADEMY
Leader in continuing dental education
Post fixed appliance therapy , retainers
routinely fitted by the orthodontists are worn by
the patient for 6 to 12 months while the soft and
hard tissues remodel around the teeth.
In the long term retention might be necessary
until growth is complete or indefinitely, if teeth
are in unstable positions.
Hawley retainers and vacuum formed retainers
are the 2 most commonly prescribed retainers
in the UK NHS.
This is probably due to their improved
esthetics, ease of fabrication and lower costs.
There is no evidence to support the use of
VFR’s over Hawley’s retainers .
But evidence suggests that the Hawley's
might be the retainer of choice when a lateral
open bite is present before debond.
Although studies have mentioned that there is
little to choose between Hawley and VFR,
except in open bite patients ,the evidence is
weak because of the small sample sizes.
However ,the potential cost savings in a health
care system with the routine use of VFR’s
rather than Hawley's are significant which
alone justifies more research and greater
statistical power to enable valid clinical and
economic considerations to be reached.
The aim of this randomized clinical trial was to
compare the clinical effectiveness of Hawley
and VFR’s over a 6-month period after
debonding , in terms of Little’s index of
irregularity (LII), tooth rotation, intercanine
width (ICW), intermolar width (IMW), over jet,
and overbite .
Material and methods
Clinical trial was conducted in an orthodontic
practice with a large sample treated by an
orthodontist approved by local research and
ethics committee at united Bristol health care
Patients who were due to have their fixed
orthodontic appliances removed.
Treated under the NHS by the same orthodontist.
fixed appliance treatment involving both arches.
preadjusted edgewise appliances.
study models available.
willingness to wear maxillary and mandibular
Single-arch or sectional fixed appliance treatment.
Hypodontia requiring tooth replacement on the
retainer as a temporary measure.
Rapid maxillary expansion.
Poor periodontal status.
Cleft lip or palate.
Potential participants were identified before
debonding, and the study’s purpose was
explained to the patients and their parents or
Written information about the study was given
to all potential participants, and written consent
was obtained before the debond appointment.
For patients under 16 years, written consent
was also obtained from the parent or legal
Gillick competence was applied when
Enrolment started in March 2003 and was
completed by December 2004.
The orthodontist assessed 531 subjects for
55 did not meet the inclusion criteria.
79 refused to participate,
recruitment rate was 75%.
Three hundred ninety-seven subjects agreed to
take part in the study.
At the debond appointment after appliance
removal (T1), the orthodontist recorded over jet
One set of maxillary and mandibular alginate
impressions were made, and study models and
working models were cast on which the retainers
were to be made.
All subjects were randomized by the research
team to receive either maxillary and mandibular
Hawley retainers or VFR’s.
A blocked randomization method and retainers
were allocated per block of 20 patients.
randomization was undertaken after obtaining
patient consent to ensure concealment of
196 patients were randomized to Hawley retainers
and 201 to VFRs.
Two fully qualified, blinded lab. technicians
fabricated the retainers to standardized designs.
The Hawley retainer
acrylic base plate
Adams clasps of 0.7-
mm s.s wire on the
A Hawley bow (open
looped short labial bow)
from 0.7-mm s.s wire
extending from canine to
The Hawley bow was
then contoured with
acrylic resin to contact
the labial surfaces of the
Erkodur blank (Erkodent,
Erich Kopp, GmbH,
Germany) 1.5 mm in
thickness was used.
The retainer was
trimmed to provide 1 to 2
mm buccal and 3 to 4
mm lingual extensions
past the gingival margin.
All occlusal surfaces
were covered up to and
including the most distal
The retainers were fitted within 1 week after debond.
The duration of retainer wear was standardized
based on the standard protocol for retainer wear.
Hawley retainers were to be worn 24 hours a day for
3 mths, including while eating, but to remove them
when brushing their teeth. After 3 mths, wear time
was reduced to 12 hours a day.
the VFRs were to be worn 24 hours a day for the 1st
week except while eating and brushing teeth. After
week, wear time was reduced to 12 hours a
The subjects were reviewed by a member of the
research team at 2 intervals; 3 months and 6 months
after debond (T2).
At the 6-month review appointment, over jet and
overbite were recorded, and alginate impressions for
end-of-trial study models were taken.
The subjects were asked to remove their retainers
before their appointments so that the research team
would be blind to the type of retainers that they were
Orthodontic study models collected at T1 and T2.
were examined by 1blind researcher . Casts of poor
quality were excluded from the analysis .
The number of models excluded and the reasons for
exclusion were documented.
The method used to measure changes in the study
models between debond and 6 months was based on
the study of Tran et al, in which the LII was measured
on 2-dimensional scanned and printed images of
Methodology for the analysis of the study models
The heels of the maxillary and mandibular models
were trimmed so that all occlusal surfaces of the
teeth contacted the glass bed of the scanner.
The mesiopalatal/mesiolingual cusp of the molars,
the buccal and mesiopalatal/mesiolingual cusps of
the premolars, and the canine cusp tips were
marked with a pencil.
The models were then placed on the glass of the
flatbed scanner (Agfa SnapScan 1236 flatbed
scanner; Agfa-Gevaert N.V., Mortsel, Belgium),
with their occlusal surfaces facing down and in
contact with the glass. Each was scanned at a
resolution of 600 dpi, and the resulting image was
saved to a PC as a JPEG file.www.indiandentalacademy.com
The JPEG image was enlarged to 200% by using
Paint Shop Pro 9 software (Corel UK Limited,
Maidenhead, Berkshire, United Kingdom) to make
point identification easier during subsequent
The image was then printed in color with a laser
printer . A total of 34 points were digitized in
sequence from point 1 to point 34 by using a GTC
digitizer (GTCO Cal Comp, Columbia, Md) on each
printed image of a study model
A computer program, written specifically for the
study, automatically calculated the following
outcomes in both arches for each digitized image.
Tooth rotations mesial to the first permanent molars.
The rotations of the incisors and
canines was determined by
constructing a line that bisected
2 points per tooth that best
marked its rotational angulation .
The angle formed by the
intersection of this line with the
line forming arch depth gave the
measurement of rotation of the
Arch depth was defined as the
length of a line perpendicular to
the intermolar width that passed
through the midpoint of the
contact points of the central
The LII was defined as the sum of the
displacements of the 5 contact points of the
The method described by Little used the true
anatomic contact point to assess tooth
However, with a printed 2-dimensional image, it
was almost impossible to determine the true
anatomic contact point.
The LII was therefore redefined for this study as
the displacement between the midpoint of the
ICW was the
canine cusp tips
IMW was the
distance between the
of the first molars
The measurement of rotation for the premolars
was calculated by
constructing a line that
bisected the buccal and the
palatal/lingual cusp tips .
In premolars with 2
lingual/palatal cusps, the
mesiopalatal / mesiolingual
cusp was bisected to form
The angle formed by the
intersection of this line with
the line forming arch depth
gave the rotation of the
The digitization of 1 model resulted in creation of a
“comma-separated-variable-string” file that enabled
the data to be exported electronically into a database
(version 13.0; SPSS, Chicago, Ill) for statistical
To record the reproducibility of the method, 1
examiner (H.R.) made all measurements on 30
models on 2 occasions ,a week apart. Intra observer
reliability coefficients were then calculated.
An intention-to-treat analysis was used wherever
data were available so that the data from all
patients who were successfully randomized and for
whom baseline and final records were available
were included in the analysis.
Relapse amounts for LII, ICW, IMW, tooth rotation,
and over jet were determined by comparing the
difference between the measurements at T1 and
T2. Absolute values for these outcome measures
were calculated because any change in either a
positive or a negative direction could be considered
relapse. The absolute difference was calculated so
that positive and negative changes did not cancel
Visual inspection of the histograms showed that the
data were considerably skewed and did not follow a
The median and the interquartile range were
therefore calculated for each outcome at T1 and T2.
Mann-Whitney tests were used to compare the
Hawley and the VFR groups in terms of the changes
between T1 and T2.
Relapse of overbite between T1 and T2 was
calculated by first determining the numbers of
subjects who stayed the same and whose overbite
changed in each group. The differences between the
overbite change for both groups were assessed by
using the Fisher exact test.
Because of the number of tests performed, a P value
of .01 was taken to be statistically significant.
355 subjects (172 Hawley, 183 VFR) attended the 6-
month review, giving a completion rate of 89%. 155
models were analyzed in the Hawley group and 155
in the VFR group.
Both groups had a median change in over jet
between T1 and T2 of 0.5 mm . In 54 subjects (32%)
in the Hawley group and 49 subjects (27%) in the
VFR group, a change in overbite was observed at
T2 . Overall, there was no statistically significant
difference in overbite between the 2 retainers.
The intraobserver reliability coefficients ranged from
0.96 to 1.0 for linear measurements and from 0.93 to
1.0 for angular measurements, demonstrating that
the method had good reliability.
Conducting this study in a practice setting enabled
the research team to recruit and randomize 397
patients treated by 1 operator over a relatively short
time period (18 months). To date, this is the largest
such clinical trial on the effectiveness of the Hawley
and the VFR.
In this study, the retainer groups matched favorably
for baseline characteristics, and it is therefore likely
that the 2 groups were equally matched and that the
randomization process worked well.
No statistically significant differences were found in
the effectiveness of the Hawley and the VFR to retain
tooth rotations, ICW, and IMW in both arches.
Anecdotal concerns that VFRs lack rigidity and might
not support transarch stability were not upheld in this
However, a statistically significant difference was
found between the retainers in the maintenance of
incisor irregularity, because the Hawley group had
double the change in irregularity over 6 months
compared with the VFR group. These differences
were 0.56 mm in the mandibular arch and 0.25 mm in
the maxillary arch.
Although this difference is unlikely to be clinically
significant in the maxillary arch, it might be
considered clinically significant in the mandibular
arch, particularly if the relapse was located to a single
The results contrast with those of the previous
studies comparing the Hawley and the VFR. The
differences in results from the previous trials might in
part be explained by the much larger sample and its
considerably greater statistical power.
Greater irregularity was seen in the mand.labial
segment compared to the max. labial segment
which follows the trend that irregularity is most
marked in the mandibular labial segment.
This study can perhaps be criticized for using 2
retainer wear regimens. However, the protocols
were chosen to match the wear regimens already
in place at the practice.
An advantage of conducting a trial in this manner
was that the findings should be more
representative of what occurs in everyday clinical
practice, measuring effectiveness rather than
Although the Hawley retainers were worn full time for
a longer period than the VFRs in this study, the latter
were still more effective in maintaining incisor
alignment, particularly in the mandibular arch.
It could perhaps be argued that if relapse of incisor
position is truly to be minimized, then consideration
should be given to the use of a bonded retainer.
However, a recent Cochrane review examining a
number of aspects of retention, including removable
vs fixed retention, found the quality of the studies to
be poor, and there is as yet no reliable evidence that
fixed retainers are more effective than VFRs.
If there is little difference in the clinical effectiveness
between the 2, questions could arise as to whether
any other factors might influence the choice of
retainer, including cost, ease of fabrication, risk of
breakage, patient compliance, and patient preference
The answers to these questions will be addressed in
a parallel study. Each patient should, however, be
assessed individually because Hawley retainers still
offer the additional benefit of allowing superior
vertical settling compared with VFRs.
The results of this study suggest that VFR’s are more
effective than Hawley retainers at holding corrections
in irregularity in the mand. labial segment compared
with the max.labial segment.
With regard to long-term occlusal changes, this
follows the trend that irregularity is most marked in
the maxillary and mandibular labial segments.
This is likely to be clinically significant only in the
mandibular arch if located to a single tooth
displacement. In addition, this trial supports the need
for further research in primary care.
Comparison of occlusal
contacts with use of
Hawley and clear overlay
David A. Covell,
Roger P. Boero,
William S. Lieber.
Angle Orthodontist, 1997,
No. 3, 223 - 230
After orthodontic repositioning of teeth,
retention devices are used to maintain arch
form and minimize the tendency of teeth to
undesirable changes - “relapse,”
desirable changes - “settling.”
With settling, the number of occlusal contacts
increases, improving the fit of the teeth. The
best retention device would be one that allows
settling but prevents relapse.
Commonly prescribed retainers include the
Hawley, wrap, fixed, clear overlay, and tooth
The designs of these retainers differ, particularly
the extent of the retainer-tooth contacts.
Due to these contrasts in retainer design,
characteristic differences in tooth position
following their use would be anticipated
The design of the Hawley retainer has remained
The original method of fabrication used lingual and
palatal plates made of vulcanized rubber that were
accurately adapted to the lingual surfaces of the
teeth, and a labial wire with adjustment loops at
the canines. Today, acrylic has replaced the
The clear overlay retainer, by Ponitz in 1971, is
made of thin (0.025 inch), vacuum-formed
thermoplastic material that adapts closely to the
lingual, facial, and occlusal surfaces of the teeth.
Tibbetts compared Hawley retainers, clear overlay
retainers, and tooth positioners by analyzing dental
casts at debonding and after a 6-month retention
The results showed no statistically significant
differences in Angle’s molar classification, overbite,
over jet, maxillary or mandibular intercanine width,
intermolar width, or arch length.
Aim of this study was to use changes in occlusal
contacts for comparing the retention characteristics of
the Hawley and clear overlay retainers.
Occlusal contacts between the maxillary and
mandibular teeth were statistically compared at
debanding, when retainers were delivered, and after
3 months of retention.
Materials and methods
30 patients from the Orthodontic Clinic at the
University of the Pacific School of Dentistry were
prescribed alternately, Hawley retainers or clear
overlay retainers .
13 patients ( 8 females, 5 males) received maxillary
and mandibular Hawley retainers.
2 patients (both female) received maxillary Hawley
retainers with mandibular fixed lingual retainers.
15 patients (9 females, 6 males) received maxillary
and mandibular clear overlay retainers.
All patients had been in orthodontic treatment for at
least 18 months.
The Hawley retainer sample contained
5 patients - premolar extractions,
8 patients – non extraction,
2 patients - congenitally missing maxillary lateral
mean age - 18 yrs 8 mths (range: 13 yrs 11 mths to
35 yrs 10 mths).
The clear overlay retainer sample included
6 patients - premolar extractions,
8 - non extraction,
1 - missing maxillary lateral incisors.
The mean age was 19 years 6 months (range: 13
years 9 months to 42 years 2 months).
Immediately following removal
of the fixed appliances, models
of the maxillary and
mandibular arches were
the retainers were delivered
1week later and the Hawley
appliances were adjusted so
the labial bow made uniform,
passive contact with each
The mandibular incisors were
in light contact with the acrylic,
lingual to the maxillary
incisors, when the posterior
teeth were in maximum
The clear overlay retainers
were fabricated from 0.025
inch thermoplastic (Tru –
Tain; Rochester, Minn)
vacuum-heat adapted to dry
The facial surfaces of the
retainers were trimmed to
cover the incisal 1/3rd
incisors and to extend 3 mm
beyond the gingival margin
Occlusal coverage extended
distally to cover approx the
mesial half of the maxillary
and mandibular second
Patients receiving Hawley retainers were instructed
to wear them full-time, except during meals.
Those prescribed clear overlay retainers were
instructed to wear their retainers full-time for the first
three days (except during meals), and nightly
Vinyl polysiloxane impression material (Regisil PB;
Caulk– Dentsply, Milford, Del) was used to record the
Patients were seated upright in a dental chair and the
registration material was applied over the occlusal
surfaces of the mandibular teeth. The patient was
told to bite firmly in maximum intercuspation .
A second bite registration was made within 15
minutes to test the reproducibility.
The two bite registrations
were examined on a light box
and contacts appearing as
transparencies in the material,
If a subjective difference in
the pattern of contacts was
observed, another registration
was made. In no case was a
fourth registration needed.
To objectively analyze the bite
registrations, each was
labelled with a randomized
identification code and the
For analysis of the occlusal contacts, individual
registrations accumulated from multiple patients were
selected at random.
Occlusal contacts were evaluated and classified as
either true or near contacts.
True contacts perforated the impression material;
near contacts appeared as thin translucencies and
were counted only if they were 0.20 mm or less as
measured with an Iwanson caliper.
Observing from the maxillary side, the locations of
the contacts were assigned by tooth and then
grouped as either anterior (incisors and canines) or
posterior (premolars, first molars, and second
All registrations were evaluated and measured by the
Error of method
The registrations were made within 30 minutes of
debanding (T1), at the time of retainer delivery (T2),
and three months later (T3).
All registrations were made in the afternoon by the
same clinician. To test the measurement accuracy,
10 bite registrations were selected at random and the
near contacts measured. The same registrations
were remeasured on a different day.
The standard measurement error (Sx) was calculated
using Dahlberg’s formula, Sx = sq.root of D2
where D is the difference between duplicated
measurements and n is the number of double
The standard measurement error (Sx) from repeated
thickness measurements of the same bite registration
was 0.014 mm.
Comparison of measurements between paired
records made on the same day showed an error of
Thus the variation found in repeated registrations
approximated the limits of the measurement
Occlusal contacts at debanding (T1)
a wide variation was seen between individuals of
both retainer groups with regard to the number of
total occlusal contacts.
The Hawley retainers had a mean of 34.3 occlusal
contacts (± 10.45 standard deviation) and the clear
overlay retainers had a mean of 31.8 .
Comparing the Hawley and clear overlay retainer
groups at debanding, there were no statistically
significant differences between the mean number of
total contacts, true contacts, near contacts, or
Occlusal contacts at retainer delivery T2
At the time of retainer delivery, T2, there were no
significant differences between the two retainer
groups in the average number of each classification
of occlusal contacts
Within each retainer group there were no significant
changes between T1 and T2 except for an increase
in posterior true contacts in the Hawley group (T1:
10.9 ± 4.0; T2: 14.1 ± 4.0, P<0.05).
Occlusal contacts after 3 months
At T3 The mean number of posterior true contacts
(Hawley: 16.4; clear overlay: 11.9) and the mean
number of total true contacts (Hawley: 20.2; clear
overlay: 15.1) were significantly different between the
Neither sample showed a significant within–group
change between T2 and T3.
In the Hawley group, between T1 and T3,
significant increases were found in the average
number of total contacts, the mean number of total
true contacts, near contacts, posterior contacts, and
posterior true contacts
The average number of posterior near contacts
approached statistical significance (P=0.06). There
were no differences in anterior contacts.
The clear overlay group displayed no significant
differences in any category between T1 and T3
Comparison of changes between
No significant changes occurred between the two
retainer groups from T1 to T2 in any of the occlusal
From T2 to T3 the number of total contacts and
posterior contacts increased significantly more in the
Hawley group than the clear overlay group
There was a small reduction in the number of true
posterior contacts with the clear overlay retainers.
Most of the decrease occurred at the first molars and
to a lesser extent at the first premolars. The mean
changes in anterior contacts were not significant
From T1 to T3, the occlusal contact changes in the
Hawley group compared with the clear overlay group
showed a similar pattern to that found from T2 to T3
Results from this study show statistically significant
differences in the number of occlusal contacts
between Hawley and clear overlay retainers.
After 3 months of retention with the Hawley retainers,
there was a statistically significant increase in the
number of total contacts.
In contrast, over the same time period with the clear
overlay retainers, there was no change in the number
of occlusal contacts.
We believe these results are reliable due to minimal
number of confounders.
The two samples matched favorably for size, age,
gender, and numbers of cases with teeth extracted or
With regard to the methods, the bite technique for
recording occlusal contacts was highly reproducible.
In addition, the method has been validated in several
Finally, because diurnal variation in occlusal contacts
has been reported, the bite registrations were made
only during the afternoon.
The number of occlusal contacts at debonding in both
retainer samples was similar to that reported by
Radolsky and Sadowsky.
The mean number of total contacts in their study was
36.6 (17.1 near contacts, 19.1 actual contacts), while
this study recorded 34.3 ± 10.5 total contacts (18.7 ±
7.0 near contacts, 15.6 ± 5.8 true contacts) for the
Hawley retainer group and 31.8 ± 11.8 total contacts
(14.0 ± 6.5 near, 17.8 ± 7.5 true) in the clear overlay
The increase in contacts observed in the Hawley
retainer group agrees with the findings of Durbin and
Sadowsky, who compared Hawley retainers with
With the Hawley retainer they found the total number
of contacts increased significantly during the first 3
months of retention, with most of the increase
associated with posterior contacts.
From these results it is apparent that with a Hawley
retainer, the posterior teeth settle after the bands are
Razdolsky and Sadowsky described minimal
migration of the contacts toward the central groove.
No attempt was made in this study to characterize
the location, or alteration of location, of contacts on
From appliance removal to retainer delivery, any
alteration in occlusal contacts in both samples should
Both showed a small increase in the number of
posterior contacts from T1 to T2, with a greater
increase in the Hawley retainer group
Several possibilities can be proposed to account for
the differences between retainer groups from T1 to
First, no attempt was made to adjust the overlay
retainers to optimal occlusal contact.
With up to 0.05 inches of retainer material between
the teeth, initial contact at closure was between the
more posterior teeth.
This contact may have loaded the molars more than
the anterior teeth and have prevented further eruption
or settling, or possibly intruded the molars.
However, the differential occlusal loading when the
retainers were worn at night would have been
counteracted during the day when the retainers were
Alternately, if the mandibular condyles had been
distracted to produce a more uniform distribution of
occlusal contact with the retainers in place, there
should have been an increase in posterior contacts
when the overlay retainers were removed and the
condyle assumed its normal position.
The data shows the opposite occurred. Because the
second molars were only partially covered by the
overlay retainers, they may have erupted more
relative to the more mesial teeth. The second molars
would then become an occlusal stop when the
retainers were removed. However, this explanation is
unlikely because the second molars did not show an
increase in occlusal contacts.
It is most likely that the overlay retainers reverse the
settling occurring between T1 and T2 because the
retainers are fabricated on casts taken at T1.
This hypothesis is consistent with data from the clear
overlay group showing a slight reduction in posterior
contacts from T2 to T3, but no difference in the
number of contacts at T3 compared to T1.
The Hawley retainer, on the other hand, may
encourage posterior tooth eruption. Since the Hawley
retainers were worn full time, the anterior bite plane
and labial wire may have held the anterior teeth,
allowing the posterior teeth to extrude.
This suggestion is supported by data showing no
change in the anterior contacts in the Hawley group,
while the posterior contacts increased.
Assuming some tooth settling had occurred during
the day in the clear overlay retainer patients, it is
likely that had the bite registrations been made in the
morning, differences between the two retainer groups
would have been even greater.
Based on previous studies, additional increases in
occlusal contacts during retention should be
expected over time, particularly as daily retainer wear
In the present study, greater increases would be
anticipated in the clear overlay patient group if
retainer use were to be discontinued.
Areas for future investigation include comparisons of
changes in occlusal contacts with other types of
removable as well as fixed retainers, and long-term
follow-up on changes occurring over an extended
retention period. Ultimately, it would be of interest to
establish whether the differences in occlusal contact
patterns after 3 months retention will result in differing
tendencies toward settling or relapse at extended
retention and post retention intervals.
This study demonstrates that significantly more
occlusal contacts appear during the first 3 months of
retention with use of the Hawley retainer, whereas
little change is found with the clear overlay retainer.
These findings suggest that Hawley retainers should
be prescribed if one of the objectives of retention is to
allow for relative vertical tooth eruption (tooth
settling), particularly of posterior teeth.
Conversely, if the desired occlusion is established
before retainer fabrication, for example with a
positioner, the clear overlay retainers should function
well to maintain the occlusal contact pattern.
Comparison of Essix and
STEVEN J. LINDAUER,
ROBERT C. SHOFF,
JCO 2003 ,VOL 35 ,1998
Essix retainers were introduced in 1993, as an
esthetic, comfortable, and inexpensive alternative
to traditional fixed and removable orthodontic
They are thermoformed from plastic, copolyester
Essix sheet material and trimmed to fit over the
anterior teeth from canine to canine. Patients are
instructed to wear them only at night after a short
period of nearly full-time wear.
Materials & Methods
Patients completing full orthodontic treatment at the
Medical College of Virginia clinic were alternately
assigned to Essix and Hawley retention groups.
Those who had posterior cross bites or anterior open
bites before treatment were excluded from the study.
Twenty-eight patients were assigned to each group
for observation during the first six months of active
The Essix retainers were thermoformed from .030"
sheets according to the manufacturer's instructions.
The patients were instructed to wear their mandibular
retainers full-time and their maxillary retainers half-
time for the first four weeks, and both retainers only
at night thereafter.
Patients were given two retainers per arch, with one
serving as a replacement in case the other was lost
Patients wore the retainers full -time for the first 3
mths and only at night for the next 3 mths.
Occlusal measurements were taken from study casts
made before treatment, after treatment, and after six
months of retention.
Anterior crowding was evaluated with Little's
Irregularity Index, and overbite and over jet were
measured as usual.
The differences between groups were tested with
multivariate analysis of variance.
16 of the 56 patients were eventually eliminated from
7 patients--5 in the Essix group and 2 in the Hawley
group--lost their retainers and did not wear them for
more than a week.
The difference in loss rates was not statistically
significant. Four patients from each group moved out
of the area or did not show up for their 6 month
One Hawley patient requested that a fixed retainer be
placed instead of the removable appliance.
This left 19 patients in the Essix group and 21 in the
The Hawley patients showed slightly more incisor
irregularity in both arches than the Essix group did
but the difference was significant only for the
maxillary arch .
There were no significant differences between
groups in the change in irregularity recorded for
either arch over the six-month retention period.
Likewise, there were no significant differences
between groups in the amount of change in overbite
or over jet .
Two Essix patients and three Hawley patients
showed small decreases in over bite of about .5mm
each. No patient in either group developed anterior
Various clinicians have reported individual cases of
anterior open bite in patients wearing Essix retainers,
probably because of the posterior disclusion caused
by the anterior contact of the Essix material .
In the present study, with patients wearing the
appliances only at night after the first four weeks,
there were no such cases.
The number of patients with minor decreases in
overbite during retention was similar to that of the
It has also been claimed that Essix retainers are
more easily lost than traditional appliances because
they are transparent.
In this study, the number of Essix patients who lost
their retainers was not significantly greater than
One method to reduce the loss of Essix retainer is to
add a color stripe along the lingual edge of the
appliance making it more visible when out of the
Another disadv is that Essix retainers may wear out
and will have to be replaced annually. No remake
was done during this study but several became
perforated or cracked after 6 to 12 mths.
manufacturer claims the durability of the material has
been recently improved.
When Essix retainers are used as recommended,
they do not appear to be any less effective than
Hawley retainers in maintaining orthodontic
The Essix patients in this study did not show any
increased tendency to develop anterior open bites.
Essix retainers were somewhat more likely than
Hawley retainers to be lost, but this finding was not
If patients and clinicians keep in mind that
replacements may be needed as Essix retainers age,
these appliances can serve effectively as alternatives
to traditional Hawley retainers.
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