Vacuum-formed retainers are clear or transparent retainers, that hold the teeth in the new position after active orthodontic treatment. These custom made appliances are becoming popular these days due to the aesthetics value among patients.

Vacuum-formed retainers can be made through a process that softens the clear plastic and vacuumed to follow the shape of the dental model before it cools off and hardens again. These dental models can be made from conventional method or through a 3D reconstruction process. Recently, it was found that there is no difference in terms of stability of the teeth and oral health related quality of life of the patients wearing vacuum-formed retainers constructed on either types of models.

Physically, the surface roughness of the retainers appear different because the conventional models and 3D printed models are constructed in a different manner.

Our interest is to determine whether the difference in surface roughness would affect microbial colonisation which can eventually affect the oral health.

So this study aims to find the association between microbial colonisation and surface roughness of vacuum-formed retainers constructed on conventional models and also 3D reconstructed models.

RATIONALE OF STUDY

The vacuum-formed retainers are widely preferred today but there is limited research on the effects of the retainers on microbial colonisation, which can have an impact on the oral health. There is possibility that a rough surface finishing of the vacuum-formed retainers may lead to increased microbial colonisation. Therefore, there is a need for us to investigate if the vacuum formed retainers made on 3D reconstructed models may produce increased surface roughness which then can lead to increased microbial colonisation and later impacts the oral health.

Primary Objective :

1. To determine the association between different surface roughness of vacuum- formed retainers and microbial colonisation.

Secondary Objectives :

1. To compare the surface roughness of vacuum-formed retainers constructed on conventional models and 3D reconstructed models.
2. To compare the microbial colonisation on vacuum-formed retainers with different roughness as constructed on conventional models and 3D reconstructed models.
3. To compare the microbial colonisation between upper and lower vacuum-formed retainers with different surface roughness.
4. To compare the microbial colonisation on vacuum-formed retainers with different surface roughness between full time wear and part time wear.

SAMPLE SIZE CALCULATION

Sample size calculation is done based on a type 1 error frequency of 5% and the power of the statistical test is set at 80%. This is based on a study done by Farhadian et al, 2016 on Streptococcus colonisation on orthodontic retainers. The total number of participant needed for the trial was 27 with a minimum of 9 participants per group. With an anticipated 20% drop outs, a total number of 36 patients will be recruited.

Methodology

Patients who are currently undergoing fixed appliance treatment at Faculty of Dentistry, University of Malaya will be screened for their progress of treatment and whether they are ready for debond. During screening, patients who fit the inclusion and exclusion criteria will be selected and given a patient information sheet and a detailed explanation of the clinical trial. Voluntarily participant will then be recruited into this study and informed consent will be obtained. A total number of 36 participants will be recruited for this clinical trial.

Participants will be drawing lots to obtain their study number. Then, the orthodontic resident will have to check the group allocation with the orthodontic consultant.

During the first appointment, debond procedure will be done according to the standard protocol. Three sets of impression will be taken for the construction of study model, construction of the standard retainers and also for the research purpose. The standard retainers will then be issued on the same day of debond (T0). Participants will be instructed to wear the retainers full time except during brushing, cleaning of the appliance and during meals.

Participants will be reviewed one week post debond (T1). During this appointment, the standard retainers will be taken and kept by the orthodontic resident. The first interventional retainers will be issued and participants are advised to wear the retainers full time / 24 hours except during meals, brushing and cleaning of the appliance. Participants will be given a new retainer box to keep their retainers as well as a new toothbrush for cleaning their appliance. A pamphlet that contains detailed information on the care of retainers will also be provided to every participant. Participants will be reminded regularly to wear their retainers full time / 24 hours for three months.

Participants will be reviewed again 3 months post debond (T2). During this appointment, the first interventional retainers will be taken and kept by the orthodontic resident. Then the second interventional retainers will be issued and participants are advised to wear the retainers for 10 hours only. Participants will also be given a new retainer box to keep their retainers as well as a new toothbrush for cleaning their appliance. Analysis of the first interventional retainers will then be carried out. Participants will also be reminded regularly to wear their retainers for 10 hours only for 3 months.

Participants will be reviewed again 6 months post debond (T3). During this appointment, the second interventional retainers will be taken and kept by the orthodontic resident. Then the standard retainers will be issued back and participants are advised to continue wearing the retainers for 10 hours only. Analysis of the second interventional retainers will then be carried out.

STATISTICAL ANALYSIS

Statistical Analysis will be done using SPSS software version 21. P < 0.05 will be set as the level of significance.

i. One way analysis of variance (ANOVA) will be used to compare the surface roughness and microbial colonization on vacuum-formed retainers constructed on conventional models and 3D reconstructed models.

ii. Paired Sample T-Test will be used to compare the microbial colonization between the upper and lower vacuum-formed retainers with different surface roughness as well as between full time wear and part time wear.

iii. Correlation will be used to determine the association between surface roughness of vacuum-formed retainers and microbial colonization.

Inclusion Criteria:

i. Fixed appliance on upper and lower arches ii. About to debond iii. Planned for vacuum-formed retainers for retention iv. Non smoking patients v. No systemic disease

Exclusion Criteria:

i. Undergoing sectional fixed appliance / single arch treatment ii. Indicated for double retention regime with bonded retainers iii. Patient with smoking habit iv. Any systemic disease that may affect the salivary flow v. History of use of antimicrobial mouthwash less than 1 month prior to debond

Investigator will be masked with the randomization sequance & allocation.