Comparison of Relapse Arch Width in Modified Vacuum Formed Retainers Covering the Palate Versus Hawley Retainer: A Prospective Randomized Control Trial
Phase: NA
Conditions: Orthodontic Retainers, Clinical Trial
Sponsor: National University of Malaysia

 
 
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RESEARCH PROPOSAL 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Comparison of relapse arch width in modified vacuum formed retainers covering the 
palate versus Hawley retainer – A prospective randomized control trial 
 
Grant code: GGPM-2018-049 
Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Project Leader 
Dr. Asma binti Ashari (K019831) 
Centre of Family Oral Health, Faculty of Dentistry, UKM, Malaysia 
 
REC UKM: Medical Research and Ethics Committee HUKM, Jalan Yaacob Latif, Bandar Tun Razak, 56000 Batu 9 Cheras, Wilayah 
Persekutuan Kuala Lumpur 
REC KKM: Medical Research and Ethics Committee, National Institutes of Health, Ministry of Health Malaysia, Block A, Level 2, No 1, Jalan 
Setia Murni U13/52, Seksyen U13, Setia Alam, 40170, Shah Alam, Selangor 
 
 

 
 
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Table of Contents 
 
 
 
1.0 EXECUTIVE SUMMARY 
3 
2.0 INTRODUCTION 
4 
3.0 HYPOTHESIS 
5 
4.0 AIMS AND OBJECTIVES 
5 
5.0 METHODOLOGY  
5 
5.1 Sampling 
5 
5.2 Study Design 
6 
5.3 Ethics 
8 
5.4 Data Management and Analysis 
8 
 
6.0 MILESTONES 
10 
7.0 BUDGET 
11 
8.0 REFERENCES 
12 
 
 
 
 
 

 
 
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1.0 
EXECUTIVE SUMMARY 
 
 
Relapse is inevitable in orthodontic treatment. Teeth will want to return to their 
original position after fixed appliances are removed. Regardless with or without fixed 
appliances, changes and physiological relapse will still occur due to time and age changes. 
This is why retention is a crucial part in orthodontic treatment, where it would aim to 
maintain the corrections achieved after orthodontic treatment. 
 
Literature regarding retainers is quite substantial, where a recent Cochrane review was 
published comparing the different types of retainers. However, evidence is lacking in terms 
of comparison of arch width relapse between modified vacuum formed retainers and 
Hawley retainers specifically in expansion cases.  
 
This study aims to compare the relapse in arch width in expansion cases with modified 
vacuum formed retainers with palatal coverage versus Hawley type retainers in Unit 
Ortodontik Universiti Kebangsaan Malaysia (UKM), Klinik Pakar Ortodontik Klinik Kesihatan 
Bandar Botanik and Unit Pakar Ortodontik Klinik Pergigian Sungai Chua patients. Although 
other types of modified vacuum formed retainers effective for maintaining palatal 
expansion have been described, these retainers require a wire outlining the 
Cementoenamel junction of the teeth palatally. This technique requires experience of the 
technician, is at a higher cost and requires more lab time. The modified retainer that we 
described in this study would be as efficient and as quick as the normal vacuum formed 
retainers, which would usually take a couple of hours to make (same day or next day fit). 
The present practice at all 3 locations constructs Hawley and normal VFR retainers for all 
orthodontic patients. There are technicians and laboratory facilities to construct normal VFR 
as well as Hawley retainer. The only difference between modified and normal vacuum 
formed retainer is the outline of the retainers where the technician would trim the retainer, 
where it would cover the hard palate. Therefore it is only the location of trimming that is 
different using the same special trimming appliances for normal VFRs. 
 
A number of subjects who fulfil the criteria will be invited to participate in this study. The 
study will involve arch width analysis using study models pre, post-debond, 3 months review 
post-debond, 6 months review post-debond and 12 months review post-debond. All data 
will be analyses using Statistical Package for Social Sciences (SPSS).  The arch width of 
subjects post-fixed appliances will be compared. Most studies compare the arch width, as 
well as lower incisor irregularity in evaluating relapse in different groups of retainers. 
However, there are currently no randomized control trials comparing expansion cases of 
Hawley vs vacuum formed retainers, hence why this study will be conducted. 
 
We expect to see no difference between the modified vacuum formed retainer and Hawley 
retainer in terms of maintaining arch expansion post-orthodontic treatment. This would 
therefore mean that there would be a simpler method and would be a suitable more cost-
effective alternative as compared to constructing Hawley retainers or adding a palatal wire 
on the vacuum formed retainers. 
 
  

 
 
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2.0 
INTRODUCTION 
 
Relapse is an unfortunate event post-orthodontic treatment. Around 70% of patients post-
orthodontic treatment are subjected to relapse (1,2). Patients usually talk about retention in 
a negative light in social media(3), where the main themes expressed included compliance, 
impact, maintenance, patient-clinician relationship, and positive and negative feelings. It is 
therefore important to ensure that the retention regime is effective and convenient for the 
patient.  
 
Arch expansion is a common modality of treatment in correcting posterior 
crossbites. Methods of expansion often used in removable/fixed appliances would include 
archwire expansion, quadhelix, rapid maxillary expansion or removable appliances with a 
midline screw. Surgical methods have also been described (SARPE- Surgical Assisted Rapid 
Palatal Expansion) for severe cases. Expansion of the arches is considered very unstable and 
prone to 40% of relapse, regardless of any type of expansion, and this is mostly due to post-
treatment growth pattern of the patient (4,5). 
 
There are various methods of retention, and a recent Cochrane review (6) has produced a 
very good summary and update of all the different types of retainers. In terms of expansion, 
a Hawley type retainer was indicated to be the best type of retainer to maintain expansion. 
In terms of material, acrylic is more durable than vacuum formed polyeurethane material, 
which explains the property. There is limited evidence comparing the relapse in expansion 
between these two methods. This is mainly due to the fact that there is acrylic coverage of 
the palatal surfaces, as compared with a vacuum formed retainer where the coverage only 
extends a few millimetres beyond the cement-enamel junction of the palatal surfaces of the 
teeth. A modified vacuum formed retainer was described where the vacuum formed 
retainer was extended for palatal coverage, which in theory could maintain expansion 
better. Different versions of this modified retainer were described (7). The only difference in 
constructing the retainers would be the outline where the technician would trim the 
retainer, where it would cover the hard palate. The use of this modified vacuum formed 
retainer was shown to be as effective as other methods of retention such as fixed bonded 
retainer (8)(9). The systematic review by Littlewood also showed that the normal vacuum 
formed retainer to be as effective as other retainers in terms of maintaining the inter-arch 
width (6). However, the cases selected were normal Class 1 cases with normal antero-
posterior and transverse skeletal dimensions, where our study would focus on expansion 
cases as the main subjects. Even with the robust evidence showing the strength of the 
vacuum formed retainer, clinicians in general still use the Hawley retainer in expansion 
cases with no existing clinical trial evaluating its effectiveness. However in the United 
Kingdom, there have been noted usage of this modified vacuum formed retainer in 
expansion cases, especially in emergency situations where retainers need to be made 
quickly. 
 
Therefore, this study will focus on the relapse of arch width in two types of retention 
regimes, which are modified vacuum formed retainers and Hawley type retainers in patients 
after fixed appliance treatment. This will subsequently be of valuable information for 
clinicians in choosing the appropriate type of retainers after removal of their fixed 
appliances.  This is because the modified vacuum formed retainers will be significantly 

 
 
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cheaper, quicker and easier to fabricate. There is a small risk of relapse using the modified 
vacuum formed retainers in expansion cases, however as mentioned earlier a lot of studies 
show good maintenance of arch width in normal cases (6)(8)(9). If relapse does occur, we 
anticipate that it will be minimal and a new retainer or retreatment can commence to easily 
rectify the situation as the patients are reviewed every 3 months. Other advantage is that 
most patients would prefer the appearance of vacuum formed retainers and superiority in 
terms of incisor alignment (6)(10). Literature showed that 40%-60% of allergic reaction was 
caused by formaldehyde (11). Formaldehyde may be released from methacrylate-based 
dental materials, such as composites and denture bases (12). An vitro study reported that 
there was minimal leaching of formaldehyde from thermoplastic materials (e.g. VFRs) while 
it was found higher leaching from poly-methyl methacrylate (PMMA) based orthodontic 
materials of the powder and liquid type (e.g. Hawley retainers) (13). Up to date, there is no 
reported case of sensitivity and contact allergy to VFRs while there was reported case of oral 
lesion in patient with Hawley retainer (14). 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Hawley retainer 
Characteristics 
 
Benefits 
Risks 
Clasps 
and 
wires 
anchored in a relatively 
thick plastic body 
 
Personal opinion: suggested retainer 
to maintain expansion (Blake & Garvey 
1998) compared with normal VFR (not 
modified) 
 
More likely to break (Hichens et al. 
2007) 
 
Steel wire run across 
front teeth 
More 
durable 
from 
patients’ 
perception (Saleh et al. 2017) 
  
Higher cost (Hichens et al. 2007) 
 
 
Require greater man power (Hichens et 
al. 2007) 
 
 
 
More difficult to fabricate (Saleh et al. 
2017) 
 
 
 
Less aesthetic (Saleh et al. 2017) 
  
 
 
Heavier (Saleh et al. 2017) 

 
 
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Blake, M. & Garvey, M. T. 1998. Rationale for retention following orthodontic treatment. Journal of the Canadian Dental 
Association 64(9): 640–643. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/9812432 
Hichens, L., Rowland, H., Williams, A., Hollinghurst, S., Ewings, P., Clark, S., Ireland, A., et al. 2007. Cost-effectiveness and 
patient satisfaction: Hawley and vacuum-formed retainers. The European Journal of Orthodontics 29(4): 372–378. 
doi:10.1093/ejo/cjm039 
Saleh, M., Hajeer, M. Y. & Muessig, D. 2017. Acceptability comparison between Hawley retainers and vacuum-formed 
retainers in orthodontic adult patients: A single-centre, randomized controlled trial. European Journal of Orthodontics 
39(4): 453–461. doi:10.1093/ejo/cjx024 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Normal & Modified vacuum-formed retainer 
Characteristics 
 
Benefits 
Risks 
Made up of thin and 
strong 
copolyester 
plastic sheets 
 
Low cost (Hichens et al. 2007) 
 
 
Less durable from patients’ perception 
(Saleh et al. 2017) – Normal VFRs 
Transparent 
Easy to fabricate (Hichens et al. 2007)  
 
 
 
Require less man power (Hichens et al. 
2007) 
 
 
 
More aesthetic (Saleh et al. 2017) 
 
 
 
 
Lighter (Saleh et al. 2017) 
 
 
 
Less likely to break (Hichens et al. 
2007) 
 

 
 
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3.0 
HYPOTHESIS 
 
There is a difference in the degree of relapse in terms of relapse of arch expansion between 
Modified Vacuum formed retainers and Hawley retainers. 
 
NULL HYPOTHESIS 
 
There is no difference in the degree of relapse in terms of arch expansion between Modified 
Vacuum formed retainers and Hawley retainers.  
 
 
 
4.0 
AIMS AND OBJECTIVES 
 
To measure the effectiveness of two different retainers in maintaining arch width post 
orthodontic treatment:  
i) 
Modified vacuum formed retainers 
ii) 
Hawley retainers 
Measurement in terms of: 
i) 
Canine arch width 
ii) 
Premolar arch width 
iii) 
Molar arch width 
 
 
5.0 
METHODOLOGY 
 
5.1 Participants Sampling 
 
The sample will be selected from patients attending for orthodontic debond appointments 
at the Orthodontic Unit of Universiti Kebangsaan Malaysia (UKM), Klinik Pakar Ortodontik 
Klinik Kesihatan Bandar Botanik and Unit Pakar Ortodontik Klinik Pergigian Sungai Chua 
patients. The present practice at all 3 locations constructs Hawley and normal VFR retainers 
for all orthodontic patients. There are technicians and laboratory facilities to construct 
normal VFR as well as Hawley retainer. The only difference between modified and normal 
vacuum formed retainer is the outline of the retainers where the technician would trim the 
retainer, where it would cover the hard palate. Therefore it is only the location of trimming 
that is different using the same special trimming appliances for normal VFRs. Clinicians from 
KKM involved would be Dr Malathi Deva Tata and Dr Yeoh Chiew Kit. A screening will be 
done to select patients who are suitable of the study. Only patients who fulfil the criteria 
will be invited to participate in this study. Participant will be approached in the dental chair 
once deemed suitable, and will be given 5-10 minutes to decide on participation of the 
study. Consent will be gathered from the patients or the carer if the patient is below 18 
years of age. The patients will then be randomly allocated into two groups using a 
randomized number computer generator, either the Hawley or the modified vacuumed 
formed retainers. The expected sample size to be of statistical significance will be calculated 
using the formula of sample size calculation relevant to this study. The sample size 
 

 
 
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calculation is based on a significance level of 0.05 and 80 percent power to detach a 
clinically meaningful difference of 2.0mm (SD=2.0mm) between the two groups in terms of 
arch width differences, where this difference are based on previous studies by Tynelius et al. 
(9) and Shawesh et al. (15). The power analysis gave a total sample size of 16 patients in 
each group. To account for attrition, 24 patients will be recruited in each group 
 
The inclusion criteria of the subjects that will be included in the study are: 
a. Patients who are at least 13 years old at time of debond. 
b. Treatment plan of extraction or non-extraction followed by straight wire appliances 
in the upper arch only or both arches  
c. Undergone expansion treatment in the upper arch causing an arch width increase of 
3-10mm, either using a Quadhelix, Rapid Maxillary Expansion, expansion with 
archwires, or URA with midline screw. Patients’ interarch measurements at the time 
of debond will be compared with their interarch measurements using the pre-
treatment model available at the clinic. 
d. No chronic medical conditions  
 
The criteria for suspending or terminating the study are: 
a. Relapse due to compliance issue 
b. Relapse due to investigative product 
c. Subject did not come for follow-up 
 
The subject withdrawal criteria are: 
a. Voluntary 
 
If relapse is found and/or if subjects request to withdraw from the study, subjects will be 
informed that they will not need to take impressions at follow-up but they still can make 
appointment with their orthodontist for a normal retainer review. If insignificant relapse is 
found, new Hawley retainers will be provided free of charge. If significant relapse is found in 
subjects from intervention group, free treatment will be provided. The withdrawn subjects 
will not be replaced and an Intention to Treat analysis (ITT) will be done. 
 
The generation of randomization sequence will be performed in blocks of 12 to ensure that 
equal number of patients was allocated to each of the two retention groups. A randomized 
generator will be used for allocation. In this multi-centre trial, a centralized randomization 
technique which incorporated external involvement is used. Individuals who recruit subjects 
from each centre will contact a central methods centre by phone after patient enrolled in 
order to prevent selection bias and protect the assignment sequence until allocation. 
Calibrated researcher will collect the study models which the ID and intervention are 
covered by opaque tape once they are ready for measurement. Only one dental cast at a 
time will be picked out of its box without showing any previous measurements. Two dental 
casts from the same patient will not be measured in connection with each other. Due to the 
prospective nature of the study, it was inconvenient to anonymize dental casts from the 
start of the study. 
 

 
 
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       Hawley retainer                    Normal VFR retainer                   Modified VFR (palatal 
coverage) 
 
5.2 Study design 
 
This is a prospective randomised controlled trial to evaluate the differences in relapse after 
expansion treatment between a Hawley and a modified vacuum formed retainer.  
 
The study will involve: 
a. Clinical: An upper and lower impression with alginate will be taken for dental cast 
and retainer construction. This procedure is a normal procedure done in all 
orthodontic appointments upon removal of fixed appliances. However one extra 
upper impression will be taken for the research. It will take approximately 5-10 
minutes. All retention appliances will be distributed within 24 hours after debonding. 
The retainers will be washed under tap water before delivering to the patient. When 
subjects are given the retainers, clinicians will provide post-debond instructions, 
where the patient has to wear the retainers for 24 hours except during eating and 
brushing their teeth. Researcher will send reminders of wearing retainer in 1-month 
interval to ensure they are following the instructions and to enquire if they have any 
problems. The patients will be instructed to wear the retainers for 24 hours for the 
next 6 months and night-time only for month 7 to month 12.  At a 3 month and 6 
month follow-up, an upper alginate impression will be taken for a dental cast 
construction at each follow-up visit. Clinical examination will allow clinician to detect 
relapse which is by examining the arch width.The whole duration of participation of 
each patient may total up to 40 minutes overall. If any unknown allergic reaction to 
alginate impression occurs, the procedure will be terminated immediately and 
appropriate first aid action will be given to participant, however these will most 
likely be anticipated as these subjects have had impressions taken at the start of 
treatment. 
b. Data Measurement: Dental casts will be analysed using digital callipers and arch 
width will be recorded in the posterior region. 
c. Data analysis: Data will be analysed using SPSS. The descriptive statistics on     group 
level at times corresponding to measurements at removal of fixed appliances (T0), 3 
months post retention (T1), 6 months post retention(T2) and 12 months post 
retention(T3) will be calculated for each variable. 

 
 
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RELAPSE DUE TO POOR COMPLIANCE: 
• 
Poor compliance can be detected by the clinician, such as poor adaptation to speech, 
appliance looks “clean”, patient unable to seat and remove the appliance, or appliance is 
lost and not looked after properly.  
• 
Arch width reduced 
• 
Retainer will not fit in mouth 
 
RELAPSE DUE TO INTERVENTION 
• 
Patient able to adapt to retainers well, good adaptation to speech, appliance looks 
used, patient able to seat and remove retainers easily 
• 
Arch width reduced 
• 
Retainer should still fit in the mouth if patient wears it all the time 
 
Compliance can be confirmed by the use of Thermosensors. Thermo-sensor is not used in 
this study because it is costly, not entirely accurate and it will not reflect the real-life 
situation. Most clinical studies do not use Thermosensors to ensure compliance. Using 
sensors will give out the Hawthorne effect where subjects will tend to perform better since 
they are aware of the presence of thermos-sensors. This as mentioned earlier does not 
reflect the real-life scenario. 
 
 
Monitoring for adverse events 
 
T0: Removal of braces 
T1: 3-month review 
T2: 6-month review 
-Duration: 10-20 minutes 
-Subjects who have had 
3mm 
of 
expansion 
(compared 
with 
pre-
treatment models) will be 
selected, subjects given 5-
10 minutes to think if they 
want to participate 
-Impression will be taken for 
construction of retainer and 
study models which will 
take 5-10 minutes 
-Adverse 
reaction 
i.e. 
allergic 
reaction 
to 
the 
impression material will be 
monitored 
however 
this 
would 
have 
been 
anticipated or recorded in 
the notes as these patients 
-Duration: 5-10 minutes 
-Subjects will be reviewed 
and any adverse effect such 
as relapse will be detected 
at this point  
-An upper impression will 
be taken 
-Adverse 
reaction 
i.e. 
allergic 
reaction 
to 
the 
impression material will be 
monitored 
however 
this 
would 
have 
been 
anticipated or recorded in 
the notes as these patients 
would have had impressions 
taken 
at 
the 
start 
of 
orthodontic treatment.  
-If any allergic reaction 
occurs, 
first 
aid 
-Duration: 5-10 minutes 
-Subjects will be reviewed 
and any adverse effect such 
as relapse will be detected 
at this point 
-An upper impression will 
be taken 
-Adverse 
reaction 
i.e. 
allergic 
reaction 
to 
the 
impression material will be 
monitored 
however 
this 
would 
have 
been 
anticipated or recorded in 
the notes as these patients 
would have had impressions 
taken 
at 
the 
start 
of 
orthodontic treatment.  
-If any allergic reaction 
occurs, 
first 
aid 

 
 
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would have had impressions 
taken 
at 
the 
start 
of 
orthodontic treatment  
-Using 
the 
randomized 
generator, patient will be 
allocated to either a: 
1- Hawley retainer 
2-Modified vacuum formed 
retainer 
-If any allergic reaction 
occurs, 
first 
aid 
management 
will 
be 
provided and an alternative 
impression material will be 
used 
 
management 
will 
be 
provided and an alternative 
impression material will be 
used 
 
management 
will 
be 
provided and an alternative 
impression material will be 
used 
 
 
 
 
5.3 Ethics 
 
A detailed protocol, ethical approval and site approval will be obtained from the KKM Ethics 
Committee before the study commenced. This research has been approved by the UKM 
Research Ethics Committee (Ethical approval number, UKM PPI/111/8/JEP-2018-724). All 
researchers in the study will adhere to the Good Clinical Practice Guidelines. A letter of 
consent will be obtained from each participant after explaining the nature and purpose of 
the study in verbal and in written. The data from the study will be made into a report which 
may be published. Participant’s identity will be private and confidential, and will not be 
reported in any form of report. During the study, with respect to method of retention, if 
found in any patient for the relapse with VFR to be significant; new Hawley retainers (2-3 
days) or retreat of fixed appliances (estimated 6-12 months) without any charge will be 
provided to the patient. Should subjects develop complications related to the study, 
treatment will be given at no cost at Faculty of Dentistry UKM Kuala Lumpur but subject will 
have to bear the travel expenses. Although theoretically the material of Hawley is more 
durable, there are no high quality long term studies comparing durability of both Hawley 
and VFRs. In fact long term follow-up studies have shown Hawley to have more breakages 
(Hitchens et al 2007). However if it does break, since it is an investigative product, we will 
replace the retainer with Hawley and subject will be considered dropout. During or after the 
study is completed, at any point if the research results are validated and if the modified VFR 
were found to be significantly less retentive than the Hawley retainer, subjects will be 
informed of the findings and new Hawley retainers will be provided to the modified VFR 

 
 
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group free of charge. If subject is not contacted regarding the results, it would mean that 
the modified vacuum is just as superior as the Hawley and the subjects in the modified 
vacuum can continue to use their retainer. 
 
 
5.4 
Data management and analysis 
 
Intra-examiner reliability of the measurements will be undertaken on two occasions in a 
random order and following an interval of two weeks. 
 
A normality test will be conducted to determine whether a parametric or non-parametric 
test should be conducted. The outcome measures assessed will be the differences in means 
between groups, which will be assessed by one-way analysis of variance, using Statistical 
Package for Social Sciences (SPSS) version 17.0.  
 
[4] -- Monday, July 08, 2019 -- 15:58:42 
 
F tests - ANOVA: Repeated measures, between factors 
Analysis: 
A priori: Compute required sample size  
Input: Effect size f 
 
 
 
= 
0.42 
 
α err prob 
 
 
 
= 
0.05 
 
Power (1-β err prob)  
 
= 
0.80 
 
Number of groups 
 
 
= 
2 
 
Number of measurements 
 
= 
3 
 
Corr among rep measures 
 
= 
0.5 
Output: 
Noncentrality parameter λ 
= 
8.4672000 
 
Critical F 
 
 
 
= 
4.1708768 
 
Numerator df  
 
 
= 
1.0000000 
 
Denominator df 
 
 
= 
30.0000000 
 
Total sample size 
 
 
= 
32 
 
Actual power  
 
 
= 
0.8038973 
 
A reliability test will also be performed to calibrate the measurements made. The data will 
be reported in a collective manner with no reference to the specific individual. Publication 
policy by most journals would require removal of any personal details of any patient in any 
part of the article or in any supplementary materials (including all illustrations and videos) 
prior to submission, therefore the personal information from each individual will remain 
confidential. Access to the data is only by the research team (which involves orthodontists, 
dentists, personnel) and the REC UKM and KKM. The hard copy of the data obtained will be 
stored in a locked cupboard in a private room that could only be accessed by the research 
team. Soft copy of the data will be contained in a USB protection lock which password is 
only known to the research team. Data will be allowed for inspection or auditing by 
regulatory authorities. Data could be stored for at least 7 years before being destroyed 
(shredded) or deleted (electronic copy). Individuals have a right to know the results of their 
study and can contact the researchers if interested. 
 
 

 
 
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5.4.1 Dental casts 
 
Dental casts of four occasions will be obtained, on the day of removal of orthodontic 
appliances (T0), 3 months post- removal of orthodontic appliances (T1), 6 months post-
removal of orthodontic appliances (T2) and 12 months post-removal of orthodontic 
appliances (T3). Based on a previous study (9), linear measurements will be made with an 
electronic digital calliper on the dental cusps to a precision of 0.01mm: 
● Intercanine width in the maxilla- the distance between the canine cusp tips 
● Interpremolar width in the maxilla- the distance between the premolar cusp 
tips 
● Intermolar width in the maxilla- the distance between the mesiobuccal cusp 
tips of the first molars 
 
Landmarks of cusp tips are identified based on guidelines described in the literature, where 
the most prominent tip is selected (9). If attrition is present, the centre of the surface area is 
determined to be the point of measure. 
 
 
5.4.2 Resources 
 
A researcher will assist in screening and randomizing, while site investigators from MOH and 
their qualified staff will assist in screening and taking impressions. Technicians will facilitate 
in preparing the dental casts and retainers. Cast preparation will be done in the dental 
laboratory of the Faculty of Dentistry, UKM, and dental laboratory of Klinik Pakar Ortodontik 
Klinik Kesihatan Bandar Botanik and Unit Pakar Ortodontik Klinik Pergigian Sungai Chua. 
 
Equipment that is readily available includes alginate impression material, impression trays, 
digital callipers, examination tray and data analyses software (SPSS version 17.0) 
 
 
5.4.3 Result presentation 
 
Results will be presented in a table and chart format 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
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14 
 
6.0 
MILESTONES 
 
 
 
 
 
 
 
 
 
 
Milestones 
 
Dates 
 
Literature review and search                                                                       
Proposal writing 
Ethical approval 
 
15 June 2019 
 
Sampling of participants                                                                               
Measurements from study casts 
 
15 November 2020 
 
Data collection                                                                                               
Data entry and analysis 
 
15 July 2021 
 
Report writing: Introduction and Methodology                                       
Report writing: Result and Discussion 
Conference presentation, journal writings of findings 
 
15 Mac 2022 
 
Final report: Conclusion                                                                               
Conference presentation, journal writing of findings 
 
14 April 2022 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
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7.0 
BUDGET 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
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8.0 
REFERENCES 
 
1.  
Paquette DE, Beattie JR. A long-term comparison of nonextraction and premolar 
extraction edgewise therapy in “ borderline ” Class II patients. Am J Orthod Dentofac 
Orthop. 1992;102(l):1–14.  
2.  
Little RM, Riedel RA, Artun J. An evaluation of changes in mandibular anterior 
alignment from 10 to 20 years postretention. Am J Orthod Dentofac Orthop. 
1988;93(5):423–8.  
3.  
Al-Moghrabi D, Johal A, Fleming PS. What are people tweeting about orthodontic 
retention? A cross-sectional content analysis. Am J Orthod Dentofac Orthop 
[Internet]. American Association of Orthodontists; 2017;152(4):516–22.  
4.  
Herold JS. Maxillary expansion: a retrospective study of three methods of expansion 
and their long-term sequelae. Br J Orthod [Internet]. 1989;16(3):195–200.  
5.  
Melrose CA, Millett DT. Toward a perspective on orthodontic retention? Am J Orthod 
Dentofac Orthop. 1998;113(5):507–14.  
6.  
Littlewood SJ, Millett DT, Doubleday B, Bearn DR, Worthington H V. Retention 
procedures for stabilising tooth position after treatment with orthodontic braces. 
Cochrane Database Syst Rev. 2016;2016(1).  
7.  
Theroux KL. A new vacuum-formed phase I retainer. J Clin Orthod [Internet]. 
2003;37(7):384–7. A 
8.  
Cope JF, Lamont T. Orthodontic retention - Three methods trialed. Evid Based Dent 
[Internet]. Nature Publishing Group; 2016;17(1):29–30. 
9.  
Edman Tynelius G, Petrén S, Bondemark L, Lilja-Karlander E. Five-year postretention 
outcomes of three retention methods - A randomized controlled trial. Eur J Orthod. 
2015;37(4):345–53.  
10.  
Rowland H, Hichens L, Williams A, Hills D, Killingback N, Ewings P, et al. The 
effectiveness of Hawley and vacuum-formed retainers: A single-center randomized 
controlled trial. Am J Orthod Dentofac Orthop. 2007;132(6):730–7.  
11. 
de Groot, A., White, I. R., Flyvholm, M.-A., Lensen, G. & Coenraads, P.-J. 2010. 
Formaldehyde-releasers in cosmetics: relationship to formaldehyde contact allergy. 
Contact Dermatitis 62(1): 18–31. 
12.   International Agency for Research on Cancer. 2006. IARC monographs on the 
evaluation of carcinogenic risks to humans. World Health Organization Press 88: 280. 
13.  
Kopperud, H. M., Kleven, I. S. & Wellendorf, H. 2011. Identification and quantification 
of leachable substances from polymer-based orthodontic base-plate materials. The 
European Journal of Orthodontics 33(1). 
14.  
Bishara, S. E. 1995. Oral lesions caused by an orthodontic retainer: A case report. 
American Journal of Orthodontics and Dentofacial Orthopedics 108(2): 115–117. 
15. 
Shawesh M, Bhatti B, Usmani T, Mandall N. Hawley retainers full- or part-time? A 
randomized clinical trial. Eur J Orthod. 2010;32(2):165–70.