Introduction:

Orthodontic retainers are used after the completion of orthodontic treatment to assure dental occlusal stability and to maintain the achieved end-result. However, without retention teeth could go back to their initial dental malposition or could even take a different unpredicted position resulting once again in dental malocclusion (a deviation from normal occlusion).

There are different types of retainers, some are fixed (glued to the back of the front teeth), and others are removable (can be removed and replaced into the mouth by the patient).

While there are various retainers used for retention (stability), there is no perfect method. Fixed retainers (FRs) are used worldwide. On the one hand, FRs focus on preventing relapse. On the other hand, there are sometimes some adverse effects of retainers; they could fail at a certain point (break/get loose), or cause unwanted tooth movements. Until now, the choice of a retention method is based solely on clinicians' experience as there is no substantial evidence regarding the best retention method or the duration of the retention period. Some clinicians prolong the retention period while others prefer to keep the retainers for an indefinite time.

As the world is advancing, so is the orthodontic science. New FR fabricated by CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing), are assumed to have greater accuracy, better fit, and most importantly, might offer a passive positioning of the retainer. However, the evidence about CAD/CAM FRs is very limited.

Purpose:

To investigate and compare the clinical effectiveness of two types of FRs; CAD/CAM vs. multistranded wire, in terms of stability (primary outcome), failure rate, adverse effects, cost-effectiveness, and patient satisfaction (secondary outcomes), substantial up to 5 years after retainer placement.

Hypotheses:

Compared to traditional multistranded FRs, CAD/CAM FRs have:

• Better long term stability,
• Similar failure rate,
• Fewer adverse effects,
• Similar cost-effectiveness and patient satisfaction.

Material and Methods

Setting: Section of Orthodontics, Department of Dentistry and Oral Health, Aarhus University, Denmark and Department of Orthodontics, Faculty of Dentistry, University of Oslo, Norway.

Sample size: 126 participants are needed for this study.

Randomization: After oral and written consent is obtained, allocation to groups, either conventional multistranded Stainless Steel fixed retainers, or CAD/CAM custom-cut Nickel Titanium fixed retainers, will take place at the last appointment before debonding. Subjects will be allocated 1:1 into one of the two groups.

Intervention protocol: After completing a full active orthodontic treatment, at both centers. The achieved treatment end result has to be maintained in the long term in order to prevent relapse (movement of teeth to the initial malocclusion). One of either two different fixed retainers will be bonded (to the upper and lower anterior teeth) by one operator in each center.

This study follows a standard retention protocol procedure carried at both centers and has a long term posttreatment follow-up of 5 years. Patients will be recalled for follow-up appointments after 1, 3, 6, 12, 24, 36 and 60 months. At follow-up visits, we will perform the following: at 1, and 3 months - a clinical examination. At 6, 12, 24, 36, and 60 months - a clinical examination, a digital impression of the teeth known as "an intraoral scan" (Trios 3, 3Shape, Copenhagen, Denmark) and intraoral photographs. In addition, at 1, 6, and 12 months patients will be asked to fill out a Visual Analogue Scale (VAS) form regarding patient satisfaction Furthermore, we will investigate stability by superimposition (Orthoanalyzer, 3Shape, Copenhagen, Denmark) together with recording of adverse effects (i.e. any changes in torque and/or rotations of the teeth).

Inclusion Criteria:

1. Healthy patients.
2. Age: 12-25 years old (at time of debonding).
3. Presence of all maxillary and mandibular anterior teeth, with normal shape and size.
4. Completion of a course of fixed appliance therapy involving both dental arches.
5. Subjects willing to consent to the trial and comply with the trial regime.

No restriction to presenting initial malocclusion, type of active orthodontic treatment undertaken provided that it included full fixed appliances (functional/removable appliances in combination with fixed appliances - extraction or non-extraction)

Exclusion Criteria:

1. Patients with cleft lip or palate, or both or any other craniofacial syndrome.
2. Patients who had surgical correction of the jaws: Le fort I (2- or 3-piece maxilla) or SARPE (surgically assisted rapid palatal expansion).
3. Lingual appliance treatments.
4. Periodontal disease.
5. Hypoplasia of enamel.
6. Fluorosis.
7. Active caries, restorations or fractures in the anterior teeth.
8. Patients who have had separate debonding appointments for each jaw, with a difference of more than 2 months in between.
9. Re-treated patients.

The outcome assessor will be blinded only to the patient satisfaction and cost-effectiveness outcomes.