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Title A retrospective comparison study of the effectiveness of Hawleys vs. Vacuum Formed Retainers demonstrated that both appliances are equally effective.
Clinical Question One hundred seventy consecutive orthodontic patients completing a course of upper and lower fixed appliance therapy using the straight wire appliance at the Orthodontic Department of North Hampshire Hospital, Basingstoke, United Kingdom
Clinical Bottom Line There is no statistical or clinically significant difference in the measured arch width, arch length, or modified Little’s index over a 12-month between Hawleys and vacuum-formed retainers when worn full-time. (See Comments on the CAT below)
Best Evidence (you may view more info by clicking on the PubMed ID link)
PubMed ID Author / Year Patient Group Study type
(level of evidence)
#1) 21261482Barlin/2011.Randomized Control Trial
Key resultsA. There is little difference in intercanine width (CW) using each type of retainer over the four time periods (0, 2, 6 and 12 months). Using the Kruskal-Wallis one way analysis of variance (Upper CW, P = .98; Lower CW, P=.74) for each arch, it would appear there is no statistically significant effect of retainer type. B. For the intermolar widths (MW), the Kruskal-Wallis one way analysis of variance once again showed that there appears to be no significant difference between the Hawley and vacuum-formed retainers (UMW, P = .78; LMW, P = .99) over the four time periods that were studied. C. Similarly with arch length, there was no statistically significant difference between the Hawley and vacuum-formed retainers with time in either the upper (P = 1.00) or lower (P = .31) arches. When considering the modified Little’s index, there was again no difference between the Hawley and vacuum-formed retainers in either the upper (P = .99) or the lower arches (P = .77) during this time.
Evidence Search hawley[All Fields] AND ("Vet Surg"[Journal] OR "vs"[All Fields]) AND vacuum-formed[All Fields] AND retainer[All Fields]
Comments on
The Evidence
The subjects were selected randomly and the study used a large sample size, which may not be clinically meaningful since it may show small differences between the two groups. The exclusion criteria were the following: 1. cases requiring bonded retainers, 2. cases requiring adjunctive procedures (eg, pericision or interdental stripping), and 3. any case requiring orthognathic surgery. . Of the 170 cases originally identified, only 82 complete record sets were available 12 months after debond: 42 in the Hawley retainer group, and 40 in the vacuum-formed retainer group. This was mainly due to nonattendance at review appointments and less often due to patients losing or breaking retainers that had not immediately been repaired/replaced. The retainer type for each case was randomly allocated by the technician using a single throw of a dice, thus decreasing bias, yet not eliminating it since the retainer being used was apparent. All of the laboratory work was carried out in one laboratory by the same technician. The design and fabrication were maintained the same for each appliance. Although the study is described as double-blind, this may not be correct as patients would be aware of what type of retainer they were using.
Applicability The findings of this study regarding retention are not only statistically significant but also clinically significant. The results show that both Hawley and vacuum-formed retainers are effective, thus other factors may be more important when deciding on the most appropriate form of retainer to be used following a course of orthodontic treatment.
Specialty/Discipline (General Dentistry) (Orthodontics) (Pediatric Dentistry)
Keywords Hawley, Vacuum-formed retainers, Retention
ID# 2329
Date of submission: 08/17/2012spacer
E-mail pabonc@uthscsa.com
Author Alessandra Chacon
Co-author(s) e-mail
Faculty mentor/Co-author Peter T. Gakunga, BDS, MS, PhD
Faculty mentor/Co-author e-mail gakunga@uthscsa.edu
Basic Science Rationale
(Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?)
post a rationale
by Alessandra M. Chacon Pabon (San Antonio, Texas) on 09/20/2012
Retention is holding teeth in a particular position. Relapse occurs when teeth slide back towards their original site. Biologically, retention is needed for three reasons: 1) the periodontal tissue requires time to reorganize and accommodate new tooth positioning after tooth movement; 2) if teeth are in an unstable position, pressure from soft tissue may cause tendency; 3) continued growth creates further changes. The main concern for relapse is the elastic recoil of gingival fibers. Furthermore, collagenous fibers remodel in 4-6 months compared to elastic fibers, which may take up to a year. This study showed that both retainers met the requirement for prolonged retention according to these biological principles. Contemporary Orthodontics. William Proffit.Editorial: Elsevier 5th Edition. 2012.
Comments on the CAT
post a comment
by Alessandra M. Chacon (San Antonio, Texas) on 09/20/2012
In this study the use of Hawleys and Vaccum Formed Retainers showed to have similar effectiveness for long-term transverse dimension and arch length retention. However, it would be helpful to also evaluate the retention effectiveness in an antero-posterior and vertical dimension. Also, this study is mostly based on transverse growth, which is completed first and is less of a problem clinically than changes from late anteroposterior and vertical growth.

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