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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Type of registration
Prospectively registered

Titles & IDs
Public title
Comparative assessment of survival, stability and occlusal settling between full-time and part-time wear regime of two types of thermoplastic retainers: A randomised controlled clinical trial
Scientific title
Comparative assessment of the survival rate of two types of thermoplastic retainers in patients that have undergone clear aligner therapy.
Secondary ID [1] 296790 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Orthodontic relapse 310687 0
Condition category
Condition code
Oral and Gastrointestinal 309387 309387 0 0
Other diseases of the mouth, teeth, oesophagus, digestive system including liver and colon

Study type
Description of intervention(s) / exposure
Participants will be recruited from a private orthodontic practice located in Melbourne. Each patient will already have their retainer type (ie; Vivera® or Duran®) assigned in accordance with their preference. If they consent to be included in the study, they will then be randomly allocated in to either the full time (minimum 20hours of wear per day) or night time (Minimum 8hours and maximum 10hours) wear regime group for their respective retainer material and followed over a 6 month period. Adherence to the wear regime will be patient reported.
The retainers and their care instructions will be delivered in person by specialist orthodontists with over 10years experience.
In summary,
Four patient groups:
Vivera® - Full time and Night Time groups within this
Duran® - Full time and Night Time groups within this
Observation Period of 6 months
- T0: Intra-oral scan for retainer manufacturing
- T1: Insert retainers and begin observation period
- T2: 8 week review including intra-oral scan
- T3: 6 month review including intra-oral scan
Primary Outcome: Survival rate compared between Vivera® and Duran®. This will be assessed for both a full time and night time only wear regime.
Secondary Outcome/s: Occlusal stability and occlusal settling
Intervention code [1] 313123 0
Treatment: Devices
Comparator / control treatment
Duran® retainer groups will act as the active controls to be compared with their respective groups using Vivera® retainers. Duran® is a polyethylene terephthalate glycol (PETG) based material, which is a common material for a number thermoplastic retainer brands.

Two different wear regimes (ie; Full time vs Full time; Night time vs Night time) will be compared between the retainer types to see if this has any impact on the primary outcome of survival rate (eg; night time only wear regime makes survival rate similar) whilst also maintaining similar occlusal stability and occlusal settling results.
Control group

Primary outcome [1] 308394 0
Average survival rate of the retainers (upper and lower) in days.
This will be assessed by the specialist orthodontist at the 8 week and 6 month review appointments. Any voluntary presentation by a patient between these times due to issues with a retainer will also be recorded.
Fracture/split of the retainer material or the material being worn through on the occlusal surface will be classified as a failure and the retainer will be replaced. All details regarding where the failure occurred on the retainer, how soon after insertion, etc will be recorded for each failure.
Timepoint [1] 308394 0
The primary outcome of retainer survival rate will be assessed over a 6 month period (primary timepoint). Within this time frame, participant retainers will be reviewed for failure at their scheduled 8 week and 6 month review appointments and any voluntary patient presentations between these times during that 6 month period will also be recorded.
Secondary outcome [1] 354850 0
Occlusal Stability
Timepoint [1] 354850 0
T0: Intra-oral scan taken
T1: Retainer insert appointment (commencement of observation period)
T2: 8 week review appointment. New intra-oral scan taken
T3: 6 month review appointment. New intra-oral scan taken
Secondary outcome [2] 354851 0
Occlusal Settling
Timepoint [2] 354851 0
T0: Intra-oral scan taken
T1: Retainer insert appointment (commencement of observation period)
T2: 8 week review appointment. New intra-oral scan taken
T3: 6 month review appointment. New intra-oral scan taken

Key inclusion criteria
(1) Participant is over 15 years of age
(2) Participant and/or parent signed consent form
(3) Full permanent dentition present, excluding second and third molar teeth
(4) Completed Invisalign for minimum of 9 months
(5) Been prescribed upper and lower removable retainers only (no fixed retainer)
Minimum age
15 Years
Maximum age
No limit
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
Patient receiving a fixed retainer

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Sealed opaque envelopes will be used to randomise patients in to either full time or night time wear groups.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Simple randomisation using a computer software to generate a sequence.
The sealed opaque envelopes will be arranged in the order generated by the computer software and then provided to the clinicians.
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?

The people assessing the outcomes
Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
Originally two sample size calculations were undertaken due to the possibility of either survival time or post-treatment stability being the primary outcome.
The sample size calculation for occlusal stability was based on the disparity between Little’s Irregularity Index between retainer groups and was undertaken using the software G*Power. The assumption was that a clinically meaningful difference between groups would be a measured change of 1mm. Based on this, a common standard deviation of 0.5mm with a significance level of 0.05 and a power of 90% was used for the calculation. The results showed that seven subjects would be required for each group with a randomisation allocation of 1:1.
The sample size calculation was also determined based on survival time in days between the retainer groups. It was assumed that a clinically meaningful difference in survival time would be thirty days, with a standard deviation of 20 being two-thirds of the difference. Again, a significance level of 0.05 and a power of 90% were employed and the calculation showed that nine subjects (ie; retainers) would be required in each group with a 1:1 randomisation allocation.
Based on these calculations, each group will require a minimum seven participants (2 retainers per participant), so 28 participants overall. To allow for some drop outs, the study will aim to recruit up to fifteen participants per group.

The primary outcome, being any difference in the survival rate between Vivera® and Duran® retainers, results in nominal data collected from parallel but independent samples. As it is a small sample size, Fisher’s Exact Test would be utilized to determine if there is a statistical difference between the means of the two overall groups.
Secondary outcomes:
Occlusal Stability: If the data from each retainer group show a normal distribution, then an independent T-test would be warranted.
Occlusal Settling: If this collected data again shows a normal distribution, then a two-way ANOVA of repeated measure method would be utilized.

Recruitment status
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)

Funding & Sponsors
Funding source category [1] 301369 0
Name [1] 301369 0
University of Melbourne
Address [1] 301369 0
720 Swanston Street
Vic 3053
Country [1] 301369 0
Primary sponsor type
Australian Foundation for Orthodontic Research and Education
ASO Secretariat
P.O. Box 543
Secondary sponsor category [1] 301035 0
Name [1] 301035 0
Address [1] 301035 0
Country [1] 301035 0

Ethics approval
Ethics application status
Ethics committee name [1] 302107 0
The University of Melbourne Office for Research Ethics and Integrity: Medicine and Dentistry Human Ethics Sub-Committee
Ethics committee address [1] 302107 0
720 Swanston Street
VIC 3035

Level 3, 780 Elizabeth St
The University of Melbourne
Vic 3010)
Ethics committee country [1] 302107 0
Date submitted for ethics approval [1] 302107 0
Approval date [1] 302107 0
Ethics approval number [1] 302107 0

Brief summary
This study will compare two types of thermoplastic retainer materials in terms of their survival rate over a 6month period. It is hypothesised that one of these materials will show an improved survival rate when compared with the other. Secondary outcomes to be assessed include occlusal stability and occlusal settling.
These outcomes will be assessed for two different wear regimes (ie; Full time vs Full time; Night time vs Night time) to see whether this significantly impacts on the results. If the retainer types deliver similar occlusal stability and occlusal settling results regardless of the wear regime (as previous research has suggested), then it is hypothesised that survival rate may be improved by only having a night time only wear regime. This would then enable the thermoplastic retainers to have a longer lifespan resulting in less cost for patients/practitioners.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 89130 0
A/Prof Paul Schneider
Address 89130 0
University of Melbourne
School of Dentistry, Orthodontic Department
720 Swanston Street
VIC 3053
Country 89130 0
Phone 89130 0
+61 3 9341 1500
Fax 89130 0
Email 89130 0
Contact person for public queries
Name 89131 0
Dr Bethany Cunning
Address 89131 0
University of Melbourne
School of Dentistry, Orthodontic Department
720 Swanston Street
VIC 3053
Country 89131 0
Phone 89131 0
+61 3 9341 1500
Fax 89131 0
Email 89131 0
Contact person for scientific queries
Name 89132 0
Dr Bethany Cunning
Address 89132 0
University of Melbourne
School of Dentistry, Orthodontic Department
720 Swanston Street
VIC 3053
Country 89132 0
Phone 89132 0
+61 3 9341 1500
Fax 89132 0
Email 89132 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
No/undecided IPD sharing reason/comment
What supporting documents are/will be available?
No other documents available
Summary results
No Results