A century of Hawley retainer

Abstract

Introduction: The use of Hawley retainer has crossed a century with same basic principles incorporated one hundred years back accompanying little improvisation in material. The innovation of Hawley retainer was a simple orthodontic appliance yet innovative device of retention of that period of time. The primitive appliance is still continuing over a century; is an achievement in itself. This clearly reflects the intense invention of an inquisitive mind of its creator, Dr. Charles Augustus Hawley.

The present article reviews the chronological events of the life of Dr. Charles Augustus Hawley and his contributions to the profession. Special emphasis has been laid on the evolution, development and clinical aspects of Hawley retainer
commemorating its completion of a century.

KEYWORDS: Hawley retainer, Orthodontic Appliance, Retention

Full text

Orthodontic Journal of Nepal, Vol. 11 No. 2 July - December 2021
80
Dr. Samikshya Paudel1; Dr. Rabindra Man Shrestha2; Dr. Sristi Napit3
1Post- Graduate Resident, 2Professor
Department of Orthodontics, Kantipur Dental College- Kathmandu University, Kathmandu, Nepal
3Dental Surgeon, Lotus Dental Clinic, Pokhara, Nepal
Corresponding author: Dr. Samikshya Paudel; Email: paudelkeshari@gmail.com
Introduction: The use of Hawley retainer has crossed a century with same basic principles incorporated one hundred
years back accompanying little improvisation in material. The innovation of Hawley retainer was a simple orthodontic
appliance yet innovative device of retention of that period of time. The primitive appliance is still continuing over a
century; is an achievement in itself. This clearly reects the intense invention of an inquisitive mind of its creator, Dr.
Charles Augustus Hawley.
The present article reviews the chronological events of the life of Dr. Charles Augustus Hawley and his contributions to
the profession. Special emphasis has been laid on the evolution, development and clinical aspects of Hawley retainer
commemorating its completion of a century.
KEYWORDS: Hawley retainer, Orthodontic Appliance, Retention.
INTRODUCTION
About Dr. Charles Augustus Hawley
Dr. Charles Augustus Hawley (Figure 1), was born in
Avery, Ohio, USA on March 13, 1861 as a son of Noah
M and Abigail (Mowry) Hawley.1,2 He attended public
schools of Columbus, Ohio and the Ohio State University,
and graduated from the University of Michigan Dental
School in 1893.2 After that, he worked at Ann Arbor in the
Department of Operative Dentistry, wherein he became
the rst person to use nitrous oxide as an anesthetic
agent for the removal of teeth.3 Later, he joined Edward
H. Angle School of Orthodontia and graduated in 1905.3
After graduation, Hawley moved to Washington
DC in 1908 and worked there as the rst certied
orthodontist.4 Also, he upgraded his studies on anatomy
and physiology of dentition at the National History
Museum at Washington.5
Coupled with great mechanical dexterity and practical
mind, Hawley invented new instruments and methods
for carrying out his treatment strategies. According
to Hoffman, he was one of the rst few orthodontists
who recognized an association between unpleasing
facial prole and protrusive dentition.3 He has given
invaluable contributions to the profession of dentistry
and orthodontic specialty; such as: gold annealer,
different orthodontic instruments, geometrical charts
for predetermining the dental arch and Hawley retainer.1,6
Besides, Hawley had published outstanding literature
in the eld of dentistry and orthodontic specialty in his
lifetime,2 which are enlisted below in Table 1.
A century of Hawley retainer
ABSTRACT
Review Article
Figure 1: Dr. Charles Augustus Hawley (Redrawn from:
Wahl N. Orthodontics in 3 millennia)1

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81
Paudel S, Shrestha R.M, Napit S : A century of Hawley retainer
Year Literature topics
1903 The cohesion of gold
1904 Relief from pain in Orthodontia
1904 The determination of the normal arch and
its application to Orthodontia
1906 An accurate method in Orthodontia
1910 The function of the teeth in the development
of the face
1919 A removable retainer
1920 The problem of retention
1921 The postoperative treatment of Class II
1923 The principles and art of retention
1924 The use of the round wire in bracket bands
preliminary to adjusting the ribbon arch
1925 Orthodontic Photography
1925 The value of gnathostatic models
1929 Treatment of Class II or disto-occlusion
Table 1: Topics of literature published by Dr. Charles
Augustus Hawley
(Source: FTM. In memorium: Hawley CA. Int J Orthod Dent
Children. 1929)2
Hawley was actively involved in various scholarly
groups of the specialty. In 1908, he became President
of the American Society of Orthodontists (presently,
American Association of Orthodontists). He also
served as the President of District of Columbia Dental
Society (1920) and a Fellow of the American College
of Dentists. Later, he was President of the New York
Society of Orthodontists (1929) and President-elect of
the Southern Society of Orthodontists (1929).3
At the age of sixty-eight on 22nd July 1929, he died
at Gareld Hospital, Washington DC, following the
complications of an operation, leaving behind his wife
Evelyn Frank Hawley, a step-son Archibald Donovan
Hawley and a daughter Carlotta Augusta Hawley.1-3 His
daughter followed his footsteps after his death, became
an ABO-certied orthodontist and worked as the rst
woman secretary of Washington-Baltimore Society of
Orthodontics.1,7,8
From his memoirs, one can nd that he was a far-
sighted orthodontist and a simple man who loved duck
hunting, playing golf and photography.2 He has left us
with a simple innovative option for retention, the Hawley
retainer, that is serving us beyond a century with the
same principle and eciency.
The “Hawley Removable Retainer”
In 1906, Hawley visited the oce of Dr. R.D. McBride
where he encountered a retaining device (Figure 2), that
was useful to retain the corrected position of rotated
teeth. It was ecient, but it had some repulsive features
that needed alterations. The at pieces between
rst molar and second premolar were a site for food
lodgments demanding the removal of retainer for few
days.6 The labial bar was too heavy without supports
and the bite planes for holding it mesiodistally were
interfering the stability of appliance.9
Figure 2: Removable retainer made by Dr. R.D. McBride
(Redrawn from: Hawley CA. A removable retainer).6
Inspired from the retaining device, Hawley developed a
new appliance and started using it. He discussed about
the retainer in the meeting of the American Society of
Orthodontists on July 1918 at Chicago. After one year,
on 1st June 1919, he introduced this appliance (Figure
3 and 4), in his paper as “A removable retainer”, which
was made from four components, namely; a at labial
wire from cuspid to cuspid of 0.022 x 0.036, 19-gauge
gold wire formed into loops, a bicuspid clasp extending
backward from the wire, all of which get support from
palatal/lingual plate made from vulcanite.1 In lower
arch, a wire spur extends into occlusal surface between
lingual cusps to prevent the plate from downward
displacement during mastication.
Figure 3: Removable Hawley retainer: A. In upper arch,
B. In lower arch (Redrawn from: Hawley CA. A removable
retainer).6
In 1922-1923, Hawley presented a paper titled “The

Orthodontic Journal of Nepal, Vol. 11 No. 2 July - December 2021
82
principle and art of retention” in European Orthodontic
Society (as cited in the Transactions of the European
Orthodontic Society), wherein he perceived mixed
comments about Hawley retainer.9 He also introduced
a modied bicuspid clasp (Figure 5), with a spring
or elastic adjustment loop above the attachment to
the main wire such that it can be raised or lowered.
An important remark was from W.S. Davenport, who
mentioned that Hawley retainer was a simple device
made from the combination of old features of clasp
and plate with equal consideration on fundamental
principles of retention. Further, he stated that it
excluded the shortcomings of retaining device made by
Dr. Mcbride and Kingsley Appliance.9
Figure 4: Removable Hawley retainer with modied
bicuspid clasp (Redrawn from: Hawley CA. The principle
and art of retention).9
With time, Hawley retainer gained popularity among
orthodontists and had undergone series of modications
in its components. Ernest Bach (1927),10 Holt (1928),11
Hutchinson (1931),12 Reid (1935),13 Anderson (1936),14
McIntosh (1940),15 Sved (1944)16 presented modied
versions of Hawley retainer to improve clinical failures.
After the development of acrylic resins in dentistry,
Stevenson improvised Hawley retainer (1941), using
acrylic instead of vulcanite, thus making the fabrication
simpler and more economic.17 With the introduction
of modied arrowhead clasp (Figure 6 and 7) and its
modications by Phillip Adams (1953); the Adams
clasp gained popularity in removable appliances.18 It
ensured retention in clinical situations, which otherwise
was dicult with removable appliances.19 Since then,
Adams clasp has been incorporated in Hawley retainer.
Figure 5: Modied arrowhead clasp. A: Front view, B: Lateral
view (Redrawn from: Adams CP. The retention of removable
appliances with the modied arrowhead clasp).18
Ideal requirements of Hawley retainer
1. Hawley retainer should maintain the corrected functional
occlusion,20 periodontal health21-24 and muscular
balance,19 achieved by the orthodontic treatment.
2. It should hold the expansion and form of the arch.6
3. The appliance should prevent the rotation of teeth
after treatment.6
4. The overbite must be established.6
5. The retainer should be biocompatible, economical
and easy to clean with its components resistant to
tarnish and corrosion.
Fabrication
Hawley retainer is fabricated with acrylic resin that
covers the palate, a stainless-steel bow contouring the
labial aspect of maxillary anterior teeth, with U loops
extending from distal surface of canines, and palatally
embedding in the acrylic resin.25 Besides, it incorporates
clasps like Adams clasp, circumferential clasp or ball-
end clasp, for retention.
The acrylic plate is processed with heat-cure or chemical
cure resin. The thickness of plate is made of adequate bulk
of 2-3 mm to retain the wire components, with maximal
attention to the patient comfort and adaptation into
embrasures.26 Its distal margin terminates distal to rst
molars, and is thinned to merge with the palatal mucosa.
The wire component includes stainless steel wire of 0.7
mm for Adams clasp, 0.9 mm for circumferential clasp
or ball end clasp and 0.7 mm for labial bow.27 The U
loop is fabricated 2-3 mm above the gingival margin of
canine and free from gingival contact to avoid injury or
pressure effect in gingiva. The labial bow is kept passive
and in gentle contacts with labial surface of the teeth.26
Modications
Hawley retainer can be modied according to the clinical
requirement for retention.6,28 The selection of clasp
design is important as clasp crossing the occlusal table
can disrupt the corrected tooth relationships.23 Some
modications are listed in Table 2.
Paudel S, Shrestha R.M, Napit S : A century of Hawley retainer
Figure 5 A
Figure 5 B

Orthodontic Journal of Nepal, Vol. 11 No. 2 July - December 2021
83
Paudel S, Shrestha R.M, Napit S : A century of Hawley retainer
Modication Uses
Hawley with anterior bite plane Anterior bite plane can be fabricated in its palatal portion to control bite depth,
in corrected deep bite cases.6
Hawley with bow soldered to
buccal section of Adams clasp
In tight contacts, there can be wedging effect due to cross-over wire. To
overcome this, labial bow can be soldered to the bridge of Adams clasp which
helps to maintain the closed extraction site.28
Hawley with long labial bow The drawback of space opening between canine and premolar, with standard
Hawley retainer can be prevented with the use of labial bow extending from
rst premolar of one side to another side.28
Hawley with C-clasp on second
molars distally
When there is chance of occlusal interference over posterior occlusion, c-clasp
with distally approaching ring on second molars, can be fabricated.23
Hawley with tted labial bow Fitted labial bow anteriorly and the base plate posteriorly is used for better
incisors control.
Hawley with nger/Z-spring The incorporation of nger/ Z-springs makes it active appliance used to
achieve tipping movement.
Table 2: Modications of Hawley retainers
Recent Advances
Hawley with clear outer bow: The aesthetic variant
of Hawley retainer was presented by Needham et al
in 2015. The appliance was made aesthetic with the
incorporation of clear outer bow made of food-grade
polyethylene terephthalate of 2.75 mm width, joined
at a Coiltight-Joint® to the Adams clasp. It adapts
more accurately to the contour of all anterior teeth
while posteriorly the wire segment provides retentive
component.29
Advantages of Hawley Retainer
1. The armamentarium required for fabrication
of Hawley retainer are easily available and
sophisticated laboratory set up are not necessary.
2. Being a removable retainer, it can be removed
for cleaning, brushing and sometimes, in social
occasions.
3. It allows posterior settling and improvement in
occlusal contacts.30
4. It can be adjusted according to clinical condition
for nished treatments.
5. It is a durable retainer and easily repairable if the
components are broken.
6. For a larger period of time, patient compliance is
better with Hawley retainer.31
Disadvantages
1. Success of the treatment depends upon patient’s
compliance.
2. The display of labial wire is unaesthetic, which
affects the patient’s satisfaction.
3. There is a higher evidence of breakage of this
retainer than its loss.32
4. It may not hold the corrected labial segments in
upper and lower arch for a larger period of time due
to insucient contact surfaces leading to relapse
and incisor crowding.33,34
5. In the rst few weeks, patients experience problem
in speech articulations.32,35-37
Duration of wear and retention protocol
For the rst 2-6 months, Hawley had advised the
continuous use of the retainer with removal only
during cleaning. After six months, night time wear is
recommended for about a year followed by several days
or week of left out periods and again usage at nights to
ensure that teeth are not changing their positions.6
However, a comprehensive research conducted at the
University of Washington, highlighted that retention for
life is the only way to ensure satisfactory alignment
of the teeth as orthodontic treatment were mostly
unstable over a long time.23
Many studies have been performed by different
authors regarding the duration of wear,23,38 material
biocompatibility,39 monitoring of its wear by the
orthodontist,40 hygiene,41,42 durability,32,43 function,30,34-36,44
and patient satisfaction.31 Also, there are comparison
studies between Hawley retainers (HRs) and vacuum
formed retainers (VFRs) or positioners highlighting its
merits and demerits.30-36,39,41-44 Some of the studies are
tabulated in Table 3

Orthodontic Journal of Nepal, Vol. 11 No. 2 July - December 2021
84
Author Inference
Sauget (1997)30 During rst three months of retention, Hawley retainer allowed relative settling of
posterior teeth while clear overlay retainers maintained the corrected tooth position.
Zhang & Wang (2003)41 Positioner had more periodontal index grading than HRs necessitating proper oral
health care to preserve periodontal tissues.
Hichens (2007)32 HRs had more breakages, was costlier and associated with less patient satisfaction
than VFRs.
Rowland (2007)33 HRs were found to have clinically less signicant retention of the mandibular labial
segment than VFRs.
Rinchuse (2007)23 Life-time of retainer wear, whether removable or xed, was a suitable option for
orthodontic treatment stability.
Valiathan & Hughes (2010)47 In maxilla Hawley retainers; and in mandible xed lingual retainers are most
commonly used.
Shawesh (2010)38 Full or part-time wear regimen of HRs, both was equally effective during one-year
period. Clinically, only night time wear for one year can be recommended to the
patients.
Barlin (2011)34 Relapse is not affected by the choice of retainer as it occurred in both groups of HRs
and VFRs group
Sun (2011)43 Hawley retainer and VFRs both had undergone fractures but the site of fracture was
different. The clinician should avoid increase in buccal root torque and reinforce the
retainer base plates to prevent it.
Pratt (2011)31 For periods longer than two years after debonding, patient compliance was greater
with Hawley retainers.
Demir (2012)44 Over two-year period, retention characteristics of VFRs and HRs were similar as
irregularity index increased in both groups.
Hyun (2015)40 The compliance of patient increased clinically, when patient was aware of being
monitored over the use of Hawley retainer.
Raghavan (2017)39 Hawley retainer fabricated by heat-cure acrylic resin was a favorable choice over
cold-cure acrylic and VFRs in terms of bis-phenol A release.
Wan (2017)35 Changes in articulation were more obvious in the HR group than VFRs group.
Atik (2017)36 Articulation in consonant-vowel combination were affected by Hawley retainers
more than Essix retainers.
Manzon (2018)42 Oral hygiene and retainer hygiene were better with Hawley retainers while Essix
retainers were more comfortable and esthetic.
DISCUSSION
The retention of corrected occlusion is the most
important step after orthodontic treatment. As such,
incorporation of basic principles in a retaining device
to avoid rotation, tipping, and maintenance of bite
depth, is a must. The innovation of Hawley retainer by
Dr. Charles Hawley, has been an impeccable addition in
this retention phase.
Hawley retainers (HRs) have crossed hundred years
of its fabrication and still, these are the most used
removable appliance for maxillary retention.23,24 These
are available in majority of clinic with least laboratory
instruments and costs. Having a lot of modications,
it covers a range of clinical conditions from occlusal
settling to anterior deep bite correction. A traditional
Hawley retainer allows settling and thus an improvement
in posterior occlusal contacts.30
In our clinical context, Hawley retainer is an appropriate
Table 3: Studies related to Hawley retainers
Paudel S, Shrestha R.M, Napit S : A century of Hawley retainer

Orthodontic Journal of Nepal, Vol. 11 No. 2 July - December 2021 85
Paudel S, Shrestha R.M, Napit S : A century of Hawley retainer
choice when durability is a question. Some authors
have inferred that Hawley retainers lasts longer than 15
years.23 However, a study by Hichens et al. found that
there are greater breakages in HRs group than its loss.32
For most patients, rst few weeks of use of this
retainer is a demanding process with diculties in
speech articulations and chewing.32,35,36 According to a
systematic review by Chen J et al., HRs had often caused
speech distortion of /s/, /z/, /t/, /d/, /i/, /ӡ/, /θ/, and /∫/
sounds, and the impairment could last up to 3 months.37
There is an esthetic concern for the appliance, due
to metallic display of wire, creating an unpleasing
experience among patients. Hawley retainer with clear
outer bow (aesthetic Clearbow®) can be used in such
circumstances.28,29 It also provides benets of being
free from bisphenol-A.
Bisphenol-A (BPA) is a synthetic compound enlisted by
WHO (2011), as an endocrine disruptive chemical.39 A
study by Raghavan et al concluded that Vacuum formed
retainers (VFRs) showed greatest release of BPA
followed by chemically cured HRs and least with HRs
processed by heat cure.39 Thus, Hawley retainer (either
with Clearbow® or heat-cured resin), is a biocompatible
option among the retainers.
Being a removable appliance, it can be cleaned
thoroughly by the patient. Comparison of these
retainers with thermoplastic resins concluded that HRs
were more hygienic with less accumulation of plaque in
the teeth or retainer.41
When retainer is prescribed for a short period of six
months, VFRs have been found to be cost-effective with
better compliance but for a duration of more than two
years, Hawley retainers were more effective.31 Similarly,
in developing countries, HRs are considered a cheaper
alternative over clear thermoplastic retainers. However,
systematic reviews on comparison of these retainers
could not draw a high level of evidence to support
the benets of one above the other in terms of cost-
effectiveness and patient satisfaction.26,45,46
Relapse was evident over two years in the anterior
region of mandibular teeth in majority of retainers.44
Though irregularity index decreased in VFRs groups, it
could not be concluded that HRs are less effective than
VFRs in terms of irregularity of incisors and intercanine
and intermolar widths.44
In terms of appliance wear, a survey-based study in
US reported that eighty-one per cent of orthodontists
prescribed a full-time wear period between 3-9 months
for Hawley retainers compared with clear thermoplastic
retainers (less than 3 months).47 Reitan’s concept of
rearrangement of gingival and periodontal bers after 8
months might explain the rationale behind the full-time
wear for 3-9 months.48 However, there is unavailability
of sucient evidence to favor a particular regimen.49
In majority of clinical scenarios, patients are reviewed
for over two years after the end of active orthodontic
treatment.50 Thus, the retention protocol is largely
determined by orthodontist’s experience, patient’s
expectations, and clinical circumstances.
There are certain limitations to this study. It is not
a systematic research and do not follow a certain
protocol. Thus, it lacks the profundity of comprehensive
knowledge beyond the topic of interest and may
be subjected to bias during selection of literature.
However, it provides an overview about the appliance,
its associated history and its use through the century.
Conflict of Interest
None.
Acknowledgement
The gures were charcoal sketches redrawn by coauthor
Dr. Sristi Napit.
OJN

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List of gures
Figure 1: Dr. Charles Augustus Hawley (Redrawn from: Wahl N. Orthodontics in 3 millennia. Chapter 5: the American
Board of Orthodontics, Albert Ketcham, and early 20th-century appliances).1
Figure 2: Removable retainer made by Dr. R.D. McBride (Redrawn from: Hawley CA. A removable retainer).6
Figure 3: Removable Hawley retainer A. Upper arch, B. Lower arch (Redrawn from: Hawley CA. A removable retainer).6
Figure 4: Removable Hawley retainer with modied bicuspid clasp (Redrawn from: Hawley CA. The principle and art
of retention).9
Figure 5: Modied arrowhead clasp; A. Front view, B. Lateral view (Redrawn from: Adams CP. The retention of
removable appliances with the modied arrowhead clasp).18